Effect of fiber orientation and process parameters on shrinkage in injection molding of thin-wall parts

Injection molding of high quality thin-wall parts is a challenge due to the high values of the shear stress in the melt flow, which affect the morphology of the moldings and their consequent shrinkage and warpage. In this work, the effect of the injection molding processing conditions on the dimensional accuracy of thin-wall fiber-reinforced parts was studied. The reduction of the shrinkage was taken in consideration analyzing how processing parameters affected the final dimensions of a specifically designed part. Moreover, the relation between the distribution of short glass fibers within the part and its dimensional accuracy was investigated by means of X-ray micro computed tomography. The experimental results showed that a selection of high values for both melt temperature and packing pressure allowed the minimization of the dimensional difference between the mold and the final parts. The analysis of the cross sections of the thin-wall parts, obtained from the micro computed tomography scans, allowed the observation of the 'skin-shear-core' morphology indicating that the thickness ratio between the shear and core layers is affected in particular by the injection speed.