What is investment casting? The lost-wax process explained
What investment casting is, how the lost-wax process works, what it does well (fine detail, near-net shape, tough alloys), cost drivers, and when to pick it over machining or sand casting.
Investment casting (lost-wax casting) builds a ceramic shell around a wax pattern, melts the wax out, and pours molten metal into the cavity. It produces fine detail, smooth surfaces and near-net shapes in almost any alloy, including the steels and superalloys that are hard to machine. It costs more per part than sand casting and needs tooling, so it pays off for complex shapes in moderate volume, or where machining the same part from solid would waste too much material and time.
How the lost-wax process works
- A wax pattern of the part is injection-moulded in a die.
- Patterns are assembled onto a wax "tree" so many pour at once.
- The tree is dipped in ceramic slurry and stucco, repeatedly, to build a hard shell.
- The wax is melted out, the "lost wax" that gives the process its name.
- The shell is fired, then filled with molten metal.
- The shell is broken away and the parts are cut from the tree and finished.
What investment casting is good at
- Fine detail and thin walls with a smooth as-cast surface, so little or no machining.
- Near-net shape: far less material removed than machining a part from solid billet.
- Tough and high-temperature alloys: stainless, tool steel, Inconel and other superalloys, titanium and bronze.
- One-piece complexity: shapes that would otherwise be several machined and welded parts, which is why aerospace uses it for turbine and structural components.
Investment vs sand casting vs machining
| Investment casting | Sand casting | Machining from solid | |
|---|---|---|---|
| Detail and surface | Fine, smooth | Coarser, rougher | Any, but cut feature by feature |
| Tooling cost | Moderate (wax die) | Low | None |
| Economical volume | Dozens to thousands | One-off to large | One-off to low volume |
| Material waste | Low (near-net) | Low | High (chips) |
| Best for | Complex near-net parts | Large or low-volume parts | Prismatic and tight-tolerance parts |
Cost drivers
The wax tooling, part complexity, the alloy, the quantity, and the finish machining of critical features. Most castings still need machining on mating surfaces and bores, so quote the casting and the machining together rather than separately.
What to send for a quote
A 3D model and a drawing that marks which surfaces will be machined after casting, the alloy or the mechanical and certification requirements, the quantity, and any finishing. Request quotes from Canadian casting and machining shops.
FAQ
What is investment casting also called?
Lost-wax casting, or precision casting. All three names describe the same process of pouring metal into a ceramic shell formed around a wax pattern.
What materials can be investment cast?
Most metals: carbon and stainless steels, tool steel, Inconel and other superalloys, aluminum, titanium and bronze. Its ability to cast hard-to-machine alloys is a big part of its appeal.
What is the difference between investment casting and sand casting?
Investment casting gives finer detail and a smoother surface at higher tooling cost; sand casting is cheaper and better for large or very low-volume parts but leaves a rougher surface.
When is investment casting cheaper than machining?
For complex near-net shapes in moderate volume, where machining the same part from solid would waste a lot of material and machine time. Simple prismatic parts are usually cheaper machined.
Does an investment casting still need machining?
Usually yes, on the critical mating surfaces, bores and threads. The non-critical surfaces can be left as-cast, which is where the process saves money.
Last reviewed: October 2026. Related reading: forging vs casting and what is CNC machining.
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