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The requirements for geometric shapes of injection molding process Jan 25, 2018

Injection molding is the method of injecting plastic injection into the mold, which is cooled and solidified. Injection molding is suitable for batch production and processing of complex products.

The geometrical shape of plastic parts mainly has the following basic requirements.

1. Shape of the plastic part: it is easy to take out the plastic parts in order to open the mold, and the shape should be avoided with concave convex surface and side hole.

2. The wall thickness of the plastic parts: the wall thickness of the plastic parts should not be too small or too large. If the wall thickness is too small, the strength and rigidity of the plastic parts will not be enough, which will bring difficulties to the molding. If the wall thickness is too large, it will not only cause the waste of materials, but also easily produce bubbles, shrinkage holes and other defects. Meanwhile, the cooling time will be too long to reduce the productivity.

3. Deformability: the slant of the product depends on the shape and thickness of the product and the shrinkage of the plastic. If the slant is too small, it will cause the surface damage or rupture of the plastic parts. But it also affects the size accuracy of the products. It is only when the plastic parts are very small (< 5mm) and the plastic forming with small shrinkage rate can be used to avoid the dissection slope.

4. Reinforcement: in order to ensure the strength and rigidity of the plastic parts, the wall thickness of the plastic parts shall not be too large. The reinforcement can be designed in the proper position of the plastic parts. When designing reinforcing bars, avoid the high concentration of plastic, so as to avoid shrinkage and blister, and the end face of reinforcing rib should not be flush with the supporting surface of plastic parts.

5. Supporting surface of plastic parts. The design support surface should not be supported by a surface of the plastic part, usually with a frame or base foot (three or four points) as the supporting surface.

6. Rounded corners of plastic parts: avoid sharp corners as far as possible from the corner of the plastic parts, but should be excessively arc, and the radius should be greater than 0.5t (t is wall thickness).

7. Design of the holes in the plastic parts: holes in the plastic parts, holes, holes and so on. The design should meet the requirements. The shape of the hole should be simple, easy to form and simplify the mold structure. The relationship between the hole spacing, hole margin and pore diameter of the thermosetting plastic hole should be in line with the holes of the fastening holes and other forces on the plastic parts.