Draft angle is critical in plastic injected workpiece design since this directly affects how easily a object can be ejected from a mold but without be damaged as shown in the Fig 1. The draft angle is determined by several factors such as plastic material selected, geometry of workpiece and ejection system. The draft andgle changes the size of the plastic paroducts, which are not included in the products of tolerance range. Draft angle design principles are as follows.
On the premise of guaranteeing the products dimension tolerances, the draft angle can choose larger values. For large shrinkage rate of materials, the draft angle can choose larger values. For wall thickness size of products, the draft angle can choose larger values. For large height and size of products, the draft angle should choose small values; For small height of products, we can not set draft angle. For the high precision products, the draft angle should be small. When you open the mold, products are usually on the core, because the ejection mechanism in dynamic mode. When the products stay within the cavity, the draft angle value of the core should be greater than the cavity.
For smooth and textured surface products, draft angle is different, qualitatively describe the draft angle values of the product are as follows:
Products outside surface are smooth, small-diameter plastic part draft angle ≤ 1 °, large-diameter plastic part draft angle ≤ 3 °. Products outside surface are textured and Ra<6.3μm, the draft angle ≤ 3 °; When Ra≥6.3μm，the draft angle ≤ 4 °
When determining plastic draft angle, we need to ensure assembly of plastic parts and appearance requirements. Commonly used plastic parts of the draft angle as shown in the Tab 1.
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