This guest contribution on Innovation Intelligence is written by Stephen Chung of CoreTech System, developers of Moldex3D. Moldex3D is available through the Altair Partner Alliance.
Warpage is one of the key issues faced in the development of plastic products due to its potential to effect the quality of matching dimensional criteria and even structural strength. Serious warpage on a part can result in appearance defect, assembling difficulty or breakage. The differential temperature effect and differential shrinkage effect are the two main factors of leading up to part deformation, and the comparison of these two effects to the overall effect on the deformation result can help achieve a better understanding of the problem and resolve the warpage.
Differential temperature effect is considered displacement by shrinkage due to the temperature difference throughout the thickness of the part. To improve warpage caused by this effect, a better cooling process and system layout is often the solution to reduce the temperature difference between core and cavity side.
Differential shrinkage effect is the displacement caused by the volumetric shrinkage distribution along the part plane, and highly depends on the thickness variation throughout the part. To minimize warpage from this effect, it requires a better geometry and material design.
The below example shows the molding analysis of a driller cover with grooved geometry and a simple cooling channel layout. Moldex3D allows users to evaluate the effect of differential temperature and differential shrinkage separately in the displacement analysis results. Through the molding simulation, one can use maximum displacement (z-direction) to check if the part can be nicely assembled with others after molding is complete. Figure 3 shows the warpage analysis results in a significant part deformation, meaning there is a high risk of assembly failure if this part were actually produced.
Because of the grooved geometry, the designer may think that the warpage is from the mold temperature and seek a design revision on the cooling system, like adjusting the channel layout. Looking into the results of the displacement from the differential temperature and shrinkage effects, however, one can find that the differential temperature effect is significantly smaller than the other (Fig. 4), meaning the warpage is actually not influenced much by uneven cooling between the core and cavity side.
To validate the statement from the differential temperature/shrinkage analysis, the advanced cooling system with a conformal layout is applied to reduce the uneven cooling between core and cavity side. The improvement on cooling performance is clearly observed with its lower and more uniform temperature on the core side. However, the warpage improvement is proven minor in the displacement result, as indicated in the analysis of differential temperature effect. Although the design effort can be dramatically reduced with current CAD/CAE tools, a hint to help designers understand where a revision is necessary can still save a lot of time and work, and help avoid ineffective revisions.
To summarize, differential temperature/shrinkage effect analysis with molding simulation can direct designers toward the correct design revision to solve warpage issues. High differential temperature effect in displacement result indicates the need to improve the cooling system or process. On the other hand, it leads designers to revise other part/mold designs or process controls if differential shrinkage effect is comparatively higher. Using CAE tools, the product development process can speed up with minimized cost in the early stage of manufacturing.
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