What is the classification of forging?

Release time:

09 Mar,2023

Forging and stamping are mainly classified according to the forming method and deformation temperature. According to the forming method, forging can be divided into two categories: forging and stamping; according to the deformation temperature, forgings can be divided into hot forging, cold forging, warm forging and isothermal forging.

hot forging

Its forging temperature is higher than the recrystallization temperature of the metal. Increasing the temperature can increase the plasticity of the metal, which is beneficial to improve the internal quality of the workpiece and make it difficult to crack. High temperatures can also reduce the deformation resistance of the metal and reduce the tonnage of forging machinery required. However, there are many hot forging processes, the accuracy of the workpiece is poor, the surface is not smooth and clean, and the forgings are easy to oxidize, decarburize and burn. When the workpiece is large and thick, the material strength is high, and the plasticity is low (such as the rolling and bending of extra-thick plates, the drawing of high-carbon steel rods, etc.), hot forging is used. Cold forging is usually used instead of hot forging when the metal (e. g., lead, tin, zinc, copper, aluminum, etc.) has sufficient plasticity and small deformation (as in most stamping processes), or when the total deformation is large and the forging process used (e. g., extrusion, radial forging, etc.) facilitates plastic deformation of the metal. In order to complete as much forging work as possible by one heating, the temperature range between the initial forging temperature and the final forging temperature of hot forging should be as large as possible. However, too high initial forging temperature will cause excessive growth and overheating of metal grains, thereby reducing the quality of forged parts. When the temperature is close to the melting point of the metal, the intergranular low melting point material will melt, intergranular oxidation will occur, and overfire will be formed. When forging, overburned billets often break. Commonly used hot forging temperature: carbon steel 800~1250 ℃; alloy structural steel 850~1150 ℃; high-speed steel 900~1100 ℃; ordinary aluminum alloy 380~500 ℃; titanium alloy 850~1000 ℃; brass 700~900 ℃.

cold forging

It refers to forging and pressing at a temperature lower than the recrystallization temperature of the metal. Generally speaking, cold forging refers to forging at room temperature, while forging at a temperature higher than room temperature but not higher than the recrystallization temperature is called warm forging. Warm forging has high precision, smooth surface and small deformation resistance.

The workpiece formed by normal temperature cold forging has high shape and size accuracy, smooth surface, few processing procedures, and is convenient for automatic production. Many cold forged and cold stamped parts can be directly used as parts or products without machining. However, in the process of cold forging, due to the low plasticity of the metal, it is easy to crack during deformation, and the deformation resistance is large, and large tonnage forging machinery is required.

warm forging

Forging performed at a temperature higher than the normal temperature but not higher than the recrystallization temperature is called warm forging. The metal is preheated and the heating temperature is much lower than the heating temperature of hot forging. Warm forging has high precision, smooth surface and small deformation resistance.

isothermal forging

It is to keep the blank temperature constant during the entire forming process. Isothermal forging is to make full use of the high plasticity of some metals at the same temperature, or to obtain a specific organization and performance. Isothermal forging requires that the die and billet be kept at a constant temperature together and is costly. It is only used for special forging processes, such as superplastic forming.