Prevent Deformation of Injection Molding

Influence of plasticizing stage on product warping deformation:
In the plasticizing stage, the glass particles are transformed into a viscous fluid state to provide the melt required for filling the mold. In this process, the temperature difference of the polymer in the axial direction and the radial direction (relative to the screw) will cause stress in the plastic. In addition, parameters such as injection pressure and speed of the injection machine will greatly affect the degree of molecular orientation during filling, which will cause warping and deformation.

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The influence of the mold filling and cooling stages on the warping deformation of the product
Under the action of injection pressure, the molten plastic is filled into the mold cavity, cooled and solidified in the cavity, which is the key link of injection molding. In this process, temperature, pressure, and speed are coupled with each other, which has a great impact on the quality and production efficiency of plastic parts. Higher pressures and flow velocities generate high shear rates, which cause differences in the orientation of molecules parallel to and perpendicular to the direction of flow, creating a “freezing effect”. The “freezing effect” will generate freezing stress and form the internal stress of the plastic part. The influence of temperature on warping deformation is reflected in the following aspects.
(1) The temperature difference between the upper and lower surfaces of plastic parts will cause thermal stress and thermal deformation;
(2) The temperature difference between different areas of the plastic part will cause uneven shrinkage between different areas;
(3) Different temperature states will affect the shrinkage rate of plastic parts.2. The effect of the demoulding stage on the warping deformation of the product

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Plastic parts are mostly glassy polymers during the process of leaving the cavity and cooling to room temperature. Unbalanced demoulding force, unstable movement of the ejection mechanism or improper ejection area of the demoulding can easily deform the product. At the same time, the stress frozen in the plastic part during the filling and cooling stages will be released in the form of deformation due to the loss of external constraints, resulting in warping deformation.Influence of Shrinkage of Injection Molded Products on Warping Deformation
The direct cause of warpage of injection molded products is the uneven shrinkage of plastic parts. If the impact of shrinkage during the filling process is not considered in the mold design stage, the geometric shape of the product will differ greatly from the design requirements, and severe deformation will cause the product to be scrapped. In addition to the deformation caused by the filling stage, the temperature difference between the upper and lower walls of the mold will also cause the difference in shrinkage between the upper and lower surfaces of the plastic part, resulting in warping deformation.
For warpage analysis, shrinkage itself is not important, but the difference in shrinkage is important. In the injection molding process, the shrinkage rate of the plastic in the flow direction is larger than the shrinkage rate in the vertical direction due to the arrangement of polymer molecules along the flow direction during the injection molding stage of the molten plastic, resulting in warping deformation of the injection molded part. Generally, uniform shrinkage only causes changes in the volume of plastic parts, and only uneven shrinkage can cause warping deformation. The difference between the shrinkage rate of crystalline plastics in the flow direction and the vertical direction is larger than that of amorphous plastics, and its shrinkage rate is also larger than that of amorphous plastics. The superposition of the large shrinkage rate of crystalline plastics and the anisotropy of shrinkage leads to a much greater tendency of warping deformation of crystalline plastics than amorphous plastics.

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