DfM: Injection Molding

Criterion E and F of your IA requires you modify your design so that it can be commercially manufactured.

These modifications should be based on the Design for Manufacturing approaches.

Your work in Criterion E should show examples of how your design is modified to optimize the commercial manufacturing process you have chosen.

If you have chosen injection molding as one of the commercial processes in Criterion E1 of your IA, you will need to show how your design would be modified to accommodate this process. Injection molding is a complex process with many factors to consider; However, there are several key factors you should consider in your redesign for commercial manufacture.

3D Hubs provides a very detailed overview of the steps you need to take. We've summarized some of those steps here.

Resources

Add draft angles

A draft is an angle added to a a vertical wall to make it more easily release from the mold. Basically, by adding 2-5° to the angle, the injection molded piece will release more easily.

Minimize or eliminate undercuts

A simple two-part mold has no undercuts. More complex shapes will have undercuts and will need multi-part molds to manufacture, or they will need to be manufactured in several pieces and then re-assembled. Regardless, this will increase time and costs.

Making simple changes to your design to eliminate or reduce undercuts will make it more commercially viable.

This video provides a detailed description of undercuts and how to deal with them in the Design process

Round all edges

injection molding doesn't like sharp corners. Filleting the inside and outside edges will ensure a stronger design and help it more easily release from the mold. The edges should be a uniform thickness.

Uniform wall thickness

Use a constant wall thickness throughout the part. This will ensure more uniform cooling.

Use bosses for points of assembly

This will allow for assembly using screws or bolts.

Use snap fit joints

Snap fit joints allow for quick assembly. Two common types are shown here, but there are many types of snap fit joints; The ideal type should be chosen to match the design needs (re-usable, locking, design for disassembly, design for repair, etc)

Additional resources for snap-fit joints:

Types and applications (3Dsystems)
Snap fit joints for plastics (Youtube)