Investment CastingLost-wax castings · Stainless, carbon & alloy steel
Lost-wax casting
Precision investment casting for complex metal parts
Investment casting, also called lost-wax or precision casting, reproduces a wax pattern in metal. Wax patterns are injected in a metal die, assembled into a tree and dipped in ceramic slurry and sand, coat by coat, to build a shell. The wax is melted out, the shell is fired, and molten metal is poured into the hot shell. After cooling the shell is knocked off and the castings are cut from the tree.
The result is a near-net-shape part with fine detail, thin walls and a smooth as-cast surface, in stainless, carbon or alloy steel. Usually only bores, threads, sealing faces and datums need machining. Typical annual volumes run from a few hundred to tens of thousands of pieces; prototypes can be cast from 3D printed patterns before the die is made.
The lost-wax process in eight steps
| 1. Wax injection | Pattern wax is injected into an aluminum or steel die. The cavity is oversized by the wax and metal shrinkage, typically about 1.5–2.5% for steel. |
|---|---|
| 2. Tree assembly | Patterns are welded by their gates to a wax sprue with a pouring cup to form a cluster, or “tree”. |
| 3. Shell building | The tree is dipped in ceramic slurry and stuccoed with refractory sand. Face coats use fine zircon; back-up coats use coarser sand. Typically 5–7 coats for silica sol and 4–6 for water glass, each dried or hardened before the next. |
| 4. Dewaxing | Silica sol shells are typically dewaxed in a steam autoclave; water glass shells in hot water at about 90–95 °C. The wax is reclaimed. |
| 5. Firing | The shell is fired to burn out wax residue and gain strength, typically at about 1,000–1,100 °C for silica sol and 850–950 °C for water glass, and is poured while still hot. |
| 6. Pouring | Metal melted in an induction furnace is poured by gravity into the preheated shell. |
| 7. Knockout and cut-off | After cooling the shell is knocked off by vibration or hammer, and the castings are cut from the sprue with an abrasive wheel or saw. |
| 8. Finishing and inspection | Gate grinding, shot blasting, heat treatment, straightening where needed, machining and inspection to the drawing. |
Silica sol shells for the best surface finish and dimensional accuracy.
Sodium silicate shells for economical carbon and low-alloy steel castings.
304, 316, 17-4PH, duplex and martensitic stainless steel castings.
Carbon steel and low-alloy steel investment castings, heat treated for strength.
CNC machining, heat treatment and surface finishing of investment castings to your drawing.
Investment casting at a glance (typical)
| Process | Lost-wax investment casting (silica sol or water glass shell) |
|---|---|
| Typical part weight | A few grams to a few kilograms for most parts; heavier parts are possible, more often by water glass |
| Minimum wall | Typically about 1.5–2 mm for small steel parts in silica sol; thicker for long flow lengths and for water glass |
| Dimensional tolerance | Typically ISO 8062-3 DCTG 4–6 for silica sol, DCTG 7–9 for water glass |
| As-cast surface | Typically Ra 3.2–6.3 µm for silica sol (about 1.6 µm on favorable faces); Ra 6.3–12.5 µm for water glass |
| Machining allowance | Typically about 0.5–1.5 mm on silica sol castings, more on water glass |
| Materials | Stainless, carbon, alloy and tool steels |
| Secondary operations | Heat treatment, machining, blasting, passivation, polishing, plating |
Investment casting FAQ
What is investment casting?
A casting process in which a wax pattern is coated with ceramic to form a shell, the wax is melted out, and molten metal is poured into the hot shell. It is also called lost-wax or precision casting.
Why choose investment casting over machining from solid?
For complex shapes in volume, a near-net-shape casting saves most of the material and machining time. Only the features with tight tolerances are machined. For a few simple parts, machining from bar is often cheaper because there is no wax die.
What do you need for a quotation?
A 2D drawing with tolerances and a 3D model (STEP or IGES), the alloy grade and standard, the heat treatment, the order quantity and annual volume, which faces are machined, and any NDT or certificate requirements.