Application and development of the hottest superpl

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Application and development of superplastic die forging Abstract: the essence and process of superplastic die forging were introduced; The application status and die materials of superplastic die forging are listed; The characteristics and advantages of superplastic die forging process are described

key words: superplastic die forging; Application; characteristic; Advantages

1. Introduction

with the rapid development of aerospace industry and the increasing expansion of export-oriented economy, the competition for the quality and cost of die forgings is becoming more and more fierce. Superplastic die forging is a new forging process with less cutting and precision forming technology developed in recent years. It makes use of the superplastic properties of metal materials to form the blank and obtain forgings with complex shapes and accurate dimensions

in recent years, the use of superalloys and titanium alloys has been increasing. These alloys are characterized by high rheological resistance, low plasticity, sensitivity to anisotropy of mechanical properties caused by uneven deformation, difficulty in machining and high cost. For example, when the common hot deformation forging process is adopted, the metal loss in machining is up to and the key factor affecting the diversification of raw material structure is about 80% of the oil price, which often can not meet the mechanical properties required for aviation parts; But adopting superplastic die forging method can change the backward forging process of fat head and big ears in the past

superplasticity of metallic materials means that metals can have greater plasticity than general conditions under specific conditions (grain refinement, extremely low deformation speed and isothermal deformation). For example, the elongation of low carbon steel with good plasticity is only 30% ~ 40%, and that of non-ferrous metal with good plasticity is only 60% ~ 70%. However, in Superplastic State, it is generally considered that the elongation of metal with poor plasticity is within 100% ~ 200%, and that of metal with good plasticity is within 500% ~ 2000%

II. Technological process of superplastic die forging [1,8]

the technological process of superplastic die forging is as follows: firstly, the alloy is thermally deformed (extruded, rolled or forged) near the normal recrystallization temperature to obtain ultra-fine grain structure; Then, at the superplastic temperature, the desired shape is formed by die forging in the preheated die; Finally, the forgings are heat treated to restore the high strength state of the alloy

according to the existing conditions of superplasticity, superplastic die forging requires the blank to maintain constant temperature during the forming process, that is, a forging process in which the die and the deformed alloy are heated to the same temperature

Figure 1 Comparison of two die forging processes

(a) common die forging (b) superplastic die forging

1 Blank 2 Forging

Figure 1 shows the process comparison of obtaining the same turbine disk forging (titanium alloy) by ordinary die forging and superplastic die forging. Table 1 lists the comparison of the main process parameters of the two die forging methods. Table 1 Comparison of two die forging processes (titanium alloy turbine disk forging)

process parameters common die forging superplastic die forging blank heating temperature (℃) 940940 die heating temperature (℃) 480940 deformation speed (mm/s) 12.7 ~ 42.30.025 average units, in which the single chip microcomputer control system circuit is as shown in the figure pressure (MPA) 500 ~ 583117 process times during die forging 41

according to the superplastic conditions, Superplastic die forging requires low forming speed (if forging precision parts, the speed should be lower). The adjustable speed slow hydraulic press can be used to gradually slow down the speed when the workpiece is deformed, so as to obtain good fullness. The practice of superplastic die forging shows that it takes about 2 ~ 8min to forge a finished product, which is similar to creep die forging

III. application status of superplastic die forging [1, 2, 3, 8]

superplastic die forging of various parts is introduced as follows:

(1) superplastic die forging is used to manufacture ti-6al-6v-2sn titanium alloy aircraft girders in the United States. Due to the narrow forging temperature range, the deformation resistance of this alloy increases rapidly with the decrease of deformation temperature, so it is difficult to die forge. However, it is easy to form by superplastic die forging. The die forging process parameters are as follows: the titanium alloy of the flat blank is heated to 980 ℃, isothermal die forging is carried out in the precision cast mar-m200 alloy die, the deformation speed is 0.04mm/s, the forming time is 3 ~ 5min, and the total die forging pressure is 2670kn

(2) the U.S. uses superplastic die forging ti-6al-6v-2sn titanium alloy landing gear front wheels, so that the alloy can not only significantly reduce the deformation resistance, but also forge into a precise shape. The die forging process parameters are as follows: the round blank titanium alloy with holes is heated to 980 ℃, isothermal die forging is carried out in the precision cast mar-m200 alloy die, the deformation speed is 0.04mm/s, and the forming time is 5 ~ 8min. The average unit pressure during die forging is 114mpa. To prevent oxidation of forgings during die forging, argon gas shall be used for protection

(3) superplastic die forged Ti-6Al-4V titanium alloy frame reinforcing plate and supporting base parts for Alcoa. The alloy is superplastic die forged at 950 ℃. The projected area of the frame reinforcing plate is 10320mm2, the weight of the forgings after superplastic die forging is 0.32kg, the minimum wall thickness of the reinforcing rib is 3.17mm, and the weight of the ordinary die forgings is 3.63kg. The projected area of supporting base parts is 13545mm2, the weight of forgings after superplastic die forging is 0.82kg, the minimum thickness is 2.67mm, and the weight of ordinary die forgings is 6.36kg

(4) superplastic die forging of turbine blades of taz-8a superalloy for NASA. Taz-8a is a new type of casting alloy developed in the United States in recent years. It is non malleable and will break if it is slightly forged, but the turbine blade is forged by superplasticity. Die forging process parameters are as follows: diameter Φ When the 25.4mm fine grain round billet is heated to 1093 ℃ and isothermal die forging is carried out in the heated die, the one-time deformation can reach 75%. The mold material is TZM molybdenum base cast superalloy

