Designing plastic parts for injection molding requires a deep understanding of thermodynamics and material flow. If a part is not designed with the molding process in mind, it will suffer from cosmetic and structural defects such as sink marks, voids, and warppage.
The first rule of injection molding is maintaining constant wall thickness. When plastic cools, it shrinks. Thicker sections cool more slowly than thin ones, creating internal stresses that pull the outer surface inward, forming sink marks. Keep walls uniform and use ribs to add structural stiffness.
"Uniform wall thickness is the absolute cornerstone of high-quality plastic part design."
Incorporating Draft Angles
Without draft angles, molded parts cannot be ejected from the steel tool core without scratching or tearing the plastic. A minimum draft of 1 to 2 degrees is standard for all vertical faces, with additional draft needed for textured surfaces.
Preventing Warpage
Warpage is caused by non-uniform shrinkage during cooling. Designing symmetric features and placing gates at optimal flow locations helps distribute cooling rates evenly, ensuring plastic casings assemble tightly and look premium.