How to Design for Sheet Metal Fabrication: DFM Best Practices

Design for Manufacturability (DFM) is the practice of designing parts with manufacturing in mind. For sheet metal fabrication, following DFM principles can reduce costs by 20-40%, improve quality, and speed up production.

In this guide, we’ll share practical DFM tips from our engineering team to help you design better sheet metal parts.

Why DFM Matters

The Cost of Poor Design

30-50% higher manufacturing costs
2-3x longer lead times
Higher defect rates
Multiple design iterations

Benefits of Good DFM

✅ 20-40% cost reduction
✅ 50% faster production
✅ Better quality consistency
✅ Fewer revisions and delays

1. Material Selection

Choose the Right Material for Your Application

Material	Properties	Best For	Cost
Cold Rolled Steel (CRS)	Strong, affordable	Enclosures, brackets	$
Stainless Steel 304	Corrosion resistant	Food grade, outdoor	$$$
Stainless Steel 316	Marine grade	Harsh environments	$$$$
Aluminum 5052	Lightweight, formable	Lightweight parts	$$
Aluminum 6061	Strong, structural	Structural components	$$$
Copper	Conductive	Electrical parts	$$$$
Brass	Decorative, corrosion resistant	Architectural	$$$$

DFM Tips for Material Selection

✅ Use Standard Gauges

Steel: 20, 18, 16, 14, 12, 10 gauge
Aluminum: 0.5, 0.8, 1.0, 1.5, 2.0, 3.0mm
Avoid non-standard thicknesses

✅ Consider Availability

Popular materials = lower cost
Exotic materials = longer lead times

✅ Match Material to Environment

Indoor: CRS with powder coat
Outdoor: Stainless or galvanized
Marine: 316 stainless or aluminum

2. Bend Design

Bend Radius Guidelines

Minimum Inside Bend Radius:

Material	Thickness	Min Inside Radius
Aluminum 5052	1mm	0.8mm
Aluminum 5052	2mm	1.5mm
Steel CRS	1mm	0.8mm
Steel CRS	2mm	1.5mm
Stainless 304	1mm	1.0mm
Stainless 304	2mm	2.0mm

Rule of Thumb: Inside radius ≥ material thickness

Bend Relief Design

Prevent tearing at bend edges with proper relief:

Incorrect:          Correct:
┌─────┐            ┌─────┐
│     │            │     │
│     │            │    ╱│
│     │     →      │   ╱ │
│     │            │  ╱  │
└─────┘            └─╱───┘
                    ↑
              Bend relief

Relief Dimensions:

Width: ≥ material thickness
Depth: ≥ bend radius + material thickness

Bend Deduction

Account for material stretch in flat pattern:

Formula:

Flat Length = Leg1 + Leg2 - Bend Deduction

Example:

Leg1: 50mm
Leg2: 50mm
90° bend, 2mm steel
Bend deduction: 3.4mm
Flat length: 96.6mm

DFM Tip: Work with your manufacturer to get accurate bend deductions for their specific equipment.

3. Hole Design

Minimum Hole Sizes

Material Thickness	Min Hole Diameter
1mm	1.0mm
2mm	2.0mm
3mm	3.0mm
4mm	4.0mm

Rule: Hole diameter ≥ material thickness

Hole Spacing

Prevent distortion with proper spacing:

Incorrect:          Correct:
○ ○ ○              ○   ○   ○
↑ Too close        ↑ Proper spacing

Minimum Edge Distance:

≥ 2.5 × material thickness
Example: 2mm material → 5mm minimum from edge

Minimum Hole Spacing:

≥ 2 × material thickness
Example: 2mm material → 4mm minimum between holes

Hole Types

Feature	Recommended	Avoid
Simple holes	✓ Round	✓ Complex shapes
Slots	✓ Radius ends	✓ Square ends
Countersink	✓ Standard angles	✓ Custom angles
Threads	✓ Standard sizes	✓ Non-standard

4. Flanges and Tabs

Minimum Flange Width

Material Thickness	Min Flange Width
1mm	6mm
2mm	10mm
3mm	14mm
4mm	18mm

Formula: Min flange ≥ (4 × thickness) + bend radius

Tab Design for Welding

Design tabs for easy alignment:

