A scanning electron beam-brazing composite welding method suitable for closed cavity structure

Abstract

The application provides a scanning electron beam-brazing composite welding method suitable for a closed cavity structure, and steps are as follows: S1, trial welding; determining critical penetration welding parameters of an electron beam; determining scanning parameters of the critical penetration welding of the scanning electron beam; determining scanning electron beam-brazing composite welding parameters; S2, welding seam processing and cleaning treatment; S3, brazing filler metal selection and filling; S4, tool fixing and spot welding; S5, scanning electron beam-brazing composite welding; the parts fixed by the tool are placed into a vacuum chamber of an electron beam welding machine, then the parts are welded by using the determined electron beam welding and scanning parameters of the S1 trial welding step, and scanning electron beam-brazing composite welding of the parts is realized. The application solves the problems that the closed cavity structure is easily burned by an electron beam current which is too large and causes the metal on the opposite side of the welding seam to be burned or the electron beam current which is too small and causes the parts to be not welded, so that high-quality welding of the closed cavity structure is realized.

Description

TECHNICAL FIELD

[0001] The present application provides a scanning electron beam-brazing composite welding method suitable for closed cavity structure, belonging to the field of electron beam welding. BACKGROUND

[0002] In engineering manufacturing, there are often some closed cavity welding structures (such as shown in Figure 1a , Figure 1b ), when using electron beam welding, because the weld is in the form of butt joint and has no stop, if the beam current is slightly large, it is easy to burn the metal on the opposite side of the weld, which reduces the performance of the welded joint; if the beam current is too small, it will produce un-welded gaps, which will become the cause of bending cracks and fatigue fracture during work, greatly reducing the service life of the part. In actual welding production, it is difficult to adjust and control the electron beam current to just penetrate the weld without burning the opposite metal, so when the weld is formed and detected, welding defects such as un-welded gaps and workpiece metal burns often exist in the weld area, which seriously affects the welding quality of such closed cavity structure parts. Therefore, how to solve the problem of burning the opposite metal due to too large beam current or producing un-welded gaps due to too small beam current is the key to realizing high-quality welding of closed cavity structure.

[0003] The conventional solution is to use a slightly larger beam current than the penetration weld to ensure complete fusion of the weld; at the same time, a layer of metal backing plate is pre-placed under the weld to absorb the penetrating beam to prevent the beam from burning the opposite metal, but after welding is completed, the pre-placed metal backing plate cannot be removed. Another solution is to design the weld of the closed cavity structure as a stop structure (as shown in Figure 2 ), and adjust the size of the electron beam current through process test during welding to make the electron beam penetrate the weld without penetrating the stop, thereby ensuring that the opposite metal is not burned; however, the stop structure not only increases the thickness of the part, making the welded joint more complex to process, but also has un-welded gaps after welding, which may also become the cause of cracks, seriously affecting the quality of the welded joint.

[0004] The scanning electron beam-brazing composite welding process refers to using electron beam to melt and weld the weld, while controlling the electron beam to scan in the vertical direction of the weld at high frequency, using the heat generated by electron beam welding and scanning to perform brazing, so that the filler metal pre-filled on the back of the weld melts and fills the gap between the welds. In this way, when using electron beam welding for closed cavity structure, filler metal can be pre-filled on the back of the weld of the closed cavity structure, and then a beam current slightly smaller than the penetration weld is used for welding, brazing is realized at the same time of electron beam welding, and after the filler metal melts, it can fill the un-welded gaps after electron beam welding, thereby improving the welding quality of the closed cavity structure.

