Abstract: This work aims at investigating the causes affecting the dimensional and geometrical accuracy of holes in metal binder jetting stainless steel parts. Parallelepiped samples with a through hole were produced using AISI 316L and 17-4PH powders, differing for diameter (3, 4, 5 mm), and position of the axes with respect to the building plane (6, 9, 12 mm distance). Dimensions and geometrical characteristics were measured at green and sintered state by a coordinate measuring machine, determining the dimensional change and the geometrical characteristics. As expected, the shrinkage of linear dimensions is anisotropic; moreover, change in volume and sintered density are significantly affected by the position in the printing chamber. Higher shrinkage was measured along building direction (Z) – 18.5 ÷ 19.5%, than in the building plane – 16.5 ÷ 17.5%, and slightly higher shrinkage – 0.5 ÷ 0.8% was measured along powder spreading direction (X) than binder injection direction (Y). A variation up to 3% in relative density of sintered parts depending on the position in the building plane was observed in 316L. The dimensional change of diameters generally confirmed the shrinkage predicted by the model previously developed—difference between real and expected dimensional changes lower than 3%, except for three geometries (4 ÷ 6%). The cylindricity form error of sintered parts was strongly underestimated by the prediction model (up to 0.15 mm), but underestimation was considerably reduced (generally lower than 0.05 mm) adding the cylindricity form error due to printing. Dimensional and geometrical accuracy of holes are strongly affected by shape distortion of the parallelepiped geometry, in turn due to layer shifting and inhomogeneous green density during printing, and to the effect of frictional forces with trays during sintering. Gravity load effect was also observed on the holes closest to the building plane. Future work will improve the reliability of the prediction model implementing the results of the present work.

Keywords: Additive manufacturing | Dimensional and geometrical accuracy and precision | Metal binder jetting | Shrinkage on sintering

Abstract: This work aims at evaluating the dimensional precision and the accuracy achievable through the Metal Binder Jetting Additive Manufacturing process. An artifact was designed, and 36 replicates were produced using a 17-4PH stainless steel powder aiming at evaluating different feature sizes. The dimensions of the samples were measured by a coordinate measuring machine (CMM) before and after sintering. At green state, the distribution of measured dimensions parallel to the building direction was centered on the nominal dimension, while the distribution of measured dimensions parallel to the building plane was shifted from the nominal ones. Dimensions of cavities were found to be significantly smaller than nominal ones (Z position for fundamental deviation), whereas the dimensions of outer features were larger than the nominal sizes probably on the reason of excessive binder saturation. The dimensional precision ranged from IT9 to IT11. After sintering, the inaccuracy increased with the distance of samples from the building plane, in turn related to non-uniform shrinkage on sintering. Additionally, sintering determined worsening in the dimensional precision, which ranged from IT11 to IT15.

Keywords: Design for AM | Dimensional Precision and Accuracy | Metal Binder Jetting

Abstract: Using theory and simulations, the challenge of gravity-induced distortions during sintering is addressed and a mitigation strategy is proposed. Based on the continuum theory of sintering, the finite element simulation demonstrates the advantages of a rotating furnace to counteract gravity forces during sintering. Its application for stainless steel hollow parts produced by additive manufacturing (binder jetting) is demonstrated, numerically, for reliable industrial production of complex shapes. Sintering a tube in a very slow rotating motion exhibits an improvement in the final deformation ratio compared to a conventional sintering process. The same concept has been adapted for higher furnace revolution speeds and the centrifugal force is now surpassing the effects of gravity. An extended study of sintering under microgravity for space-borne applications is also widely depicted with the same model. Indeed, it shows the possibility of reproducing Earth's sintering conditions at places where gravity is insufficient to provide acceptable densification and shape conservation during sintering.

Keywords: Binder jetting | Deformation | Finite element methods | Rotating sintering | Sintering

Abstract: Additive Manufacturing (AM) technologies theoretically allow the production of complex products without any geometrical restriction. Nevertheless, production process delineates some limitations on the resulting dimensional and geometrical precision. This is a critical issue mainly for Metal Binder Jetting (MBJ) process, on the reason of anisotropic dimensional change and distortion on sintering. Literature reports fairly reliable models for predicting the deformation on sintering. However, the application of such methods might be time consuming from industrial perspective, because of the extensive experimental analysis required to assemble a robust material database. For that reason, this work aims at proposing an alternative approach for compensating dimensional and geometrical change on sintering. Two complex geometries, having similar geometrical features with different sizes, were printed and measured by a coordinate measuring machine before and after sintering process. The analysis of cylindricity form errors reveals an excellent geometrical stability of smaller geometry. Therefore, dimensional change along printing direction was derived in order to obtain a precise scaling factor for improving the dimensional and geometrical precision. By contrast, bigger samples encountered a dramatic distortion, which required a complete redesign. The shape of the distorted cylinder was approximated with an ellipse and a corrective function has been proposed for compensating green geometry.

Keywords: Additive manufacturing | Binder jetting | Design for AM | Distortion

Abstract: The anisotropy of dimensional change in compaction plane of rings made of three low alloyed steels was investigated as a function of green density and geometry. Increasing green density and (D ext–D int)/H ratio, the anisotropy of both shrinkage and swelling increases. A correlation with springback during ejection of the rings from die cavity after cold compaction was found. The ratio between the dimensional changes of diameters, as a function of the ratio between springback of diameters, describes a linear correlation intersecting point (1,1), representative of isotropic behaviour. This correlation confirms the hypothesis of an effect of micropores, generated in the green parts during ejection from die cavity, on dimensional change anisotropy. An analytical correlation was determined for the anisotropy of dimensional change in the compaction plane as a function of green density and geometrical parameter, which can be implemented in the design methodology accounting for the anisotropic dimensional change previously proposed.

Keywords: Anisotropy | cold compaction | design for sintering | dimensional changes | low alloyed steels

Abstract: Metal binder jetting (MBJ) is an additive manufacturing (AM) technology split into two process steps: printing and sintering. Firstly, product is built up layer-by-layer by the selective deposition of a binder agent on a powder bed. Secondly, a thermal treatment (sintering) consolidates the metal structure. MBJ is currently becoming more and more attractive on the reason of high potential scalability, cost-effective production and wide range of available material feedstocks. However, the transition towards industrial scale production is restrained by the critical control of dimensional and geometrical precision of parts after sintering operation. In fact, product geometry is affected by anisotropic dimensional change or even shape distortion. This study aims at investigating the dimensional and geometrical precision of through holes. Three sample geometries were designed, having a through hole with axis perpendicular to the building direction and located at different levels along sample height. Samples were measured by a coordinate measuring machine before and after sintering, in order to assess the shrinkage and any shape change. Results highlight the inhomogeneous volumetric and linear shrinkage of the three geometries, which is influenced by the printing position in the building plane. A macroscopic deformation of parallelepiped geometry was also evidenced, caused by the superposition of layer shifting originated on printing, and by the frictional forces between sample surface and alumina support during sintering. Such distortion significantly affects the shrinkage and form error of holes.

Keywords: Design for AM | Dimensional and Geometrical Precision | Metal Binder Jetting | Shape Distortion

Abstract: Design for Sintering 2 is an EPMA Club Project aimed at improving the previously developed design procedure accounting for anisotropic dimensional changes on sintering. Goal of the project is both enlarging the reference database through the fruitful cooperation of the industrial partners and investigating in depth the mechanisms responsible for anisotropic dimensional changes. This work is focused on the second part of the project, aimed at studying the influence of compaction parameters. Axisymmetric parts characterized by different materials and geometrical parameters were produced at different green densities with different compaction strategies. Focusing the attention on the anisotropy in the compaction plane, dimensional changes were measured and evaluated, also relating them to the attainable dimensional tolerances. The influence of compaction strategy was analyzed in depth, and for the different materials and geometries the more robust process conditions for dimensional precision were highlighted.

Abstract: Previous studies have systematically investigated densification in ring-shaped parts. Additionally, the effect of filling parameters on filling and green density was explored, demonstrating the strong influence of the die cavity on the origin of inhomogeneous powder distribution. A uniform density is mandatory for industrial production, so further investigation is necessary, also including the contribution of powder transfer. This work aims at investigating the effect of powder transfer on the density distribution and the geometrical precision in 2-level axi-symmetric parts. Sample geometry was compacted by varying: the filling parameters, powder transfer strategies, and compaction forces. Reference samples were produced by excluding the powder transfer step from the compaction cycle. Green and sintered density distribution were derived, highlighting the effect of filling, powder transfer, and compaction strategies.

Abstract: Recent research has been focused on the binder jetting (BJ) additive manufacturing technique due to the high potential possibilities in industrial applications. The actual limitation of BJ process can be attributed to the difficult control of the product quality. In fact, a high dimensional variation occurs on sintering, which can detrimentally affect dimensional and geometrical precision, when not properly considered in the design step. This paper aims at investigating the influence of sintering on the dimensional change of through holes, with different diameter size and different axis orientation with respect to the building direction. Samples were measured in the green and sintered state by means of a coordinate measuring machine in order to calculate the diameter shrinkage. The empirical data were successfully compared with the prevision of an analytical model demonstrating that diameter shrinkage is influenced by: the anisotropic dimensional change, the axis orientation and the position of the two diametral opposite points used to identify the diameter. A deep analysis of the results showed a non-negligible effect of the gravity-induced load and of the inhomogeneous shrinkage on sample geometry. This study highlighted that the analytical model may serve as a basis in the design step for improving the dimensional quality of BJ product.

Keywords: Binder jetting | Design for additive manufacturing | Dimensional and geometrical precision

Abstract: The anisotropic dimensional changes during sintering were investigated for rings made of eight different materials with different green densities and H/(Dext −Dint) ratio. Dimensional changes are affected by green density, as shown in previous works, while the geometrical parameter does not display a clear influence. The anisotropy parameter K defined in a previous work does not describe anisotropy of dimensional change unambiguously, due to the anisotropy of shrinkage/swelling in the compaction plane. A new anisotropy parameter (K 3D) was therefore defined considering the dimensional changes of internal diameter, external diameter and height. This parameter displays an unambiguous dependence on the equivalent isotropic dimensional change and will be used in further work to develop a predictive model for the prediction of the anisotropic dimensional change during sintering of parts with different green densities and geometry.

Keywords: anisotropy | Dimensional change

Abstract: The influence of compaction strategy on compressibility and densification of metal powders has been extensively studied in previous work; effective compaction mechanics relationships and a densification model have been derived on experimental basis. Nevertheless, such studies also highlighted the need for further investigation concerning filling step, playing major role in obtaining high density, homogeneously distributed. This work focuses on filling step, considering the influence of both geometry, and filling strategy. Ring shaped parts with different height to thickness ratios (H/T) have been produced, also varying filling parameters as filling shoe speed, suction speed, and number of shakes of the filling shoe. Filling density was derived, as a function of above parameters, also highlighting the most critical parameters affecting filling density. Moreover, green density was measured in different points, referring to filling shoe movement, aiming at identifying the effect of filling strategy on flatness and parallelism of planes resulting from compaction.

Keywords: Compaction | Powder metallurgy | Powder metals

Abstract: Anisotropic dimensional change on sintering has been studied in depth in previous work, as affected by powder mix, geometry, sintering conditions etc. Previous results also revealed anisotropic dimensional changes in the compaction plane, to be necessarily considered when designing precise and accurate parts. Anisotropy in the compaction plane is expected to be markedly affected by inhomogeneities in green density distribution, in turn related to compaction strategy. Aiming at investigating in depth the influence of the compaction strategy, compaction speed, hold down force, and hold down time were selected as parameters. Full factorial testing was performed, three levels for each parameter, and three different materials were considered. Dimensional changes were measured, and the effect of the selected parameters was analyzed, also referring to the different sintering mechanisms occurring in the different materials. As a result, relationships describing the effect of the compaction parameters on the dimensional changes are proposed.

Keywords: Anisotropy | Powder metallurgy | Sintering

Abstract: The influence of sintering on dimensional and geometrical precision has been widely investigated in previous works, both on ring-shaped parts and on industrial products. Results clearly correlated the dimensional precision to the anisotropic dimensional change during sintering, and geometrical precision is also affected by the sintering process. However, both dimensions and geometrical characteristics markedly depend on the result of the compaction process. The origin of geometric errors has been generally attributed to inhomogeneous filling density distribution, but it has never been analyzed systematically. In this study, a commercial Fe-Mo powder mix was used for compacting ring-shaped samples at different height to thickness ratios (H/T). Focusing on the filling strategy, different values for filling shoe speed, suction speed, and number of shakes of the filling shoe were considered. The influence of both geometry and filling strategy on filling density has been derived, and the results have been related to the geometric characteristics.

