A laser welding device integrated with dry ice peening and a process method thereof

Abstract

The application comprises a laser welding unit, a dry ice shot blasting unit, an integrated control unit and a follow-up mechanism. The shot blasting nozzle is fixed behind the welding head at an angle of 30-60 degrees. The process method is as follows: in the laser welding process, spherical dry ice particles are synchronously sprayed to the heat affected zone of the weld and the area behind the molten pool which has not been completely cooled, so as to improve the weld performance through deformation strengthening and phase transformation strengthening. The application synchronously completes the strengthening and welding, so that the yield strength of the stainless steel weld at-196 DEG C to high temperature is improved by 20-35%, and the comprehensive performance reaches more than 90% of the base material. The dry ice sublimation has no residue, avoiding secondary pollution. No subsequent heat treatment is needed, and the application is suitable for large thin-walled components, solving the problems of insufficient high-temperature strength, easy deformation and complicated process in the traditional process.

Description

Technical Field

[0001] This invention belongs to the field of laser welding and surface strengthening technology for metallic materials, specifically relating to an integrated laser welding and dry ice shot peening composite processing equipment and process for reusable rocket shells and fuel tanks. Background Technology

[0002] The shells and fuel tanks of reusable rockets are mostly made of high-strength austenitic stainless steel such as 301 and 304 through laser welding. During service, these components must withstand multiple extreme temperature loads, including the deep cryogenic temperature (down to -196°C) caused by propellants such as liquid oxygen / liquid hydrogen, the aerodynamic heating high temperature during atmospheric reentry (up to 300°C-600°C), and room temperature. Therefore, the comprehensive mechanical properties of the welds are subject to extremely stringent requirements.

[0003] When welding this type of stainless steel using traditional laser welding processes, the weld zone microstructure is mainly composed of coarse-grained cast austenite, resulting in significantly lower yield strength and tensile strength of the weld at both room temperature and high temperatures compared to the base metal. Furthermore, the high residual austenite content in the weld may lead to incomplete martensitic transformation at deep cryogenic temperatures, affecting low-temperature toughness. Existing post-treatment strengthening methods (such as aging treatment and overall heat treatment) have limitations, including long processing cycles, susceptibility to deformation in large thin-walled components, difficulty in applying to large-sized structures such as rocket shells, and potential damage to the original properties of the base metal.

[0004] Therefore, developing a process that can simultaneously strengthen the weld during the welding process without affecting the properties of the base material and is applicable to large thin-walled components has significant engineering application value. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems of insufficient weld strength, easy deformation of large thin-walled components and complicated procedures in the existing laser welding of austenitic stainless steel. It provides a laser welding equipment and process that integrates dry ice shot peening strengthening. By implementing dry ice shot peening treatment simultaneously during the welding process, the synergistic effect of deformation strengthening and phase transformation strengthening of the weld is achieved, thereby improving the strength and comprehensive mechanical properties of stainless steel welds in a wide temperature range from -196℃ to high temperature.

[0006] The technical solution of the present invention is as follows: On the one hand, the present invention provides a laser welding device with integrated dry ice shot peening strengthening, characterized in that it includes: A laser welding unit includes a laser, a welding head, and an inert gas protection device. The welding head is used to focus the laser beam onto the surface of the workpiece to be welded to form a molten pool. A dry ice shot peening unit includes a dry ice particle supply device, a high-pressure gas supply system, and a shot peening nozzle. The shot peening nozzle is used to propel dry ice particles accelerated by high-pressure gas onto the weld surface. An integrated control unit is electrically connected to the laser welding unit and the dry ice shot peening unit for coordinated control of welding parameters and shot peening parameters. A follow-up mechanism connects the shot peening nozzle to the welding head, keeping the spatial position of the shot peening nozzle relative to the welding head fixed and enabling it to move synchronously with the welding head; the shot peening nozzle is located behind the welding head along the welding direction, and the angle between the centerline of the shot peening nozzle and the centerline of the weld is 30° to 60°, and the distance between the outlet of the shot peening nozzle and the weld surface is 2mm to 200mm.

[0007] Furthermore, the shot peening nozzle is arranged on the upper surface side and / or the lower surface side of the workpiece to be welded.

[0008] Furthermore, it also includes a temperature monitoring module, which is installed on the follow-up mechanism. Its detection end is aligned with the spraying area of ​​the shot peening nozzle to monitor the surface temperature of the weld shot peening area in real time. The temperature monitoring module is electrically connected to the integrated control unit, which adjusts the welding speed and / or shot peening flow rate according to the feedback signal from the temperature monitoring module.

