Warpage prediction of the injection-molded strip-like plastic parts

For most strip-like plastic injection molded parts, whose cross section size is much smaller than their length, the traditional Hele-Shaw model and three-dimensional model do not work well in the prediction of the warpage because of their special shape. A new solution was suggested in this work. The strip-like plastic part was regarded as a little-curved beam macroscopically, and was divided into a few one-dimensional elements. On the section of each elemental node location, two-dimensional thermal finite element analysis was made to obtain the non-uniform thermal stress caused by the time difference of the solidification of the plastic melt in the mold. The stress relaxation, or equivalently, strain creep was dealt with by using a special computing model. On the bases of in-mold elastic stress, the final bending moment to the beam was obtained and the warpage was predicted in good agreement with practical cases.

For most strip-like plastic injection molded parts, whose cross section size is much smaller than their length, as shown in Fig. 1, the traditional Hele-Shaw model and three-dimensional model do not work well in the prediction of the warpage. A new solution was suggested in this work. The part was regarded as a little-curved beam macroscopically, and was divided into a few one-dimensional elements. On the section of each elemental node location, the mesh was drawn, as shown in Fig. 2, and the thermal analysis was done to obtain the non-uniform thermal stress. The stress relaxation was dealt with by using a special computing model. On the bases of in-mold elastic stress, the final bending moment to the beam was obtained and the warpage was predicted in good agreement with practical cases.Figure optionsDownload as PowerPoint slide