Die casting forces molten metal into a hardened steel mold (the die) under pressures of 1,500 to 30,000 psi, then ejects a near-net-shape part in seconds. Unlike sand or investment casting, the die is permanent and reusable — which is why die casting dominates when you need millions of identical parts with tight tolerances and good surface finish straight off the machine.

Two main flavors:

• Hot-chamber die casting: The injection mechanism sits submerged in the molten metal pool. Fast cycle times (under 1 second for small parts), but only works with low-melting-point alloys — zinc, magnesium, lead — because iron components would dissolve in hotter melts.
• Cold-chamber die casting: Molten metal is ladled into a separate injection sleeve for each shot. Slower (5–15 second cycles), but handles aluminum, brass, and high-temp magnesium. Aluminum specifically would attack a hot-chamber's steel plunger.

Real-world example: Your laptop's chassis, the housing on an automotive transmission, GoPro camera bodies, and Stanley socket wrench heads are all aluminum cold-chamber die castings. A modern engine block can have 60+ cored passages cast in a single shot — drilling those holes would take hours.

Why it dominates at scale: Tooling is brutally expensive ($50K–$500K+ for a production die), but per-part cost drops to cents at volume. Crossover vs. machining usually happens around 10,000–50,000 parts. Below that, machine from billet. Above it, die cast.

The tradeoffs nobody mentions in the brochure:

• Porosity: Trapped air during high-velocity fill creates internal voids. Die-cast parts generally can't be heat-treated (voids expand and blister) and shouldn't be welded for the same reason.
• Draft angles required: Every surface parallel to the pull direction needs 1–3° draft to release from the die. Designers who forget this get parts that won't eject.
• Wall thickness: Keep walls uniform — typically 1.5–4 mm. Thick sections shrink, sink, and form porosity at the center.

Rule of thumb for cycle time: Cycle time ≈ part wall thickness in mm × 2 seconds for aluminum. A 3 mm wall part runs about a 6-second cycle, meaning ~600 parts/hour per machine — which is why a single cell can supply an entire car program.

Tolerance capability lands around ±0.1 mm for the first 25 mm of any dimension, plus ±0.025 mm per additional 25 mm. Tighter than that? Plan for secondary machining on critical features.