[0009] Furthermore, the temperature monitoring module is an infrared thermal imaging sensor or a single-point pyrometer.

[0010] Furthermore, the follow-up mechanism is a rigid connecting seat, and the shot peening nozzle and the welding head are fixedly connected to the same mounting base through the rigid connecting seat, and the spatial position of the two is locked by mechanical locking or common base method.

[0011] Furthermore, the high-pressure gas supply system provides compressed air or nitrogen at a pressure of 0.6 MPa to 1.5 MPa.

[0012] Furthermore, the dry ice shot peening unit adopts a pre-mixing structure, including a gas source, a pressure regulating valve, a dry ice hopper, a quantitative feeding mechanism, a mixer, and a conveying hose connected in sequence, with the outlet of the mixer connected to the shot peening nozzle through the conveying hose; or, the dry ice shot peening unit adopts a post-mixing structure, with high-pressure gas and dry ice particles being conveyed to the shot peening nozzle through independent hoses for mixing.

[0013] On the other hand, the present invention also provides a laser welding process method using the above-mentioned equipment, characterized by comprising the following steps: Step 1: Set the laser welding parameters and dry ice shot peening parameters; Step Two: Activate the laser welding unit and the dry ice shot peening unit, causing the laser beam to form a molten pool on the surface of the workpiece and move forward along the welding direction. Simultaneously, dry ice particles are accelerated by high-pressure gas and sprayed into the heat-affected zone of the weld and the weld surface area behind the molten pool that has not yet fully cooled; and Step 3: Improve weld strength through the synergistic effect of deformation strengthening and phase transformation strengthening generated by dry ice shot peening.

[0014] Furthermore, the dry ice particles are spherical or near-spherical particles with a diameter of 0.5 mm to 5.0 mm, an injection speed of 50 m / s to 200 m / s, and an injection flow rate of 0.5 kg / min to 3 kg / min.

[0015] Furthermore, the longitudinal distance between the shot peening nozzle and the center of the molten pool in the welding direction is 2mm to 150mm, and the dry ice particles are sprayed onto the area where the surface temperature of the weld drops to 300℃ to 900℃.

[0016] Furthermore, the surface temperature of the shot-peened area of ​​the weld is monitored in real time by a thermal imaging sensor, and the temperature signal is fed back to the integrated control unit. When the surface temperature of the weld is detected to be higher than 900℃ or lower than 300℃, the integrated control unit automatically adjusts the welding speed and / or shot peening flow rate to maintain the surface temperature of the weld in the shot-peened area within the range of 300℃ to 900℃.

[0017] Furthermore, for multi-welded structures, the shot peening process is repeated after each weld is completed to achieve layer-by-layer strengthening.

[0018] Furthermore, the laser power is 2kW to 8kW, the welding speed is 0.5m / min to 3m / min, and the shielding gas flow rate is 15L / min to 30L / min.

[0019] Furthermore, the workpiece to be welded is an austenitic stainless steel component, and the yield strength of the weld at temperatures ranging from -196℃ to high temperatures is increased by 20% to 35% compared to the laser weld without shot peening treatment, with the overall performance reaching more than 90% of the base material.

[0020] Furthermore, the equipment is used for laser welding and synchronous strengthening of thin-walled austenitic stainless steel components of reusable rocket casings or fuel tanks.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention uses a follower mechanism to fix the nozzle to the welding head, thus achieving process integration. In the martensitic phase transformation sensitive range (300℃~900℃) of austenitic stainless steel, the performance of the weld is improved by synergistic deformation strengthening and phase transformation strengthening. Deformation strengthening and low-temperature phase transformation strengthening are integrated into the same process, which increases the yield strength of the weld at room temperature and high temperature by 20%~35%, solving the problem of insufficient high-temperature strength of traditional laser welds.

[0022] 2) Dry ice sublimates directly after shot peening, leaving no abrasive residue and eliminating the need for secondary cleaning, thus avoiding damage to the high cleanliness requirements of the rocket casing. 3) The strengthening process is completed simultaneously with welding, without the need for additional heat treatment procedures, thus avoiding component deformation and energy consumption caused by overall heat treatment. It is particularly suitable for welding and manufacturing large thin-walled cylindrical sections. Attached Figure Description

[0023] Figure 1 This is a side view of the structure of the laser welding equipment with integrated dry ice shot peening reinforcement provided in an embodiment of the present invention, wherein the arrow indicates the welding travel direction. Figure 2 for Figure 1 The diagram shows the relationship between the temperature distribution curve along the welding direction from the center of the laser molten pool and the shot peening reinforcement area (temperature window of 300℃~900℃) on the weld centerline when the equipment is working.

