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Draft angles of plastic injection Mold design
Jan 29, 2018


          Draft angle design is an important factor when designing plastic parts. Because of shrinkage of plastic material, injection molded parts have a tendency to shrink onto a core. This creates higher contact pressure on the core surface and increases friction between the core and the part, thus making ejection of the part from the mold difficult. Hence, draft angles should be designed properly to assist in part ejection. This also reduces cycle time and improves productivity. Draft angles should be used on interior and exterior walls of the part along the pulling direction.



Profile view of a drafted cylinder, showing the draft dimension

The minimum allowable draft angle is harder to quantify. Plastic material suppliers and molders are the authority on what is the lowest acceptable draft. In most instances, 1degree per side will be sufficient, but between 2 degree and 5 degree per side would be preferable. If the design is not compatible with 1 degree, then allow for 0.5 degree on each side. Even a small draft angle, such as 0.25 degree, is preferable to none at all.

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