Optimization of the Weldline Strength in Gas-assist Injection Molded Thermoplastic

Gas assist injection molding has increasingly become an important process in industry because of its tremendous flexibility in the design and manufacture of plastic parts. However, there are some unsolved problems that confound the overall success of this technique. Weldlines form 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 optimize the weldline strength of gas assist injection molded thermoplastics. Experiments were carried out on an 80-ton injection molding machine equipped with a high-pressure nitrogen-gas injection unit. A dumbbell-shape mold cavity was used. After molding, the weldline strength of the parts was measured by a tensile tester. For the factors selected in the main experiments, melt temperature and mold temperature were found to be the principal factors affecting the weldline property of gas assist injection molded thermoplastics. Weld strength decreases with the length of gas penetration. In addition the weldline strength of gas assist injection molded parts was found to be generally weaker than that of conventional injection molded parts.