When sourcing custom mechanical parts, many customers focus solely on the unit price, overlooking the key factor that truly determines total cost: the manufacturability of the design itself. DFM (Design for Manufacturability) analysis is a method of identifying and eliminating potential manufacturing difficulties during the design phase. It can significantly reduce machining complexity, shorten lead times, improve yield, and ultimately lower total cost — all without compromising part function.

This article shares several practical DFM recommendations for both CNC machining and sheet metal fabrication.

Part I: DFM Recommendations for CNC Machined Parts

1. Avoid Very Small Internal Radii

Many engineers design small internal corner radii (e.g., R0.5mm) on milled parts. This requires tiny diameter end mills, which increase machining time and are prone to breakage.
Recommendation: Increase non‑critical radii to R2mm or larger. Standard tool diameters can be used, reducing machining time by more than 30%.

2. Limit Depth-to-Diameter Ratio in Deep Cavities

When cavity depth exceeds 4x the tool diameter, chip evacuation becomes difficult and tool deflection risk rises sharply.
Recommendation: For deep cavities, consider EDM or a split design instead of aggressive milling.

3. Standardize Thread Sizes

Using too many different thread sizes (e.g., M3, M4, M5, M6 mixed together) increases tool changes and inventory.
Recommendation: Standardise to 1–2 common sizes, such as M4 and M6, where assembly permits.

4. Avoid Tolerancing Every Dimension Tightly

Some drawings apply ±0.01mm tolerance to every dimension — a very expensive approach.
Recommendation: Apply tight tolerances only to functional mating surfaces. Relax other dimensions to ±0.1mm or larger, reducing machining cost by 40%–60%.

Part II: DFM Recommendations for Sheet Metal Parts

1. Match Bend Radius to Material Thickness

A bend radius that is too small causes cracking on the outside of the bend.
Recommendation: The minimum inside bend radius should generally equal the material thickness (e.g., for 1.5mm sheet, inside radius ≥1.5mm). An incorrect radius may require special tooling or cause scrap.

2. Keep Holes Away from Bend Lines

A hole too close to a bend line will distort into an oval due to material stretching.
Recommendation: Maintain a distance from hole centre to bend line of at least 2.5x material thickness.

3. Design Louvers and Forming Features Reasonably

Complex louvers, bridge lances, or long slots require tool access and material flow consideration.
Recommendation: Use standard punch shapes whenever possible. Non‑standard shapes significantly increase tooling cost.

4. Plan Weld Paths Thoughtfully

When designing welded assemblies, avoid excessively long continuous welds or inaccessible weld locations.
Recommendation: Use stitch welds instead of continuous welds. This reduces heat distortion and cuts welding labour by more than 30%.

Part III: A Real Case – How One DFM Review Saved 35% of Cost

A customer in the automation industry needed a machine base part. The original design was a one‑piece aluminium CNC machined component measuring 300×200×80mm, with a deep cavity and multiple threaded holes. During our DFM review, we proposed:

• Split the solid part into two shallower cavities, then bolt them together.
• Reduce thread types from 4 to 2.
• Increase non‑critical fillets from R1mm to R3mm.

Results: Machining time dropped from 4.5 hours to 2.8 hours per part. Tool consumption decreased by 40%, and material utilisation increased from 18% to 32%. The final unit cost fell by 35%, and lead time shortened by 8 days. The customer validated the modified design – function and strength fully met requirements.

Part IV: Best Practice DFM Process

1. Engage early – Ideally, involve your supplier in DFM reviews during the design phase.
2. Provide 3D models, not just 2D drawings – 3D models allow better manufacturability simulation.
3. Identify critical characteristics – Clearly mark which dimensions must be held tight and which can be relaxed.
4. Establish a feedback loop – Document DFM suggestions so the same issues are avoided in future designs.

Conclusion

DFM is not about cutting corners; it is about achieving the same function using smarter manufacturing methods. For both CNC machined and sheet metal parts, a professional, thorough DFM analysis often yields 20%–50% cost savings, shorter lead times, and improved quality stability. The next time you source parts, ask your supplier: “Can you perform a DFM review for us?”

If you have a specific part that needs DFM analysis, please contact us for a free manufacturability evaluation report.