Abstract: Additive manufacturing allows high complexity of manufactured structures, permitting entirely new design capabilities. In the context of complex design, lattice structures hold the most promise for high complexity, tailorable and ultra-lightweight structures. These unique structures are suitable for various applications including light-weighting, energy absorption, vibration isolation, thermal management amongst many others. This new complexity leads to new manufacturing quality control and metrology challenges. Traditional metrology tools cannot access the entire structure, and the only reliable method to inspect the inner details of these structures is by X-ray computed tomography (CT). This work highlights the challenges of this process, demonstrating a novel workflow for dimensional metrology of coupon lattice samples—using a combination of surface and internal metrology using tactile probe and CT. This dual combined approach uses traditional surface coordinate measurement on exterior accessible surfaces, which is followed by internal lattice measurements. The results show a clear method and workflow for combining these technologies for a holistic dimensional inspection. The confidence gained by inspection of such lattice coupons will support the application of these lattices in end-use parts.

Keywords: calibration | laser powder bed fusion | lattice structures | metal additive manufacturing | metrology | X-ray tomography

Abstract: Dimensional and geometrical precision of parts produced by binder jetting is a crucial issue to be considered aiming at promoting the transition to industrial production. The influence of both the printing and the sintering processes has to be evaluated, and the high shrinkage has to be considered. The task is further complicated by the anisotropy of dimensional change on sintering. The aim of this work is to investigate the dimensional and geometrical precision of cylindrical holes, as affected by the anisotropy of dimensional change on sintering after binder jetting. AISI 316 L powder was used to produce five different geometries, characterized by four holes with different orientation with respect to the printing direction. The geometrical features were measured both in the green and in the sintered state with a coordinate measuring machine, and the dimensional changes, as well as the geometrical variations, were calculated. According to the author's previous experience, a theoretical model has been defined, which aims at predicting the geometry of the holes as derived by the anisotropic dimensional change on sintering. The expected dimensional change of hole diameters, the variation of cylindricity, and the variation of the axis inclination were calculated by the model and compared to those derived from measurement. Good agreement between predicted and measured results has been observed, providing that the influence of printing process parameters is considered.

Keywords: Binder jetting | Dimensional and geometrical precision | Metal additive manufacturing | Shrinkage on sintering

Abstract: The precision of parts produced by Powder Metallurgy (PM) strongly depends on the careful design of PM process parameters. Among them, high sintering temperature is generally considered as detrimental for dimensional and geometrical precision, and therefore neglected in industrial production. Nevertheless, high sintering temperature would strongly improve mechanical characteristics of PM parts, so that the real influence of high sintering temperature on dimensional and geometrical precision is of great interest for PM companies. This study investigates the influence of sintering temperature (up to 1350 °C) on dimensional and geometrical precision of real parts. Dimensional changes on sintering and the effect of sintering temperature have been evaluated. Geometrical characteristics have been measured both in the green and in the sintered state, and the real influence of sintering temperature has been highlighted. As a conclusion, it has been demonstrated that the larger shrinkage due to the high sintering temperature is not detrimental with respect to the dimensional precision, being it reliably predictable. Moreover, the influence on geometrical characteristics is unexpectedly low. The encouraging results of this study convinced the main PM companies in Europe to further investigate the influence of high sintering temperature, as partners in a Club Project within the European Powder Metallurgy Association (EPMA).

Keywords: Design for powder metallurgy | Dimensional and geometrical precision | High temperature sintering process | Precision engineering | Product development

Abstract: The paper presents the results of a project aiming at investigating the potentiality of Die Wall Lubrication (DWL) in powder compaction. A DWL system was developed and installed on a 200 T hydraulic press and specimens were produced to investigate mechanical properties, dimensional and geometrical precision after sintering at high temperature. DWL increases density, while the effect on pore size and morphology in the sintered parts is negligible. Tensile strength and elongation of the sintered specimens are noticeably increased with reference to specimens produced with Bulk Lubrication (BL), while the positive effect on the bending fatigue resistance is less pronounced. Tooth root fatigue resistance of low pressure carburized gears is 71% of that of wrought 20MnCr5 carburized gears. Dimensional and geometrical precision of the parts produced with DWL is very good, comparable if not better than that typical of the parts produced with BL.

Keywords: die wall lubrication | dimensional and geometrical precision | mechanical properties

Abstract: The influence of high temperature sintering (HTS) on the microstructure and the dimensional stability of ring specimens was investigated in a previous EPMA Club Project. HTS improved density and porosity morphology and did not impair dimensional and geometrical precision. A second Club Project was therefore carried out, to investigate mechanical properties and precision of parts characterized by a complex geometry. Three low alloyed steels with either a very low amount of Ni or Ni-free were used. The manufacturing process was carried out in industrial plants. The results confirm that HTS does not impair dimensional and geometrical precision and allows to achieve better tensile strength, slightly lower tensile elongation and impact strength than those of high Ni diffusion bonded steel sintered at 1120°C, taken as a reference. HTS widens the possibilities for new alloy systems with opportunities to reduce cost and achieve improvements related to processing rules (REACH). © European Powder Metallurgy Association (EPMA)

Keywords: dimensional and geometrical precision | high temperature sintering | mechanical properties

Abstract: Powder behavior during compaction has been studied in depth during the long-lasting cooperation between Sacmi Imola s.c and the powder metallurgy research group at the University of Trento. The strong influence of many different parameters on compressibility and densification of powders has been highlighted, and synergistic effects have been observed. The experimental data continuously recorded by industrial presses served as a basis to derive compaction mechanics relationships and the densification model. This work is focused on the densification equation. The coefficients in the densification equation are critically evaluated as a function of the variables considered, using data coming from different materials, with different particle size, forming different geometries through different compaction strategies. The goal is to identify the relationships describing the variation of coefficients as a function of such variables. As a consequence, it will be possible to distinguish the relative weight of the variables governing the densification process.

Keywords: densification equation | powder compaction

Abstract: In the previous Design for Sintering Club Project the design procedure developed in previous studies has been applied to real industrial parts, aiming at verifying the reliability in predicting the anisotropic dimensional changes on sintering. Satisfactory results were obtained, and directions for further improvements were also highlighted, so that a new Club Project was proposed to the industrial partners involved in the first one. Design for Sintering 2 Club Project aims at improving the effectiveness and reliability of the design procedure, both enlarging the reference database, and investigating in depth the mechanisms responsible for anisotropic dimensional change on sintering. In the first part of the three years project the influence of geometry and green density is studied, considering different materials representing both solid-state sintering and liquid-phase sintering. New anisotropy parameter describing anisotropic dimensional changes is proposed based on the analysis of results. © European Powder Metallurgy Association (EPMA)

Keywords: anisotropy | design for sintering | dimensional change

Abstract: The influence of die wall lubrication during warm die compaction on densification, microstructure and mechanical properties of three low alloy ferrous powders was investigated. Specimens were sintered at 1250°C. Die wall lubrication leads to higher green and sintered density and enhances the dimensional stability. It does not affect the microstructure of the matrix, while pores are smaller and more rounded than in bulk lubricated specimens. In TRS tests, both strength and deformation are higher in die wall lubricated specimens than bulk lubricated ones.

Keywords: Die wall lubrication | warm die compaction

Abstract: The effect of high-temperature sintering (1180°C and 1250°C) on the dimensional stability, geometrical precision, density and microstructure of rings made of five different low alloy steels was studied. Density and dimensional shrinkage slightly increase with temperature, but the dimensional and the geometrical precision of parts, do not depend on sintering temperature. Sintering temperature maybe therefore increased up to 1250°C without impairing the dimensional and geometrical precision of the investigated rings. An estimation of the effect of the high sintering temperature on tensile properties is presented, based on the microstructure and on the fraction of the load-bearing section. A significant increase in both tensile strength and tensile ductility may be expected, in particular when the sintering temperature is increased up to 1250°C.

Keywords: dimensional and geometrical precision | High temperature sintering

Abstract: The mechanics relationships describing powder behaviour in uniaxial cold compaction have been derived in previous work on the basis of experimental data, as affected by many different variables in the compaction process. The influence of geometry, chemical composition, compaction strategy etc. were investigated in depth. This work focuses on warm die compaction, which stands for an interesting opportunity to increase density, also obtaining more homogeneous density distribution. Cylindrical specimens have been produced using a commercial diffusion bonded low alloy steel powder, to which different lubricants, in different amounts, have been added. The influence of type and amount of lubricant has been directly highlighted by the comparison of ejection force and energy. Axial and radial spring-back have been also evaluated. A deeper knowledge of the behaviour of the different powder mixes in warm die compaction has been obtained comparing the derived friction coefficients and constitutive models.

Keywords: Compaction mechanics | Constitutive models | Ejection | Warm die compaction

Abstract: Powder behavior in uniaxial cold compaction has been extensively investigated in previous work. The constitutive model of different powder mixes has been derived, and the influence of several variables, such as geometry, chemical composition, lubricant type and amount etc., has been studied in depth. This work focuses on the influence of warm die compaction. A commercial diffusion bonded low alloy steel powder, added with 0.6% wt. lubricant, has been used producing cylindrical specimens with two different H/D ratios, both in cold and in warm die compaction. Concerning warm die compaction, two different lubricants have been added. The constitutive model and the densification curves have been derived for all the powder mixes using the data recorded by the press, in terms of forces and displacements. Comparing ejection force and energy, the influence of warm die compaction, type of lubricant, and height of the specimens have been highlighted.

Abstract: The effectiveness of powder metallurgy as net-shape/near net-shape manufacturing technology is determined by the possibility of obtaining complex parts matching the required narrow tolerances. Sintering process determines change in volume of the green, and the related dimensional changes are significantly anisotropic. Anisotropy is affected by several variables, such as material, compaction and sintering parameters, geometry, whose influence is difficult to be distinguished and determined. Anisotropic dimensional change on sintering has been investigated in depth using an experimental approach, relating measurements results to the mechanisms responsible for the phenomenon. Main results concerning the influence of different variables are briefly presented in this work. Such results served as the basis for the development and further improvement of a design method, aimed at predicting anisotropic dimensional change. Main steps of the design method are presented and an example of application to a real part is described. Strong agreement between predicted and real dimensional changes has been observed, and compared to the attainable dimensional tolerances.

Keywords: Design for powder metallurgy | Precision engineering | Product development

Abstract: The increase of the sintering temperature from 1120 °C up to 1280 °C of a 0.2%C Cu–Mo–Ni diffusion bonded steels with 6.9 g/cm3 and 7.2 g/cm3 green density slightly increases sintered density and improves the pore morphology. The fraction of the load bearing section increases consequently. Moreover, high sintering temperature enhances the compositional homogeneity of the metallic matrix, and the microstructure evolves from a mixture of ferrite, pearlite, bainite, martensite and Ni-austenite to a bainitic/martensitic microstructure, with a decreasing amount of the Ni-austenite. Tensile strength and ductility increase with the sintering temperature. The paper clearly demonstrates the role of the pore morphology on the mechanical properties that are therefore better correlated to the fraction of the load bearing section than to density. It also highlights that sintering temperature may represent a solution to enhance mechanical properties of porous sintered steels as an alternative to the increase in green density.

Keywords: Fraction of load bearing section | Sintering temperature | Tensile ductility | Tensile strength

Abstract: Anisotropic dimensional change on sintering may strongly affect the precision of parts produced by press and sinter. In previous work a design procedure accounting for anisotropic dimensional change of axi-symmetric parts (disks and rings) has been developed on the basis of experimental data. In this work the procedure has been applied to predict the anisotropic dimensional change of real parts produced in industrial conditions, providing that coaxial rings were identified in the geometry of the actual parts. Parts were highly different for material, complexity of geometry, green density and process conditions. Parts were measured in the green and sintered state and the measured dimensional changes were compared to the predicted ones, finding a good agreement. The procedure was also adapted to predict dimensional change of an oval feature, and highly satisfactory results were obtained.

Keywords: Anisotropy | Dimensional change | Powder metallurgy | Precision of PM parts

Abstract: AISI 316L powder mix was sieved in three particle sizes and successively compacted on rings with two different H/(D ext -D int ) ratios. The height and diameters were measured by a CMM at the green and at the sintered state. The shrinkage was calculated to study the influence of particle size and geometry on the anisotropy of dimensional change. As expected, the volumetric shrinkage increases moving from coarser to finer particle size, and the measurements confirmed the anisotropy of the dimensional variation. The measurements revealed that the lowest rings shrink more than the taller rings. The reference to the radial and axial stress during prior cold compaction shows an interesting correlation, in which shrinkage increases on increasing the stress. The further investigation of the deviatoric stress and the deviatoric shrinkage provided a possible explanation of the anisotropy of dimensional change on sintering as a function of the inhomogeneity of the compaction stress.

