Metal fabrication is building a part or assembly from stock material by cutting, forming, machining, joining and finishing, as opposed to casting or moulding it in one piece. Almost every decision that affects cost is a decision about which method is used at one of those stages, and most of them are made by the designer without necessarily realising it.
The stages in order
Material is cut to shape by laser, plasma, waterjet, saw or shear. It is formed by bending, rolling or pressing. Features that need precision are machined. Parts are joined by welding, fastening or bonding. Finally the assembly is finished by deburring, coating or plating. Every quote is a sum of these, plus material, plus handling between them.
Design decisions that reach into each stage
One material thickness throughout saves setups at the cutting and forming stages. One bend radius saves a tool change. Self locating tabs and slots remove a welding fixture. Fasteners instead of welds remove distortion and a skilled operation. And deciding the finish early decides the order everything else has to happen in, since welding after coating is not possible.
Where fabrication beats casting
At low and medium volume, because there is no pattern or die. When the part is large, since a fabricated frame costs a fraction of a casting of the same size. When the design is still moving. When certified wrought material properties are required. And when lead time matters, because fabrication starts the day the file arrives.
Where casting or moulding wins
At high volume, where tooling amortises and each part is near net shape. On complex three dimensional shapes that would take many fabricated pieces and many welds. Where a single piece is needed for strength or sealing. And where the fabricated alternative would need so much machining afterwards that the saving disappears.
Questions people ask about metal fabrication design
What is metal fabrication?
Building parts and assemblies from stock material by cutting, forming, machining, joining and finishing, rather than casting or moulding them in one piece.
What is the biggest cost driver?
Setups. Multiple thicknesses, multiple bend radii, welded sub assemblies and multiple finishes each add one, and at low volume setups dominate the price.
Fabrication or casting?
Fabrication at low to medium volume, for large parts and for certified wrought properties. Casting at high volume and for complex three dimensional shapes.
How do I reduce fabrication cost?
One thickness, one bend radius, self locating joints, fewer welds, and one finish. Each removes a setup or an operation without usually changing what the part does.