What Is Forging? Different Types of Forging Processes

Forging is the process in which metal is first heated and then hammered to the required shape and size. Plastic deformation is caused by compress operations, applied by hand hammer, power hammer, or power press. It can be hot forging or cold forging. Both ferrous and non-ferrous metals can be forged. Forging does not produce defects like porosity, voids, inclusion, etc. As in the case of casting. Low and medium carbon steel can be forged easily but high carbon steel and alloy steel are difficult to forge. Modern forging operations make use of machine-driven blocks like hammers or presses which deform the material by controlled pressure. Forging generally has great strength as compared to other methods of manufacturing products. In forging operations, the grain remains unbroken and assumes the contour of the part.

               Forging involves three basic operations in the first one, the length of the metal is increased at the expense of the cross-sectional area. The second operation involves upsetting the metal. Upsetting reduces the length of metal and increases its area of cross-section.  The third operation is squeezing. Squeezing increases the length of the metal without affecting its cross-sectional area. These three operations can be achieved when the flow stress is reached.

• Open die forging operations:- open die forging operation is carried out between flat or simple contoured dies. Dies do not completely cover the workpiece.  In the open die forging operations, metals are worked above their recrystallization temperature.  Upsetting operation is a very common example of an open die forging operation.
• Hand forging:- it is also called smithy or blacksmithy. It is the simplest form of forging. The metal to be forged is first heated to a red hot state and then beaten by a hammer on a metal anvil to give it the desired shape. In smithy's shop, charcoal, coke, and coal are generally used as fuels in the forging operations.

• Power forging:- power forging is employed to produce identical and standard parts on a large scale. Devices that work on forgings by blow are known as hammers and those which work by pressure are called presses.
• Closed die forging:- in this forging operation, the workpiece is completely surrounded by dies. In this process, a billet is deformed by a punch to fill the die cavity without any wastage of material. The metal enclosed in the die cavity is deformed due to high pressure. In this way, a high precision forged component with close dimensional tolerances is produced. Presses used for closed die forging are two kinds:-
• Mechanical presses:- Mechanical forging presses of crank type are widely used in forging operations. Mechanical presses are powered by a motor mounted on the press frame. These presses are used for the production of rivets, screws, nuts, where high operating speed is desired.
• Hydraulic presses:- It has the same working principle as that for smithy except for the construction of dies. In Smithy,  press die have flat surfaces while in a closed die forging, the press die has shaped impression cut on the dies. Precision forgings, hollow forgings, elbows forgings, etc. It can be produced by closed die forging operations.
• Impression dies forging:- in this type of forging, two or more dies containing the impression of the part shape are brought together, the metal undergoes plastic deformation until its enlarged sides come in contact with the die sidewalls. During this process, flash is formed because some of the molten metal for the original metal piece flows outside the die impression. On cooling, flash imparts deformation resistance to the metal and thus strengthening the final product. The final product resembles the die impression. Complex shapes can be produced more easily than in open die forging operation. For example- spherical shape, block-like solids, disc-like objects, etc. Impression die forging is further classified into the following categories:-
• Drop forging:- in this forging, the upper half of the die is dropped onto the lower half. The workpiece is divided equally in the upper and lower die block. When the upper die block falls on the lower die block, the metal is squeezed in the die cavity because of impact. Die block is made to fall from a height of 3 to 5 meters. A series of punch and die operations are performed to change the shape of a material.
• Press forging:- in this operation,  a slow continuous pressure is applied to the area to be forged. In this forging operation, only one blow is given as compared with several impacts in drop forging. These forges are more accurate dimensionally than drop forgings.
• Machine forging:- in this forging operation,  powered hammers or presses are used instead of hand hammers or sledges used in hand forging. Powered hammers or presses can be either mechanical or pneumatic type. These operations are accomplished by the use of a series of dies mounted on the same press or hammer.