Plastic mold is an important tool for plastic shell injection molding, but also the core parts, in injection molding, there will always be one or another problems, I summarized about 9 problems, for the reference of industry technicians. 
1. It is difficult to remove material from the gate of plastic mold During the injection molding process, the gate is stuck in the gate sleeve and is not easy to come out. When the mold is opened, the plastic shell shows cracks and damage. In addition, it is necessary for the operator to knock out the top of the copper rod from the nozzle to loosen it before it can be demoulded, which seriously affects the production efficiency. The main disadvantage is the poor light of the gate cone hole, and the knife mark in the circular direction of the inner hole. Secondly, the gate steel material is too soft, the small end of the cone hole is deformed or damaged after a period of use, and the spherical arc of the nozzle is too small, resulting in the gate steel material rivet here. The cone hole of the gate cover is more difficult to process, and qualified standard parts should be selected as far as possible. If you need to process it by yourself, special reamer should be bought. The taper hole should be ground to Ra0.4 or more. In addition, it is necessary to set the gate pulling bar or gate ejection. 
2. Large plastic mold dynamic mold and fixed mold offset Large plastic molds have dynamic and fixed mold deviation due to different filling rates and the influence of die weight during mold loading. In the above cases, the lateral deflection force will be applied to the guide post during injection, the guide post appearance will be strained and damaged when opening the mold, and the guide post will be zigzagged or blocked when severe, and even the mold cannot be opened. In order to deal with the above questions, a high-strength positioning key is added to the four sides of the plastic mold parting surface, and the most concise and useful is the selection of cylindrical keys. The straightness of the guide column hole and the parting die surface is very important. After the clamping of the moving and fixed die alignment during processing, the boring machine is completed at one time, so as to ensure the concentricity of the moving and fixed die holes and minimize the straightness error. In addition, the heat treatment hardness of the guide column and guide sleeve is necessary to reach the program requirements. 
3. The guide post of the plastic mold is damaged The guide column mainly plays a guiding role in the plastic mold to ensure that the forming surface of the core and the cavity do not touch each other under any circumstances, and the guide column cannot be used as a force or positioning part. In several cases, there will be an infinite lateral deflection force between the moving die and the fixed die during injection. When the wall thickness of the plastic parts is not uniform, the hot melt adhesive material flow through the thick wall at a high speed, and a large pressure occurs here. The side surface of the plastic part is not symmetrical, such as the reverse pressure on the opposite two side surfaces of the stepped parting surface of the plastic mold is not equal. 4. Plastic mold moving template twists When the plastic mold is injected, the hot melt plastic in the mold cavity has infinite reverse pressure, usually in the range of 600~1000 kg/cm. Plastic mold makers sometimes do not pay attention to this question, usually change the original program standard, perhaps replace the moving template with a low-strength steel plate, in the plastic mold with the top rod, due to the large span of both sides of the seat, forming the template when the injection is bent. Therefore, it is necessary to choose excellent steel, to meet the thickness, must not use low-strength steel plate such as A3, when necessary, should be set under the moving template support column or support block, in order to reduce the thickness of the template, forward load before adjustment. 5. The top rod of the plastic mold is tortuous, cracking or leaking material The top rod is usually used qualified standard parts, the gap between the top rod and the hole is assumed to be too large, then there is leakage, but if the gap is too small, the top rod will swell and get stuck when the injection is due to the increase in plastic mold temperature. There will also be an anomaly is that sometimes the ejector rod is usually pushed out at intervals and broken, and the exposed ejector rod cannot be restored and the concave die is damaged when the action is made once. In order to deal with this problem, the top rod is ground from the beginning, and the collaborating section of 10 to 15 mm is saved in the front end of the top rod, and some of the base is ground 0.2 mm smaller. After all the ejector rods are installed, it is necessary to strictly check the coordination gap, usually within 0.05-0.08 mm, to ensure that all ejector arrangements can advance and fall. 6. Poor cooling of plastic mold or water leakage The cooling effect of the plastic mold directly affects the quality and production power of the finished product, such as poor cooling, large shortening of the finished product, or uneven shortening and warping deformation. On the other hand, all the plastic molds are overheated, so that the plastic molds can not be formed normally and stopped production, and the severe parts such as the top rod are damaged by thermal expansion and stuck. The cooling system scheme is reviewed by the engineer, and this individual system is not omitted because the mold structure is messy or the processing is difficult. 