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Common troubleshooting in injection mold
- Oct 10, 2018 -

The structure and quality of injection mold directly affect the quality and efficiency of plastic parts. Injection mold production and plastic production practices in the most common, the most common mold breakdowns and their main causes are analyzed and eliminated as follows

1. It is difficult to remove the gate.


In the injection process, the gate is glued to the gate sleeve and is not easy to escape. When the die is opened, the product is cracked. In addition, the operator must tap the tip of the copper rod from the nozzle to make it loose before demoulding, seriously affecting production efficiency. The main reason for this failure is the poor smoothness of the taper hole and the knife marks in the circumferential 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, and the nozzle spherical curvature is too small, resulting in the gate rivet head here. The taper hole of gate sleeve is difficult to be machined. Standard parts should be used as far as possible. If self-machined, special reamers should be made or purchased. The tapered hole needs to be milled to more than Ra0.4. In addition, gate sprue or gate ejection mechanism must be set up.

2, guide pillar damage.


The guide post plays a leading role in the mold to ensure that the core and the cavity forming surface do not touch each other under any circumstances, and can not be used as a force or positioning part. In the following cases, the dynamic and fixed modes of injection will produce a great lateral offset force.

(1) when the thickness of plastic parts is not uniform, the velocity of material flow through the thick wall is high, which produces greater pressure here; (2) the side of plastic parts is asymmetrical, such as the mold with stepped parting surface, the opposite side of the opposite side of the pressure is not equal.

3. The dynamic and fixed die deviations of large dies are caused by the different filling rates in different directions and by the influence of the die weight during the loading process.


In these cases, the lateral offset force will be applied to the guide post during injection, and the surface of the guide post will be pulled, damaged, and the guide post will be bent or cut off, even unable to open the mold. In order to solve the above problems, a high-strength positioning key is added to the parting surface of the die on each side. The most convenient and effective way is to use the cylindrical key. The perpendicularity between guide hole and parting surface is very important. In the process is to adopt moving, fixed mold alignment position clamping, boring in a boring machine, so as to ensure the concentricity of moving, fixed mold hole, and make the verticality error minimum. Besides, the heat treatment hardness of the guide post and guide sleeve must meet the design requirements.

4. Dynamic template bending.


When the mold is injected, the molten plastic in the mold cavity produces enormous back pressure, usually 600-1000kg/cm 2. Mould manufacturer sometimes does not pay attention to this problem, often change the original design size, or the moving template with low-strength steel plate instead, in the use of ejector ejector die, due to the large span between the two sides of the seat, resulting in injection mold bending. Therefore, the movable formwork must be made of high-quality steel, with sufficient thickness. Low-strength steel plates such as A3 should not be used. When necessary, support columns or blocks should be set under the movable formwork to reduce the thickness of the formwork and improve the bearing capacity.

5. The bent rod is bent, broken or leaked.


The quality of the self-made ejector rod is better, that is, the machining cost is too high. Now the standard parts are generally used and the quality is poor. If the gap between the ejector rod and the hole is too large, the leakage will occur, but if the gap is too small, the ejector rod will be stuck because of the mold temperature rising and the ejector rod expanding. Even more dangerous, sometimes the ejector rod is ejected from a general distance on the ejector and break, resulting in the next closure of the exposed ejector rod can not be restored and hit the concave die. In order to solve this problem, the ejector rod is regrinded, and the 10-15mm mating section is reserved at the front of the ejector rod, and the middle part is ground down by 0.2mm. After assembling, all ejectors must strictly check the fit clearance, generally within 0.05-0.08mm, to ensure that the entire ejector can move in and out freely.

6, poor cooling or water leakage.


The cooling effect of the die has a direct impact on the quality and production efficiency of the product, such as poor cooling, large shrinkage of the product, or uneven shrinkage and warping deformation. On the other hand, the whole or part of the mold is overheated, so that the mold can not be formed normally and stop production, serious expansion of the ejector rod and other movable parts jammed and damaged. Cooling system design, processing depends on the shape of the product, do not omit this system because of complex mold structure or processing difficulties, especially large and medium-sized molds must fully consider the cooling problem.

7, the fixed distance tension mechanism is out of order.


The fixed distance tension mechanism such as swing hook and lap is usually used in the mould for core pulling or some secondary demoulding. Because the mechanism is set in pairs on both sides of the mould, its action must be synchronous, that is, clamping the mould at the same time and releasing the hook at the same time when the mould is opened to a certain position. Once losing synchronization, it is bound to cause the die to be pulled to be skewed and damaged, the parts of these mechanisms have higher stiffness and wear resistance, adjustment is also difficult, the life of the mechanism is shorter, as far as possible to avoid the use of other mechanisms can be used. When the pulling force is relatively small, the spring pushing method can be adopted to fix the mold. When the pulling force is relatively large, the core sliding can be adopted when the dynamic mold is withdrawn. The core pulling action can be completed first and then the mold is divided. The hydraulic cylinder core pulling can be used in the large mold. The slanting pin sliding core pulling mechanism is damaged. Most of the faults of this kind of mechanism are inadequate processing and too small material. There are two main problems: the large tilt angle A, the advantage is that it can produce a larger core pulling distance in a shorter opening stroke. But if the angle A is too large, when the pulling force F is a certain value, the bending force P = F / COSA of the inclined pin in the process of core pulling is larger, and the deformation of the inclined pin and the wear of the inclined hole are easy to occur. At the same time, the more thrust N = FTGA produced by the inclined pin on the slider, the greater the positive pressure of the slider on the guide surface in the guide groove, thus increasing the friction resistance when the slider slides. Easy to cause slippage, guide groove wear. According to experience, the inclination A should not be greater than 25 degrees.

8, the length of mold changes.


Same 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, so it is easy to cause the slider tilt in the post-core pulling stage and the initial stage of the clamping reset, especially in the clamping process, the slider is not repositioned smoothly, so that the slider damage, even bending damage. According to experience, the length of the slider remaining in the groove should not be less than 2/3 of the full length of the guide groove after the core pulling action is completed.


9. In the final design and manufacture of the mold, according to the requirements of the quality of the plastic parts, the size of the batch, the requirements of the manufacturing period and other specific circumstances, not only can meet the requirements of the product, but also in the structure of the mold is the most simple and reliable, easy to process, so that the cost is low, this is the most perfect mold.