[0005] Therefore, the application proposes a scanning electron beam-brazing composite welding process suitable for closed cavity, which uses slightly smaller electron beam current than penetration welding to weld, controls the electron beam to high-frequency scan along the perpendicular direction of the weld, melts the brazing filler pre-filled on the back of the weld and fills the unwelded gap by using the heat generated during the scanning electron beam welding process, completes the brazing of the closed cavity structure, and thus obtains a closed cavity structure with high welding quality. SUMMARY

[0006] 1. Object: The application proposes a scanning electron beam-brazing composite welding method to solve the problems of burn on the opposite metal caused by too large beam current and unwelded gap caused by too small beam current during electron beam welding of closed cavity structure. When welding the closed cavity structure, slightly smaller electron beam current than penetration welding is selected to weld the workpiece, and the electron beam is controlled to high-frequency scan along the perpendicular direction of the weld. The brazing filler pre-filled on the back of the weld is melted and the unwelded gap is filled by using the heat generated during the scanning electron beam welding process, and the brazing of the closed cavity structure is completed, thereby realizing high-quality welding of the closed cavity structure. Since the electron beam spot is small, the energy is concentrated, and the welding speed is fast, when critical penetration welding is used, the high-temperature area on the back of the weld where the brazing filler can be melted is narrow and the high-temperature duration is short. Therefore, the purpose of high-frequency scanning of the electron beam along the perpendicular direction of the weld at the same time of welding is to increase the heat input of the brazing filler pre-filled area on the back of the weld, increase the temperature, and make the brazing filler have high enough temperature and time to melt, wet, and fill the unwelded gap.

[0007] 2. Technical solution: The purpose of the application is realized by the following technical solution.

[0008] Based on the above purpose, the application provides a scanning electron beam-brazing composite welding method suitable for closed cavity structure, mainly including trial welding, weld processing and cleaning treatment, tool fixing, brazing filler selection and filling, scanning electron beam-brazing composite welding, etc. Among them, the brazing filler should be selected according to the material of the parts to be welded.

[0009] The specific operation steps are as follows.

[0010] S1: Trial welding

[0011] S1-01: Determine the critical penetration welding parameters of electron beam. Prepare test plates consistent with the material and thickness of the parts to be welded, and use different electron beam welding process parameters to carry out test welding. Through a large number of process tests, the appropriate welding process parameters are selected, mainly including welding beam current, welding speed, etc. The principle of determining the critical penetration welding parameters is: using the current welding process parameters to weld the test plate, the test plate has not been completely penetrated, but slightly changing the welding parameters (such as increasing the welding beam current or reducing the welding speed), the test plate is immediately welded through, thus the current welding parameters can be initially determined as the critical penetration welding parameters, which can be used for the critical penetration welding parameters of subsequent parts;

[0012] S1-02: Determine the scanning parameters of the critical penetration welding of the scanning electron beam. Use the test plate welded by the critical penetration welding parameters determined in step S1-01, and control the electron beam to perform high-frequency scanning along the perpendicular direction of the weld, and determine the scanning waveform, scanning amplitude and scanning speed, etc. critical penetration welding parameters through a large number of process tests.

[0013] S1-03: Determine the scanning electron beam-brazing composite welding parameters. Apply brazing filler metal on the back surface area of the test plate weld, and then use the electron beam critical penetration welding parameters and scanning parameters determined in steps S1-01 and S1-02 to carry out scanning electron beam-brazing composite welding process test, and optimize the welding process parameters to make the brazing filler metal applied on the back surface of the weld fully melt and wet the test plate, thereby determining the appropriate part scanning electron beam-brazing composite welding process parameters.

[0014] The scanning electron beam-brazing composite welding process parameters mainly include acceleration voltage, electron beam current, welding speed, scanning speed, scanning amplitude, brazing temperature, etc. The acceleration voltage is determined according to the selected electron beam welding equipment, which can select a medium-voltage electron beam welding equipment of 60kV or a high-voltage electron beam welding equipment of 150kV; the electron beam current and the welding speed are mainly determined according to the material, thickness and structure of the workpiece to be welded, which can be referred to the relevant electron beam welding process manual; the electron beam scanning speed, scanning amplitude and brazing temperature are determined according to the brazing temperature and wetting effect of the selected brazing filler metal; all the scanning electron beam-brazing composite welding process parameters need to be determined through test welding to obtain the optimal welding parameters.

