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There is no specific standard for the draft angle, and most of them are determined by experience. Usually, any sidewall of the molded product has a draft angle so that the product can be taken out of the mold. However, in the actual drawing, in order to improve efficiency, the designer only makes the demolding inclination of the appearance surface and the structural surface that affects the assembly, and the other can be solved by the mold supplier. For example, the reinforcement ribs and shallow through holes cannot need to be made with an inclination. Its size depends on the performance of the plastic, the shrinkage, and geometry of the parts, etc. The general parts are between 0.5° and 1.5°. For structural parts of engineering plastics, generally, the draft angle should be reduced as much as possible under the premise of ensuring smooth demolding.
As the part cools, it will shrink toward the core. The draft angle helps the part avoid being affected by the core. Even if you have the idea of canceling draft angle, you must not cancel draft angle. If the draft angle is reduced, the locking force of the part will increase, so will the force required to remove the part from the mold. The molding time also has to be extended, because in this way, the parts can be fully cooled to ensure that they can be removed from the mold. Because the parts must be cooled to enough rigidity, they can be ejected without deformation. The cooling time can account for 50% - 80% of the whole molding time. On the contrary, the larger the draft angle, the smaller the force needed to remove the part from the mold, and the shorter the time for the part to be removed from the mold.
1. Choose a smaller draft angle: First, the plastic parts require high accuracy; Second, the higher the parts and the deeper the holes, or the higher and larger size parts; Third, the lower the plastic hardness And the smaller the shrinkage rate; the fourth is the thinner the wall thickness;
2. Choose a larger draft angle: First, the shrinkage rate is larger; Second, the thicker the wall thickness; Third, the transparent part (to avoid the influence of scratches on transparency);
3. Influence of materials: Except PE and PP can be demolded forcibly, other plastics cannot be demolded forcibly;
4. Value of transparent parts: generally, above 3°, the draft angle of ABS and PC materials is at least greater than 2°;
5. For the direction of the slope, the inner hole is generally based on the small end, as in the angle A in the above figure, the slope is obtained from the expansion direction, and the shape is based on the large end, as in the angle B in the above picture, the slope is obtained from the reduction direction .
6. The draft angle of the shell surface is greater than or equal to 3°, and the draft angle of the insertion surface is generally 1°~3°;
7. Compared with soft plastics, the draft angle of hard plastics is larger;
8. The influence of etch: generally, it is about 5 ° larger than the gradient of etch. the draft angle of 3 ° ~ 5 ° shall be added to the side wall of plastic parts with leather grain, sand blasting and other appearance treatment, depending on the specific depth of undercut, the deeper the undercut depth is, the larger the draft angle is. The recommended value is 1 ° + H / 0.0254 ° (H is the undercut depth).
