Modelling and simulation of residual stress and warpage in injection moulding

Nowadays, moulders and customers pay increasing attention to parts warpage, which becomes a determining quality criterion for parts acceptance. The accurate prediction of warpage of injection-moulded parts is an important and challenging task for numerical simulation of injection moulding. In this paper, the numerical analysis of warpage in injection-moulded parts was carried out in consideration of the residual stresses produced during both the packing and the cooling stages. For residual stress analysis, a thermorheologically simple viscoelastic material model was introduced to consider the stress relaxation effect and to describe the mechanical behaviour according to the temperature change. The deformation of injection-moulded parts induced by the residual stress was calculated on the basis of the theory of shells, represented as an assembly of flat elements formed by combining the constant strain and the discrete Kirchhoff triangular element. Experimental research on a flat plate was also performed to study the effect of mould structure and processing parameters on warpage. The simulation results were also compared with the experimental data for verification of the developed programme. It was found that the predictions were in agreement with experimental data, especially in qualitative analysis.