Mastars is dedicated to the extrusion, injection molding, and machining of various plastic products. We specialize in PEEK, PI, PPS, PEI, and provide special engineering plastic finished parts and semi-finished profiles for different industries.|rapid cnc machining|metal prototype maker

Plastic and metal thermal expansion coefficient difference of 5 to 10 times, and therefore with metal insert plastic products in the cooling, the formation of the two shrinkage degree is different, because the plastic shrinkage is relatively large and clinging to the metal insert, in the insert around the inner layer of plastic compressive stress, while the outer layer of tensile stress, resulting in stress concentration phenomenon.

In the specific set juice insert, the following points should be noted to help reduce or eliminate internal stress.

   a. As far as possible, choose plastic parts as inserts.

   b. As far as possible to choose and plastic coefficient of thermal expansion of the small difference between the metal material as an insert material, such as aluminum, aluminum alloy and copper, etc..

   c. In the metal insert coated with a layer of rubber or polyurethane elastic buffer layer, and ensure that the coating layer does not melt when forming, can reduce the difference between the two shrinkage.

   d. Degreasing the surface of the metal insert can prevent grease from accelerating the stress cracking of the product.

   e. Appropriate preheating treatment for metal insert.

   f. The thickness of the plastic around the metal insert should be sufficient. For example, the outer diameter of the insert is D, the plastic thickness around the insert is h, then the aluminum insert plastic thickness h ≥ 0.8 D; for copper inserts, plastic thickness h ≥ 0.9 D.

   g. Metal inserts should be designed into a rounded shape, preferably with a delicate knurling pattern.

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