PowderMet2009: prospects improving after automotive debacle

Abstract

A homogeneous powder and binder distribution in the green body in powder injection moulding (PIM) is important. In the present study, the mould filling model of PIM has been developed, based on the multiphase fluid theory, viscosity model of feedstock and powder-binder drag force model. The particle Reynolds number is influenced by the particle size and density, resulting in the different drag force between powder and binder. Furthermore, the varied velocity of binder and powder will be obtained with numerical calculation of the continuity equations, leading to the change of green body homogeneity. CFX was used to simulate the mould filling in PIM. The results showed that the homogeneity of green bodies was relative to the filling patterns, which varied with different powder densities. The powders were not suitable for PIM when the particle size was bigger than 20 μm, and the fine powders were beneficial to improve the homogeneity.     

Process simulation of powder injection moulding: identification of significant parameters during mould filling phase

Abstract

Simulating and optimising the powder injection process are complex problems since a number of linked material, geometry and process variables have to be considered. In addition, it is very difficult to identify critical parameters for designing binder systems, feedstocks, parts, moulds and processing conditions owing to the fact that multiple objective functions have to be considered. Towards the goal of identifying the level of significance of various material, process and geometry parameters during powder injection moulding, a systematic procedure for sensitivity analysis has been successfully developed for the mould filling phase of the PIM process. In this sensitivity analysis, all input parameters were defined for the mould filling simulation and all output parameters for optimum design of part, mould and processing conditions and dimensionless sensitivity values for all input and output parameters were calculated, which allow parameters with different units to be compared quantitatively. The sensitivity analysis procedure developed will be an invaluable tool for both the design engineer in the PIM industry who has to determine the critical input parameters for given design targets, as well as for the production engineer who has to optimise and monitor the production stage.     

Characterisation of 316L powder injection moulding feedstock for purpose of numerical simulation of PIM process

Abstract

Viscosity, specific heat and thermal conductivity of the standard feedstock of 316L stainless steel have been measured under the typical conditions of a real powder injection moulding (PIM) process. The viscosity was measured in a wide range of shear rates at four different temperatures. The experimental viscosity data were fitted into the Carreau-Yasuda model. Both specific heat and thermal conductivity were measured in the temperature range that overlaps the recommended processing range for the studied feedstock. It has been shown that at high cooling rates the transition temperature of the binder material is shifted towards lower temperatures. Tabulated values of thermal conductivity and specific heat for the studied feedstock are presented. The obtained data can be used for numerical simulation of the powder injection moulding process.     

Influence of injection moulding and sintering parameters on properties of 316L MIM compact

Abstract

This study elucidates the effects of key injection moulding and sintering factors on the dimensions and mechanical properties of 316L stainless steel metal injection moulded compact. Sintered parts of optimal quality can be produced by properly setting the process parameters. Taguchi method and principal component analysis are performed initially to elucidate and optimise the key control factors that affect the qualities of metal injection moulded compact. Next, a feasible process window is tested by observing the powder and binder distribution of green parts, for various control factors of injection moulding. Experimental findings show that, first, a proper injection speed facilitates mould filling during injection moulding and so improving the quality of sintered parts; second, temperature critically determines the rate of dimensional shrinkage, density and hardness of sintered parts; Third, optimal parameters setting can efficiently improve the quality of 316L metal injection moulded compact.     

Hot micro-embossing: effect of pressure on 316L metal parts

Abstract

The use of replicative processes has become strategic and critical in industry to produce precise, microscopically detailed metallic parts and devices via low cost manufacturing routes. Metal powder hot embossing is an emerging process that brings some advantages associated with the reduction of production costs relative to powder injection moulding (PIM). The technology involves four distinct steps: preparation of the selected feedstock material (powder and binder); hot embossing; debinding; and sintering. The effect of continuous pressure during the hot embossing step as a means of replicating microdetails in 316L stainless steel parts is examined. Dimensional accuracy, microstructure and mechanical properties of the parts produced were evaluated. For the configuration tested, the most promising results were achieved when processing at 180°C for 30 min at a pressure of 14 MPa.     

