Most of the castings that hold up machines, bridges, pumps, and tractors were made the same way: molten metal poured into a mould made of sand. The process is older than the industrial revolution, and it is still the first answer for the majority of the parts that cross our desk. This is what a buyer needs to know about it.
How a sand casting is made
A pattern — a replica of your part, usually in wood, plastic, or metal — is packed in sand and withdrawn, leaving a cavity. Cores, also of sand, form the internal passages. The mould is closed, the metal is poured through a gating system, and the part cools inside the sand. Then the mould is broken away, the gates and risers are cut off, and the casting is cleaned and, if the print calls for it, machined.
Three variants matter to a buyer. Green sand is the workhorse for volume and for anything large. No-bake, where the sand is chemically bonded, holds tighter tolerances and handles heavier sections. Shell moulding gives a finer surface on smaller parts. The foundry chooses among them based on your geometry, your volume, and the finish your print specifies.
Why it is still the default
Sand casting tolerates almost any shape. Internal passages, varying wall thickness, ribs, bosses, and undercuts are all routine. It works at nearly any size — the network GW manages pours parts from a few ounces to more than 30,000 pounds, and the largest of those are all sand castings. It runs in every common material: grey and ductile iron, steel, stainless, aluminum, bronze, and custom alloys.
And tooling is competitive. A pattern is a one-time cost, amortised over every part it produces, which is why sand casting is practical for a prototype run of five and for a production program of fifty thousand.
What it means for your print
Sand casting has a tolerance envelope, and it is wider than a machined surface. That is not a problem; it is a design fact. Critical features get a machining allowance and are finished after casting. Non-critical surfaces stay as-cast. A print that flags which is which — and gives realistic as-cast tolerances on the rest — quotes faster and costs less than one that asks for machined tolerances everywhere.
Draft, fillets, and uniform wall thickness all help the metal fill and cool cleanly. If your part was designed for a weldment or a machined billet, a manufacturability review before tooling is cut is worth the day it takes.
What it means for your lead time
First articles on new tooling are the long pole. After that, sand casting scales with the foundry's capacity — and that is where sourcing matters. A single foundry quotes you its own schedule. A qualified network can quote the schedule that fits the part: domestic when tooling and logistics favour it, international when price and capacity do, and both when the program is large enough to warrant a second source.
Where GW comes in
GW spent decades operating its own iron foundries. Today we place sand castings with the foundry in our qualified domestic and international network that fits the part, oversee production, verify quality before parts ship, and deliver them machined, finished, and ready for your line. One PO, one invoice, one partner accountable for the result.