Keywords: anisotropic shrinkage | compaction stresses | Sintered steels

Abstract: Compaction mechanics relationships describing the behaviour of AISI 316L powder mixes during uniaxial cold compaction were derived in previous work by continuously recording the data of an industrial press. The reliability of the relationships depends on the accuracy in identifying the threshold of elasto-plastic transition, what is a difficult task due to the peculiar characteristics of powder mixes. The influence of particle size on the transition threshold has been investigated in the present work. Standard commercial AISI 316L powder was sieved in three particle sizes (fine - intermediate - coarse), 1% Acrawax was added as a lubricant and ring-shaped parts were produced by uniaxial cold compaction. Processing the data recorded during compaction, the mean relative density corresponding to the beginning of prevailing plastic deformation has been identified for all the powder mixes by means of a recursive procedure. The mechanisms responsible for the different transition thresholds have been studied in depth.

Keywords: Compaction mechanics | Particle size | Uniaxial cold compaction

Abstract: The influence of high temperature sintering on the dimensional stability and the microstructural and mechanical properties of some low alloyed steels was investigated in the EPMA Club Project “HTS”. The materials investigated were five different powders: Ancorsteel 4300 and FeSiVC (Hoeganaes Corporation grades), AstaloyCrM, AstaloyCrA+2%Ni and DistaloyAE (Höganäs AB grades). Rings (55 mm external diameter, 45 mm internal diameter, 5 mm height) were cold compacted and sintered at the standard temperature of 1120°C and at high temperature in the 1180-1260°C range in different continuous furnaces. The whole manufacturing process was carried out in industrial plants. In spite of the larger shrinkage than at 1120°C, high temperature sintering does not impair the dimensional precision and stability of the rings. HTS processing widens the possibilities for new alloy systems in industrial applications with opportunities to reduce cost and achieve improvements related to processing (REACH).

Keywords: Dimensional control | High sintering temperature

Abstract: The influence of die wall lubrication (DWL) during cold compaction on the sintering shrinkage and the properties of three low alloy sintered steels, 1.5%Mo, 1.8%Cr, 3%Cr and 0.5%Mo, were investigated. Carbon content was 0.3%. The lubricant content was adjusted to the compaction strategy. Compaction was carried out at 1000 MPa, with either bulk (BL) or die wall lubrication, warm die compaction at 90°C. Three points bending specimens were produced, and sintering was carried out at 1250°C in a vacuum furnace, with nitrogen backfilling. Die wall lubrication allows a much higher green and sintered density to be achieved respect to bulk lubrication; in addition, sintering shrinkage is less than in bulk lubricated specimens. The pore characteristics are slightly improved by die wall lubrication, while the microstructure of the matrix is almost unaffected, while both strength and ductility are greatly improved by die wall lubrication.

Keywords: Die wall lubrication | High sintering temperature

Abstract: The influence of green density and geometry on the anisotropy of sintering shrinkage of large rings (100 mm external diameter, 42 mm internal diameter) produced with water atomized iron powder has been studied in previous work. In this work water atomized iron powder and sponge iron powder have been used to produce small ring-shaped parts (40 mm external diameter, 20 mm internal diameter, three different heights), compacted up to five different compaction pressures and sintered at 1120 °C in low C potential endogas atmosphere (30 mins). Diameters and height of green and sintered specimens have been measured by CMM, and dimensional changes, as well as change in volume, have been derived. Data have been compared with previous sampling, and the influence of the several variables on the anisotropic dimensional change has been highlighted, also evaluating the trend of the anisotropy coefficient K.

Keywords: Anisotropy | Dimensional change | Sintering shrinkage

Abstract: Several models have been proposed in literature for decades to describe the relationships between the compaction pressure and green density. Some of them are almost empirical, others are based on a theoretical approach starting from the phenomena occurring during cold compaction. The authors of the present paper have recently (2018) proposed a model based on the investigation of the deformation experienced by the powder mix when subject to the application of the compaction pressure. In this work, the model is compared with the three most recently published ones: the Aryanpour and Farzaneh model (2015), evaluating the contribution of rearrangement; the Parilak et al. model (2017) that was validated with experimental data relevant to 205 powder mixes, and the Montes et al. equation (2018) that was developed considering the local stress and strain in the interparticle contacts. Compaction experiments were carried out on a commercial AISI 316L stainless steel powder mix, sieved in different particle size ranges, and the data collected by the compaction press control unit were used.

Abstract: Martensite strengthening increases the contact fatigue resistance of sintered steels, but the microstructural hardening may result in the formation of surface brittle cracks due to the combined effect of high hardness and porosity. Therefore, there is a hardness threshold above which the achieved resistance to the formation of the subsurface Hertzian cracks is cancelled out by the surface brittle damage. Such a threshold depends on density and on the mechanical properties of the metallic matrix. Analytical models for the prediction of the nucleation of the subsurface fatigue cracks and of the brittle surface cracks in carburized steels were developed and verified experimentally. In this work, these models are described and implemented in a design procedure for sinterhardened parts subject to contact stresses, aiming at selecting the material and its heat treatment for applications where contact stresses may cause both contact fatigue and brittle surface.

Abstract: This work investigates the influence of geometry on the behaviour of a commercial diffusion bonded low alloy steel powder (added by 0.65% graphite and 0.6% lubricant) during uniaxial cold compaction. Cylindrical specimens and ring-shaped specimens were produced, characterized by different geometrical parameters. The whole analysis has been performed using experimental data, the forces and displacements continuously recorded by an industrial press without any additional device, aiming at obtaining results representing the actual conditions in the production of real parts. The stress field acting on the powder column was derived from the recorded data, obtained from two different compaction strategies. By single action cold compaction experiments the parameters characteristics of the powder mix were derived, such as the radial stress transmission coefficient, the flow stress, the friction coefficient with the die walls, and the friction coefficient with the core in case of rings. These results were used investigating the powder behaviour during double action cold compaction, which represents the most common compaction strategy. Densification curves were derived from this analysis, reporting the relative density as a function of both the applied and the mean axial stress. The influence of the geometry on the densification was highlighted and discussed.

Keywords: Constitutive model | Low alloy steel powder | Uniaxial cold compaction

Abstract: The influence of the microstructure of uniaxial cold-compacted green iron on the sintering shrinkage was investigated. Pores in the green parts are very slightly oriented, while the dimension of the interparticle contact areas is anisotropic. A large and anisotropic anisothermal shrinkage in alpha iron was measured, greater than isothermal shrinkage at the 1120°C. The results were interpreted on the basis of the geometrical and of the structural activity, and the effective diffusivity responsible for neck growth was determined.

Keywords: anisotropy | microstructure | Shrinkage

Abstract: Sintering shrinkage of prior cold compacted iron rings with different geometry (height to wall thickness ratio) and green density in the 6.5–7.3 g/cm3 range was investigated. It displays a minimum at an intermediate green density. Axial, tangential and radial shrinkages are different, due to the gradients of green density along the axial and the radial directions. Therefore, the effect of height on shrinkage and its anisotropy is the result of their effect on the stress distribution in the green parts during cold compaction, and the resulting green density and deformation experienced by the powder. Anisotropy decreases on increasing shrinkage.

Keywords: geometry | green density | Shrinkage anisotropy

Abstract: Carburizing increases the contact fatigue resistance of sintered steels, but the surface hardening may result the formation of surface brittle cracks due to the combined effect of high hardness and porosity. The effect of carburizing on the embrittlement of the case of a 7.3 g/cm3 1.5%Mo-0.25%C sintered steel was studied. The phenomenon was analyzed theoretically and verified by experiments. The resistance of the carburized steel to surface brittle cracking increases with the load bearing surface and the decrease of the maximum pore size, of the surface microhardness and the friction coefficient. The theoretical analysis was implemented in a design procedure for parts subject to contact stresses.

Keywords: brittleness | Carburizing | design | hardening | rolling-sliding

Abstract: A new densification equation for uniaxial cold compaction of four low alloy steel powders was determined from the deformation vs. mean axial stress correlation. Both deformation and stress are averaged along the height of the powder column. A power law relation, with two parameters representing the plasticity and the inverse of the resistance to deformation (densification) of the powder mix, respectively, fits the curves that are divided in two steps, distinguished by the prevailingdeformation/densification mechanism (rearrangement or plastic deformation). Densification of the four powder mixes is greatly affected by the starting density in the die cavity, while the chemical composition of the base iron powder has a less significant effect.

Keywords: Cold compaction | deformation | densification

Abstract: Coordinate measuring machines (CMM's) are widely used in the field of geometrical and dimensional metrology, especially in areas dealing with quality systems and manufacturing process monitoring. Concerning PM parts, the influence of process parameters on the product characteristics can be highlighted measuring dimensions and geometrical characteristics in the green and sintered state, so that proper measurement can be used as a tool to improve production strategies. In current work, two of the extrinsic factors that can affect the measurement results in PM parts, have been investigated, namely the effect of different clamping and measurement strategies. Specific clamps have been designed aiming at ensuring the proper access to all the surfaces and the derived dimensions have been compared to those obtained as distances from the measurement plate. Different measurement strategies and data processing have been used to reconstruct features and the results have been compared also in terms of geometrical tolerances.

Abstract: In previous work the data recorded by an industrial press (forces and displacements) were extensively used to describe powder behavior during uniaxial cold compaction. Satisfactory models describing densification were proposed, as the result of the axial and radial stresses acting on the powder column. The recorded data are very precise from an industrial perspective, mainly in the last stage of compaction, directly related to final green density. Nevertheless, they are slightly scattered in the first stage, which is interesting from a scientific perspective, as the step where rearrangement occurs. To overcome this limit, this work proposes a methodology to analyze the signal of forces in the frequency domain to increase the signal to noise ratio. The signal was decomposed through the Fourier transformation, and the noise was smoothed by a low-pass filter specifically designed for the press. Reliability of the data and effectiveness of the derived relationships result significantly improved.

Keywords: Compaction mechanics | Signal analysis | Smoothing operation

Abstract: A densification equation derived from deformation occurring in the powder mix during cold compaction was applied to investigate densification of a commercial water atomized AISI 316 stainless steel powder with different particle size distribution, mixed with 1% organic binder, in the production of rings with different H/(Dext-Dint). Knowing the constitutive model of the powder mixes, the mean compaction pressure was determined and correlated to the deformation of the powder column. From these correlations it is possible to derive a densification equation having a physical meaning, also individuating the parameters describing the densification behavior, and in turn the compressibility, of the different powders investigated.

Keywords: Densification equation | Particle size | Powder compaction

Abstract: The influence of compaction strategy (lubrication, temperature and pressure) on springback and on sintering shrinkage of a 0.5%C and 1.5%Mo steel was investigated. The aim is to study dimensional and geometrical stability of this material, when processed to obtain a sintered density above 96% of the theoretical one. Specimens with 25 mm diameter and 20 mm height were compacted in in rigid die at different temperatures, with different lubrication conditions and at pressures in the range 800-1200 MPa. They were sintered at 1250°C in a vacuum furnace. Green and sintered dimensions were measured by CMM to determine springback and sintering shrinkage, and their anisotropy, as well as the evolution in sintering of the geometrical features as a function of the compaction conditions.

Keywords: Dimensional stability | Lubrication | Powder compaction

Abstract: In previous work the anisotropic dimensional change on sintering has been investigated in depth. An anisotropy parameter has been identified, depending both on geometry and on sintering conditions, and it has been used to define a model for the anisotropic behaviour. A design procedure accounting for anisotropic dimensional changes has been proposed. This work summarizes the main results obtained within the Design for Sintering Club Project, aimed at validating and enlarging the aforementioned design procedure by the application on real industrial parts. Project partners provided axi-symmetric parts, which were measured both in the green state and after sintering in standard industrial conditions. The real dimensional changes were compared to the dimensional changes predicted by means of the design procedure based on the anisotropy model. The results, also compared to the attainable dimensional tolerances, allowed validating the design procedure, and showing directions to further improvement.

Keywords: Anisotropy | Design for sintering | Dimensional change

Abstract: Compaction mechanics has been investigated in previous work using the data continuously recorded by an industrial press, aiming at obtaining the constitutive model of powder mixes actually representing powder behaviour during uniaxial cold compaction. The influence of geometry and powder mix has been previously investigated. In this work the same experimental approach was followed, aiming at highlighting the influence of the lubricant admixed to the metal powder. Two different lubricants, in two different amounts have been added to a commercial diffusion bonded low alloy steel powder. Different compaction strategies have been used to produce ring shaped parts, characterized by different H/(Dext-Dmt) ratios (0.5, 1,1.5, 2) and different green densities (6.7, 6.9, 7.1 g/cm3). The recorded data have been used to derive the mechanics relationships governing densification for each powder mix. The results have been compared to highlight the innuence of lubricant type and amount.

