With the development of science and technology and the advancement of society, the degree of persecution of various industrialized production on the environment is increasing. However, the superior properties of titanium alloys are increasingly reflected in the production of the chemical industry.
Like isothermal forging, hot die forging is also a more promising precision forging process. The difference is that the mold temperature of hot die forging is higher than that of ordinary forging, but lower than that of isothermal forging. The temperature of the typical hot die forging die is 110～225℃ lower than the temperature of the blank. Compared with isothermal forging, the lowering of the mold temperature allows a wider selection of mold materials, but the ability to form thin and complex forgings is slightly worse.
Compared with conventional forging, hot die forging has the following advantages:
(1) Reduce material consumption of forgings. During hot die forging, the chilling of the die contacting the blank and the work hardening of the material are reduced, and the forgeability of the material is improved. Therefore, the forging is allowed to have a smaller fillet radius and a smaller draft The slope and small forging allowance greatly reduce the quality of forgings. For example, for a Ti-6Al-4V alloy structural part, the mass is 28kg, the mass of the forging produced by the conventional forging process is 154kg, and the mass of the forging produced by the hot die forging process is 109kg, the difference between the two methods is 45kg.
(2) Reduce the number of forging operations and improve the working capacity of the press. For hot die forging, the temperature of the die is higher, and the temperature drop of the blank is less. Conventional forging requires two fires, three fires or more to form forgings, hot die forging It only needs to be done once and at most two fires. And because of hot die forging, the deformation resistance of metal is low, which increases the working capacity of the equipment relatively.
(3) Reduce the amount of machining for forgings. Because the forgings produced are close to the weight and outline dimensions of the parts, compared with the forgings produced by conventional forgings, the amount of material removed during machining is reduced.
(4) The uniformity of the product is better. During the forging process, the temperature gradient is greatly reduced, and the uneven deformation caused by the temperature gradient is easily reduced. Therefore, the uniformity and consistency of the structure and performance of the product are better than that of conventional forging production forgings , But not as good as forgings produced by isothermal forging.
In hot die forging, although the temperature of the billet drops, it is still in the forging temperature range, and the deformation resistance does not rise as sharply as in conventional forging. The strain rate used in hot die forging varies in the range of 0.05 to 0.2s-1. If the strain rate is too low, the temperature of the blank may decrease.
In hot die forging of titanium alloy, forging heating temperature, strain rate, microstructure of preform and holding time are extremely important factors, which play a decisive role in the dimensional accuracy and microstructure of the formed part. Generally lower strain rates and longer holding times increase the possibility of precision forming. The microstructure of the preform has a direct impact on the flow stress and superplasticity of the material, especially the structure after forging. It is not possible to completely eliminate the defects and uneven grains in the raw material through isothermal forging or hot die forging.
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