Injection Molding: Drafting and Wall Thickness

Draft and wall thickness are two of the most critical and overlooked fundamentals when manufacturing and designing for injection molding.

Draft

Draft is a design feature that involves tapering the side walls of a part to allow it to be released from the mold when the mold opens. Drafting walls in the direction of the mold helps to prevent sticking and dragging as the part ejects.The recommended draft angle for parts is 0.5 to 1 full degree of draft on all surfaces. If your part includes textured walls, you will need to increase the amount of draft to ensure clean ejection. We suggest that 1.5 – 2 degrees of draft be used per 0.001″ of texture depth. This rule is for sidewalls of the tool that will shrink away from the cavity. Areas in the part that will shrink toward the core of the tool will require more draft. The amount of draft needed for these walls will vary based on part design.

Wall Thickness

Wall thickness is another critical component of design that can affect the success of your injection molded part. If the walls of your part are too thin, you may have cracking or warping of your part. The type of plastic resin that you choose will help determine the wall thickness needed. Each resin has a unique blend of properties that include varying amounts of plasticizers, stabilizers, fillers, and other additives. These properties determine each resin’s flow and strength values. Refer to the chart to the to see the recommended wall thicknesses of some common resins.