Sheet Metal Fabrication
When your product needs an enclosure, bracket, chassis, or panel — and plastic won’t do — sheet metal is how you get strength, EMI shielding, and structure at a competitive cost.
Sheet metal fabrication is a cold-forming process that transforms flat metal sheets into three-dimensional parts through cutting, bending, punching, and welding. Unlike CNC machining — which removes material from a solid block — or casting — which pours molten metal into a mold — sheet metal starts flat and gains its shape through deformation. This makes it fast, material-efficient, and ideal for enclosures, brackets, chassis, and panels.
For hardware founders, sheet metal is often the answer when plastic lacks strength or EMI shielding and CNC machining is too expensive at volume. A sheet metal enclosure costs a fraction of a fully machined aluminum housing while offering comparable durability. Understanding the basics — bend radii, material gauges, and finishing options — lets you design parts that are both functional and manufacturable.
The process begins with a flat metal sheet, typically steel (cold-rolled, stainless, galvanized) or aluminum (5052, 6061). The sheet is cut to size by laser cutting for precise contours, turret punching for high-speed hole patterns, or shearing for straight cuts. Laser cutting is the dominant method for prototyping and low-to-mid volume because it handles complex profiles with no tooling cost.
After cutting, the flat blank moves to a press brake for bending. A press brake uses a punch and die to fold the metal along a straight line. The key parameter is the bend radius — the inside radius of the fold — which is determined by the die opening and material thickness. A typical rule: the inside bend radius should be at least equal to the material thickness. Tighter bends risk cracking, especially in aluminum.
For parts that need more than bends — threaded inserts, welded joints, or riveted assemblies — secondary operations add fasteners and join multiple pieces. PEM inserts (self-clinching nuts and studs) are pressed into pre-punched holes to provide strong, reusable threads in thin sheet metal. Spot welding and TIG welding join separate panels into rigid assemblies.
Finishing is the final step and often the most visually important. Powder coating is the most common — a durable, even finish available in any color. Anodizing works for aluminum and provides a harder surface with a metallic look. Electroplating (zinc, nickel, chrome) adds corrosion resistance. Passivation is used for stainless steel to remove free iron and enhance corrosion resistance.
Sheet metal design mistakes
Bend radii too tight for the material
Aluminum cracks at bend radii under 1x material thickness. Steel tolerates tighter bends. If your design needs a tight fold, orient the bend line across the material grain, not parallel to it.
Holes too close to bend lines
A hole within 2x material thickness of a bend line will distort during forming — the hole stretches into an oval. Move holes away from bends or punch them after forming.
Ignoring the K-factor
Metal stretches when bent. The K-factor accounts for this elongation and determines the flat pattern dimensions. Without the correct K-factor, your bent part comes out the wrong size. Your sheet metal shop should provide their standard K-factor.
Designing welds where bends would work
A welded corner costs more, takes longer, and requires post-weld grinding compared to a bent corner. Whenever possible, design the part to bend into shape rather than weld separate pieces together.
Specifying tight flatness tolerances on large panels
Sheet metal warps slightly during cutting and bending. A 2 mm flatness tolerance on a 500 mm panel is achievable. 0.5 mm is not — unless you add stiffening ribs or pay for post-fabrication flattening.
What founders should remember
Sheet metal beats CNC machining on cost above ~50 units
A simple sheet metal bracket might cost $5–15 at 100 units vs. $30–60 for the same part CNC-machined from billet. The gap widens with volume as sheet metal benefits from nesting and automation.
Design for standard sheet gauges
Metal sheets come in standard thicknesses — 1.0 mm, 1.5 mm, 2.0 mm, 3.0 mm are common. Designing to 1.37 mm forces the shop to either machine from a thicker sheet (waste) or order custom stock (delay and cost).
Material choice affects both manufacturing and end-use
5052 aluminum forms well but cannot be heat-treated. 6061-T6 is stronger but more prone to cracking on tight bends. Cold-rolled steel is cheap and strong but rusts without coating. Stainless is corrosion-proof but 3x the material cost. Match the material to the environment.