Due to the high pressure, the life of the titanium rectangular bar is reduced, so when the titanium rod is forged by the closed die forging method, the closed die forging must strictly limit the volume of the original blank, which complicates the material preparation process.
Whether to use closed die forging should be considered from the two aspects of interest and process feasibility. During open die forging, the burr loss accounts for 15%-20% of the weight of the blank. The technological waste of the clamping part (if this part must be left 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 decreases and increases. For some forgings with asymmetrical structure, large cross-sectional area difference and difficult filling, the burr consumption can be as high as 50%. Although closed die forging has no burr loss, the billet making process is complex and needs to be added. Multiple transition grooves will undoubtedly increase auxiliary costs.
Only the final blank is then heat treated and machined. The forging temperature and the degree of deformation are the basic factors that determine the structure and properties of the alloy. The heat treatment of titanium rod is different from that of steel, and die forging is usually used to make a shape and size close to scrap. It does not play a decisive role in the structure of the alloy. Therefore, the process specification of the final step of the titanium rod plays a particularly important role. It is necessary to make the overall deformation of the blank not less than 30% and the deformation temperature does not exceed the phase transition temperature. In order to obtain high strength and plasticity of the titanium rod at the same time, and the temperature and deformation degree should be distributed as uniformly as possible in the entire deformed blank.
After recrystallization heat treatment, titanium rods and property uniformity are not as good as steel forgings. In the intense metal flow area, the low magnification is fuzzy crystal, and the high magnification is equiaxed fine grain; in the hard-to-deform area, due to the small amount of deformation or no deformation, the structure is often kept in 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 the appropriate deformation level, it is very important to control the structure of the original blank. Otherwise, the coarse grain structure or Certain defects will be inherited into the forging, and the subsequent heat treatment cannot be eliminated, which will lead to the scrapping of the forging.
In the rapid deformation area where the thermal effect is locally concentrated, when the hammer is forged with complex titanium bar forgings. Even if the heating temperature is strictly controlled, the temperature of the metal may still exceed the TB of the alloy. For example, when a titanium rod blank with an I-shaped cross-section is forged, the hammering is too heavy, and the local temperature in the middle (web area) is affected by the thermal effect of deformation. The edge is locally about 100°C higher. In addition, in the hard-to-deform region and the region with a critical deformation level, it is easy to form a coarse-grained structure with relatively low plasticity and durability during the heating process after die forging. Therefore, forgings with complex shapes on hammer die forging often have unstable mechanical properties. However, it will lead to a sharp increase in deformation resistance, although reducing the heating temperature of die forging can eliminate the risk of local overheating of the blank. Increased tool wear and power consumption necessitates the use of more powerful equipment.
The local overheating of the blank can also be mitigated by using multiple light strokes. However, it is necessary to increase the number of heating times during die forging on the hammer. to make up for the heat lost from the contact between the blank and the cooler mold. And when the requirements for the plasticity and durability strength of the deformed metal are not too high, the forging shape is relatively simple. It is better to use hammer forging. However, hammer forging is not suitable for beta alloys, because multiple heating in the die forging process will have a favorable 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 thermal effect of the alloy. When the titanium rod is forged on the hydraulic press, the unit die forging force of the blank is about 30% lower than that of the hammer die forging, which can improve the life of the die. The reduction in thermal effects also reduces the risk of metal overheating and temperature rise exceeding TB.
Under the same conditions as forging hammer die forging, when die forging with a press. The blank heating temperature can be reduced by 50100℃. In this way, the interaction between the heated metal and the periodic gas and the temperature difference between the blank and the die 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. . When the deformation speed is reduced, the area shrinkage rate increases most obviously, and the area shrinkage rate is the most sensitive to tissue defects caused by overheating.
The friction with the tool is high and the contact surface of the blank cools too quickly. In order to improve the fluidity of the titanium rod and increase the life of the mold. The usual practice is to increase the die forging slope and fillet radius and use a lubricant: the burr bridge height on the forging die is greater than that of steel, and the deformation of titanium rods is characterized by more difficult flow into deep and narrow die grooves than steel. This is because of the high deformation resistance of titanium. Generally about 2mm larger. Flash grooves with non-uniform bridge dimensions are sometimes used to restrict 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 side walls; left and right side walls are thicker. When the burr groove shown in B-B is used around the box-shaped part, due to the small resistance of the metal flowing into the left and right side walls, it is difficult for the metal to flow to the thinner front and rear side walls, and the filling is not satisfied. Later, the front and rear side walls still use the burr grooves shown in BB, while the left and right side walls use the burr grooves shown in AA. Due to the wide size of the bridge and the obstruction of the damping groove, the front and rear thinner side walls are completely filled, and the metal is relatively thin. Use the aforementioned burr groove method to save.
It provides a feasible method for solving the forming of large and complex titanium rod precision forgings. This method has been widely used for titanium rod production. One of the most effective ways to improve the fluidity of titanium rods 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 20 to 30 years at home and abroad.
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