Plastic Parts
Injection molding common problems and solutions
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The injection molding process is a complex process involving mold design, mold manufacturing, raw material characteristics and raw material pretreatment methods, molding process, injection molding machine operation, etc., and is closely related to processing environmental conditions, product cooling time, and post-treatment process. Process. Therefore, the quality of plastic products depends not only on the injection molding precision, measurement accuracy, but also on the quality of the mold design and the accuracy level of the mold processing. Usually, it is also affected by other factors mentioned above. Restricted.Tools/raw materials
Injection molding machine
Method / step
1. Burr: The occurrence of burrs is caused by the overflow of the molten injection molding resin from the mold parting surface, which is the worst state in the forming operation. Especially when the burr firmly adheres to the mold parting surface and is clamped, it will damage the mold parting surface. After the mold is damaged, the molded article will generate new burrs when it is reworked. It also aggravates the damage of the mold and causes it to be unusable. So pay special attention.
(1) Do not use excessive injection pressure
(2) Improve the clamping force
(3) Keep the mold in a safe place
(4) Adjust the injection volume and lower the temperature
2. Insufficient filling: insufficient forming is a forming defect formed by the cooling and hardening of the molten injection resin when it has not completely filled the cavity. The main reason is insufficient resin capacity, insufficient pressure in the cavity, insufficient resin fluidity, and exhaust effect. not good. In the case where the injection amount of the molding machine is sufficient, if the condition of insufficient molding is still not improved, it is considered whether the injection pressure is insufficient or the set temperature of the molten resin is low.
3. Weld mark: The weld line is a thin line-shaped seam mark produced on the surface of the molded article because the front end portion of the molten resin from different directions is cooled and is not completely fused at the joint. It is difficult to find when not paying attention to observation. The weld line often occurs on the fusion surface of the molten resin flowing in the cavity. Mainly affects the appearance, affecting the coating and plating. In severe cases, it affects the strength of the product. In order to ensure the quality of the molded product, such defects should be eliminated as much as possible. Adjust molding conditions to improve fluidity.
4. Depression: The occurrence of depressions is most common in surface defects of molded articles. It is a defect that is caused by heat shrinkage of the molded article and is formed in the wall thickness portion. The depression is a lesser degree than the under molding. It often occurs when the cavity is filled with molten resin, but the holding pressure is insufficient.
5. Bubbles: Bubbles are likely to occur in thicker parts of the molded article, and the cause of the formation is exactly the same as that of the molded product. A depression is formed on the surface of the molded article, and a cavity formed in the middle of the thick wall of the molded product is a bubble. According to the cause of the bubble, the countermeasures are as follows: when the wall thickness of the product is large, the outer surface is cooled faster than the center portion. Therefore, as the cooling progresses, the resin edge of the center portion shrinks toward the side. The surface is dilated, causing insufficient filling at the center. This condition is called a vacuum bubble.
The main solutions are:
1. According to the wall thickness, determine the reasonable gate and runner size. Generally, the height of the gate should be 50% to 60% of the wall thickness of the product.
2. Until the gate is sealed, a certain amount of supplementary injection material is left.
3. The injection time should be slightly longer than the gate sealing time.
4. Reduce the injection speed, increase the injection pressure, and use a material with a high melt viscosity grade.
5. The bubbles caused by the generation of volatile gases mainly include: (1) Full pre-drying. (2) Lower the resin temperature to avoid decomposition gas. Air bubbles caused by poor fluidity can be solved by increasing the temperature of the resin and the mold and increasing the injection speed.
6. Warpage and deformation of warped and deformed injection molded products are very difficult problems. The main problem should be solved from the mold design, and the adjustment effect of the molding conditions is very limited. When deformation is caused by residual stress caused by molding conditions, the stress can be relieved by lowering the injection pressure, increasing the mold temperature, and making the mold temperature uniform and increasing the resin temperature or by annealing.
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