Due to the high pressure, the life of the titanium rod is reduced. Therefore, when the titanium die is forged by the closed die forging method, the volume of the original blank must be strictly limited, which complicates the preparation process. Whether to adopt closed die forging should be considered from both interest and process feasibility. In open die forging, the flash loss accounts for 15% -20% of the blank weight. The process scrap (if this part must be retained according to the die forging conditions) 10% of the blank weight. The relative loss of the flash metal is usually with the blank. The weight decreases and increases. For some forgings with asymmetrical structure, large cross-sectional area difference and difficult to fill, the burr consumption can be up to 50%. Although closed die forging has no burr loss, but the blank making process is complicated, it needs Multi-transition shaped grooves will undoubtedly increase auxiliary costs.
Then only the final blank for heat treatment and cutting. Forging temperature and deformation degree are the basic factors that determine the structure and performance of the alloy. The heat treatment of titanium rods is different from the heat treatment of steel. Die forging is usually used to produce shapes and sizes close to scrap. Has no decisive effect on the structure of the alloy. Therefore, the process specification of the last step of the titanium rod has a particularly important role. It is necessary to make the overall deformation of the blank not less than 30% deformation temperature and not exceed the phase transition temperature. In order to obtain high strength and plasticity of the titanium rod at the same time and stress the temperature and the degree of deformation throughout the deformed blank as uniformly as possible.
After recrystallization heat treatment, the titanium rod and the performance uniformity are not as good as steel forgings. In the fierce metal flow area, the low magnification is fuzzy crystals, and the high magnification is equiaxed fine crystals. In the hard deformation area, because the amount of deformation is small or no deformation, its structure is often kept in the state before deformation. Therefore, in the forging of some important titanium rod parts (such as compressor disks, blades, etc.), in addition to controlling the deformation temperature below TB and the appropriate deformation level, it is very important to control the structure of the original blank. Otherwise, the coarse grain structure or Some defects will be inherited in the forgings, and the subsequent heat treatment cannot be eliminated, which will result in the scrapping of the forgings.
When the thermal effect is locally concentrated in a sharp deformation area, the forging of a titanium rod forging with a complicated shape is forged on the hammer. Even if the heating temperature is strictly controlled, the temperature of the metal may exceed the TB of the alloy, such as a titanium rod blank with a I-shaped cross section, the hammer is too heavy, and the temperature in the middle (web area) is due to the deformation heat effect. The edge is locally about 100 ° C high. In addition, the hard-to-deform area and the area with critical deformation level are likely to form coarse-grained structures with relatively low plasticity and durable strength during heating after die forging. Therefore, the mechanical properties of forgings with complex shapes forged on the hammer are often very unstable. But it will lead to a sharp increase in deformation resistance, and lowering the heating temperature of the die forging can eliminate the risk of local overheating of the blank. Increasing tool wear and power consumption also requires the use of more powerful equipment.
Multiple taps can also reduce local overheating of the blank. However, this is necessary to increase the number of heating fires, when forging on the hammer. To make up for the heat lost by the blank contacting the colder mold. And when the plasticity and durability strength requirements of the deformed metal are not too high, the forging with a relatively simple shape is die-forged. It is better to use hammer forging. However, hammer forging is not suitable for β alloy, because multiple heating during die forging will have a beneficial effect on mechanical properties. Compared with the forging hammer, the working speed of the press (hydraulic machine, etc.) is greatly reduced, which can reduce the deformation resistance and deformation thermal effect of the alloy. When forging titanium rods on the hydraulic press, the unit forging force of the blank is about 30% lower than that of the upper die forging, which can increase the life of the die. The reduction in thermal effects also reduces the risk of metal overheating and temperature rise exceeding TB.
When the unit pressure is the same as forging hammer forging, when forging with a press. It can reduce the heating temperature of the blank by 50100 ℃. In this way, the interaction between the heated metal and the periodic gas and the temperature difference between the blank and the mold are correspondingly reduced, thereby improving the uniformity of deformation, the uniformity of the structure of the die forging is also greatly improved, and the consistency of mechanical properties is also improved . Decrease the deformation speed, the most obvious increase in the surface shrinkage rate, the surface shrinkage rate is the most sensitive to tissue defects caused by overheating.
The friction with the tool is large and the contact with the blank cools down too quickly. To improve the fluidity of the titanium rod and increase the life of the mold. The usual method is to increase the swaging pitch and fillet radius and use lubricant: the height of the burr bridge on the forging die is larger than that of steel, and the characteristic of titanium rod deformation is that it is more difficult to flow into deep and narrow die slots than steel. This is because titanium has a high resistance to deformation. Generally about 2mm larger. Sometimes burrs with non-uniform bridge dimensions can be used to limit or accelerate the flow of metal to a certain part of the groove. For example, to make the groove easy to fill. A rectangular box-shaped forging (as shown in Figure 12) has thinner front and rear side walls; thicker left and right side walls. When the burr groove shown in B-B is used around the box-shaped member, due to the small resistance of metal flowing into the left and right side walls, it is difficult for the metal to flow to the thin front and rear side walls, and the filling is not full. Later, the front and rear side walls still use the burr groove shown in BB, and the left and right side walls are changed to the burr groove shown in AA. Due to the wide size of the bridge and the obstruction of the damping groove, the front and rear side walls are completely filled, and the metal Use the aforementioned flash groove method to save.
Provides a feasible method to solve the forming of large and complex titanium rod precision forgings. This method has been widely used in the production of titanium rods. One of the most effective ways to improve the fluidity of the titanium rod and reduce the deformation resistance is to increase the preheating temperature of the mold. Isothermal die forging and hot die forging developed in the past two or three decades at home and abroad.
