Warpage Analysis FAQ
Definition:
Warpage analysis provides the capability to determine the effects of part design, material selection, mold design, and processing on the warpage of a molded part. Through computer simulation, we have the ability to isolate the causes of warpage to help reduce its effects and achieve the desired molded shape of the part.
- What can a warpage analysis determine?
- Warped shape of the part as it is ejected from the mold
- The individual effects of filling, packing, and cooling
- A ballpark estimate of the shrinkage to which a mold should be cut.
What is CRIMS data?
C.R.I.M.S or Corrected Residual In Molded Stress, is empirical data generated from molded test samples. It is a correction factor to the theoretical warpage calculations.
How accurately can you predict warpage? Is there a range you can predict warpage to target? Thousandths, etc.?
The accuracy of warpage results depends on the accuracy of the simulation model, which includes the part model, the material model, and the solver. Inaccuracies in any of these four items can lead to inaccurate results. Great care must then be taken to have these inputs as accurate as possible. Accuracy depends on the size of the part, i.e., don’t expect warpage prediction on a bumper fascia to be within a few thousandths!
What information do you provide with a warpage analysis?
- Overall warped shape of the part
- Overall warpage in X, Y, and Z directions
- Individual effects of filling, packing, cooling
Have you ever used warpage analysis to bias a mold for windage?
Yes, we have used warpage analysis to bias the mold to achieve a flatter part. In many cases, due to part design issues, the molded part may still have significant warpage. In these, cases, the only way to improve on the warpage is to bias the mold steel. Warpage analysis is very useful in these cases.
How much does CRIMS data impact results?
The amount that CRIMS data impacts the warpage results varies, and it is mostly based on the type of material. Amorphous materials are least effected, followed by semi-crystalline materials, and finally glass-fiber filled material.
How much does proper cooling affect results?
Cooling can have a significant effect on the warpage results if not done properly. The actual amount varies from mold to mold. Much of that depends on the stiffness of the material and the stiffness of the part design.
How accurate is Moldflow in regards to actual processing? Are there any case studies verifying Moldflow vs. actual part processing?
It depends on how much attention to detail was given in the modeling effort. We have done follow up simulations that have shown a strong correlation between model and actual “real world” processing.
Can we use a substitute material if the exact grade is not characterized appropriately for warpage?
A substitute material should only be used in cases where warpage trends are required. If exact warpage numbers are required, then the material being used should be specifically characterized for warpage analysis. If a substitute material is to be used, it is necessary to match fiber content, melt flow index, and any other properties that are possible to match. This will ensure the best possible results.
Can we still do a warpage analysis without CRIMS data?
Yes, a warpage analysis can still be done without CRIMS data, but directional shrinkage effects will not be accounted for. Amorphous materials would be the least affected, followed by semi-crystalline and fiber filled materials. Warpage analysis done without CRIMS on a fiber-filled material should not be trusted at all.
Can you do just warpage alone or do you need to do flow, pack, and cool as well?
Flow and pack are minimum prerequisites for a warpage analysis. This would reveal the impact of gating and processing on the warpage. For obvious reasons, however, we recommend including the cooling analysis with the warpage.
What does warpage bring to the table?
Warpage analysis gives us he ability to identify the key factors that are causing the warpage, which steers us in as certain direction towards the proper solution.
What happens if Moldflow does not match actual processing results? What variables are attributed to that?
If there is some disagreement between simulation and the real-world processing, we would review the process setup sheet to determine where the discrepancies are and the severity. The nature and severity of the discrepancy would determine the coarse of action to identify and recommend a solution.
Can post-molding shrinkage/warpage be predicted?
No, warpage prediction is based on the parts ejected from the molding machine. However, residual stress data from the analysis may be transported to other structural analysis programs for post-mold shrinkage/warpage simulation.
