Piercing (metalworking)

Blanking and piercing are shearing processes in which a punch and die are used to modify webs. The tooling and processes are the same between the two, only the terminology is different: in blanking the punched out piece is used and called a blank; in piercing the punched out piece is scrap. The process for parts manufactured simultaneously with both techniques is often termed "pierce and blank." An alternative name of piercing is punching.

Burrs and die rolls are typical defects of trimmed surfaces. The surface finish will be lower in the so-called fracture zone, i.e. where the material is irregularly stripped away from the matching surface, at the end of the shearing operation. Die roll is a plastic deformation of the sheet edge, which causes permanent edge rounding.

Burr height is typically used as an index to measure tool wear, because it is easy to measure during production.

The selection criteria of all process parameters are governed by the sheet thickness and by the strength of the work-piece material being pierced.

The punch/die clearance is a crucial parameter, which determines the load or pressure experienced at the cutting edge of the tool, commonly known as point pressure. Excessive point pressure can lead to accelerated wear and ultimately failure. the surface quality of the trimmed edge is severely affected by the clearance, too.

Material specific design guidelines are developed by companies in order to define the minimum acceptable values of hole diameters, bridge sizes, slot dimensions. Similarly, the strip lay-out must be determined (strip width and pitch). The bridge width between the parts and the edge allowance between the part and the edge of the strip have to be selected, too.

A simple operation may only need a pancake die. While many dies perform complex procedures simultaneously, a pancake die may only perform one simple procedure with the finished product being removed by hand.

There are various types of blanking and piercing: lancing, perforating, notching, nibbling, shaving, cutoff, and dinking.

Lancing is a piercing operation in which the workpiece is sheared and bent with one strike of the die. A key part of this process is that there is not reduction of material, only a modification in its geometry. This operation is used to make tabs, vents, and louvers.

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