Advantages of hot die forging and conventional forging of titanium alloys

Like isothermal forging, hot die forging of titanium alloy processing technology is also a 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. Typical hot die forging die temperature is 110-225°C lower than the billet temperature. Compared with isothermal forging, the reduction of mold temperature can make a wider selection of mold materials, but the ability to form very thin and complex-shaped forgings is slightly worse.

Compared with conventional titanium alloy flange, hot die forging has the following advantages:

(1) Reduce the 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, so the forgings are allowed to have a smaller fillet radius and a smaller draft The inclination and small forging allowance greatly reduce the quality of forgings. For example, a Ti-6Al-4V alloy structural part has a mass of 28kg. The mass of forging produced by conventional forging process is 154kg, while the mass of forging produced by 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. During hot die forging, the mold temperature is higher and the temperature drop of the billet is less. Conventional forging requires two fires, three fires or more fires to form forgings. Hot die forging Only one time, as many as two fires can be completed. And because of hot die forging, the deformation resistance of the metal is low, which relatively increases the working capacity of the equipment.

(3) Reduce the amount of machining of forgings Because the forgings produced are close to the weight and contour size of the parts, compared with the forgings produced by conventional forging, the amount of material removal in 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 easy to reduce. Therefore, the uniformity and consistency of the structure and performance of the product are better than those produced by conventional forging. , but less than forgings produced by isothermal forging.

During hot die forging, although the billet has a temperature drop, 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 within the range of 0.05-0.2s-1. If the strain rate is too low, the blank temperature may decrease.

In hot die forging of titanium alloys, 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 formed parts. Usually lower strain rates and longer dwell times increase the possibility of precision forming. However, the microstructure of the preform has a direct impact on the flow stress and superplasticity of the material, especially on the microstructure after forging. It cannot be attempted to completely eliminate the defects and uneven grains in the raw material through isothermal forging or hot die forging.

At present, whether titanium alloys and high-temperature alloys use hot die forging technology mainly depends on the total cost of forgings or the need for uniformity and consistency of products. The development trend of this process is to use conventional forging preforms, and finally carry out isothermal or hot die final forging.