As I mentioned to you last week, I wanted to review what a casting was and this is part of a series of manufacturing disciplines that we do at UGS.
Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various cold setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster, and clay. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods.
What is a sand casting?
A sand casting or a sand molded casting is a cast part produced by forming a mold with the help of a model or pattern pressed into a sand mixture and then removed, after which molten liquid metal is poured into the cavity in the mold. The mold is then cooled until the metal has solidified. In the last stage, the casting is separated from the mold. There are six steps in this process:
- Place a pattern in sand to create a mold.
- Incorporate the pattern and sand in a gating system.
- Remove the pattern.
- Fill the mold cavity with molten metal.
- Allow the metal to cool.
- Break away the sand mold and remove the casting.
What is a die cast part?
Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity, which is machined into two hardened tool steel dies. Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminum, magnesium, lead, pewter and tin based alloys. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.
The casting equipment and the metal dies represent large capital costs and this tends to limit the process to high volume production. Manufacture of parts using die casting is relatively simple, involving only four main steps, which keeps the incremental cost per item low. It is especially suited for a large quantity of small to medium sized castings, which is why die casting produces more castings than any other casting process. Die castings are characterized by a very good surface finish (by casting standards) and dimensional consistency.
What is an investment cast?
Investment casting is an industrial process based on and also called lost-wax casting, one of the oldest known metal-forming techniques. From 5,000 years ago, when beeswax formed the pattern, to today’s high-technology waxes, refractory materials and specialist alloys, the castings allow the production of components with accuracy, repeatability, versatility and integrity in a variety of metals and high-performance alloys. Lost foam casting is a modern form of investment casting that eliminates certain steps in the process.
The process is generally used for small castings, but has been used to produce complete aircraft door frames, steel castings of up to 300 kg and aluminium castings of up to 30 kg. It is generally more expensive per unit than die casting or sand casting, but has lower equipment costs. It can produce complicated shapes that would be difficult or impossible with die casting, yet like that process, it requires little surface finishing and only minor machining.