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The structural feature types and production processing quality of precision injection molds directly affect the quality and work efficiency of plastic handicrafts. There are various phenomena in the process of precision injection mold processing, and the following are solutions to several common phenomena.
It is difficult to remove the material from the gate: during the injection molding operation, the gate adheres to the gate sleeve and is not easy to slip off. During mold opening, handicrafts often show cracks and damage. In addition, the operator must use a copper rod tip to knock it out from the nozzle to loosen it before demolding, which greatly affects work efficiency. The key factor for this type of phenomenon is the poor smoothness of the gate cone hole and the presence of knife marks in the circumferential direction of the inner hole. Another issue is that the material is too soft, causing deformation or damage to the small end of the conical hole after use for a period of time, and the curvature of the nozzle surface is too small, resulting in the formation of rivet heads in the gate material here. The tapered hole of the gate sleeve is difficult to produce and process, so standard parts should be used as much as possible. If self production and processing are required, a dedicated reamer should also be self-made or purchased. The tapered hole needs to be ground to Ra0.4 or less. In addition, it is necessary to set the gate pulling rod or gate ejection mechanism.
Damaged positioning pins: Positioning pins play a crucial guiding role in precision injection molds to ensure that the molding surfaces of the core and cavity do not collide with each other under all conditions, and cannot be used as load-bearing or positioning components. Under the following conditions, the dynamic and fixed molds during injection will generate significant lateral displacement forces: (1) When the wall thickness requirements of plastic parts are uneven, the rate of material flow passing through the thick wall is high, resulting in relatively high pressure; (2) The sides of plastic parts are different, such as the trapezoidal parting surface mold, and the corresponding two sides are subjected to different back pressures.
Moving and fixed mold offset: Large molds have different filling rates in each direction and are affected by the weight of the mold itself during mold installation, resulting in moving and fixed mold offset. In these situations, the lateral displacement force during injection will be applied to the positioning pin, causing the surface layer of the positioning pin to become rough and damaged during mold opening. In severe cases, the positioning pin may deform or break, even making it difficult to open the mold. In order to better improve these phenomena, high-strength positioning keys are added on the parting surface of the mold, one on each side, and the simplest and most reasonable method is to use cylindrical keys. The perpendicularity between the positioning pin hole and the parting surface is very important. During production and processing, the movable and fixed molds are aligned and clamped, and then bored on the boring machine in one go. This ensures the concentricity of the movable and fixed mold holes and minimizes the verticality deviation. In addition, the heat treatment hardness center of the positioning pin and guide sleeve must meet the design requirements.
Dynamic template deformation: During injection of precision injection molds, the molten plastic inside the mold cavity forms a great back pressure, usually between 600~1000 kg/cm2. Mold manufacturers sometimes do not pay attention to this phenomenon and often change the original design dimensions or replace the moving template with low strength steel plates. In molds that use a top bar to top the material, due to the large span of the two seats on both sides, the template bends down during injection. Therefore, the movable formwork must be made of high-quality steel with sufficient wall thickness, and low strength steel plates such as A3 should be avoided. When necessary, support columns or blocks should be set under the movable formwork to reduce the wall thickness of the formwork and enhance its load-bearing capacity.