Pressure die casting

Pressure die casting (PDC, also called high-pressure die casting) forces molten aluminium or zinc into a hardened steel die. It makes thin-walled, accurate parts with a good finish at high speed, so it suits parts you need in thousands, such as housings, covers, brackets and fittings.

A die casting machine injects the metal at high pressure; cold-chamber machines are used for aluminium and hot-chamber machines for zinc alloys such as Zamak 3 and Zamak 5. The machine's tonnage limits how big a part it can cast.

The die is a costly tool made from hot-work steel such as H13. After casting, parts are trimmed, then often fettled, shot blasted, machined and given a surface finish such as powder coating or plating.

Materials commonly used

• Aluminium die-casting alloys such as ADC12 and LM24
• LM6 where pressure tightness and good flow matter
• Zinc alloys: Zamak 3, Zamak 5 and Zamak 2
• Magnesium alloys such as AZ91D, from fewer workshops

What to send with your requirement

• A 3D model (STEP) and a drawing marking the machined faces, critical dimensions and tolerances
• The alloy, and whether it must be pressure tight or meet a standard
• The quantity per order and per year, which decides the die and the number of cavities
• Whether you already own a die, or one must be made
• The finish and machining you need after casting, and who arranges them

What affects the cost

• The die: its size, cavities, slides and steel; it is paid once and shared over the parts
• Part weight and the alloy used
• Machine tonnage needed for the projected area of the part
• Trimming, machining, impregnation for leak tightness, and surface finish
• Rejection allowance for porosity, and how parts are inspected

Common mistakes to avoid

• Choosing pressure die casting for a few hundred parts, where the die cost dominates; gravity or sand casting may suit better
• Designing thick, uneven walls, which cause porosity and sink marks
• Not marking which faces will be machined, so there is no machining allowance
• Not agreeing who owns the die and how many shots it is expected to last

Frequently asked questions

What quantity makes pressure die casting worth it?

It depends on the part and the die cost, but it is normally a process for repeat volumes in the thousands. For smaller quantities, ask a workshop to compare it with gravity die casting or sand casting.

Can die-cast parts be leak tight?

Die castings can have some internal porosity. For parts that must hold pressure, say so: the foundry can adjust the design, the alloy and the process, and many use vacuum impregnation to seal the pores.

Aluminium or zinc?

Zinc alloys such as Zamak cast very fine detail and thin walls, take plating well and are heavier. Aluminium is lighter and suits larger parts. The workshop can advise once it sees the part and its use.