Abstract: This work aims at determining the constitutive model of four commercial water atomised low alloyed steel powders during cold compaction. Single-action experiments were performed, obtaining cylindrical specimens with different H/D ratios. The distribution of axial and radial stresses was investigated, and the relationships describing both the radial stress transmission coefficient and the flow stress as functions of the relative density were determined. The radial stress transmission coefficient also confirmed the hypothesised value of Poisson’s coefficient. The friction coefficient between the powder column and the die wall was determined, also highlighting the influence of the H/D ratio. Measuring the axial and radial strains due to spring-back, the axial and radial elastic moduli were determined, as functions of the relative density. The results obtained for the four materials were compared, also highlighting both differences and similarities.

Keywords: Cold compaction | constitutive model | low alloyed steel powders

Abstract: A densification equation for a commercial water-atomized 316L stainless steel powder mixed with 1 wt.% lubricant was derived from deformation occurring in the powder mix during cold compaction, and experimentally verified through compaction tests to produce specimens with different geometry, green density, and particle-size distribution. In contrast to other densification models reported in the literature, the newly proposed densification equation highlights the influence of the variables investigated on the resistance of the powder mix to densification.

Abstract: In previous work the relationships were determined which describe the densification of the powder column during uniaxial cold compaction and the stress field for the constitutive model. An improved processing method totally based on experimental data was defined. The present work exploits this improved experimental method to highlight the influence of material, investigating the behaviour of two commercial iron based powder mixes, which differ in chemical composition, alloying method, and apparent density. Densification is described by means of a new densification equation, based on the in-situ density and its correlation to the deformation experienced by the powder mix within the die cavity. The parameters in the power law equation allow to identify and compare the influence of the powder mix. The stress field acting on the powder column is investigated, and the relationships and parameters describing the constitutive model of the powder column are determined and compared for both materials.

Keywords: Cold compaction | Compaction mechanics | Densification | Hydraulic press

Abstract: Sintering shrinkage of uniaxially cold compacted axi-symmetrical parts is anisotropic. Not only is the shrinkage of height (parallel to the compaction direction) different from that of the diameters (in the compaction plane), but even the dimensional changes of the inner and of the outer diameters differ significantly. This behaviour has been investigated on iron rings with different geometry and green density. In the compaction plane radial and tangential shrinkages are different, and tangential shrinkage significantly changes along the wall thickness. This is due to the distribution of radial and tangential stresses during cold compaction that in turn depends on the axial stress. The stress field and its dependence on both green density and geometry were hypothesized to propose a working direction to interpret the anisotropy of sintering shrinkage in real parts.

Keywords: Geometry | Green density | Sintering shrinkage

Abstract: In previous works the deformation of the powder column during uniaxial cold compaction was studied by means of experimental data, also deriving relationships with densification and the axial and radial stresses distribution. Cylindrical specimens were considered in all the previous works. Aiming at enlarging the field of application of the results, obtained by the data continuously recorded by an industrial press without any additional device, the influence of geometry is investigated in this work. Rings characterised by different H/T ratios (Height on Thickness equal to 1, 2, 3, 4), considerably higher than in the previous works, were produced using different compaction strategies. Densification curves are derived, where density is reported as a function of the pressure applied by the upper punch, also highlighting density gradients. The deformation of the powder column is derived from experimental data and related to the densification. The results are compared with those obtained investigating cylindrical specimens.

Abstract: The behavior during uniaxial cold compaction of a commercial mix of a water atomized austenitic stainless steel powder and a lubricant was investigated by carrying out single action tests and recording the force applied by the upper punch to the powder column, the force applied to the die, and the displacements of the crosshead and of the die. Data collected during the experiments were elaborated using different correlations between the axial stress and the radial stress in the powder column: the Poisson correlation for the elastic deformation of the powder column, and the Von Mises criterion for plastic deformation.Friction coefficient decreases on increasing relative density up to ρr = 0.7, then it stabilizes on 0.15. The flow stress of the powder mix increases with the relative density by a power law. The radial stress transmission coefficient increases with relative density, with two distinct trends in the ranges where either elastic or plastic deformation of the powder column predominate.

Keywords: Compaction mechanics | Metal powder compaction

Abstract: Densification in cold compaction of metallic powders is due to rearrangement and plastic deformation. The two phenomena are partially overlapped during the compaction cycle, but the former prevails at the lower forces, while plastic deformation increases on increasing the compaction force. AISI 316L green cylindrical parts were compacted at different forces, corresponding to different steps of the compaction process, and sintered at 1250°C in a vacuum furnace. At the lower forces, when plastic deformation is negligible and densification is due to rearrangement, the radial shrinkage is almost isotropic. On increasing force, the increasing plastic deformation causes a progressive deviation from this behaviour, the axial shrinkage becomes larger than the radial one. An interpretation of this behaviour is proposed, based on the analysis of the multiaxial stress field acting on the powder column in the whole of the force range investigated.

Abstract: In previous works a preliminary analytical model describing the reversible and irreversible deformations of the powder column during uniaxial cold compaction was developed using experimental data. Densification curves were derived, density was reported as a function of the pressure applied by the upper punch. This work aims at investigating in depth the distribution of axial and radial stresses, again from experimental data, relating the force applied to the die to the frictional force at the die surface. Single action experiments are performed, both using only upper punch compression, and using only lower punch compression. The friction coefficient between the powder column and the die wall, the radial stress transmission coefficient and the dependence of the flow stress of the material on density are determined. The results are used to process the data obtained by double action experiments. Densification curves are obtained, where density is reported as a function of the whole stress field acting on the powder column.

Abstract: This work investigated the behaviour of a low alloy steel powder (diffusion bonded iron powder, graphite and lubricant mix) in uniaxial cold compaction, aiming at determining the characteristics of the powder affecting densification. Single action compaction tests were performed, both upwards and downwards, producing specimens with two different H/D ratios. The data recorded by the press (forces applied to the upper punch and the die, displacements of both upper punch and die) were used to calculate the mean axial stress applied by the upper punch to the powder column and the mean radial stress exerted by the die. The relationships between axial and radial stress, relevant both to the elastic and to the plastic deformation, allowed determining the friction coefficient between the powder column and the die wall, the radial stress transmission coefficient and the flow stress of the material as functions of the relative density.

Keywords: Cold compaction | Hydraulic press | Powder behaviour in compaction

Abstract: The classical theory of sintering does not consider the deformation of the powder particles promoted by prior cold compaction. In green parts, particles are instead plastically deformed and strain hardened. The interparticle regions emitting atoms diffusing towards the neck surface have a starting extension that depends on the green density and on their orientation respect to the compaction direction. Moreover, the density of structural defects, that enhances diffusivity, is higher than that in the loose powder. Shrinkage of iron green specimens with different density and geometry was measured along the compaction direction and in the compaction plane, resulting anisotropic as it was expected. Based on the microstructure of the green parts and on the results of dilatometry analysis, a model describing the shrinkage kinetics accounting for the actual condition of the powder particles in the green part was verified.

Keywords: Sintering shrinkage | Uniaxial cold compaction

Abstract: The behaviour of austenitic stainless steel powder column during uniaxial cold compaction was investigated in this work. Powders with different particle size were compacted to the same green density in a hydraulic press, also providing different H/D ratios in order to account for the influence of geometry. The analysis of the data continuously recorded by the press allowed distinguishing the contribution of the reversible phenomena (elastic deformation of powders and tools) and of the irreversible phenomena (rearrangement and plastic deformation of the powders). An analytical model for densification was proposed, considering both density and increase in density versus the applied pressure. The trend of reversible and permanent deformations versus the applied pressure was evaluated, also proposing an analytical model. The comparison between the densification curves and the curves of permanent deformation allowed highlighting the physical meaning of the model describing the increase in density for the different particle size.

Keywords: Cold compaction | Hydraulic press | Powder behaviour in compaction

Abstract: The effect of the most representative variables of selective laser melting (SLM) technology was evaluated by means of a design of experiment (DOE) approach, with respect to the quality of final specimens. The variables taken into account were laser power, scanning speed, and thickness of the powder layer. The aim of this paper is to determine powder chemical-physical characteristics that ensure the best results with the SLM technique. Analysis of the influence of chemical composition and powder particle-size distribution on porosity and roughness of the final items was studied. This work describes the progress obtained with SLM technology in recent years, demonstrating the importance of optimizing process parameters. All of the results presented were obtained using precious metal alloys.

Abstract: Press and sinter is a near net-shape technology, and its cost effectiveness is strictly related to the geometrical and dimensional precision of the component itself. In this work an analytical model to describe the dimensional variations due to the sintering process of iron components has been proposed and discussed. This model has been developed using experimental data coming from a well designed sampling. The sampling is a set of axisymmetric geometries, rings and cylinders, having different diameters and heights. The different features (diameters and heights) have then been compared with the dimensional variations to study the influence of the geometry on the dimensional variations. Every sample has been measured both in the green state and after the sintering process. The dimensional variations concerning the diameters and the heights have been evaluated. The measuring procedure has been implemented using a coordinate measuring machine. The sintering process has been carried at three different temperatures under the same operating conditions. The anisotropy of the dimensional variations has been studied and described within the proposed model, introducing the anisotropy parameter (K). Basically the parameter K identifies the difference between the dimensional variations occurring in an ideal isotropic volumetric change and the actual anisotropic volumetric variation. The model can describe the difference between the dimensional variations occurring on the compaction plane (diameters) and the dimensional variations occurring along the compaction axis (height). The effect of the geometry and the sintering temperature on the anisotropy of the dimensional variations has been evaluated.

Keywords: Anisotropy | Dimensional control | Modeling | Process capability | Sintering

Abstract: The effect of the presence of a liquid phase during sintering on anisotropy has been investigated by dilatometry on specimens that have been obtained cutting prismatic green parts in different directions: parallel to the compaction direction (longitudinal), and perpendicular to the compaction direction (transverse), respectively. The spreading of the liquid phase occurs easily throughout the particle contacts in the transverse region and all the sintering phenomena related to the liquid phase are enhanced along this direction: swelling and subsequent shrinkage in iron-copper, shrinkage in iron-phosphorus, compensating for the larger shrinkage along the longitudinal direction that occurred in the solid state.

Abstract: In a previous work it has been demonstrated that shot peening improves the contact fatigue resistance of a Cu-Mo diffusion bonded sintered steel by 30%. Such an improvement is due to the combination of compressive residual stresses, surface densification and strain hardening. By means of a theoretical model to predict contact fatigue crack nucleation, it has been concluded that the effect of phenomena related to plastic deformation (surface densification and strain hardening) prevails on that of residual stresses. In the present work, the study was extended to other materials, having a lower resistance to plastic deformation resulting from either a lower density or the presence of diffusion bonded Ni. Even in this case, shot peening improves the contact fatigue resistance but surface modifications related to plastic deformation are enhanced in comparison to the Ni-free steel with a higher density. As a consequence, compressive residual stresses are smaller. The theoretical model was applied and the effect of the resistance to plastic deformation of the base material on the improvement of the contact fatigue resistance is discussed.

Keywords: Contact fatigue | Shot peening

Abstract: A model to evaluate the anisotropy of the dimensional variation of sintered components has been developed in previous works. The procedure evaluates the anisotropy coefficient of an axisymmetric part; this coefficient is used in the model to predict the dimensions of the sintered part. Combining the dimensional changes expected for basic geometries, a procedure to compute the dimensional changes of a multilevel component has been proposed. In this work the model has been validated comparing the predicted dimensions to the actual ones considering a chromium steel mechanical component. The component is a three level rotor sintered at four different temperatures. The parts have been measured with a coordinate measuring machine before and after sintering in a batch furnace. A Monte Carlo like method has been used to evaluate the error distribution and the stability of the model. The results show a narrow distribution of the error, which means a good stability and robustness of the model.

Abstract: In this work the behaviour of austenitic stainless steel powder column during uniaxial cold compaction was investigated; experiments were carried out in a hydraulic press, using powder mixtures with different particle size. The powders were compacted to the same green density; moreover, compaction tests at intermediate forces were carried out, and the data continuously recorded by the press in terms of force and displacement of the axes were analysed, allowing to distinguish the contribution of the reversible phenomena (elastic deformation of powders and tools) and of the irreversible phenomena (rearrangement and plastic deformation of the powders). An analytical model describing the trend of reversible and irreversible displacements versus the applied force was proposed. The influence of particle size on the resistance to rearrangement, elastic deformation and plastic deformation was therefore experimentally determined. The results are implemented into a knowledge base data, to be used as a design tool for PM structural parts.

Keywords: Cold Compaction | Hydraulic Press | Powder Behaviour In Compaction

Abstract: In this work the behaviour of ferrous powder during uniaxial compaction was investigated; experiments were carried out in a hydraulic press, producing green parts with different H/D ratio and different density. The data continuously recorded by the press in terms of force and displacement of the axes were analysed, allowing to distinguish the contribution of the reversible phenomena (elastic deformation of powders and tools) and of the irreversible phenomena (rearrangement and plastic deformation of the powders). A preliminary analytical model describing the trend of reversible and permanent deformations of the column of powder versus the applied pressure was proposed. From the analysis of the data recorded in different compaction cycles, densification curves have also been derived.

