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Thermal Flow Instability in Metal Injection Molding: Experiment and Simulation

  • J. F. Stevenson and F. Ilinca
Published/Copyright: April 6, 2013
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International Polymer Processing
From the journal International Polymer Processing Volume 21 Issue 2

Abstract

Metal injection molding (MIM) is similar to plastic molding in many respects, but MIM compounds (metal powders with polymer binders) are more susceptible to thermally induced flow instability because of their higher thermal diffusivity. The flow patterns for a 17-4PH MIM compound were observed and simulated for mold filling through a diaphragm gate over a range of filling times and melt-mold interface temperatures. Simulation predicted the observed free annular jet and internal voids in the molded part and also predicted that initial contact with the outside wall of the gate would eliminate the jet, thereby reducing voids and surface defects. Parts made using a mold with a thicker gate verified these predictions. For combinations of operating conditions and mold geometry that gave large thermally induced viscosity gradients, both observation and simulation showed unstable, asymmetric flow. In these cases, flow slowed and stopped in one region of the gate and accelerated in other regions. When the flow was inherently unstable, simulations predicted an exponential growth in maximum temperature differences at symmetric locations in the mold gate. Based on 34 experimental observations and 102 simulations, a boundary was established between regions of stable and unstable flow in terms of the dimensionless Graetz number Gz (ratio of heat conduction time to fill time) and B, a dimensionless ratio indicating the sensitivity of viscosity to temperature differences in the mold. To establish a common basis for comparison of simulation and experiment, the melt-mold interface temperature was estimated using a heat transfer coefficient, which was a fixed value for experiment and a parameter for simulation.

∗ Mail address: J. Stevenson, Honeywell International, 101 Columbia Road, Morristown, NJ 07962, U.S.A. E-mail:

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Received: 2005-3-10
Accepted: 2005-10-1
Published Online: 2013-04-06
Published in Print: 2006-05-01

© 2006, Hanser Publishers, Munich

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  5. Correlations between Injection Molding Parameters, Morphology and Mechanical Properties of PPS Using Artificial Neural Networks
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  9. Investigation of the Heat Affected Zone of Hot-gas Welded PP Joints
  10. Method for the Optimisation of Screw Elements for Tightly Intermeshing, Co-rotating Twin Screw Extruders
  11. Rheology and Processing of Molten Poly(methyl methacrylate) Resins
  12. PLLA Morphology Controlled by Dry-cast Process
  13. Two Component Injection Molding of Phase Separating Blends
  14. A Low Force Valve for Dynamic Control of Molten Plastics in a Mold
  15. Influence of Drawing and Temperature on the Optical and Structural Properties of Monofilament PP Sutures
  16. Mechanical Properties of Rubber-toughened Post-industrial Glass-fiber-reinforced PA66
  17. Thermal Flow Instability in Metal Injection Molding: Experiment and Simulation
  18. Review Paper
  19. State of the Art: Recycling of EPDM Rubber Vulcanizates
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https://doi.org/10.3139/217.1908

Articles in the same Issue

  1. Contents
  2. Contents
  3. Regular Contributed Articles
  4. Pressure and Temperature Dependence of LDPE Viscosity and Free Volume: The Effect of Molecular Structure
  5. Correlations between Injection Molding Parameters, Morphology and Mechanical Properties of PPS Using Artificial Neural Networks
  6. Investigations into Kinematic Reversal in Non-isothermal Flows in Single-screw Machines
  7. The Effect of Post-extrusion Conditions in Ribbon Extrusion of Polymer Blends
  8. Effect of the Chemical and Morphological Conditions of the Die Wall on the Extrusion of Linear Polyolefins
  9. Investigation of the Heat Affected Zone of Hot-gas Welded PP Joints
  10. Method for the Optimisation of Screw Elements for Tightly Intermeshing, Co-rotating Twin Screw Extruders
  11. Rheology and Processing of Molten Poly(methyl methacrylate) Resins
  12. PLLA Morphology Controlled by Dry-cast Process
  13. Two Component Injection Molding of Phase Separating Blends
  14. A Low Force Valve for Dynamic Control of Molten Plastics in a Mold
  15. Influence of Drawing and Temperature on the Optical and Structural Properties of Monofilament PP Sutures
  16. Mechanical Properties of Rubber-toughened Post-industrial Glass-fiber-reinforced PA66
  17. Thermal Flow Instability in Metal Injection Molding: Experiment and Simulation
  18. Review Paper
  19. State of the Art: Recycling of EPDM Rubber Vulcanizates
  20. PPS News
  21. PPS News
  22. Seikei-Kakou Abstracts
  23. Seikei-Kakou Abstracts
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