GlossaryKind of term: Manufacturing termSheet metal
What is sheet metal?
Sheet metal work makes parts from flat sheet by cutting, bending, sometimes rolling, and joining with welds, rivets or fasteners.
Sheet metal work is the group of processes that make parts from flat sheet of a fixed thickness, usually steel, stainless steel or aluminium. The flat pattern is cut by laser, plasma, waterjet or punching, then bent on a press brake, sometimes rolled, and welded, riveted or joined with press-in fasteners into an assembly. Wall thickness stays close to the sheet thickness throughout. Where sheet ends and plate begins differs by source and by shop.
What does the flat pattern depend on?
The drawing or 3D model shows the folded shape; the flat pattern is derived from it. In a bend the outside stretches and the inside compresses, with the neutral line in between. Its position is usually expressed as a K-factor, a fraction of the sheet thickness, or through bend allowance tables per material, thickness and tooling. A wrong K-factor leaves the dimensions off after bending. Manufacturability depends on minimum flange length, the distance from holes and cut-outs to the bend line, inside radius relative to thickness, grain direction and bend sequence. A hole too close to the bend line distorts when the part is bent. The cutting machine usually works from a 2D flat pattern, the press brake from the folded geometry.
How does sheet metal work in practice?
Cost builds up differently from machining. Material is bought per sheet, and how many parts fit on one sheet drives the material cost per piece; how you charge the remnant is an estimating convention. Cutting time depends on cut length, thickness and the number of pierces, bending on the number of bends, turnovers and tool changes, welding on seam length, preparation and straightening. A machining cost model that treats the part as a block gives no usable basis for sheet metal.
What is sheet metal often confused with?
Sheet metal is not machining from plate: a 20 mm plate with milled pockets is machining, even though it started as plate. And sheet metal is more than laser cutting: cutting is one step, and bending and joining usually follow.
How do you see sheet metal in Blake?
In Blake a sheet metal part you buy in can sit as a bought part in an assembly, next to your made parts and the assembly's own work; while its price is missing, the line stays open instead of showing zero. More on estimating.
Frequently asked questions
Why can't I price sheet metal like a milled part?
Because the time is not in removing material but in cut length, pierces, bends and welds, and material cost depends on how many parts fit on a sheet. A machining model that prices a block around the part can land far off.
What is a flat pattern?
The flat shape of a sheet metal part before bending, with the stretch in each bend allowed for through a K-factor or bend allowance. It is what the cutting machine cuts; if that allowance is wrong, the dimensions are off after bending.
What is a K-factor?
The position of the neutral line in a bend, as a fraction of the sheet thickness measured from the inside. It depends on material, thickness, inside radius and bending method, and in practice is often set from test bends.