Residual stresses (R.S.) in a microcomputer-controlled injection molded ABS terpolymers have been determined. The layer-removal method and the microscopic measurement techniques were used to evaluate the stresses in these molded articles. The relationship between the R.S. and the processing parameters such as injection pressure, holding pressure, holding time, injection rate, and mold temperature was studied. Experimental results indicated that, at the higher injection rates (>10g/s), the R.S. are compressive in the surface layer and tensile in the interior; however, at the lower injection rates (<10g/s), the residual stresses are tensile in the surface layer and compressive in the interior. The results also indicated that the higher the injection rate, the lower the residual stresses; the compressive residual stresses increased in proportion to the increase of holding pressure; the residual stresses could be decreased by keeping a higher mold temperature; the longer the holding time, the higher the compressive R.S. and the lower the tensile R.S.

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