Gas assisted injection moulding has become one of the most important methods for the manufacture of plastic products. However, there are several unsolved problems that confound the overall success of this technique. The weldline caused by the ow lead eVect in the polymer melt is one of them. In this report, an Lê 18 orthogonal array design based on the Taguchi method has been conducted to investigate the ow lead induced weldlines in gas assisted injection moulded parts. A plate cavity with a gas channel on the side was used for moulding. Experiments were carried out on an 80 t reciprocating screw injection moulding machine equipped with a high pressure gas injection unit. After moulding, the depth of the weldline was measured. For the factors selected in the main experiments, melt injection temperature and mould temperature were found to be the principal factors aVecting the weldline depth of gas assisted injection moulded parts. Experimental investigation of a gas assisted injection moulding problem can help in better understanding the weldlines caused by ow lead eVects, so that steps can be taken to optimise the surface quality of moulded parts.
The injection molding of thermoplastic composite materials has become an important process in industry, due to the possibility of producing near shape article having exceptional physical and mechanical properties. However there are still some problems that confound the overall success of this technology. The forming of weldlines wherever polymer flow fronts meet is one of them. In this report, an L'18 experimental matrix design based on the Taguchi method was conducted to study the effect of different processing parameters on the weldline strength of injection-molded thermoplastic composites. Experiments were carried out on a 4.1 oz reciprocating injection molding machine. The materials used were acrylonitrile-butadiene-styrene, and 20 and 30% glass-fiber-filled ABS composites. A plate cavity with an obstacle in the center was used to create a weldline. After molding, the weldline strength of the composites was determined by a tensile tester. Various processing variables were studied in terms of their influence on the weldline strength of injectionmolded composites: melt temperature, mold temperature, melt filling speed, melt filling pressure, packing pressure, and size of the obstacle. For the factors selected in the experiments, size of obstacle and melt temperature were found to be the important parameters affecting the weldline strengths of injection-molded composites. The weldline strength of virgin material increased with the distance from the obstacle, while the weldline strength of composites decreased with the distance.
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