Forging is the oldest of all processes of metalworking, entailing compressive stress application that exceeds the metal's flow stress. It's an indirect compression process which can be applied slowly or quickly in hot or cold temperature environments. Temperature decisions are taken based on factors such as the metal's ease of deformation, requirement of certain surface finishes or mechanical properties. However, above 90% of forging is done through hot forging process. Forging processes can be broadly classified into two types namely:
Impact forging – A quick forging process that involves impact applied for short periods of time. This process is mainly used for smaller work pieces as larger cast pieces would not comply well enough (in terms of impact penetration). They are of three sub categories namely:
Smith Forging – It's the oldest type of forging that involves manually shaping the metals to the desired shape. The surface on which the metal is shaped is termed 'anvil'. The anvil is a flat surfaced metal of heavy mass, containing a curved horn for attaining the desired shape and square hole atop it to accommodate fittings. The work piece is held through the square hole on one end and is hammered on the other with the help of a sledge hammer. This process has become uncommon, replaced with machined process.
Drop Forging – In drop forging the blacksmith is replaced with a steam or a mechanical hammer. However the quality of the product is still dependent on the skill of the forger. There are two means of drop forging namely open forging where the work pieces' size is reduced through repeated blows; the objective being reducing the thickness of the work piece with width pre-laid width constraints and drop die forging where the square hole or the tup is replaced with dies to accommodate various grooves and depressions.
Upset Forging – A double acting press using horizontal work motions in place of vertical, this process was initially developed to upset or gather metal for head formations on bolts, However it was later widened to incorporate a wide variety of forgings. there are six different heading tools and dies to be used in turns for producing outputs of varied sizes.
Press forging – This process entails the gradual build up of pressure on the work piece for it to yield. Press forging is used for larger metal chunks, where the penetration of the impact takes time. These make for more homogeneous and high quality products that characterize better physical and mechanical properties. Therefore they are more expensive as compared to impact forged products. While impact forging is carried out on a mechanical press, press forgings require hydraulic presses that have vertically moving rams, producing large forgings. These hydraulic presses are capable of handing load capacities from 6,000 tons to 10,000 tons while producing high quality large forgings.
The majority of products like forged flanges manufacturer in India at CHW Forge produce through the hot forging process, since it produces better quality and high capacity products. Since products like rolled rings, self reinforced nozzles and flanges are mostly used for high pressure environments, manufacturers in India state that hot forging processes make outputs that are sturdier, uniform, homogeneous and better yielding.
What are your takes on the forging processes? Which do you think is the best yielding? Share your comments and opinions with us.