[0015] S2: Welding seam processing and cleaning treatment

[0016] S2-01: Butt weld processing. According to the assembly accuracy requirements of the butt weld of the part, the butt joint position of the part is processed by mechanical processing, and a 0.1mm×45° chamfer is processed on the back surface of the butt weld to fill the brazing filler metal.

[0017] S2-02: cleaning treatment. The part weld position and the surrounding area are cleaned with acetone to remove oil, sandpaper to remove oxide film, and then cleaned with anhydrous ethanol.

[0018] S3: filler metal selection and filling

[0019] S3-01: selection of filler metal. The specific filler metal should be selected according to the material of the parts to be welded. For example, for TC4 titanium alloy, silver-based filler metal, titanium-based filler metal or aluminum-based filler metal can be selected.

[0020] S3-02: adding filler metal. The selected filler metal is filled at the back chamfer of the weld, and an appropriate method is selected to fix the filler metal at the back of the weld to ensure that the subsequent assembly and welding are not dropped; the paste-shaped filler metal and the powder-shaped filler metal can be bonded together with the workpiece by selecting the adhesive; the powder-shaped filler metal can also be connected with the workpiece by selecting the sintering method; the sheet-shaped filler metal can be bonded, spot welded, etc.

[0021] S4: tool fixing and spot welding. The parts filled with filler metal are spliced, and then fixed with a special tool (the form of closed cavity structure is more diverse, and the same tool cannot be used for various closed cavity structures, so a special tool needs to be designed according to the closed cavity structure to be welded, such as the rotary structure weld shown in FIG. 1, which can select a special tool for rotary structure Figure 6 Yes, the rotary table structure special tool) is used, and then electron beam is used for spot welding.

[0022] S5: scanning electron beam-brazing composite welding. The parts fixed by the tool are placed in the vacuum chamber of the electron beam welding machine, and then the electron beam welding and scanning parameters determined in the S1 welding step are used to weld the parts, that is, the scanning electron beam-brazing composite welding of the parts can be realized.

[0023] 3. Advantages and effects:

[0024] 1) A scanning electron beam-brazing composite welding method suitable for closed cavity structure is proposed, which can solve the problems of easy burn of weld opposite metal by too large electron beam current or incomplete welding caused by too small electron beam current during electron beam welding of closed cavity structure. The method selects an electron beam current slightly smaller than the penetration welding to weld the workpiece, and controls the electron beam to scan in the vertical direction of the weld at high frequency, and uses the heat generated during the scanning electron beam welding process to melt the filler metal pre-filled at the back of the weld and fill the incomplete gap, complete the brazing of the closed cavity structure, and realize high-quality welding of the closed cavity structure.

[0025] 2) In the welding process, butt joints are used instead of lock bottom structure joints, which can simplify the process and reduce the cost.

[0026] 3) Using scanning electron beam as welding heat source, the welding speed can be greatly improved, and the scanning of electron beam can increase the heating area, which is more conducive to the melting of the filler metal, ensuring that the filler metal can fully wet the base material and fill the gap of the welded joint.

[0027] 4) The process has wide applicability and can be widely used in welding of TC4 workpieces of various thicknesses and shapes. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1a 、 Figure 1b is a schematic diagram of a closed cavity structure in the background art.

[0029] Figure 2 is a schematic diagram of a counter joint in the background art.

[0030] Figure 3 is a schematic diagram of chamfering of a closed cavity structure part at a butt joint position.

[0031] Figure 4 is a schematic diagram of pre-filling filler metal at the chamfered back of the weld.

[0032] Figure 5 is a schematic diagram of a scanning electron beam-brazing composite welding method.

