A method and apparatus for double-kidney spot laser narrow-gap welding

Abstract

The application provides a method and device for double-kidney-shaped light spot laser narrow-gap welding, and the method comprises the following steps: (1) performing base layer welding in the welding space of a workpiece to be welded, and performing weld cleaning to obtain a first welding piece; the weld of the workpiece to be welded comprises a weld surface and a groove surface on the weld surface; (2) performing double-kidney-shaped light spot laser welding in the welding space of the first welding piece, wherein the light spot of the double-kidney-shaped light spot laser welding simultaneously acts on the side wall of the groove surface and the corner of the weld surface of the workpiece to be welded, the welding wire is swung in the process, the first pass of the filling layer is completed, and then the weld is cleaned; and (3) repeating step (2) until the welding is completed. The application has excellent welding effect for low-temperature steel with a narrow gap, and can be applied to the welding of nuclear fusion steel.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and in particular to a method and apparatus for narrow-gap welding using a double-kidney-shaped laser spot. Background Technology

[0002] Currently, the highest field of the longitudinal field coil will increase from 11.8T to 15T, and the electromagnetic force that the coil structure needs to withstand will increase significantly. This places higher demands on the low-temperature strength and toughness of the structural materials.

[0003] On the one hand, in order to ensure the stable operation of superconducting magnets in harsh environments of extremely low temperature, strong magnetic field and high stress, it is required that stainless steel materials with a yield strength greater than 1300MPa at 4K temperature be used in the high stress area of ​​superconducting magnet structural components, such as N50 austenitic stainless steel.

[0004] On the other hand, in order to reduce the overall manufacturing cost of nuclear fusion structural components, low-temperature structural materials with matching strength are used in areas with lower electromagnetic forces, such as austenitic stainless steels like 316L / 316LN, which currently have good low-temperature performance.

[0005] The magnet system in a fusion device is quite large, and the structural components used to support and protect the superconducting coils inevitably require welding during manufacturing. The thickness of the structural materials used ranges from 20mm to 300mm. During the welding of these thick components, under non-equilibrium thermodynamic conditions and high restraint stress, defects such as porosity, lack of fusion, and cracks are prone to occur in the weld metal during solidification. Large welding heat inputs can also cause welding deformation of the structural components, affecting the assembly accuracy of the device. Furthermore, the rapid solidification of the molten metal in the weld pool during the joining of dissimilar materials can lead to insufficient flow of the molten pool, resulting in uneven weld composition.

[0006] Therefore, it is necessary to develop special welding methods for the above-mentioned materials. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a method and apparatus for narrow gap laser welding with a double kidney-shaped spot. The method improves the welding quality of thick plate laser narrow gap welding by using a double kidney-shaped spot and an oscillating welding wire, effectively solving the defects and deficiencies of incomplete fusion of the groove, reduction of weld stress and welding deformation in narrow gap welding of thick plates of low temperature steel for nuclear fusion, while improving weld formation and welding process stability.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for narrow-gap laser welding with a double-kidney-shaped spot, the method comprising:

[0010] (1) Perform the root pass welding in the welding space of the workpiece to be welded, and clean the weld seam to obtain the first welded part; the weld seam of the workpiece to be welded includes the weld seam surface and the bevel surface located on the weld seam surface.

[0011] (2) Perform double-kidney-shaped laser welding in the welding space of the first weldment. The laser spot of the double-kidney-shaped laser welding acts simultaneously on the side wall of the bevel surface of the workpiece to be welded and the corner of the weld surface. During the process, the welding wire swings to complete the first welding of the filler layer, and then the weld is cleaned.

[0012] (3) Repeat step (2) until welding is completed.

[0013] The welding process of the present invention has the following special advantages:

[0014] A. The process employs a double-kidney-shaped laser beam, where the double-kidney-shaped laser beam does not act entirely directly on the weld surface, but partially on the bevel surface. This portion of the beam is reflected from the bevel surface of the workpiece and then acts on the weld surface, reducing the maximum temperature amplitude and improving the uniformity of the temperature distribution of the weld pool and its surrounding area. Moreover, this portion of the beam acting on the bevel surface provides energy on one hand, by reflecting it back to the weld surface, and on the other hand, by conducting energy to the weld surface through the heat conduction of the workpiece itself, further heating both sides of the bevel and eliminating sidewall incomplete fusion defects. The other part of the double-kidney-shaped laser beam acts on the corners of the weld surface, compensating for the previous problem of low heat at the corners of the weld surface, thereby significantly improving the uniformity of the temperature distribution of the weld pool and its surrounding area, and reducing welding deformation and cracking tendency.

[0015] B. The process of using a combination of double-kidney-shaped laser spot and oscillating welding wire can suppress the formation of coarse columnar crystals in the center of the weld, thereby increasing the compositional uniformity of the weld structure and the uniform dispersion of the second phase particles, and improving the mechanical properties of the weld.

