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Difference Between Casting and Forging/Forming Processes

Difference Between Casting and Forging Processes 

Casting is the process where metal is heated until molten. While in the molten or liquid state it is poured into a mold or vessel to create a desired shape.

Forging is the application of thermal and mechanical energy to steel billets or ingots to cause the material to change shape while in a solid state.

Casting Vs Forging
Casting Vs Forging
Metal casting process
Differences
Metal forming process
Casting is a manufacturing process where a solid is melted, heated to proper temperature (sometimes treated to modify its chemical composition), and is then poured into a cavity or mould, which contains it in the proper shape during solidification. Thus, in a single step, simple or complex shapes can be made from any metal that can be melted. The resulting product can have virtually any configuration the designer desires.
Working Principle
The plastic deformation of a metal in order to produce a useful shape. Metal forming is done at elevated or hot-working temperatures with processes such as forging, or it is done at cold-working room temperatures with processes such as stamping or bending.
OBTAINING THE CASTING GEOMETRY-The traditional method of obtaining the casting geometry is by sending blueprint drawings to the foundry. This is usually done during the request for quotation process. However, more and more customers and foundries are exchanging part geometry via the exchange of computer aided design files.

PATTERNMARKING-The pattern is a physical model of the casting used to make the mould.
The mould is made by packing some readily formed aggregate material, such as moulding sand, around the pattern. When the pattern is withdrawn, its imprint provides the mould cavity, which is ultimately filled with metal to become the casting.
If the casting is to be hollow, as in the case of pipe fittings, additional patterns, referred to as cores, are used to form these cavities.

COREMAKING-Cores are forms, usually made of sand, which are placed into a mould cavity to form the interior surfaces of castings. Thus the void space between the core and mould-cavity surface is what eventually becomes the casting.

MOULDING-Moulding consists of all operations necessary to prepare a mould for receiving molten metal. Moulding usually involves placing a moulding aggregate around a pattern held with a supporting frame, withdrawing the pattern to leave the mould cavity, setting the cores in the mould cavity and finishing and closing the mould.

MELTING AND POURING-The preparation of molten metal for casting is referred to simply as melting. Melting is usually done in a specifically designated area of the foundry, and the molten metal is transferred to the pouring area where the moulds are filled.

CLEANING-Cleaning refers to all operations necessary to the removal of sand, scale, and excess metal from the casting. The casting is separated from the mould and transported to the cleaning department. Burned-on sand and scale are removed to improve the surface appearance of the casting. Excess metal, in the form of fins, wires, parting line fins, and gates, is removed. Castings may be upgraded by welding or other procedures. Inspection of the casting for defects and general quality is performed.

OTHER PROCESS-Before shipment, further processing such as heat-treatment, surface treatment, additional inspection, or machining may be performed as required by the customer's specifications.
Procedures
Metal-forming processes: Processes that cause changes in the shape of solid metal articles via plastic (permanent) deformations.

Drawing: Metal forming process whereby the workpiece is a shaped longitudinal prism that undergoes a reduction and change in its cross section area and shape while being pulled through a shaped converging die.

Extrusion: Metal forming process whereby the workpiece is placed in a chamber with an opening and is forced to escape through the opening, usually being pushed out by a mandrel.

Forging: Metal forming process whereby the workpiece is placed between an anvil and a hammer and subjected to compressive force between them.

Rolling: Metal forming process whereby the workpiece is a longitudinal prism, which is placed between two opposing circular rolls that rotate in opposite directions, drag the workpiece along, and force it to reduce in cross section.

Metal forming is normally performed after the primary processes of extraction, casting, and powder compaction and before the finishing processes of metal cutting, grinding, polishing, painting, and assembly. With few exceptions, the bulk of the products of the metal fabrication industry are shaped by forming or a combination of forming and other processes like metal cutting or joining. Forming operations are classified as those processes where the desired shape is achieved by imparting plastic deformation to the workpiece in the solid state. Classification by
(1) product,
(2) material,
(3) forming temperature, and
(4) Nature of deformation (sheet metal versus bulk deformation) can also be helpful.

However, the boundaries between categories are not perfectly defined. 
1) the most intricate of shapes, both external and internal, may be cast. 
As a result, many other operations, such as machining, forging and welding can be minimized or eliminated.

2) due to their physical properties, some metals can only be cast to shape (since they cannot be hot-worked into bars, rods, plates, or other shapes) from ingot form as a preliminary to other processing.

3) construction may be simplified. Objects may be cast in a single piece which would otherwise require assembly of several pieces if made by other methods.

4) casting is a process highly adapted to the requirements of mass production. Large numbers of a given casting may be produced very rapidly.

5) large and heavy objects may be cast when they would be difficult or uneconomic to produces otherwise.
Advantages
1) no or very small loss of material

2) little or no scrap

3) increase in ductility (hot forming of cast ingots)

4) increase in strength and hardness

5) high production rate, generate final shape in short time

6) better mechanical and metallurgical properties (strength, toughness, grain size)
1. limitation on mechanical properties

2. porosity

3. surface finish

4. dimensional accuracy

5. safety hazards to humans

6. environmental concerns
Limitations
1) equipment expensive because of the large forces involved

2) suited for a large number of parts only

3) Large capital  expenditure because of heavy presses and die
1) more uniform properties from a directional standpoint

2) strength and lightness in certain light metal alloys, which can be produced only as castings.

3) good bearing qualities are obtained in casting metals
Quality
1) near net-shaping forming

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