How to Design the Draft Angle of Plastic Products?
Ways to design the draft angle of plastic products
In both the inner and outer surfaces of plastic components, a sufficient draft angle should be designed along the demolding direction to facilitate demolding. Otherwise, it may be difficult to demold or result in damaging or scratching the plastic parts.
Commonly used draft angles are 1 to 1.5 degrees, but they can be as small as 0.5 degrees. When there are special requirements, the draft angles can be 5 degrees for external surfaces and 10 to 20 degrees for internal surfaces. When the height of the component is not significant, it may be allowed to have no draft angle.
For protrusions or ribs on the component, a one-sided draft angle of 4 to 5 degrees is recommended.
When the component has holes along the demolding direction or a rectangular grid pattern that increases demolding resistance, a draft angle of 4 to 5 degrees is suitable.
If the side walls have a leather texture pattern, a draft angle of 4 to 6 degrees should be used.
Generally, if the draft angle doesn’t hinder the use of the product, a larger draft angle is allowed.
Sometimes, to ensure that the component remains on the male or female mold during demolding, the draft angle on one side may intentionally be reduced, or the draft angle on the opposite side increased.
For dimensions with tolerance requirements, the draft angle values can fall within the tolerance range of the component or outside of it.
When producing components with greater depth, it is necessary to have sufficient draft angles on both male and female molds. It’s also advisable to make the draft angle on the male mold larger than that on the female mold so that the lower part of the component’s side walls is thicker than the upper part.
During mold closure, the wedge effect ensures the density of the upper part of the component is maintained.
Draft angle selection should follow the following principles:
(1) For plastics with high shrinkage rates and thicker walls, larger draft angles should be chosen. While for the opposite case, smaller draft angles are preferable.
(2) When the plastic component has a complex structure and higher demolding resistance, larger draft angles should be used.
(3) When the height of the plastic component is not significant (usually less than 2mm), draft angles can be omitted. However, for long or deep core or cavity components, smaller draft angles should be considered.
In general, to facilitate demolding, draft angles can be chosen on the larger side while still meeting the component’s use and dimensional tolerance requirements.
(4) Typically, the draft angle on the outer surface of the component can be smaller than that on the inner surface.
And sometimes, the draft angles on both the inner and outer surfaces can be determined based on the component’s intended location (whether in the female or male mold).
(5) Thermosetting plastics generally have smaller shrinkage rates compared to thermoplastic plastics, so draft angles should also be chosen on the smaller side.
