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 die temperature of hot die forging is higher than that of ordinary forging, but lower than that of isothermal forging. A typical hot die forging die temperature is 110-225°C lower than the billet temperature. Compared with isothermal forging, the reduction of mold temperature allows a wider selection of mold materials, but the ability to form very thin and complex shape forgings is slightly worse.

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

(1) Reduce the material consumption of titanium forged disc. 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. Slope and small forging allowance, thus greatly reducing the quality of the forging. For example, a Ti-6Al-4V alloy structural part has a mass of 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, and 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 temperature of the die is higher and the temperature drop of the billet is less. Conventional Titanium Eye Bolt requires two, three or more fires to form forgings, hot die forging Just one time, as many as two fires can be completed. And due to hot die forging, the deformation resistance of the metal is relatively low, which relatively increases the working capacity of the equipment.

(3) Reduce the amount of machining of forgings Because the produced forgings are close to the weight and contour size of the parts, the amount of material removed in machining is reduced compared to forgings produced by conventional forging.

(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 those produced by conventional forging. , but not as good as 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 increase in deformation resistance is not as sharp 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 billet temperature may decrease.

In the hot die forging of titanium alloys, the forging heating temperature, strain rate, microstructure of the preform and holding time are extremely important factors, which play a decisive role in the dimensional accuracy and microstructure of the formed parts. Typically lower strain rates and longer dwell times increase the likelihood of precision forming. The microstructure of the preform has a direct impact on the flow stress and superplasticity of the material, especially the post-forging structure. It is impossible to completely eliminate the defects and grain inhomogeneity in the raw material by isothermal forging or hot die forging.

At present, the use of hot die forging process for titanium alloys and superalloys mainly depends on the total cost of forgings or the needs of product uniformity and consistency. The trend in this process is to use conventional forging preforms, followed by final isothermal or hot die forging.