Resources/Sheet Metal Documentation

Sheet Metal Fabrication Documentation

Complete reference for sheet metal design — gauge thickness charts, bend allowances, K-factors, stamping and laser cutting tolerances, material selection guide, and detailed design rules.

1. Standard Sheet Metal Thickness (Gauge)

Sheet metal thickness is commonly specified by gauge number. Use the charts below to convert gauge to actual thickness for your material.

Gauge	Steel (mm)	Stainless (mm)	Aluminum (mm)	Copper (mm)	Typical Use
10	3.42	3.57	2.59	2.59	Heavy structural brackets, chassis
12	2.66	2.78	2.05	2.05	Automotive body panels, enclosures
14	1.90	1.98	1.63	1.63	General-purpose housings, panels
16	1.52	1.59	1.29	1.29	Electrical enclosures, covers
18	1.21	1.27	1.02	1.02	Consumer electronics chassis
20	0.91	0.95	0.81	0.81	Light-duty brackets, clips
22	0.76	0.79	0.64	0.64	Shielding, small brackets
24	0.61	0.64	0.51	0.51	Spring contacts, EMI shielding
26	0.45	0.48	0.40	0.40	Thin shims, washers, clips

2. Bend Allowance & K-Factor

Understanding bend allowance is critical for accurate flat pattern development. The K-factor and bend allowance determine the final dimensions of bent sheet metal parts.

Bend Allowance Formula

BA = (π/180) × A × (R + K × T)

A = Bend angle (degrees)
R = Inside bend radius (mm)
K = K-factor
T = Material thickness (mm)

Standard K-Factors

R < TK = 0.25

R = T to 2TK = 0.33

R = 2T to 3TK = 0.40

R > 3TK = 0.45

Minimum Bend Radius

Steel (CRS)0.5T – 1T

Stainless Steel0.75T – 1.5T

Aluminum 50521T – 2T

Aluminum 60611.5T – 3T (may crack at 1T)

Copper0.5T – 1T

Brass1T – 2T

Minimum Flange Length

For 90° bends≥ 4T + R

Single bend≥ 3 mm practical min

Multiple bends≥ 6 mm between bends

Near edges≥ 2.5T from hole edge

Near slots≥ 3T from slot end

Hole to bend≥ 2T + R

3. Stamping Tolerances

Feature	Standard	Precision	Notes
Blanked edge profile	±0.1 mm	±0.05 mm	Sharp-edged tooling; better for thinner material
Pierced hole diameter	±0.05 mm	±0.02 mm	Punch-to-die clearance is critical
Hole-to-hole position	±0.1 mm	±0.05 mm	Progressive die: station-to-station accuracy
Hole-to-bend position	±0.15 mm	±0.1 mm	Affected by springback; bend before pierce
Bend angle	±1°	±0.5°	Overbend to compensate for springback
Formed feature depth	±0.2 mm	±0.1 mm	Coin or restrike for precision
Flatness	0.1 mm/100 mm	0.05 mm/100 mm	Leveling/stretcher after stamping
Burr height	≤ 0.1 mm	≤ 0.05 mm	Deburring available; specify on drawing

4. Laser Cutting Specifications

Material	Max Thickness	Min Kerf	Position Tol.	Quality
Carbon Steel	25 mm	0.15 mm	±0.1 mm	Clean edge; slight HAZ
Stainless Steel	20 mm	0.15 mm	±0.1 mm	Oxide edge — pickling available
Aluminum	12 mm	0.2 mm	±0.15 mm	Dross on thick sections
Copper	8 mm	0.2 mm	±0.15 mm	Reflective — fiber laser required
Brass	8 mm	0.2 mm	±0.15 mm	Zinc fumes — extraction needed
Titanium	6 mm	0.15 mm	±0.1 mm	Inert gas shield required

5. Sheet Metal Material Selection Guide

Cold-Rolled Steel SPCC

Best:General stamping, brackets, enclosures

Avoid:Outdoor use without coating

Bend:Excellent

Stainless Steel 304

Best:Corrosion resistance, food-grade, medical

Avoid:Chloride/salt water (use 316)

Bend:Good

Stainless Steel 316

Best:Marine, chemical, high-corrosion environments

Avoid:Cost-sensitive applications

Bend:Good

Aluminum 5052

Best:Marine, chemical tanks, street signs

Avoid:High-strength structural parts

Bend:Excellent

Aluminum 6061

Best:Structural, heat-treatable, aerospace

Avoid:Tight-radius bends (cracking risk)

Bend:Fair

Copper C110

Best:Electrical bus bars, thermal, decorative

Avoid:High-strength mechanical loads

Bend:Excellent

Brass C260

Best:Decorative hardware, electrical contacts

Avoid:Stress corrosion with ammonia

Bend:Excellent

Spring Steel 65Mn

Best:Spring clips, retaining rings, washers

Avoid:Corrosive environments uncoated

Bend:Good

Zinc Sheet

Best:Roofing, flashing, battery cases

Avoid:High-temperature applications

Bend:Good

Titanium Grade 2

Best:Aerospace, medical, chemical processing

Avoid:Cost-sensitive; difficult to form

Bend:Fair

6. Sheet Metal Design Guidelines

Hole-to-Edge Distance

Minimum 2T from hole center to edge for punched holes. For laser-cut holes, 1T minimum. Insufficient edge distance causes bulging or tearing.

Hole Diameter vs. Thickness

Punched hole diameter must be ≥ material thickness (Ø ≥ T). Smaller holes require drilling or laser cutting. For holes < 1 mm, laser cutting is preferred.

Corner Radii on Blanks

External corners: minimum R = 0.5T. Internal corners: minimum R = 1T. Sharp corners create stress concentrations and accelerate tool wear.

Notch & Tab Width

Minimum notch/tab width = 1.5T. Width less than 1.5T risks tearing during stamping. For laser cutting, minimum slot width = material thickness.

Forming Height

Drawn/formed features: height ≤ 3× diameter for single-stage. Deeper draws require progressive stages and may need annealing between stages.

Grain Direction

Bend perpendicular to grain direction where possible. Bending parallel to grain increases cracking risk. Specify grain direction on drawings for critical parts.

Relief Cuts at Bends

Add relief notches at bend corners to prevent tearing. Relief width ≥ T, relief depth ≥ R + T. No relief = tearing at bend intersections.

Flat Pattern Design

Unfold your model to verify flat layout. Check for collisions. All bends must be linear — curved bends require special tooling and are cost-prohibitive.