[0016] C. The layer-by-layer welding process, which involves first performing the bottom layer welding and then performing layer-by-layer filler welding, has advantages such as low welding heat input and lower welding residual stress and residual deformation.

[0017] Preferably, the workpiece to be welded in step (1) is low-temperature steel for nuclear fusion.

[0018] The double-kidney-shaped laser narrow gap welding method described in this invention is particularly applicable to low-temperature steel used in nuclear fusion. These low-temperature steels need to meet the condition that the yield strength is greater than 1300MPa at a temperature of 4-20K in high-stress areas. The uniformity of the weld has a significant impact on the service life of the product.

[0019] Preferably, the low-temperature steel for nuclear fusion includes any one or a combination of at least two of N50 austenitic stainless steel, 316LN austenitic stainless steel, 304 stainless steel, 316L stainless steel or JJ1 stainless steel.

[0020] Preferably, the applicable low-temperature range of the low-temperature steel for nuclear fusion is 4 to 20 K.

[0021] Preferably, the width of the weld surface is 2 to 4 mm, for example, it can be 2 mm, 2.2 mm, 2.3 mm, 2.5 mm, 2.8 mm, 3.0 mm, 3.2 mm, 3.5 mm, 3.8 mm or 4.0 mm.

[0022] It is worth noting that the narrower the weld, the more likely it is to cause uneven temperature field during the welding process, making welding more difficult. The method of the present invention is applicable to workpieces with a weld width of only 2 to 4 mm, and the welding effect is excellent.

[0023] Preferably, the inclination angle of the bevel surface is 1 to 4°, for example, it can be 1°, 2°, 2.5°, 3°, 3.5° or 4°, etc.

[0024] Preferably, the thickness of the workpiece to be welded is 20 to 300 mm, for example, it can be 20 mm, 30 mm, 50 mm, 80 mm, 100 mm, 120 mm, 150 mm, 200 mm, 250 mm or 300 mm.

[0025] It is worth noting that during the welding of thick structural components, under non-equilibrium thermodynamic conditions and high restraint stress, the weld metal is prone to defects such as porosity, lack of fusion, and cracks during solidification. Large welding heat input can also cause welding deformation of the structural components, affecting the assembly accuracy of the device.

[0026] Preferably, before the bottom layer welding, the bevel surface of the workpiece to be welded is first laser cleaned.

[0027] Preferably, the laser cleaning is performed within 15 minutes to 1 hour before the bottom layer welding, for example, it can be 15 minutes, 0.5 hours, 40 minutes, 50 minutes or 1 hour.

[0028] Preferably, before the root pass welding, the workpiece to be welded is placed on the welding platform, and a back shielding gas fixture is installed, and the gas flow rates of the shielding gas and the back shielding gas are adjusted.

[0029] Preferably, the protective gas comprises argon. The argon gas used in this invention has a purity of 99.999%.

[0030] Preferably, the shielding gas flow rate for the root pass welding is 15-25 L / min, and the back shielding gas flow rate is 5-10 L / min.

[0031] The protective gas flow rate can be, for example, 15L / min, 16L / min, 17L / min, 18L / min, 19L / min, 20L / min, 21L / min, 22L / min, 23L / min, 24L / min or 25L / min, etc.

[0032] The back protection gas flow rate can be, for example, 5L / min, 5.5L / min, 6L / min, 6.5L / min, 7L / min, 7.5L / min, 8L / min, 8.5L / min, 9L / min, 9.5L / min, or 10L / min.

[0033] Preferably, the pre-laser power for the bottom layer welding is 4.0 to 6.0 kW, the defocusing amount is 0 to 5.0 mm, and the welding speed is 1.0 to 1.5 m / min.

[0034] The power of the pre-laser can be, for example, 4.0kW, 4.2kW, 4.5kW, 4.8kW, 5.0kW, 5.2kW, 5.5kW, 5.8kW, or 6.0kW. The defocusing amount can be, for example, 0mm, 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, or 5mm. The welding speed can be, for example, 1.0m / min, 1.1m / min, 1.2m / min, 1.3m / min, or 1.5m / min.

[0035] Preferably, the post-laser power for the root pass welding is 3.0–5.0 kW, the defocusing amount is 0–5.0 mm, and the welding speed is 1.0–1.5 m / min. The post-laser power can be, for example, 3.0 kW, 3.2 kW, 3.5 kW, 3.8 kW, 4.0 kW, 4.2 kW, 4.5 kW, 4.8 kW, or 5.0 kW. The defocusing amount can be, for example, 0 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 4 mm, or 5 mm. The welding speed can be, for example, 1.0 m / min, 1.1 m / min, 1.2 m / min, 1.3 m / min, or 1.5 m / min.

[0036] Preferably, the circular scanning radius of the bottom layer welding is 0.5 to 1.0 mm, for example, it can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm or 1.0 mm.

