Describe the processes used to fabricate products from sheet metal, including pattern development, cutting and shearing, bending and folding, forming and joining, and explain their application in fabrication

What this dot point is asking

Fabrication turns flat sheet and section into useful three-dimensional products, and sheet metal work has its own set of processes. NESA expects you to describe how a product is developed as a flat pattern and then cut, bent, formed and joined into shape. This is core production knowledge for the focus area, examined in the written paper and applied whenever your Major Project uses sheet or fabricated metal.

Pattern development

A three-dimensional sheet product is made from a flat blank, so fabrication begins by working out the flat shape, the development, that folds up into the finished item. The developed pattern must account for the metal taken up in each bend so the folded product comes out the right size. Geometric methods such as parallel-line and radial-line development produce the patterns for boxes, ducts, cones and cylinders. Accurate development is what separates a part that folds up correctly from one that does not fit.

Cutting and shearing

Once marked out from the pattern, the sheet is cut to size:

• Guillotine (shear): makes long, straight, clean cuts in sheet.
• Tin snips and shears: cut curves and smaller shapes by hand or power.
• Nibbling and laser or plasma cutting: cut complex profiles, with laser and plasma giving fast, accurate, automated cuts in industry.

Edges left by cutting are sharp and are deburred for safety and fit.

Bending and folding

Flat sheet becomes three-dimensional by bending along straight lines:

• Folder (box and pan brake): clamps the sheet and folds it to a set angle along a line, used for boxes, trays and brackets.
• Press brake: uses a punch and die to fold heavier sheet to accurate angles, the production tool for folded components.

Metal springs back slightly after bending, so allowances are made to reach the intended angle. Folding adds stiffness as well as shape, which is why edges are often folded to strengthen a panel.

Forming processes

Beyond simple folds, sheet is shaped into curves and contours:

• Rolling: passing sheet between rollers to form cylinders and curves.
• Pressing and stamping: forcing sheet between matched dies to form dished, raised or complex shapes in one stroke, ideal for high-volume parts such as panels.
• Spinning: forming a rotating disc over a former to make round hollow shapes.

These processes give the curved and contoured forms that folding alone cannot.

Joining and finishing fabrication

Fabricated parts are joined by the methods covered elsewhere in the focus area: welding for strong permanent joints, riveting for sheet, folded and locked seams for sheet-metal ducting and containers, and fasteners where the joint must come apart. After assembly, edges are dressed, the work is cleaned, and a protective finish is applied because fabricated steel rusts. Throughout, sheet edges and corners are sharp, so deburring and careful handling are constant safety concerns.

Putting it together

A typical fabrication runs from development to a flat pattern, to cutting and shearing, to bending and forming, to joining and finishing. When you plan or justify fabrication in your folio, work through these stages in order, account for bend allowances and springback, and identify the cutting, forming and joining processes that suit the product and the quantity required.