Forging presses typically include a ram that moves in a vertical direction to exert a compressive action on a workpiece as opposed to the repeated impact characteristics of forging. In general, forging presses can produce all of the same kind of forgings made on hammers, and they can forge some alloys of moderate toughness that would break apart when rapidly struck by a hammer die. Powered by an engine and operated by an air clutch, mechanical presses have a fully eccentric type of crankshaft that transmits a fixed-length stroke to the vertical piston.
Forging presses form metal into large numbers of identical parts. It is often used in the car manufacturing process and to improve the properties of the metal used. Forged products can be large or very small and can be made of steel or other metal. Forging, either hot and cold forging, does not alter the volume of the part, only its shape, and size.
Forging presses use a process that involves applying gradual pressure to the die holding the workpiece. This can be done as an open or closed forging operation. In the open-press forging process, only one side of the metal is surrounded by a die. In the case of closed die or die forging processes, the metal workpiece is enclosed in a die and the die is pressurized. Closed die forging presses have lessoutflow and requires less draft than open forging. Some of the traditional press forging methods that use closed dies are punching and cutting. The plastic deformation of the workpiece occurs when the die cavities are filled.
Mechanical forging presses are best suited for low-profile forgings and typically incorporate punch and pull pins in the dies that automatically slide the forging out of the die, allowing the die to be designed and thus forgings with a lower draw allowance. This can reduce weight and post-processing. The stresses in press dies are usually high, but the impact load is very low, so harder dies can be used without the risk of breakage that can occur with a power hammer.
Hydraulic forging presses are not widely used for conventional hot forging due to the extremely low ram speed and long die contact time. However, forging presses are widely used in open die forging applications as well as very high tonnage applications, mainly for forging materials other than steel. These machines are ideal for isothermal forging applications due to their slow extrusion operation. Generally, a hydraulic water system is used to drive these machines.
The most obvious difference between hot and cold forging is temperature: cold forging deforms and stresses metals at room temperature, while hot forging heats metals near or at their melting points. The key to the temperature range is recrystallization: cold forging takes place before recrystallization, while hot forging heats the metal above its recrystallization point. The choice of cold forging or hot forging depends on the equipment and processing, customer requirements, and the types of parts produced. Often, the constraints on choosing the right process are determined by the design of the part, as certain parts can be hot forged while others are ideal for cold forging. The designs of cold-forged parts are simple and contain no intricate details, while hot forging produces components with extremely precise, fine features.
Hot forging takes place at extremely high temperatures. The increased temperatures help to avoid strain and hardening as well as lowers the stress flow and the amount of energy needed to deform and shape metals with hot forging presses. When metals cool, they retain their deformed shape. Hydraulic, pneumatic, and mechanical presses are used in the forming process. or the part to be hot forged is heated to a temperature above its recrystallization point, which changes its microstructure. When it is heated, its internal stresses and strength are eliminated to make it more malleable.
Cold forging does not require heating, thanks to which the metal retains its strength and microstructure. High productivity is associated with cold forging. Working conditions are not only more favorable at room temperature, but also energy-saving. This environment also ensures high product performance. The cold forging process, like others, improves the mechanical properties of the workpiece. The finished product is usually stronger than the starting material when using a cold forging press. Besides, the dimensions of the finished, cold-forged product are the most accurate among other forging methods.
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