These injection mold failure, can be so excluded

- Jun 27, 2017-

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    The structure and quality of the injection mold directly affect the quality and production efficiency of plastic parts. Mold production process in a variety of failures are very much, the following are several common fault solution.

 

    Gate off the material difficult: in the injection process, the gates glued in the gate sets, easy to prolapse. When the mold is opened, the product is cracked. In addition, the operator must use the copper rod tip from the nozzle to knock out, so that after the release can be stripped, seriously affecting the production efficiency. The main reason for this failure is the gate cone hole finish is poor, the hole in the circumferential direction of the knife marks. There is a material too soft, the use of a period of time after the small deformation or damage to the cone hole, and the nozzle spherical curvature is too small, resulting in the production of rivets here. The taper hole of the pouring sleeve is difficult to be processed, and the standard parts should be used as far as possible. For self-processing, the special reamer should be made or purchased. The taper hole is subjected to grinding to Ra0.4 or less. In addition, it is necessary to provide a gate puller or gate ejection mechanism.

 

    Guide column damage: guide column in the injection mold mainly from the role of guidance to ensure that the core and cavity molding surface in any case do not touch each other, can not lead the column as a force or positioning pieces. In the following cases, the injection will move, the mold will produce a huge lateral bias force: (1) plastic wall thickness requirements are not uniform, the flow rate through the thick wall, where the larger Of the pressure; (2) plastic side of the asymmetry, such as stepped shaped surface of the mold, the opposite side of the back pressure is not equal.

 

    Moving, fixed-mode shift: large-scale mold, due to the different feed rate, and in the mold when the mold by the weight of the impact, resulting in moving, fixed-mode shift. In these cases, the lateral bias force will be added to the guide post during injection. When the mold is opened, the surface of the guide post is pulled and damaged, and the guide post is bent or cut, and even can not be opened. In order to solve the above problems, in the mold parting surface to add high-intensity positioning keys on each side, the most simple and effective is the use of cylindrical keys. The verticality of the guide hole and the parting surface is critical. In the processing is the use of dynamic, fixed-mode alignment after clamping, boring machine in a boring finish, which can ensure that the dynamic and fixed hole concentricity, and the vertical error of the smallest. In addition, the guide rod and guide sleeve heat treatment hardness must meet the design requirements.

 

    Dynamic template bending: injection mold injection, the cavity of molten plastic produced a huge anti-pressure, generally in the 600 ~ 1000 kg / cm 2. Mold manufacturers sometimes do not attach importance to this problem, often change the original design size, or the use of low-strength steel plate instead of the template, with the top of the top of the mold, due to the large side of the span, resulting in injection mold bending. Therefore, the use of high-quality steel, must have enough thickness, must not use A3 and other low-strength steel plate, if necessary, should be set in the dynamic template below the support column or support block to reduce the template thickness and improve the carrying capacity.

 

    Mandrel bent, broken or leakage material: homemade jack quality is better, is the processing cost is too high, and now usually use standard parts, the quality of the general. If the gap between the mandrel and the hole is too large, if the gap is too small, the plunger is swollen and stuck due to the mold temperature during injection. More dangerous, sometimes the mandrel is ejected from the top of the distance on the top of the fixed and broken, the result of the next mold when the exposed mandrel can not be reset and hit the die. In order to solve this problem, the mandrel re-grinding, in the top of the mandrel to retain 10 ~ 15 mm with the section, the middle part of the mill 0.2 mm small. All the mandrel in the assembly, must be strictly checked with the gap, usually in the 0.05 ~ 0.08 mm, to ensure that the entire top of the body can advance and retreat freely.

 

    Poor cooling or waterway leakage: injection mold cooling effect directly affect the quality of products and production efficiency, such as poor cooling, product shrinkage, or shrinkage uneven appearance and other defects. On the other hand the whole model or local overheating, so that the mold can not be normal and stop production, in particular, so that the mandrel and other activities such as thermal expansion and damage. The design and processing of the cooling system depends on the shape of the product. Do not save the system because of the complicated structure of the mold or the difficulty of processing. Especially the large and medium molds must give full consideration to the cooling problem.

 

    Stretch tension mechanism: the hook, buckle and the like fixed-length tensioning mechanism is generally used for fixed-mode core or some secondary mold release mold, because these institutions in the mold on both sides of the set in pairs, Its action requirements must be synchronized, that is, mold at the same time buckle, open to a certain position at the same time decoupling. Once the loss of synchronization, is bound to cause the mold is tilted and damaged, these parts of the body to have a high stiffness and wear resistance, adjustment is also very difficult, shorter life expectancy, try to avoid use, you can switch to other institutions. In the case of relatively small pumping force can be used to push the mold out of the spring method, in the case of relatively large core pulling force can be used when the dynamic die back when the core slide, the first completion of core pulling action after the sub-mold structure, Mold can be used on the hydraulic cylinder core. Misplug the slider type core pulling mechanism. This kind of mechanism is often more than the problems are not in place and the use of materials is too small, mainly in the following two issues: inclined pin angle A, the advantage is that in a shorter open mold travel within the larger core distance. However, when the draft angle F is too large, the bending force P = F / COSA is also increased during the core pulling process, and the misalignment and oblique hole wear are likely to occur. At the same time, the nip pin produces an upward thrust on the slider N = the greater the FTGA, which increases the positive pressure on the guide surface of the slider, thereby increasing the frictional resistance when the slider slides. Easy to cause smooth sliding, groove wear. According to experience, the inclination angle A should not be greater than 25 °.

 

    The length of the guide groove is too small: some mold due to the template area limit, guide groove length is too small, the slider in the core after the action is exposed to the outside of the channel, so in the core after the end of the mold and mold reset the initial stage are likely to cause the slider tilt , Especially in the mold, the slider reset is not smooth, so that the slider damage, or even bending broken. According to experience, the slider to complete the core action, stay in the chute length should not be less than 2/3 of the full length of the guide groove. In the design, manufacture mold, should be based on the quality requirements of plastic parts, the size of the batch, the requirements of the manufacturing period and other specific circumstances, both to meet the requirements of the product in the mold structure and the most simple and reliable, easy processing, Is the most perfect mold.


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