Injection molding common problems and solutions

Injection molding common problems and solutions

The process of injection molding is a complex processing process that involves many factors such as mold design, mold manufacturing, raw material characteristics and raw material pretreatment method, molding process, injection molding machine operation, and is closely related to the processing environment, product cooling time and post-processing technology. Therefore, the quality of plastic products not only depends on the injection molding machine precision, measurement precision, or just by the mold design of the pros and cons and mold processing precision level decision, usually, it will also be affected by the other factors and constraints.

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One, burr (or called flash, overflow, overflow) : burr is caused by melting injection resin from the mold parting surface overflow and formation, is the worst state in the forming operation.Especially when the burr sticks firmly to the parting surface of the mold, it will damage the parting surface of the mold.After the die is damaged, new burrs will appear when the product is reworked.It also aggravates the damage to the mold and makes it unusable.So pay special attention.

(1) do not use too high injection pressure

(2) improve mold locking force

(3) keep the mold properly

(4) adjust injection volume and reduce temperature.

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Two, fill insufficient (or called to form insufficient) : forming insufficient is due to melt injection molding resin is not fully filled with mold cavity has been cooling hardening and forming defects, the main reason is insufficient resin capacity, insufficient pressure in the cavity, resin liquidity, exhaust effect is not good.When the injection volume of the molding machine is sufficient and the forming condition is not improved, it should be considered whether the injection pressure is insufficient or the setting temperature of molten resin is too low.

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Three, weld mark (or bond line) : weld mark refers to the formation of thin line on the surface of the joint marks, is due to the different direction of the fused resin front part of the cooling, in the joint failed to fully fuse.It's hard to see when you're not looking.Weld marks often occur on the fusion surface of molten resin flowing in the die cavity.Mainly affect the appearance, coating, electroplating impact.Serious, on the strength of products, in order to ensure the quality of forming products, should try to eliminate such defects.Adjust forming conditions to improve fluidity.

Four, depressions (or shrinkage pits) : depressions are most common in surface defects of formed products.It is a defect in the wall thickness caused by the thermal shrinkage of the forming products.Pitting is a minor defect compared to lack of forming.The cavity is often filled with molten resin, but the pressure is not sufficient occasions.

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The solutions are as follows:

1. Determine the reasonable gate and runner size according to the wall thickness.Generally, the height of gate should be 50% ~ 60% of the product wall thickness.

2. Some supplementary injection materials are left until the gate is sealed.

3. The injection time should be slightly longer than the gate sealing time.

4. Reduce the injection speed, increase the injection pressure, the use of high melt viscosity grade material.

5. Due to the production of volatile gas bubbles, the main solutions are :

   (1) fully pre-drying.

  (2) reduce the temperature of resin to avoid the generation of decomposition gas.The bubbles caused by poor fluidity can be solved by increasing the temperature of resin and mold and increasing the injection speed.

6. Warping, deformation injection products warping, deformation is a very tricky problem.Mainly from the mold design to solve, and forming conditions of the adjustment effect is very limited.When the residual stress is caused by the forming conditions, the stress can be eliminated by reducing the injection pressure, increasing the mold temperature and making the mold temperature uniform, increasing the resin temperature or adopting annealing method.(injection molding)

7. Silver wire (or silver thread).

 

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