Types Of Casting Processes and their Applications
Metal casting process begins by creating a mold, which is the ‘reverse’ shape of the part we need. The mold is made from a refractory material, for example, sand. The metal is heated in an oven until it melts, and the molten metal is poured into the mould cavity. The liquid takes the shape of cavity, which is the shape of the part. It is cooled until it solidifies. Finally, the solidified metal part is removed from the mould.
A large number of metal components in designs we use every day are made by casting.
The reasons for this include:
(a) Casting can produce very complex geometry parts with internal cavities and hollow sections.
(b) It can be used to make small (few hundred grams) to very large size parts (thousands of kilograms)
(c) It is economical, with very little wastage: the extra metal in each casting is re-melted and re-used
(d) Cast metal is isotropic – it has the same physical/mechanical properties along any direction.
Common examples: door handles, locks, the outer casing or housing for motors, pumps, etc., wheels of many cars. Casting is also heavily used in the toy industry to make parts, e.g. toy cars, planes, and so on.
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| Types of casting |
Different types of castings, their advantages, disadvantages and examples.
1. Sand Casting :
Sand casting is one of the most popular and simplest types of casting, and has been used for centuries. Sand casting allows for smaller batches than permanent mold casting and at a very reasonable cost.
Advantages of Sand casting - Wide range of metals, sizes, shapes, low cost
Disadvantages of sand casting-poor finish, wide tolerance
Examples of sand casting -Engine blocks, Cylinder heads
Disadvantages of sand casting-poor finish, wide tolerance
Examples of sand casting -Engine blocks, Cylinder heads
2. Shell mold Casting :
Shell molding is similar to sand casting, but the molding cavity is formed by a hardened "shell" of sand instead of a flask filled with sand. The sand used is finer than sand casting sand and is mixed with a resin so that it can be heated by the pattern and hardened into a shell around the pattern. Because of the resin and finer sand, it gives a much finer surface finish.
Advantages of shell mold casting : better accuracy, finish, higher production rate
Disadvantages of shell mold casting : limited part size
Examples of shell mold casting : connecting rods, gear housings.
Disadvantages of shell mold casting : limited part size
Examples of shell mold casting : connecting rods, gear housings.
3.Investment Casting :
Investment casting (known as lost-wax casting in art) is a process that has been practiced for thousands of years, with the lost-wax process being one of the oldest known metal forming techniques. From 5000 years ago, when beeswax formed the pattern, to today’s high technology waxes, refractory materials and specialist alloys, the castings ensure high-quality components are produced with the key benefits of accuracy, repeatability, versatility and integrity.
Read More : Steps in Investment Casting Process
Advantages of Investment casting - complex shapes, excellent finish
Disadvantages of Investment casting- small parts, expensive
Examples of Investment casting -jewellery
Disadvantages of Investment casting- small parts, expensive
Examples of Investment casting -jewellery
4. Centrifugal casting
In this process molten metal is poured in the mold and allowed to solidify while the mold is rotating. Metal is poured into the center of the mold at its axis of rotation. Due to centrifugal force the liquid metal is thrown out towards the periphery.
Centrifugal casting is both gravity- and pressure-independent since it creates its own force feed using a temporary sand mold held in a spinning chamber at up to 900 N. Lead time varies with the application. Semi- and true-centrifugal processing permit 30–50 pieces/hr-mold to be produced, with a practical limit for batch processing of approximately 9000 kg total mass with a typical per-item limit of 2.3–4.5 kg.
- Advantages of centrifugal casting - Large cylindrical parts, good quality
- Disadvantages of centrifugal casting- Expensive, limited shapes
- Examples of centrifugal casting -pipes, boilers, flywheels
5.Permanent mold casting
Permanent mold casting is a metal casting process that employs reusable molds ("permanent molds"), usually made from metal. The most common process uses gravity to fill the mold. However, gas pressure or a vacuum are also used. A variation on the typical gravity casting process, called slush casting, produces hollow castings. Common casting metals are aluminum, magnesium, and copper alloys.
Advantages of permanent mold casting -good finish, low porosity, high production rate
Disadvantages of permanent mold casting- Expensive, limited shapes
Examples of permanent mold casting -gears, gear housings
Disadvantages of permanent mold casting- Expensive, limited shapes
Examples of permanent mold casting -gears, gear housings
6. Die Casting :
The die casting process forces molten metal under high pressure into mold cavities (which are machined into dies). Most die castings are made from nonferrous metals, specifically zinc, copper, and aluminium-based alloys, but ferrous metal die castings are possible. The die casting method is especially suited for applications where many small to medium-sized parts are needed with good detail, a fine surface quality and dimensional consistency.
Advantages of die casting -Excellent dimensional accuracy, high production rate
Disadvantages of die mold casting- costly dies, small parts, non-ferrous metals
Examples of die mold casting -precision gears, camera bodies, car wheels
Disadvantages of die mold casting- costly dies, small parts, non-ferrous metals
Examples of die mold casting -precision gears, camera bodies, car wheels
7. Plaster mold casting
Plaster casting is similar to sand casting except that plaster of paris is substituted for sand as a mold material. Generally, the form takes less than a week to prepare, after which a production rate of 1–10 units/hr·mold is achieved, with items as massive as 45 kg (99 lb) and as small as 30 g (1 oz) with very good surface finish and close tolerances.
- Advantages of plaster mold casting - complex shapes, good surface finish
- Disadvantages of plaster mold casting- non-ferrous metals, low production rate
- Examples of plaster mold casting -prototypes of mechanical parts
8. Continuous casting
Continuous casting is a refinement of the casting process for the continuous, high-volume production of metal sections with a constant cross-section. Molten metal is poured into an open-ended, water-cooled mold, which allows a 'skin' of solid metal to form over the still-liquid centre, gradually solidifying the metal from the outside in. After solidification, the strand, as it is sometimes called, is continuously withdrawn from the mold.
Read More: What are the Casting Defects ?