Quick Answer
Investment casting builds a one-time ceramic mold around a wax copy of your part. Wax patterns are injected, assembled onto a tree, coated in ceramic slurry layer by layer, melted out (“lost wax”), and the fired shell is filled with molten metal. The payoff: complex geometry, thin walls, fine surfaces (Ra 3.2–6.3 µm as-cast) and tolerances around ±0.1–0.3 mm — in almost any castable alloy from carbon steel to CF8M stainless and nickel alloys.
The Eight Steps
- 1. Tooling. An aluminum die is machined for wax injection. Cost scales with part complexity; for many parts it is a fraction of a die-casting tool.
- 2. Wax injection. Wax is injected to form a precise, shrink-compensated replica of the part. Each casting starts as one wax.
- 3. Tree assembly. Dozens of waxes attach to a central runner — one pour fills the whole cluster, which is how unit costs stay low.
- 4. Shell building. The tree is dipped in ceramic slurry and stuccoed with sand, then dried — repeated 5–9 times over several days. Silica sol binder systems (our standard) give the best surface and dimensional stability.
- 5. Dewax. A steam autoclave melts the wax out, leaving a hollow shell. The wax is recycled.
- 6. Fire and pour. The shell is fired to ~1,000°C for strength, then filled with metal, often while still hot to feed thin sections.
- 7. Knockout and cutoff. After solidification the shell is vibrated and blasted away; parts are cut off the tree and gates ground flush.
- 8. Heat treat, inspect, machine. Castings are heat treated per grade, inspected, and finish machined where drawings demand tighter than as-cast tolerance.
What the Process Is Best At
- Complex shapes in hard alloys — internal passages, thin vanes, undercuts that would be unmachinable or wasteful from bar stock
- Near-net weight savings: parts commonly ship at 60–90% less machining than hogging from solid
- Alloy freedom: carbon steels (WCB class), stainless (CF8/CF8M/17-4 PH), tool steels, cobalt and nickel alloys — one process covers them all
- Size range roughly 0.02–80 kg; sweet spot under 15 kg
Timeline and Cost Drivers
| Stage | Typical duration |
|---|---|
| Tooling (first order only) | 2–4 weeks |
| First article samples | 2–3 weeks after tooling |
| Production batch | 3–5 weeks including heat treat and machining |
Piece price is driven by weight, alloy, shell complexity (slender cores and deep slots add dips), inspection level, and machining scope. Volume helps mainly through tree utilization and setup amortization.
Buyer Tips That Save Money
- Send a 3D model, not just 2D — foundry DFM feedback on radii, wall transitions and gate placement happens in days and often removes cost before tooling exists
- Mark only functional surfaces for machining; leave the rest as-cast
- State the real tolerance need per feature — blanket tight tolerances are the most common cost inflator we see
- Ask for first article inspection reports before releasing production — our process is described in the first piece approval vs FAI guide
Full capability details are on our lost wax investment casting page; parts needing tight finished dimensions continue into in-house CNC machining.
FAQ
Investment casting vs sand casting — how do I choose?
Complexity and finish favor investment; large size and lowest tooling cost favor sand. Many buyers use both across one BOM.
What does “silica sol” mean and why does it matter?
It is the ceramic binder used for shell building. Silica sol shells hold finer detail and better dimensions than cheaper water-glass shells — specify it when surfaces and tolerances matter.
Is there a minimum order quantity?
Practically, the tree economics favor batches of dozens and up, but sampling starts from a handful of pieces once tooling exists.