Sheet Metal Fabrication Design Guide: DFM Tips to Reduce Cost

Sheet metal fabrication design directly determines manufacturing cost, lead time and quality. A well-designed part is easier to cut, bend and weld, meaning lower setup time, less scrap and faster turnaround. A poorly designed part generates rework, cost overruns and delays even before production begins.

Design for Manufacturability (DFM) is the discipline of reviewing a part design before production to identify and correct features that add cost without adding function. This guide documents the ten most important DFM rules for sheet metal, the rules Manufyn’s engineers check on every drawing before issuing a quote.

What is DFM and Why Does It Matter for Sheet Metal Fabrication?

Design for Manufacturability (DFM) is the engineering practice of designing parts in a way that makes them straightforward to manufacture at the lowest possible cost, at the required quality and within the specified lead time. In sheet metal fabrication, DFM analysis is applied before any material is cut, it reviews the drawing for features that are:

• Geometrically impossible with standard tooling
• Theoretically possible but excessively expensive to produce
•  Likely to cause quality problems during cutting, bending or welding
• Calling out tighter tolerances than the application actually requires

At Manufyn, DFM review is not an optional add-on, it is the first stage of every order. Engineers review your drawing before quoting. Any DFM issues are documented in a report sent back for your review. This protects both sides: you avoid expensive surprises, and Manufyn avoids manufacturing non-conforming parts.

The cost impact of DFM is significant. Studies across the manufacturing industry consistently show that 70–80% of a part’s lifetime cost is locked in at the design stage. Getting DFM right before production starts, not after the first batch arrives with quality issues, is the single highest-leverage action an engineer or procurement manager can take.

Rule 1: Minimum Bend Radius, The Most Common DFM Violation

Every sheet metal material has a minimum bend radius below which the outer face of the bend cracks during forming. This minimum radius is a function of material type, grain direction and thickness. Specifying a tighter radius than the material can tolerate is the single most common DFM error Manufyn encounters.

 

Design rule: always specify an inside bend radius equal to or greater than the ‘with grain’ minimum for your material and thickness. If your design requires a radius tighter than this, either change the material, reduce thickness, specify annealing, or accept that the feature cannot be bent, it must be machined or cast instead.

Rule 2: Hole-to-Bend Distance, Minimum Clearance

Holes and cut-outs located too close to a bend line will distort during forming. The bend force deforms the material in the bend zone, and if a hole falls within that zone, it will elongate or tear, making the part non-conforming.

Design fix: if the design requires a hole close to a bend, add a relief slot between the hole and the bend line. The relief slot breaks the stress path and prevents distortion. Alternatively, move the hole further from the bend if the function allows it.

Rule 3: Bend Relief, When and Where to Add It

Bend relief is a small notch or cut-out at the end of a bend line where it meets a flange edge or another feature. Without bend relief, the corner of the bend will tear or create unwanted material deformation as the press brake forces the bend.

Bend relief is required whenever a bend terminates at or near a part edge. The relief allows the material to deform cleanly during bending without propagating a tear into the adjacent flange. Minimum bend relief dimensions:

•  Minimum relief width: equal to material thickness
•  Minimum relief depth: equal to bend radius + material thickness
•  Relief shape: square cut-out or radius cut, both are acceptable

Rule 4: Consistent Material Gauge Across the Part

Sheet metal fabrication is most cost-effective when a single part uses a single material thickness throughout. Mixed gauges within one part require multiple material setups, additional nesting operations and sometimes separate cutting runs. They also complicate bend radius calculations.

If your design requires different thicknesses in different areas, consider whether the part can be redesigned as a welded assembly of two separately cut and formed pieces. This is almost always more cost-effective than attempting to machine or step-form a single sheet to multiple thicknesses.

The only common exception is sandwich or composite sheet metal, where a thin cladding is bonded to a thicker structural substrate. This is a specialised process and should be discussed with Manufyn’s engineers at the DFM stage.

Rule 5: Avoid Sharp Internal Corners

Sharp internal corners (0mm radius) on cut-outs and pockets create stress concentration points that can initiate cracks in service. They are also impossible to produce with standard punch tooling, punches have a minimum corner radius.

For laser-cut parts: a theoretical 0mm internal corner is achievable with laser cutting, the laser can cut perfectly square corners. However, internal corners on formed features (pressed forms, embosses) must always have a radius equal to at least the material thickness.

Rule 6: Minimum Flange Length

Press brake bending requires the material to be supported in the die during the bend. If a flange (the face of material on one side of a bend) is shorter than a minimum length, the press brake cannot form the bend, the flange slips off the die.

Frequently Asked Questions