There is no certain criterion for size of demolding angle, most of which are determined based on experience and depth of product. In addition, molding method, wall thickness and plastic selection are also considered.

 

Generally speaking, for any side of molded product, a certain amount of demolding slope is required so that product can be removed from mold smoothly. Size of demolding angle is generally 0.5°～1°.
Pay attention to following points when selecting draft angle:
Surface of plastic part is smooth, dimensional accuracy is required, and shrinkage rate is small, so a smaller demolding angle, such as 0.5°, should be used.
For higher and larger sizes, take smaller draft angle according to actual calculations.
If shrinkage rate of plastic parts is large, a larger slope value should be selected.
When wall thickness of plastic part is thicker, molding shrinkage will increase, and a larger value should be adopted for demolding angle.
Drafting angle of transparent parts should be increased to avoid scratches. Under normal circumstances, demolding slope of PS material should be no less than 2.5°～3°, demolding slope of ABS and PC material should be no less than 1.5°～2°.
Side wall of plastic part with skin texture, sandblasting and other appearance treatments should take a demoulding slope of 2°～5° according to specific situation, depending on specific skin texture depth. The deeper dermatoglyph, the greater draft angle should be.
When structure is designed to be inserted in pairs, inclination of insertion surface is generally 1°～3°.
Take direction of slope. Generally, inner hole is based on small end and conforms to pattern. Slope is obtained from expanding direction. Shape is based on large end, which conforms to pattern.
Under normal circumstances, draft angle is not included in tolerance range of plastic part.
Demolding slope of shell surface is greater than or equal to 3°. Except for shell surface, demolding slope of the other features of shell is 1° as standard demolding slope. In particular, it can also be selected according to following principles: demolding slope of ribs less than 3mm high is 0.5°, 3～5mm is 1°, and the rest is 1.5°; demolding slope of cavity less than 3mm high is 0.5°, 3～5mm is 1°, and the rest is 1.5°.

It is very important to determine wall thickness of plastic parts reasonably. Wall thickness of a plastic part is first determined by use requirements of plastic part: including strength of part, quality cost, electrical performance, dimensional stability, and assembly requirements. Generally, wall thickness has an empirical value, which can be determined by referring to similar.
Points to note are as follows:
Wall thickness of plastic parts should be as uniform as possible, avoid too thin, too thick and sudden wall thickness changes. If wall thickness changes are required for plastic parts, a gradual change or arc transition should be adopted, otherwise it will deform plastic parts due to uneven shrinkage, affect strength of plastic parts, affect fluidity during injection molding and other molding process problems. Thickness difference should be controlled within 25% of basic wall thickness as far as possible. Minimum wall thickness of the entire part should not be less than 0.4mm, back of part should not be a Grade A appearance surface, and required area should not be greater than 100mm².
Wall thickness of plastic parts is generally in the range of 1 to 5 mm. The most commonly used value is 2 to 3 mm.
Try not to design stiffeners and screw columns too thick. Generally, it is recommended to take half of wall thickness of body to be safer, otherwise it is easy to cause appearance problems such as miniatures.
Try not to design parts as separate flat plates. Size is small, otherwise parts will be uneven due to deformation.
Minimum wall thickness of plastic products and recommended value of common wall thickness are shown in following table: