Laser welding method for medium-thick-wall solid rocket engine shell

Abstract

The invention provides a laser welding method for a medium-thick-wall solid rocket engine shell. The laser welding method comprises the following steps that S1, a welding face is pretreated; s2, fixing to form a shell assembly; step S3, hoisting; s4, determining a circular seam program by utilizing an industrial robot demonstrator; and S5, a front end socket welding seam between the front end socket and the combustion chamber shell is welded, and the welding process comprises the following steps that S5.1, laser spot welding is conducted; s5.2, laser oscillation penetration fusion welding is carried out; s5.3, MIG welding is carried out; and S6, a rear end socket welding seam between the rear end socket and the combustion chamber shell is welded. According to the method, the welding process is divided into three processes, the operation difficulty is greatly reduced, the fault tolerance range of the process interval range is larger, and the reliability of batch production is higher; and through a step-by-step welding method, digging and discharging are easy, the production precision is greatly improved, and the risk of reworking is reduced.

Description

Technical Field

[0001] This invention relates to the field of solid rocket motor casing welding, and more specifically, to a laser welding method for medium-thick-walled solid rocket motor casings. Background Technology

[0002] Ultra-high strength steel 30Si2MnCrMoVE (D406A) has a tensile strength exceeding 1620 MPa and an elongation greater than 8%, and is primarily used for solid rocket motor casings. Solid rocket motor casings must withstand high temperatures and pressures, requiring extremely high weld quality. TIG welding and vacuum electron beam welding are commonly used. For large, medium-thick-walled solid rocket motor casings with a wall thickness greater than 4 mm, a diameter greater than 400 mm, and a length exceeding 4000 mm, the vacuuming process is more difficult and costly, often requiring multi-layer, multi-pass TiG welding.

[0003] A Chinese patent with publication number CN110328449A discloses a laser-MIG arc hybrid welding method for medium-thick pipeline steel plates, including the following steps: for medium-thick pipeline steel plates, the joint is a butt joint, a single V-groove is opened with a groove angle of 30° and a blunt edge of 8mm; filler wire is selected according to the performance of the steel plate being welded; the laser is used in front and the arc is used behind to perform root pass welding and filler pass welding, the laser defocusing amount is set to -2~0mm, the wire spacing is 1~2mm, and the laser-MIG arc hybrid welding is completed.

[0004] Currently, TIG welding is primarily used for the casings of large solid rocket motors. TIG welding offers relatively stable quality, but its welding speed is slow. Thick-walled casings require beveling and multi-layer, multi-pass welding, resulting in a large heat-affected zone and increased material usage. Laser welding, on the other hand, boasts high energy density, a small heating area, a small heat-affected zone, minimal deformation, a large weld depth-to-width ratio, high weld quality, and low residual stress and deformation. Laser welding is fast and efficient, and can be performed in atmospheric or vacuum environments. In atmospheric environments, laser welding of plates less than 4mm thick has significant advantages; however, thicknesses exceeding 4mm are prone to defects such as porosity, sagging, and depressions. Laser-MIG arc hybrid welding is a novel welding method that combines the advantages of both laser and arc welding, offering high efficiency and quality, and is widely used in the shipbuilding industry. However, its porosity is slightly higher than both laser and MIG welding, especially at the joints of circumferential seams, where it is difficult to completely eliminate porosity.

[0005] Therefore, there is a need to provide a laser welding method suitable for medium-thick-walled solid rocket motor casings that can combine the advantages of various welding methods, reduce operational difficulty, improve production accuracy, and thus enable mass production. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a laser welding method for medium-thick-walled solid rocket motor casings.

[0007] A laser welding method for a medium-thick-walled solid rocket motor casing according to the present invention includes the following steps: Step S1: Pre-treat the welding surfaces of the front end cap, rear end cap, and combustion chamber shell; Step S2: Fix the front end cap and the rear end cap to both ends of the combustion chamber shell to form a shell assembly; Step S3: Hoist the fixed housing assembly onto the assembly fixture; Step S4: Using an industrial robot teach pendant, determine the left and right positions by aligning the red circular spot with the weld seam, and determine the up and down positions by aligning the line laser with the center of the red circle. Edit 8-12 position points to determine a circumferential seam program. Step S5 involves welding the weld between the front end cap and the combustion chamber shell, including the following steps: Step S5.1, laser spot welding, the laser power for spot welding is 2000-4000W, the defocus is -5mm to +2mm, the oscillation amplitude is 0, the spot welding speed is 0.4-0.6m / min, the spot welding penetration depth shall not be less than 1 / 3 of the total thickness, the number of spot welding is 10, the shielding gas is 99.99%Ar, and the flow rate is 30L / min; Step S5.2, laser oscillation deep penetration welding, laser power is 7000-10000w, oscillation frequency is 200-300Hz, oscillation amplitude is 2-3mm, shielding gas flow rate, laser defocusing, welding speed are the same as in step S5.1, arc start time and arc end time are both 5-15s; Step S5.3, MIG welding: After the laser deep penetration welding is completed, a 0.5-1mm depression will be generated on the weld surface. MIG welding is used for surface finishing. The welding speed and shielding gas flow rate remain unchanged. The shielding gas is switched to a mixture of 92%Ar + 8%CO2. The laser power is 0-1000W, the wire feed speed is 5-6m / min, the arc starting current is 100%, the arc ending current is 0%, the welding angle is 363°, and the horizontal angle between the welding torch and the workpiece is 55°. Step S6: After the front end cap and combustion chamber shell are welded, the robot moves along the ground rail and uses the same welding method as in step S5 to weld the rear end cap weld between the rear end cap and combustion chamber shell.

[0008] Preferably, in step S1, the pretreatment process includes: polishing, removing oxide film, wiping the welding surface with gasoline or alcohol, and removing oil and dust.

[0009] Preferably, in step S2, the front end cap, the rear end cap, and the combustion chamber shell are fixed by TIG spot welding or mechanical assembly, and the misalignment of the three is less than 0.3 mm.

[0010] Preferably, in step S3, the assembly fixture includes: a drive shaft jaw, a movable bracket, and a driven shaft jaw. The front end is fixedly mounted on the drive shaft jaw, and the rear end is fixedly mounted on the driven shaft jaw. Multiple movable brackets are provided between the drive shaft jaw and the driven shaft jaw, and the multiple movable brackets cooperate to support the driven shaft jaw.

[0011] Preferably, the assembly gap between the front end cap and the drive shaft jaw is less than 0.2 mm, and the assembly gap between the rear end cap and the driven shaft jaw is less than 0.2 mm.

[0012] Preferably, in step S4, the vertical error of the circumferential seam programming teaching is less than 0.5 mm, and the horizontal error is less than 0.3 mm.

[0013] Preferably, in step S5, after the MIG weld surface is finished, X-ray inspection is performed. If the detected porosity and defects do not meet the QJ175-1993 Grade 0 weld standard, rework is required.

[0014] Preferably, if the depth of the pores and defects is less than 2.5 mm, the defect location is found according to the X-ray film, the defect is polished with tools, then manual TIG filler wire welding is performed, and X-ray inspection is performed after the welding is completed.

[0015] Preferably, in step S5, if X-ray detection reveals undercut with a depth greater than 0.2 mm on both sides of the back of the weld, the laser power is reduced or the defocus is raised to reduce heat input, and the depth of the undercut on the back is controlled within 0.1 mm.

