How do I ask a supplier for DFM feedback before release?
Send a STEP file and a PDF drawing marked "for DFM review, not for production", with the material, finish and expected volume, plus five or six specific questions about the features you're unsure of. Ask for answers marked against the drawing by a set date, and release only after the agreed changes are in.
Why "any DFM comments?" gets nothing back
A supplier who receives a model with "let us know if you have any DFM comments" has no reason to spend an hour on it. They quote what they were sent, add a note about the one feature they can't make, and move on.
The comments you actually need are about the features you already suspect: a thin wall, a tight tolerance, a snap fit, a cosmetic face. Ask about those by name and the supplier can answer in minutes. Ask in general and the problems turn up at first article, when they cost the most to fix.
Worked example: 600-0072 sensor cover, before Rev A
The sensor cover is an injection-molded PC/ABS part. The design is at pre-release iteration P4, and the team wants feedback from the molder before releasing Rev A and asking for a tooling quote.
/600-0072 Sensor cover/
/dfm/
600-0072_P4_DFM-review.pdf every sheet stamped "for DFM review, not for production"
600-0072_P4.step
600-0072_P4_DFM-questions.pdf the questions below, each with a view
600-0072_P4_DFM-log.csv replies and decisions
Step 1: Give them what they'd need to quote. Material (PC/ABS), color and texture, expected annual volume, and which faces are cosmetic. A molder can't judge a gate location or a texture without knowing which face the customer sees.
Step 2: Ask specific questions, each tied to a view.
| # | View | Question |
|---|---|---|
| Q1 | V01 | The inner walls have 0.5° draft. Is that enough at 22 mm deep, or should we go to 1°? |
| Q2 | V02 | Wall is 2.0 mm, thickening to 3.2 mm at the screw bosses. Do you expect sink on the cosmetic face? |
| Q3 | V03 | Where would you put the gate, given face A is cosmetic? |
| Q4 | V04 | Can the snap hook be molded without a side action? |
| Q5 | V01 | We want a light texture on face A. How much draft does that need with your texture? |
| Q6 | Sheet 1 | Which tolerances on the drawing would you change, and to what? |
General guidance helps you write these. Protolabs, for example, advises 0.5 degrees of draft on all vertical faces, says 1 to 2 degrees works well in most situations, and gives 1 degree per inch of cavity depth as a rule of thumb, with more for textured faces (Protolabs). Your molder's own answer is the one that counts.
Step 3: Set a reply date and a format. Ask for replies by a date, marked on the PDF or answered by question number. If the design is confidential, put an NDA in place before you send anything.
Step 4: Log every answer and decision. Each reply goes into the log with your decision: change, keep with a reason, or test. For 600-0072, the molder asked for 1.5° on the inner walls and moved the gate to the inside rim. Both changes went into P5.
Step 5: Release, then quote. Release Rev A with the agreed changes, and ask for the tooling quote against Rev A by revision. The PO should name that revision too; see How do I make sure my supplier builds the right revision?
Ways to get DFM feedback
| Method | Good for | Main risk |
|---|---|---|
| "Any comments?" on the RFQ | Nothing extra to prepare | Little or no feedback; problems show up at first article |
| Automated DFM check from an online quoting service | Fast flags on geometry problems | Checks rules, not your use case or which faces are cosmetic |
| Specific questions with a reply date | Getting answers on the features you're worried about | Takes an hour to prepare; only covers what you thought to ask |
| A review call with the supplier's engineer | Complex parts and trade-offs | Answers stay in someone's notes unless you log them |
| DFM report at tooling kickoff | Molded and cast parts where the toolmaker owns the mold design | Late: changes now cost tooling time |
When this stops working
- Several suppliers are reviewing the same part, and their answers conflict.
- The supplier's markups come back against an older iteration than the one you're on.
- DFM changes turn up in the model without anyone remembering which supplier asked for them.
- A change after release, rather than before, becomes the usual way DFM feedback arrives. That path is covered in How do I send a supplier a design change after the PO is placed?
FAQ
Should I send native CAD files for a DFM review?
Usually a STEP file and a PDF drawing are enough, and they work in any CAD system. Send native files only if the supplier asks and uses the same CAD.
When should I ask a supplier for DFM feedback?
Before release, once the geometry is close to final but changes are still cheap. For molded parts, ask before the tooling quote, not after the mold design starts.
What should a DFM review cover for an injection-molded part?
Draft, wall thickness and sink, gate location relative to cosmetic faces, undercuts and side actions, and which tolerances the process can hold. Ask about each one for the features where you're unsure.
How do I keep track of DFM changes?
Log each supplier answer with your decision and the iteration where the change went in. At release, the log shows which supplier comments shaped the part.
Internal links
- How do I make sure my supplier builds the right revision?
- How do I send a supplier a design change after the PO is placed?
- How do I share a SolidWorks file with someone who doesn't have SolidWorks?
Sources
- Protolabs, Draft Angle Guidelines for Injection Molding: https://protolabs.com/resources/design-tips/improving-part-moldability-with-draft/
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