Forging Process: Forging Process Of Titanium Alloy Forging
Forging process: forging process of titanium alloy forging
Die forging is usually used to make shapes and dimensions close to the finished product, and then only heat treatment and machining of the final blank. The forging temperature and deformation degree are the basic factors to determine the microstructure and properties of the alloy. The heat treatment of titanium alloy is different from the heat treatment of steel, and the structure of the alloy does not play a decisive role. Therefore, the final step of the titanium alloy forging process specification has a particularly important role.
In order to make titanium alloy die forgings and obtain higher strength and plasticity, must make the blank overall deformation amount not less than 30%, deformation temperature does not exceed the phase change temperature and strive to temperature and degree of deformation in the blank deformation as much as possible uniform distribution.
The microstructure and properties of titanium alloy die forgings are less uniform than steel forgings. In the intense metal flow area, the low times of the crystal is fuzzy, and the high magnification is equal to that of the fine grain. In the hard deformation zone, the microstructure is usually retained before the deformation. Therefore in forging some important titanium alloy parts (such as compressor disk, blades, etc.), in addition to controlling the deformation temperature in TB following and an appropriate degree of deformation and control the organization of the original blank is very important of. Otherwise, coarse grain structure or some defects will genetic to the forging and subsequent heat treatment and cannot be eliminated, will lead to forging scrap.
When the forging of titanium alloy forging is complicated, the temperature of the metal is more than that of the alloy, even if the heating temperature is strictly controlled, the temperature of the metal is still more than that of the alloy. For example, when the cross section of the forging process is a titanium alloy blank, the temperature of the part of the middle (web section) is higher than the edge part about 100 degrees Celsius. In addition, in the hard deformation zone and the region with the critical deformation degree, the coarse grain structure is easy to be formed during the heating process after the die forging. Therefore, the mechanical properties of the forging, which is complicated by the forging of the hammer, are often unstable.
Although it is necessary to reduce the risk of overheating of the blank, the heating temperature can be eliminated, but it will lead to a sharp increase in the deformation resistance and increase tool wear and power consumption.
Hammer forging, multiple tap method also can reduce blank local overheating. However, it is necessary to increase the heat of the fire, in order to compensate for the loss of heat from the contact of the rough and the cold mold.
Die forging is relatively simple, and the plastic and durable strength of the deformed metal is not too high. However, it is not suitable to use the hammer forging, because many heating during the die forging will have adverse effects on the mechanical properties. Compared with the hammer, press, hydraulic press, such as the work speed is reduced greatly, and can reduce the alloy deformation resistance and deformation heat effect. During the forging of titanium alloy on the hydraulic press, the unit die forging force of the blank is about 30% lower than that of the hammer, so the service life of the die can be improved. The reduction of thermal effects also decreases the risk of overheating and temperature rise over TB.
Press forging, in the same conditions of unit pressure and forging hammer, can reduce the billet heating temperature of 50 to 100 DEG C. So that heating the metal in the periodic gas interaction and the billet and the die temperature is correspondingly reduced, so as to improve the uniformity of deformation, forging microstructure uniformity is greatly enhanced, mechanical properties of consistency increases. To reduce the deformation rate, increase the value of the most obvious is the reduction of area, the most sensitive tissue defects on the surface shrinkage caused by overheating.
The deformation of titanium alloy is more difficult than steel to flow into the deep and narrow groove. This is because of the high deformation resistance of titanium, and the friction of the tool is larger and the contact surface of the rough cooling too fast. In order to improve the mobility of titanium alloy and to improve the die life. The usual approach is to increase the die angle and fillet radius and the use of lubricant: forging die flash bridge height is steel, 2mm or so
In order to make the groove is easy to fill, sometimes using the bridge size of non uniform flash groove to limit or to accelerate the metal flow to a portion of the groove. For example, a rectangular box shaped forging (shown in Figure 12), the front and back side walls are relatively thin; the left and right sides of the forging. When the in box shaped parts surrounding the B-B shown in the flash tank, due to the metal to flow into the left and right, the small resistance of the side wall, resulting in metal to thinner and the front and the rear side walls are difficult flowing and filling dissatisfaction. Later, in the front and the back side wall still use B-B shown in the flash groove, and a left and a right side wall switch to A-A shown in flash groove, because the bridge width, coupled with damping ditch obstacles, the before and after the thinner side wall full and metal compared with the aforementioned flash groove savings.
One of the most effective ways to improve the mobility and reduce the deformation resistance of the titanium alloy is to improve the preheating temperature of the die. The isothermal forging and hot die forging, which developed in the last twenty or thirty years at home and abroad, provide a feasible method to solve the forming of large and complicated titanium alloy precision forging. This method has been widely used in the production of titanium alloy forgings.
When the titanium alloy is forged by the closed die forging method, the life of the die is reduced due to the great pressure. Therefore, the closed die forging must be strictly limited to the original blank size, which makes the preparation process complex. Whether the use of closed die forging, from the cost and the feasibility of the process to consider two aspects. Open die forging, flash loss accounted for blank weight of 15% ~ 20%, clip to part of the process of waste (if by forging conditions must leave this part) accounted for 10% of the weight of blank. Flash metal relative loss is usually increases with the decrease in weight of blank and some asymmetric structure, cross-sectional area difference large and difficult to filling the part of forgings, burr consumption can be as high as 50%. Closed die forging, although no burr loss, but of billet is a complex process, need to add more transition groove will undoubtedly increase ancillary costs.