[0024] Figure 3 This is a schematic diagram illustrating the air supply and material supply principle of the dry ice shot peening unit in this embodiment of the invention. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0026] like Figure 1 As shown, this embodiment provides a laser welding device with integrated dry ice shot peening strengthening, including a laser welding unit, a dry ice shot peening unit, an integrated control unit (not shown in the figure), and a follow-up mechanism.

[0027] Laser welding unit: Consists of a fiber laser, a welding head, and a coaxial or off-axis inert gas protection device (such as an argon gas protection nozzle). The welding head is fixed on a robotic arm or gantry and moves along a predetermined weld seam trajectory to output a laser beam to form a molten pool.

[0028] Dry ice shot peening unit: includes dry ice particle supply device (hopper + quantitative feeding mechanism), high pressure gas supply system (compressed air or nitrogen), shot peening nozzle and particle speed and flow control system.

[0029] Connection: High-pressure gas enters the main gas pipe after passing through the pressure regulating valve and the on / off valve; the main gas pipe is divided into two paths: one to the gas inlet of the mixer, and the other (optional) to the pneumatic booster port of the supply device. The bottom of the hopper is connected to the inlet of the feeding mechanism (rotary air brake / screw), and the outlet of the feeding mechanism is connected to the feed inlet of the mixer. The outlet of the mixer is connected to the shot peening nozzle. The control system is connected to the pressure regulating valve and the drive motor of the feeding mechanism to achieve closed-loop regulation, such as... Figure 3 As shown.

[0030] Mixing methods: Divided into pre-mixing (pressure delivery) and post-mixing (ejector delivery). Pre-mixing: Dry ice particles are mixed with high-pressure gas before entering the hose, forming a uniform solid-gas two-phase flow, which is then delivered to the nozzle via a single hose. Post-mixing: Gas first passes through the Venturi structure inside the nozzle to create negative pressure, drawing in dry ice particles from the side wall. These particles meet in the nozzle's mixing chamber and are accelerated before being ejected. Typically, dual hoses are used to deliver gas and particles separately. The former provides uniform mixing and is suitable for automated integration, while the latter has a simpler structure and faster particle start / stop response.

[0031] Typical equipment: For pre-mixing, options include Cold Jet Aero 80FP and IS 77S; for post-mixing, options include ASCOJET2001RX and KÄRCHER L2P ICE Blaster. Domestic models such as Suzhou Huanaier DIC-A use a dual-hose, post-mixing principle.

[0032] Workflow: The control system sets the gas pressure and feed rate. High-pressure gas carries dry ice particles to form a solid-gas two-phase flow in the mixer. After being accelerated by the nozzle, it is sprayed into the welding area to cool the surface and apply pressure to the sample surface. The pressure and feed are controlled by a dual closed loop to ensure stable spray speed and flow rate.

[0033] The dry ice particles are preferably spherical or near-spherical (commonly known as dry ice rice), with a diameter of 0.5 mm to 5.0 mm, a spray speed of 50 m / s to 200 m / s, and a spray flow rate of 0.5 kg / min to 3 kg / min.

[0034] Integrated control unit: Employing a PLC or industrial computer, it is electrically connected to the laser welding unit, dry ice shot peening unit, and subsequent temperature monitoring module. The control unit adjusts the laser power, welding speed, gas pressure, and feed rate in real time based on preset welding speed, shot peening flow rate, and temperature feedback signals to ensure that the shot peening always operates within the optimal temperature range.

[0035] Follow-up mechanism: connects the shot peening nozzle to the welding head, so that the spatial position of the shot peening nozzle relative to the welding head remains fixed and moves synchronously with the welding head.

[0036] The shot peening nozzle and the welding head are fixedly connected to the same mounting base, ensuring that the spatial position of the shot peening nozzle relative to the welding head remains constant, and that the shot peening nozzle can move synchronously with the welding head. Specifically, the shot peening nozzle and the welding head are jointly mounted on a rigid connecting seat or a three-dimensional adjustment mechanism, and their spatial orientation is fixed through mechanical locking or a shared base. When the welding head moves along a predetermined welding path, there is no relative displacement between the shot peening nozzle and the welding head, ensuring that the relative position of the dry ice shot peening area and the weld pool remains consistent. Dedicated adjustment mechanism. The working principle of this invention is as follows: The operator or automated control system moves the shot peening nozzle to the desired spatial position relative to the welding head by driving the X, Y, and Z axis adjustment components. After adjustment, the locking mechanism is activated to lock the position in each direction. Subsequently, as the welding head moves along the welding path, the shot peening nozzle moves synchronously with the welding head, and the spatial orientation between the two remains unchanged, thus ensuring the precise and stable relative position of the dry ice shot peening area and the weld pool.

