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The mould design determines the warpage tendency of the part

Update:21 Sep 2018
Summary:

Fundamentally speaking, the mould design determines the […]

Fundamentally speaking, the mould design determines the warpage tendency of the part. It is very difficult to suppress this tendency by changing the moulding conditions. Finally, the problem must be solved from mould design and improvement. This phenomenon is mainly caused by the following aspects:
1. mould aspect:

(1) The thickness and quality of the parts should be uniform.

(2) The design of the cooling system is to make the temperature of each part of the mould cavity uniform, and the pouring system should make the flow symmetry avoid the warpage caused by the different flow direction and shrinkage rate, and appropriately thicken the shunting channel and the mainstream which are difficult to form part. Road, try to eliminate the density difference, pressure difference, temperature difference in the cavity.

(3) The transition zone and corner of the workpiece should be sufficiently rounded and have good demoulding properties, such as increasing the demoulding margin and improving the polishing of the die face. The ejector system should be balanced.

(4) The exhaust should be good.

(5) Increase the wall thickness of the part or increase the direction of warpage resistance, and strengthen the rib to enhance the anti-warping ability of the part.

(6) The strength of the material used in the mould is insufficient.

2. Plastics:

The crystal type has more chance of warping deformation than the amorphous plastic, and the crystal type plastic can be used to correct the warpage deformation by using a crystallization process in which the crystallinity decreases as the cooling rate increases and the shrinkage rate becomes smaller.

3. Processing:

(1) The injection pressure is too high, the holding time is too long, and the melt temperature is too low. The speed is too fast, which causes the internal stress to increase and warpage.

(2) The mould temperature is too high, and the cooling time is too short, so that the parts at the time of demoulding are overheated and the ejection deformation occurs.

(3) Reducing the screw speed and the back pressure reduction density while maintaining the minimum charge amount to limit the generation of internal stress.

(4) If necessary, the mould can be soft-shaped or demoulded after the mould is easily warped and deformed.

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