What is a DFM review?

A review of a design against the specific process that will actually make it — not against generic good practice. For a moulded or cast part that means wall sections, draft, parting line placement, gate and ejector positions, tolerance chains and finish, each assessed for what it will cost and what it risks. A review that does not name the process it is reviewing against is not a DFM review.

When should DFM happen?

Before tooling is released, and ideally before the design is frozen. The same change costs roughly an hour of engineering time at concept, a CAD revision before tooling, and a steel re-cut plus schedule slip afterwards. The window where changes are nearly free is short and it closes quietly.

What does a DFM review cost?

Quoted per part, and it is almost always the cheapest line in the project. The comparison worth making is not review cost versus zero — it is review cost versus one avoided tooling re-cut, which typically runs into thousands and costs weeks of schedule.

Design for Manufacturing: When Changes Are Free

Q: Why do factories send a DFM checklist instead of real feedback?

Because a genuine review is unpaid work performed before there is a purchase order. A careful review of a die cast housing is several hours of a senior engineer's time. Quoting fast wins the job; quoting carefully loses it to whoever asked no questions. The behaviour is an incentive problem, not an ignorance problem — which is also why the fastest quote is a reliable warning sign.

DFM at concept costs an hour. DFM after tooling costs a re-cut.

It is the same change. Same drawing, same engineer, same twenty minutes of thinking. What differs is only when it happens — and that difference is worth more than almost any other decision in the project.

The short version

The same change costs an hour at concept and a steel re-cut after tooling.
A review that does not name the process it reviews against is not a DFM review.
Factories send checklists because a real review is unpaid work before a PO. It is an incentive, not ignorance.

The same change, priced at four moments

Nothing about the change gets harder. Only the number of things already built on top of it. This is why the highest-leverage hour in a hardware project is spent before anyone cuts steel.

What a real review looks at

A DFM review that does not name the process it is reviewing against is not a DFM review — it is generic advice. The same housing gets completely different feedback depending on whether it is going to be moulded, cast or machined.

Geometry against the process

Wall sections and uniformity — why thickness is the price
Draft, and whether it survives the texture — 0° / 1° / 3° compared
Parting line and where it lands on a visible face
Gate and ejector positions versus cosmetic surfaces
Undercuts, and whether they justify side actions

The commercial consequences

Tolerance chains and which ones drive the price — stack-up →
Cavity count against realistic annual volume
Whether the finish can exist on that alloy — anodizing on castings →
Cast-and-machine versus machine-from-solid at your volume
Which features can be loosened to pay for the two that cannot

Why most factories send a checklist instead

Founders often read a thin DFM report as incompetence. It usually is not. It is an incentive.

A genuine review is unpaid work performed before there is a purchase order. A careful review of a die cast housing is several hours of a senior engineer's time. Quoting fast wins the job. Quoting carefully loses it to whoever asked no questions.

Watch whether the factory asks you anything at all.

A supplier that comes back with questions about your application, your volume and your critical surfaces is showing you how they will behave for the next three years. One that returns a price in an hour is showing you that too.

The uncomfortable version, from the factory side: I am describing my own industry's incentive, and I have no clean solution to it. What I can tell you is that the fastest quote is the one that did not ask any questions — and in casting, that is very often the most expensive outcome.

Read: the factory that refused a $38,000 tool order →

Who does the reviewing

30 tool engineers, 15 project engineers, 15 CNC programmers and 6 product designers, working in UG, Pro/E, CATIA, SolidWorks, AutoCAD and Moldflow — on the same site as the machines that will make the part.

Engineer at a CAD workstation — Design review where the tool will actually be built

Mould open in the machine — Where the design decisions become permanent

CMM verifying a part — And where they get checked — six CMMs to ≤0.0005 mm