[0037] The shot peening nozzle is located behind the welding head (along the welding direction), with its centerline forming an angle θ of 30° to 60° with the weld centerline. The vertical distance H between the nozzle outlet and the weld surface is 2mm to 200mm. The shot peening nozzle can be arranged on the upper surface of the workpiece, on the lower surface, or both simultaneously (for double-sided shot peening).

[0038] As a preferred embodiment, the equipment also includes a temperature monitoring module, such as an infrared thermal imaging sensor or a single-point pyrometer, mounted on the follow-up mechanism with its lens aimed at the shot peening area. The temperature monitoring module is connected to the integrated control unit. When the weld surface temperature is detected to be higher than 900℃ or lower than 300℃, the control unit automatically adjusts the welding speed (e.g., by ±0.2 m / min) or the shot peening flow rate (e.g., by ±0.2 kg / min) to maintain the temperature of the shot peening area within the optimal range of 300℃ to 900℃.

[0039] Example 1 The equipment of this invention is used to perform butt laser welding on 1.5mm thick 301 stainless steel 3 / 4H hard state plates.

[0040] Bulk material properties (301 3 / 4H hard state): • Room temperature (25℃): Tensile strength 1200MPa, yield strength 930MPa • Deep low temperature (-196℃): Tensile strength 2000MPa, yield strength 1000MPa • High temperature (100℃): Tensile strength 1090MPa, yield strength 880MPa Target performance of weld: To achieve 90% of the performance of the weld body, that is: • Room temperature: Tensile strength ≥ 1080 MPa, Yield strength ≥ 837 MPa • Deep low temperature: Tensile strength ≥ 1800 MPa, Yield strength ≥ 900 MPa • High temperature (100℃): Tensile strength ≥ 981 MPa, Yield strength ≥ 792 MPa Laser welding parameters: • Laser power: 3.5kW • Welding speed: 1.5m / min • Shielding gas: Argon, flow rate 18L / min Dry ice shot peening parameters: • Dry ice particle shape: spherical or near-spherical microparticles (dry ice grains) • Dry ice particle diameter: 1.5mm • Spraying speed: 130m / s • Spraying flow rate: 1.2kg / min • High-pressure gas: compressed air, pressure 0.9MPa • Shot peening nozzle position behind the weld joint: 90mm • Distance between nozzle and weld surface: 70mm • Spraying angle: 45° • Shot peening zone temperature: monitored in real time by an infrared thermal imaging sensor to ensure application to an area with a weld surface temperature of approximately 350℃~450℃. Process: The laser welding unit and dry ice shot peening unit are activated, causing the laser beam to form a molten pool and move forward. Dry ice particles are continuously sprayed under high-pressure gas acceleration onto the heat-affected zone of the weld and the weld surface area behind the molten pool that has not yet fully cooled. During welding, the follow-up mechanism drives the shot peening nozzle to move synchronously with the welding head, ensuring that the shot peening always acts within the temperature window zone.

[0041] Performance test results: Mechanical property tests were performed on the obtained weld. • Room temperature (25℃): Tensile strength 1120MPa (93.3% of the original strength), yield strength 865MPa (93.0% of the original strength) • Deep low temperature (-196℃): Tensile strength 1900MPa (95.0% of the original strength), yield strength 945MPa (94.5% of the original strength) • High temperature (100℃): Tensile strength 1025MPa (94.0% of the original strength), yield strength 835MPa (94.9% of the original strength) The overall performance of the weld reaches more than 90% of the performance of the base material, which is 25% to 35% higher than that of traditional laser welding (without dry ice shot peening).

[0042] Example 2 The equipment of this invention is used to perform butt laser welding on 2.5mm thick 301 stainless steel 3 / 4H hard state plates.

