| 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).
