Press Forging – Metallurgical Processes

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Press forging may be defined as the process of shaping a metal that is placed between two dies by applying mechanical or hydraulic pressure. Press forging is usually done on a forge press - a machine that applies gradual pressure on the forging dies. The shape of the metal is usually accomplished by a single stroke of the press for each die station.

The key difference between impact forging and press forging is that in the former method a sudden impact force is applied on the die, while in the latter method a gradually increasing pressure is applied on the die.

Press forging may be undertaken as a hot or cold forging process. Press forging is suitable for high volume productivity of forgings. The various forging operations in a press forge and its applications are described below.

Technique of Press Forging

Press forging is a technique that applies gradual pressure on a die holding a work piece. This can be done as an open die or closed die forging process. In an open die press forging process, the metal is surrounded by the die on one side only. In the case of impression die or closed die forging methods, the metal work piece is enclosed in a die and pressure is applied on the die. Plastic deformation of the work piece occurs and it fills the die cavities.

Press forging in closed die method leads to less flash and needs less draft when compared to open die forging. Some of the common press forging methods that use closed dies are coining and hubbing.

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Coining

This forging method is used to make coins. The metal is enclosed in a closed die and high pressures (almost 5-6 times the strength of the metal) are applied to obtain fine details of the die. Lubricants are not used in coining.

Hubbing

In this type of press forging, a pattern is pressed onto the die, such that the pattern flows into the die cavities. This process is often used in making of silverware.

Types of Forging Presses

The three main types of forging presses used for press forging are listed below:

• Mechanical Press ' converts the rotation of the motor into linear motion of the ram.
• Hydraulic Press ' hydraulic motion of the piston moves the ram.
• Screw press ' screw mechanism actuates the ram movement.

Advantages of Press Forging

The advantages that press forging offers over impact of drop forging are listed below:

• Deforms the work piece completely
• Compression rate of the work piece can be controlled
• More economical for high volume productions
• Any size and shape can be created
• Requires less draft and produces lesser scrap.

Industrial Applications

Some of the industrial applications of press forgings are listed below:

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• Making of coins and silver articles
• Automatic forging.

Sources and Further Reading

Comparison Drop Forging Press Forging Method Uses a hammer to shape metal into the desired form Uses a press to apply pressure to the metal, forcing it into the desired shape Equipment Requires a drop hammer or power hammer Requires a hydraulic or mechanical press Production speed Generally slower than press forging Generally faster than drop forging Material shape Works best with simple shapes and small to medium-sized parts Can handle more complex shapes and larger parts Surface finish Generally results in a rougher surface finish than press forging Can produce a smoother surface finish Material waste Produces more waste material than press forging due to the need for trimming and finishing operations Produces less waste material Cost Often more expensive due to the specialized equipment required Often less expensive due to the versatility of the equipment Strength Generally results in stronger parts due to the deformation and compression of the metal Generally produces slightly weaker parts due to the less intense deformation of the metal