[0016] Preferably, if the thickness of the weldment is greater than 10mm, a 2-3mm bevel is made on the front side of the weldment, and then the missing material at the bevel is filled with MIG.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention divides the welding process into three steps: laser spot welding, laser oscillation deep penetration welding, and MIG welding. This significantly reduces the difficulty of operation and the technical requirements for operators, thus helping to reduce labor costs. Moreover, the process range has a wider tolerance for errors, resulting in greater reliability for mass production. Through the step-by-step welding method, almost no porosity is generated at the joint between the first and last parts. The porosity exceedance rate during MIG surface finishing welding is less than 5%, and the porosity depth is generally less than 2.5 mm, making it easy to remove. This greatly improves production accuracy and reduces the risk of rework. Attached Figure Description

[0018] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram illustrating the assembly process of welding a medium-thick-walled solid rocket motor casing, which is the main feature of this invention.

[0019] The figure shows: drive shaft chuck 1, front head weld 2, movable bracket 3, rear head weld 4, driven shaft chuck 5. Detailed Implementation

[0020] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0021] like Figure 1 As shown, a laser welding method for a medium-thick-walled solid rocket motor casing according to the present invention includes the following steps: Step S1: Pre-treat the welding surfaces of the front end cap, rear end cap, and combustion chamber shell; Step S2: Fix the front end cap and the rear end cap to both ends of the combustion chamber shell to form a shell assembly; Step S3: Hoist the fixed housing assembly onto the assembly fixture; Step S4: The operator uses the industrial robot teach pendant to determine the left and right positions by visually aligning the red circular spot with the weld seam, and determines the up and down positions by visually aligning the laser with the center of the red circle. The operator then edits 8-12 position points to determine a circumferential seam program. Step S5 involves welding the weld seam 2 between the front end cap and the combustion chamber shell, including the following steps: Step S5.1, laser spot welding, the laser power for spot welding is 2000-4000W, the defocus is -5mm to +2mm, the oscillation amplitude is 0, the spot welding speed is 0.4-0.6m / min, the spot weld penetration depth shall not be less than 1 / 3 of the total thickness, the number of spot welds is 10, the total length of spot welds must be firm and reliable, the shielding gas is 99.99%Ar, the flow rate is 30L / min, generally, it is recommended to use the Fonnis arc welding gun nozzle for gas output; Step S5.2, laser oscillation deep penetration welding, laser power is 7000-10000w, oscillation frequency is 200-300Hz, oscillation amplitude is 2-3mm, shielding gas flow rate, laser defocusing, welding speed are the same as in step S5.1, arc start time and arc end time are both 5-15s; Step S5.3, MIG welding: After the laser deep penetration welding is completed, a 0.5-1mm depression will be generated on the weld surface. MIG welding is used for surface finishing. The welding speed and shielding gas flow rate remain unchanged. The shielding gas is switched to a mixture of 92%Ar + 8%CO2. The laser power is 0-1000W, the wire feed speed is 5-6m / min, the arc starting current is 100%, the arc ending current is 0%, the welding angle is 363°, and the horizontal angle between the welding torch and the workpiece is 55°. In step S6, after the front end cap and the combustion chamber shell are welded, the robot is moved along the ground rail and the rear end cap weld 4 between the rear end cap and the combustion chamber shell is welded using the same welding method as in step S5.

[0022] In step S1, the pretreatment process includes: polishing, removing oxide film, wiping the welding surface with gasoline or alcohol, and removing oil and dust.

[0023] In step S2, the front end cap, the rear end cap, and the combustion chamber shell are fixed by TIG manual spot welding or mechanical assembly, and the misalignment of the three is less than 0.3 mm.

[0024] In step S3, the assembly fixture includes: a drive shaft jaw 1, a movable bracket 3, and a driven shaft jaw 5. The drive shaft jaw 1 and driven shaft jaw 5 are generally three-jaw jaws. The front end cap is securely mounted on the drive shaft jaw 1, and the rear end cap is securely mounted on the driven shaft jaw 5. Multiple movable brackets 3 are arranged between the drive shaft jaw 1 and the driven shaft jaw 5. Each movable bracket 3 has rollers at its bottom, and the multiple movable brackets 3 cooperate to support the driven shaft jaw 5. The assembly gap between the front end cap and the drive shaft jaw 1 is less than 0.2 mm, and the assembly gap between the rear end cap and the driven shaft jaw 5 is less than 0.2 mm.

