Forming method of ultra-thin short-wave S-shaped metal expansion joint

Abstract

The application discloses a forming method of an ultrathin short-wave S-shaped metal expansion joint, and steps are as follows: designing a prefabricated metal sheet; determining a bending width and a bending times; bending the metal sheet; bending a corrugated sheet; welding the corrugated sheet; air-expanding and shaping a corrugated pipe; cutting off a process section; and welding an end joint. The corrugated sheet is bent to form the corrugated pipe, the thinning rate of the sheet is extremely small, the thickness of the corrugated sheet is uniform, the wall thickness error is small, the rigidity and fatigue life of the corrugated pipe can be improved, the corrugated pipe can be directly formed by bending, the wave distance and the wave height can be adjusted by changing the crease position, the forming mode is simple, all the corrugated pipes can be formed at one time, the forming efficiency is high, corrugated pipes with different cross-sectional shapes can be formed by bending, the cross-sectional circumference of the corrugated pipe formed by the method is not limited, the corrugated shape of the corrugated pipe can be adjusted, the corrugated pipe with a complex diaphragm shape with high forming precision and small corrugated spacing can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to a forming method of metal expansion joint, in particular to a forming method of ultra-thin short-wave S-shaped metal expansion joint. BACKGROUND

[0002] With the progress of aerospace technology, aircraft is developing rapidly towards high Mach number, high carrying capacity, super-long endurance and super-long range, which puts forward higher requirements on the performance and reliability of the engine. In the face of higher service temperature and more severe working conditions, it is necessary to improve the strength and reliability of the aero-engine parts. For example, in the engine parts, due to thermal elongation or temperature stress, the pipeline is deformed or damaged, and a compensator needs to be provided on the pipeline to reduce the stress of the pipe wall and the force acting on the valve. The expansion joint has the functions of displacement compensation and vibration absorption, and is an important compensation structure in the aero-engine. The expansion joint is composed of a bellows and other parts, and the thermal compensation performance of the expansion joint is mainly determined by the bellows. The bellows compensates for the displacement change of the engine internal pipeline or tubular part caused by temperature and load through its own elastic expansion.

[0003] At present, metal bellows are usually prepared by forming methods such as hydraulic forming, roll forming and welding forming [Manufacturing and application of bellows assemblies. Xu Kaixian. 1998. Research on internal high-pressure forming mechanism of hollow crankshaft. Lin Junfeng. 2007]. (1) Hydraulic forming process: The hydraulic forming process is to use the pressure of liquid in the pipe blank to expand the pipe blank in the restriction ring until the yield occurs along the ring, and then compress the pipe blank to the required length. In the hydraulic forming process, the axial pressure expansion can improve the expansion degree of the material, so the hydraulic forming process is beneficial to the forming of bellows with deep corrugations and can improve the forming rate of bellows. It is the main forming method of metal bellows at present [Numerical simulation and experimental study on hydraulic forming process of bellows. Tang Zhidong. 2015. Application progress of internal high-pressure forming. Yuan Shijian, Wang Zhongren. 2002]. (2) Roll forming process: Roll forming is to place the pipe material in the roll forming machine, and the driving wheel and the two driven wheels drive the pipe material to rotate through friction, while the driving wheel and the driven wheel continuously reduce the distance under the action of axial force, and finally roll the bellows in the circumferential direction. Roll forming is mainly suitable for the production of large-scale bellows with arc shape or relatively long wavelength [Research on repeated bending failure mechanism, structure optimization and performance control of metal bellows. Hao Zengliang. 2020]. (3) Welding forming process: The welding forming process is to form a single wave by welding the inner edge of the pre-punched multiple pairs of ring-shaped wave pieces, and then weld the inner and outer edges of the membrane to form a bellows, and finally form a thin shell type part with corrugated shape in space. The welding forming process is mainly used to manufacture bellows with large wave height size. In order to ensure the welding precision, multiple shaping is often required, and the welding difficulty is high [Research on axial performance and bending performance of welded metal bellows. Zhang Zedong. 2016].

