Die Casting
Also: high pressure die casting, HPDC, aluminum die casting, zinc die casting, zamak, magnesium die casting, pressure casting, die cast parts, diecasting
Die casting injects molten aluminum, zinc or magnesium into a steel die under high pressure: thin walls, fine detail and fast cycles behind a $20k-$200k tool.
150 shops tagged Die casting among 514 metal casting companies in the Noramark directory
Molten metal is forced into a hardened H13 steel die at 10-150 MPa (1,500-20,000 psi) and held under pressure until it freezes, then the die opens and ejector pins push the casting out; the cycle is 30-90 seconds for aluminum and faster for zinc. Zinc and magnesium run on hot-chamber machines with the injection system immersed in the melt; aluminum attacks steel and runs on cold-chamber machines where a ladle fills the shot sleeve each cycle. Dies last 100,000 or more shots in aluminum and a million or more in zinc.
The result is the most accurate and detailed cast part available in these alloys: walls of 1-3 mm (0.040-0.120") in aluminum and 0.5-1.5 mm in zinc, cast-in holes, bosses, ribs and lettering, a surface of 0.8-1.6 µm Ra (32-63 µin), and tolerances of ±0.1 mm (±0.004") on the first 25 mm. Parts come out needing only trim, deburr and, where fits matter, light machining. The alloys are casting alloys: A380, A383, A360 and ADC12 in aluminum (ASTM B85), Zamak 3, 5 and ZA-8 in zinc (ASTM B86), AZ91D in magnesium (ASTM B94).
The limits come from the pressure and speed. Air is trapped in the metal, so conventional die castings contain porosity: they are not welded, not heat treated to a T6 temper (the pores blister), not pressure-tight without impregnation, and machining can open pores. Vacuum, squeeze and semi-solid variants reduce this at a cost. Every undercut needs a slide in the die, every vertical face needs draft, and the die itself is a $20,000-200,000 investment that takes 8-16 weeks, so die casting is a volume process, from a few thousand parts a year in zinc to millions in aluminum.
At a glance
| Typical tolerances | Linear ±0.1 mm (±0.004") on the first 25 mm (1") in aluminum, adding ±0.025-0.05 mm (±0.001-0.002") for each further 25 mm; zinc holds about 30% tighter. Precision-class tolerances of ±0.05 mm (±0.002") on the first 25 mm with care and die tuning. Add ±0.1-0.2 mm (±0.004-0.008") across the parting line and ±0.13 mm (±0.005") for features formed by slides. Flatness 0.2 mm per 100 mm (0.008" per 4"). NADCA publishes the standard and precision tables. Machined features ±0.025 mm (±0.001"). |
|---|---|
| Size limits | Aluminum from about 10 g to 25 kg (0.4 oz to 55 lb) on 400-4,000 ton machines, with envelopes to about 1,000 x 700 mm (40 x 28") on the largest job-shop presses; structural and giga-casting presses of 6,000 tons and more cast 100 kg parts. Zinc from under 1 g to about 10 kg. Minimum walls 1.0-1.5 mm (0.040-0.060") over small areas in aluminum, 2-2.5 mm in general; 0.5-1 mm in zinc; 1-1.5 mm in magnesium. |
| Surface finish | As cast 0.8-1.6 µm Ra (32-63 µin), finer where the die is polished, with ejector-pin marks, parting-line flash and a gate witness on surfaces the drawing did not protect. Blasting and tumbling even the surface; chem film, powder coat, e-coat and paint are the usual aluminum finishes. Zinc takes chrome plating well. Anodizing A380 gives a dark, mottled gray because of the silicon; use A360 or a machined wrought part when cosmetic anodize is required. |
| Lead time | Dies 8-16 weeks (6-8 for simple single-cavity tools, 14-20 with slides and multiple cavities); samples 1-2 weeks after tryout, then PPAP if required. Production lots in days once the die is qualified. Bridge parts come from sand casting or machining. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
Die-casting alloys have no wrought equivalent. Aluminum A380 is the general-purpose grade (tensile about 320 MPa (46 ksi), yield 160 MPa (23 ksi), 3.5% elongation as cast), A383 for thin walls and complex fills, A360 and A413 for pressure tightness and corrosion, ADC12 in Asian-sourced parts. Zinc Zamak 3 (tensile 283 MPa (41 ksi)) and Zamak 5 for small precise parts and chrome plating; ZA-8 and ZA-27 for strength and bearings. Magnesium AZ91D and AM60 for the lightest housings. Brass and bronze are die cast in a few foundries. The buyer is usually choosing die-cast A380 over a machined 6061 or 6063 part or a molded plastic housing; the die itself is H13 tool steel.