Properties of Anisotropic Nd(Fe,Co)B Type Sintered Magnets Produced by Powder Injection Moulding

Abstract

Anisotropic Nd(Fe,Co)B type sintered permanent magnets were fabricated by powder injection moulding (PIM) using paraffin wax as a binder. A conventional process was also used in order to compare the resultant properties with those of sintered magnets produced by PIM. Magnetic properties, microstructure, and constituents were investigated by dc fluxmeter, scanning electron microscopy, X-ray diffractometry, wavelength dispersive X-ray analysis, and ir absorption analysis. Effects of particle alignment of the sintered magnets on the magnetic properties and anisometric linear shrinkage ratios were studied. Particle alignment of sintered magnets produced by PIM was 4% lower than that of the conventional process. The PIM sintered magnet exhibited a maximum energy product of 232 kJ m^?3. The residual carbon after debinding affected the magnetic properties and sintering characteristics by contaminating the liquid phase during PIM sintering. PM/0782     

Netshaping concepts for tungsten alloys and composites

Abstract

The conventional powder metallurgy (PM) approach of compaction and sintering has been used extensively in the fabrication of tungsten alloys and composite hardmetals based on WC-Co. In fact, these are some of the earliest known materials to have been fabricated by the PM route. The last 15-20 years have seen the emergence of a new shaping technique of powder injection moulding (PIM) which can shape such tungsten metal alloys and composites into complex near net shaped components. The PIM process starts with the mixing of an organic binder with the desired powders in the form of a homogeneous mixture, known as a feedstock. The feedstock, like plastics, can be moulded into near net shapes from which the organic part is removed and then the material can be sintered to almost theoretical density. This produces complex, near net shaped parts that have properties that are comparable to that of the press and sintered materials. This paper will provide a brief overview of the use of PIM in tungsten based alloys and composites and discuss some of the applications of these materials.     

Mechanical alloying of FeAl intermetallic powder for metal injection moulding process

Abstract

The Fe–48 at.-%Al powder used for powder injection moulding (PIM) was prepared by mechanical alloying in a high energy planetary ball mill and subsequent vacuum annealing. The effects of stearic acid (SA) as the process control agent on powder characteristics were investigated using X-ray diffractometer, laser particle size analysis and scanning electron microscopy. The dependence of solvent debinding efficiency of PIM feedstock on the powder characteristics was also studied. The results indicate that a low SA content for ball milling helps to prepare near spherical, coarse powder particles that exhibit good solvent debinding efficiency. On the contrary, a high SA content leads to thin layered, small particles with poor PIM solvent debinding efficiency. An intermediate SA content such as 1 wt-% makes the ball milled powder combine the advantageous characteristics for PIM process.     

Injection Moulding (Review)

Powder injection moulding, a relatively new technique for manufacturing articles of complex shape from metal or ceramic powders, is considered. Production operations are described in detail: powder mixing with a binder to form a slip, injection of the slip into a mold, binder removal, sintering of the billets obtained. Fields of application for articles prepared by injection moulding are listed.     

Processing of Mn–Zn ferrites using mould casting with acrylic thermosetting binder

Abstract

In this paper, a simple manufacturing process for Mn–Zn ferrite powder is described, which can be considered as a modified powder injection moulding process. This method uses acrylic thermosetting resin as the binder. The moulding is carried out at room temperature by directly pouring the slurry (resin and ferrite) in the mould. The mixture is heated at the curing temperature (70°C) of resin to permit polymerisation and cross linking of the polymer. In order to optimise the moulding step, different volume fractions of powder with resin were mixed. The optimal powder load was 50 vol.-%. The best thermal debinding cycle was determined by means of thermo-gravimetric analysis. Sintering was performed according to oxygen partial pressure equilibrium curves at 1330°C for 3 h. Magnetic properties were compared with those obtained by uniaxial compacted parts.     

