One of the most important questions customers look for today is how much their part will warp. As the deflection results in Simulation Moldflow shows the amount a part will deflect from its original position, the validity and accuracy of this result is necessary.
Issue:
One of the biggest problems though is, properly capturing how the material used in the molding of a part will react as all materials behave differently under different circumstances. This extends to Simulation Moldflow based on how this data is presented to the software for simulation. As Simulation Moldflow uses laborartory material data for a large percentage of material classifications (whether tested internally or provided by a material supplier) the solvers don't always capture the effects of processing parameters on the material behavior. Due to this, theoretical calculations of part shrinkage may often exhibit unacceptably large errors.
Resolution:
To address this, CRIMS was introduced for our Dual Domain and Midplane mesh options. In this, 3D was excluded due to the use of volumetric shrinkage and CTE rather than residual stress. CRIMS (Corrected Residual In Mold Stress) provides a unique method that combines the theoretical model for residual stress and a model for morphology development. This provides a correction of errors due to the use of material data that are obtained under lab conditions rather than those experienced by the material during actual injection molding.
The testing for CRIMS includes trials that are performed on a matrix of 28 molding conditions in order to take into account the material's shrinkage behavior as a result of:
- Part thickness
- Melt temperature
- Mold temperature
- Injection time and profile
- Packing time and profile
- Cooling time
When comparing the influence on results, the impact is quite noticeable. As seen, the percent shrinkage captured is overpredicted with the default uncorrected residual stress model. When using CRIMS, the impact of the actual injection molding process more accurately captures the shrink that occurs due to this.
Because of this we see an improvement in total deflection calculated as well. This is vital to ensuring the most accurate representation of warp if that is the end goal for Dual Domain and Midplane meshed geometries. Without it, error is introduced simply by assuming the theoretical representation of the material will behave as expected regardless of other variable influence such as processing or geometry.
It's suggested that when your goal is to understand and optimize warp/deflection, the best option is to use a material that has been tested for CRIMS if you'll be doing so in Midplane or Dual Domain. For more information regarding the testing procedure and how to get a material in the database that has CRIMS data available, contact our Moldflow Plastics Lab ([email protected]).
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