Warpage occurs when there are variations of internal stresses in the material caused by a variation in shrinkage.
Warped parts may not be functional or visually acceptable.
Non-uniform cooling. Temperature differences from one side of the mold to the other can lead to layers freezing and shrinking at different times and generating internal stresses.
Inconsistent shrinkage. Resulting from:
Material variations such as property variations, varying moisture content, inconsistent melt and pigmentation;
Process conditions variations such as inconsistent packing and varying mold and melt temperatures;
Machine variations such as a damaged check ring and unstable controller.
Solving one problem can often introduce other problems to the injection molding process. Each option hence requires consideration of all relevant aspects of the mold design specification.