(5) Russian Institute of Aeronautical dynamics used superplastic die forging method to carry out multi piece die forging of BT9 titanium alloy compressor blades. Titanium alloy blank Φ 38mm × 205mm is heated to 960 ℃, isothermal deformation is carried out on 10000kN oil press, the deformation speed is 1.5mm/s, and the average unit pressure is 300 ~ 320MPa. Die material is Ж C6-K П Nickel base casting alloy. use Э Bt-24 glass lubricant. The edge cutting and separation process is carried out on the edge cutting press for the forged multiple die forgings

(6) superplastic die forging for Russia Ж C6-K П Alloy guide vanes. The material is a kind of casting alloy. After thermal hydrostatic pressure, uniform fine grain structure is obtained. The tensile test shows that the alloy has superplasticity between 1075 ℃ and 1125 ℃, and the maximum elongation can reach 500%. A 1000KN oil press is used for superplastic die forging of guide vane. The heating temperature of die and blank is 1100 ℃, and the deformation speed is 1 ~ 2mm/s. The total pressure of die forging is 250kN, and the average unit pressure is 150MPa. The surface quality of the blade is good without cracks or other defects

(7) American Wyman Gordon company can successfully grasp a specific object (such as paper cup and ball) under the control of ideas by using the current international brain computer interface technology in the human brain. The superplastic die forging aircraft horizontal stabilizer connecting rod, compartment and bearing support can be achieved. Compartment size 560mm × 610mm, when common die forging, the weight of compartment forging is 150kg, while the weight of superplastic die forging is 30kg. The weight of common die forging bearing support is 54kg, and the weight of superplastic die forging is 21kg

IV. die materials for superplastic die forging [7, 8]

the superplastic temperature range of superalloys and titanium alloys is mostly above 800 ℃, so the superplastic die forging must have the following requirements for die materials:

(1) high temperature strength

(2) high wear resistance and certain high temperature hardness

(3) excellent heat fatigue resistance and oxidation resistance

(4) appropriate impact toughness

(5) good hardenability and thermal conductivity

at present, nickel base cast superalloys are mostly used in production, such as IN-100, mar-m200 Ж C6-K П Molybdenum base alloy TZM is also used, but when the operating temperature exceeds 500 ℃, due to the serious oxide scale of molybdenum, argon protection is required

v. characteristics and advantages of superplastic die forging process [4, 5, 6, 8]

from many die forgings mentioned above, superplastic die forging process has the following four characteristics:

(1) significantly improve the plasticity of metal materials. For example, IN-100, which was considered not deformable in the past, Ж C6-K П And astroloy and other cast nickel base alloys can also make them superplastic and can die forge turbine discs, blades and even integral turbines with blades

(2) greatly reduce the flow resistance of metal. In the Superplastic State, the flow resistance of metal is very low. The total pressure of general superplastic die forging is only a fraction to a few tens of that of ordinary die forging. Therefore, larger workpieces can be forged on forging equipment with smaller tonnage

(3) the Superplasticity of metal makes the forgings with complex shape, thin wall and high rib forged in one-time die forging. However, when forging high-strength alloy with ordinary die, it needs to be forged for many times, and it is even difficult to forge. This can not only reduce the heating times and save fuel, but also eliminate the surface oxidation defects formed in multiple heating. For example, in common die forging, the surface thickness of forging defects is 0.25mm or more, while in superplastic die forging, it is 0.05mm

(4) in the superplastic die forging process, the metal continues to maintain uniform and fine grain structure. Therefore, the product has uniform mechanical properties as a whole. The mechanical properties are isotropic because the metal grains are still equiaxed after superplastic forming. However, it is anisotropic in common die forging, which reduces the transverse fatigue property and fracture toughness of the workpiece

due to the characteristics of superplastic die forging process, the forgings have the following six advantages:

(1) high precision. During superplastic deformation, due to the high fluidity of the alloy, the filling property is good. After die forging, the size is precise, the amount of machining is very small, and even can no longer be processed, which is particularly beneficial to the high-temperature alloy and titanium alloy forgings that are difficult to be machined. The comparison of the two die forging process parameters is shown in Table 2. Table 2 Comparison of two die forging process parameters

process parameters common die forging superplastic die forging

die forging slope (°) 50 ~ 1 external fillet radius (mm) 2210 internal fillet radius (mm) 10

3.3 insufficient forging (mm) 0.76 ~ 3.30 ~ 1

dislocation (mm) 1.270.51 distortion (mm) 1.520.38 length and width tolerance (mm) ± 1.0 ± 0.38 thickness of rib (mm) 12.72.5 ~ 3.2

(2) high mechanical properties because the forgings obtain uniform fine grain structure and are isotropic, The yield strength, low frequency fatigue and stress corrosion resistance of the alloy have been significantly improved

(3) high material utilization rate the process parameters change greatly due to its superplastic properties. According to statistics, compared with ordinary die forging, the metal consumption of superplastic die forging is reduced by more than half

(4) high die life due to the significantly reduced rheological resistance of the forged materials, the service life of the die can be prolonged, the die loss can be reduced, and the cost can be reduced

(5) forgings with low scrap rate and not full can be re superplastic die forged without affecting the properties of the alloy, thus greatly reducing the scrap rate

(6) no residual stress due to plastic deformation at a very slow speed, there is no residual stress and cold working reserve energy in the forging, so there is no rebound problem, and the size is stable during heat treatment, which is very beneficial to titanium alloy

VI. conclusion

in the production of aviation superalloy and titanium alloy parts, the superplastic die forging process is obviously superior to the conventional die forging process in technology and economy. It improves product quality and qualification rate, reduces machining hours, saves materials and basic equipment investment, and achieves the purpose of reducing forging cost. Superplastic die forging process is especially suitable for forming parts with complex shapes, holes or steps. This process

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