Excluding some common faults in injection molds

- Jul 19, 2017-

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  1. Gate 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 copper rod tip from the nozzle to knock out, so that after the release of the mold, 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.


Followed by the material is too soft, the use of a period of time after the tip of the small hole deformation or damage, and the nozzle spherical curvature is too small, resulting in the production of rivets here atlas. 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 holes need to be ground to Ra0.4 or higher. In addition, it is necessary to provide a gate puller or gate ejection mechanism.


2. Guide column damage.


The guide column is mainly guided in the mold to ensure that the molding surface of the core and the cavity 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 parts wall thickness is not uniform, the flow through the thick wall at the rate of large, where a greater 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.


3. 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 ﹑ die shift.


In the above-mentioned cases, the lateral bias force will be applied 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. Guide hole and the parting surface of the vertical degree is essential in the processing is to use dynamic, fixed-mode alignment after clamping, boring machine in a boring finish, which can ensure that the dynamic and fixed hole concentricity, and So that the vertical error is minimal. In addition, the guide column and guide sleeve heat treatment hardness must meet the design requirements.


4. Dynamic template bending. Mold in the 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, because the two sides of the seat span, resulting in injection mold bending. Therefore, the use of high-quality steel, must have enough thickness, must not be used 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.


5. The mandrel is bent, broken or leaked.


Homemade mandrel quality is better, is the processing cost is too high, and now generally use standard parts, poor quality. If the gap between the mandrel and the hole is too large, the leakage is expected, but if the gap is too small, the plunger expands and stuck due to the mold temperature during injection. More dangerous is that 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 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.


6. Poor cooling or water leakage. The cooling effect of the mold directly affects the quality and production efficiency of the products, 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, 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. In particular, the medium and large mold must fully consider the cooling problem.


7. Timing tensioning mechanism failure.


Hooks, buckles and the like fixed-type tensioning mechanism is generally used for mold 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 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 pulling force can be used when the dynamic die back when the core slide, the first core action after the completion of sub-mold structure, Mold can be used on the hydraulic cylinder core pulling. Slant pin slider mechanism is damaged. This type of institutions are 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 large, the advantage is that in a shorter open mold travel within the larger pull core distance. However, when the draft angle F is too large, the bending force P = F / COSA, which is subjected to the misalignment during the core pulling process, is also larger, prone to misalignment and oblique hole wear. At the same time, the downward thrust of the slider produces an upward thrust N = the higher 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 is sliding. Easy to cause smooth sliding, groove wear. According to experience, the angle A should not be greater than 25


8. Some molds 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 guide groove, so in the core after the stage and the beginning of the mold reset are likely to cause the slider tilt, When the mold is closed, the slider is not reset, causing the slider to be damaged, or even bending. 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.


9. Finally, in the design, manufacture mold, according to 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 to process, Low, this is the most perfect mold.


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