Requirements for Shape of Injection Molded Parts

Injection molding refers to the method of injecting heated and melted plastic into a mold, cooling and solidifying it to obtain a molded product. This method is suitable for processing complex shaped products in mass production.

Injection molded parts have the following basic requirements for shape.

1. Appearance of plastic parts: In order to facilitate the removal of plastic parts during injection molding, the appearance should avoid concave and convex surfaces and lateral holes as much as possible.

2. Wall thickness of plastic parts: The wall thickness of plastic parts should not be too small or too large. If the wall thickness is too small, the strength and stiffness of the plastic parts will be insufficient, and it will also bring difficulties to injection molding processing until molding; If the wall thickness is too large, it not only causes material waste, but also easily produces defects such as bubbles and shrinkage holes. At the same time, it will reduce productivity due to the long cooling time during the injection molding process.

3. Demoulding slope: The demoulding slope of the product depends on the shape and wall thickness of the product, as well as the shrinkage rate of the plastic. If the inclination is too small, it will be difficult to demold and cause surface damage or cracking of the plastic parts; However, excessive slope also affects the dimensional accuracy of the product. Only when the height of the plastic part is very small (<5mm) and plastic injection molding with low shrinkage rate is used, can the demolding slope be ignored.

4. Strengthening ribs: In order to ensure the strength and stiffness of the plastic parts throughout the injection molding process without making the wall thickness of the plastic parts too large. Reinforcing ribs can be designed at appropriate positions on the plastic parts. When designing reinforcement bars, attention should be paid to:

·Avoid high concentration of plastic to prevent shrinkage and foaming during injection molding process;

·The end face of the reinforcing rib should not be flush with the support surface of the plastic part, and there should be some clearance.

5. The supporting surface of the plastic part during injection molding processing. When designing the support surface, one surface of the plastic part should not be used as the support surface. A frame or base (three or four points) is often used as the support surface.

6. Rounded corners of plastic parts: The corners on plastic parts should avoid sharp corners as much as possible, and should be transitioned by arcs. The radius of the rounded corners should be greater than 0.5t (t is the wall thickness).

7. Design of holes on plastic parts: The holes on plastic parts include through holes, threaded holes, etc., and the following requirements must be met during design.