Gravity die casting pours molten metal, usually aluminium, into a reusable steel or cast iron mould under gravity alone. It gives stronger, more accurate castings with a better finish than sand casting, at a lower tooling cost than pressure die casting.
Quick facts
- Common alloys
- Aluminium (LM6, LM25, LM4), also brass and zinc
- Typical tolerance
- About ±0.3–0.5 mm (±0.0118–0.0197 inch) on small sizes
- Surface finish
- Better than sand casting
- Tooling
- Metal die; cheaper than a pressure die
- Suitable quantity
- Medium volumes, hundreds to tens of thousands
- Usually priced
- Per piece or per kg, plus die cost
Gravity, sand or pressure die casting?
| Method | Tooling cost | Best for |
|---|---|---|
| Sand casting | Low | Few pieces, large or heavy parts |
| Gravity die casting | Medium | Medium volumes, sound and strong parts, can be heat treated |
| Pressure die casting | High | Large volumes of thin-walled, detailed parts |
Advantages
- Denser, stronger castings than sand casting; can be heat treated (e.g. LM25-TF)
- Good repeatability and finish
- Sand cores can make internal passages
- Lower die cost than pressure die casting
What to send the foundry
- 3D model or drawing, with the alloy and any heat treatment
- Machining allowance on faces to be machined
- Quantity per year and per batch
- Tests needed: X-ray, pressure test, chemical and mechanical reports
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Questions
- Why choose gravity die casting over pressure die casting?
- For medium quantities, thicker walls, parts that need heat treatment or pressure tightness, and when the high cost of a pressure die is not justified.
- Which aluminium alloy is used for gravity die casting?
- LM25 is common for strong, heat-treatable parts; LM6 for thin, complex or corrosion-resistant parts; LM4 for general work.
- How long does a gravity die last?
- Typically tens of thousands of castings, depending on the alloy, part shape and how the die is maintained.
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 9 October 2026.