[0033] Figure 6 is a schematic diagram of a special tool for a closed cavity structure in the specific embodiment. DETAILED DESCRIPTION

[0034] The present application provides a scanning electron beam-brazing composite welding method for a closed cavity structure, wherein a typical 3mm thick TC4 titanium alloy cylindrical closed cavity structure is taken as an example, as shown in Figure 1a 、 Figure 1b the closed cavity structure in the specific embodiment is shown in Figure 1a , Figure 1b However, there are many types of closed cavity structures, and the present application is only taken as an example of the closed cavity structure shown in the figure for the closed cavity structure used, and the specific embodiment is:

[0035] S1: trial welding

[0036] S1-01: Determine the critical penetration welding parameters of electron beam. Prepare 3mm thick TC4 titanium alloy test plate, and use different electron beam welding process parameters to carry out test welding. Through a large number of process tests, suitable welding process parameters are selected, mainly including welding beam current, welding speed, etc. The principle of determining the critical penetration welding parameters is: using the current welding process parameters to weld the test plate, the test plate has not been completely penetrated, but the welding parameters are slightly changed (such as increasing the welding beam current or reducing the welding speed), and the test plate is immediately welded through, thus the current welding parameters can be initially determined as the critical welding parameters, which can be used for the critical penetration welding parameters of subsequent parts. The critical welding parameters of 3mm thick TC4 titanium alloy closed cavity structure parts obtained through test welding are: accelerating voltage 60kV, electron beam current 8mA, and welding speed 500mm / min.

[0037] S1-02: Determine the scanning parameters of the critical penetration welding of scanning electron beam. Weld the TC4 test plate using the critical penetration welding parameters determined in step S1-01, and control the electron beam to perform high-frequency scanning along the vertical weld direction. Through a large number of process tests, the scanning waveform, scanning amplitude and scanning speed of the critical penetration welding parameters are determined. Finally, the scanning waveform of the critical penetration welding is determined as a circle, the scanning amplitude is 1.05mm, and the scanning speed is 420mm / s.

[0038] S1-03: Determine the scanning electron beam-brazing composite welding parameters. Apply brazing filler metal on the back surface area of the test plate at the weld position, and then use the electron beam critical penetration welding parameters and scanning parameters determined in steps S1-01 and S1-02 to carry out scanning electron beam-brazing composite welding process test. Optimize the welding process parameters to make the brazing filler metal applied on the back surface of the weld fully melt and wet the test plate. Thus, the scanning electron beam-brazing composite welding parameters of 3mm thick TC4 titanium alloy closed cavity structure parts are determined as: accelerating voltage 60kV, electron beam current 9mA, welding speed 500mm / min, scanning waveform circle, scanning amplitude 1.05mm, and scanning speed 420mm / s.

[0039] S2: Welding seam processing and cleaning treatment

[0040] S2-01: Butt weld processing. According to the assembly accuracy requirements of the butt weld of the part, the butt joint position of the 3mm thick TC4 closed cavity structure part is processed by mechanical processing, and a chamfer of about 0.1mm x 45° is processed at the back surface position of the butt weld, which is used to fill the brazing filler metal, as shown in Figure 3

[0041] S2-02: Cleaning treatment. The welding position and the surrounding area of the part are cleaned by removing oil stains with acetone, removing oxide film with sandpaper, and then cleaning with anhydrous ethanol.

[0042] ​S3: filler metal selection and filling

[0043] S3-01: Select filler metal. The specific filler metal should be selected according to the material of the parts to be welded. The brazing of TC4 titanium alloy can select silver-based filler metal, titanium-based filler metal or aluminum-based filler metal. For 3mm thick TC4 titanium alloy parts, scanning electron beam-brazing composite welding selects paste AgCuInTi filler metal, and the brazing temperature of the filler metal is about 750℃.