[0025] In step S4, the vertical error of the circumferential seam programming teaching is less than 0.5mm, and the horizontal error is less than 0.3mm.

[0026] In step S5, after the MIG weld surface finishing is completed, X-ray inspection is performed. If the detected porosity and other defects do not meet the QJ175-1993 Grade 0 weld standard, rework is required. Generally, the rework rate is less than 5%. Due to the shallow penetration of the arc, if the porosity and defect depth is less than 2.5mm, during rework, the defect location is found based on the X-ray film, the defect is manually ground out using special tools, and then manual TIG filler wire welding is performed. After the repair welding, X-ray inspection is performed again.

[0027] In step S5, due to the lack of solder filler, if the welding heat input is too high, a small amount of undercut with a depth of about 0.1mm-0.2mm is easily generated on both sides of the back of the weld. If X-ray detection shows undercut with a depth greater than 0.2mm on both sides of the back of the weld, the X-ray inspection may show a "lack of fusion" defect; if it is less than 0.1mm, the X-ray imaging will not show a defect. In this case, it is necessary to reduce the heat input by adjusting and reducing the laser power or raising the defocus, which can control the undercut depth on the back side to within 0.1mm, or even prevent undercut from occurring. If the heat input is too low, although undercut will be completely avoided, the tendency for porosity will increase, and a suitable range of process parameters needs to be found.

[0028] Furthermore, if the thickness of the weldment is too large, such as greater than 10mm, the undercut defect on the back side may be more difficult to solve. It is advisable to open a 2-3mm bevel on the front side of the weldment to reduce the thickness of the laser root pass. Then, the missing material at the bevel can be filled with MIG or MIG + low power laser welding, which also has greater process reliability.

[0029] This application divides the welding process into three steps: laser spot welding, laser oscillating deep penetration welding, and MIG welding. Compared to conventional laser-MIG hybrid welding, this method is simpler to operate, requiring only basic training for operators. Furthermore, it offers a wider tolerance range within the process area, resulting in greater reliability for mass production. Using this welding method, almost no porosity is generated at the weld joint. While conventional laser-MIG hybrid welding can guarantee no porosity in the normal welding section, it struggles to ensure no porosity at the weld joint, let alone achieve 20 consecutive welds without porosity. The porosity rate at the weld joint increases with the thickness of the weld. In contrast, the laser root pass welding in this application generates almost no porosity, with occasional porosity only occurring during MIG surface finishing welding. The porosity exceedance rate is less than 5%, and the porosity depth is generally less than 2.5 mm, making it easy to remove. In contrast, the porosity generated by conventional laser-MIG hybrid welding often extends close to the bottom of the weld, making removal more difficult.

