Aluminum high-pressure die casting

Aluminum high-pressure die casting (HPDC) involves forcing molten aluminum alloy into a steel die under high pressure in a very short time, usually a fraction of a second. The metal solidifies under pressure, so the casting reproduces the die faithfully: thin walls, accurate dimensions and a smooth surface.

How a Cold-Chamber Machine Works

Aluminum is die cast on cold-chamber machines. The shot sleeve is not immersed in molten metal – a portion of alloy is ladled into it from a furnace standing next to the machine, and a plunger then forces it into the die. Hot-chamber machines are suitable only for lower-melting-point alloys such as zinc, because molten aluminum would destroy the components immersed in it.

Injection Phases

1. Dosing – a measured portion of alloy is poured into the shot sleeve.
2. Slow phase – the plunger slowly pushes the metal up to the gate so that no air is trapped in it.
3. Fast phase – the metal fills the die cavity in several dozen milliseconds, at a gate velocity on the order of several dozen meters per second.
4. Intensification – once the die is filled, the metal pressure rises to several hundred bar; intensification reduces shrinkage porosity during solidification.
5. Die Opening and Casting Ejection – ejector pins remove the casting, and the die is sprayed with a release agent before the next cycle.

These are indicative values – actual parameters are set for the specific casting and machine.

What Determines Die Casting Quality

• Die Temperature – the die is preheated before production and held at the set temperature by heating-cooling units and cooling channels. A die that is too cold causes misruns; one that is too hot causes the alloy to stick.
• Gating System and Venting – these are designed together with the die, often with fill simulation, so that the metal flows evenly and the air has somewhere to escape.
• Alloy – high-pressure die casting mainly uses alloys with silicon and copper: EN AC-46200, EN AC-46500 and near-eutectic EN AC-47100.
• Vacuum – in vacuum-assisted casting, air is evacuated from the cavity before injection, which reduces casting porosity.

Limitations of High-Pressure Die Casting

A die casting die is expensive, so the method pays off for large production runs. Small gas pores may remain in the casting, which is why conventional die castings are usually not solution heat treated or welded – on heating, the gas would form blisters. When higher strength is required, artificial aging alone (T5 temper) or another technology is used, e.g. permanent mold casting.

Aluminum High-Pressure Die Casting in Our Foundry in Poznań

We design die casting dies in CAD/CAM systems with fill simulation and machine them on our own CNC machines. Castings are produced on an automated line, and dimensional tolerances often reach ±0.1 mm. Details of how production is organized can be found on the page high-pressure die casting foundry, and the full scope of the service is in the offer high-pressure die casting.

See also: die casting – how this method works, aluminum die castings – applications i aluminum casting alloys.