blanking

Blanking is a shearing operation that cuts a complete, closed outline from sheet metal in a single stroke. A punch descends into a die, forcing the workpiece material to shear along a predetermined path. The piece between the punch and die wall becomes the blank, while the surrounding material, called scrap or skeleton, falls away. The process produces a flat part with a finished perimeter, ready for subsequent forming or machining operations.

The die geometry determines everything. The punch cavity and die opening must match precisely, usually held to tenths of a millimeter tolerance. Clearance between punch and die typically ranges from 5 to 15 percent of material thickness, depending on stock hardness. Too tight and the punch binds; too loose and the edge tears rather than shears cleanly. The die sits in a press bed; hydraulic or mechanical presses deliver the shearing force, which can exceed hundreds of tons for large parts or heavy gauge material.

Blanking differs from piercing in one critical respect: blanking removes the outer boundary to create the finished part, while piercing creates holes or openings within a part that remains attached to scrap. Often both operations occur in sequence on the same coil stock. Progressive dies perform blanking, piercing, and forming in stages as material advances through the press, making high-volume production economical.

Quality and edge condition

The cut edge from blanking shows three distinct zones: a burnished region where material compressed elastically, a shear zone where plastic deformation occurred, and a fractured zone where material tore. Softer metals like aluminum and annealed steel produce longer burnished zones and cleaner edges. Hard or brittle materials fracture more readily, leaving ragged or chipped edges. Lubrication during blanking reduces friction heat and improves edge quality.

Blanks enter the supply chain as loose parts or nested on carrier strips. Downstream operations such as bending, drawing, or coating must account for burrs and edge roughness if blanks are not deburred. High-speed blanking on specialized presses can achieve deburring simultaneously, though this requires careful die design and material selection. For precision applications, blanks often receive secondary finishing before assembly.