High pressure die casting is the process of injecting molten aluminum into a hardened steel die at 40 to 100 MPa and gate velocities of 30 to 50 m/s, then holding intensification pressure until the casting solidifies. CharMax Precision runs cold chamber HPDC cells from 160 to 1,250 tons of clamping force for aluminum parts weighing 20 g to 12 kg.
High pressure die casting is the process of injecting molten aluminum into a hardened steel die at 40 to 100 MPa and gate velocities of 30 to 50 m/s, then holding intensification pressure until the casting solidifies. CharMax Precision runs cold chamber HPDC cells from 160 to 1,250 tons of clamping force for aluminum parts weighing 20 g to 12 kg.
Aluminum can only be cast on cold chamber machines. Molten aluminum dissolves iron on contact, so the injection system is kept out of the melt and charged one shot at a time. That single equipment constraint sets everything downstream: dose control, shot sleeve fill fraction, the speed at which the plunger may accelerate, and the reason aluminum cycles run longer than zinc.
The engineering work on an HPDC program is choosing machine tonnage from projected area, tuning the three phases of the shot, balancing die temperature so solidification is even, and deciding cavity count against annual demand. Those four decisions determine porosity level, dimensional stability and piece price far more than the alloy choice does.
| Machine type | Horizontal cold chamber HPDC |
|---|---|
| Clamping force | 160 to 1,250 tons (1.6 to 12.3 MN) |
| Injection pressure | 40 to 100 MPa (5,800 to 14,500 psi) |
| Gate velocity | 30 to 50 m/s |
| Slow shot plunger speed | 0.15 to 0.4 m/s |
| Fast shot plunger speed | 2 to 5 m/s |
| Cavity fill time | 20 to 100 ms |
| Melt temperature | 660 to 700 °C |
| Die temperature | 180 to 280 °C |
| Vacuum level with assist | 50 to 150 mbar absolute |
| Cycle time | 30 to 90 s depending on section thickness |
| Tool life | 80,000 to 150,000 shots |
Die casting machines come in two families, and the choice is made by the metal rather than by the part. In a hot chamber machine the injection system sits inside the melt: a gooseneck and plunger are permanently submerged, so each shot is drawn and fired without any transfer step. In a cold chamber machine the furnace is separate, a measured dose is ladled into a horizontal shot sleeve, and the plunger fires that dose before the next one is poured.
Aluminum has to run cold chamber because molten aluminum at 660 to 700 °C dissolves iron. A submerged steel gooseneck would erode within days, and the iron it gave up would push the melt past the 1.3% Fe ceiling of A380, embrittling the alloy and changing how it solders to the die. Keeping the steel out of the bath is not a preference, it is the only way to hold alloy chemistry.
The consequence is that a cold chamber shot has a short window. Metal starts losing heat the moment it hits the sleeve, so dose weight, sleeve temperature and the delay between pour and shot all become process variables that a hot chamber machine simply does not have. This is why aluminum cycles sit at 30 to 90 seconds while zinc runs at 5 to 30.
| Attribute | Cold chamber | Hot chamber |
|---|---|---|
| Alloys | Aluminum, brass, some magnesium | Zinc, magnesium, lead, tin |
| Injection system | Separate furnace, dose ladled per shot | Gooseneck submerged in the melt |
| Melt temperature | 660-700 °C for aluminum | 400-430 °C for zinc |
| Injection pressure | 40-100 MPa | 10-40 MPa |
| Cycle time | 30-90 s | 5-30 s |
| Metal heat loss before injection | Significant, in the shot sleeve | None, metal stays at temperature |
| Why aluminum cannot use the other | Not applicable | Molten aluminum dissolves the steel gooseneck |
| Typical clamping range | 160-4,000 tons | 20-400 tons |
Every machine in our plant is cold chamber. If a supplier offers hot chamber aluminum die casting, they are describing something that does not exist in production practice.
Clamping force has to exceed the force trying to push the two die halves apart during injection. That separating force is simply the projected area of everything on the parting plane multiplied by the pressure acting on it. Projected area means the shadow of the part, the runner, the biscuit and every overflow, not the part alone, and on a small casting the runner system can add 25 to 40% to the number.
