Insert Molding Process Employing Vapour Chamber

Abstract

Insert molding process is a simplified injection molding method that eliminates secondary processing and assembly. In this process, the metal inserts are firstly formed, and placed in the mold during injection molding (the metal inserts can be designed into a grooved pattern, allowing them to be connected closely with the plastics), and then the mold is closed for injection molding. Although insert molding process can greatly improve the assembly and manufacturing procedure, the joining of two materials is the main problem yet to be solved. Because the molten plastic drives the air out of the mold cavity from the vent resulting in welding lines of a plastic part during the filling step in an injection molding process, then there will be a V-notch formed between the plastic and the mold wall if the air cannot exhaust before the melted plastic fronts meet. Thus, this chapter concerns about a V-notch found on the exterior surfaces of welding lines, which will form between the plastic and the mold wall. Not only are they appearance defects, but they also decrease the mechanical strength of the parts. Once the plastics are filled, the temperature of plastics bypassing one side of the inserts may decline more quickly than that of plastics contacting the temperature side of the mold wall, so a weld line may be formed when meeting again after bypassing the inserts. The strength at the position of weld line is generally lower than that at the region of plastics; moreover, the metal inserts are generally located at the stress region when the product is utilized. Hence, the rupture of plastics often occurs from the weld line at the rear of the metal inserts, leading to damage of products (Wang & Tsai 2011). The key approach is to rapidly and uniformly increase the temperature of inserts before the plastics enter into the mold cavity. Some studies indicated that, during the injection molding process, the defect of weld line could be resolved by adjusting the mold temperature. The locations of the welding lines are usually decided by the part shapes and the gate locations. Welding lines can be eliminated by the following three methods. The first method is increasing the molten plastic temperature. The viscosity of the molten plastic fluid decreases with the increasing temperature, which improves the flow pattern of the plastic, and reduces the depth of the V-notch of the welding lines. However, degradation of the material strength sometimes occurred if the melting temperature is too high. The second method is increasing the number of the vents. Increasing the number of the vents (eg. ejecting pin or inserts) at the