[0037] Preferably, the weld cleaning includes laser cleaning.

[0038] Preferably, the double-kidney-shaped laser welding includes: applying dual-beam lasers to the sidewall of the bevel surface and the corner of the weld surface through double-kidney-shaped laser spots respectively; adjusting the wire feeding end to be located at the center of the weld and between the two laser spots; and oscillating the welding wire to perform double-kidney-shaped laser welding.

[0039] Preferably, the two beams of the dual-beam laser are arranged in a cross pattern.

[0040] Preferably, the double-kidney-shaped light spot is symmetrically arranged.

[0041] Preferably, the ratio of the area of ​​the spot of the dual-beam laser acting on the side wall of the bevel surface and the corner of the weld surface is 0.2 to 1:1, for example, it can be 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1 or 1:1, etc.

[0042] Since this invention aims to address the problem of uneven temperature field distribution during the process, the ratio of the area of ​​the laser spot distributed on the sidewall of the bevel face and the weld surface is crucial to the uniformity of the temperature field distribution. When the area of ​​the laser spot distributed on the sidewall of the bevel face is too large, there is excessive heat reflection and conduction, resulting in insufficient melting of the welding wire or a slow melting rate, leading to insufficient amount of top wire or filler metal. Moreover, excessive melting of the sidewall widens the weld and increases deformation. When the area of ​​the laser spot distributed on the sidewall of the bevel face is too small, it leads to insufficient melting of the sidewall and easily forms cold shuts (lack of fusion of the sidewall). This invention preferably controls the area ratio of the two to bevel faces to be between 0.2 and 1:1, which can achieve excellent welding results for welding narrow gaps and reduce the generation of cracks.

[0043] Preferably, the range of the welding wire oscillation is -2 to 2 mm.

[0044] Preferably, the laser power for the double-kidney-shaped laser welding is 4.0–6.0 kW, and the defocusing amount is 20–40 mm. The laser power can be, for example, 4.0 kW, 4.2 kW, 4.5 kW, 4.8 kW, 5.0 kW, 5.5 kW, or 6.0 kW. The defocusing amount can be, for example, 20 mm, 23 mm, 25 mm, 28 mm, 30 mm, 33 mm, 35 mm, 38 mm, or 40 mm.

[0045] Preferably, the welding speed of the double-kidney-shaped laser welding is 0.6–1.5 m / min, and the wire feed speed is 1.0–3.0 m / min. The welding speed can be, for example, 0.6 m / min, 0.7 m / min, 0.8 m / min, 0.9 m / min, 1.0 m / min, 1.1 m / min, 1.2 m / min, 1.3 m / min, 1.4 m / min, or 1.5 m / min. The wire feed speed can be, for example, 1.0 m / min, 1.2 m / min, 1.3 m / min, 1.5 m / min, 1.8 m / min, 2.0 m / min, 2.2 m / min, 2.5 m / min, or 3.0 m / min.

[0046] Preferably, the shielding gas flow rate for the double-kidney-shaped laser welding is 15-25 L / min, for example, it can be 15 L / min, 16 L / min, 17 L / min, 18 L / min, 19 L / min, 20 L / min, 21 L / min, 22 L / min, 23 L / min, 24 L / min or 25 L / min, etc.

[0047] Preferably, after the double-kidney-shaped laser welding is completed, the workpiece is cooled to room temperature.

[0048] As a preferred technical solution of the present invention, a method for narrow-gap laser welding with a double-kidney-shaped spot is provided, the method comprising:

[0049] (1) The workpiece to be welded (the weld of the workpiece to be welded includes the weld surface and the bevel surface located on the weld surface; the width of the weld surface is 2-4 mm, the inclination angle of the bevel surface is 1-4°, and the thickness of the workpiece to be welded is 20-300 mm) is laser cleaned within 15 min to 1 h before welding.

[0050] Then place the workpiece to be welded on the welding platform and install the back shielding gas fixture, and adjust the gas flow rate of the shielding gas and the back shielding gas; the shielding gas flow rate is 15-25 L / min, and the back shielding gas flow rate is 5-10 L / min.

[0051] A root pass welding is performed within the welding space of the workpiece to be welded. The pre-laser power for the root pass welding is 4.0–6.0 kW, the defocusing amount is 0–5.0 mm, and the welding speed is 1.0–1.5 m / min. The post-laser power is 3.0–5.0 kW, the defocusing amount is 0–5.0 mm, the welding speed is 1.0–1.5 m / min, and the circular scanning radius is 0.5–1.0 mm. Weld seam cleaning is then performed, which is laser cleaning, to obtain the first weldment.

