Residual stress analysis in cross section of optical parts by co-injection molding

The residual stresses measured by photo-elastic method in cross section along the thickness direction of optical parts were compared quantitatively between injection molding and co-injection molding. The results show that the residual stress distributions of both injection molded slices and co-injection molded slices are double-parabolic shape, however, the latter has a higher stress level than that of the former. Besides, PC/PC and PMMA/PMMA disks by co-injection molding have no low-stress layer or zero-stress layer on both sides of the interface, on the contrary, there is a high stress peak at the interface. The stress in the PMMA layer of both PC/PMMA and PMMA/PC slices is increased gradually along the side surface toward the interface, which is different from the double-parabolic shape distribution of PMMA and PMMA/PMMA slices. The injection sequence of PC and PMMA layers has remarkable influence on the residual stress at the interface and in the PC layer of co-injection molded composite disks. The residual stress at the interface of PC/PMMA slices is significantly higher than that of PMMA/PC slices, and there still exists low stress layer and zero stress layer near the interface in the PC layer of PC/PMMA slices, while there are no such two stress layers in PMMA/PC slices.