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Injection molded parts with rounded corners

by:CSSSLD     2021-01-23
Plastic gear is mainly used for the transmission system of the precision and intensity is not high, its main characteristic is light weight, small noise, used for plastic gear with nylon, polycarbonate, pom, polysulfone, etc. In order to adapt the plastic gear processing injection molding process, gear, wheel disk and the outline of wheel hub should have certain thickness. In order to reduce the Angle of stress concentration and residual stress of the gear during forming, the sudden change of the section, should avoid as far as possible should as far as possible more rounded corners and transition arc radius.

plastic pieces of the common holes are through holes, blind holes, special-shaped hole and threaded hole, etc. These holes should be set in the place where is not easy to weaken the strength of plastic mechanical parts, between holes and hole, hole should have enough distance between the side wall. When two hole diameter is not the same, according to the small aperture value. Fixed with hole and other plastic pieces of the stress around the hole can be designed to strengthen a convex or concave. Blind hole can only with one end fixed core forming, therefore the depth should be shallow in the hole.

thread direct molding methods are: using thread core or ring type screw plastic pieces, after forming mould clamping method is used for the external thread forming, the forming of high efficiency, but the precision is poor, has the flash, undemanding RuanSu molding internal thread, forced demoulding, this thread is shallow, cross-section oval. On the same core, when we have two periods before and after the thread should make two pieces of thread of the screw to the same, equal pitch, otherwise you won't make the plastic parts from spin off the core. When pitch range or rotate to not at the same time, to adopt two cores together, forming after turning down respectively.

molding or injection molding, the hole depth shall not exceed the aperture of 4 times. Compression molding, deep hole should be shallow, in parallel to the direction of the down hole diameter is generally not more than 2. Five times, perpendicular to the direction of the hole diameter is generally not more than 2 times. A diameter of less than 1. Holes or depth of 5 mm too big hole machining again after the best molding method. If can when molding pressure out of the hole position shallow hole, is after processing will bring great convenience.

when bore plastic parts for the alien, often adopt the method of split to molding, so that you can avoid side core-pulling. Plastic pieces of the thread can directly use molding, can also by machining molding after forming. For often force larger thread, and installation should use metal thread insert. Plastic pieces of the thread should choose larger screw tooth size, diameter is lesser also unfavorable choose fine thread, otherwise it will affect the intensity of use.

in order to avoid stress concentration, improve the strength of the plastic parts, improve the melt flow and facilitate stripping, both inside and outside surface of joint in the injection molding processing, and transition arc should be adopted. In addition, the circular arc also become beautiful, plastic and mold cavity during quenching or use also is not due to stress concentration and cracking. For some parts of the plastic parts, the molding must be in the parting surface and core and cavity with position, the inconvenience made rounded corners, and use sharp corners.

the diameter of the plastic pieces of the thread shoulds not be too small, screw diameter should not less than 4 mm, inside diameter should not less than 2 mm, precision is less than level 3. Thread pitch did not consider if mold shrinkage value, then the plastic thread with metallic thread with the length is not too long, generally no more than 1 the diameter of the thread. 5 - 2 times, otherwise may cause additional stress due to the interference, the lower the strength of threaded connection. In order to prevent the thread in the split or deformation, should make the thread in the outer ring and the most circle with the steps.

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