Influence of sintering conditions on tensile and high cycle fatigue behaviour of powder injection moulded Ti–6Al–4V at ambient and elevated temperatures

Abstract

Tensile and high cycle fatigue properties of Ti–6Al–4V samples fabricated by powder injection moulding (PIM) are examined at room temperature and elevated temperatures. Standard wrought Ti–6Al–4V material is used for comparison. The tensile and the fatigue strength of samples fabricated by powder injection moulding are found to be significantly lower than conventional wrought material. On the other hand, strength and ductility of metal injection moulded (MIM) samples are high enough to be of large practical interest, in particular if the low processing costs for intricate shapes are taken into account. The inferior properties of the MIM material are caused by considerable remaining porosity, enlarged grain size and increased interstitial content. Prolonged sintering times lead to improved density and strength. At the same time, the room temperature ductility is observed to drop to very low levels, presumably because of additional grain growth.     

Metal injection moulding of bronze using thermoplastic binder based on HDPE

Abstract

In the present work, the injection moulding process of a Cu–10Sn bronze has been studied. Different formulations of binders based on high density polyethylene, paraffin wax and polyethylene glycol have been used. The optimisation of the metallic load is based on torque measurements and rheological studies. The optimum powder loading was 60 vol.-%. The moulding parameters are selected to obtain homogeneous specimens with three different geometries and without distortions. The green parts have an adequate strength for handling. The organic binder was eliminated by thermal debinding under N₂/10%H₂ atmosphere. The debinding process has been designed by means of thermogravimetrical analysis of binder and feedstock and considering the maximum heating rates at which the samples do not present cracks. The specimens were sintered at temperatures between 875 and 950°C in the same reducing atmosphere.     

温压工艺最新进展--流动温压技术

流动温压技术兼有温压技术和金属注射成形技术的优点,既克服了传统粉末冶金技术在成形方面的不足,又避免了注射成形技术的高成本.由于微细粉末的加入和较多的润滑剂含量而使混合粉末在温压时转变成一种具有良好流动性和充填能力的黏流体,从而可以直接成形零件的复杂几何形状如侧凹、螺纹孔等而不需要其后的二次机加工,具有很大的应用潜力.     

Optimisation of process conditions in powder injection moulding of microsystem components using robust design method Part 2 – Secondary design parameters

Abstract

Powder injection moulding (PIM) is a proper fabrication method for microsystem technology components. This paper studies the process control of PIM to create thin walled, high aspect ratio geometries, which can be easily found in microtechnology based electro chemical, mechanical and biological systems (MECS). The powder used in this study is gas atomised 316L stainless steel with a median particle size of 10 μm. The effects of reducing the thickness of high aspect ratio geometries on the secondary design parameters including the maximum wall shear stress, cooling time and standard deviations of the melt front velocity and areas are studied. The study shows process parameters including fill time, feedstock injection temperature, mould wall temperature and switchover position can be optimised using the Taguchi robust design method.     

Injection moulding of oxide reduced copper powders

Abstract

Fine oxide reduced copper powders of about 10 μm mean grain size are irregular in particle shape and high in oxygen content, which poses a difficulty in achieving good properties from injection moulding. Injection moulding was possible when a multicomponent binder with a large fraction of the backbone polymer was used. Injection moulded parts could be sintered to a density of about 95% theoretical, if reduction of the residual oxides in the powder was effectively carried out prior to closure of pores during sintering. Under such a condition, the injection moulded parts could attain an electrical conductivity higher than 80% of pure copper. July 2004.     

Variability of feedstock viscosity and its correlation with dimensional variability of green powder injection moulded components

Abstract

In this study, a correlation between green part dimensional variation and feedstock viscosity variation is presented for the powder injection moulding (PIM) manufacturing process. A correlation of an increase in green part dimensional variation as feedstock viscosity variation increases has been found and the correlation was independent of powder type (316L gas atomised and water atomised) and mixing technique (batch and continuous). The variation of feedstock viscosity was lowest over the greatest temperature range for high shear continuous compounding with a broad distribution of irregularly shaped powder. Thus, this feedstock material would have the greatest process window for injection moulding with the least variation.     