Worked example. A gearbox cover measures 180 by 120 mm, giving 21,600 mm² of part projected area. Its runner, biscuit and overflows add roughly 27%, so total projected area is about 27,500 mm². The program calls for 70 MPa intensification pressure, so separating force is 27,500 mm² × 70 N/mm² = 1,925,000 N, or 196 tonnes. Adding a 25% margin for pressure spikes and die wear gives 245 tonnes required, so the part is scheduled on the 280 ton cell rather than the 400.
The margin matters. Running a die at 95% of rated clamping force produces flash on the parting line, drives the die apart at the far corners, and shortens tool life because the parting faces batter each other every shot. We size to roughly 75 to 80% of rated force and keep the remainder as headroom for the process window.
| Machine size | Max total projected area | Typical part weight | Example parts |
|---|---|---|---|
| 160 tons | 180 cm² | 20-300 g | Connector shells, sensor housings, small brackets |
| 280 tons | 310 cm² | 0.1-0.8 kg | Motor end caps, compact LED heat sinks |
| 400 tons | 450 cm² | 0.3-1.5 kg | Pump covers, instrument enclosures |
| 500 tons | 560 cm² | 0.5-2.5 kg | Gearbox housings, robot joint covers |
| 630 tons | 700 cm² | 1-4 kg | Motor housings, valve bodies |
| 800 tons | 900 cm² | 2-6 kg | Large sealed enclosures, structural brackets |
| 1,000 tons | 1,120 cm² | 3-9 kg | Machine frames, large finned heat sinks |
| 1,250 tons | 1,400 cm² | 4-12 kg | Large structural housings and covers |
Figures assume 70 MPa intensification pressure and a 25% clamping margin. High-integrity and thin-wall parts run at higher pressure, so the same footprint may need the next machine up. Send a model and we will calculate projected area from the actual parting plane.
A die casting shot is not one movement. The plunger runs a programmed velocity profile with three distinct phases, and almost every gas porosity problem traces back to one of them being wrong. We log the position, velocity and pressure curve of every shot, which is what makes a drifting result diagnosable rather than a guess.
The plunger moves at 0.15 to 0.4 m/s to seal the pour hole and push metal along the sleeve to the gate. The goal is to advance the metal as a rolling wave that keeps air ahead of it. Accelerate too fast and the wave breaks and folds air into the melt; too slow and the metal loses heat and starts freezing in the sleeve.
At the switch point, usually just as metal reaches the gate, the plunger accelerates to 2 to 5 m/s. Metal passes the gate at 30 to 50 m/s and fills the cavity in 20 to 100 milliseconds. Fill has to complete before the leading edge drops below the coherency temperature, which is what gate area and gate velocity are calculated to guarantee.
Once the cavity is full, hydraulic pressure is boosted to 60 to 100 MPa within 10 to 30 milliseconds and held for 2 to 5 seconds. This feeds solidification shrinkage through the still-liquid gate and compresses whatever gas was entrained into much smaller pores. Intensification is the single most effective control over shrinkage porosity.
The dose should fill 40 to 60% of the shot sleeve volume. Below 40% the slow shot has to accelerate a shallow wave that folds air; above 60% dose accuracy becomes hard to hold and the biscuit runs heavy. Fill fraction is set at the quoting stage by matching part weight to sleeve diameter.
The biscuit is the slug of metal left in the sleeve, held at 15 to 25 mm. It is the hydraulic path through which intensification pressure reaches the casting. A biscuit that is too thin freezes first and disconnects the pressure before the part has finished shrinking.
The changeover from slow to fast is set in millimetres of plunger position and is the most sensitive parameter on the machine. Switching early sprays metal into the cavity ahead of the wave; switching late compresses air against the gate. We establish it during T1 and lock it into the process sheet.
Even a perfectly tuned shot pushes the air that was in the cavity somewhere. Conventional dies vent it through overflows and vent lands, but at 20 to 100 millisecond fill times the vents cannot clear everything and a residue of compressed air ends up inside the casting. Vacuum assist attacks the problem at source by evacuating the cavity to 50 to 150 mbar absolute before the fast shot begins.
The benefit is measurable: gas content typically drops from around 15 to 25 cm³ per 100 g in a conventional casting to below 5 cm³ per 100 g with vacuum. That is the threshold at which a die casting can be heat treated without blistering, welded without porous seams, or machined deeply into an area that has to stay pressure tight.