[0052] (2) Perform double-kidney-shaped laser welding in the welding space of the first weldment, specifically including: applying double-beam lasers to the side wall of the bevel surface and the corner of the weld surface through double-kidney-shaped lasers respectively. The two beams of the double-beam lasers are arranged in a cross pattern, and the double-kidney-shaped lasers are symmetrically arranged. The area ratio of the laser spots applied by the double-beam lasers to the side wall of the bevel surface and the corner of the weld surface is 0.2 to 1:1. Adjust the wire feeding end to be located at the center of the weld and between the two laser spots. The welding wire oscillates within a range of -2 to 2 mm to perform double-kidney-shaped laser welding, complete the first welding of the filler layer, and then clean the weld.

[0053] The laser power of the double-kidney-shaped laser welding is 4.0–6.0 kW, the defocusing amount is 20–40 mm, the welding speed is 0.6–1.5 m / min, the wire feed speed is 1.0–3.0 m / min, and the shielding gas flow rate is 15–25 L / min.

[0054] (3) Repeat step (2) until welding is completed. After the double kidney-shaped laser welding is completed, cool the workpiece to room temperature.

[0055] In a second aspect, the present invention provides an apparatus for narrow-gap laser welding with a double-kidney-shaped spot, the apparatus being capable of operating the narrow-gap laser welding method with a double-kidney-shaped spot described in the first aspect.

[0056] Preferably, the device includes a laser optical path section and a welding wire oscillation section.

[0057] The laser optical path includes a laser beam emitter for emitting laser light and a focusing lens for focusing and reflecting the laser emitted by the laser beam emitter into a double-kidney-shaped spot; the double-kidney-shaped spot acts simultaneously on the sidewall of the bevel surface of the workpiece to be welded and the corner of the weld surface.

[0058] The welding wire swinging part includes a drive motor, a swing arm, and a welding wire;

[0059] The welding wire swinging part is driven by a drive motor to drive the swing arm to make the welding wire reciprocate in the laser strip spot.

[0060] Compared with the prior art, the present invention has at least the following beneficial effects:

[0061] (1) The double-kidney-shaped laser narrow gap welding method provided by the present invention can be well applied to the welding of low-temperature steel for nuclear fusion, and effectively reduces welding deformation and cracking.

[0062] (2) The double-kidney-shaped laser narrow gap welding method provided by the present invention solves the problems of incomplete fusion of groove, reduced weld stress and welding deformation in narrow gap welding of low-temperature steel thick plates for nuclear fusion, and improves weld formation and welding process stability.

[0063] (3) The device for narrow gap laser welding with double kidney-shaped spot provided by the present invention can effectively achieve welding of low-temperature steel thick plates for nuclear fusion, and the welding quality is high. Attached Figure Description

[0064] Figure 1 This is a schematic diagram of narrow-gap laser welding with a double-kidney-shaped spot provided in Embodiment 1 of the present invention.

[0065] In the figure: 1-First beam; 2-Second beam; 3-First spot forming part; 4-Second spot forming part; 5-Welding wire; 6-Side wall of the bevel surface; 7-Welding wire oscillation displacement; 8-Reflected light; 9-First workpiece; 10-Second workpiece. Detailed Implementation

[0066] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0067] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0068] As a specific embodiment of the present invention, an apparatus for narrow-gap laser welding with a double-kidney-shaped spot is provided, the apparatus comprising a laser optical path section and a welding wire oscillation section.

[0069] The laser optical path includes a laser beam emitter for emitting laser light and a focusing lens for focusing and reflecting the laser emitted by the laser beam emitter into a double-kidney-shaped spot; the double-kidney-shaped spot acts simultaneously on the sidewall of the bevel surface of the workpiece to be welded and the corner of the weld surface.

[0070] The welding wire swinging part includes a drive motor, a swing arm, and a welding wire;

[0071] The welding wire swinging part is driven by a drive motor to drive the swing arm to make the welding wire reciprocate in the laser strip spot.

[0072] As another specific embodiment of the present invention, a schematic diagram of the double-kidney-shaped spot laser narrow gap welding method provided by the present invention is shown below. Figure 1 As shown, from Figure 1 It can be seen from this:

[0073] (1) The first workpiece 9 and the second workpiece 10 are joined together to form a workpiece to be welded. The bottom layer welding is performed in the welding space of the workpiece to be welded, and the weld is cleaned to obtain the first welded part. The weld of the workpiece to be welded includes a weld surface and a bevel surface located on the weld surface.

[0074] (2) Double kidney-shaped laser welding is performed in the welding space of the first workpiece. The laser spot of the double kidney-shaped laser welding includes a first spot formed by the first beam 1 passing through the first spot forming part 3 and a second spot formed by the second beam 2 passing through the second spot forming part 4. These spots act simultaneously on the side wall 6 of the bevel surface of the workpiece to be welded and the corner of the weld surface, and form reflected light 8 on the side wall 6 of the bevel surface. During the process, the welding wire 5 oscillates according to the welding wire oscillation displacement 7 to complete the first welding of the filler layer, and then the weld is cleaned.

