Reasons for common shortcomings of automobile injection molds and their elimination methods

Automobile injection mold is a tool that produces plastic products; it is also a tool that gives plastic products complete structure and size. The structural form and mold processing quality of automobile injection molds directly affect the quality and production efficiency of plastic parts. In the production of automobile injection molds and plastic products, the most common, the most common reasons for the shortcomings of automobile injection molds and their elimination methods are described in detail as follows:

1. Gate stripping is difficult. During the injection molding process, the gate sticks to the gate sleeve and is not easy to come out. When the mold is opened, the product exhibits crack damage. In addition, the operator must knock out the copper rod from the nozzle to loosen it before demoulding, which seriously affects the production efficiency. The main reason for this shortcoming is the poor finish of the gate taper hole and the knife marks in the circumferential direction of the inner hole. The second is that the material is too soft, the small end of the taper hole is deformed or damaged after a period of use, and the spherical arc of the nozzle is too small, causing the gate material to have a rivet head here. The taper hole of the sprue sleeve is difficult to process, and standard parts should be used as far as possible. The taper hole needs to be ground to above Ra0.4. In addition, it is necessary to set gate pull rod or gate ejector structure.

2. The guide post is damaged. The guide post mainly plays a guiding role in the mold to ensure that the molding surfaces of the core and the cavity do not touch each other under any circumstances, and the guide post cannot be used as a force-bearing part or a positioning part. In the following cases, when the needle is moved, the fixed mold will generate a huge lateral offset force: (1). When the wall thickness of the plastic part is not uniform, the flow rate of the material passing through the thick wall is large, and a relatively large amount of pressure will occur here. (2) The side surfaces of the plastic parts are asymmetrical, such as the opposite sides of the mold of the stepped parting surface are not equal to the back pressure.

3. For large molds, due to the different filling rates in each direction and the influence of the mold's own weight during mold installation, the moving and fixed molds shift. In the above cases, the lateral deflection force will be applied to the guide post during injection, and the surface of the guide post will be rough and damaged when the mold is opened. In order to deal with the above problems, a high-strength positioning key is added on each of the four sides of the mold parting surface. The most concise and useful thing is to use a cylindrical key. The straightness of the guide hole and the parting surface is very important. In the process of processing, the movable and fixed die are aligned and clamped, and then the boring machine is finished at one time, so as to ensure the concentricity of the movable and fixed die holes and ensure the smoothness Make the straightness error Z small. In addition, the heat treatment hardness of the guide post and guide bush must meet the planning requirements.

4. The moving template is bent. When the mold is injected, the molten plastic in the mold cavity generates a huge back pressure, generally 600~1000 kg/cm². Mold makers sometimes do not pay attention to this problem, and often change the original design size, or replace the moving template with low-strength steel plates. Therefore, it is necessary to use high-quality steel for the moving formwork, and it must be thick enough. Low-strength steel plates such as A3 should not be used. When necessary, support columns or support blocks should be set under the moving formwork to reduce the thickness of the formwork and improve the bearing capacity.

5. The ejector rod is bent, cracked or leaked. The quality of Keji's ejector is better, but the processing cost is too high. Now, standard parts are generally used, and the quality is poor. If the gap between the ejector pin and the hole is too large, there will be material leakage, but if the gap is too small, the ejector pin will be stuck due to the increase in mold temperature during injection. What is more risky is that sometimes the ejector pin is pushed out of the normal distance, and the ejector pin does not move and breaks. As a result, the exposed ejector pin cannot be reset during the next mold clamping, and the die is damaged. In order to deal with this problem, the ejector rod is ground from the beginning, and the cooperating section of 10-15 mm is reserved at the front end of the ejector rod, and the middle part is ground smaller by 0.2 mm. After all ejectors are assembled, it is necessary to strictly check the cooperation gap, generally within 0.05~0.08 mm, to ensure that the entire ejector organization 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 product, such as poor cooling, large shortening of the product, or uneven shortening and warping deformation. On the other hand, the whole or part of the mold is overheated, so that the mold cannot be formed normally and production is stopped. The planning and processing of the cooling system depends on the shape of the product. Do not omit this system because the mold structure is complex or difficult to process. Especially for large and medium-sized molds, the cooling problem must be fully considered.

7. The fixed-distance tensioning organization fails. Swing hooks, hasps and other fixed-distance tensioning structures are generally used in fixed core pulling or some secondary demolding molds. Because these structures are set in pairs on both sides of the mold, their actions must be synchronized. , that is, the mold is clamped at the same time, and the mold is opened to a certain position and unhooked at the same time. Once the synchronization is lost, the template of the drawn mold will inevitably be skewed and damaged. The parts of these structures must have high rigidity and wear resistance, and it is difficult to adjust. . In the case of a relatively small core pulling force, the method of pushing out the fixed die with a spring can be used. In the case of a relatively large core pulling force, the core sliding when the moving die retreats can be used, and the core pulling action is completed first and then the mold is split. The hydraulic cylinder can be used for core pulling on the mold. The inclined pin slider core pulling structure is damaged. Most of the disadvantages of this kind of structure are that the processing is not in place and the materials are too small. There are mainly the following two problems. The inclined pin angle A is large, and the advantage is that a large core-pulling distance can occur 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 on the inclined pin during the core-pulling process is also larger, and the inclined pin is easily deformed and the inclined hole is worn. At the same time, the upward thrust N=FTGA generated by the oblique 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, and then increases the frictional resistance when the slider slides. It is easy to cause uneven sliding and wear of the guide groove. According to experience, the inclination angle A should not be greater than 25

8. Some molds are limited by the area of the template, and the length of the guide groove is too small. When the mold is closed, the reset of the slider is not smooth, which damages the slider and even damages it by bending. According to experience, after the slider completes the core-pulling action, the length left in the chute should not be less than 2/3 of the total length of the guide groove.

9. In the final planning, when making molds, it should be based on the requirements of the quality of plastic parts, the size of the batch, the requirements of the production period and other specific conditions, which can not only meet the requirements of the product, but also be simple and reliable in the mold structure, easy to process, so that the The cost is low, and it is excellent to produce such a mold.