Casting

Casting makes a part by pouring molten metal into a mould. It is the economical way to make complex shapes and larger parts, and there are several casting methods, each suited to different sizes, quantities and finishes.

Sand casting is flexible and used for iron, steel, aluminium and brass parts in almost any size. Gravity die casting and pressure die casting use metal moulds and suit repeat parts in aluminium and other non-ferrous alloys. Investment casting gives fine detail and a good finish for smaller parts.

Most cast parts need some machining after casting, so many foundries either machine in-house or work with machining partners. Tell the foundry if you need the part machined.

Materials commonly used

• Grey and ductile iron
• Carbon and alloy steel, and stainless steel
• Aluminium alloys
• Brass, bronze and copper alloys

What to send with your requirement

• A drawing, and a 3D model if available, marking the machined surfaces
• The alloy or grade and any standard it must meet
• The quantity per order and per year
• Whether patterns or moulds already exist, or must be made
• Testing you need, such as pressure or hardness tests, and who does the machining

What affects the cost

• Method: sand, die or investment casting, driven by quantity and finish
• Weight of the casting and the metal used
• Pattern or die cost, which is paid once and then shared over the parts
• Machining, heat treatment, testing and surface finish
• Quality requirements: rejection allowances and inspection

Common mistakes to avoid

• Not saying which surfaces will be machined, so the machining allowance is missing
• Choosing die casting for a very small quantity, where the die cost dominates
• Not agreeing on inspection and acceptance standards before pouring
• Not asking who owns and stores the pattern or die

Frequently asked questions

Which casting method should I choose?

For a few pieces or large parts, sand casting is usually the practical choice. For repeat parts in aluminium at good volume, die casting can bring the part price down. For small parts with fine detail, investment casting is worth considering. A foundry can advise once they see your drawing.

Who makes the pattern?

Often the foundry, or a pattern maker they work with. The cost is normally paid once. Agree in writing who owns it and where it is stored.

Can I get machined castings from one place?

Some foundries machine in-house or through partners. Say so in your requirement, so that workshops quote the full job.