[0075] (3) Repeat step (2) until welding is completed.

[0076] For ease of testing, the laser source used in the following embodiments and comparative examples is a single-mode or multi-mode solid-state laser. The welding wire material is ER316LMn with a diameter of 1.2 mm. However, this does not mean that the technical solution of the present invention adopts the above-described solution; other feasible solutions recognized by the art can be used.

[0077] Example 1

[0078] This embodiment provides a method for narrow-gap laser welding with a double-kidney-shaped spot, the method comprising:

[0079] (1) Within 15 minutes before welding, the workpiece to be welded (the weld of the workpiece to be welded includes a weld surface and a bevel surface located on the weld surface; the width of the weld surface is 3mm, the inclination angle of the bevel surface is 2°, the workpiece to be welded includes a first workpiece and a second workpiece, the first workpiece and the second workpiece are symmetrical, the first workpiece is N50 austenitic stainless steel with a thickness of 30mm, and the second workpiece is 316LN austenitic stainless steel with a thickness of 30mm) is laser cleaned.

[0080] Then, the workpiece to be welded is placed on the welding platform, and the back shielding gas fixture is installed. The gas flow rates of the shielding gas and the back shielding gas are adjusted; the shielding gas flow rate is 20 L / min, and the back shielding gas flow rate is 5 L / min; the shielding gas is argon with a purity of 99.999%.

[0081] A root pass welding is performed within the welding space of the workpiece to be welded. The pre-laser power for the root pass welding is 5.0kW, the defocusing amount is 3.0mm, and the welding speed is 1.2m / min. The post-laser power is 4.0kW, the defocusing amount is 2.5mm, the welding speed is 1.3m / min, and the circular scanning radius is 0.8mm. Weld seam cleaning is then performed, which is laser cleaning, to obtain the first weldment.

[0082] (2) Perform double-kidney-shaped laser welding in the welding space of the first weldment, specifically including: applying double-beam lasers to the side wall of the bevel surface and the corner of the weld surface through double-kidney-shaped lasers respectively. The two beams of the double-beam lasers are arranged in a cross pattern, and the double-kidney-shaped lasers are symmetrically arranged. The area ratio of the laser spots applied by the double-beam lasers to the side wall of the bevel surface and the corner of the weld surface is 0.4:1. Adjust the wire feeding end to be located at the center of the weld and between the two laser spots. The welding wire oscillates within a range of -2 to 2 mm to perform double-kidney-shaped laser welding, complete the first welding of the filler layer, and then clean the weld.

[0083] The laser power for the double-kidney-shaped laser welding is 5.0kW, the defocusing amount is 30mm, the welding speed is 0.8m / min, the wire feed speed is 2.0m / min, and the shielding gas flow rate is 20L / min.

[0084] (3) Repeat step (2) until welding is completed. After the double kidney-shaped laser welding is completed, cool the workpiece to room temperature.

[0085] The double-kidney-shaped laser narrow-gap welding method provided in this embodiment exhibits excellent welding results for low-temperature steel with narrow gaps, and is applicable to the welding of steel used in nuclear fusion. By using the double-kidney-shaped laser spot and the oscillation of the welding wire, the uniformity of the temperature distribution in the weld pool and surrounding area is improved, reducing the maximum temperature amplitude and the stress generated during weld pool solidification, thereby reducing welding deformation and cracking tendency. Furthermore, the combined effect of reducing the maximum temperature of the weld pool and the oscillation of the welding wire can suppress the formation of coarse columnar crystals in the weld center, increase the compositional uniformity of the weld microstructure, and promote the dispersed and uniform distribution of second-phase particles, thus improving the mechanical properties of the weld. Moreover, heating both sides of the bevel with the double-kidney-shaped laser spot can eliminate sidewall incomplete fusion defects.

[0086] Example 2

[0087] This embodiment provides a method for narrow-gap laser welding with a double-kidney-shaped spot, the method comprising:

[0088] (1) Within 1 hour before welding, the workpiece to be welded (the weld of the workpiece to be welded includes a weld surface and a bevel surface located on the weld surface; the width of the weld surface is 4mm, the inclination angle of the bevel surface is 4°, the workpiece to be welded includes a first workpiece and a second workpiece, the first workpiece and the second workpiece are symmetrical, the first workpiece is N50 austenitic stainless steel with a thickness of 25mm, and the second workpiece is 316LN austenitic stainless steel with a thickness of 25mm) is laser cleaned.

[0089] Then, the workpiece to be welded is placed on the welding platform, and the back shielding gas fixture is installed. The gas flow rates of the shielding gas and the back shielding gas are adjusted; the shielding gas flow rate is 15 L / min, and the back shielding gas flow rate is 10 L / min; the shielding gas is argon with a purity of 99.999%.