[0030] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A laser welding method for a medium-thick-walled solid rocket motor casing, characterized in that, Includes the following steps: Step S1: Pre-treat the welding surfaces of the front end cap, rear end cap, and combustion chamber shell; Step S2: Fix the front end cap and the rear end cap to both ends of the combustion chamber shell to form a shell assembly; Step S3: Hoist the fixed housing assembly onto the assembly fixture; Step S4: Using an industrial robot teach pendant, determine the left and right positions by aligning the red circular spot with the weld seam, and determine the up and down positions by aligning the line laser with the center of the red circle. Edit 8-12 position points to determine a circumferential seam program. Step S5 involves welding the weld seam (2) between the front end cap and the combustion chamber shell, including the following steps: Step S5.1, laser spot welding, the laser power for spot welding is 2000-4000W, the defocus is -5mm to +2mm, the oscillation amplitude is 0, the spot welding speed is 0.4-0.6m / min, the spot welding penetration depth shall not be less than 1 / 3 of the total thickness, the number of spot welding is 10, the shielding gas is 99.99%Ar, and the flow rate is 30L / min; Step S5.2, laser oscillation deep penetration welding, laser power is 7000-10000w, oscillation frequency is 200-300Hz, oscillation amplitude is 2-3mm, shielding gas flow rate, laser defocusing, welding speed are the same as in step S5.1, arc start time and arc end time are both 5-15s; Step S5.3, MIG welding: After the laser deep penetration welding is completed, a 0.5-1mm depression will be generated on the weld surface. MIG welding is used for surface finishing. The welding speed and shielding gas flow rate remain unchanged. The shielding gas is switched to a mixture of 92%Ar + 8%CO2. The laser power is 0-1000W, the wire feed speed is 5-6m / min, the arc starting current is 100%, the arc ending current is 0%, the welding angle is 363°, and the horizontal angle between the welding torch and the workpiece is 55°. In step S6, after the front end cap and the combustion chamber shell are welded, the robot ground rail is moved and the rear end cap weld (4) between the rear end cap and the combustion chamber shell is welded using the same welding method as in step S5.

2. The laser welding method for medium-thick-walled solid rocket motor casing as described in claim 1, characterized in that, In step S1, the pretreatment process includes: polishing, removing oxide film, wiping the welding surface with gasoline or alcohol, and removing oil and dust.

3. The laser welding method for medium-thick-walled solid rocket motor casing as described in claim 1, characterized in that, In step S2, the front end cap, the rear end cap, and the combustion chamber shell are fixed by TIG spot welding or mechanical assembly, and the misalignment of the three is less than 0.3 mm.

4. The laser welding method for medium-thick-walled solid rocket motor casing as described in claim 1, characterized in that, In step S3, the assembly fixture includes: a drive shaft jaw (1), a movable bracket (3), and a driven shaft jaw (5). The front end is fixedly installed on the drive shaft jaw (1), and the rear end is fixedly installed on the driven shaft jaw (5). Multiple movable brackets (3) are provided between the drive shaft jaw (1) and the driven shaft jaw (5), and the multiple movable brackets (3) cooperate to support the driven shaft jaw (5).

5. The laser welding method for medium-thick-walled solid rocket motor casing as described in claim 4, characterized in that, The assembly gap between the front end cap and the drive shaft jaw (1) is less than 0.2 mm, and the assembly gap between the rear end cap and the driven shaft jaw (5) is less than 0.2 mm.

6. The laser welding method for medium-thick-walled solid rocket motor casing as described in claim 1, characterized in that, In step S4, the vertical error of the circumferential seam programming teaching is less than 0.5 mm, and the horizontal error is less than 0.3 mm.

7. The laser welding method for medium-thick-walled solid rocket motor casing as described in claim 1, characterized in that, In step S5, after the MIG weld surface is finished, X-ray inspection is performed. If the detected porosity and defects do not meet the QJ175-1993 Grade 0 weld standard, rework is required.

8. The laser welding method for medium-thick-walled solid rocket motor casing as described in claim 7, characterized in that, If the pores and defects are less than 2.5mm deep, locate the defects using the X-ray film, grind them with tools, then perform manual TIG filler wire welding, and finally perform X-ray inspection after the welding is completed.

9. The laser welding method for medium-thick-walled solid rocket motor casing as described in claim 7, characterized in that, In step S5, if X-ray detection reveals undercut greater than 0.2 mm on both sides of the back of the weld, the laser power is reduced or the defocus is raised to reduce heat input and control the undercut depth to within 0.1 mm.

10. The laser welding method for medium-thick-walled solid rocket motor casing as described in claim 9, characterized in that, If the thickness of the weldment is greater than 10mm, make a 2-3mm bevel on the front side of the weldment, and then fill the missing material at the bevel with MIG.

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