Aug 26 2013
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.
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:
- Making of coins and silver articles
- Automatic forging.
Sources and Further Reading