Abstract: The anisotropy of dimensional change on sintering of uniaxially cold compacted green parts is mainly caused by the inhomogeneous distribution of pressure during compaction. The difference between the axial and the radial pressure leads to an inhomogeneous deformation of the powder particles and in particular to a different extension of the interparticle contact areas. These areas are larger for contacts perpendicular to the compaction direction than for those parallel to it. This contributes to anisotropy of sintering shrinkage, since the interparticle contact area is the source of atoms diffusing towards the neck. Such an anisotropy of the neck region geometry may have an influence on anisotropy of the sintering stress, too. These features of the uniaxially cold compacted iron parts were investigated by SEM on the metallographic sections, using a geometrical model of the green parts to correct data taken from 2D images. The results were correlated to shrinkage at different temperatures measured by dilatometry.

Abstract: Properly modelling the anisotropic dimensional change on sintering is a difficult task, given the large number of variables involved, which depend on material, process, and geometry. In previous works a preliminary analysis was performed, and an analytical model, based on experimental data, was proposed. This work investigates in depth the influence of geometry and process variables on the anisotropy parameter K, which allows estimating the entity of anisotropy. Axisymmetric iron parts were considered; the influence of the ratio between internal and external diameter was investigated. Special attention was paid to the dimensional changes in the compaction plane, those mainly affecting the design of the compaction tools, being different the influence of the process variables on the dimensional variation in the external and internal diameter. The influence of process parameters, specifically green density and sintering temperature, was also studied. A relationship between K and process variables is proposed.

Abstract: Sizing is studied in this work as a post-sintering operation aimed at improving the dimensional and geometrical precision of sintered parts. The required dimensional and geometrical characteristics are obtained by the plastic deformation due to sizing, which is related to the applied stress. In this work, the relationships between applied force, resulting deformation, attainable geometrical characteristics have been investigated. By means of the data recorded by a hydraulic press, force-displacement curves have been derived. The analysis of these curves allowed identifying the elastic deformation of part and tool, as well as the plastic deformation of the part. The plastic deformation has been correlated to the actual dimensional changes measured on the part, as well as to the change in the required geometrical characteristic (conicity). On the basis of these relationships, a design procedure to optimise the sizing strategy has been proposed.

Keywords: Dimensional and geometrical control of sintered parts | Sizing

Abstract: A conservative approach to predict the Rolling Contact Fatigue (RCF) behavior of two different sintered and heat treated steels with heterogeneous microstructure was proposed. It is based on the assumption that the RCF crack nucleation is anticipated by the local plastic deformation of the material, which occurs when the maximum local stress, calculated using equations (1), (2) and (3), exceeds the yield strength of the matrix, calculated using equation (5). Two steels were considered, having composition, density, fractional porosity and elastic constants reported in Table 1. The theoretical predictions were validated by contact fatigue experiments carried out with a test configuration (disk-on-disk) shown in Figure 2. The fraction of the load bearing section, which influences the maximum stress, has been calculated by equation (4); the shape factor of the pores was measured by Image analysis on metallographic images (Figure 2), and both the whole of the pore population, as well as the larger pores corresponding to 10% of the whole population were considered, obtaining the results reported in Table 2. Since the microstructure of the two steels is heterogeneous (Figure 3), not only the mean microhardness reported in Figure 4 was considered, but even the microhardness of the microstructural constituents where the large pores are located. This way, a mean approach and a localized approach were used to implement the theoretical model. Figure 5 shows the results of theoretical prediction and of the experimental validation in case of material A under a mean pressure of 600 MPa. The yield strength of the matrix (5a) and the maximum stress profile (5b) were calculated with the two approaches above described, and the difference between yield strength and maximum stress is plotted in fig. 5c. Only the localized approach predicts plastic deformation in the subsurface layers and, in turn, crack nucleation, as actually observed in the metallographic section of the tested specimen. Indeed, large pores are localized in the softer constituent. In case of material B at the same mean pressure (figure 6), the two approaches do not predict crack nucleation, which in fact does not occur. On increasing mean pressure up to 1 GPa (figure 7), the mean approach predicts crack nucleation, whilst the localized one does not predict it. The experimental verification does not show any crack. In this case, the large pores are localized in the harder constituent, and the mean approach underestimates the resistance to plastic deformation of the matrix subject to the enhanced stress. The theoretical model proposed works satisfactorily in predicting the contact fatigue behavior of the two materials (it also has been verified on other sintered steels), provided that the peculiar characteristics of the microstructure of these materials are taken into account, which means that the model has to applied with a local approach.

Keywords: Crack nucleation | Localized damage | Rolling Contact Fatigue | Sintered steels

Abstract: The dry sliding wear behavior of two sintered and carburized steels with different Ni amounts has been investigated. The microstructure of the two steels comprises martensite, bainite, and the Ni-rich austenite. Under the sliding conditions investigated, wear is either oxidative or adhesive. In both cases, the lower amount of the soft Ni-rich austenite results in a better wear resistance. A design procedure for parts subject to dry sliding wear applications is proposed, based on the maximum acceptable wear depth, in order to evaluate the practical significance of the differences between the two materials.

Keywords: corrosion and wear | life prediction | powder metallurgy

Abstract: A conservative approach to predict the contact fatigue behavior of a Powder Metallurgy steel, in the sinter-hardened condition and after shot peening, was proposed. It is based on the assumption that the contact fatigue crack nucleation is anticipated by the local plastic deformation of the material, which occurs when the maximum local stress exceeds the yield strength of the matrix. A model to predict contact fatigue crack nucleation has been proposed and validated by experiments. A local approach is used, based on the characteristics of the largest pores, which promote fatigue crack nucleation, and on the microhardness of the microstructural constituents where they are localized. Shot peening improves the contact fatigue resistance of the sinterhardened steel by 30%. © 2014 Elsevier B.V.

Keywords: Contact fatigue | Crack nucleation | Shot peening | Sintered steels

Abstract: In the conventional press and sinter process, dimensional change on sintering determines the precision of the final parts, providing that a good dimensional precision of green parts is ensured. Anisotropic dimensional change on sintering may be detrimental to the precision of Powder Metallurgy (PM) parts, and it should be considered in the design step. The effect of material and geometry on the anisotropic dimensional change is studied in this work. Four different iron alloys and five different geometries were considered. Dimensions were measured both on green and on sintered parts and the anisotropy of dimensional change was evaluated and correlated to the material and geometry. The effect of neglecting anisotropy in the design step was investigated, in terms of dimensional tolerances, which can be obtained with different process capabilities. A model to describe the effect of material and geometry on the anisotropic dimensional change is also being developed.

Keywords: Anisotropy | Dimensional change | Powder metallurgy | Precision of PM parts

Abstract: High-temperature sintering can be a key to increase the material strength of powder metal components. The dimensional change due to high-temperature sintering can lower the precision of PM parts, therefore press and sinter processes could be less cost effective. The aim of this work is to evaluate the loss of dimensional and geometrical precision of the components in comparison with the material strength improvements. Two mechanical parts made of chromium steel were sintered at different temperatures. The porosity evolution was investigated by image analysis. The mechanical properties were estimated by the computation of the fraction of load bearing section. Both the dimensional and the geometrical precision were calculated by implementing a specific procedure with a coordinate measuring machine. The results show a significant improvement of porosity increasing the sintering temperature and so does the fraction of load bearing section. Increasing the sintering temperature the dimensional change increases as well, while the geometrical characteristics and the dimensional precision remain within the same tolerances.

Abstract: Cold compaction experiments were carried out on stainless steel powders, using a 200 tons hydraulic press. The force and the displacement of the axes were recorded and a force-displacement curve was determined. Green parts with different H/D ratio and different green density were produced. The measured displacement is due to the contribution of the following phenomena: powder rearrangement, elastic and plastic deformation of the powder, elastic deformation of the tools (punches, bearings and the plate supporting the die). Rearrangement and plastic deformation of the powder are irreversible. The contribution of the reversible phenomena (elastic deformation of powder and tools) and of the irreversible phenomena (rearrangement and plastic deformation) was investigated analysing the loading and unloading curves of the compaction cycle at different maximum forces.

Keywords: Cold compaction | Hydraulic press | Powder behaviour in compaction

Abstract: The results previously obtained with gold alloys for selective laser melting (SLM) underlined the key role not only of process parameters but also of powder chemical composition for producing quality precious metal jewellery. This paper illustrates the effect of some selected chemical elements to improve laser radiation absorption and to favour the melting of metallic particles. In addition, the impact of the structure and morphology of the supports was examined in order to optimize their density and maintain an adequate thermal dissipation of laser energy.

Abstract: Anisotropy of sintering shrinkage of a 3%Cr-0.5%Mo-0.5%C green compact was investigated by dilatometry. Specimens were cut along the compaction direction (longitudinal) and in the compaction plane (transversal), and isothermal sintering cycles were carried out at different temperatures in the 1150-1300°C range. Longitudinal shrinkage is larger than the transversal one, and the difference decreases on increasing temperature until at 1300°C transversal shrinkage becomes larger than the longitudinal one. Isothermal shrinkage curves were elaborated using the shrinkage kinetics model Δl/l0=Ktn, to determine the mass transport mechanism and to calculate the effective diffusivity along the two directions and its dependence on temperature. The results were discussed in relation to the structural modifications introduced by prior cold compaction in the powder particles.

Abstract: The anisotropic dimensional change on sintering can be detrimental to the precision of PM parts if not properly considered in the design step. Ferrous axial-symmetrical parts sintered at different temperatures have been investigated in this work. The anisotropy of dimensional change in height and in the internal and external diameter, and their relationships, were analysed in depth. An anisotropy parameter has been identified, depending both on geometry and on sintering conditions, and it has been used to define a model for the anisotropic behaviour. A design procedure accounting for anisotropic dimensional changes has been proposed. The data coming from measurement of industrial multilevel parts (measured both in the green and in the sintered state) have been used to compare the real dimensional changes to the dimensional changes predicted by means of the design procedure based on the anisotropy model.

Abstract: The effect of high temperature on dimensional change, porosity, microstructure, dimensional and geometrical characteristics of parts is analyzed. On increasing the sintering temperature shrinkage increases and anisotropy of dimensional change gets progressively attenuated. The fraction of the load bearing section increases and the microstructure of the ferrous matrix may result unmodified, hardened (enhanced diffusion of alloying elements), softened (decarburizing). Sintering temperature may be increased up to 1350°C without affecting dimensional and geometrical precision of steel parts.

Abstract: A systematic characterisation of the porosity in the bulk and surface regions of a sintered Cr-Mo low alloy steel was carried out using image analysis. Fractional porosity in the different regions varies, mainly due to the scatter of the maximum pore size. A higher porosity is found in the bulk region and lower porosity in the regions that contact the die surface during compaction. The maximum pore size is larger in the bulk region than in the surface layers. The large pores are more irregular. With increasing green density, both the fractional porosity and maximum pore size decrease. The fraction of load bearing section in the bulk and surface regions was calculated from fractional porosity and the shape factor of the pores and compared in the different regions. The load bearing section fraction and the maximum pore size were used to predict tensile and fatigue resistance for different densities. The data from the characterisation of the bulk images can predict tensile strength. For fatigue, where the crack nucleates in the surface regions, the use of bulk data underestimates the fatigue resistance. © 2014 Elsevier Inc.

Keywords: Image analysis | Mechanical properties | Porosity | Sintered steels

Abstract: The cost effectiveness of PM as a net-shape technology is strongly related to the possibility of guaranteeing the required dimensional precision on sintered parts. Providing a good dimensional precision on green parts, dimensional change on sintering determines the dimensional characteristics on the sintered ones. Correctly foreseeing dimensional change may lead to properly design PM parts. Dimensional change may be anisotropic, due to a different shrinkage/swelling in the axial and transversal direction during sintering, which is determined both by the geometry and by the material. Anisotropy of dimensional change was studied in this work on differently shaped PM parts made by different iron alloys. Cylinders and ring-shaped parts were studied, characterised by same height or same H/D ratio. Dimensions were measured both on green and on sintered parts and the anisotropy of dimensional change was evaluated and correlated to the geometry.

Abstract: The dimensional change during sintering of ferrous green parts was investigated by dilatometry. Shrinkage starts during heating still in alpha phase due to volume diffusion. Shrinkage kinetics is faster than that predicted from the diffusion coefficients of iron corresponding to an equilibrium density of structural defects. The concept of "structural activity" can therefore be utilized to justify such an enhanced kinetics and to modify the shrinkage equations, considering the large amount of structural defects introduced by prior cold compaction in the contact regions between the powder particles. This approach is also used to describe anisotropy of dimensional change.

