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The structural method and processing quality of precision injection molds directly affect the quality and output power of plastic products. There are many defects during the mold production process, and the following are treatment plans for several common defects.
Difficulty in demolding the gate: During the injection molding process, the gate adheres to the gate sleeve, making it difficult to demobilize. During mold opening, the product exhibits crack damage. In addition, it is necessary for the operator to use the top end of a copper rod to knock it out from the nozzle to loosen it before demolding, which seriously affects the output power. The main reason for this defect 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 a period of use, and the curvature of the nozzle spherical surface is too small, resulting in riveting of the gate material here. The taper hole of the gate sleeve is difficult to machine, so standard parts should be used as much as possible. If you need to machine it yourself, you should also restrain yourself or purchase a special reamer. The tapered hole needs to be ground to Ra0.4 or less. In addition, it is necessary to set up gate pulling rods or gate ejection structures.
Guide pillar damage: The guide pillar plays a leading role in precision injection molds to ensure that the molding surfaces of the core and cavity do not collide with each other under any circumstances, and cannot be used as a load-bearing or positioning component. In the following situations, significant lateral displacement forces will occur during injection of the moving and fixed molds: (1) When the wall thickness of the plastic part is uneven, the rate of material flow passing through the thick wall is high, resulting in significant pressure; (2) The surrounding surfaces of plastic parts are asymmetric, such as precision molds with stepped parting surfaces, where the opposing two surrounding surfaces are subjected to unequal back pressure.
Dynamic and fixed mold offset: Large precision molds experience dynamic and fixed mold offset due to different filling rates in all directions and the influence of the precision mold's self weight during mold installation. In these cases, the lateral displacement force during injection will be applied to the guide pillar, causing galling and damage to the surface of the guide pillar during mold opening. In severe cases, the guide pillar may be twisted or blocked, and even unable to open the mold. To address the above issues, high-strength positioning keys are added on each side of the precision mold parting surface, and the most concise and useful option is to use cylindrical keys. The perpendicularity between the guide pillar hole and the parting surface is crucial. During processing, the movable and fixed molds are selected to align and clamp in the direction, and then bored in one operation on the boring machine. This ensures the concentricity of the movable and fixed mold holes and minimizes the error in perpendicularity. In addition, the heat treatment hardness of the guide pillar and guide sleeve must meet the planning requirements.
Flexible template: When precision injection molds inject needles, there is a huge back pressure on the molten plastic inside the mold cavity, usually ranging from 600 to 1000 kg/cm2. Precision mold makers sometimes do not attach importance to this issue and often modify the original planning specifications, perhaps replacing the moving template with low strength steel plates. In precision molds that use a top bar to top the material, due to the large span between the two ends, the template bends downward during injection. Therefore, it is necessary to use high-quality steel for the movable formwork, with sufficient thickness. Low strength steel plates such as A3 should not be used. If necessary, support columns or blocks should be set below the movable formwork to reduce the thickness of the formwork and improve its load-bearing capacity.
The top rod is twisted, cracked, or may leak materials: the quality of the self restraining top rod is good, but the processing cost is too high. Nowadays, standard parts are usually used, and the quality is average. If the gap between the top rod and the hole is too large, there may be material leakage, but if the gap is too small, it may cause mold temperature rise during injection