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What resistances need to be overcome during the mold opening process?

Update:05-08-2022
Summary:The first is to overcome the direct mold opening force. When the mold is opened,...
The first is to overcome the direct mold opening force. When the mold is opened, the plastic will have a certain adhesion force parallel to the mold opening direction. This is because when the mold is cooled, the plastic parts are not cooled enough, and the elastic expansion of the cavity is not fully recovered. The size of this adhesive force is related to the properties of the plastic, the surface quality of the mold, and the demolding slope.​​
In addition, it is also necessary to overcome the indirect mold opening resistance, that is, to overcome the pulling resistance during the core pulling process of the motorized side during mold opening.​​
It is also necessary to overcome the frictional resistance caused by the movement of the mold moving template and the movable template.​​
Finally, it is necessary to overcome the participating pressure of the cavity. When the mold is opened, the pressure of the cavity may not be equal to the atmospheric pressure, and the pressure in the cavity is not equal to the external pressure.​​
In order to solve the above two problems, it is necessary to properly improve the design of the mold. Select the appropriate mold material to improve the thermal strength and wear resistance of the mold. Reasonable mold structure design and manufacture, appropriately increase the thickness of the push plate and the middle backing plate, improve the rigidity of the mold, and reduce the elastic deformation of the mold.​​
Improve the manufacturing and matching accuracy of the core pulling mechanism and motion system, reduce the surface roughness of the cavity, core and punch components, and reduce the demoulding force. Due to the requirement of higher design and matching accuracy after the product is thinned, an interlocking device is usually installed to prevent the relative displacement of the mold core and the mold cavity.​​
Reasonable design of the gating system, the design of the runner should make the plastic parts transition from the thicker area to the thinner area during the injection process. There also needs to be enough exhaust ports. In the injection process, the internal stress of automotive plastic parts should be minimized, the injection speed should be increased, and the cooling rate should be reduced. It is therefore necessary to increase the melt temperature and the die temperature for relaxation of the orientation. It is also necessary to select a reasonable injection pressure, dwell time and cooling rate.
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