Green Vitality Industry Co., Ltd.
Green Vitality Industry Co., Ltd.

We often fail in mold processing due to various factors, such as shrinkage and depression in the products during injection molding. Don't worry, it is generally caused by the following four points. Let's analyze the specific reasons in detail below. When injection molding, if there is shrinkage or depression in the product, the main reasons are as follows.

Machine factors causing shrinkage and depression in injection molding products

  • Shrinkage occurs when the nozzle hole is too large and the molten material flows back, and when the resistance is too great, the material is not enough and shrinkage occurs.

  • Insufficient clamping force can cause flash and shrinkage, so the locking system should be checked for problems.

  • When the plasticizing amount is insufficient, a table with a large plasticizing amount should be selected, and the wear of the screw and barrel should be checked.

The configuration and maintenance of the frame equipment should not be careless. CNC machining centers, precision carving, spark machines, and various types of injection molding machines all strictly control every link from design and opening to injection molding, aiming to provide more professional and perfect services.

Mold factors causing shrinkage and depression in injection molded products

  • The design of the injection molded part should ensure uniform wall thickness and consistent shrinkage.

  • The cooling and heating system of the mold should ensure that the temperature of each part is consistent.

  • The gating system should be smooth, and the resistance should not be too great. The size of the main runner, sub-runner, and gate should be appropriate, the smoothness should be sufficient, and the transition zone should be arc-shaped.

  • The temperature should be increased for thin plates to ensure smooth flow, and the mold temperature should be reduced for thick-walled parts.

  • The gate should be symmetrical, and it should be processed at the thick-walled part of the product as much as possible, and the volume of the cold material well should be increased.

Plastic factors causing shrinkage and depression in injection molded products

Crystalline plastics shrink more severely than non-crystalline plastics. When processing, the amount of material should be appropriately increased, or nucleating agents should be added to the plastic to accelerate crystallization and reduce shrinkage and depression.

Processing factors causing shrinkage and depression in injection molded products

  • When the barrel temperature is too high, the volume changes greatly, especially the front temperature. For plastics with poor fluidity, the temperature should be appropriately increased to ensure smoothness.

  • Injection pressure, speed, back pressure are too low, injection time is too short, and insufficient material or density will cause shrinkage pressure, speed, back pressure are too high, time is too long, and flash will cause shrinkage.

  • When the feeding amount or cushion is too large, the injection pressure is consumed. When it is too small, the material is insufficient.

  • For injection molded parts that do not require precision, after the pressure is maintained, the outer layer condenses and hardens, and the sandwich part is still soft and removable, the parts should be demolded as soon as possible and slowly cooled in the air or hot water so that the shrinkage and depression will be flat and not obvious and will not affect use.

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