[0004] The three forming methods have certain limitations when forming the ultra-thin short-pitch S-shaped bellows with a thickness less than 0.2 mm, a wave pitch less than 12 mm and a complex shape. The ultra-thin short-pitch S-shaped bellows is a key part of an aero-engine, has the characteristics of ultra-thin wall thickness, large deformation of wave peak position and complex local deformation. High dimensional accuracy and surface quality are required, and the wall thickness thinning rate of the part is required to be controlled within 10%, so it is difficult to guarantee the forming quality by using the traditional process. When hydraulic forming is used, due to the complex shape of the S-shaped bellows and the large deformation of the wave peak position, a large internal pressure is required to guarantee the forming accuracy and avoid wrinkling. The increase of the internal pressure will lead to serious thinning of the wave peak position, poor wall thickness uniformity and easy cracking at the initial stage of forming. In addition, due to the shortening of the wave pitch and the increase of the bulging curvature radius, the internal pressure will also increase, the thinning will be serious and the risk of cracking will increase. The wall thickness error is large in roll forming, and the wall thickness difference at the wave peak and wave valley is 10% to 20%. Therefore, when the ultra-thin short-pitch S-shaped bellows is formed by using roll forming, the forming accuracy of the wall thickness is difficult to guarantee. The wave peak position is seriously thinned, and cracking is prone to occur, and the surface quality is poor. When the ultra-thin short-pitch S-shaped bellows is formed by using the welding process, the forming accuracy can be guaranteed. However, there are too many welds, the reliability is low, the service performance is poor, it is difficult to apply to the working environment of the aero-engine with high load, and the forming efficiency is low.

[0005] To solve the problems of low forming accuracy, easy cracking, poor wall thickness uniformity and difficulty in applying to extreme working environment due to too many welds of the ultra-thin short-pitch S-shaped metal expansion joint formed by using the traditional forming method, a new forming method of the ultra-thin short-pitch S-shaped metal expansion joint needs to be developed. SUMMARY

[0006] The purpose of the present application is to provide a forming method of an ultra-thin short-pitch S-shaped metal expansion joint to solve the problems of poor forming accuracy, easy cracking and difficulty in adapting to extreme working environment of the formed part caused by the limitation of the shape and size of the bellows during the forming process by using the traditional forming method.

[0007] The technical scheme of the present application is as follows:

[0008] A forming method of an ultra-thin short-pitch S-shaped metal expansion joint, the steps are as follows:

[0009] Step 1, design a preformed metal sheet: analyze the characteristics of the ultra-thin short-pitch S-shaped metal expansion joint, determine the material and outer shape profile of the required original metal sheet by theoretical calculation or simulation method;

[0010] Step two, determine the bending width and bending times: according to the corrugated pipe wave shape and wave height, determine the bending width, and according to the corrugated pipe wave number and the prefabricated metal sheet determined in step one, determine the bending times and bending position; wherein, the number of bending (bending angle) = corrugated pipe wave number * 2 + 1;

[0011] Step three, metal sheet bending: according to the bending width, bending position and bending times determined in step two, the metal sheet determined in step one is bent along the width direction to obtain a corrugated plate with process section at both ends;

[0012] Step four, bending of corrugated plate: the corrugated plate obtained in step three is placed in the bending die for bending; during the forming process, the clamping block and the bending die block clamping hold the front end of the corrugated plate, and the corrugated plate is formed by rotating around the center of the bending die, so that the required bending angle is obtained, and the rear end of the corrugated plate is pressed on the anti-wrinkle block by the pressing block;

[0013] Step five, corrugated plate welding: the bent corrugated plate obtained in step four is placed in the welding fixture, and the corrugated plate is welded at the two ends to obtain a corrugated pipe semi-finished product;

[0014] Step six, corrugated pipe gas expansion shaping: the corrugated pipe semi-finished product obtained in step five is placed in the expansion die, and the insufficient part of the corrugated pipe semi-finished product is expanded by gas pressure to make the corrugated pipe semi-finished product fully adhere to the expansion die to obtain the required corrugated pipe product;

[0015] Step seven, process section cutting: the process section on both sides of the corrugated pipe obtained in step six is cut by wire cutting to obtain a corrugated pipe without process section;

[0016] Step eight, end joint welding: the corrugated pipe obtained in step seven is welded with an end joint (generally a flange) to obtain a final expansion joint.