7. The slider is tilted and the reset is not smooth Some plastic molds are bound by the template area, the length of the guide groove is too small, and the slide is exposed outside the guide groove after the core pulling action, which simply constitutes the slide tilt in the initial period of the core pulling and the mold restoration, usually when the mold is closed, the slide is not smooth, so that the slide damage, and even bending damage. As a rule of thumb, the length of the slide left in the chute after the end of the core-pulling action should not be less than 2/3 of the total length of the guide groove. 8. The spacing tension arrangement fails The fixed distance tension such as the swing hook and the buckle is usually arranged for the fixed mold core-pulling or some secondary release plastic molds, because this arrangement is set in pairs on the two sides of the plastic mold, its action should be necessary to synchronize, that is, the mold is fastened together, and the mold is unhooked together in a certain direction. But the loss of synchronization, must constitute the template of the pulled mold tilt and damage, these arrangements of spare parts to have higher stiffness and wear resistance, adjustment is also very difficult, the arrangement life is short, as far as possible to prevent use, can use other arrangements. In the case of small suction force ratio, the spring can be used to push out the fixed mold method, in the case of large core pulling force ratio, the core sliding can be used when the dynamic mold is withdrawn, the core is finished after the core pulling action and then the mold structure, and the hydraulic cylinder can be used to pull the core on the large plastic mold. The inclined pin slider core-pulling arrangement is damaged. The disadvantages of this arrangement are mostly that the processing is not in place and the material is too small, and the following two questions are the first: ① The Angle of the inclined pin is large, and the effect is that A larger core-pulling distance can occur in a shorter opening stroke. However, if the inclination Angle A is too large, when the pulling force F is a certain value, the zigzag force P=F/COSA encountered by the inclined pin in the core pulling process is larger, and it is easy to present the inclined pin deformation and inclined hole wear. ② The upward thrust N=FTGA produced by the inclined pin on the slider is also larger, and this force increases the positive pressure of the slider on the guide surface in the guide groove, and then increases the resistance of the slider when sliding. Easy to form sliding, guide wear. The rule of thumb is that inclination A should not be greater than 25. 9. The exhaust in the plastic mold is not smooth Gas often occurs in plastic molds. What causes this? The air in the pouring system and the cavity of the plastic mold; Some plastic raw materials are rich in moisture that is not dried away, and they will vaporize into water vapor at high temperatures. Due to the high temperature during injection molding, some unstable plastic raw materials will differentiate and gas will occur; Certain additives in plastic raw materials transpirate gases that may chemically react with each other. The causes of poor exhaust should also be quickly found. The poor exhaust of the plastic mold will bring a series of damage to the quality of the plastic shell and many other aspects, mainly reflected: in the injection process, the hot melt adhesive will replace the gas in the cavity, assuming that the gas is not discharged in time will constitute the hot melt adhesive filling difficult, resulting in a short injection amount and can not fill the cavity; The gas that is not smooth will form high pressure in the cavity, and enter the interior of the plastic shell at a certain degree of contraction, forming emptiness and porosity, arranging sparse and silver and other quality defects; Because the gas is highly compressed, the temperature in the cavity rises sharply, which causes the surrounding hot melt adhesive to differentiate and roast, making the plastic shell show some carbonization and charring. It is mainly at the confluence of the two strands of hot melt adhesive and the flange of the gate; The gas cleaning is not smooth, so that the speed of hot melt adhesive entering each cavity is not the same, so it is easy to form active marks and fusion marks, and the mechanical function of the plastic shell is reduced; Due to the obstruction of the gas in the cavity, the filling speed will be reduced, the molding cycle will be affected, and the injection efficiency will be reduced. The spread of bubbles in the plastic shell, and the bubbles caused by the accumulated air in the mold cavity are often scattered on the opposite part of the gate; The bubbles of differentiation or chemical reaction in the plastic raw materials are dispersed along the thickness of the plastic shell; The remaining bubbles of water gasification in the plastic raw materials are erratically scattered on all the plastic shells.
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