1. Guide pillar damage
The guide pillar mainly plays a guiding role in the mold to ensure that the forming surfaces of the core and cavity do not collide with each other in any case, and the guide pillar can not be used as a force-bearing or positioning part.
In the following two cases, the dynamic and fixed mold will produce huge lateral offset force during injection:
When the thickness of the plastic part is not uniform, the velocity of the material flow through the thick wall is high, and the pressure is large;
The side of the plastic part is not symmetrical, such as the mould of the stepped parting surface, and the counter pressure on the opposite two sides is not equal.
2. It is difficult to discharge the gate
In the process of injection molding, the gate is stuck in the gate sleeve and is not easy to come out. When the mold is opened, the product appears crack damage. In addition, the operator must knock out the tip of the copper rod from the nozzle to make it loose before demoulding, which seriously affects the production efficiency.
The main reason for this kind of failure is poor finish of the taper hole of the gate, and there are knife marks in the circumferential direction of the inner hole. Secondly, the material is too soft, the small end of the taper hole is deformed or damaged after using for a period of time, and the spherical arc of the nozzle is too small, which causes the gate material to produce riveting head here. It is difficult to machine the taper hole of the gate sleeve, so the standard parts should be used as far as possible. If it needs to be processed by ourselves, we should also make or buy a special reamer. RA4 to 0.0.
In addition, gate pulling rod or gate ejection mechanism must be set.
3. Moving and fixed die offset
Due to the different filling rate in each direction and the influence of the die weight on the large die, the dynamic and fixed die offset occurs.
In these cases, the lateral offset force will be added to the guide pillar during injection, and the surface of the guide pillar will be roughened and damaged when the mold is opened. If it is serious, the guide pillar 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 on the parting surface of the mold, and the most convenient and effective way is to use the cylindrical key. The perpendicularity of guide pillar hole and parting surface is very important.
In the process of machining, the moving and fixed die are aligned with the position and clamped, and then the boring is finished at one time on the boring machine. In this way, the concentricity of the moving and fixed die holes can be ensured and the perpendicularity error can be minimized. In addition, the heat treatment hardness of guide pillar and guide sleeve must meet the design requirements.
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4. Bending of movable formwork
During the injection process, the molten plastic in the mold cavity produces a huge back pressure, which is generally in the range of 600-1000 kg / cm2. Mold makers sometimes do not pay attention to this problem, often change the original design size, or replace the movable template with low strength steel plate. In the mold with ejector pin, due to the large span of both sides, the mold plate bends down during injection.
Therefore, the movable formwork must be made of high-quality steel with sufficient thickness. Low strength steel plates such as A3 shall not be used. If necessary, supporting columns or supporting blocks shall be set under the movable formwork to reduce the thickness of formwork and improve the bearing capacity.
5. The ejector pin is bent, broken or leaked
The quality of the self-made ejector pin is better, that is, the processing cost is too high. Now the standard parts are usually selected, and the quality is ordinary. If the clearance between the ejector pin and the hole is too large, there will be leakage, but if the clearance is too small, the ejector will be stuck due to the increase of mold temperature during injection. What's more dangerous is that sometimes the ejector pin will not move when it is ejected for a general distance, which will break the die. As a result, the exposed ejector can not be reset in the next mold closing and the die will be damaged.
In order to solve this problem, the ejector pin is reground, and a 10 ~ 15mm matching section is reserved at the front end of the ejector rod, and the middle part is ground 0.2mm smaller. After assembly, all ejector pins must be strictly checked for clearance, generally within 0.05 ~ 0.08 mm, to ensure that the whole ejection mechanism can advance and retreat freely.
6. Poor cooling or water leakage
The cooling effect of die directly affects the quality and production efficiency of products, such as poor cooling, large shrinkage of products, or warping deformation caused by uneven shrinkage. On the other hand, the whole or part of the die is overheated, so that the mold can not be formed normally and stop production. In serious cases, the ejector pin and other moving parts are blocked by thermal expansion and damaged.
The design and processing of the cooling system depends on the shape of the product. Do not omit this system because of the complex structure of the mold or the difficulty in processing. Especially for large and medium-sized molds, the cooling problem must be fully considered.
7. The length of guide groove is too small
Due to the limitation of template area, the length of guide groove of some dies is too small, and the slide block is exposed outside the guide groove after the core pulling operation is completed. In this way, it is easy to cause the slide block to tilt in the later stage of core pulling and the initial stage of mold closing and resetting. Especially, when the mold is closed, the sliding block is not reset smoothly, which damages the slide block and even damages the bending.
According to experience, the length of the slide in the chute should not be less than 2 / 3 of the total length of the guide groove after the core pulling action of the slide block is completed.
8. Fixed distance tension mechanism failure
The fixed distance tension mechanism, such as swing hook and buckle, is generally used in fixed die core pulling or some secondary demoulding molds. Because these mechanisms are set in pairs on both sides of the mold, their action requirements must be synchronous, that is, closing the mold at the same time, and opening the mold to a certain position at the same time unhooking.
Once out of sync, it is bound to cause the die template to be pulled skew and damaged. The parts of these mechanisms should have high stiffness and wear resistance, and it is difficult to adjust them. The service life of the mechanism is short, so it can be avoided to use as much as possible, and other mechanisms can be used. When the core pulling force is relatively small, the spring can be used to push out the fixed mold. When the core pulling force is relatively large, the core sliding structure can be adopted when the moving die moves backward, and the core pulling action is completed before the mold is divided. The hydraulic cylinder core pulling can be used on the large mold.
9. The inclined pin slider core pulling mechanism is damaged.
The common problems of this kind of mechanism are that the processing is not in place and the materials used are too small. There are two main problems:
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