Quick Answer
Die casting process — high pressure die casting (HPDC) injects molten metal into a precision steel die at 1,000–10,000+ bar pressure, producing high-volume aluminum and zinc parts with excellent dimensional accuracy and surface finish. The process: close die → inject metal → cool → open die → eject part. Cycle time is 2–10 seconds, making it ideal for 10,000+ parts per year.
How High Pressure Die Casting Works
The die casting process has five stages:
- Die close: Two steel die halves close under hydraulic pressure (typically 300–1,500 tonnes)
- Metal injection: Molten metal (aluminum 600–700°C, zinc 380–420°C) is injected at 1,000–10,000 bar through a narrow gate into the die cavity at high speed (30–60 m/s)
- Solidification: Metal cools and solidifies inside the die; cooling is accelerated by internal die cooling channels
- Die open: Die halves separate after solidification
- Ejection: Ejector pins push the part out of the die; cycle repeats
Die Casting Process Parameters
| Parameter | Aluminum HPDC | Zinc HPDC | Notes |
|---|---|---|---|
| Metal temperature | 600–700°C | 380–420°C | Optimized for fluidity |
| Injection pressure | 30–100 MPa (300–1,000 bar) | 10–40 MPa (100–400 bar) | Higher for thin walls |
| Injection speed | 30–60 m/s | 10–30 m/s | Fast fill critical for thin walls |
| Die temperature | 150–300°C | 100–200°C | Controlled by cooling channels |
| Cycle time | 3–10 seconds | 2–5 seconds | Varies by part size |
| Die life (shots) | 100,000–500,000 | 200,000–1,000,000 | Depends on material and design |
Aluminum vs Zinc Die Casting
| Factor | Aluminum Die Casting | Zinc Die Casting |
|---|---|---|
| Density | 2.7 g/cm³ (light) | 6.7 g/cm³ (heavy) |
| Melting point | 660°C | 420°C |
| Tensile strength | 220–330 MPa | 300–400 MPa |
| Minimum wall | 0.8–1.5 mm | 0.3–0.8 mm |
| Tolerance | ±0.1–0.25 mm | ±0.05–0.15 mm |
| Surface finish | Ra 0.8–3.2 µm | Ra 0.4–1.6 µm |
| Max practical size | 20 kg | 2–5 kg |
| Tooling cost | $30,000–$150,000 | $15,000–$80,000 |
| Material cost | $/kg (lower) | $$/kg (higher) |
Die Casting Tolerances and Surface Finish
Typical Tolerances
Die casting achieves tighter tolerances than sand or investment casting:
| Dimension Type | HPDC Tolerance | Notes |
|---|---|---|
| Standard dimensions | ±0.1–0.25 mm per 100 mm | Much better than sand casting |
| Best achievable | ±0.05 mm per 100 mm | Requires precision tooling |
| Wall thickness | ±0.1–0.15 mm | Can hold tight wall uniformity |
| Flatness | 0.05–0.1 mm per 100 mm | Excellent as-cast flatness |
Surface Finish
Die casting produces smooth as-cast surfaces:
- As-cast: Ra 0.8–3.2 µm (excellent)
- After polishing: Ra 0.2–0.4 µm (mirror-like)
- Note: The gate area has rougher surface (Ra 3.2–6.3 µm); mark gate location away from appearance surfaces
Porosity in Die Casting
The biggest challenge in die casting is porosity (internal gas pockets from high-pressure injection):
Sources of Porosity
- Gas entrapment: Air or gas trapped during fast injection
- Shrinkage: Solidification shrinkage in thick sections
- Die lubrication: Excess lubricant creates gas
Solutions for Porosity
| Method | How It Works | Cost | Best For |
|---|---|---|---|
| Vacuum-assisted (VAD) | Vacuum removes gas during injection | +20–40% | Pressure-tight parts |
| Squeeze casting | High pressure applied during solidification | +30–50% | Structural parts |
| Semi-solid casting | Metal injected in semi-solid state | +20–40% | Thick sections |
| Improved gating design | Better gate location reduces gas entrapment | Design change | All parts |
Warning: Standard HPDC is not pressure-tight without vacuum or squeeze casting. If your part must hold pressure (hydraulic, pneumatic), specify vacuum-assisted or squeeze casting, or use gravity die casting.
Die Casting Design Rules
- Minimum wall thickness: 0.8–1.5 mm for aluminum, 0.3–0.8 mm for zinc
- Draft angle: 0.5–1° minimum on external, 1–2° on internal
- Uniform wall thickness: Avoid 3:1+ transitions; use graduated transitions
- Fillets: Minimum 0.5 mm internal radius; larger is better
- bosses: Reinforce around holes to prevent sink marks
- Gate location: Place where surface finish is least critical
Die Casting vs Other Processes
| Factor | HPDC | Gravity Die | Investment | Sand |
|---|---|---|---|---|
| Volume | 10,000+/year | 500–10,000/year | 50–5,000/year | 10–500/year |
| Tooling | $50,000+ | $10,000–$50,000 | $5,000–$30,000 | $500–$15,000 |
| Surface | Best (Ra 0.8–3.2) | Good (Ra 3.2–12.5) | Good (Ra 3.2–6.3) | Rough (Ra 12.5–25) |
| Porosity | Higher (needs VAD) | Low | Low | Low |
| Size range | Up to 20 kg | Up to 100 kg | Up to 50 kg | Unlimited |
Before finalizing the sourcing decision, many OEM buyers also compare Aluminum Casting Buyer Guide, Gravity Casting vs HPDC, Casting Tolerances, and Surface Finish Guide to clarify process fit, cost trade-offs, tolerance expectations, and supplier risk.
If you need application-specific guidance, drawing review, or a quotation, you can Contact YCUMETAL.
Buyer Checklist
- Is HPDC the right volume for your application (10,000+/year)?
- Does your part need pressure-tightness? If yes, specify vacuum-assisted or squeeze casting
- Is the minimum wall thickness achievable (0.8–1.5 mm for aluminum)?
- Have you specified surface finish requirements and gate location?
- Who owns the die? Can you transfer it?
- What is the die life guarantee? Who pays for die maintenance?
- Does the quotation include tooling amortization or separate line item?
FAQ
Can die casting produce pressure-tight parts?
Standard HPDC has inherent porosity from gas entrapment and cannot reliably hold pressure without leakage. For pressure-tight parts, specify vacuum-assisted die casting (VAD) or squeeze casting. Gravity die casting is another option for pressure-tight aluminum parts.
What is the difference between hot chamber and cold chamber die casting?
Hot chamber: Metal is held in a furnace integrated with the machine; used for zinc, magnesium, and low-melting-point alloys. Cold chamber: Metal is ladled into the machine from an external furnace; used for aluminum, copper, and high-melting-point alloys. Most aluminum die casting is cold chamber.