Sand casting wins on very low volume, thick sections and large envelopes because pattern cost is a few hundred to a few thousand dollars and there is almost no part-size ceiling. High pressure die casting wins as soon as you need thin walls, as-cast detail and a piece price that survives thousands of repeats: a steel die costs more ($3,000 to $25,000) and then produces a 1.5 to 4 mm wall at cycle times of 30 to 90 seconds. For a 1.2 kg housing, sand casting is usually cheaper below a few hundred parts; die casting is usually cheaper above 1,000 to 2,000 parts and is the only practical route if the wall must be under about 4 mm. The processes are not substitutes. Choose sand for prototypes, huge parts and thick-section industrial castings; choose HPDC for volume OEM housings, covers and structural brackets.
Sand casting and high pressure die casting both pour aluminum into a mould. That is where the similarity ends. One makes a new sand mould for every part. The other slams metal into the same steel cavity tens of thousands of times. They serve different drawings, different volumes and different conversations with purchasing.
If you are choosing between them, you are usually choosing between a thick industrial casting and a thin-wall OEM part. This article keeps that distinction explicit.
Side-by-side
| Factor | High pressure die casting | Sand casting |
|---|---|---|
| Tooling | Steel die, typically $3,000–$25,000 | Pattern, typically $400–$4,000 |
| Tool life | 80,000–150,000 shots | Pattern lasts; each mould is single-use |
| Cycle | 30–90 s on a machine | Minutes to hours per pour, plus mould making |
| Typical walls | 1.5–4 mm | 4–12 mm+ |
| As-cast tolerance | About ±0.1 mm first 25 mm | About ±0.8 to ±2.0 mm, size-dependent |
| As-cast surface | Ra 1.6–3.2 µm | Ra 6–25 µm typical |
| Part size | Best under ~12 kg / 700 mm envelope here | Very large parts are routine |
| Best volume | ~1,000 to 500,000+ / year | Prototypes, spares, low hundreds |
| Alloys we see | A380, ADC12, A360, A413 | 319, 356, 535 and others; heat-treatable grades more common |
Gravity die casting (permanent mould, gravity pour) sits between these columns: metal mould, slower fill, thicker walls than HPDC, better surface than sand. It is the right call for some wheels, cookware and thick covers. It is still not a 2 mm electronics housing process.
Tooling and piece price
Sand casting is cheap to start and expensive to repeat. Die casting is the opposite.
Take a 1.2 kg industrial cover.
| Annual volume | Sand cast (pattern $1,800, piece $28) | HPDC (die $11,000, piece $9.40) |
|---|---|---|
| 50 | $43 + pattern share ≈ $79 | $9.40 + $220 = $229 |
| 200 | $28 + $9 = $37 | $9.40 + $55 = $64 |
| 500 | $26 + $3.60 = $30 | $9.20 + $22 = $31 |
| 2,000 | $24 + $0.90 = $25 | $8.90 + $5.50 = $14 |
| 10,000 | $22 + $0.18 = $22 | $8.40 + $1.10 = $9.50 |
The crossover on this cover sits near 500 parts. The practical switch is often higher if the sand part can stay thick and the HPDC design must be redrawn for draft and uniform walls. Once the steel die exists, every additional year widens the gap.
Tooling cost and MOQ / break-even cover the HPDC side in more detail. Sand-side pattern cost is mostly geometry and core boxes, not cavity count.
Geometry: walls, draft and detail
High pressure fill is why die castings can be thin. Metal enters at 30 to 50 m/s and fills in tens of milliseconds. Sand fill is gravity or low pressure; the metal has time to freeze in a 2 mm section, so designers add thickness.
That single fact decides most housings.
- Need 2 mm walls, ribs, fins, logos, as-cast bosses. Die casting.
- Need a 20 kg gearbox case, 8 mm walls, a few dozen a year. Sand casting.
- Need a sealed electronics box at 8,000 a year. Die casting, then machine the sealing face.
Draft still exists in both. Sand often wants more of it. Internal sand cores can form passages that would need slides or lose cores in a die, which is why sand remains useful for manifolds and pump bodies even at moderate volume.
Properties and porosity
Do not assume one process is “stronger.”
Sand-cast 356-T6 can exceed A380 die castings in yield and elongation after heat treatment. High pressure A380 cannot take a conventional T6 without blistering, because injected gas expands at solution temperature. Die castings win on stiffness per dollar when ribs are free. They lose when the drawing needs wrought-like ductility or a heat-treated temper.
Porosity modes differ. HPDC porosity is often gas and turbulent fill. Sand porosity is often shrinkage in heavy sections and inclusions from the mould. Neither is automatically pressure-tight. Specify leak test or impregnation against the function, not against the process name.
Surface and secondary operations
Die castings come out closer to the finished part. Sand castings usually need more machining to find a datum, a seal or a bearing bore. That machining can erase a piece-price advantage you thought you had at 400 parts.
Powder coat hides sand texture better than anodize. If the part is a visible consumer housing, die casting or machining will look like the product. Sand will look like a casting.
A decision rule that holds up in reviews
| If this is true | Choose |
|---|---|
| Under ~300 parts, design still moving | CNC the die-cast geometry, or sand if the part is already thick |
| Under ~500 parts, thick industrial shape | Sand casting |
| 500–2,000 parts, thin walls required | Die casting, or machine until the design freezes |
| 2,000+ parts, OEM housing / cover / bracket | High pressure die casting |
| Part larger than an HPDC cell can hold | Sand or gravity |
| Drawing says 6061 / 7075 | Not either casting route; machine it |
CharMax does not sand-cast. We high-pressure die-cast aluminum and we machine aluminum. If your part is a sand job, we will say so rather than force it into a steel die. If it is a volume HPDC job, send the model and the annual volume; the quote will include the tooling class that matches the run-rate.
