Precautions for the design of injection molding parts demolding angle and product wall thickness

1. Demoulding angle of plastic parts:

There is no certain criterion for the size of the ejection angle, most of which are determined based on experience and the depth of the product. In addition, the molding method, wall thickness and plastic selection are also considered. Generally speaking, for any side of the molded product, a certain amount of demolding slope is required so that the product can be removed from the mold smoothly. The size of the demolding angle is generally 0.5°～1°.

Pay attention to the following points when choosing the draft angle:

(1) The surface of the plastic part is smooth, if the dimensional accuracy is high, and the shrinkage rate is small, a smaller draft angle, such as 0.5°, should be used.

(2) For higher and larger sizes, take the smaller draft angle according to actual calculations.

(3) If the shrinkage rate of plastic parts is large, a larger slope value should be selected.

(4) When the wall thickness of the plastic part is thicker, the molding shrinkage will increase, and the demolding slope should adopt a larger value.

(5) The drafting angle of transparent parts should be increased to avoid scratches. Under normal circumstances, the demolding slope of PS material should be no less than 2.5°～3°, and the demolding slope of ABS and PC material should be no less than 1.5°～2°.

(6) The side wall of plastic parts with skin texture, sandblasting and other appearance treatments should take a demoulding slope of 2°～5° according to the specific situation, depending on the specific skin texture depth. The deeper the dermatoglyph, the greater the draft angle.

(7) When the structure is designed to be inserted in pairs, the inclination of the insertion surface is generally 1°～3°.

(8) Take the direction of the slope. Generally, the inner hole is based on the small end and conforms to the drawing. The slope is obtained from the expansion direction, and the shape is based on the large end, which conforms to the drawing. The slope is taken from the shrinking direction.

(9) Under normal circumstances, the draft angle is not included in the tolerance range of plastic parts.

(10) The demolding slope of the shell surface is greater than or equal to 3°. Except for the shell surface, the demolding slope of the other features of the shell is 1° as the standard demolding slope. In particular, it can also be selected according to the following principles: the demolding slope of the ribs less than 3mm high is 0.5°, 3～5mm is 1°, and the rest is 1.5°; the demolding slope of the cavity less than 3mm high The degree is 0.5°, 3～5mm is 1°, and the rest is 1.5°.

2. Plastic part wall thickness determination and wall thickness treatment

It is very important to determine the wall thickness of plastic parts reasonably. The wall thickness of a plastic part is first determined by the use requirements of the plastic part: including the strength of the part, quality cost, electrical performance, dimensional stability, and assembly requirements. Generally, the wall thickness has an empirical value, which can be determined by referring to similar.

The points of attention are as follows:

(1) The wall thickness of the plastic parts should be as uniform as possible, avoid too thin, too thick and sudden wall thickness changes. If the wall thickness changes are required for the plastic parts, a gradual change or arc transition should be adopted, otherwise the plastic parts will be caused by uneven shrinkage. Molding process issues such as deformation, affecting the strength of plastic parts, and affecting fluidity during injection molding. The thickness difference should be controlled within 25% of the basic wall thickness as much as possible. The minimum wall thickness of the entire part should not be less than 0.4mm, and the back of the part should not be a Grade A appearance surface, and the required area should not be greater than 100mm².

(2) The 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.

(3) Try not to design the stiffeners and screw columns to be too thick. Generally, it is recommended to use half of the wall thickness of the body to be safer, otherwise it will easily cause appearance problems such as miniatures.

(4) Try not to design the parts as separate flat plates. The size is small, otherwise the parts will be uneven due to deformation.