[0090] A root pass welding is performed within the welding space of the workpiece to be welded. The pre-laser power for the root pass welding is 4.0kW, the defocusing amount is 5.0mm, and the welding speed is 1.5m / min. The post-laser power is 5.0kW, the defocusing amount is 5.0mm, the welding speed is 1.5m / min, and the circular scanning radius is 1.0mm. Weld seam cleaning is then performed, which is laser cleaning, to obtain the first weldment.

[0091] (2) Perform double-kidney-shaped laser welding in the welding space of the first weldment, specifically including: the double-beam laser acts on the side wall of the bevel surface and the corner of the weld surface through the double-kidney-shaped spot respectively. The two beams of the double-beam laser are arranged in a cross pattern, and the double-kidney-shaped spot is symmetrically arranged. The area ratio of the spot of the double-beam laser acting on the side wall of the bevel surface and the corner of the weld surface is 0.2:1. Adjust the wire feeding end to be located at the center of the weld and between the two spots. The welding wire oscillates within the range of -1 to 1 mm to perform double-kidney-shaped laser welding to complete the first welding of the filler layer, and then perform weld cleaning.

[0092] The laser power for the double-kidney-shaped laser welding is 4.0kW, the defocusing amount is 20mm, the welding speed is 0.6m / min, the wire feed speed is 1.0m / min, and the shielding gas flow rate is 25L / min.

[0093] (3) Repeat step (2) until welding is completed. After the double kidney-shaped laser welding is completed, cool the workpiece to room temperature.

[0094] The double-kidney-shaped laser narrow-gap welding method provided in this embodiment exhibits excellent welding results for low-temperature steel with narrow gaps, and is applicable to the welding of steel used in nuclear fusion. By using the double-kidney-shaped laser spot and the oscillation of the welding wire, the uniformity of the temperature distribution in the weld pool and surrounding area is improved, reducing the maximum temperature amplitude and the stress generated during weld pool solidification, thereby reducing welding deformation and cracking tendency. Furthermore, the combined effect of reducing the maximum temperature of the weld pool and the oscillation of the welding wire can suppress the formation of coarse columnar crystals in the weld center, increase the compositional uniformity of the weld microstructure, and promote the dispersed and uniform distribution of second-phase particles, thus improving the mechanical properties of the weld. Moreover, heating both sides of the bevel with the double-kidney-shaped laser spot can eliminate sidewall incomplete fusion defects.

[0095] Example 3

[0096] This embodiment provides a method for narrow-gap laser welding with a double-kidney-shaped spot, the method comprising:

[0097] (1) Within 0.5 hours before welding, the workpiece to be welded (the weld of the workpiece to be welded includes a weld surface and a bevel surface located on the weld surface; the width of the weld surface is 2mm, the inclination angle of the bevel surface is 4°, the workpiece to be welded includes a first workpiece and a second workpiece, the first workpiece and the second workpiece are symmetrical, the first workpiece is N50 austenitic stainless steel with a thickness of 35mm, and the second workpiece is 316LN austenitic stainless steel with a thickness of 35mm) is laser cleaned.

[0098] Then, the workpiece to be welded is placed on the welding platform, and the back shielding gas fixture is installed. The gas flow rates of the shielding gas and the back shielding gas are adjusted; the shielding gas flow rate is 25 L / min, and the back shielding gas flow rate is 8 L / min; the shielding gas is argon with a purity of 99.999%.

[0099] A root pass welding is performed within the welding space of the workpiece to be welded. The pre-laser power for the root pass welding is 6.0kW, the defocusing amount is 3.0mm, and the welding speed is 1.0m / min. The post-laser power is 3.0kW, the defocusing amount is 1.0mm, the welding speed is 1.0m / min, and the circular scanning radius is 0.5mm. Weld seam cleaning is then performed, which is laser cleaning, to obtain the first weldment.

[0100] (2) Perform double-kidney-shaped laser welding in the welding space of the first weldment, specifically including: the double-beam laser acts on the side wall of the bevel surface and the corner of the weld surface through the double-kidney-shaped spot respectively. The two beams of the double-beam laser are arranged in a cross pattern, and the double-kidney-shaped spot is symmetrically set. The area ratio of the spot of the double-beam laser acting on the side wall of the bevel surface and the corner of the weld surface is 1:1. Adjust the wire feeding end to be located at the center of the weld and between the two spots. The welding wire oscillates within the range of -2 to 2 mm to perform double-kidney-shaped laser welding to complete the first welding of the filler layer, and then perform weld cleaning.

[0101] The laser power for the double-kidney-shaped laser welding is 6.0kW, the defocusing distance is 40mm, the welding speed is 1.5m / min, the wire feed speed is 3.0m / min, and the shielding gas flow rate is 15L / min.

[0102] (3) Repeat step (2) until welding is completed. After the double kidney-shaped laser welding is completed, cool the workpiece to room temperature.