[0017] The beneficial effects of the present application are:

[0018] I. The present application adopts the method of bending and forming corrugations of metal sheet, and the corrugations are obtained by bending and forming the sheet. The thinning rate of the sheet is very small, the corrugation thickness is uniform, the wall thickness error is small, and the stiffness and fatigue life of the corrugated pipe can be improved.

[0019] II. The present application adopts the method of bending and forming corrugations of metal sheet, and the corrugations can be directly formed by bending and forming. The pitch and height of the corrugations can be adjusted by changing the crease position, the forming method is simple, and all corrugations can be formed at one time, and the forming efficiency is high.

[0020] III. The present application adopts the method of bending and forming corrugations of metal sheet, and the corrugated pipe with different cross-sectional shapes such as rectangular, circular and racetrack shape can be formed by bending and forming. In addition, the cross-sectional circumference of the corrugated pipe formed by the method is not limited.

[0021] Four, the corrugated pipe gas expansion shaping method of the present application can adjust the corrugated shape of the corrugated pipe, and the corrugated pipe with complex diaphragm shape and high forming precision and small corrugated pitch can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The ultra-thin short-wave S-shaped metal expansion joint forming process flow chart adopted by the present application.

[0023] Figure 2 The corrugated plate bending forming principle diagram of the present application.

[0024] Figure 3 The corrugated plate bending forming principle diagram of the present application.

[0025] Figure 4 The corrugated plate bending forming principle diagram of the present application.

[0026] Figure 5 The corrugated plate bending forming principle diagram of the present application.

[0027] Figure 6 The corrugated plate bending forming principle diagram of the present application.

[0028] Figure 7 The corrugated plate bending forming principle diagram of the present application.

[0029] Figure 8 The corrugated plate bending forming principle diagram of the present application.

[0030] Figure 9 The expansion joint finished product diagram of the present application.

[0031] Figure 10 The corrugated pipe and traditional welded corrugated pipe compression simulation stress distribution diagram of the present application,

[0032] Among them,

[0033] a) The corrugated pipe compression simulation stress distribution cloud diagram obtained by using the forming method of the present application when λ = 2

[0034] b) The corrugated pipe compression simulation stress distribution cloud diagram of the traditional welded corrugated pipe when λ = 2

[0035] c) The corrugated pipe compression simulation stress distribution cloud diagram obtained by using the forming method of the present application when λ = 3

[0036] d) The corrugated pipe compression simulation stress distribution cloud diagram of the traditional welded corrugated pipe when λ = 3

[0037] e) The corrugated pipe compression simulation stress distribution cloud diagram obtained by using the forming method of the present application when λ = 4

[0038] f) Traditional welded bellows compression simulation stress distribution cloud map when λ = 4.

[0039] In the figure: 1 is a bent plate, 2 is an unbent plate, 3 is a bent corrugated plate, 4 is a bending roller, 5 is a supporting mandrel, 6 is a pressing block, 7 is an anti-wrinkle block, 8 is an inlay block, 9 is a clamping block, 10 is a bent corrugated plate, 11 is a welded corrugated tube, 12 is an air expansion shaping die, and 13 is an expansion joint product. DETAILED DESCRIPTION

[0040] The specific embodiments of the present application are further described below in combination with the drawings and technical solutions.

[0041] Example 1: Combination Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 It is explained that the present application proposes a forming method of an ultra-thin short-pitch S-shaped metal expansion joint, which is performed according to the following steps:

[0042] Step one, design a prefabricated metal sheet. Analyze the characteristics of the ultra-thin short-pitch S-shaped metal expansion joint, determine the material and outline of the original metal sheet by theoretical calculation or simulation, etc. Determine the width of the sheet bending direction according to the overall length of the bellows axial, and determine the length of the sheet according to the length of the bellows peak ring.

