AN ASSESSMENT OF THERMAL-STRESSES IN INJECTION-MOLDED ABS COPOLYMER

Thermal residual stresses in injection moulding result from the non-un iform cooling of the melt in the mould. Normally, compressive stresses develop at the surface and tensile ones within the core of the mouldi ngs. The magnitude of these residual stresses was examined for an acry lonitrile-butadiene-styrene copolymer (ABS) under various injection mo ulding conditions. Although the occurrences of thermal stresses are in evitable, the warpage results only when the residual stresses are out of balance. The imbalance of the residual stresses are caused by the n on-uniform temperature distribution through the thickness of the mould ing which may be caused by variation in cross section, part geometry a nd temperature difference between the two surfaces. The magnitudes of thermal residual stresses in injection moulded ABS flat plaques were d etermined using a layer removal technique. The development of warpage in a 3D component (an L-shaped bracket) was modelled using the residua l stresses obtained for the flat plaques and the predictions were comp ared with the experimental warpage measurements.