Investment casting

Investment casting, or lost-wax casting, makes a wax copy of the part, coats it in ceramic, melts the wax out and pours metal into the shell. It gives fine detail, thin sections and a smooth finish, often close to the final size, which saves machining on small and complex parts.

A wax die (a metal tool) makes the wax patterns. These are assembled on a tree, dipped in ceramic slurry several times, dewaxed and fired, then filled with molten metal. The shell is broken off and the parts are cut off and finished.

It is widely used for valve, pump, automotive and machinery parts in carbon steel, stainless steel and alloy steel. Parts usually range from a few grams up to several kilograms.

Materials commonly used

• Stainless steels such as CF8 (304) and CF8M (316)
• Carbon and low-alloy steels such as WCB
• Martensitic stainless such as CA15 and 17-4 PH
• Brass, bronze and some aluminium alloys

What to send with your requirement

• A drawing with tolerances and marked machined faces, and a 3D model (STEP)
• The grade and standard, and whether you need a material test certificate
• The quantity per order and per year
• Whether a wax die already exists, or must be made
• Heat treatment, testing (radiography, hardness) and machining needed after casting

What affects the cost

• The wax die, paid once and then shared over the parts
• Part weight and the alloy
• How many parts fit on one tree, and the yield
• Heat treatment, testing and inspection requirements
• Machining and finishing after casting

Common mistakes to avoid

• Asking for tight tolerances on every surface when the as-cast tolerance is enough on most of them
• Not stating the material standard and the tests needed
• Not saying which faces will be machined
• Comparing a quote that includes the wax die with one that does not

Frequently asked questions

When is investment casting better than sand casting?

For smaller parts that need fine detail, thin walls, a smooth finish or less machining. For large, heavy or simple parts, sand casting is usually more economical.

Do I need a wax die?

For repeat production, yes: it makes the wax patterns. For prototypes, some workshops can make patterns by 3D printing instead.

Can I get a material certificate?

Many foundries supply a test certificate with chemical analysis and mechanical properties. Ask for it in your requirement so it is included in the quote.