Design for Molding and Machining When Your Team Is Full

Here is the usual order. The part is designed, then someone who knows molding or machining looks it over and marks it up. That works, but it is the expensive order. By the time a part reaches review, its walls, ribs and corners are tied to everything around it, and every change ripples outward.

Design for molding and machining means shaping a part around how it will be made while it is still being designed. When your own team is full, the useful outside help is someone who works that way from the start, close enough to the machines to know what a feature will cost before it is drawn.

Between 2020 and 2025 the shop made rigs and fixtures for university research, molded and machined parts and fixtures for electronics manufacturers, and parts, mounts and test pieces for medical and scientific research instruments.

Three things an early review catches

Ribs and sink marks. A rib stiffens a molded part without thickening it. The common guideline is a rib about half to two-thirds as thick as the wall it stands on. Make it thicker and the plastic where rib meets wall cools last and pulls inward, leaving a sink mark on the face opposite. On a cosmetic face, that is a rejected part.

Inside corners. A milling cutter is round, so an inside corner is only as sharp as the cutter's radius. Square inside corners and deep narrow slots can turn a machining job into an EDM job, with an electrode to make and burn in. If the corner has to be sharp, that is fine, and what sinker EDM is for covers it. If it is only sharp because nobody gave it a radius in CAD, a radius slightly larger than the cutter saves real work.

Draft. A machined prototype can have perfectly straight walls. A molded part can't, because it has to slide out of the mold. Walls in the direction the mold opens usually need one to two degrees of taper, and more under a texture. A part moving from machined prototypes to molded production almost always needs this work, and it is easier to add before the mating parts are designed around straight walls.

What the work covers

• 3D modelling and production drawings
• Design for molding: draft, wall thickness, ribs, gate location, undercuts
• Design for machining: features a machinist can hold at a sensible cost
• Fixtures, jigs and test rigs
• GD&T and tolerance stack-up work
• Embedded electronics: device integration, controllers and firmware, with PCB and circuit design through partner engineers

Our design work happens beside the machines. A feature that can't be made, or can only be made at great cost, tends to get caught by the people who would have to make it.

Working with your files

If you have your own design environment, we can work inside it, so the files never sit on our systems. If you don't, the work is done under a signed NDA. Who owns what at the end of the job is set out in who owns the tool and the production CAD.

When to keep it in-house

If your team has the time, and someone who has designed parts for molding before, keep the work in-house. Outside design adds a handoff, and a handoff can lose something. The case for outside help is narrower than it sounds: the work is waiting, or the skill isn't on staff.

The cheapest design review is the one that happens before the part is finished.

If a part is about to move from machined prototypes to a mold, that is the moment to have it looked at, before the mold design starts.

Related services: Product realization and prototyping Full products Shop capabilities