Powder Injection Molding (PIM) for Low Cost Manufacturing of Intricate Parts to Net-Shape
Abstract : Powder Injection Molding (PIM) is a low cost manufacturing process that produces very complex parts to net-shape in a wide variety of materials and unique alloys, including superalloys, stainless steels and carbides, resulting in minimal secondary and assembly operations. PIM offers significant cost savings, increased design and materials flexibility, increased possibility of miniaturization, high mechanical properties, good surface finish and high speed production. The activities and expertise in powder metallurgy as well as in process numerical modeling related to powder injection molding at the Industrial Materials Institute of the National Research Council of Canada (NRC-IMI) and at Maetta Sciences, a company that has research and development facilities at the NRC-IMI, will be presented. Selected solutions and examples realized by NRC-IMI and by Maetta Sciences using respectively their high pressure and their scalable PIM platforms will be presented and described. Potential applications for the military, transportation and aerospace sectors will be highlighted.
Partially Water-Soluble Binder Formulation for Injection Molding Submicrometer Zirconia
A binder system containing 60% by volume of a water-soluble major constituent was formulated and tested for powder injection molding ceramic materials. The main components of the binder phase were a low molecular weight polyethylene glycol, an oxidized high density polyethylene, polyvinyl butyral and stearic acid. Ceramic powder-binder mixes containing these binder components and up to 45% by volume of a submicrometer stabilized zirconia powder were prepared and characterized. The apparent viscosity of these mixes at a temperature of 190°C and a shear rate of 100 s-1 was determined to be 700–800 Pa·s. Binder removal from parts produced by injection molding these feedstocks was accomplished using a two-stage process. The water-soluble constituent, polyethylene glycol, was removed by dissolution in water at 50°C. Tests showed that approximately 90% of the polyethylene glycol could be removed from a 2-mm thick part during a 2 h immersion in water. The remaining binder constituents were removed using a thermal treatment to 500°C at a heating rate of 100°C/h. Thermogravimetric analysis revealed a good separation of the decomposition regions for the various components when heated in an argon atmosphere. A final sintering step in air at 1500°C produced parts having a density above 99%.
Finite element solution of three-dimensional turbulent flows applied to mold-filling problems
This paper presents a finite element solution algorithm for three-dimensional isothermal turbulent flows for mold-filling applications. The problems of interest present unusual challenges for both the physical modelling and the solution algorithm. High-Reynolds number transient turbulent flows with free surfaces have to be computed on complex three-dimensional geometries. In this work, a segregated algorithm is used to solve the Navier–Stokes, turbulence and front-tracking equations. The streamline–upwind/Petrov–Galerkin method is used to obtain stable solutions to convection-dominated problems. Turbulence is modelled using either a one-equation turbulence model or the κ–e two-equation model with wall functions. Turbulence equations are solved for the natural logarithm of the turbulence variables. The change of dependent variables allows for a robust solution algorithm and good predictions even on coarse meshes. This is very important in the case of large three-dimensional applications for which highly refined meshes result in untreatable large numbers of elements. The position of the flow front in the mold cavity is computed using a level set approach. Finally, equations are integrated in time using an implicit Euler scheme. The methodology presents the robustness and cost effectiveness needed to tackle complex industrial applications. Copyright © 2000 John Wiley & Sons, Ltd.