Study On Forming Mechanism And Control Of Weld Line On Large Injection Molding Products

The injection molding is a very important molding method of plastic parts producing. There are several problems having not yet been solved because the complexity of the overall injection molding process and weld line is a common problem. Being one of common appearance defects of injection molding products, it not only influences the appearance quality, leads to the color aberration in the painting and electroplating process of injection molding, but also damages the strength and mechanic property of the products and causes the hidden dangers in normal using. It also influences the quality of products and leads to the tremendous waste of the raw material and energy. So how to improve the property of the weld line area of the products and eliminate the weld line is the focus of research.With the rapid development of computer technology and finite element theory, FEM has been widely used in plastic injection analysis. This method can consider the rheology property, mold temperature, injection pressure, and many other effects of the melt, so the analysis is more accurate. This research built the three-dimensional model by the mold CAD technology and used Moldflow to analyze the filling process. This subject analyzed the reasons of weld line in the injecting process, and proposed the improved measures after researching the weld line influenced by process parameter and the material. We adopted the sequence control injecting method—installing the hydraulic circuit controlled by configuration software on the basis of original hot runner of injecting molding machine, made the melt branch from each pouring gate flow step by step and mix completely with each other, then reduced or eliminated the weld line significantly,or transferred it to the non-important surface to achieve the producing standard. This paper have used this method to simulation analyze by inserted and non-inserted molding cavity. By changing the position of pouring gates and the opening—closing time of the valve gate to further optimize the sequence control technology.Take the front bumper of cars as an example, we have analyzed data and made numerical simulation by the Moldflow software, and compared the results with the traditional methods of injection molding. The results suggested that the sequence control injection method could not only eliminate the weld line in the bumper, but also optimize other production processes. It is of practical significance on the bumper production.