Low-Volume Castings: How to Quote 25, 50 or 100 Pieces of a Cast and Machined Part

There is no single answer; it depends on the part's size, shape and surface needs, and the quantity decides how much tooling you can afford to pay for.

• Sand casting usually has the lowest tooling cost (a pattern and core box), so it is often the first option for heavy, chunky parts in small batches. The as-cast surface is rougher and the tolerance wider, so more surfaces are machined.
• Investment (lost-wax) casting needs a wax injection die, which costs more, but it gives a smoother surface and closer as-cast tolerances (CT4–CT6 on our parts), so less material is removed afterwards. It becomes attractive as the quantity rises or when the shape is complex.
• Machining from bar or plate needs no casting tooling at all and can win for simple shapes at 25 pieces, but it wastes material and machine time on parts with a lot of volume to remove.

Ask your supplier to quote two routes for the same quantities so you can see where the crossover happens.

Tooling is a one-time cost, so its share of each piece falls as the batch grows. The share per piece is simply the tooling price divided by the quantity: doubling the batch from 50 to 100 halves it, and from 25 to 100 cuts it to a quarter.

That is why a quote for 25 pieces can look expensive per piece even when the foundry's unit cost is unchanged. If the tooling is shared over a first batch and later reorders, ask the supplier to show tooling as a separate line and to state who owns the tooling and how long it is kept, so a repeat order does not pay for it twice.

Often yes, but the acceptable minimum depends on the part and the route, so we review each drawing instead of quoting a fixed number. Small castings of a few kilograms are easier to take in small lots than very large or very complex ones.

If your customer can only commit to 25 pieces now, tell us whether a larger repeat order is likely within a year. A realistic outlook (for example 25 now and a few hundred per year) lets us choose the process and tooling that suits the full volume instead of the cheapest route for the first batch only.

Make the casting near net shape and machine only the surfaces that must fit or seal. Typical steps are:

• Leave a machining allowance only on the faces that need it, and keep the rest as cast.
• Group machined faces so they can be done in one or two set-ups.
• Avoid deep pockets and thin walls that the foundry has to fill and that the machinist then has to fixture.
• Add cast-in datum features so the part can be clamped and measured the same way in the foundry and in machining.
• Specify tolerances only where they matter: our CNC machining holds ±0.01 mm on features that need it, but every tight tolerance adds time and cost.

Sending both the as-cast and the machined STEP files, as buyers often do, helps us see exactly which surfaces are removed.

Send the information that decides the process, the material and the delivery.

• 3D files (STEP) of the as-cast and machined part, and a 2D drawing marking machined surfaces and tolerances.
• Material grade and any heat treatment, and whether you need an EN 10204 3.1 certificate.
• Approximate finished weight and the largest dimension.
• Quantities to compare, such as 25, 50 and 100, and the likely annual demand.
• Whether the batch is a one-off or a repeating order, and your target price if you have one.
• Destination, incoterm and the date the parts are needed.
• A photo of the part or its use, which helps us judge which surfaces matter.

Yes. Our production network across Guangdong, Zhejiang, Jiangsu, Shandong and Fujian includes foundries and machining shops, and we can review the part with them and return the quotation as separate lines for tooling, samples, each quantity, machining, finishing and shipping. Send the drawings through our contact page for a DFM review.