[0044] S3-02: Add filler metal. The selected AgCuInTi filler metal is filled to the chamfered back of the weld, and the filler metal is fixed on the back of the weld by using adhesive or sintering method, so as to ensure that the filler metal will not fall off in the subsequent assembly and welding process, as shown in Figure 4

[0045] S4: Fix the tool. The parts filled with filler metal are spliced neatly, and then a special tool is used to fix (as shown in Figure 6 ), and then the electron beam is used for spot welding fixation.

[0046] S5: Scanning electron beam-brazing composite welding. The parts fixed by the tool are placed in the vacuum chamber of the electron beam welding machine, and then the electron beam welding and scanning parameters determined in the S1 welding step are used to weld the parts, that is, the scanning electron beam-brazing composite welding of the parts can be realized, as shown in Figure 5

[0047] The application will be further described in combination with the drawings.

[0048] Figure 1 is a schematic view of the closed cavity structure part. Referring to Figure 1, the weld of the closed cavity structure part is in the form of butt joint, and a slightly smaller electron beam current than the penetration welding is used for welding, and the electron beam is controlled to scan in the vertical direction of the weld at high frequency, and the heat generated in the process of electron beam scanning is used to melt the filler metal pre-filled on the back of the weld and fill the unfilled gap, so as to complete the brazing of the closed cavity structure and obtain a well-welded closed cavity structure.

[0049] Figure 2 is a schematic view of the stop structure of the weld. Referring to Figure 2 , the stop structure can ensure that the electron beam does not penetrate the stop during welding and burn the opposite metal, but the stop structure increases the thickness of the part, making the processing of the welded joint more complex, and the stop structure after welding mostly has an unfilled gap, which is easy to become a crack inducement, seriously affecting the quality of the welded joint.

[0050] Figure 3 is a schematic view of the butt joint position processing of the closed cavity structure part. Referring to Figure 3 ​​According to the butt joint welding seam assembly requirements of the parts, the butt joint position of the parts is processed by machining method, and a chamfer of about 0.1mm*45° is processed at the back position of the butt joint welding seam, to fill the brazing filler metal.

[0051] Figure 4 is a schematic diagram of the brazing filler metal filling and tooling of the closed cavity structure part. Referring to Figure 4 The selected brazing filler metal is filled at the chamfer of the back of the welding seam, and the brazing filler metal is fixed at the back of the welding seam by selecting appropriate methods such as bonding, sintering, spot welding, etc., to ensure that the brazing filler metal will not fall off during the subsequent assembly and welding process of the parts. The paste brazing filler metal can be bonded by selecting a bonding agent, the powder brazing filler metal can be sintered or bonded by selecting a bonding agent, and other sheet brazing filler metals can be spot welded, bonded, etc.

[0052] Figure 5 is a schematic diagram of the scanning electron beam-brazing composite welding of the closed cavity structure part. Referring to Figure 5 The part with completed brazing filler metal filling and tooling is placed in the vacuum chamber of the electron beam welding machine to complete the scanning electron beam-brazing composite welding.

[0053] Figure 6 is a schematic diagram of the special tooling for the typical closed cavity structure in the specific embodiment. Referring to Figure 6 The special tooling fixes the workpiece to be welded by the three-jaw chuck 1 on the fixed support 1 and the chuck 2 on the fixed support 2, and adjusts the distance between the two chucks through the guide rail to fix the workpiece to be welded. The motor is installed inside the fixed support 2, which drives the chuck 2 to rotate and drives the workpiece to be welded and the chuck 1 to rotate, thereby realizing high-quality welding of the annular welding seam of this closed cavity structure.

[0054] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this. Any changes or replacements within the technical range disclosed by the present application can be easily thought by those skilled in the art, which should be covered within the protection scope of the present application.