Good Tab Design:
┌────────┐
│        │
│        │ 2-3mm
│        │
└────────┘
    ↑
  5-10mm wide

Benefits:

Easier welding
Better alignment
Stronger joints

5. Tolerances

Standard vs Precision Tolerances

Feature	Standard	Precision	Cost Impact
Linear dimensions	±0.5mm	±0.1mm	+20-30%
Hole positions	±0.3mm	±0.05mm	+25-35%
Bend angles	±1°	±0.5°	+15-25%
Flatness	2mm/m	0.5mm/m	+30-40%

DFM Tolerance Tips

✅ Use Standard Tolerances When Possible

±0.5mm is fine for most applications
Only specify tight tolerances where critical

✅ Tolerance Stack-Up

Consider cumulative effects
Don’t over-constrain the design

✅ Datum Structure

Define clear reference surfaces
Consistent measurement points

6. Feature Placement

Keep Features Away from Bends

Incorrect:          Correct:
     ___               ___
    |   |○            |   |
____|   |____    →   __|   |___
    |___|             |___|
      ↑                   ↑
   Too close          Proper distance

Minimum Distance:

≥ 2.5 × material thickness + bend radius
Example: 2mm material, R2 bend → ≥ 7mm from bend

Avoid Features on Flanges

Place holes and cutouts on flat surfaces when possible:

Better Design:
┌─────┐
│ ○ ○ │  ← Holes on flat surface
│     │
└─────┘

7. Assembly Considerations

Design for Easy Assembly

✅ Self-Locating Features

Tabs and slots
Alignment pins
Interlocking features

✅ Access for Tools

Space for wrenches
Screwdriver clearance
Welding gun access

✅ Modular Design

Break complex assemblies into simpler parts
Easier to manufacture and repair

Fastener Selection

Fastener	Best For	Cost
Self-tapping screws	Thin materials	$
PEM inserts	Repeated assembly	$$
Weld nuts	Permanent, strong	$$
Rivets	Quick assembly	$
Bolts + nuts	Disassembly	$

8. Surface Finish

Specify Finish Early

Finish	Application	Cost
As-fabricated	Hidden parts	Included
Deburred	Safe handling	+$0.50-1.50/sq ft
Powder coat	General use	+$2-5/sq ft
Anodize	Aluminum parts	+$3-8/sq ft
Plating	Corrosion resistance	+$4-10/sq ft

DFM Tips for Finishing

✅ Design for Coating

Avoid tight corners (powder won’t reach)
Include drainage holes
Specify masking areas

✅ Consider Color Matching

Use RAL or Pantone numbers
Request color samples

✅ Account for Coating Thickness

Powder coat: 0.05-0.1mm per side
Adjust hole sizes if needed

9. Cost Optimization Checklist

Design Review Questions

Can I use a thinner material?
Are tolerances necessary?
Can I reduce the number of bends?
Are hole sizes standardized?
Can parts be combined?
Is the finish appropriate for the application?
Have I considered manufacturing sequence?

Common Cost Drivers

❌ Avoid These:

Unnecessarily tight tolerances
Non-standard materials
Complex bends
Too many unique hole sizes
Over-specifying surface finish

✅ Do These:

Use standard tolerances
Choose common materials
Simplify bend geometry
Standardize hole sizes
Specify finish only where needed

10. File Preparation

Recommended File Formats

Best:

STEP (.stp, .step)
IGES (.igs, .iges)
SAT (.sat)

Acceptable:

DXF (.dxf) - 2D only
DWG (.dwg) - 2D only

Include:

3D model
2D drawing (with critical dimensions)
Material specification
Finish requirements
Quantity needed

Drawing Requirements

✅ Must Include:

All critical dimensions
Tolerances (where important)
Material specification
Surface finish requirements
Deburring requirements

✅ Helpful:

Assembly drawings
Exploded views
Special instructions

Free DFM Review

Want expert feedback on your design? We offer:

✅ Free DFM Review - Our engineers review your design
✅ Cost Optimization - Suggestions to reduce costs
✅ Quick Turnaround - Feedback within 24 hours
✅ No Obligation - Use our feedback however you want

Submit Your Design for Review

Download DFM Guide

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Last Updated: March 2026
Author: Fabex Engineering Team