die-design

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).