What is Casting Process

What is Casting Process?

  • Casting or founding is the process of producing metal or alloy parts.
  • The parts of desired shapes are produced by pouring the molten metal or alloy into a prepared mould and then allowing the metal or alloy to cool and solidify.
  • This solidified piece of metal or alloy is called as casting.

Basic Terminology in Casting Process

1. Mould

  • It is a container having a cavity of the shape which is to be manufactured. The molten metal is poured in the mould. The process of making the mould is called as mould making.

2. Pattern

  • It is a model or replica of the object to be cast. For effective casting, various types of allowances are provided on the pattern. If only one object has to be cast, then also pattern is required. Pattern is surrounded with sand to give rise to a mould cavity, in which molten metal is poured and casting is produced.

3. Core

  • Core is an obstruction which when positioned in the mould, does not permit the molten poured metal to fill the space occupied by the core, hence produces hollow casting.

4. Mould Box

  • Mould box is combination of two halves; upper half and lower -half. Upper half is called as cope and lower half is called as drag.
  • It is important to note that, drag half is inverted (turn-over) and then kept on the board.

5. Mould material

  • Mould material is the one out of which mould is made. Mould material should be such that, the cavity of the mould retains its shape till the metal has solidified. Moulds can be made up of wax, plaster of paris, ceramics, etc.

6. Pouring cup

  • It is a funnel shaped cup which forms the top portion of the sprue. It makes easier to the operator to direct the flow of metal from crucible to sprue.

7. Pouring basin

  • Molten metal is initially poured into a pouring basin which acts as a reservoir from which it moves smoothly into the sprue. It holds back the slag and dirt. Which foals on the top and allows only the clean metal to enter into the sprue.

Components of gating system

8. Sprue

  • It is the channel through which the molten metal is brought into the parting plane where it enters the runner and gate. It may be square or round in shape.

9. Runner

  • In case of large components, molten metal is carried from the sprue base to the several gates through a passage called as runner.

10. Gate

  • A gate is a channel which connects the runner with the mould cavity, through which molten metal flows to fill the mould cavity. For large components, more than one gates are used.

11. Riser

  • It is a passage of sand, made in the cope to permit the molten metal to rise above the highest point in the casting after the mould cavity is filled up. It permits the escape of air and mould gases. It indicates that, the mould cavity has been completely filled or not.

12. Ladle

  • Ladles are used to carry the molten metal from the furnace to the moulding boxes.

Steps Involved in Casting Process

Following are the steps to be followed while making a sand casting:

1. Pattern making

  • Make the pattern of wood, metal or plastic.

2. Sand mixing and preparation

  • Select a particular sand, test it and prepare the necessary sand mixtures for mould and core making.

3. Core making

  • With the help of patterns prepare the mould and required cores.

4. Melting

  • Melt the metal or alloy to be cast.

5. Pouring

  • Pour the molten metal or alloy into the mould and remove the casting from the mould after solidification of metal.

6. Finishing

  • Clean and finish the casting.

7. Testing

  • Test and inspect the casting and remove the defects, if any.

8. Heat treatment

  • Relieve the casting stresses by using various heat treatments.

9. Re-testing

  • Again inspect the casting and deliver it.

Advantages of Casting Process

  • Caging is one of the most versatile manufacturing processes.
  • It provides the greatest freedom of design in terms of shape, size and quality of product.
  • Casting provides uniform directional properties and better vibration damping capacity to the cast components.
  • Complex and uneconomical shapes which are difficult to produce by other processes can be easily produced by casting process.
  • A product obtained by casting is one piece; hence there is no need of metal joining processes.
  • Very heavy and bulky parts which are difficult to get fabricated, may be cast.
  • It also produces machine parts.
  • Casting process can be mechanised and generally used for mass production of components.

Disadvantages of Casting Process

  • Cast components require more machine finish.
  • Cast components are generally brittle i.e. weak in tension
  • Welding of cast components is difficult.
  • Defects like cracks, blow holes, etc. make the casting weak and unsuitable for use.
  • Accuracy of cast components is less.
  • During the casting process, metal is melted for which large amount of heat and space is rewired. This step in casting process pollutes the atmosphere.

Applications of Casting Process

Casting or cast components are widely used in engineering field. Few applications of cast components are as follows:

  • Automobile parts (pistons, cylinders, dutch and gear housings, gear blanks, etc.)
  • Machine parts (pulleys, gear blanks, beds, frames, etc.).
  • Aircraft parts (Engine blades, motor housings, etc.).
  • Turbine vanes, power generators, pump parts, filters, valves, etc.
  • Agricultural parts, railway crossings, sanitary fittings, etc.
  • Construction, communication and atomic energy applications.

Difference between Casting Processes and Forging Processes

Casting Processes

  • In casting process, there is no grain flow.
  • Due to no grain flow and weak crystalline structure, casting is weak in withstanding working stresses.
  • Requires more machine finish.
  • Cast components are brittle that is weak in tension. Also they have poor resistance to shock and vibrations.
  • Welding of cast parts is difficult.
  • Defects like cracks and blow holes make the casting weak and unsuitable for use.
  • Accuracy is less.
  • Complicated shapes can be produced.
  • Generally used for small parts.
  • As there are no dies, casting is less expensive.

Forging Processes

  • In forging process, grain flow is continuous.
  • Due to improved grain size and true grain flow, forging give greater strength and toughness.
  • Requires minimum machine finish.
  • Forged components have better mechanical properties like strength, toughness, resistance to shock and vibrations.
  • Welding of forged parts is easy.
  • During the operation, cracks and blow holes are welded up.
  • Accuracy is more.
  • Complicated shapes cannot be produced.
  • Generally used for large parts.
  • Because of cost of dies, process is costly.

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