Process
HPDC process parameters: shot phases, speeds, pressures and temperatures
The settings that decide whether an aluminium die casting is sound: slow shot, fast shot, intensification, metal and die temperatures, clamping force and what to monitor.
The three phases of an HPDC shot
Every high pressure die casting shot runs in three controlled phases. Getting each one right, and repeating it on every shot, is what separates a sound casting from a porous one.
| Phase | What happens | Typical setting | Why it matters |
|---|---|---|---|
| 1. Slow shot | The plunger moves slowly, filling the shot sleeve and pushing metal up to the gate | Plunger speed about 0.1 to 0.5 m/s, set so a wave forms without folding over | Too fast traps air in the sleeve; too slow lets metal cool and pre solidify |
| 2. Fast shot | The plunger accelerates and fills the cavity | Gate velocity about 30 to 60 m/s for aluminium; cavity fill time about 10 to 100 ms depending on wall thickness | Fills thin walls before they freeze and atomises metal for a good surface |
| 3. Intensification | Pressure is raised sharply once the cavity is full | Specific metal pressure about 400 to 1,000 bar, applied within milliseconds | Feeds shrinkage and compresses gas porosity while the metal is still mushy |
Metal and die temperatures
| Parameter | Typical range | Notes |
|---|---|---|
| Metal temperature, ADC12 and A380 type alloys | About 650 to 700 °C at the furnace | Lower in thick parts to reduce shrinkage, higher for thin walls |
| Die operating temperature | About 180 to 280 °C | Held with oil or water thermal control units and cooling lines |
| Die preheat before the first shot | About 150 to 200 °C | Prevents thermal shock cracking and cold first parts |
| Shot sleeve fill ratio | About 30 to 60% | Low fill ratios trap more air in the sleeve |
Sizing the machine: clamping force
The metal pressure acting on the projected area of the casting, runners and overflows tries to open the die. The machine's clamping force must exceed it with a margin.
Clamping force (kN) = projected area (cm²) × specific metal pressure (bar) ÷ 100 × safety factor (about 1.1 to 1.2)
Example: 400 cm² of projected area at 600 bar needs about 2,400 kN, or roughly 265 to 290 tonnes with margin, so a 280 t machine is marginal and a 500 t machine is safe. Shot weight, die size and tie bar spacing must also fit the machine.
Checking fill capability with a PQ² diagram
A PQ² diagram plots the machine's available metal pressure against flow rate squared, and the die's resistance through its gate. Where the two lines cross shows the gate velocity and fill time the combination can achieve. It is used at die design stage to choose gate area and plunger diameter before steel is cut.
What we monitor on every shot
- Plunger speed and position through slow shot, fast shot and intensification
- Intensification pressure and rise time
- Biscuit length, as a check on shot weight
- Die temperatures at key points, and spray time
- Metal temperature in the holding furnace
- Cycle time, and any shot outside its limits
At Alcast, process parameters are recorded for every shot and held within limits set during trials. That is how the thousandth part matches the first.
Values are typical published ranges for guidance. Every part is different: process windows are set and proven for each component through trials, and the governing standard and your drawing take precedence. Reviewed by the Alcast engineering team, November 2026.
Questions engineers ask
What gate velocity is used for aluminium HPDC?
Typically about 30 to 60 m/s. Thin walled parts and good surface finish need the higher end; thicker parts can run lower to reduce die erosion.
How is clamping force calculated for die casting?
Multiply the total projected area in cm² by the specific metal pressure in bar, divide by 100 to get kN, and add a safety factor of about 10 to 20%.
Why does slow shot speed matter?
The slow shot pushes metal up the sleeve as a single wave. Too fast and the wave folds over and traps air, which becomes porosity in the casting.
What is intensification pressure in HPDC?
A pressure boost applied in milliseconds after the cavity fills, typically 400 to 1,000 bar on the metal, to feed shrinkage and compress gas porosity.