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The Stimulating News About Plastic Injection Molding Simulation

October 30, 2016

You would think “they” (read:  industry scientists) would have thought of this long ago:  use computer software to simulate the plastic injection molding process, consigning “trial-and-error” testing to the plastic slag heap, and saving enormous amounts of time and money.
At the risk of stating the obvious, plastic injection mold simulation utilizes software to simulate the filling, packing and cooling processes of an injection molded plastic part.

No surprise there –computer simulation software is unrivaled in its ability to test virtually thousands of different variables in thousands of different combinations in a matter of hours.  By comparison, trial-and-error testing could take months to find the same solution, costing hundreds-of-thousands of dollars in the process.

The chief variables in the plastic injection molding process always include:

  • Plastic flow rates
  • Plastic pressure
  • Cooling rates and timing
  • Plastic melt temperatures

Done correctly, a simulation shows potential problems and allows for designers to make vital decisions for the part and/or mold design before the mold is ever manufactured.  This is a huge advantage over trial-and-error, which always takes place after the mold is created.  Problems discovered then necessitate a new or improved mold, which could potentially take millions of dollars to fix or completely redesign and manufacture.

The issues or problems which computer simulation could potentially uncover include:

  1. Areas of the part that will not completely fill with plastic.
  2. “Weld lines”, or areas on the part where two different flow fronts meet, which can be analyzed to determine if they are structurally sound or not.
  3. Pressure inside the filling plastic, which could point towards potential problems with a specific type of resin.
  4. Gate locations, which determine flow distance, which in turn affects  the amount of pressure required to fill the mold.  More pressure means more clamp force required to hold the injection mold shut during the molding process.
  5. Gate sizing. Gates need to be placed in the most appropriate locations in order to allow enough melted plastic to completely fill the cavity.
  6. Cooling lines, which are vital for mold temperature and maintaining a minimum cycle time.
  7. Trapped air, which has to be properly vented or it could produce “burn marks.”  Worse yet, trapped air could restrict the flow of resin which produces parts that are incomplete.

Mold fill computer simulation can also be used to optimize existing molds that may be having production problems, such as uneven fill times, filling problems, and heating or cooling issues.



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