Stamping uses a press and die to apply external force to sheet, strip, tube, or profile stock, causing plastic deformation or separation to obtain the required shape and size. Among the separation operations, blanking and piercing are the two most basic: in blanking, the punched-out slug is the finished part, while in piercing, the slug is scrap. The die structure is similar, but the discharge method is reversed—blanking dies typically push the part out from the die side, while piercing dies eject the scrap through the die opening. Getting this distinction right at the design stage avoids costly rework after the tool is built, especially on compound dies where both operations run in one stroke.
In actual strip layout, the web allowance is usually taken as 1.2 to 1.5 times the material thickness. Too narrow, and the strip tends to tear at the edge; too wide, and material is wasted, which directly raises the per-part cost quoted to the customer. For blanking clearance, select 5% to 8% of material thickness. If the clearance is applied in the wrong direction—offset to the wrong side of the punch-die interface—burr height increases noticeably. When troubleshooting excessive burr during tryout or repair, check clearance direction first before touching anything else. In our shop, this single check has resolved more burr complaints than any other adjustment.
These values are starting points, not absolutes: harder or thicker stock may call for clearance toward the upper end of the range, and progressive dies with multiple stations need each station checked independently. Document the chosen web allowance and clearance on the die drawing so the toolroom and the tryout team work from the same numbers. For more mold sourcing information, visit MoldSo at www.moldso.com.