Claims

1. A scanning electron beam-brazing hybrid welding method suitable for closed cavity structures, characterized in that, Includes the following steps: S1: Test welding; including: S1-01: Determine the critical penetration welding parameters of the electron beam; S1-02: Determine the scanning parameters for critical penetration welding with scanning electron beam; S1-03: Determine the parameters for scanning electron beam-brazing composite welding; S2: Weld processing and cleaning; including: S2-01: Butt weld processing; According to the assembly accuracy requirements of the butt weld of the parts, the butt joint position of the parts is processed by mechanical processing method, and a 0.1mm×45° chamfer is processed on the back of the butt weld to fill the brazing filler metal; S2-02: Cleaning treatment; use acetone to remove oil stains from the weld seams and surrounding areas of the parts, use sandpaper to remove the oxide film, and then clean with anhydrous ethanol; S3: Brazing filler metal selection and loading; including: S3-01: Select the brazing filler metal; the specific brazing filler metal should be selected according to the material of the parts to be soldered; S3-02: Add brazing filler metal; fill the selected brazing filler metal into the chamfered area on the back of the weld, and use an appropriate method to fix the brazing filler metal to the back of the weld to ensure that it will not fall off during subsequent assembly and welding; S4: Fixture fixing and spot welding; Assemble the parts filled with brazing filler metal, then fix them with special fixtures, and then spot weld them with an electron beam; S5: Scanning electron beam-brazing composite welding; The tooled part is placed in the vacuum chamber of the electron beam welding machine, and then the electron beam welding and scanning parameters determined by the S1 trial welding step are used to weld the part, realizing the scanning electron beam-brazing composite welding of the part.

2. The scanning electron beam-brazing composite welding method for closed cavity structures according to claim 1, characterized in that: In step S1-01, the critical penetration welding parameters are determined: the test plate is welded using the current welding process parameters. The test plate has not been completely penetrated, but the welding parameters are changed, i.e., the welding current is increased or the welding speed is decreased, and the test plate is then welded through. Thus, the current welding parameters are determined as the critical penetration welding parameters, which are used as the critical penetration welding parameters for subsequent parts.

3. The scanning electron beam-brazing composite welding method for closed cavity structures according to claim 2, characterized in that: In step S1-02, the scanning parameters for critical penetration welding of the scanning electron beam are determined; using the welding test plate with the critical penetration welding parameters determined in step S1-01, the electron beam is simultaneously controlled to perform high-frequency scanning along the direction perpendicular to the weld seam to determine the critical penetration welding parameters, including the scanning waveform, scanning amplitude, and scanning speed.

4. The scanning electron beam-brazing composite welding method for closed cavity structures according to claim 3, characterized in that: In step S1-03, the scanning electron beam-brazing composite welding parameters are determined; brazing filler metal is applied to the back area of ​​the weld position on the test plate, and then the electron beam critical penetration welding parameters and scanning parameters determined in steps S1-01 and S1-02 are used to ensure that the brazing filler metal applied to the back of the weld can be fully melted and wetted on the test plate, thereby determining the scanning electron beam-brazing composite welding process parameters for the part.

5. The scanning electron beam-brazing composite welding method for closed cavity structures according to claim 1, characterized in that: In step S3-01, silver-based brazing filler metal, titanium-based brazing filler metal, or aluminum-based brazing filler metal are selected.

6. The scanning electron beam-brazing composite welding method for closed cavity structures according to claim 1, characterized in that: In step S3-02, paste-like brazing filler metal and powder-like brazing filler metal are bonded to the workpiece using an adhesive; powder-like brazing filler metal is connected to the workpiece by sintering; and sheet-like brazing filler metal is bonded or spot-welded.

7. The scanning electron beam-brazing composite welding method for closed cavity structures according to claim 1, characterized in that: In step S4, the special tooling uses a 3-jaw chuck 1 on a fixed support 1 and a chuck 2 on a fixed support 2 to fix the workpiece to be welded, and adjusts the distance between the two chucks by a guide rail to fix the workpiece to be welded; the motor is installed inside the fixed support 2 to drive the chuck 2 to rotate, and drive the workpiece to be welded and the chuck 1 to rotate, so as to realize the welding of the annular weld of the closed cavity structure.

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