Abstract: This work proposes a hypothesis for the interpretation of shrinkage anisotropy during sintering of an Fe-Cu-C alloy based on the effect of the structural modifications of the powder, due to the prior compaction, on the mass transport phenomena. Dislocations are introduced by cold compaction in the contact regions between particles, with different densities along the compaction direction and the transversal one. Therefore, the mass transport by volume diffusion is strongly activated in both directions, and a prevailing effect in the compaction direction is shown. The volume diffusion coefficients derived from the kinetic model correspond to the dislocation pipe diffusion mechanism. © 2013 Institute of Materials.

Keywords: Dislocations | Shrinkage anisotropy | Volume diffusion

Abstract: In the framework of the EURISOL [1] program to define a second generation RIB (Radioactive Ion Beam) facility, LNL-INFN is constructing in the next five years a specialized national facility for exotic beams based on ISOL method with a uranium compound target, named SPES (Selective Production of Exotic Species) [2]. The RIBs are produced inside the target chamber complex. For radioprotection issues, the SPES target chamber [3] must be easily and safely removed, for servicing or storing, from the beam lines after the irradiation process. The design of the SPES layout strongly takes into account this effect. In fact, two independent devices are designed for the handling process, one in horizontal and the other in vertical direction, of the target chamber unit device, which contains the production target and ion source complex. The remote handling system, at present adopted for the SPES project, is presented and discussed in this work. © 2013 IEEE.

Abstract: This work improves the systematic approach proposed in previous papers, aimed at defining design criteria specific for powder metallurgy (PM) parts subject to wear in application. Dry rolling-sliding tests have been performed on PM steels obtained under different process conditions, and the results have been used as a knowledge base in the proposed design procedure to evaluate the effect of the material variables (porosity and microhardness) and geometrical parameters (contact length) on wear resistance. The failure criterion considered here to ensure the functionality provides to compare the wear thickness with a value deriving from the dimensional tolerances. If the failure criterion is not matched, then a change in the material variables and/or geometrical parameters is proposed. The occurrence of plastic deformation and/ or brittle contact at the surface region is also considered. Examples of application show that the most significant improvement is obtained by modifying both material variables and geometrical parameters. © 2013 Institute of Materials, Minerals and Mining.

Keywords: Design criteria for PM | Wear

Abstract: The scatter of height is an intrinsic characteristic of sintered parts. Depending on material, green density, sintering conditions and part geometry, it may range between ±0.02 and ±0.05 mm. In case of displacement control sizing, the scatter of height affects the sizing force, while in case of force control sizing, it affects the displacement. In both cases, an effect on dimensional and geometrical precision of sized parts may be expected. In order to evaluate this effect, both displacement and force control sizing experiments were carried out, on as sintered parts as well as on ground ones, the latter being characterized by a smaller scatter of height. The aim of this work is that of investigating if the influence of the height scatter is more pronounced in displacement or in force control sizing. The influence is evaluated in terms of the attainable dimensional and geometrical precision of sized parts.

Keywords: Dimensional and geometrical control | Sizing

Abstract: The aim of this work is to determine the safe working conditions of PM steels in order to avoid damage caused by rolling contact fatigue (RCF). To avoid the possible damage on the material, any pit formation on the surface or crack nucleation in the subsurface should be prevented. RCF crack promotes by plastic deformation in the subsurface layers and the plastic deformation occurs when the applied stress is higher than yield strength of the material. By considering this relation as a base of an approach, a mechanical model was proposed which gives an overview for the possibility of the crack nucleation in the mechanism for a specific case by highlighting the role of different conditions such as Hertzian pressure and the property of the materials such as density, microhardness, carbon content, surface treatment etc. All the predictions from the model were confirmed by performing experimental tests in different conditions.

Keywords: Rolling contact fatigue | Steels

Abstract: The effect of the sintering and sinter-hardening temperature on the dimensional and geometrical precision of ring-shaped parts was investigated. The parts were produced with a 3%Cr-0.5%Mo-0.5%C steel, compacted to 6.8 g/cm3 and sinter/sinter-hardened at 1250°C, 1300°C and 1350°C. The increase in the sintering temperature enhances the fraction of load bearing section and leads to an expected significant improvement of mechanical properties. Dimensional shrinkage increases with the sintering temperature, however, the dimensional and geometrical precision obtained in all the cases is very good even at very high sintering temperature. Dimensional variations are anisotropic, and the effect of anisotropy was estimated by evaluating the lack of precision attained when green parts are designed assuming an isotropic behavior. © 2013 Korean Society for Precision Engineering and Springer-Verlag Berlin Heidelberg.

Keywords: Anisotropy | DG&T | Sintered steels | Sintering temperature

Abstract: The macro-and micro-geometrical characteristics of the surface of porous sintered steel parts were investigated. While the macro-geometry influences waviness and geometrical precision, that means functionality and assembly, micro-geometry affects roughness and surface bearing section and, in turn, fatigue, corrosion and wear resistance. During compaction, the powder in contact to the die is exposed to different forces and constrain with respect to that in contact to the punches. As a consequence, the punches and die surfaces show different characteristics, which have been highlighted. Moreover, surface porosity is greater than the core porosity. The characterization was carried out on low alloyed Cr-Mn steels, which have been compacted to different green densities and sintered at different temperatures, to evaluate their effect on the geometrical characteristics of the surfaces.

Abstract: This study represents a preliminary activity for the biomechanical numerical modeling aimed at the prediction of the human foot behavior and the deformation under different load conditions. It also represents the starting point to develop a scientific approach for the functional mass customization aimed at the optimization of comfort in footwear. Reverse Engineering (RE) methodologies developed for building up the external shape of the human foot are presented and discussed. Aim of this work is to study the problem of the digitalization of human feet under different conditions using three technologies: shape from stereo, from silhouette and from shading. The foot is one of the most difficult human parts to reconstruct taking into account the complex surface and the high curvature. In this article the disadvantage and advantage of each technique are analyzed. In particular tests about reliability and precision of the measure are considered. ©2010 Society for Experimental Mechanics Inc.

Abstract: Dimensional change on sintering and its effect on the dimensional precision of iron-copper-carbon ring- shaped parts produced by powder metallurgy (PM) were investigated. The effect of different variables on dimensional change was studied by design of experiments (DOE). The type and composition of the powder, as well as the height of the parts, were considered. The effect of chemical composition was significant on all the dimensions, while the other variables had only a slight effect on the dimensions in the compaction plane. To determine the anisotropy of the dimensional change upon sintering, the wall thickness in the compaction plane was considered, which is directly related to shrinking/swelling. No systematic effect of the parameters investigated on the dimensional precision of the PM parts was observed, and the excellent precision of green parts is maintained after sintering. The anisotropic behavior did not significantly affect the dimensional precision of the parts evaluated.

Abstract: The dimensional characteristics of ring-shaped parts produced with an Fe-Cu-P alloy by a conventional powder metallurgy process were measured on both green and sintered parts. The dimensional change was investigated by dilatometry, and the work highlighted that the anisotropy observed is mainly due to the early sintering stage. In this study, where the alloy is characterised by a slight densification, the anisotropic behaviour has a negligible effect on the precision of the height and the internal diameter, while the effect on the precision of the external diameter may be relevant. The results have been generalised, considering larger volume variations and different anisotropy parameters, and some relations between the anisotropy parameters and the attainable ISO tolerance classes have been determined. © 2012 Elsevier B.V. All rights reserved.

Keywords: Anisotropy | Dimensional precision | Powder metallurgy

Abstract: In this paper, we describe the current status of the LISA Pathfinder mission, a precursor mission aimed at demonstrating key technologies for future space-based gravitational wave detectors, like LISA. Since much of the flight hardware has already been constructed and tested, we will show that performance measurements and analysis of these flight components lead to an expected performance of the LISA Pathfinder which is a significant improvement over the mission requirements, and which actually reaches the LISA requirements over the entire LISA Pathfinder measurement band. © 2012 IOP Publishing Ltd.

Abstract: Anisotropy of dimensional change on sintering is a well recognized phenomenon in powder metallurgy. In the present work, anisotropy has been investigated by dilatometry experiments on specimens cut from real parts, parallel and perpendicular to the compaction direction, to study the sintering phenomena responsible for the different dimensional change along the two directions. Anisotropy of dimensional change was also analysed by comparing axial and radial dimensions of green and sintered parts. The effect on dimensional precision has been estimated by means of a simplified model, which includes both isotropic and anisotropic behaviour in ring shaped parts with different height and wall thickness.

Keywords: Anisotropy | Dimensional change | Dimensional precision | Sintering

Abstract: In this work a hydraulic press has been used to size sintered gears to the required conicity. Experiments have been carried out both in force control and in displacement control. The effect of die movement was investigated too. Parts have been measured by continuous scan in a Coordinate Measuring Machine (CMM). The influence of the process parameters on the dimensional and geometrical characteristics of sized gears has been investigated with reference to those of sintered ones, to highlight the optimum sizing conditions.

Keywords: Dimensional and geometrical control | Sizing

Abstract: Wear is a cause of failure for many industrial parts produced by Powder Metallurgy (PM), for example gears or cams, which are subjected to rolling and rolling-sliding wear, dry or lubricated depending on the application. The aim of this work is to improve the systematic design approach proposed in a previous work highlighting how the characteristics of the materials can be modified to enhance the wear resistance of PM components. The work is focused on components subject to dry rolling-sliding wear. The results obtained from the dry rolling-sliding tests performed on PM steels obtained under different process conditions have been used as knowledge base in the proposed design methodology. The application of the design criteria allowed identification of the material characteristics and how they can be modified to improve wear resistance.

Abstract: Sintered bronze with the addition of graphite as self lubricant is widely used in sliding bearings and bushes applications, especially where grease and oil lubricant cannot be considered. Aim of this work is to study the dry sliding wear behavior of a porous sintered bronze-graphite composite, which is characterized by a transition from solid lubrication to adhesive wear. In this last condition graphite loses its efficiency as solid lubricant due to the frictional heat. The efficiency of the solid lubrication was examined at different loads and sliding velocities; it decreases on increasing both load and velocity. The behavior in the different dry sliding conditions was investigated and the corresponding flash temperature was calculated. Results indicate that transition occurs when the flash temperature reaches at least 360K. Some design guidelines were then proposed, based on a P0 vs. v map, which defines the parameters ensuring both that no plastic deformation occurs and that solid lubrication is efficient during dry sliding. The relative design scheme gives a tool to verify if the dimensional and geometrical characteristics of the part are guaranteed during its expected life. © 2011 Elsevier Ltd.

Keywords: Non-ferrous metals and alloys | Selection for material properties | Wear

Abstract: As the launch of LISA Pathfinder (LPF) draws near, more and more effort is being put in to the preparation of the data analysis activities that will be carried out during the mission operations. The operations phase of the mission will be composed of a series of experiments that will be carried out on the satellite. These experiments will be directed and analysed by the data analysis team, which is part of the operations team. The operations phase will last about 90 days, during which time the data analysis team aims to fully characterize the LPF, and in particular, its core instrument the LISA Technology Package. By analysing the various couplings present in the system, the different noise sources that will disturb the system, and through the identification of the key physical parameters of the system, a detailed noise budget of the instrument will be constructed that will allow the performance of the different subsystems to be assessed and projected towards LISA. This paper describes the various aspects of the full data analysis chain that are needed to successfully characterize the LPF and build up the noise budget during mission operations. © 2011 IOP Publishing Ltd.

Abstract: This paper presents a quantitative assessment of the performance of the upcoming LISA Pathfinder geodesic explorer mission. The findings are based on the results of extensive ground testing and simulation campaigns using flight hardware, flight control and operations algorithms. The results show that, for the central experiment of measuring the stray differential acceleration between the LISA test masses, LISA Pathfinder will be able to verify the overall acceleration noise to within a factor 2 of the LISA requirement at 1 mHz and within a factor 6 at 0.1 mHz. We also discuss the key elements of the physical model of disturbances, coming from LISA Pathfinder and ground measurement that will guarantee the LISA performance. © 2011 IOP Publishing Ltd.

Abstract: LISA Pathfinder, the second of the European Space Agency's Small Missions for Advanced Research in Technology (SMART), is a dedicated technology demonstrator for the joint ESA/NASA Laser Interferometer Space Antenna (LISA) mission. The technologies required for LISA are many and extremely challenging. This coupled with the fact that some flight hardware cannot be fully tested on ground due to Earth-induced noise led to the implementation of the LISA Pathfinder mission to test the critical LISA technologies in a flight environment. LISA Pathfinder essentially mimics one arm of the LISA constellation by shrinking the 5 million kilometre armlength down to a few tens of centimetres, giving up the sensitivity to gravitational waves, but keeping the measurement technology: the distance between the two test masses is measured using a laser interferometric technique similar to one aspect of the LISA interferometry system. The scientific objective of the LISA Pathfinder mission consists then of the first in-flight test of low frequency gravitational wave detection metrology. LISA Pathfinder is due to be launched in 2013 on-board a dedicated small launch vehicle (VEGA). After a series of apogee raising manoeuvres using an expendable propulsion module, LISA Pathfinder will enter a transfer orbit towards the first Sun-Earth Lagrange point (L1). After separation from the propulsion module, the LPF spacecraft will be stabilized using the micro-Newton thrusters, entering a 500 000 km by 800 000 km Lissajous orbit around L1. Science results will be available approximately 2 months after launch. © 2011 IOP Publishing Ltd.

