Forging can be divided into cold forging and hot forging according to the temperature of blank,in the progress of using forging press machine. Cold forging is generally processed at room temperature, while hot forging is processed at a recrystallization temperature higher than that of the billet metal. Forging is sometimes called warm forging when it is heated but not above the recrystallization temperature.
Cold forging: Under room temperature ,using the forging press to forging the blank material .
Hot forging: forging process in which a metal material is heated above the recrystallization temperature and is pressed by a forging press, forging hammer, or hydraulic press.
Recrystallization temperature: the recrystallization temperature can be calculated roughly as 0.4 times of the melting point of the metal.
For forging products, good flatness can be obtained by cold forging, the flatness of hot forging is the worst, and the flatness of warm forging is medium.
Cold forging, also known as cold volume forming, is a manufacturing process and a processing method. And cold stamping process is basically the same. The equipment mainly includes forging hammer, electric screw forging press, hydraulic press and so on.
Advantages and disadvantages of hot forging
Advantages: if the temperature of the forging material is still much higher than the recrystallization temperature after the processing is completed, the grains will have a longer time to grow, resulting in coarser grains, which can increase fracture toughness (low crack growth rate).
(1) because of high temperature operation, it is more dangerous to the safety of personnel and materials.
(2) the material is easy to be oxidized at high temperature, resulting in scale on the surface, poor smoothness and smoothness.
(3) after the hot forging is completed, the forging materials will shrink in the process of cooling, which will affect the precision of the forging size.
(4) high temperature operation requires high equipment and maintenance costs.
Advantages and disadvantages of cold forging
(1) forging materials are not easy to produce oxide skin, surface finish is better.
(2) the precision of forging size is good.
(3) in the process of processing will produce work hardening (strain hardening), can make the strength and hardness increase.
(4) the direction of the metal fiber direction of the forging can be obtained.
(5) no heating is needed to minimize the pollution problem.
(6) no heating expense is needed to reduce production cost.
(1) the plasticity and toughness of the forging materials are reduced, which is adverse to the subsequent processing.
(2) the required deformation force is greater than that of hot forging.
(3) residual stress will be generated inside the material.
(4) metal grain can be deformed or broken.
(5) the directivity in the process of forging press and forging hammer may be unfavorable to the use of products in the future.