Die Casting
When you need metal parts with complex geometry at volume — thin walls, fine details, minimal post-processing — die casting delivers what CNC and sheet metal cannot match on unit cost.
Die casting is a metal forming process where molten metal is forced under high pressure into a precision steel mold (called a die). The metal solidifies in seconds, the die opens, and a near-net-shape part is ejected. The same die can produce tens or hundreds of thousands of identical parts. Cost per unit drops dramatically with volume, making die casting the go-to for metal parts that need to be produced at scale.
For hardware founders, die casting sits between CNC machining and injection molding conceptually. Like injection molding, the die is a front-loaded cost that amortizes over volume. Like CNC, the output is metal. Die casting is the right choice when you need a metal part with complex geometry, thin walls, and a surface finish that does not require extensive post-machining — and your volume justifies the tooling.
Hot chamber die casting is used for low-melting-point metals — primarily zinc and magnesium alloys. The injection mechanism is submerged in the molten metal bath, so the metal stays hot and fluid throughout the shot. Cycle times are fast (15–30 seconds per shot) and the process handles thin walls and fine detail well. The downside: the submerged mechanism limits hot chamber to metals that will not attack the steel components.
Cold chamber die casting is used for aluminum alloys and higher-melting-point metals. Molten metal is ladled into a separate shot chamber, then a plunger forces it into the die. The metal is not in constant contact with the machine, so there is less chemical attack. Cycle times are slower (30–60 seconds) and the process is more thermally demanding on the die. Cold chamber is the dominant method for aluminum die casting — which is the most common die-cast material for consumer products.
The die itself is a complex, multi-part steel tool. It includes the cavity, cores, slides for undercuts, ejector pins, and a cooling system. Die life ranges from 50,000 to 300,000+ shots depending on material, part complexity, and maintenance. Aluminum alloys wear dies faster than zinc. A well-maintained zinc die can last 1 million shots. An aluminum die running abrasive alloys may need refurbishment after 50,000.
Common die-cast alloys: Zamak (zinc-aluminum) for consumer hardware, decorative parts, and anything that needs chrome plating. A380 aluminum for general-purpose structural parts — good strength, good castability. ADC12 (Japanese standard aluminum) is the most common in China — nearly identical to A380. Magnesium AZ91D for ultra-lightweight parts where grams matter.
Die casting design failures
Porosity
Tiny gas bubbles trapped in the metal as it solidifies create internal voids. Visible on machined surfaces, weakens the part, and prevents pressure-tight applications. Fix: proper venting, vacuum assist, and avoiding overly thick sections that trap gas.
Sharp corners and sudden wall thickness changes
Metal flows like a viscous liquid under pressure. Sharp internal corners cause turbulence and gas entrapment. Sudden thick-to-thin transitions create shrinkage porosity. Design with generous radii and gradual transitions.
Undercuts without planning for slides
Like injection molding, die cast parts must release from a two-part die. An undercut requires a side slide — a moving die component that retracts before ejection. Each slide adds $1,000–3,000 to die cost. Minimize undercuts or budget for slides.
Tight tolerances where the die splits
The parting line between die halves is never perfectly flush. A small witness line and slight mismatch are normal. Do not tolerance-critical features across the parting line.
Expecting injection-molding-level surface finish
Die-cast surfaces have a characteristic matte texture — not the glossy finish of a polished injection mold. If you need a premium finish, plan for powder coating, painting, or chrome plating as a secondary process.
What founders should remember
Die casting wins on cost at ~500–1,000+ units
A die-cast aluminum bracket at 1,000 units might cost $2–4 per part vs. $15–30 for CNC. The die costs $3,000–8,000, but the per-unit savings add up fast.
Zinc for details, aluminum for strength, magnesium for weight
Zinc fills fine details and plates beautifully. Aluminum gives you strength and heat resistance. Magnesium cuts weight by 35% vs. aluminum but costs more and requires special handling.
Design the part for die casting, not for CNC or molding
Die casting has its own design rules — draft angles (1–3 degrees), uniform wall thickness (1.5–4 mm), radiused corners. A part designed for CNC and sent to a die caster will cause problems.