What is Forging? Different types of Forging Process

 

Early man discovered native metals around 5000 BC, however, the methods to work on them were developed many centuries later. Metals are extracted from ores found deep inside the earth's surface. They are extracted in solid form, which must be remodelled to the desired shape using various techniques.

Metallurgy is the study of extracting metals in their purest form and processing it to make them available for use. Various metallurgical processes are involved in changing the shape, form, texture, and size of metals. In the olden days, a metalsmith heated the metal slightly below its melting point and used a hammer to reshape it. This process is called forging.

 

What is the Forging Process?

Forging is the process of reshaping or forming metals to the desired shape by pressing or by applying forces. In this process, a billet is squeezed in between two dies with the help of a hammer. The billet is the metal rod or bar ready to be formed. The primary advantage of forging is that the mass production of similar components can be achieved at ease. Crane hooks, spanners, shafts, hinges, landing gear cylinders and many other components are manufactured through the forging process. Forged products have been proven to have better mechanical properties like strength, ductility and fatigue resistance.

 

Evolution of the Forging Industry

The forging process evolved during 4000 BC or earlier. Early humans forged iron to make weapons for war. During the 19th century, the Blacksmiths became skilful in open die forging of wrought iron. In 1862, the process of closed die forging began in the United States. The industrial revolution and world war II positively impacted the forging industry due to the need for improved machinery components. Earlier smiths used hammers for forging, which involved heavy manual work. Today computer-controlled hydraulic and pneumatic hammers are used for forging. These advanced methods have improved productivity with less human intervention.

The two significant types of forging are hot forging and cold forging. 

 

Hot Forging

In hot forging, the metal is heated above the recrystallisation temperature and is reshaped. Recrystallisation temperature is the point at which new grains are formed. 

 

Advantages of Hot Forging

• The metal is heated to a high temperature to enhance the flow of metal; hence less force is required for the hot forging process.
• A wide range of metals can be processed, and complex shapes can be achieved.

 

Disadvantages of Hot Forging

• Lubrication of the die is difficult.
• Oxidation and scaling may occur on the workpiece.
• Warping of material during the cooling process reduces the precision of finished products.

 

Cold Forging

In cold forging or cold forming, the metal is processed at room temperature. The metal is pounded against the die until it acquires the profile of the die. Soft metals like steel can be cold-formed easily. 

 

Advantages of Cold Forging

•  Unlike in hot forging, oxidation does not take place, and it is easy to lubricate the dies.
• The forged products have a better surface finish.

 

Disadvantages of Cold Forging

• Not all metals can be cold forged. Steels with carbon content above 0.5% cannot be cold-formed.
• High force is required.
• Designing and manufacturing tools for cold forging are tedious.

 

 

Defects of Forging

Forging yields better strength than casting and improves the mechanical properties. A manufacturing engineer must optimise the parameters and design the process to obtain a  properly forged component. Forging defects may occur when the parameters are not optimised.

• If the force of the hammer blow is not sufficient, dendritic structures will form on the inner surfaces. Proper forging happens only at the outer surface of the metal. This defect is called incomplete forging penetration.
• Excessive working on the surface at a low temperature can cause surface cracking.
• Some small sections of the die cavity can go unfilled due to the die's improper design.

 

Many recent developments were made in the forging industry to increase the accuracy of forged components. Using the micro forging process, biomedical instruments with high precision can be mass-produced economically. Whenever a small portion of the workpieces has to be forged, the rotary forging technique is used. In rotary forging, the metal is placed inside a rotating die and a pressing anvil. 

Biomedical, automotive, aerospace and many manufacturing industries use forging. The global automotive forging market is expected to reach USD 56,801.7 million by 2030. The average annual salary of a Forge Engineer is around ₹ 3,94,510 per annum.

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