An injection mold is a tool for producing plastic products; it is also a tool that gives plastic products a complete structure size. The structure of the injection mold the quality of the mold processing directly affect the quality production efficiency of plastic parts. The most common most common causes of injection mold failures their elimination methods are described in the following:

1. Gate discharge is difficult

During the injection molding process, the gate is stuck in the gate sleeve is easy to come out. When the mold is opened, the product appears crack damage. In addition, the operator must knock out the nozzle with the tip of the copper rod to loosen it before demoulding, which seriously affects the production efficiency. The main reason for this failure is the poor finish of the taper hole of the gate, there are knife marks in the circumferential direction of the inner hole. Secondly, the material is too soft, the small end of the tapered hole is deformed damaged after a period of use, the spherical radius of the nozzle is too small, which causes the gate material to produce a rivet head here. The taper hole of the gate sleeve is difficult to process. Standard parts should be used as much as possible. If you need to process it yourself, you should also make buy a special reamer. Taper holes need to be ground to Ra0.4 more. In addition, a gate pulling rod a gate ejection mechanism must be provided.

2. Guide pillar damage

The guide post mainly plays a guiding role in the mold to ensure that the molding surfaces of the core the cavity do touch each other under any circumstances, the guide post cannot be used as a force positioning member. In the following cases, when the injection is moved, the fixed mold will generate a huge lateral offset force: (1). When the wall thickness of the plastic part is uniform, the velocity of the material passing through the thick wall is large. Large pressure; (2). The side of the plastic part is asymmetric, such as the opposite pressure on the two opposite sides of the mold of the stepped parting surface.

3.Large mold

Due to the different filling rates in each direction, the influence of the mold's own weight during the mold loading, the dynamic fixed mold offsets occur. In the above several cases, the lateral offset force will be added to the guide post during injection, the surface of the guide post will be fuzzed damaged when the mold is opened. In severe cases, the guide post will be bent cut off, even the mold cannot be opened.

In order to solve the above problems, a high-strength positioning key is added on each side of the mold parting surface, the most convenient effective is to use a cylindrical key. The perpendicularity of the guide post hole the parting surface is very important. During processing, the moving is used. After the fixed mold is aligned clamped, it is bored on the boring machine once. Minimize verticality errors. In addition, the heat treatment hardness of the guide post guide sleeve must meet the design requirements.

4.Moving template bending

When the mold is injected, the molten plastic in the mold cavity generates a huge back pressure, which is generally 600 ~ 1000 kg / cm. The mold maker sometimes does pay attention to this problem, often changes the original design size, replaces the movable template with a low-strength steel plate. In the mold using the ejector pin, due to the large span between the two sides, the template is bent down during injection. Therefore, the moving formwork must be made of high-quality steel. It must be of sufficient thickness. Low-strength steel plates such as A3 must be used. When necessary, support columns blocks should be set under the moving formwork to reduce the thickness of the formwork improve the carrying capacity.

5. The ejector pin is bent, broken leaking.

The quality of the self-made ejector is good, which means that the processing cost is too high. Nowadays, standard parts are generally used, the quality is poor. If the gap between the ejector pin the hole is too large, material leakage will occur, but if the clearance is too small, the ejector pin will swell due to the rise of the mold temperature during injection. What is more dangerous is that sometimes the ejector pin is broken pushed off at a normal distance. As a result, the exposed ejector pin cannot be reset when the next mold is closed, the concave mold is damaged. In order to solve this problem, the ejector rod was reground, a fitting section of 10-15 mm was retained at the front end of the ejector rod, the middle part was milled 0.2 mm smaller. After assembly of all ejector rods, the fit clearance must be strictly checked, generally within 0.05 ~ 0.08 mm, to ensure that the entire ejector mechanism can move forward backward freely.

6. Poor cooling leaking water

The cooling effect of the mold directly affects the quality production efficiency of the product, such as defects such as poor cooling, large shrinkage of the product, uneven shrinkage deformation of the warped surface. On the other hand, the mold is overheated in whole in part, which makes the mold unable to form stop production. In severe cases, the movable parts such as the ejector pin are thermally expanded stuck damaged. The design processing of the cooling system are determined by the shape of the product. Do omit this system because of the complex mold structure difficult processing, especially the large medium-sized molds must fully consider the cooling problem.

7. The fixed tensioning mechanism fails

Fixed distance tensioning mechanisms such as pendulum hooks buckles are generally used in fixed core pulling some secondary demoulding molds.Because such mechanisms are arranged in pairs on both sides of the mold, their actions must be synchronized, that is, The mold is buckled at the same time, the mold is released to a certain position unhooked at the same time. Once the synchronization is lost, the template of the drawn mold will inevitably be skewed damaged. The parts of these mechanisms must have high rigidity wear resistance, adjustment is difficult, the life of the mechanism is short. Avoid using it as much as possible, you can use other mechanisms.

In the case of relatively small core-pulling force, a spring can be used to push the fixed mold.In the case of relatively large core-pulling force, the core can slide when the movable mold is retracted, the structure of the core-pulling is completed after the core-pulling action is completed. The hydraulic cylinder can be used for core pulling on the mold. The oblique pin slider core pulling mechanism is damaged. The most common faults of this mechanism are mostly inadequate processing too small materials, which mainly have the following two problems.

The oblique pin inclination angle A is large, the advantage is that a relatively large core pulling distance can be generated in a short mold opening 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 that the oblique pin receives during the core drawing process is larger, the oblique pin deformation oblique hole wear are likely to occur. At the same time, the oblique pin produces an upward thrust N = FTGA on the slider, which increases the positive pressure of the slider on the guide surface in the guide groove, thereby increasing the frictional resistance when the slider slides. Easy to cause sliding irregularities, guide groove wear. According to experience, the inclination angle A should 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 is exposed outside the guide groove after the core pulling operation is completed.In this way, the slider is easy to tilt during the core pulling stage the initial stage of the mold reset, especially when the mold is closed, the slider is reset smoothly. Damage to the slider, even bending damage. According to experience, after the slider completes the core pulling action, the length remaining in the chute should be less than 2/3 of the total length of the guide groove.

9. Finally in design

When manufacturing the mold, it should be based on the specific requirements of the quality of the plastic parts, the size of the batch, the requirements of the manufacturing period, etc., which can meet the requirements of the product, the mold structure is the most simple reliable, easy to process, the production cost is low. The mold is excellent.