Advantages
- Complex geometry in one piece. Undercuts, internal cavities, curved passages and fine detail are cast in. Assemblies of several machined or welded parts can often be consolidated into a single casting.
- Little or no draft. Most surfaces need no draft because the mould is not opened to remove the pattern; only the wax die requires small draft on deep features.
- Thin walls and low weight. The preheated shell allows thinner sections than sand casting, which supports weight reduction.
- Wide alloy choice. The process is not limited to low-melting alloys as pressure die casting is, and it handles grades that are hard to forge or machine.
- Accuracy and surface. As-cast tolerances and surface texture reduce machining to functional features such as fits, threads and sealing faces.
- No parting line. Flash and mismatch from mould halves do not occur on the casting; witness lines from the wax die are small.
- Flexible quantities. Moderate tooling cost, and tool-free prototypes from printed patterns.
Limitations
- Size and mass. Handling of wax clusters and shells limits part size; most industrial investment castings weigh well below 50 kg.
- Process length. Many sequential steps with drying times mean longer lead times than machining from stock, especially for first samples.
- Cost at very high volumes. For simple shapes in aluminium or zinc in very large series, pressure die casting is cheaper; for simple steel shapes, forging or sintering may be.
- Very deep or narrow features. Slots, blind holes and long thin cores are limited by how well slurry can coat and dry inside them; ceramic cores extend the range at additional cost.
- Heavy sections. Thick, isolated masses are difficult to feed and tend towards shrinkage porosity; the process favours moderate, uniform walls.
- Cast structure. Like all castings, properties are not directional as in a forging, and internal soundness depends on feeding. Fatigue-critical parts may require additional measures such as hot isostatic pressing and closer inspection.
- Tolerances are not machining tolerances. Tight fits and geometrical tolerances on functional features still require machining.
When investment casting is usually the right choice
| Part characteristic | Tendency |
|---|---|
| Complex shape that would need extensive multi-axis machining | Favours investment casting |
| Alloy difficult to machine or forge (stainless, nickel, cobalt) | Favours investment casting |
| Several parts can be combined into one | Favours investment casting |
| Simple prismatic or rotational shape | Favours machining from bar or forging |
| Very large series in aluminium with thin walls | Favours pressure die casting |
| Large, heavy part with generous tolerances | Favours sand casting |
| Highest fatigue strength in a simple shape | Favours forging |
The decision should be based on the complete manufacturing route. A structured comparison is given under process comparison, and practical design rules under design guidelines.