Abstract: Preparations for the LISA Pathfinder mission have reached an exciting stage. Tests of the engineering model (EM) of the optical metrology system have recently been completed at the Albert Einstein Institute, Hannover, and flight model tests are now underway. Significantly, they represent the first complete integration and testing of the space-qualified hardware and are the first tests on an optical system level. The results and test procedures of these campaigns will be utilized directly in the ground-based flight hardware tests, and subsequently during in-flight operations. In addition, they allow valuable testing of the data analysis methods using the MATLAB-based LTP data analysis toolbox. This paper presents an overview of the results from the EM test campaign that was successfully completed in December 2009. © 2011 IOP Publishing Ltd.

Abstract: Aim of this work is proposing a systematic design approach for wear resistant components produced by Powder Metallurgy (PM). Wear is a cause of failure for many industrial PM parts. Gears and cams, for example, are subjected to rolling and rolling-sliding wear, dry or lubricated depending on the applications. The design criteria are mostly empirical, thus resulting fully conservative, sometimes excessively conservative. A need for defining design criteria for wear resistant PM parts is thus revealed, to exploit at best the specific characteristics of both technology and materials. The focus is on the case of components subject to dry wear. Particularly, this work analyses the parameters affecting dry rolling-sliding wear of PM steel parts. Dry rolling-sliding tests were performed on different PM steels, wear mechanisms were investigated and materials were characterized to obtain the knowledge base for the proposed design methodology. A diagram indicating the main steps for the design of wear resistant PM parts is described and applied. This approach can also be applied to other wear mechanisms found in PM steel parts. © 2010 Elsevier Ltd.

Keywords: Ferrous metal and alloys | Powder Metallurgy | Selection for material properties | Wear

Abstract: The effect of shot peening on the plane bending fatigue strength of a 7.1g/cm3 sintered Cr-Mo steel was investigated. Shot peening provides surface densification, strain hardening, compressive residual stresses up to -700MPa, without impairing the dimensional and geometrical precision of specimens. Plane bending fatigue strength increases of 30%, irrespective to the different residual stress profiles obtained by changing the shot peening parameters. The improvement is mainly due to the surface densification and strain hardening. © 2010 Elsevier B.V.

Keywords: Fatigue | Powder metallurgy | Steels

Abstract: The influence of the compaction speed on the dimensional and geometrical precision of a multilevel part compacted to two green densities was investigated. Dimensions and geometrical characteristics, as well as density distribution in the different columns, were firstly evaluated in the green parts, to highlight the influence of the compaction step with respect to that of sintering. Dimensional and geometrical variation on sintering and sinter-hardening were then investigated, focusing the attention on the inhomogeneity and anisotropy of the variations. The class of tolerance for green and sintered parts was evaluated, both for dimensional and for geometrical characteristics.

Abstract: The geometrical precision of PM parts depends on several factors, among them the dimensional variation in sintering is particularly relevant. The copper steels swell on sintering and the dimensional growth depends on composition, size of the copper powders, mix type, homogeneity of the mixture, density distribution in the green parts, sintering time, temperature and atmosphere. Some of these parameters also affect the geometrical characteristics of the green parts. Chemical composition, type of copper and lubricant, as well as the H/D ratio were considered in this study by a DOE approach to evaluate their influence on the geometrical characteristics. The interaction between the variables and their effect was studied.

Keywords: Design of experiments (DOE) | Geometric dimensioning and tolerancing (GDandT) | Robust design

Abstract: The Design Guidelines Collaborative Framework describes a knowledge-based 'design for multi-X' method, aimed at improving and assisting the work of designers, manufacturers, and inspectors in the areas of product redesign and process reconfiguration. Designers are not necessarily experts in manufacturing and verification processes; likewise, manufacturers and inspectors may not be experts in design. For this reason, the Design Guidelines Collaborative Framework (DGLs-CF) constitutes a meeting point for all three parties, where their knowledge is formalized, expanded upon, and put at the designers' disposal, thereby maximizing the user-friendliness of the results. The DGLs-CF is characterized by the homogeneous union of different algorithms, clear interfaces among the modules that implement them, and clear roles assigned to the different actors. These elements, together with a strong adherence to the ISO GPS standards, make the DGLs-CF the perfect environment for researchers, experts in different fields, and industrial partners to formalize their knowledge, and develop and implement their own algorithms and procedures. The Design Guidelines Collaborative Framework uses the simple IDEF0 formalism to describe the DGLs-CF framework in a top-down way, in order to facilitate readers' comprehension, and their adoption and development of the framework. Several case studies on the application of the DGLs-CF in industrial environments show the framework's effectiveness and robustness. Industrial and academic researchers will find this book a useful guide to the DGLs-CF and mechanical engineers will be quick to appreciate the streamlined approach it describes. © Springer-Verlag London Limited 2010.

Abstract: The effect of shot peening on the plane bending fatigue of a 7.2 g/cm 3 0.5%C Cr-Mo sintered steel was investigated. Shot peening experiments were first carried out with different parameters (shot diameter and hardness, coverage) and surface densification, work hardening and residual stresses were monitored. The dimensional and geometrical characteristics of the shot peened specimens were measured, as well. The improvement in the fatigue resistance is noticeable, up to 30% with respect to the as sintered material. © 2010 Metal Powder Industries Federation.

Abstract: The effect of the sintering temperature on the dimensional and geometrical precision of a 3%Cr-0.5%Mo- 0.5%C ring-shaped part produced in an industrial plant was studied. The part was compacted to 6.8 g/cm3 green density and sinter-hardened at 1120°C, 1250°C, 1300°C and 1350°C. Despite the large shrinkages (up to 1.24% at the highest temperature), dimensional and geometrical characteristics do not worsen noticeably on sintering, except for the dimensional tolerances on the diameter, which anyway keep a good precision level, from IT3 to IT4-IT5 (internal diameter) and from IT5 to IT6-IT7 (external diameter). According to the results, sintering at high temperature up to 1350°C does not seem to impair the most important characteristic of sintered parts, i.e. the precision. © 2010 Metal Powder Industries Federation.

Abstract: This study represents a preliminary activity for the biomechanical numerical modeling aimed at the prediction of the human foot behavior and the deformation under different load conditions. It also represents the starting point to develop a scientific approach for the functional mass customization aimed at the optimization of comfort in footwear. Reverse Engineering (RE) methodologies developed for building up the external shape of the human foot are presented and discussed. Aim of this work is to study the problem of the digitalization of human feet under different conditions using three technologies: shape from stereo, from silhouette and from shading. The foot is one of the most difficult human parts to reconstruct taking into account the complex surface and the high curvature. In this article the disadvantage and advantage of each technique are analyzed. In particular tests about reliability and precision of the measure are considered. © 2010 Society for Experimental Mechanics Inc.

Abstract: The dimensional and geometrical characteristics of Charpy bars produced with two different steels were investigated to evaluate the effect of increasing the sintering temperature from 1120 °C (conventional sintering temperature) up to 1350 °C. The problem was approached from the Geometric Dimensioning and Tolerancing (GD&T) point of view, referring to the standard ASME Y14.5 (2009). The dimensional and geometrical characteristics were evaluated using a Coordinate Measuring Machine (CMM), measuring the surfaces by scanning mode. The work highlights that the increase in the sintering temperature, aimed at improving the mechanical properties, does not prevent the main benefit of this technology, i.e., the possibility of producing parts with good dimensional and geometrical precision. Moreover, a methodology establishing the measurement procedures and data processing, to be used in future work for the characterisation of more complex shapes, was defined. © 2010 Elsevier B.V.

Keywords: Geometric dimensioning and tolerancing | Powder metallurgy | Shrinkage

Abstract: The SPES Project at INFN Laboratori Nazionali di Legnaro SPES Technichal Design Report - www.lnl.infn.it/~spes/TDR2008/ is now in its early construction phase. SPES is an ISOL type Radioactive Ion Beam (RIB) J.Khalili, E. Roeckl, The Euroschool Lect. on Phys. with Exotic Beams, Vol. II, Springer (2006) facility for the production of neutron-rich radioactive nuclei by uranium fission. RIBs will be produced by proton induced fission on a UCx multi foil direct target at a rate of 1013 fps, more than one order of magnitude larger than the currently available beam intensities. The recent developments on the production, ionization and acceleration of RIBs at SPES are hereafter presented. © 2010 Elsevier B.V. All rights reserved.

Abstract: Considering the conventional process involving the three main steps of powder preparation, cold compaction in rigid dies, and sintering, the dimensional characteristic of PM parts are mainly determined by the compaction step and their precision depends on the compaction tools and on the compaction parameters. This work aims at studying the powder compaction to improve the homogeneity of density and the dimensional characteristics without detrimental of productiveness. The study is focused on a pulley showing a quite complex shape and strict dimensional requirements. The material used is MPIF FC-0205-35, which is compacted by a 200 tons press. The reference compaction conditions are those used in the standard production. The dimensional characteristics are evaluated using a Coordinate Measuring Machine (CMM). Measurement and data processing procedures are defined according with ISO-GPS standards. The distribution of porosity is determined by Image Analysis on metallographic specimens.

Keywords: Geometric dimensioning and tolerancing | Powder compaction

Abstract: Measuring cylinders' out-of-roundness is still a big issue when high accuracy, high velocities or large cylinders are needed. The performance of the methods for roundness detection based on multi-probe scanning are strictly related to both the 3-D motion of the cylinders and the probes mounting configuration. Those effects are currently taken into account only in its 2D simplified form. Due to the lack of methods able to simulate 3D effects, a combined mathematical numerical method was developed. The cylinder is modelled making use of a mathematical description via Discrete Fourier Transform (DFT) of both its cross section and axis deviation. Efficient numerical simulation is employed to estimate the sensors' output taking also into account the cylinder shape effect interaction with unilateral constraints as a function of the cylinder rotation. Some simulations are carried out with the purpose of demonstrating the importance of modelling the entire 3D effects. Simulations show that an inaccuracy on 1° inclination of the probes support can result in an error of 1mm on the sensors output even considering a max amplitude of harmonics of 0.1 mm. Finally a reconstruction using the three point method based on FFT is applied to simulated measures showing that the 3D effects can increase the fluctuating part of the radius reconstruction error by 100 times.

Keywords: Cylinder | Measurement | Milling | Modelling | Roundness | Simulation

Abstract: Previous work developed a knowledge-based method named Design GuideLines Collaborative Framework (DGLs-CF), adopted during product redesign and process reconfiguration and aimed at dealing and matching with particular manufacturing and verification technologies, according to ISO GPS concepts. Aim of present work is improving the role of the ISO GPS within the DGLs-CF, not only to raise coherence in terms of concepts, but to gain some important internal and external improvements for the DGLs-CF. The main activity toward achieving this goal is the formalization of DGLs-CF product features by means of the ISO GPS features. The procedure is proposed and the consequences of its application on the elements of the DGLs-CF are evaluated. A case of study as an example of application is also presented. A significant improvement in the DGLs-CF is realized, both in terms of knowledge structure and organization, and in terms of the possibility of interfacing it with other methodologies, tools, and environments. Copyright © 2008 by ASME.

Keywords: ISO GPS (geometrical product specifications) | ISO TC 213 | Knowledge-based engineering | Process reconfiguration | Product features | Product redesign

Abstract: The LISA Technology Package (LTP) on board the LISA Pathfinder mission aims to demonstrate some key concepts for LISA which cannot be tested on ground. The mission consists of a series of preplanned experimental runs. The data analysis for each experiment must be designed in advance of the mission. During the mission, the analysis must be carried out promptly so that the results can be fed forward into subsequent experiments. As such a robust and flexible data analysis environment needs to be put in place. Since this software is used during mission operations and effects the mission timeline, it must be very robust and tested to a high degree. This paper presents the requirements, design and implementation of the data analysis environment (LTPDA) that will be used for analysing the data from LTP. The use of the analysis software to perform mock data challenges (MDC) is also discussed, and some highlights from the first MDC are presented. © 2009 IOP Publishing Ltd.

