| name | die-design |
| description | Die design — progressive stamping die, compound die, blanking/piercing clearance, bending springback, draw die design, tonnage calculation, tool steel selection, die life, ASTM A681/D2 tool steel standards. |
| metadata | {"priority":7,"promptSignals":{"phrases":["die design","progressive die","stamping die","blanking clearance","die tonnage","draw die"],"minScore":3}} |
Die Design — Complete Skill
Die Types
Blanking/Piercing die: cuts out shapes from sheet metal; punch shears through material
Progressive die: multiple stations in one die; strip feeds through; complete part per stroke
Compound die: blanking + piercing in one stroke; higher accuracy (±0.025 mm vs. ±0.1 mm progressive)
Draw die: forms sheet into cup/box shapes by deep drawing; punch forces metal through die ring
Transfer die: parts transferred between stations; complex 3D parts; slower than progressive
Blanking and Piercing
Clearance
Punch-die clearance (per side):
c = (0.02 to 0.10) × t_material [t = sheet thickness; higher for hard materials]
Clearance by material and thickness:
| Material | Clearance c/t |
|---|
| Low carbon steel | 5–8% |
| Stainless steel | 6–10% |
| Aluminum | 4–6% |
| Brass | 4–7% |
| High-strength steel (AHSS) | 8–14% |
Effect on cut quality:
Too small clearance: more burr; die wear; larger cutting force; no rollover
Too large clearance: excessive rollover; burr; poor surface quality; cracking instead of shearing
Blanking (punch smaller than blank; die is the blank OD):
Punch OD = Blank OD - 2c [die is basic size; punch is undersized]
Piercing (punch = hole ID; die is the blank):
Die ID = hole OD + 2c [punch is basic size; die is oversized]
Cutting Force
Shear force:
F = L_perimeter × t × τ_shear [N; τ_shear ≈ 0.6–0.8 × σ_UTS]
F = L × t × 0.7 × UTS [practical formula]
Staggered punches: shear angle on punch → reduce peak force (but not total energy)
F_staggered = F_max / (1 + shear/t) [shear angle cuts contact length]
Stripping force: F_strip = 0.02–0.10 × F_blank (depends on part complexity, lubricant)
Press tonnage:
T_press = F_blanking + F_piercing + F_stripping [tons or kN]
Add 20–30% safety margin; size press to 70–80% capacity
Bending
Springback
Springback: elastic recovery after bending; final angle > punch angle
Springback factor:
K_sb = θ_final/θ_punch ≈ 1 - σ_y/(E × R/t) × (1 - (σ_y/E × R/t)²) [Wang et al. approximation]
Springback angle:
Δθ = θ_punch - θ_part = 3 × σ_y × R / (E × t) × θ_punch / 90° [simplified linear]
For steel (σ_y = 350 MPa, E = 200 GPa, R/t = 4): Δθ ≈ 3 × 350/200,000 × 4 × θ/90 ≈ 2–5° typical
Springback compensation: overbend by Δθ; or bottom the punch (coining); or use bottoming die
Minimum bend radius:
r_min = t × f_m [f_m = minimum bend radius factor]
| Material | f_m (L/T grain) | f_m (across grain) |
|---|
| Aluminum 5052-H32 | 1.0 | 0.5 |
| Steel 1020 | 1.0 | 0.5 |
| 304 SS annealed | 1.0 | 0.5 |
| 4130 steel (annealed) | 1.5 | 1.0 |
| Ti-6Al-4V | 3.0 | 2.0 |
Bending Force (V-die)
Wipe (edge) bending:
F = k × σ_UTS × b × t² / (2L_die) [k = 0.33 for wipe; b = width; L_die = die opening]
V-bending:
F = (k × σ_UTS × b × t²) / (2 × W_v) [W_v = V-die opening width; k = 1.33 for sharp V]
Deep Drawing
Draw ratio (Limiting Draw Ratio LDR):
DR = D_blank / d_punch [LDR_max ≈ 2.0–2.2 for steel; 1.8–2.0 for stainless; 2.0–2.3 for aluminum]
Blank diameter:
