First, two things decide the route before cost is ever discussed: how many parts you will need, year after year, and how tight the tolerance grade has to be as cast. Sand casting needs only a pattern, so it takes low and medium volumes and large, thick-section parts. Die casting needs a hardened steel die, so it only creates value at high, steady volume. There it buys thin walls, fine detail and a smoother as-cast surface.
The short answer
| Deciding factor | Sand casting | Die casting |
|---|---|---|
| Tooling before the first part | A pattern and core boxes — a lower, easier-to-change commitment | A machined steel die — a much larger, one-time commitment |
| When the tooling pays back | Spreads over low and medium volumes; practical from one-offs upward | Only justified by high, stable annual volume |
| Minimum economic volume | Low — the pattern is the only fixed cost | High. The die has to pay for itself across a long run |
| Dimensional tolerance | Coarser grades in the ISO 8062 system | Finer ISO 8062 grades — but still casting grades, not a machining tolerance |
| Wall thickness and section | Must be thick enough for the metal to fill before it freezes | Thin walls and internal ribs are feasible — the die fills under pressure |
| Surface, as cast | Mould texture; usually the rougher of the two | Smoother, with finer detail straight from the die |
| Machining afterwards | Flat, sealing and mating faces normally need machining | Less machining, but critical faces are still machined |
| Changing the design after the first part | A pattern change | A die change. Once the die exists, changing the design means changing the die |
| Where it wins | Large, thick-section, low-to-medium volume parts | Small-to-medium, thin-walled, high-volume parts needing fine detail |
Tooling is the first fork in the road
A pattern is a positive model of the part that forms the cavity in a sand mould. In addition, it is fairly simple to make and simple to change, which is why sand casting accepts low volumes and late design changes. By contrast, a die is a machined block of hardened steel with the part cut into it. It costs far more to make and to change, so it only makes sense when the same geometry will run for a long time.
Therefore ask a more useful question. How many times will this part run before it changes? If the answer is uncertain, sand casting keeps your options open. If the answer is a long, steady run, die casting starts to pay its die back.
Minimum economic volume: where the payback flips
Sand casting spreads only the pattern across the run. Therefore it stays economic from low volumes upward. Die casting spreads a much larger die across the run. The more parts you make, the more the die pays for itself. Then the per-part figure falls toward material and cycle time. The crossover depends on your annual volume and how long the design will live. Below it, sand casting is the lower-commitment route. Well above it, the die is the reason to choose die casting.
Tolerance: ISO 8062 grades both processes
Casting tolerances are not one number. Instead, the ISO 8062-3 system grades them by process and by nominal size. That standard defines general dimensional and geometrical tolerances for castings, together with machining allowance grades. Sand casting, with a mould formed around a pattern, sits in the coarser grades. Die casting, with a rigid steel die, reaches finer grades. However, it is still a casting grade, not a machining tolerance.
However, where a face must be closer than the cast grade allows, we machine it after casting. On machined features we work to ±0.05 mm, and on formed or bent features to ±0.5 mm on critical dimensions. This means a casting with one or two critical features can reach a machining tolerance without turning the whole part into a machined component.
Wall thickness and section
The mould decides the minimum section. In sand, molten metal has to fill the cavity and freeze before it runs short, which pushes the design toward thicker, self-supporting walls. Inside a die, the machine injects molten metal under pressure into a hardened cavity. Thin walls and fine internal ribs therefore become practical.
In short, this is the single biggest difference in the finished part. If the enclosure or housing needs a rigid, load-bearing section in one piece, casting is the natural route. If the wall has to be thin and light, pressure die casting is the only casting route that will do it.
How we run casting and the checks behind it
Additionally, we run metal casting as one step inside a wider metal fabrication service. A cast part that also needs machining, finishing or assembly therefore never moves between suppliers. Our how sand casting and die casting differ in practice, and the wider shop covers what comes after the pour.
Finally, we check cast parts with two coordinate measuring machines, height gauges and hardness testers. We also re-inspect 100% outbound before packing. Quality runs to ISO 9001:2015, which covers incoming material checks, in-process inspection and the final dimensional check. If your drawing cites no tolerance at all, ISO 2768-1 gives the four general classes (fine, medium, coarse and very coarse) that most drawings fall back on for linear and angular dimensions.
Frequently asked questions
These are the questions buyers ask most often about this comparison.
What is the difference between sand casting and die casting?
Sand casting forms the part in a sand mould built around a pattern, so tooling is simple and low volume works. Die casting injects molten metal into a machined steel die under pressure, which gives thinner walls and finer detail but only pays off at high, steady volume.
Which casting route gives the tighter tolerance?
Die casting reaches the finer grades in the ISO 8062 system. Sand casting sits in the coarser grades. Both are casting grades, so any face that must be closer than the cast grade allows needs machining afterwards.
Can you machine and finish a casting as well?
Yes. Casting is one step in a full metal fabrication service, so machining, surface treatment and assembly run in the same shop. On machined features we work to ±0.05 mm and on formed or bent features we typically hold ±0.5 mm on critical dimensions.
What is the minimum order for cast parts?
There is no fixed minimum order quantity. Lower volumes suit sand casting because it needs only a pattern. Send the drawing with the annual volume and we will confirm the route and the lead time.