[0043] Step two, determine the bending width and bending times. According to the shape and height of the bellows wave, calculate the length of the line between the bellows peak and the bellows valley, determine the bending width, and according to the number of bellows waves and the prefabricated metal sheet determined in step one, determine the bending times and bending position. Among them, the number of bending marks (bending angle) = bellows wave number * 2 + 1.

[0044] Step three, bend the metal sheet. According to the bending width, bending position and bending times determined in step two, bend the metal sheet determined in step one along the width direction. Bend along the length direction of the plate to obtain a corrugated plate with a process section of no more than 5mm at both ends (such as Figure 3 ).

[0045] Step four, bend the corrugated plate. Place the corrugated plate obtained in step three in the bending die to bend it. The bending die radius is the same as the bellows corner radius. In order to prevent wrinkling and warping, first use the bending die inlay and clamping block to clamp the front end of the corrugated plate, and the rear end of the corrugated plate is pressed on the anti-wrinkle block by the pressing block. During the forming process of the front end of the corrugated plate, the clamping block and the bending die inlay hold the front end of the plate to rotate around the center of the bending die, so that the corrugated plate is bent and formed, and a bent corrugated plate is obtained as shown in Figure 6The circular bellows shown.

[0046] Step five, welding of the corrugated plate. The bent corrugated plate obtained in step four is placed in a welding fixture to be fixed, and the two ends of the corrugated plate are butt welded to obtain a corrugated tube semi-finished product.

[0047] Step six, air expansion and shaping of the corrugated tube. The corrugated tube semi-finished product obtained in step five is placed in an expansion die which has been uniformly heated at a forming temperature. The die is opened and closed quickly, and the left and right punches are axially fed to realize sealing. When the temperature is uniform, the expansion is performed using a set loading path, and the insufficiently formed part of the corrugated tube semi-finished product is shaped by air expansion. The gas pressure is controlled between 10-20 MPa. The corrugated tube semi-finished product is fully attached to the die to obtain the required corrugated tube semi-finished product. Then, the gas inlet valve is immediately closed, the unloading valve is opened, the internal gas pressure of the tube is gradually unloaded, and finally the die is opened to take out the product and water-cool it.

[0048] Step seven, cutting of the process section. The process section on both sides of the corrugated tube obtained in step six is cut by wire cutting to obtain a corrugated tube without the process section.

[0049] Step eight, welding of the end joint. The corrugated tube obtained in step seven is welded with an end joint (generally a flange) to obtain the final expansion joint.

[0050] The method for forming corrugations by bending a metal sheet can directly form corrugations by bending, the pitch and height of the corrugations can be adjusted by changing the crease position, the forming method is simple, and all the corrugations can be formed at one time, so that the forming efficiency is high; the corrugations are obtained by bending a sheet, the thinning rate of the sheet is extremely small, the thickness of the corrugations is uniform, and the stiffness and fatigue life of the corrugated tube can be improved; the method for forming corrugated tubes by bending a corrugated plate can form corrugated tubes with different cross-sectional shapes, such as rectangular, circular, and racetrack-shaped; the method for air expansion and shaping of the corrugated tube can adjust the shape of the corrugations of the corrugated tube, and a corrugated tube with a complex diaphragm shape, high forming precision, and small pitch between corrugations can be obtained; only one welding is used, and the expansion joint product has only one weld, which is beneficial to improving the reliability and comprehensive performance of the expansion joint in an extreme working environment.

[0051] Example 2: As shown in Figure 10 the forming method and the traditional welding method in the present application are used to obtain ultra-thin short-pitch corrugated tubes with a thickness of 0.15 mm and a pitch of λ = 2 mm, λ = 3 mm, and λ = 4 mm, respectively. The outer diameter of the corrugated tube is 304 mm, and the inner diameter is 278 mm. The corrugated tubes with different pitches obtained by the two forming methods are simulated in simulation software to be compressed to the same deformation of 18 mm.