For cup without flange: D_blank = √(d² + 4dh) [approximate; d = cup dia; h = cup height]
With flange: D_blank = √(d_f² + 4d × h - 3.44 × r_d × d) [r_d = die corner radius]
Drawing force:
F_draw = π × d_punch × t × σ_UTS × [DR - 0.7] [simplified; DR = blank/punch dia ratio]
Blank holder force:
F_BH = 0.005 × σ_UTS × A_blank_under_BH [A = area of flange under blankholder]
Too low → wrinkling; too high → tearing
Ironing (reduces wall thickness):
Reduction per pass: 30–50% (annealed); 15–25% (work-hardened)
Draw + iron: 3–6 ironing passes for beverage can (wall reduced from 0.25 to 0.10 mm)
Tool Steel Selection
For stamping dies (recommended by ASTM A681):
| Application | Tool steel | HRC | Notes |
|---|
| Light blanking (<1 mm) | D2 (high Cr) | 58–62 | High wear resistance |
| General piercing | D2, M2 | 58–62 | Good abrasion |
| Deep drawing dies | A2 | 58–60 | Less brittle than D2 |
| Progressive dies (high-volume) | M2 (HSS) or PM carbide | 60–64 | PM steel for >1M hits |
| Heavy blanking (>3 mm) | D2 + nitriding | 60–62 | Surface hardened |
| Inserts/punches (AHSS) | Powder metal (CPM) | 60–65 | High fatigue resistance |
D2 tool steel (ASTM A681):
Composition: 1.5% C, 12% Cr, 0.9% Mo, 0.9% V
Hardness: 58–62 HRC; very high wear resistance; brittle (no impact loading)
Heat treatment: harden at 1020–1040°C; temper 150–200°C; double temper recommended
Coatings for die surfaces:
TiN: general purpose; reduces adhesion/pickup; +30% die life
TiCN: better wear resistance than TiN; higher hardness (32 GPa vs. 25 GPa)
DLC: ultra-low friction; excellent for Al, Cu (non-ferrous stick to TiN)
CrN: better adhesion for stainless and AHSS; lower coating hardness but better toughness
Die Life
Die life (number of hits):
For D2 hardened, thin light-gauge steel: 500,000–2,000,000 hits (resharpen at 25–50% of this)
For AHSS (DP980, TRIP): 50,000–200,000 hits (abrasive + impact → short life)
PM carbide inserts at critical punches: 5–10× life improvement over D2
Resharpen frequency:
Grind punch and die faces when burr height > 10% of material thickness
Regrind depth: 0.05–0.15 mm per resharpen; total service life until scrapped ≈ 10–15 resharpen cycles
Progressive Die Strip Layout
Strip layout efficiency:
η = A_part / (A_pitch × n_up × N_rows) [A_part = blank area; A_pitch = pitch × strip width; n_up = parts per pitch]
Target: η > 70%; below 60% → redesign nesting orientation
Pilot holes: first station; holes for strip advancement accuracy
Station count: number of operations / operations per station (limited by press length and force)
Standards
| Standard | Scope |
|---|
| ASTM A681 | Tool steels |
| ISO 4957 | Tool steels specification |
| DIN EN 10083 | Tool steel designation (European) |
| ASTM E18 | Rockwell hardness testing |
| Machinery's Handbook | Reference for die clearances and forces |
| SME DICF | Die and stamping engineering handbook |
Output
Provide: die type (blanking/progressive/draw/compound), material (thickness [mm], UTS [MPa], σ_y [MPa]), punch-die clearance c [mm] per side and as %t, cutting force F [kN] and press tonnage required [tons], springback angle Δθ [°] and compensation method, minimum bend radius r_min [mm], blank diameter D_blank [mm] (drawing), draw ratio DR vs. LDR, blankholder force [kN], die steel (ASTM grade, HRC), coating (TiN/TiCN/DLC), estimated die life [hits], strip layout efficiency η [%], and applicable standard (ASTM A681, ISO 4957).