[0043] Bulk material properties (same as in Example 1): • Room temperature (25℃): Tensile strength 1200MPa, yield strength 930MPa • Deep low temperature (-196℃): Tensile strength 2000MPa, yield strength 1000MPa • High temperature (100℃): Tensile strength 1090MPa, yield strength 880MPa Target performance of weld (90% of the body): • Room temperature: Tensile strength ≥ 1080 MPa, Yield strength ≥ 837 MPa • Deep low temperature: Tensile strength ≥ 1800 MPa, Yield strength ≥ 900 MPa • High temperature (100℃): Tensile strength ≥ 981 MPa, Yield strength ≥ 792 MPa Laser welding parameters: • Laser power: 5.5kW • Welding speed: 1.0m / min • Shielding gas: Argon, flow rate 25L / min Dry ice shot peening parameters: • Dry ice particle shape: spherical or near-spherical microparticles (dry ice rice) • Dry ice particle diameter: 2.0 mm • Spraying speed: 110 m / s • Spraying flow rate: 2.0 kg / min • High-pressure gas: compressed air, pressure 1.1 MPa • Shot peening nozzle position behind the weld joint: 120 mm • Distance between nozzle and weld surface: 100 mm • Spraying angle: 50° • Shot peening zone temperature: monitored in real time by an infrared thermal imaging sensor to ensure application to an area with a weld surface temperature of approximately 400℃~500℃. Process: A multi-layer welding process is adopted. After the first welding is completed, dry ice shot peening is performed immediately, followed by the second welding and shot peening again to achieve layer-by-layer strengthening. The shot peening parameters are the same for each welding.

[0044] Performance test results: Mechanical property tests were performed on the obtained weld. • Room temperature (25℃): Tensile strength 1105MPa (92.1% of the original strength), yield strength 850MPa (91.4% of the original strength) • Deep low temperature (-196℃): Tensile strength 1920MPa (96% of the original strength), yield strength 920MPa (92.0% of the original strength) • High temperature (100℃): Tensile strength 1010MPa (92.7% of the original strength), yield strength 815MPa (92.6% of the original strength) The overall performance of the weld reaches over 90% of the original weld body performance. The weld microstructure is uniform, with a surface martensitic strengthening layer thickness of approximately 0.3 mm. The internal microstructure exhibits refined grains and is free from defects such as cracks and lack of fusion. Compared to traditional laser welding processes, the process of this invention improves weld strength by over 28%, 22%, and 30% at room temperature, deep cryogenic temperatures, and high temperatures, respectively.

[0045] Comparative Example Using the same laser welding parameters as in Example 1 (laser power 3.5kW, welding speed 1.5m / min, shielding gas argon flow rate 18L / min), 301 stainless steel 3 / 4H hard state plate with a thickness of 1.5mm was welded, but dry ice shot peening was not performed.

[0046] Performance test results: • Room temperature (25℃): Tensile strength 860MPa (only 71.7% of the original strength), yield strength 710MPa (only 76.3% of the original strength) • Deep low temperature (-196℃): Tensile strength 1880MPa (only 94% of the original strength), yield strength 780MPa (only 78.0% of the original strength) • High temperature (100℃): Tensile strength 780MPa (only 71.6% of the original strength), yield strength 650MPa (only 73.9% of the original strength) The strength of traditional laser-welded welds at various temperatures is far below 90% of the original material's performance, failing to meet the stringent mechanical performance requirements of reusable rocket shells and fuel tanks.

[0047] The performance data of Example 1 and the comparative example were compared, and the results are summarized in Table 1 below. Table 1 clearly shows that, compared with traditional laser welding processes, the laser welding process with integrated dry ice shot peening provided by this invention can increase the tensile strength of 301 stainless steel 3 / 4H hardened welds by more than 30% at room temperature and high temperature, and also shows a certain improvement at deep low temperature, demonstrating significant overall effectiveness.

[0048] Table 1 In summary, this invention integrates a dry ice shot peening unit with a laser welding unit and precisely controls the temperature window and process parameters of the shot peening zone, simultaneously achieving deformation strengthening and phase transformation strengthening of the weld during the welding process. This technical solution effectively solves the technical problem of insufficient weld strength, especially the room temperature and high temperature strength being far lower than that of the base material, when traditionally laser-welding austenitic stainless steel. Furthermore, the entire strengthening process requires no subsequent heat treatment and leaves no residual pollution, making it particularly suitable for the efficient and high-quality welding and manufacturing of large, thin-walled components.