[0052] The short wave distance bellows obtained by using the traditional welding method has obvious stress concentration at the welding position between the diaphragms, which will cause the reduction of the bellows stiffness and fatigue life during the actual service process. The diaphragm of the bellows obtained by using the forming method has more uniform stress and no obvious stress concentration, and the maximum stress is obviously smaller than that of the traditional welding type, so that the ultimate compression amount and fatigue life of the bellows can be improved.

[0053] Example 3: combination Figure 4 It is explained that in step four, the angle of bending is determined according to the shape of the expansion joint. When the cross-sectional shape of the expansion joint is circular, a 360° round corner needs to be bent; when the cross-sectional shape of the expansion joint is runway-shaped, only two 180° round corners need to be bent at both ends; when the cross-sectional shape of the expansion joint is rectangular, four 90° round corners need to be bent at four corners, and other steps are the same as those in example 1.

[0054] The round corner is formed by bending, and different cross-sectional shapes of the bellows can be formed by changing the bending angle and bending position, which is simple, easy to realize, and has high forming efficiency.

[0055] Example 4: combination Figure 6 It is explained that in step five, the plasma arc welding (PAW) method can be used to weld the bent bellows plate obtained in step four, and other steps are the same as those in example 1.

[0056] The welding is carried out by using the plasma arc welding method, the plasma arc concentrates on the heating of the welding parts, has strong penetration ability, fast welding speed, narrow welding cross-sectional shape, large depth-width ratio, and small welding deformation. Secondly, the plasma arc is stable, can be used for foil welding, and the welding is uniform, which is beneficial to obtain the expansion joint product with stable performance and long fatigue life.

[0057] Example 5: combination Figure 7 It is explained that in step six, the gas expansion shaping die is determined according to the shape of the expansion joint, and the shape of the bellows semi-finished product obtained in step five is close to the shape of the finished product. The shape of the die cavity is the shape of the finished product, which can be circular, rectangular, runway-shaped, etc. The bellows spacing can be large or small, and the bellows can also be wave-shaped. Other steps are the same as those in example 1.

[0058] The limitation of the hydraulic forming on the bellows shape and wave distance is broken, and the wave-shaped bellows and the bellows with small wave distance can be obtained, which is beneficial to improve the compression amount of the expansion joint.

Claims

1. A method for forming an ultrathin short-wavelength S-shaped metal expansion joint, characterized in that, The steps are as follows: Step 1: Design of prefabricated metal sheet: Perform feature analysis on the ultrathin short-wavelength S-shaped metal expansion joint, and determine the material and shape of the required original metal sheet through theoretical calculation or simulation methods; Step 2: Determine the bending width and number of bends: Based on the corrugated pipe waveform shape and height, determine the bending width, and based on the number of corrugations and the prefabricated metal sheet determined in Step 1, determine the number of bends and the bending position; where, the number of bends = number of corrugations * 2 + 1; Step 3, bending of metal sheet: According to the bending width, bending position and number of bending times determined in Step 2, the metal sheet determined in Step 1 is bent along the width direction to obtain a corrugated plate with process sections at both ends; Step 4, Corrugated Plate Bending: Place the corrugated plate obtained in Step 3 into the bending mold and bend it; during the forming process, the clamping block and the bending mold insert hold the front end of the corrugated plate and rotate it around the center of the bending mold to bend the corrugated plate to obtain the required bending angle. The rear end of the corrugated plate is pressed onto the anti-wrinkle block by the pressure block. Step 5, Corrugated Plate Welding: Place the bent corrugated plate obtained in Step 4 into the welding fixture, and weld the two ends of the corrugated plate to obtain the corrugated pipe semi-finished product. Step 6, Corrugated pipe air expansion shaping: Place the corrugated pipe semi-finished product obtained in step 5 into the expansion mold, and use air pressure to expand the unformed part of the corrugated pipe semi-finished product so that the corrugated pipe semi-finished product fully fits the expansion mold to obtain the desired corrugated pipe finished product. Step 7: Process section removal: The process sections on both sides of the corrugated pipe obtained in Step 6 are removed by wire cutting to obtain a corrugated pipe without process sections. Step 8: Welding the end joints: Weld the bellows obtained in Step 7 to the end joints to obtain the final expansion joint.

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