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Name：Rebecca Dong
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How should I deal with the problem in injection mold? |
Injection mold is a tool to produce plastic products. It is also a tool for the complete structure and precise size of the plastic products. The structure of injection mold and mold processing quality directly affect the quality and production efficiency of plastic parts. It is the most common practice in the production of injection mold and plastic products. The reasons for the failure of injection mold and the troubleshooting methods are introduced as follows:
1. Difficulty in springing. In the process of injection molding, the gate is stuck to the sprue. When the mold is opened, the product cracks. In addition, the operator must use the tip of the copper rod to knock out from the nozzle, so that it can be removed after loosening, which seriously affects the production efficiency. The main reason of this fault is the poor finish of the gate taper hole, and there is a knife mark in the inner hole circumference. The second is that the material is too soft. After a period of time, the taper hole is deformed or damaged, and the surface of the nozzle is too small, which causes the gate to be riveted here. The taper hole of gate sleeve is more difficult to process, should adopt standard parts as far as possible, if need to be processed by oneself, also should be self-made or buy special reamer. The taper hole should be ground to Ra0.4. In addition, it is necessary to set the gate pull rod or gate top out of the mechanism.
2. Guide column damage. The guide pillar plays a leading role in the mould, so as to ensure that the forming surface of the core and cavity is not mutually touching in any case, and the guide column can not be used as the force part or positioning piece. Injections in the following cases, the movement, set the mould will produce a great lateral migration force: (1). The plastic parts wall thickness nonuniformity, the material flow through rate is big, thick wall place here produce larger pressure; (2). The side asymmetry of the plastic parts, such as the two sides of the mold relative to the form of the ladder, is not equal to the pressure.
3. Large molds, due to different feeding rates, and the influence of the mold's self-weight in the loading mode, generate dynamic and fixed mode migration. In the above situations, the lateral offset force of the injection will be added to the guide column, and the surface of the guide column will be pulled and damaged when the die is open, and the guide column will be bent or cut off when it is serious, and even cannot be opened. In order to solve the above problems, a high strength positioning key is added on the mold parting surface, and the most convenient and effective way is to use the cylindrical key. Guide pin hole and the perpendicularity of the parting surface is very important. When processing is a dynamic, fixed clamping die alignment position, after boring boring last time, which can guarantee, concentricity of die hole, and minimize the perpendicularity error. In addition, the heat treatment hardness of the guide column and guide sleeve must meet the design requirements.
4. Bend the moving template. When the mold is injected, the molten plastic in the mold cavity generates a great counterpressure, usually between 600 and 1000 kg/cm. . Mold makers sometimes don't attach importance to this problem, often change the original design size, or replace with low strength steel plate, the dynamic template in the mould of material with a plunger, because on both sides of the large span, cause the injection template under bending. So the dynamic template must choose high quality steel, must have the enough thickness, must not with A3 steel such as low intensity, when necessary, or support block should be set at the bottom of the dynamic template shores, to reduce the thickness of the template, improve the bearing capacity.
5. The top rod is bent, broken or leaking. The top quality of self-made is good, it is the processing cost is too high, now commonly use standard parts, poor quality. If the gap between the top rod and the hole is too large, there will be leakage, but if the clearance is too small, due to the high mold temperature rise during injection, the ejector pin will expand and die. What is more dangerous is that sometimes the top of the rod is broken by a normal distance, and the result is that the exposed top rod cannot be reset and the die is broken in the next closing time. In order to solve this problem, the top bar is reworked, and the mating segment with 10~ 15mm is retained at the front end of the top rod, and the middle part is small 0.2mm. After assembly, all the top rods must be strictly checked for clearance, generally within 0.05~0.08 mm, to ensure that the entire ejection mechanism can move forward and backward.
6. Poor cooling or water leakage in the channel. The cooling effect of the mould directly affects the quality and production efficiency of the products, such as poor cooling, large shrinkage of the products, or uneven shrinkage of the products, etc. On the other hand, the mold or local overheating can prevent the mold from being formed normally, so that the top rod and other movable parts can be damaged. The design of the cooling system, processing to the product shape, don't cry because it is complicated or difficult to machining mould structure and eliminate the system, especially in large and medium-sized mold must give full consideration to the cooling problem.
7. Fixed distance tension mechanism failure. Pendulum hook, fastener spacing taut institutions is generally used in die core-pulling or some secondary ejection mould, because such institutions in the mold of the two sides set in pairs, its movement request must be synchronous, namely the clamping buckle at the same time, mould to a certain position at the same time. Without synchronization, it is bound to cause pulled mold template skewed and damage, the institutions of the parts to have higher rigidity and wear resistance, adjustment is hard, short life institutions, to avoid as far as possible, you can switch to other institutions. Can be used in the case of relatively small pumping heart spring launch mode method, the core pulling force is larger when the dynamic model can be used under the condition of the back slide cores, finish core-pulling action again after the structure of the die, the hydraulic oil cylinder can be used on large mould core pulling. The inclined pin sliding block type core mechanism is damaged. The most common defects of this kind of mechanism are the incomplete processing and the small materials, which mainly have the following two problems.
8. Some die because of restricted by template area, the length of the guide groove is too small, the slider on the outside of the core-pulling action after the show guide, so that after the core-pulling and mould reset at the beginning of the phase is likely to cause the slider tilt, especially when clamping, slider reset, make the slider damage, even bending failure. According to the experience, the length of the sliding block should not be less than 2/3 of the length of the guide slot after pulling the core.
9. Finally, the design manufacture of moulds, should according to the requirement of the quality of plastic parts, the size of the batch, make deadline requirements such as the specific circumstances, can not only meet the requirements of products, in the mold structure and the most convenient and reliable, easy processing, low cost, this mould is very good.
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