Injection Warpage Cause Analysis

Injection products deformation, bending, twisting phenomenon occurs mainly due to the plastic molding shrinkage flow direction than in the vertical direction is large, so that different parts of each to shrinkage and warping, and because Injection Molding unavoidable in the system the inner member has a larger residual stress caused by warping, distortion performance of these are caused by high stress orientation. So fundamentally, plastic materials mold design determines the tendency to warp parts of, to come to suppress this tendency is very difficult by changing the molding conditions, a final settlement must be designed and modified to proceed from the mold.

 This phenomenon is mainly caused by the following aspects:

1. Molds plastic materials products:

(1) The thickness of the workpiece, the quality should be uniform.

(2) The cooling system is designed to make the various parts of the mold cavity temperature uniformity, symmetry gating system to make the stream flow direction to avoid shrinkage caused by different warp, appropriate bold difficult forming part of the shunt, the mainstream road, try to eliminate the cavity density difference, pressure difference, temperature difference.

(3) the part of the transition zone thickness and angle sufficiently smooth, a good release properties, such as increased stripping redundancy, improve mold surface polishing, the top of the system to maintain balance.

(4) to the exhaust well.

(5) increase the part thickness or increase anti-warp direction, the ribs to enhance the ability of anti-warp articles.

(6) Mold materials used less rigid.

2. Plastic: the warpage opportunity crystalline appeared more than a non-crystalline plastics, combined with crystalline plastics can take advantage of the cooling rate increases with the degree of crystallinity and reduced shrinkage smaller crystallization process to correct warpage.

 3. Plastics processing:

(1) injection pressure is too high, too long dwell time, melt processing temperature is too low too fast can cause increased stress occurs warpage.

(2) mold temperature is too high, the cooling time is too short, so that parts overheat when releasing the emergence of the top of the deformation.

(3) reduction in screw speed to maintain a minimum backpressure charge quantity under reduced density and to limit the generation of internal stress.

Treatment for back-meter (4) can easily mold warpage parts soft amorphous or stripping if necessary

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