粉末注射成形模拟分析的研究现状与发展

粉末注射成形(PIM)是集塑料成形与传统粉末冶金工艺优势而产生的一种新型零部件近净成形技术。叙述了粉末注射成形的优点和有待解决的难题,利用模拟软件可以有效地避免或减少PIM各个阶段的缺陷,重点介绍了国内外在PIM喂料充模模拟技术上已经取得的成果和待解决的问题,依据目前的PIM喂料充模模拟研究现状,对PIM模拟的发展进行了展望,认为以Burracuda软件为基础的粉末颗粒模拟研究将成为PIM喂料充模模拟的主要发展趋势,并为粉末注射成形喂料模拟技术的进一步发展提供参考。     

Effect of nickel boride and boron additions on sintering characteristics of injection moulded 316L powder using water soluble binder system

Abstract

A new metal injection moulding system for 316L stainless steels has successfully been derived and tested. A mixture of small water atomised powder (average size 15 µm), larger gas atomised powder (average size 75 µm), and sintering additives has been coupled with a new water soluble binder system for economical powder injection moulding. The details for each process step and the effect of sintering additives are described. The binder system consists of poly (2-ethyl-2-oxazoline) as the leachable polymer, polyethylene as the backbone, and stearic acid as a surfactant and plasticiser. This binder system provides satisfactory mixture stability, excellent mouldability, and reasonably fast water leaching and thermal debinding rates. The optimum powder/binder compositions were determined using torque and capillary rheometry. Densification was by persistent liquid phase sintering through additives, such as nickel boride and boron. This 316L powder system was sintered to 7·9 g cm ^-3 (98·75% of theoretical) at 1285°C using nickel boride addition and at 1245°using boron addition. nickel boride additions are particularly effective at increasing the tensile strength and ductility. In contrast, the boron additions only increase the tensile strength and decrease ductility. Based on microstructure evaluations, this effect is traced to a continuous boride phase on the grain boundaries of the boron doped samples and a discontinuous boride phase on the grain boundaries of the nickel boride samples.     

Low viscosity feedstocks for powder injection moulding

Abstract

Powder injection moulding (PIM) carried out with the use of low viscosity feedstocks offers numerous benefits for manufacturing small complex shape parts. Unlike typical high pressure metal injection moulding (HPIM) viscous feedstocks, soft tooling can be employed for prototyping and small volume manufacturing. Compared to HPIM, there are very few studies on the rheology of low viscosity feedstocks. The objective of this paper is to clearly determine, using a statistical method, optimal models which define viscosity as a function of three parameters: shear rate, temperature and solid loading for low viscosity feedstocks. With the statistical method employed, it was found that the models of Herschel–Bulkley, Arrhenius, and Maron and Pierce can be used respectively to effectively model each of the three parameters stated previously. Moreover, the combination of these three models in one global model is proposed to predict the combined effect of the three parameters on low viscosity PIM feedstocks.     

粉末注射成形蜡基粘结剂溶剂脱脂行为研究

以YG8硬质合金为实验对象,研究了蜡基粘结剂注射成形生坯的溶剂脱脂行为,考察了时间、温度、生坯形状、厚度、表面积、粉末装载率和液固比对脱脂速率的影响,分析讨论了各因素影响脱脂速率的原因.结果表明:溶剂脱脂速率随温度升高而升高,随时间的延长而降低;脱脂初期扩散是控制性环节,温度是影响反应速率的主要因素,脱脂后期溶解成为控制性环节,浓度差减为影响反应速率的主要因素;液固比越大,脱脂速率越快,粘结剂最终脱除率越高;生坯粉末装载率越高,脱脂速率越慢,粘结剂最终脱除率越低;生坯形状对脱脂速率影响表现为样品厚度和表面积的影响,回归分析表明,脱脂速率与生坯表面积成正比,与生坯厚度的平方成反比.