Vacuum is not free. It requires a vacuum valve or chill block designed into the die, a sealed parting line, and a maintenance routine to keep the valve from clogging with metal and release agent. It adds 2 to 4 seconds to the cycle and roughly 8 to 15% to tooling cost. We recommend it where the drawing calls for pressure tightness, deep machining, welding or heat treatment, and we recommend against it where standard porosity levels would pass.
A die casting die is a heat exchanger that happens to have a part shape in it. Every shot dumps roughly 600 kJ per kilogram of aluminum into the steel, and the die has to move that heat out at exactly the right rate: too fast and thin sections freeze before they fill, too slow and the part cannot be ejected without distorting while the die surface starts soldering.
We hold die surface temperature between 180 and 280 °C using cooling channels of 8 to 12 mm diameter drilled 10 to 15 mm from the cavity surface, with jet cooling or bubblers inside cores and bosses that no straight-drilled line can reach. Channel layout is set during the simulation stage rather than added after the first thermal problem appears. Die temperature is checked with a thermal camera at start-up and after any process change.
Cycle time is where thermal design turns into money. Solidification and die spray together account for roughly 55 to 65% of a typical cycle, so those are the two stages worth engineering. Shaving three seconds off each on the example below lifts output from about 100 to 112 shots per hour from the same machine, the same operator and the same overhead.
| Stage | Typical duration | What controls it |
|---|---|---|
| Ladle and pour into shot sleeve | 3-5 s | Dose weight and ladle travel distance |
| Slow shot | 0.6-1.2 s | Sleeve fill fraction and acceleration profile |
| Fast shot, cavity fill | 0.02-0.10 s | Gate area and gate velocity |
| Intensification and pressure dwell | 2-5 s | Wall thickness and gate freeze time |
| Solidification before die open | 8-18 s | Heaviest section and cooling channel layout |
| Die open, eject, part extraction | 4-7 s | Ejector stroke and extractor cycle |
| Die spray and air blow-off | 4-8 s | Die temperature and release agent volume |
| Die close and lock-up | 2-3 s | Machine size and platen travel |
Total cycle for this part class is 30 to 50 s, giving 72 to 120 shots per hour. Cycle time appears directly in piece price as machine hourly rate divided by parts per hour, so a 10% cycle reduction is roughly a 10% saving on the casting portion of the cost.
Cavity count is an arithmetic decision before it is an engineering one. Required machine hours equal annual volume multiplied by cycle time, divided by 3,600, cavity count and process yield. A cell running two shifts delivers roughly 5,000 to 6,000 productive hours per year, and that number is the constraint.
At 120,000 parts per year on a 40 second cycle at 97% yield, a single cavity needs 1,374 machine hours. There is no case for a second cavity: the tool costs 60 to 80% more and the machine has capacity to spare. At 500,000 parts per year the same single-cavity tool needs 5,727 hours, which consumes an entire cell, so two cavities at 2,864 hours each becomes the obvious answer.
Two things temper the arithmetic. Doubling cavities does not halve cycle time, because twice the metal has to solidify, so expect cycle to rise 10 to 20% per doubling. And doubling cavities roughly doubles projected area, which usually moves the job onto a larger and more expensive machine. The net saving from going multi-cavity is real but is typically 15 to 30% on the casting cost rather than 50%.
Brackets, covers, motor housings and thermal plates where weight, volume and repeatability all matter. Programs run under PPAP discipline with documented process parameters and capability studies on the features you designate as critical.
Joint housings, arm segments and gearbox cases that need high stiffness-to-weight and precise machined datums. These programs are often 2,000 to 20,000 parts per year, which sits comfortably in single-cavity tooling.
Pump bodies, valve housings and gearbox cases up to 12 kg, usually with a pressure tightness requirement that drives A360 alloy, vacuum assist or both, and finishes with a leak test on every unit.
Thin-wall chassis and frames at 1.0 to 1.5 mm, where ADC12 and short flow paths are the enabling combination and the casting provides EMI shielding that a plastic housing cannot.
Finned heat sinks where the fin geometry would take hours to machine and seconds to cast. A360 and A413 are specified for their 113 to 121 W/m·K thermal conductivity.