Claims

1. A laser welding device integrating dry ice shot peening strengthening, characterized in that, include: A laser welding unit includes a laser, a welding head, and an inert gas protection device. The welding head is used to focus the laser beam onto the surface of the workpiece to be welded to form a molten pool. The dry ice shot peening unit includes a dry ice particle supply device, a high-pressure gas supply system, and a shot peening nozzle. The shot peening nozzle is used to spray dry ice particles accelerated by high-pressure gas onto the weld surface. An integrated control unit is electrically connected to the laser welding unit and the dry ice shot peening unit to coordinate the control of welding parameters and shot peening parameters. as well as A follow-up mechanism connects the shot peening nozzle to the welding head, keeping the spatial position of the shot peening nozzle relative to the welding head fixed and enabling it to move synchronously with the welding head; the shot peening nozzle is located behind the welding head along the welding direction, and the angle between the centerline of the shot peening nozzle and the centerline of the weld is 30° to 60°, and the distance between the outlet of the shot peening nozzle and the weld surface is 2mm to 200mm.

2. The laser welding equipment with integrated dry ice shot peening as described in claim 1, characterized in that, The shot peening nozzles are arranged on the upper surface and / or lower surface of the workpiece to be welded.

3. The laser welding equipment with integrated dry ice shot peening as described in claim 1, characterized in that, It also includes a temperature monitoring module, which is installed on the follow-up mechanism. Its detection end is aligned with the spraying area of ​​the shot peening nozzle to monitor the surface temperature of the weld shot peening area in real time. The temperature monitoring module is electrically connected to the integrated control unit, which adjusts the welding speed and / or shot peening flow rate according to the feedback signal from the temperature monitoring module.

4. The laser welding equipment with integrated dry ice shot peening as described in claim 3, characterized in that, The temperature monitoring module is an infrared thermal imaging sensor or a single-point pyrometer.

5. The laser welding equipment with integrated dry ice shot peening as described in claim 1, characterized in that, The follower mechanism is a rigid connecting seat. The shot peening nozzle and the welding head are fixedly connected to the same mounting base through the rigid connecting seat, and their spatial positions are locked by mechanical locking or a common base method.

6. The laser welding equipment with integrated dry ice shot peening as described in claim 1, characterized in that, The high-pressure gas supply system provides compressed air or nitrogen at a pressure of 0.6 MPa to 1.5 MPa.

7. The laser welding equipment with integrated dry ice shot peening as described in claim 1, characterized in that, The dry ice shot peening unit adopts a pre-mixing structure, including a gas source, a pressure regulating valve, a dry ice hopper, a quantitative feeding mechanism, a mixer, and a conveying hose connected in sequence. The outlet of the mixer is connected to the shot peening nozzle through the conveying hose. Alternatively, the dry ice shot peening unit adopts a post-mixing structure, in which high-pressure gas and dry ice particles are respectively conveyed to the shot peening nozzle through independent hoses for mixing.

8. A laser welding process method using the equipment described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Set the laser welding parameters and dry ice shot peening parameters; Step 2: Start the laser welding unit and the dry ice shot peening unit, so that the laser beam forms a molten pool on the surface of the workpiece to be welded and moves forward along the welding direction. At the same time, dry ice particles are sprayed into the heat-affected zone of the weld and the weld surface area behind the molten pool that has not been completely cooled under the acceleration of high pressure gas. as well as Step 3: Improve weld strength through the synergistic effect of deformation strengthening and phase transformation strengthening generated by dry ice shot peening.

9. The laser welding process method according to claim 8, characterized in that, The dry ice particles are spherical or near-spherical particles with a diameter of 0.5 mm to 5.0 mm, an injection speed of 50 m / s to 200 m / s, and an injection flow rate of 0.5 kg / min to 3 kg / min.

10. The laser welding process method according to claim 8, characterized in that, The longitudinal distance between the shot peening nozzle and the center of the molten pool in the welding direction is 2mm to 150mm, and the dry ice particles are sprayed onto the area where the surface temperature of the weld drops to 300℃ to 900℃.

11. The laser welding process method according to claim 8, characterized in that, The surface temperature of the shot-peened area of ​​the weld is monitored in real time by a thermal imaging sensor, and the temperature signal is fed back to the integrated control unit. When the surface temperature of the weld is detected to be higher than 900℃ or lower than 300℃, the integrated control unit automatically adjusts the welding speed and / or shot peening flow rate to maintain the surface temperature of the weld in the shot-peened area within the range of 300℃ to 900℃.

12. The laser welding process method according to claim 8, characterized in that, For multi-pass welded structures, the shot peening process is repeated after each weld is completed to achieve layer-by-layer strengthening.

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