Transitioning Prototypes to Injection Molded Plastics

Prototyping is faster than ever. A SolidWorks concept can sit on your desk in 6 hours via SLA printing. But scaling from 1 concept to 10,000 injection-molded plastic enclosures is riddled with traps that routinely delay launches.

If you don’t design for manufacturing (DFM) from Day 1, passing off your STL file to an injection molding house is a mistake.

Here are the critical transitions:

Uniform Wall Thickness

A 3D printer lays down plastic blindly. An injection mold fills with molten plastic under intense pressure. Without uniform wall thickness, thick sections cool slower than thin ones, leading to extreme sink marks on your visible surfaces or internal voids that weaken the part. Your beautiful EV enclosure may look like a melted candle.

Draft Angles

You can print perfectly vertical walls on an FDM machine. You cannot eject perfectly vertical walls from an immovable metal mold. Every functional surface needs at least 1-2 degrees of draft, depending on the surface texture. And if the mold is deeply textured (like a rugged portable charger), you may need upward of 3+ degrees near the parting lines.

Undercuts and Action

3D printing cares nothing about undercuts. But in injection molding, an undercut meant to clip two housing halves together requires expensive “sliders” or lifters built into the mold base. We can often eliminate sliders completely by adjusting parting lines through “pass-through” geometry or clever snap-fit modifications.

Conclusion

Our experience launching automated parking and charging systems and IP/IK-rated portable chargers has reinforced the value of treating the prototype differently than the final product. Design the prototype to validate the concept. Re-design the prototype to validate the manufacturing process.