Abstract: The data analysis of the LISA Technology Package (LTP) will comprise a series of discrete experiments, each focusing on a particular noise measurement or characterization of the instrument in various operating modes. Each of these experiments must be analysed and planned in advance of the mission because the results of a given experiment will have an impact on those that follow. As such, a series of mock data challenges (MDCs) will be developed and carried out with the aim of preparing the analysis tools and optimizing the various planned analyses. The first of these MDCs (MDC1) is a simplified treatment of the dynamics along the axis joining the two test masses onboard LISA Pathfinder. The validation of the dynamical model by predicting the spectra of the interferometer output data is shown, a prediction for the data analysis is calculated and, finally, several simulated interferometer data sets are analysed and calibrated to equivalent out-of-loop test mass acceleration. © 2009 IOP Publishing Ltd.

Abstract: LISA Pathfinder (LPF) is a science and technology demonstrator planned by the European Space Agency in view of the LISA mission. As a scientific payload, the LISA Technology Package on board LPF will be the most precise geodesies explorer flown as of today, both in terms of displacement and acceleration sensitivity. The challenges embodied by LPF make it a unique mission, paving the way towards the space-borne detection of gravitational waves with LISA. This paper summarizes the basics of LPF, and the progress made in preparing its effective implementation in flight. We hereby give an overview of the experiment philosophy and assumptions to carry on the measurement. We report on the mission plan and hardware design advances and on the progress on detailing measurements and operations. Some light will be shed on the related data processing algorithms. In particular, we show how to single out the acceleration noise from the spacecraft motion perturbations, how to account for dynamical deformation parameters distorting the measurement reference and how to decouple the actuation noise via parabolic free flight. © 2009 IOP Publishing Ltd.

Abstract: An extended work is in progress concerning the target development for the SPES (Selective Production of Exotic Species) project. The SPES will be an ISOL based facility (Isotope Separation On Line) in which a proton beam of 40 MeV and 0.2 mA impinges directly on a uranium carbide target. After the mass separation and re-acceleration on the experimental sites, the RIBs will have an intensity of the order of 109 pps (for 132Sn) and an energy up to 13 MeV/u. The new idea that characterize this project is the design of its target: we propose a target configuration capable to keep high the number of fissions, low the power deposition and fast the release of the produced isotopes.

Abstract: During product development, the verification process should already be considered at the design phase to ensure that the characteristics of the product are measured effectively and reliably. Moreover, the verification process may prove more effective if the inspector is aware of the specific designer's intents. The development of the new ISO GPS (Geometrical Product Specifications) standards is mainly founded on these considerations. In accordance with the ISO GPS concepts, previous work developed a knowledge based system named Design GuideLines (DGLs). This system provides the designer with the knowledge concerning the manufacturing and verification procedures/tools and better links the manufacturing and verification processes to the designer's activities/needs. Further research then exploited the DGLs to discover the relations among product features determined by a particular manufacturing process. This work again uses the DGLs to prove that further relations among product features may also be determined by the verification process. This knowledge helps designers in understanding the consequences of the modifications applied to the product features required to improve the measurability of the product. Moreover, inspectors can better manage the verification procedure knowing these relations among the product features.

Keywords: Geometrical product specifications (GPS) | ISO/TC 213 | Knowledge based engineering (KBE) | Product features | Verification process

Abstract: Previous work developed a knowledge-based method named Design GuideLines Collaborative Framework (DGLs- CF), adopted during product redesign and process reconfiguration and aimed at dealing and matching with particular manufacturing and verification technologies, according to ISO GPS concepts. Aim of present work is improving the role of the ISO GPS within the DGLs-CF, not only to raise coherence in terms of concepts, but to gain some important internal and external improvements for the DGLs-CF. The main activity toward achieving this goal is the formalization of DGLs-CF product features by means of the ISO GPS features. The procedure is proposed and the consequences of its application on the elements of the DGLs-CF are evaluated. A case of study as an example of application is also presented. A significant improvement in the DGLs-CF is realized, both in terms of knowledge structure and organization, and in terms of the possibility of interfacing it with other methodologies, tools, and environments. Copyright © 2008 by ASME.

Keywords: ISO GPS (geometrical product specifications) | ISO TC 213 | Knowledge-based engineering | Process reconfiguration | Product features | Product redesign

Abstract: A solution for a target aimed at the production of exotic nuclei will be analyzed. In the proposed configuration a primary proton beam (40 MeV, 0.2 mA) directly impinges on uranium carbide disks. The exotic nuclei are produced as a result of high energy fissions in 238U compounds. The system has been conceived in order to obtain both a high number of neutron-rich atoms, originating from about 1013 fissions s-1 and a low power deposition in the target. The target container is held at about 2000 °C in order to maximize the number of extracted fission fragments. © 2008 Elsevier B.V. All rights reserved.

Keywords: Fast release time | Fission fragments | Heat transfer | Isol target | Multi-foil | Power dissipation | Uranium carbide

Abstract: Product design and optimisation today involves so many fields of expertise, many of which are in rapid evolution, that it can be very difficult for the designer to manage them. This paper describes the development of the DGLs (Design Guidelines), a knowledge-based tool that could be of great help to designers and engineers in modifying their products to get compatibility with different manufacturing and verification technologies. The current release of the DGLs, heavily influenced by the adoption of some ISO-GPS (Geometrical Product Specification) concepts, has been validated using the Rapid Prototyping technique called FDM (Fluid Deposition Modelling) and the CMM (Coordinate Measuring Machine) verification technique. © Springer-Verlag London Limited 2007.

Keywords: Design Guidelines | Geometrical Products Specifications (GPS) | ISO Technical Committee 213 (ISO/TC 213) | Knowledge based systems (KBS) | Rapid Prototyping

Abstract: Aim of the LISA Test-flight Package on board the LISA Pathfinder mission is to provide in-flight demonstration of some of the LISA critical technologies in achieving the free-fall condition of a LISA-like test-mass in the bandwidth from 1 to 30mHz. Accordingly, owing to high inertial loads arising during the launch phase the test-mass needs to be firmly secured to the GRS, in order to avoid collision with the surrounding electrodes and housing parts. After the launch and orbit commissioning, the test-mass must be released to floating conditions, in compliance with strict requirements of initial position and velocity, due to the low force and torque authority made available by the capacitive actuation system. The Caging Mechanism Assembly is being designed by Alcatel Alenia Space Italia and it constitutes the GRS subsystem dedicated to cage and release the test-mass. The release phase to floating conditions has been identified as critical for the entire mission, therefore a ground-based verification of such a function has been deemed necessary. The verification approach adopted is to set both test-mass and release-dedicated plunger mock-ups in representative tribological conditions of the in-flight situation. An effort is being made to build a facility that enables to characterize the momentum transfer between the two suspended bodies and verify the compliance of the design of the release-dedicated mechanism subsystem of the Grabbing Positioning and Release Mechanism of the CMA. The proposed experiment and the facility status are here presented and discussed. © 2006 American Institute of Physics.

Abstract: Considering the whole product life-cycle, product model is usually defined during the design phase, given a set of requirements and constraints belonging to the same domain. The use of different manufacturing and verification technologies may, however, profoundly affect the characteristics of the product, so that a re-design phase is often necessary. In previous work, a Knowledge Based System named Design GuideLines (DGLs) was developed, aiming to help the designers make the product model compatible with the requirements and constraints of the specific manufacturing and verification domains. During the DGLs development, the possibility emerged to exploit them in order to identify possible relations among product features. This aspect seems very important, further helping the designer to better understand the consequences of the modifications suggested by the DGLs and applied to the product model during the re-design phase. The present work aims to identify these relations among product features. The result of DGLs exploitation has been critically analyzed to highlight the link between manufacturing characteristics and product features, and, further, among features themselves. Unpredictable relations among the product features, given a particular Rapid Prototyping technology as manufacturing technology, have been discovered and exploited. Copyright " 2006 by ASME.

Keywords: Fluid deposition modeling | Knowledge based systems | Process parameters | Product features | Rapid prototyping

Abstract: We report on the development of the LISA Technology Package (LTP) experiment that will fly onboard the LISA Pathfinder mission of the European Space Agency in 2008. We first summarize the science rationale of the experiment aimed at showing the operational feasibility of the so-called transverse-traceless coordinate frame within the accuracy needed for LISA. We then show briefly the basic features of the instrument and we finally discuss its projected sensitivity and the extrapolation of its results to LISA. © 2005 IOP Publishing Ltd.

Abstract: In a Design For Manufacturing context, Rapid Prototyping techniques are some way still considered as “new technologies”: the peculiar characteristics of the manufacturing processes are not widely known and may deeply affect the final product functionality. A Knowledge Based System, the Design Guidelines — DGLs, was developed by our Research Group at the University of Udine; it evaluated the products design, in order to verify its feasibility by DMLS (Direct Metal Laser Sintering) Rapid Prototyping technique. During the evaluation process, the DGLs also keep into consideration the aspects relating the verification step, according to the ISO-GPS principles, thus enhancing the completeness of the tool. Aim of this work was to customise the DGLs for design optimisation in FDM (Fused Deposition Modelling), also evidencing the critical aspects and proposing alternative solutions. The contents and structure of the customised version of DGLs are presented in this work.

Keywords: Fused deposition modelling | Knowledge-based systems | Rapid prototyping

Abstract: LISA (Laser Interferometer Space Antenna) is a joint mission NASA-ESA for fundamental physics studies, which aims detecting the gravitational waves. Aim of this work is focusing the attention on the Inertial Sensor (IS), the core of the experiment, for what concern quality and reliability issues. To guarantee the required IS quality a careful analysis of the geometrical characteristics and the related manufacturing technologies was performed, being the dimensional and geometrical tolerances very narrow (less than 10 microns). The verification of the geometrical characteristics conformance and the definition of the assembly step required the development of adequate procedures, aiming at guarantee the reliability of the IS output signals.

Abstract: LISA (Laser Interferometer Space Antenna) is a joint NASA-ESA mission for fundamental physics studies, which aims at directly detecting gravitational waves. Gravitational waves are expected to cause a space-time distortion, which acts on a plane perpendicular to the wave's direction and has two orthogonal components with equal modulus and opposite sign. LISA will detect such gravitational strains by means of three Michelson laser interferometers measuring variations in the relative position of three satellites forming an equilateral triangle formation and flying in heliocentric orbit. To ensure detection of gravitational waves, the interferometer end mirrors have to be shielded against any non-gravitational force, especially those acting in the same frequency range as the gravitational waves. While the performance requested to the interferometer, though high, is not exceptional, the quality and the reliability of the shielding effect require careful investigation. The present paper will illustrate the big picture of the LISA project, focusing on the most relevant issues from the QRM point of view.

Abstract: We describe the current design of the European gravitational sensor (GS) for the LISA Technology Package (LTP) that, on board the mission SMART-2, aims to demonstrate geodetic motion within one order of magnitude of the anticipated LISA performance. We report also the development of a noise model used in assessing the performance and determining the feasibility of achieving the overall noise goals for the GS. This analysis includes environmental effects that will be present in the sensor. Finally, we discuss open questions regarding the GS for LTP and LISA, ground testing, and verification issues.

Abstract: The effect of boron on sintering of austenitic stainless steel was studied with reference to atmosphere (nitrogen-hydrogen mixtures) and temperature conditions. Specimens were characterised by the usual microstructural techniques and the boron distribution in the microstructure was also studied by means of Auger electron spectroscopy and secondary ion mass spectroscopy. In addition, tensile tests were carried out to verify the influence of the process parameters on the mechanical properties of the materials. Boron strongly enhances sintering by liquid phase formation only when the process is carried out in pure hydrogen at a temperature higher than 1200°C. In those conditions a eutectic reaction between austenite and a complex boride of the type (Fe, Cr, Mo)2B occurs favouring densification through the well known mechanisms of liquid phase sintering. A very low fraction of residual porosity is obtained. Conversely, the presence of nitrogen in the sintering atmosphere impedes boron–steel interaction and sintering is inhibited. The liquid phase sintered specimens exhibit a dense microstructure which should provide good corrosion resistance. PM/0631. © 1994 Maney Publishing.

Abstract: An Auger Electron Spectroscopy study of vacuum and hydrogen sintered martensitic stainless steel is presented, aimed at interpreting the influence of the atmosphere on the sintering process. The spectroscopic analysis, carried out on the surfaces of both powder grains and pores in the sintered specimens, allows for comparison of their chemical states and discussion of the chemical-physical processes which are active during sintering and hence responsible for the destabilization of oxides that cover the powder surface. Some noticeable differences between the two atmospheres are pointed out concerning the sintering mechanisms, and a correlation with some technological properties of pieces is proposed.

Abstract: Laser beam penetrations have been carried out on URANUS 45 duplex stainless steel sheets, varying the beam power as well as the traverse speed. The microstructural results, in terms of bead geometry, microhardness and austenite content, have been related to the working parameters, with the support of an analytical thermal model of laser beam welding.