Donald F. Heaney

Gravity induced solid grain packing during liquid phase sintering

The effects of gravity on the solid grain packing in liquid phase sintering have been investigated by both theoretical and experimental analyses. This treatment relies on quantitative microstructural measurements to determine the solid volume fraction variation along the direction of gravity. The model assumes that the grain packing coordination is proportional to the gravitational pressure and density difference between solid and liquid phases. It is confirmed by sintering experiments on W-Ni, and is consistent with a computer simulation model previously reported by German.

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.

Mechanical properties of metal injection moulded 316l stainless steel using both prealloy and master alloy techniques

Abstract Stainless steel 316L MIM components can be made from either prealloyed powders or from master alloys blended with carbonyl iron powder. In this study these two techniques were compared using prealloyed and master alloyed gas atomised powders of − 16 μm and − 22 μm sizes. Four different compounds were prepared, characterised and injection moulded into tensile bars. The bars were compared for green strength, green defects, sintered strength and microstructure. The green components are stronger when carbonyl iron powder is used with the gas atomised master alloy. This material also seems to be less susceptible to moulding defects. The sintering strength of the material produced using the pre-alloyed powder was higher than the master alloyed prepared material. Little difference in mechanical properties existed between the materials fabricated from gas atomised prealloyed − 16 μm and the − 22 μm powders. Also, the viscosity of the mixtures was higher for the − 16 μm material and the master alloy mixtures than for the –22 μm gas atomised prealloyed powders.

Effect of additives on sintering response of titanium by powder injection moulding

Abstract Powder injection moulding is a maturing technology that has proven most useful for the production of complex metallic and ceramic components of modest sizes. Considering the inevitable demand for cost effectiveness in automotive applications, components manufactured from low cost sponge titanium (Ti) powder currently reflect the most advantageous economics among the available Ti powders. This paper describes the net shape fabrication of Ti components and considers the role of iron and zirconium powder additions. Sintering cycle optimisation relied on differential scanning calorimetry to identify a cycle in the 1275–1300°C range for 1–2 h. The sintered material was characterised using tensile and hardness testing and microscopic examinations. The influence of test conditions on densification, microstructure and mechanical properties was analysed.

Variability of powder characteristics and their effect on dimensional variability of powder injection moulded components

Abstract In this study, the effect of powder characteristics and their variability on the dimensional variability of green and sintered PIM components has been examined for 316L stainless steel. Three lots of gas atomised and three lots of water atomised powders were characterised and used to make six batches of PIM compound. These compound lots were injection moulded using a cavity pressure transducer and screw position regulation controls. The moulded geometry was measured in the green state and sintered state for dimensional variability. The general findings are that gas atomised powder produce less dimensional variability than the water atomised powder from lot to lot, however, the water atomised powders produce less in lot dimensional variability and are generally less susceptible to distortion of cantilevered members during sintering. Also, the lot to lot variation in the powder characteristics, such as particle size and pycnometer density, have an effect on dimensional stability whereas variations in powder characteristics such as surface area, tap and apparent density, and chemistry have little effect on dimensional stability.

Shrinkage prediction of MIM parts by finite element simulation

The aim of this paper is to verify the reliability of numerical results obtained by using Mouldflow Plastic Insight (MPI) for prediction of metal part shrinkage. The approach implemented took advantage of the Finite Element (FE) analysis to simulate component fabrication and investigate the main causes of defects. Different FE meshes as well as shrinkage models were tested and evaluated. A Design of Experiments (DOEs) Technique was then used to plan the numerical simulation activity of the injection moulding phase and compare results with those obtained from the direct measurement of green parts. This research has confirmed that the choice of the correct shrinkage model was crucial to assess the influence of process parameter variation on part manufacturability, suggesting possible adjustments to improve part quality. Future researches will be addressed to the extension of analysis to large thin components and different classes of materials with the aim to improve the proposed approach. The originality of the work was related to the possibility of analysing component fabrication at the design stage and use the results in the manufacturing stage. In this way design, fabrication and process control were linked. [Received 10 November 2005, Accepted 14 January 2007]

Powder Injection Molding of Implantable Grade Materials

In this paper the attributes of powder injection molding that influence the ability to implant a material are evaluated. Specific emphasis is given to technology readiness of stainless steel, titanium and cobalt chromium alloys since these are the most common alloys that are both implantable and metal injection moldable. Issues such as ductility and strengthening are discussed. Also, component size capability of the technology is discussed since prosthetic replacement pushes the upper size limit of the technology and implantable micro devices that require MEMS (MicroElectroMechanical Systems) scale features push the lower limit.Copyright