Feature article: PIM International, Vol.2 No. 3 September 2008, pages 36-41, 2830 words

Author: Dr. David Whittaker, DW Associates, UK

DW Associates, 231 Coalway Road, Merry Hill, Wolverhampton, WV3 7NG, UK

A group of five separate papers at the PM2008 World Congress, held in Washington DC, June 2008, highlighted the continuing focus on enhancing the capabilities of PIM through the use of computer simulation or modelling. Dr. David Whittaker reports on some of the presentations.

Modelling complex 3D shapes

Two of the papers reviewed in the following report (Jenni et al p.37), (Ahn et al p.40) sought to extend the predictive capabilities of Moldex 3D, a leading commercial software package for the modelling of plastic injection moulding, in dealing with the alterations in feedstock material characteristics arising from the introduction of high levels of powder loadings into the plastic binder system.

The Moldex 3D packages have been developed and marketed by CoreTech Systems Co. Ltd. of Taiwan. This company span out of the Technical University of Taiwan in 1995, but continues to work closely with the University in enhancing its product range and database of feedstock material properties.

This software is based on solid hybrid meshes and the High Performance Finite Volume Method (HPFPM) and can model parameters such as solid melt flow, 3D runner effects, 3D mould temperature distributions, fountain flow, inertia effects and visco-elasticity. It can help the user to simulate plastic flow through the cavity, optimise gate locations, prevent shot and weld lines, evaluate cooling circuit designs, minimise cycle times, reduce warpage, predict optical birefringencies, simulate variothermal processes etc.

The packages are equipped with an automatic 3D mesh generation engine and with a proprietary Boundary Layer Mesh (BLM) feature to make it straightforward to prepare a high-quality mesh of any complex 3D shape. BLM enhances solver accuracy in viscous heating and pressure, thus improving warpage reduction significantly. Parallel computing support for all modules reduces analysis times by 50-80%. Standard modules offer:....

Further sections of this article include:

- Predicting powder/binder separation
- Effect of powder/binder separation in moulded parts
- Measuring the mixing process
- Predicting the effects of powder/binder separation on debinding and sintering

Figures and Tables:

Fig. 1 Filling simulation of a tungsten feedstock in a square spiral mould (From 'Quantitative Study of Process and Material Parameters on Flow Behavior of Feedstocks: Experimental Design and 3-D Simulation', Courtesy MPIF)

Fig. 2 The content is shown here as a fraction of maximum flowable solid content, assumed as 68% (from 'Quantitative Study of Process and Material Parameters on Flow Behavior of Feedstocks: Experimental Design and 3-D Simulation', Courtesy MPIF)

Fig. 3 Three dimensional tomograph of the micro-bending test structure (from 'Detection of Powder–Binder Separations During MicroPIM by Synchrotron Computer Tomography', Courtesy MPIF)

Fig. 4 This gradient plot shows the local particle density (in vol.%) across the bending test structure. The local density was calculated from the average of 100 slices (from 'Detection of Powder–Binder Separations During MicroPIM by Synchrotron Computer Tomography', Courtesy MPIF)

Fig. 5 Moldflow mesh (from 'The Effect of Processing Variables on Gas-Bubble Formation in Gas-Assisted Powder Injection Molding', Courtesy MPIF)

Fig. 6 Evolution of the interface between two fluids with the exponent n=0.4 in time at several down channel positions. (a) z=0, (b) z=0.5L, (c) z=L (d) z=2L, (e) z=3L and (f) z=4L. Here L is the length of a mixing unit with a blade twisting 180oC in left or right direction. (from 'Mixing Simulation for Powder Injection Molding Feedstock: Quantification and Sensitivity Analysis', Courtesy MPIF)

Fig. 7 The progress of mixing characterised by the normalised entropy increase depending on the index n in the viscosity model (from 'Mixing Simulation for Powder Injection Molding Feedstock: Quantification and Sensitivity Analysis', Courtesy MPIF)

Fig. 8 Shape and relative density distribution for injection moulded and sintered u-shaope part (from 'Integrated Simulation of Mold Filling (Binder-Powder Separation), Debinding and Sintering in PIM', Courtesy MPIF)