What is the reason for the shrinkage and depression of injection molded products?

1. Mould:
(1) The design of the parts should make the wall thickness uniform and ensure consistent shrinkage.
(2) The cooling and heating system of the mold should ensure that the temperature of each part is consistent.
(3) The gating system should be unobstructed and the resistance should not be too large. For example, the size of the main channel, the runner and the gate should be appropriate, the finish should be sufficient, and the transition area should be arc transition. Professional plastic knowledge exchange WeChat group plus editor WeChat: NB58250988
(4) The temperature should be increased for thin parts to ensure smooth material flow, and the mold temperature should be lowered for thick-walled parts.
(5) The gate should be opened symmetrically, try to open it in the thick-walled part of the part, and the volume of the cold well should be increased.
2. Machines:
(1) The nozzle hole is too large to cause the molten material to flow back and shrink. If it is too small, the resistance is too large and the amount of material is insufficient to cause shrinkage.
(2) Insufficient clamping force will cause the flash to shrink, so check whether there is any problem with the clamping system.
(3) If the amount of plasticization is insufficient, a machine with a large amount of plasticization should be selected to check whether the screw and barrel are worn.
3. Plastic aspects:
Crystalline plastics shrink more than non-crystalline plastics, and the amount of material should be appropriately increased during processing, or a change agent should be added to the plastic to speed up crystallization and reduce shrinkage sag.
4. Processing:
(1) The temperature of the barrel is too high, and the volume changes greatly, especially the temperature of the front furnace. For plastics with poor fluidity, the temperature should be appropriately increased to ensure smoothness.
(2) The injection pressure, speed, and back pressure are too low, and the injection time is too short, so that the amount or density of the material is insufficient and the shrinkage pressure, speed, and back pressure are too large, and the time is too long, resulting in flash and shrinkage.
(3) The feeding amount, that is, when the buffer pad is too large, consumes the injection pressure, and when it is too small, the feeding amount is insufficient.
(4) For parts that do not require precision, after the injection and pressure keeping are completed, the outer layer is basically condensed and hardened, and the sandwich part is still soft and can be ejected, and the mold is released as soon as possible, so that it can be slowly cooled in air or hot water. , which can make the shrinkage depression smooth and less conspicuous without affecting the use.