Automotive stamping dies (for body panels, structural brackets, doors, hoods, fenders) follow a standard multi-stage workflow: engineering design → material preparation → machining → heat treatment → finishing → assembly → tryout & commissioning. Large panel draw dies mostly use alloy cast iron; cutting inserts use high-performance tool steel.
1. Process Design & Virtual Simulation
Analyze the stamped automotive part, sheet material (cold-rolled steel, aluminum), target tolerance and production volume.
Define stamping sequence: drawing, trimming, flanging, piercing, restriking.
Run FEA forming simulation (AutoForm, LS-DYNA) to predict wrinkling, splitting, springback. Engineers compensate die geometry in advance to offset springback.
Complete full 3D CAD die design: die base, punch, die cavity, blank holder, guide systems, nitrogen springs, ejectors. Release casting & machining drawings after internal review.
2. Raw Material Preparation
Large forming die bodies (draw dies for outer panels): Cast Mo–Cr alloy cast iron via sand casting. Castings undergo stress-relief annealing to eliminate casting internal stress.
Working inserts, trim punches, cutting edges: Tool steels such as Cr12MoV, SKD61 (H13), D2.
Standard components: Guide posts, bushings, springs, pins are sourced from certified suppliers.
3. Rough Machining
Rough removal of excess material using 3-axis CNC milling:
Machine casting/steel blanks close to near-net shape, leaving 0.3–1.0 mm stock for semi-finish & finish machining.
Drill preliminary holes for mounting and cooling channels.
Intermediate CMM inspection to avoid major dimensional errors.
4. Semi-Finish Machining & Heat Treatment
Semi-finish CNC machining of core surfaces.
Hardening & tempering for functional components:
Cast iron die surfaces: flame hardening / laser hardening (52–56 HRC)
Tool steel cutting inserts: vacuum quenching + tempering (58–62 HRC)
Heat treatment improves wear resistance and strength; it may cause minor distortion, so finish machining happens after hardening.
5. Precision Finishing Operations
5-axis CNC finish milling: Create complex free-form die faces for automotive outer panels, achieve smooth surface contour.
EDM (Sinker EDM / Wire EDM): Produce sharp internal corners, narrow slits, trim profiles unreachable by rotary cutters.
Surface grinding & hand polishing: Polish drawing die surfaces to low Ra value to prevent scratches on visible automotive panels.
Optional surface coating: Nitriding, PVD coating to extend die service life.
6. Die Assembly & Fitting
Fit all machined components: die shoe, punch, cavity inserts, guiding mechanism, stripping system. Toolmakers carefully adjust stamping clearances between punch and die (critical for clean trimming without burrs). Perform dry closing tests to check for collision or interference.
7. Tryout, Revision & Final Acceptance (Most time-consuming phase)
Mount die onto a stamping press for T0 first trial using production sheet metal.
Inspect stamped parts: check dimensions via CMM, surface defects, cracks, wrinkles, springback, burr height.
Modify die surfaces, adjust clearances, re-polish or rework inserts according to defective samples. Multiple rounds of tryout (T1, T2, T3) are common.
Once parts consistently meet OEM specifications, the die receives production approval.
8. Delivery
Clean the die, mark reference positions, prepare operation and maintenance documents, then ship to the automotive stamping plant.
