A brief analysis of the die forging process of titanium rods!
Titanium rod manufacturers briefly analyze the titanium rod die forging process. Because the high pressure reduces the life of the titanium rod, when the titanium rod is forged using the closed die forging method, the closed die forging must strictly limit the volume of the original blank, which complicates the material preparation process.
1. Whether to use closed die forging.
Consider both interest and process feasibility. During open die forging, the burr loss accounts for 15%-20% of the weight of the blank. The process waste in the clamped part (if this part must be retained according to the die forging conditions) accounts for 10% of the weight of the blank. The relative loss of burr metal usually increases with the blank. The weight increases due to the decrease in weight. For some forgings with asymmetrical structures, large cross-sectional area differences, and parts that are difficult to fill, the burr consumption can be as high as 50%. Although there is no burr loss in closed-die forging, the blank making process is complicated and requires more additions. Multiple transition tool grooves will undoubtedly increase auxiliary costs.
2. Only the final blank is then subjected to heat treatment and machining.
Forging temperature and deformation degree are the basic factors that determine the alloy structure and properties. The heat treatment of titanium rods is different from the heat treatment of steel. Die forging is usually used to produce products with shapes and sizes close to scrap. It does not play a decisive role in the structure of the alloy. Therefore, the process specifications of the final processing step of titanium rods play a particularly important role. The overall deformation of the blank must be no less than 30% and the deformation temperature must not exceed the phase transformation temperature. In order to obtain high strength and plasticity of the titanium rod at the same time, the temperature and deformation degree should be distributed as evenly as possible throughout the deformed blank.
3. After recrystallization heat treatment.
Titanium rods and performance uniformity are inferior to steel forgings. In the area of intense metal flow, there are fuzzy crystals at low magnification and equiaxed fine grains at high magnification. In the difficult-to-deform area, due to small or no deformation, the structure often retains the state before deformation. Therefore, when forging some important titanium rod parts (such as compressor discs, blades, etc.), in addition to controlling the deformation temperature below TB and an appropriate deformation level, it is very important to control the structure of the original blank. Otherwise, the coarse-grained structure or Certain defects will be inherited into the forging and cannot be eliminated by subsequent heat treatment, causing the forging to be scrapped.
4. When hammer forging titanium rod forgings with complex shapes in the sharp deformation area where the thermal effect is locally concentrated.
Even if the heating temperature is strictly controlled, the temperature of the metal may still exceed the TB of the alloy. For example, when forging a titanium rod blank with an I-shaped cross-section, the hammering is too heavy, and the local temperature in the middle (web area) will be affected by the deformation heat effect. The edge is locally high by about 100°C. In addition, in difficult-to-deform areas and areas with critical deformation levels, coarse-grained structures with relatively low plasticity and durability strength are easily formed during the heating process after die forging. Therefore, the mechanical properties of hammer forged forgings with complex shapes are often very unstable. However, it will lead to a sharp increase in deformation resistance. Although lowering the die forging heating temperature can eliminate the risk of local overheating of the blank. Increased tool wear and power consumption require the use of more powerful equipment.
5. Multiple taps can also reduce local overheating of the blank.
However, it is necessary to increase the number of heating fires when hammering and die forging. To compensate for the heat loss caused by the contact between the blank and the cooler mold. And when the plasticity and durability strength index requirements of the deformed metal are not too high, forgings with relatively simple shapes can be forged. It is better to use hammer forging. However, hammer forging is not suitable for β alloys because multiple heatings during the die forging process will have a beneficial effect on the mechanical properties. Compared with the forging hammer, the working speed of the press (hydraulic press, etc.) is greatly reduced, which can reduce the deformation resistance and deformation heat effect of the alloy. When die forging titanium rods on a hydraulic press, the unit die forging force of the blank is about 30% lower than that on a hammer, which can extend the life of the mold. The reduction in thermal effects also reduces the risk of metal overheating and temperature rise exceeding TB.
6. When die forging with a press under the same conditions as the unit pressure of the forging hammer.
It can reduce the heating temperature of the blank to 50-100℃. In this way, the interaction between the heated metal and the periodic gas and the temperature difference between the blank and the mold are also reduced accordingly, thereby improving the uniformity of deformation, the uniformity of the structure of the die forging is also greatly improved, and the consistency of the mechanical properties is also improved. . Reduce the deformation speed and the most obvious value growth is the surface shrinkage, which is the most sensitive to tissue defects caused by overheating.
7. The friction with the tool is large and the contact surface of the blank cools too quickly.
To improve the fluidity of titanium rods and increase mold life. The usual approach is to increase the forging slope and fillet radius and use lubricant: the height of the burr bridge on the forging die is larger than that of steel, and the deformation characteristic of titanium rods is that it is more difficult to flow into deep and narrow die grooves than steel. This is because titanium has high resistance to deformation. Generally about 2mm larger. Sometimes burr grooves with non-uniform bridge sizes can be used to limit or accelerate the flow of metal to certain parts of the groove. For example, in order to make the groove easy to fill. A rectangular box-shaped forging (as shown in Figure 12) has thinner front and rear sidewalls and thicker left and right sidewalls. When the burr groove shown as B-B is used around the box-shaped part, the resistance of the metal flowing into the left and right side walls is small, making it difficult for the metal to flow to the thinner front and rear side walls, resulting in insufficient filling. Later, the front and rear side walls still used the burr grooves shown as B-B, while the left and right side walls used the burr grooves shown as A-A. Due to the wide size of the bridge and the obstruction of the damping groove, the thinner side walls at the front and rear were completely filled, and the metal was thicker. Use the aforementioned burr groove method to save.
It provides a feasible method to solve the forming of large and complex titanium rod precision forgings. This method has been widely used in titanium rod production. One of the most effective ways to improve the fluidity of titanium rods and reduce deformation resistance is to increase the preheating temperature of the mold. Isothermal die forging and hot die forging have been developed in the past 20 to 30 years at home and abroad.
