Partial troubleshooting of injection mold
You know what?The structure form and processing quality of injection mold directly affect the quality and production efficiency of plastic parts.There may be a lot of failures in the process of mold production, then we will follow Shanghai pugnny to learn about several common failures and solutions.
Guide pillar damage: guide pillar mainly plays a guiding role in the injection mold, which can ensure that the molding surface of the mold core and cavity will not touch each other under any circumstances, and the guide column cannot be used as the bearing or positioning part.In the following cases, the dynamic and fixed modes during injection will generate huge lateral migration force :(1) when the requirement of the wall thickness of the plastic part is not uniform, the rate at the over-thick wall of material flow is large, which will generate large pressure here;(2) the side of the plastic part is asymmetrical, such as the mold of the stepped fractal surface, and the opposite two sides are subjected to different backpressure.
Difficulty in discharging the gate: during the injection molding process, the gate is glued in the gate sleeve, which is difficult to get out.When the mold is opened, cracks appear in the products.In addition, operators must knock out from the nozzle with the top of the copper bar to make it loose before demoulding, seriously affecting production efficiency.The main factor of the failure is poor finish of the gate cone hole and the blade mark on the circumference of the inner hole.In addition, the material is too soft, the small end of the cone hole is deformed or damaged after using for a period of time, and the spherical arc of the nozzle is too small, resulting in the riveting head of the gate material.It is very difficult to process the taper hole of the sprue bushing. Standard parts should be adopted as far as possible. If you want to process by yourself, you should also make your own or buy special reamer.The taper hole should be ground below Ra0.4.In addition, sprue puller or sprue jacking mechanism must be set.
Migration of moving and fixed mould: the large mould has migration of moving and fixed mould due to the different charging rate in all directions and the effect of die dead weight on filling.In these cases, the lateral migration force during injection will be added to the guide column, which will be sheared on the surface of the guide column during mold opening, which will be damaged, and the guide column will be bent or cut when it is seriously damaged, or even unable to open the mold.In order to solve the above problems, a high strength positioning key is added on the die parting surface, the simplest and most effective is to use cylindrical key.The perpendicularity of the guide hole to the parting surface is crucial.In the processing is to adopt moving, fixed mold alignment clamps, boring in the boring machine last time, so that can guarantee moving, fixed mold hole concentricity, and make the perpendicular degree error minimum.In addition, the heat treatment hardness of guide column and guide sleeve must meet the design requirements.
Dynamic formwork bending: when the injection mold is being injected, the molten plastic in the mold cavity produces a huge reverse pressure, which is generally between 600 and 1000 kg/cm.Mold makers sometimes do not pay enough attention to this problem, to change the original design size, or to replace the moving template with low-strength steel plate. In the mold with the top bar material, because of the large space between the two sides, the template is bent down during injection.Therefore, the movable formwork must be of high quality steel, with sufficient thickness. It is not necessary to use A3 or other low-strength steel plates. If necessary, a support column or support block should be set under the movable formwork to reduce the thickness of the formwork and improve the bearing capacity.
Top bar bending, breaking or leakage: the quality of the self-made top bar is good, which means the processing cost is too high. Now, standard parts are usually selected, with average quality.If the gap between the jacking bar and the hole is too large, there will be leakage, but if the gap is too small, the jacking bar will become inflated due to the rising mold temperature during injection.What is more dangerous is that sometimes the top bar is broken when it is pushed out at a normal distance. As a result, the exposed top bar cannot be reset at the next close and the die is damaged.In order to solve this problem, the top rod is reground. The matching section of 10~15 mm is reserved at the front end of the top rod, and the middle part is ground down by 0.2 mm.After assembly, all jacking bars must be strictly checked with clearance, usually within 0.05~0.08 mm, to ensure that the whole jacking mechanism can be back and forth freely.
Poor cooling or leakage in water channel: the cooling effect of injection mold directly affects the quality and production efficiency of products, such as poor cooling, large shrinkage of products, or uneven shrinkage and warping surface deformation.On the other hand, the mold whole or local overheating, so that the mold can not be formed normal production and production, and serious so that the top bar and other parts of the thermal expansion and stuck dead damage.The design of the cooling system depends on the shape of the product. Do not omit the system because of the complex structure of the mold or the difficulty in processing.
The length of guide slot is too small: some molds are limited by the area of the template, and the length of guide slot is too small. After the core pulling, the slide block is exposed outside the guide slot. In this way, it is easy to cause the slide block tilting in the post-core stage and the initial stage of the resetting of the mould.According to experience, the length left in the chute shall not be less than 2/3 of the full length of the guide slot after the sliding block has completed the core pulling.When designing and manufacturing molds, we should meet the requirements of the quality of plastic parts, the size of batch, the requirements of manufacturing deadline, etc., which not only meets the requirements of products, but also is the simplest and reliable in the structure of molds, easy to process, making the cost low, which is the most perfect mold.