die-casting

name	die-casting
description	Die casting — cold/hot chamber, shot parameters, injection velocity, intensification pressure, solidification, porosity defects, aluminum/zinc/magnesium alloys, die life, ASTM B85/B86, tolerance capabilities.
metadata	{"priority":7,"promptSignals":{"phrases":["die casting","high pressure die casting","HPDC","cold chamber die casting","aluminum die casting","die casting defects"],"minScore":3}}

Die Casting — Complete Skill

Process Overview

High-Pressure Die Casting (HPDC): molten metal injected at high velocity (20–80 m/s) into steel die under high pressure (40–200 MPa); solidifies rapidly (< 1 second); high production rate (50–600 shots/hr)

Cold Chamber vs. Hot Chamber

Cold chamber: metal ladled into shot sleeve; plunger injects → Al, Cu, Mg (high T alloys) Hot chamber (gooseneck): plunger submerged in molten metal; faster cycle → Zn, Pb, Sn (low T alloys; < 450°C)

Shot Parameters

Slow shot (first stage): v_slow = 0.1–0.5 m/s; fills sleeve with minimum turbulence; air pushed to overflow Slow shot distance: position plunger to just seal gate before switch to fast shot

Fast shot (second stage — filling): v_fast = 20–80 m/s at gate (Al: 30–60 m/s; Zn: 20–40 m/s; Mg: 40–80 m/s) Gate velocity: V_gate = V_plunger × (A_sleeve / A_gate_cross_section) Fill time: t_fill = V_cavity / (V_gate × A_gate) [< 0.1 s for most parts; thin walls = faster needed]

Intensification (third stage — pressure): Hydraulic intensification pressure: P_intensify = 40–120 MPa (on plunger) → equivalent die pressure Applied after metal solidifies at gate (timing critical: 10–50 ms after fill completion) Reduces porosity: P_int squeezes semi-solid region → pore collapse and feed

Plunger velocity optimization: Too slow: premature solidification; cold shuts; misruns Too fast: air entrapment (jetting); die erosion; flash

Solidification

Solidification time (Chvorinov's rule — approximate): t_s = C × (V/A)² [C = mold constant [s/m²]; V = volume; A = surface area] For HPDC: much faster than sand casting (chill die); t_s = 0.3–3 s for 2–4 mm wall

Die temperature: Aluminum: die temp 150–250°C (maintained by cooling channels + thermal equilibrium) Zinc: die temp 150–200°C Magnesium: die temp 180–250°C

Hot spot analysis: Sections with highest V/A ratio → last to solidify → shrinkage porosity if not fed Solution: overflow/runner to last-to-freeze location; intensification pressure

Alloy Properties

Aluminum Die Casting Alloys (ASTM B85)

Alloy	Si [%]	Tensile [MPa]	Yield [MPa]	Elongation [%]	Use
A380	8.5	310	165	3	General purpose; excellent castability
A383	10.5	310	150	3.5	Better flowability; less die soldering
A360	9.5	295	165	3.5	Better corrosion resistance
380.0	8.5	310	165	3	Automotive (same as A380)
A413	12	295	145	2.5	Highest fluidity; thin-wall

Zinc Die Casting Alloys (ASTM B86)

Alloy	Al [%]	Tensile [MPa]	Application
Zamak 3 (No.3)	4	282	General; highest ductility
Zamak 5 (No.5)	4+Cu	330	Higher strength; automotive
ZA-27	27	420	Highest strength zinc; bearings

Magnesium Alloys (ASTM B94)

Alloy	Tensile [MPa]	Notes
AZ91D	230	Most common; good castability
AM60B	220	Better ductility; automotive panels
AM50A	210	Best ductility; safety parts

Die Design

Draft angles: External: 1–3° (Al); 0.5–1° (Zn); 2–3° (Mg with thicker wall) Internal cores: 2–5° (higher than external; core pulls)

Gate design (fan gate typical for flat parts): Gate thickness: 1–3 mm (Al); thinner gate → higher gate velocity → better fill Gate area: A_gate = Q_fill / V_gate = V_cavity / (t_fill × V_gate) Runner: taper toward gate; area ≈ 2–3× gate area

Overflow wells: Located at end of flow paths (last-to-fill); collect first-in metal (coldest, most oxidized) Volume: 30–50% of part volume for complex parts; vent at overflow exit

Venting: Vent depth: 0.05–0.12 mm (thin enough to stop metal; allow gas to escape) Vent area: A_vent = 0.003 × A_gate (empirical minimum) Vacuum die casting: evacuate cavity before injection → lower gas porosity

Porosity Defects

Gas porosity: spherical pores from entrapped air or hydrogen; caused by turbulence, high moisture Prevention: slow shot optimization; vacuum; dry melting/holding

Shrinkage porosity: irregular voids at last-to-solidify zones; caused by insufficient feed Prevention: intensification pressure; gates at thickest sections; avoid isolated heavy sections

Cold shut: incomplete bonding where two flow fronts meet at low temperature Prevention: increase injection speed; higher metal/die temperature; better venting

Blisters (surface): subsurface gas expands on post-process heating (heat treating, painting) Prevention: lower gas content in melt; vacuum casting; avoid T6 heat treatment of gassy castings

Quality and Inspection

Density measurement: Archimedes method; ρ < ρ_theoretical → porosity Al A380: theoretical ρ = 2.71 g/cm³; actual ρ_meas < 2.68 → > 1% porosity → reject (fatigue-critical)

X-ray inspection: detects subsurface porosity; ASTM E505 (die casting radiographic standards) CT scanning: 3D porosity map; used for safety-critical automotive parts

Dimensional tolerance capability: Feature size [mm] → achievable tolerance: < 25 mm: ±0.10 mm; 25–100 mm: ±0.15–0.25 mm; > 100 mm: ±0.3–0.5 mm (Tighter possible with secondary machining)

Die casting surface finish: Ra 1.6–6.3 μm (as-cast); can achieve Ra 0.8 μm with polished die surface

Die Life

Al die casting: H13 tool steel; typically 80,000–150,000 shots (face erosion) Zn die casting: 300,000–1,000,000 shots (lower T) Mg die casting: 50,000–100,000 shots (aggressive alloy)

Die wear: soldering (Al sticks to die); erosion at gates; thermal fatigue cracks Prevention: nitriding die surface; PVD/CVD coatings (CrN, AlTiN); die lubricant release agent spray

Standards

Standard	Scope
ASTM B85	Aluminum alloy die castings
ASTM B86	Zinc alloy die castings
ASTM B94	Magnesium alloy die castings
ASTM E505	Radiographic standards for die castings
NADCA 201	Die casting product standards (NADCA)
ISO 8062	Casting tolerances — DCTG class

Output

Provide: alloy (ASTM grade), process (cold/hot chamber), part volume [cm³] and average wall thickness [mm], shot parameters (v_slow [m/s], v_fast [m/s], P_intensify [MPa]), gate velocity [m/s] and gate area [mm²], fill time [ms], solidification time [s], porosity risk (gas/shrinkage, location), die temperature [°C], draft angle [°], dimensional tolerance class (NADCA or DCTG), surface finish Ra [μm], estimated die life [shots], defect risk assessment (top 3), inspection method (X-ray/CT/density), and applicable standard (ASTM B85/B86/B94, NADCA 201).