What drives the cost
- The die: size, cavities, slides for undercuts, H13 steel, texturing, and the tool life the volume demands
- Annual volume and lot size, which the die and the setup are amortized across
- Part weight and alloy: aluminum is cheap, zinc heavier per part, magnesium costlier
- Wall thickness and complexity, which set cycle time and scrap
- Secondary machining, tapping and trimming
- Finish: chem film, powder coat, plating, and the cosmetic class of each surface
- Porosity requirements: vacuum die casting, impregnation, radiographic inspection
When to use it
- Housings, enclosures, heat sinks, brackets, handles and covers in aluminum, zinc or magnesium at 5,000 to millions a year
- Thin walls, cast-in bosses and ribs, and fine detail that would be expensive to machine
- EMI and RF housings, automotive and electrical hardware, consumer products
- Small precise zinc parts that need chrome plating or high detail
- Replacing a machined 6061 housing whose volume has grown past the die cost
When not to
- Under about 2,000 parts a year: sand or investment casting, machining, or a molded plastic housing
- Fatigue- and pressure-critical structural parts, unless vacuum or squeeze cast and qualified
- Parts that must be welded, heat treated to T6, or anodized cosmetically
- Steel, stainless or superalloy parts: investment casting
- Large, thick or heavy parts where porosity and die cost run away
Design tips
- Keep walls uniform at 2-3 mm (0.080-0.120") in aluminum, and use ribs, not thickness, for stiffness; thick bosses shrink and hold porosity.
- Draft every face: 1-2° outside, 2-3° on inside walls and cores, more with texture.
- Fillet every junction with 0.5-1 mm (0.020-0.040") radii or more; sharp corners crack the die and the part.
- Avoid undercuts, or expect a slide at $5,000-15,000 each; reorient features to the die-open direction.
- Cast holes with draft and a minimum diameter of about 2.5 mm (0.100"); machine the fits and tap the threads after casting.
- Mark the cosmetic surfaces and let the foundry put gates, ejector pins, vents and the parting line elsewhere.
- Specify the alloy by ASTM spec (B85 A380, B86 Zamak 3, B94 AZ91D), the porosity acceptance (ASTM E505 reference radiographs), impregnation if pressure-tight, and NADCA tolerance class.
- Leave 0.5-1 mm (0.020-0.040") of machining stock on fits and keep machined surfaces out of the last-to-fill areas where porosity concentrates.
Frequently asked questions
- How much does a die casting mold cost?
- Single-cavity aluminum dies for small housings start around $20,000-40,000; larger dies with slides, multiple cavities and cooling run $75,000-200,000 and beyond. Zinc dies for small parts are cheaper and last longer. Trim dies, fixtures and PPAP are quoted on top. The buyer normally owns the die and the foundry maintains it.
- What is the minimum quantity for die casting?
- The die has to pay off against the savings over machining or sand casting. A part that costs $30 machined and $4 die cast pays off a $40,000 die at about 1,500 pieces; most foundries look for 5,000 or more a year in aluminum and a few thousand in zinc. Below that, machine, sand cast or investment cast.
- Aluminum vs zinc die casting?
- Aluminum (A380) is lighter, stiffer at temperature and cheaper per part in larger housings; zinc (Zamak 3 and 5) is heavier and lower melting, casts thinner walls with finer detail and tighter tolerances, runs on faster hot-chamber machines, gives longer die life and plates well with chrome. Small precise parts and plated hardware go zinc; enclosures and heat sinks go aluminum.
- Can die cast aluminum be welded?
- Not reliably. The gas trapped in a conventional die casting boils out under the arc and leaves porous, weak welds; the same porosity blisters under solution heat treatment. Vacuum-die-cast and squeeze-cast parts in alloys such as A356 and Silafont can be welded and heat treated, but they must be specified that way from the start.
- Can die cast aluminum be anodized?
- For corrosion protection, yes; for appearance, poorly. The 8-12% silicon in A380 does not anodize and leaves the film dark gray, mottled and thin, and any porosity shows. Chem film, powder coat and e-coat are the usual finishes; if a clear or colored anodize is required, use a low-silicon alloy or a machined wrought part.