[0103] The double-kidney-shaped laser narrow-gap welding method provided in this embodiment exhibits excellent welding results for low-temperature steel with narrow gaps, and is applicable to the welding of steel used in nuclear fusion. By using the double-kidney-shaped laser spot and the oscillation of the welding wire, the uniformity of the temperature distribution in the weld pool and surrounding area is improved, reducing the maximum temperature amplitude and the stress generated during weld pool solidification, thereby reducing welding deformation and cracking tendency. Furthermore, the combined effect of reducing the maximum temperature of the weld pool and the oscillation of the welding wire can suppress the formation of coarse columnar crystals in the weld center, increase the compositional uniformity of the weld microstructure, and promote the dispersed and uniform distribution of second-phase particles, thus improving the mechanical properties of the weld. Moreover, heating both sides of the bevel with the double-kidney-shaped laser spot can eliminate sidewall incomplete fusion defects.

[0104] Example 4

[0105] This embodiment provides a method for narrow-gap laser welding with a double-kidney-shaped spot. Except that the ratio of the spot area of ​​the dual-beam laser acting on the side wall of the bevel surface and the corner of the weld surface is 0.1:1, the rest of the method is the same as that in Embodiment 1.

[0106] In this embodiment, the area ratio of the spot applied to the sidewall of the bevel surface and the corner of the weld surface is relatively small, resulting in insufficient melting of the sidewall and easy formation of cold shut, that is, the sidewall is not fused, and the welding effect is significantly reduced.

[0107] Example 5

[0108] This embodiment provides a method for narrow-gap laser welding with a double-kidney-shaped spot. Except that the ratio of the spot area of ​​the dual-beam laser acting on the side wall of the bevel surface and the corner of the weld surface is 1.4:1, the method is the same as that in Embodiment 1.

[0109] In this embodiment, the area ratio of the light spot acting on the sidewall of the bevel surface and the corner of the weld surface is too large, resulting in excessive heat reflection and heat conduction. The welding wire is not fully melted or the melting speed is slow, resulting in insufficient amount of top wire or filler metal. Moreover, excessive melting of the sidewall widens the weld, increases deformation, and reduces the mechanical properties of the weld.

[0110] Example 6

[0111] This embodiment provides a method for narrow-gap laser welding with a double-kidney-shaped spot. Except for the laser power of 1.0kW for the double-kidney-shaped spot laser welding, the method is the same as that in Embodiment 1.

[0112] Example 7

[0113] This embodiment provides a method for narrow-gap laser welding with a double-kidney spot. Except for the welding speed of 0.3 m / min, the method is the same as that in Embodiment 1.

[0114] Example 8

[0115] This embodiment provides a method for narrow-gap laser welding with a double-kidney-shaped spot. Except for the welding speed of 2.0 m / min, the method is the same as that in Embodiment 1.

[0116] Example 9

[0117] This embodiment provides a method for narrow-gap laser welding with a double-kidney-shaped spot. Except for the wire feed speed of 0.5 m / min, the method is the same as that in Embodiment 1.

[0118] Example 10

[0119] This embodiment provides a method for narrow-gap laser welding with a double-kidney-shaped spot. Except for the wire feed speed of 3.5 m / min, the method is the same as that in Embodiment 1.

[0120] Comparative Example 1

[0121] This comparative example provides a method for narrow-gap welding using a double-kidney-shaped laser spot. The method is the same as in Example 1, except that the entire dual-beam laser acts on the sidewall of the bevel surface.

[0122] In this comparative example, because the entire spot of the welding wire acts on the sidewall of the bevel surface, there is too much heat reflected and conducted, resulting in insufficient melting of the welding wire or a slow melting rate. This leads to insufficient amount of top wire or filler metal, and excessive melting of the sidewall widens the weld, increases deformation, and significantly reduces the mechanical properties of the weld compared to Example 5.

[0123] Comparative Example 2

[0124] This comparative example provides a method for narrow-gap welding using a double-kidney-shaped laser spot. The method is the same as in Example 1, except that the entire double-beam laser acts on the corner of the weld surface.

[0125] In this comparative example, because the laser spot acts entirely on the corner of the weld surface, the sidewall is not fully melted, which easily leads to cold shuts, meaning that the sidewalls are not fused and it is difficult to weld successfully.

[0126] Comparative Example 3

[0127] This comparative example provides a method for narrow-gap laser welding with a double-kidney-shaped spot. The method is the same as in Example 1 except that the double-kidney-shaped spot laser welding is performed directly without the bottom layer welding.

[0128] Because the comparative example did not perform a root pass welding, the heat input during welding was large, resulting in high residual stress and making successful welding difficult.

[0129] Comparative Example 4

[0130] This comparative example provides a method for narrow-gap laser welding with a double-kidney-shaped spot. The method is the same as that in Example 1, except that the welding wire does not oscillate during the double-kidney-shaped spot laser welding process.

