In stamping, a press and die apply external force to sheet metal to either plastically deform it or separate it. The first category—the separation process—forces the blank to fracture along a closed contour. Shearing, blanking, and notching all fall under this heading. From a die-building standpoint, the punch-to-die clearance is the single most critical parameter: it is generally set at 5% to 10% of material thickness. Go too tight and you get tall burrs plus accelerated punch wear; go too loose and the sheared edge shows an obvious rollover and a sloppy fracture zone. In practice, we size clearance per material—mild steel sits near the 5–7% end, while stainless and high-strength grades push toward 8–10%—and we always check punch and die edge condition before blaming the press.
The second category—the forming process—changes the blank's shape without fracturing it. Drawing, bending, and flanging carry most of the load here. Drawing is where dies live or die: if the draw ratio m is not controlled properly, the cup wall cracks the moment the punch comes down. That means getting the draw radius, blank-holder force, and lubrication right, and often running the part through several draw stages rather than one aggressive pass. Bending brings its own headaches—springback compensation in the die, minimum bend radius versus material thickness, and bend-line placement relative to the grain direction. Flanging adds edge stretch, so pre-cut hole size and edge quality matter just as much as the forming punch geometry.
Get these two classifications straight and the rest of the job gets easier: strip layout, station sequencing, and clearance selection all follow from knowing whether a station separates or forms. In the shop, that discipline is what separates a die that runs a million strokes from one that eats punches every shift. For more mold sourcing and supplier information, visit MoldSo at www.moldso.com.