The structural form and processing quality of plastic mold China directly affect the quality and production efficiency of plastic injection mold parts. There are many kinds of failures in the tooling mold production process. The following are solutions to several common failures.
Difficulty in gate stripping:
During the injection plastic molding process, the gate sticks to the gate sleeve and is not easy to come out. When the tooling mold is opened, the plastic injection mold parts has crack damage. In addition, the operator must knock out the tip of the copper rod from the tooling mold nozzle to loosen it before demoulding, which seriously affects the production efficiency. The main reason for this failure is the poor finish of the tooling mold gate taper hole and the knife marks in the circumferential direction of the inner hole.
In addition, 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 tooling mold gate material to produce a rivet head here. The taper hole of the sprue sleeve is difficult to process, and standard parts should be used as much as possible. If you need to process it yourself, you should also make or buy a special reamer. The tooling mold taper hole needs to be ground below Ra0.4. In addition, gate pulling rods or gate ejection mechanisms must be provided.
Guide post damage:
The guide post mainly plays a tooling mold guiding role in the injection mold to ensure that the injection plastic molding surfaces of the core and the cavity do not touch each other under any circumstances, and the tooling mold guide post cannot be used as a force-bearing part or a positioning part. In the following cases, the dynamic and fixed tooling mold will generate huge lateral offset force during injection: (1) When the wall thickness of the plastic injection mold part is not uniform, the flow rate of the material passing through the thick wall is large, and a large amount of pressure is generated here. (2) The side of the plastic part is asymmetrical, such as a mold tooling with a stepped parting surface, the opposite sides are not equal to the back pressure.
Moving and fixed mold tooling offset:
For large mold tooling, due to the different filling rates in each direction and the influence of the mold's own weight when the mold tooling is installed, the dynamic and fixed mold offsets occur. In these cases, the lateral deflection force will be applied to the mold tooling guide post during injection, and the surface of the mold tooling guide post will be rough and damaged when the mold is opened. In order to solve the above problems, a high-strength positioning key is added on each of the four sides of the mold parting surface. The most convenient and effective way is to use a cylindrical key. The verticality of the mold tooling guide hole and the parting surface is very important. In the processing, the movable and fixed die are aligned with the position and clamped, and then the boring machine is finished at one time, which can ensure the concentricity of the movable and fixed die holes and minimize the verticality error. In addition, the heat treatment hardness of the guide post and mold tooling guide bush must meet the design requirements.
Moving template bending:
When the injection plastics molding is injected, the molten plastic in the tooling mold cavity generates a huge back pressure, generally 600~1000 kg/cm2.Tooling 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. In the tooling mold with ejector, due to the large span between the seats on both sides, the template bends down during injection plastic molding. Therefore, the moving formwork must be made of high-quality steel, with sufficient thickness. A3 and other low-strength steel plates must 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.
The mold tooling ejector is bent, broken or leaking:
The quality of the self-made mold tooling ejector is better, but the processing cost is too high. Now, standard plastic injection mold parts are usually used, and the quality is average. If the mold tooling gap between the mold tooling ejector pin and the hole is too large, there will be leakage, but if the mold tooling gap is too small, the mold tooling ejector pin will be stuck due to the increase of mold temperature during injection plastic molding.
What's more dangerous is that sometimes the mold tooling ejector pin is pushed out of the normal distance and will not move and break. As a result, the exposed mold tooling ejector pin cannot be reset and the die will be damaged when the mold is closed next time. In order to solve this problem, the mold tooling ejector rod is re-ground, retaining a 10-15mm mating section at the front end of the mold tooling ejector rod, and grinding the middle part down by 0.2mm. After all mold tooling ejector rods are assembled, the matching clearance must be strictly checked, generally within 0.05~0.08 mm, to ensure that the entire mold tooling ejector mechanism can advance and retreat freely.
Poor cooling or water leaks:
The cooling effect of the injection plastic molding directly affects the quality and production efficiency of the plastic injection mold parts, such as poor cooling, large shrinkage of the plastic injection mold parts, or uneven shrinkage and deformation of the warped surface. On the other hand, the whole or part of the mold tooling is overheated, so that the mold cannot be formed normally and production is stopped. The design and processing of the cooling system depends on the shape of the plastic injection mold parts, 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.
Fixed distance tensioning mechanism failure:
Fixed-distance tensioning mechanisms such as swing hooks and hasps are generally used in fixed tooling mold core pulling or some secondary demolding molds. Because such mechanisms are arranged in pairs on both sides of the, tooling mold their actions must be synchronized, that is, When the tooling mold is closed, it is buckled at the same time, and when the tooling mold is opened to a certain position, the hook is released at the same time.
Once the synchronization is lost, the template of the drawn mold will be skewed and damaged. The plastic injection mold parts of these mechanisms must have high rigidity and wear resistance, and the adjustment is also difficult. The service life of the mechanism is short. When the core pulling force is relatively small, the method of pushing out the fixed mold by a spring can be used. When the core pulling force is relatively large, the core sliding when the moving China mold tooling retreats, and the core pulling action is completed first and then the China mold tooling is split. Hydraulic cylinders can be used to pull cores on the China mold tooling.
Diagonal pin slider core-pulling mechanism is damaged:
The most common faults of this kind of mechanism are that the processing is not in place and the materials are too small. There are mainly the following two problems: the inclination angle A of the inclined pin is large, and the advantage is that a large core pulling can be generated in a short China mold tooling opening stroke. distance. 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 oblique pin during the core pulling process is also larger, and the oblique pin deformation and oblique hole wear are prone to occur.
At the same time, the upward thrust N=FTGA generated by the oblique pin on the slider is also greater, and this force increases the positive pressure of the slider on the China mold tooling guide surface in the guide groove, thereby increasing the friction resistance when the slider slides. It is easy to cause uneven sliding and wear of the China mold tooling guide groove. As a rule of thumb, the inclination angle A should not be greater than 25°.
The length of the China mold tooling guide groove is too small:
Some molds are limited by the area of the template, and the length of the guide groove is too small. When the sliding block is not reset smoothly, the sliding block is damaged or even damaged 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.
When designing and manufacturing China mold tooling, 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 conditions, which can not only meet the requirements of the product, but also the most simple and reliable in terms of China mold tooling structure, easy to process, and low cost. It's the perfect mold.