[0131] In the comparative example, because the welding wire did not oscillate during the welding process, coarse columnar crystals were generated in the center of the weld, and the mechanical properties of the weld were significantly lower than those in Example 1.

[0132] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for narrow-gap laser welding with a double-kidney-shaped spot, characterized in that, The method includes: (1) Perform the root pass welding in the welding space of the workpiece to be welded, and clean the weld seam to obtain the first welded part; the weld seam of the workpiece to be welded includes a weld seam surface and a bevel surface located on the weld seam surface; the workpiece to be welded is low temperature steel for nuclear fusion; the width of the weld seam surface is 2~4mm; the thickness of the workpiece to be welded is 20~300mm. (2) Perform double-kidney-shaped laser welding in the welding space of the first weldment. The double-kidney-shaped laser welding includes: forming double-kidney-shaped lasers with dual-beam lasers, and each laser spot simultaneously acting on the side wall of the bevel surface and the corner of the weld surface. Adjust the wire feeding end to be located at the center of the weld and between the two laser spots. During the process, the welding wire swings to complete the first welding of the filler layer, and then clean the weld. (3) Repeat step (2) until welding is completed.

2. The method according to claim 1, characterized in that, The cryogenic steel for nuclear fusion includes any one or a combination of at least two of N50 austenitic stainless steel, 316LN austenitic stainless steel, 304 stainless steel, 316L stainless steel or JJ1 stainless steel.

3. The method according to claim 1, characterized in that, The applicable low-temperature range of the low-temperature steel for nuclear fusion is 4~20K.

4. The method according to claim 1, characterized in that, The inclination angle of the bevel surface is 1~4°.

5. The method according to claim 1 or 2, characterized in that, Before the bottom layer welding, the bevel surface of the workpiece to be welded is first laser cleaned.

6. The method according to claim 5, characterized in that, The laser cleaning is performed within 15 minutes to 1 hour before the bottom layer welding.

7. The method according to claim 1, characterized in that, Before the root pass welding, the workpiece to be welded is placed on the welding platform, and the back shielding gas fixture is installed. The gas flow rates of the shielding gas and the back shielding gas are adjusted.

8. The method according to claim 7, characterized in that, The protective gas includes argon.

9. The method according to claim 7, characterized in that, The shielding gas flow rate for the root pass welding is 15~25L / min, and the back shielding gas flow rate is 5~10L / min.

10. The method according to claim 7, characterized in that, The pre-laser power for the bottom layer welding is 4.0~6.0kW, the defocusing amount is 0~5.0mm, and the welding speed is 1.0~1.5m / min.

11. The method according to claim 10, characterized in that, The post-laser power for the bottom layer welding is 3.0~5.0kW, the defocusing amount is 0~5.0mm, and the welding speed is 1.0~1.5m / min.

12. The method according to claim 10, characterized in that, The circular scanning radius of the bottom layer welding is 0.5~1.0mm.

13. The method according to claim 1, characterized in that, The weld cleaning includes laser cleaning.

14. The method according to claim 1, characterized in that, The two beams of the dual-beam laser are arranged in a cross pattern.

15. The method according to claim 1, characterized in that, The kidney-shaped light spots are arranged symmetrically.

16. The method according to claim 1, characterized in that, The ratio of the area of ​​the laser spot acting on the sidewall of the bevel surface and the corner of the weld surface is 0.2 to 1:

1.

17. The method according to claim 1, characterized in that, The range of the welding wire oscillation is -2 to 2 mm.

18. The method according to claim 1, characterized in that, The laser power for the double-kidney-shaped laser welding is 4.0~6.0kW, and the defocusing amount is 20~40mm.

19. The method according to claim 1, characterized in that, The welding speed of the double-kidney-shaped laser welding is 0.6~1.5m / min, and the wire feed speed is 1.0~3.0m / min.

20. The method according to claim 1, characterized in that, The shielding gas flow rate for the double-kidney-shaped laser welding is 15~25L / min.

21. The method according to claim 1, characterized in that, After the double-kidney-shaped laser welding is completed, the workpiece is cooled to room temperature.

22. A device for narrow-gap laser welding with a double-kidney-shaped spot, characterized in that, The device is capable of performing the double-kidney-shaped spot laser narrow gap welding method according to any one of claims 1 to 21.

23. The apparatus according to claim 22, characterized in that, The device includes a laser optical path section and a welding wire oscillation section; The laser optical path includes a laser beam emitter for emitting laser light and a focusing lens for focusing and reflecting the laser light emitted by the laser beam emitter into a double-kidney-shaped spot; the double-kidney-shaped spot acts simultaneously on the side wall of the bevel surface of the workpiece to be welded and the corner of the weld surface. The welding wire swinging part includes a drive motor, a swing arm, and a welding wire; The welding wire swinging part is driven by a drive motor to drive the swing arm to make the welding wire reciprocate in the laser strip spot.

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