A practical overview of stamping process essentials, covering material behavior, die design considerations, and shop-floor execution tips for mold engineers.

In stamping, the material is not just a blank—it’s the first variable that decides die life and part quality. For low-carbon steel (e.g., DC01 or SPCC), the yield strength typically ranges from 180–280 MPa, with elongation above 28%, which makes it forgiving for bending and shallow drawing. But when you move to high-strength steels (DP780 or above), the springback angle can exceed 3–5 degrees on a 90-degree bend, so you must compensate by over-bending or adding a coining step. Also, watch the sheet thickness tolerance: a ±0.05 mm variation on a 1.5 mm blank can shift the trimming clearance from 10% to 15% of material thickness, causing burr height to double. Always verify the material certificate against the die design assumptions before production.

Die design is where theory meets the press. For a typical progressive die, the recommended punch-die clearance is 8–12% of material thickness for mild steel, but for stainless (SUS304) it jumps to 15–20% due to higher work hardening. The stripper force should be at least 10–15% of the total cutting force to avoid pulling the strip upward. On the die side, use a shear angle of 0.5–1.0 degrees on the punch face to reduce impact load—this can lower peak tonnage by 20–30%, which protects both the die and the press. For drawing operations, the blank holder force is often set at 20–30% of the drawing force, and the die radius should be 4–6 times the material thickness to prevent tearing. Don’t forget to add a nitrogen gas spring for the blank holder—it gives a more consistent force curve than coil springs, especially at high stroke rates.

On the shop floor, the real issues are lubrication and alignment. Use a low-viscosity drawing oil (ISO VG 15–22) for light stamping, but switch to a high-film-strength lubricant (e.g., with EP additives) for deep drawing of aluminum or stainless. The oil film thickness should be 2–5 microns—too much causes oil pitting, too little leads to galling. Also, check the press slide parallelism monthly; a deviation of more than 0.03 mm per 300 mm width will cause uneven die wear and premature edge chipping. Finally, always run a tryout with the actual production coil, not a sample strip, to catch material feed variations. For more detailed die sourcing and process troubleshooting, visit MoldWorld (www.moldw.com) for a wide range of tooling suppliers and technical references.