Injection molding has been the dominate process for producing complex, tight tolerance plastic parts. The plastic resin experiences aggressive conditions during the process, which is driven by the need to economically manufacture these components while maintaining the desired tolerances and surface aesthetics. From the shear deformation the polymer molecules experience as they are being melted and injected into the mold, to the rapid cooling of the resin as it comes into contact with the cold mold wall, the orientation and extension of the polymer chains change significantly from its original state. Additionally, the polymer chains cannot always get back into the state they want to be in, which leaves those areas of the part in a non-ideal state that develops stress from molding. This stress is often referred to as residual stress, or molded-in stress.
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