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Common troubleshooting in Plastic Injection Mold

2023-10-17

The structure form and Mold processing quality of Plastic Injection Mold directly affect the quality of plastic parts and production efficiency. It is very common in the production practice of Plastic Injection Mold. Some mold failures and their main causes are analyzed and excluded as follows:

1. Gate stripping is difficult

In the process of injection molding, the gate sticks to the gate sleeve and is not easy to come out. Crack damage occurs when the mold is opened. In addition, the operator must use the tip of the copper rod to knock out from the nozzle, so that the loose rear can be demoulded, seriously affecting the production efficiency. The main reason for this failure is the poor finish of the sprue cone hole and the knife marks in the circular direction of the inner hole. Secondly, the material is too soft, after a period of use, the small end of the cone hole deformation or damage, as well as the nozzle spherical arc is too small, resulting in the gate material in the rivet head here. The cone hole of the gate cover is difficult to process, so standard parts should be used as far as possible. If it is necessary to process by itself, special reamer should also be made by oneself or purchased. The taper hole needs to be ground to Ra0.4 or above. In addition, gate pulling bar or gate ejection mechanism must be provided.

2. Guide column damage

The guide column mainly plays a guiding role in Plastic Injection Mold to ensure that the molding surface of the core and the cavity do not touch each other in any case, and the guide column can not be used as a force or positioning part. In the following cases, the dynamic and fixed mold will produce huge lateral offset force during injection: when the wall thickness of the plastic parts is not uniform, the rate of material flow through the thick wall is large, and the greater pressure is generated here; The side of the Plastic part is asymmetrical. For example, the stepped parting surface of the Plastic Injection Mold, the opposite two sides of the reverse pressure is not equal.

3. Large Plastic Injection Mold produces dynamic and fixed Mold deviation due to different filling rates and the influence of the weight of Plastic Injection Mold during mold installation 

In the above cases, the lateral offset force will be applied to the guide post during injection, and the surface of the guide post will be pulled when the mold is opened, resulting in damage. In severe cases, the guide post will be bent or cut off, or even unable to open the mold. In order to solve the above problems, add high strength positioning key on the Plastic Injection Mold parting surface, one on all four sides, it is very simple and effective to use cylindrical key. The perpendicularity of the guide hole and the parting surface is very important. In the processing is the use of moving, fixed die alignment position clamping, boring machine after a time, so as to ensure the concentricity of the moving, fixed die hole, and the verticality error is very small. In addition, the hardness of guide column and guide sleeve must meet the design requirements.

4. Moving template bending

At the time of Injection, the molten Plastic in the Mold produces a huge back pressure, generally in 600 ~ 1000 kg/cm. Plastic Injection Mold manufacturers sometimes do not pay attention to this problem, often change the original design size, or replace the moving template with low strength steel plate, in the Plastic Injection Mold with ejector rod ejector, due to the large span of both sides of the seat, resulting in the template bending down when injection. Therefore, the moving template must choose high quality steel, to have enough thickness, A3 and other low strength steel plate must not be used, when necessary, should be set under the moving template supporting column or supporting block, in order to reduce the thickness of the template, improve the bearing capacity.

5. The ejector rod is bent, broken or leaked

The quality of the self-made ejector rod is better, but the processing cost is too high. Now, standard parts are generally used, and the quality is poor. If the clearance between the ejector rod and the hole is too large, there will be material leakage, but if the clearance is too small, the ejector rod will expand and get stuck due to the high die temperature during injection. What is more dangerous is that sometimes the ejector rod is pushed out of the general distance and then broken, resulting in the next die closing the exposed ejector rod can not be reset and crash the die. To solve this problem, the ejector rod was re-milled, leaving a 10 to 15 mm fit section at the front end of the ejector rod, and the middle part was milled 0.2 mm smaller. All ejector rods must be strictly checked after assembly, generally within 0.05~0.08 mm, to ensure that the entire ejector mechanism can advance and retreat freely.

6. Poor cooling or water leakage

The cooling effect of Plastic Injection Mold directly affects the quality and production efficiency of the products, such as poor cooling, large shrinkage of the products, or uneven shrinkage and warping deformation. On the other hand, the Mold as a whole or local overheating, so that Plastic Injection Mold can not be formed normally and production is stopped, and the top rod and other mobile parts are damaged by thermal expansion. The design of cooling system, processing to the shape of the product, do not leave out the system because of the complex structure of Plastic Injection Mold or processing difficulties, especially large and medium-sized Plastic Injection Mold must fully consider the cooling problem.

7. Fixed distance tension mechanism failure

Swing hook, buckle and other distance tension mechanism is generally used in fixed Mold core-pulling or some secondary release Plastic Injection Mold. Because this kind of mechanism is set in pairs on the two sides of Plastic Injection Mold, its action requirements must be synchronized, that is, the mold is closed at the same time buckle. Open the mold to a certain position at the same time decoupling. Once the synchronization is lost, it is bound to cause the template of the Plastic Injection Mold to be pulled skew and damaged. The parts of these mechanisms should have higher stiffness and wear resistance, and it is difficult to adjust. The service life of the mechanism is short, so it can be avoided as far as possible and other mechanisms can be used. In the case of small suction force can be used to push out the method of fixed Mold spring, in the case of large core pulling force can be used when the moving mold backward core sliding, first complete the core pulling action and then the mold structure, in the large Plastic Injection Mold can be used hydraulic cylinder core pulling. The inclined pin sliding block core-pulling mechanism is damaged. The most common faults of this mechanism are not in place on processing and too small material. There are mainly the following two problems: the inclined pin Angle A is large, and the advantage is that it can produce a large core pulling distance in a short die stroke. However, if the inclination Angle A is too large, when the pulling force F is a certain value, the bending force P=F/COSA received by the inclined pin in the process of core pulling is larger, which is easy to appear inclined pin deformation and inclined hole wear. At the same time, the upward thrust N=FTGA generated 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, thus increasing the friction resistance of the slider when sliding. Easy to cause sliding and guide groove wear. As A rule of thumb, inclination A should not be greater than 25°.

8. The length of Plastic Injection Mold changes

Some Plastic Injection Mold is limited by the template area, the length of the guide groove is too small, and the slider is exposed outside the guide groove after the core pulling action is completed. This is easy to cause the slider tilt in the stage after the core pulling and the initial stage of the mold restoration, especially in the mold closing, the slider reset is not smooth, so that the slider damage, even bending damage. As a rule of thumb, the length left in the chute should not be less than 2/3 of the total length of the guide slot after the slider completes the core-pulling action.

9. In the design and manufacture of Plastic Injection Mold, it should be based on the requirements of the quality of Plastic parts, the size of the batch, the requirements of the manufacturing period and other specific circumstances, which can not only meet the requirements of the products, but also the structure of Plastic Injection Mold is simple and reliable, easy to process, so that the cost is low. This is the perfect mold.

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