What causes shrinkageand depression in the injection molding process?
injection molding
During the injection molding process, shrinkage and depression of the product are common phenomena, which can also be encountered in the production injection molding process. So, what causes shrinkage and depression? During the injection molding process, the main reasons for product shrinkage and indentation are as follows:
1. Machine aspect
(1) The nozzle hole is too large, causing the molten material to reflux and shrink. If it is too small, the resistance is high and the amount of material is insufficient, causing shrinkage.
(2) Insufficient locking force can cause shrinkage of the flying edge, and the locking system should be checked for any issues.
(3) If the plasticization amount is insufficient, a machine with a large plasticization amount should be selected, and the screw and barrel should be checked for wear.
There is no carelessness in the configuration and maintenance inspection of machine equipment. Various precision mold production equipment such as CNC machining centers, precision carving, and Shadick spark machines, as well as various models of injection molding machines, are strictly controlled at every stage from design and mold opening to injection molding, with the aim of providing a more professional and comprehensive service.
2. In terms of molds
(1) The design of the component should ensure uniform wall thickness and consistent shrinkage.
(2) The cooling and heating system of the mold should ensure that the temperature of each part is consistent.
(3) The pouring system should ensure smoothness and resistance should not be too high. For example, the size of the main channel, diversion channel, and gate should be appropriate, the smoothness should be sufficient, and the transition zone should have a curved transition.
(4) For thin parts, the temperature should be increased to ensure smooth material flow, while for thick walled parts, the mold temperature should be reduced.
(5) The gate should be symmetrically opened, preferably in the thick walled part of the workpiece, and the volume of the cold material well should be increased.
3. Plastic aspect
Crystalline plastics are more prone to shrinkage than non crystalline plastics. Therefore, during processing, it is necessary to increase the amount of material appropriately or add additives to the plastic to accelerate crystallization and reduce shrinkage depressions.
4. Processing aspect
(1) The temperature of the material 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, resulting in insufficient material quantity or density and causing shrinkage due to excessive pressure, speed, and back pressure, and excessive time leading to flash and shrinkage.
(3) When the buffer pad is too large, the injection pressure is consumed, and when it is too small, the amount of material is insufficient.
(4) For parts that do not require precision, after injection and pressure holding, the outer layer is basically condensed and hardened, while the sandwich part is still soft and can be pushed out. Early mold removal and slow cooling in air or hot water can make the shrinkage depression smooth and less conspicuous without affecting use.