The structure and quality of the injection mold directly affect the quality and productivity of plastic parts. Mold production process in a variety of failures are numerous, the following are several common fault solution.
Gap off the material difficult:
In the injection process, the gates in the gates, easy to prolapse. When the mold is opened, the product is cracked. In addition, the operator must use the tip of the copper rod 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 tip of the small hole deformation or damage, as well as 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 set the gate puller or gate ejection mechanism.
Guide column damage:
The guide posts are mainly guided in the injection mold to ensure that the molding surfaces of the cores and cavities do not touch each other in any case and can not be used as a force or positioning member. 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, mold shifting:
Large mold, due to the different feed rate, as well as 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 at the time of injection will be applied to the guide post. When the mold is opened, the surface of the guide post is raised 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 pin 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.
Moving template bending:
Injection mold in the injection, the cavity of molten plastic to produce 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 both sides of the seat 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, 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 leaked material:
Homemade mandrel 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 ejector was ejected from the top of the distance to the top of the fixed and broken, the result of the next mold when the exposed rod can not be reset and hit the concave 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 from 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:
The cooling effect of the injection mold directly affects the quality and production efficiency of the product, such as poor cooling, shrinkage of the product, or uneven shrinkage. On the other hand the whole model or local overheating, so that the mold can not be normal and stop production, serious 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. In particular, the medium and large mold must fully consider the cooling problem.
Stretch tension mechanism:
Hooks, buckles and the like are usually used for fixed-mode core or some secondary mold release mold, because these institutions in the mold on both sides of the set, the 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 higher 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 force can be used to push the spring out of the mold 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.
Misplaced Slab-type core pulling mechanism Damaged:
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 inclination A, the advantage is that in a shorter open mold travel within the larger core distance. However, when the draw angle F is too large, the bending force P = F / COSA, which is subjected to the misalignment during the pulling process, is also larger, prone to misalignment and oblique hole wear.
At the same time, the oblique pin produces an upward thrust on the slider N = the larger the FTGA, which increases the positive pressure of the slider toward the guide surface of the guide groove, 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 channel length is too small:
Some dies are limited by the area of the template, the length of the guide groove 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, When the slider is reset, the slider is damaged, and even the bending is 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.