What is HPDC? High Pressure Die Casting Explained
What high pressure die casting (HPDC) is, how cold-chamber machines inject aluminium, how tonnage is chosen, and which parts suit HPDC — explained by a die caster.
By Sunmax Casting India Engineering TeamReviewed by [INSERT ENGINEER NAME, ROLE]6 min read
HPDC — high pressure die casting — is a process in which molten metal is injected at high velocity into a hardened steel die and held under high pressure while it solidifies. For aluminium, it is the most widely used casting process for thin-walled, high-volume components such as transmission housings, motor housings and electronic enclosures.
How HPDC differs from other casting processes
| Process | How metal enters the mould | Typical parts |
|---|---|---|
| HPDC | High-velocity injection, high pressure | Thin-walled housings, brackets, covers |
| Gravity die casting | Poured, fills by gravity | Thicker, heat-treatable parts |
| Low pressure die casting (LPDC) | Pushed up slowly from below | Wheels, structural parts |
| Sand casting | Poured into an expendable sand mould | Prototypes, large or low-volume parts |
The defining feature of HPDC is speed: the cavity fills in milliseconds, so metal reaches thin sections before it freezes. That is what makes 2–4 mm walls over large areas possible.
Hot chamber vs cold chamber
In hot-chamber machines, the injection system sits submerged in the molten metal — fast, but only suitable for low-melting alloys such as zinc. Molten aluminium would attack the submerged steel components, so aluminium uses cold-chamber machines: metal is ladled into a separate shot sleeve for each shot, and a hydraulic plunger drives it into the die.
The three phases of an HPDC shot
- First phase (slow): the plunger moves slowly to fill the sleeve and push air ahead of the metal, avoiding turbulence that traps gas.
- Second phase (fast): the plunger accelerates and the cavity fills at high gate velocity.
- Third phase (intensification): pressure is multiplied to compact the metal and feed shrinkage during solidification.
Tuning these phases — together with die temperature and venting — is how a die caster controls porosity.
How machine tonnage is chosen
The clamping force must be greater than the force generated by the metal pressure acting on the projected area of the casting plus runners and overflows. A larger projected area or higher intensification pressure needs a larger machine. That is why the same part may need a 350-tonne machine at one foundry and a 550-tonne machine at another, depending on gating and process pressure.
At our Chennai plant we run 250T and 350T cold-chamber machines — see the machinery page for specifications.
What parts suit HPDC?
HPDC is the best fit when a part has:
- thin walls and a large surface area,
- many cast-in features (ribs, bosses, holes),
- annual volumes in the thousands or more,
- a need for good as-cast surface finish and repeatable dimensions.
It is less suited to parts that need conventional solution heat treatment, very thick sections, or very low volumes.
Limitations to plan for
Because metal fills so fast, some air can be entrapped. Good gating and venting, controlled slow-shot speed and, where needed, vacuum assistance minimise this. Porosity acceptance levels should be agreed for critical zones, and parts that must be pressure-tight should be designed and tested accordingly.
Frequently asked questions
Is HPDC the same as pressure die casting?
Yes. In India and most of the industry, HPDC and pressure die casting (PDC) refer to the same process of injecting metal into a steel die under high pressure.
What is the difference between HPDC and LPDC?
HPDC injects metal at high speed and pressure for thin-walled parts and short cycles. Low pressure die casting (LPDC) fills the die slowly from below at low pressure, giving sounder, heat-treatable parts such as wheels, but with longer cycles.