Evaluation of shrinkage and weld line strength of thick flat part in injection moulding process

This paper evaluates the shrinkage and strength of weld line using Design of Experiment and Response Surface Methodology in multi-objective optimisation utilising the injection moulding parameters. A simulation process was conducted to determine the recommended setting of injection moulding parameters and the range of the variable parameters. An experimental work was conducted according to the experimental design, where regression models were established to predict the shrinkage and weld line strength. A new set of process parameters setting was found to achieve the optimum shrinkage and weld line strength of the moulded part. The results of shrinkage and weld line strength using an optimal parameter setting after optimisation process were compared with the results obtained using the recommended setting from Autodesk Moldflow Insight software. It was found that the shrinkages in the normal to and parallel to the melt flow directions were reduced by 5.969% and 4.375%, respectively, through the predicted model generated using RSM. On the other hand, the weld line strength improved by 3.758% as compared to the weld line strength obtained from the recommended setting. The shrinkages in both parallel to and normal to the melt flow directions using multi-objective optimisation were reduced by 5.891% and 4.160%, respectively, while the weld line strength was improved by 3.756%, using the combination of the following parameters; 69.93 °C of coolant inlet temperature, 270 °C of melt temperature, 70 MPa of packing pressure and 8 s of cooling time. The predicted errors ranged between 0.2 and 14.5% during the validation experiments. The packing pressure was found to be the most significant parameter affecting the shrinkage in both parallel to and normal to melt flow directions. The coolant inlet temperature on the other hand was the most significant parameter affecting the weld line strength.