Instrument housings and imaging frames with full lot traceability, documented first article inspection and finishes that survive repeated cleaning with hospital disinfectants.
These are the HPDC-specific decisions made during die design rather than part design. They do not change the shape of your part, but they decide whether it fills cleanly, where the porosity ends up, and how long the tool lasts. We resolve all of them in the DFM report before quoting tooling.
The equipment, controls and finished-part evidence used to deliver this operation in production.
Real parts we have manufactured that involved this capability.
A European industrial pump manufacturer converted a billet-machined housing to A360 die casting to reach 8,000 units a year, holding 6 bar pressure tightness, an H7 bearing bore and a 0.05 mm sealing face.
A collaborative robot manufacturer moved a joint housing from machined prototypes to ADC12 die casting at 12,000 units a year, cutting 180 g per joint while holding ±0.02 mm concentricity between the harmonic drive seat and the encoder bore.
An LED lighting brand replaced a bonded two-piece design, an extruded heat sink adhered to a die cast housing, with a single A413 casting, removing the thermal interface and taking 11 °C off the LED junction temperature at 60,000 units a year.
Cold chamber machines keep the injection system outside the melt and ladle one measured dose into the shot sleeve per cycle, while hot chamber machines have a gooseneck permanently submerged in the molten metal. Aluminum must use cold chamber because molten aluminum at 660 to 700 °C dissolves iron and would erode a submerged steel gooseneck within days, contaminating the alloy past its iron specification. Hot chamber is used for zinc and some magnesium, where lower melt temperatures do not attack the steel.
Required tonnage equals total projected area on the parting plane multiplied by intensification pressure, plus a 25% margin. Projected area includes the part, runner, biscuit and overflows, which typically add 25 to 40% to the part alone. A 180 by 120 mm part at 70 MPa works out to roughly 245 tonnes required, so it runs on our 280 ton cell. Send a 3D model and we will calculate it from your actual parting plane rather than estimating from the bounding box.
Injection pressure runs between 40 and 100 MPa, with 60 to 80 MPa covering most aluminum parts. Thin-wall parts below 2 mm and high-integrity castings sit at the top of that band, while thick-section structural parts fill adequately at the bottom. Pressure is applied in two stages: the fast shot fills the cavity in 20 to 100 milliseconds, then intensification boosts pressure within 10 to 30 milliseconds and holds it for 2 to 5 seconds to feed shrinkage.
You need vacuum if the part must be pressure tight above about 2 bar, heat treated, welded, or machined more than 1 mm below the as-cast skin on a sealing surface. Vacuum evacuates the cavity to 50 to 150 mbar before the fast shot and typically cuts gas content from 15 to 25 cm³ per 100 g down to under 5. It adds 2 to 4 seconds of cycle time and 8 to 15% to tooling cost, so for brackets, covers and unsealed housings we normally advise against it.
Cycle time runs 30 to 90 seconds depending on section thickness, part weight and cavity count. A 1.2 kg housing on a 630 ton cell typically cycles in 30 to 50 seconds, giving 72 to 120 shots per hour. Solidification and die spray together consume 55 to 65% of the cycle, so those two stages are where cycle reduction work pays off. Cycle time enters piece price directly as machine hourly rate divided by parts per hour.
Porosity is controlled at three stages: melt preparation with degassing and filtration, die design with engineered overflows, vents and gate geometry validated by flow simulation, and process control with logged shot profiles and die temperatures. Where parts must be pressure tight or heavily machined in critical areas, we design vacuum assist or use A360 alloy, and verify with leak testing or X-ray inspection.
Production tooling takes 25 to 40 days depending on part complexity and cavity count, followed by 5 to 7 days for T1 sample production. After you approve samples, production lead time is 15 to 25 days including machining, finishing and inspection. For repeat orders on existing tooling, expect 15 to 20 days.
There is no rigid minimum once tooling exists, and we regularly run batches of 500 pieces. For new programs, the economics rather than a policy set the floor: below roughly 1,000 annual pieces, we will tell you honestly whether CNC machining from billet would serve you better.
Send a 3D model and 2D drawing. You will get projected area, the machine cell your part will run on, tooling cost, piece price and a written DFM report covering gating, venting and ejection before any steel is ordered.