Method and device for reducing laser-plasma hybrid welding residual stress

Abstract

The invention provides a method and device for reducing laser-plasma hybrid welding residual stress, and relates to the technical field of welding. The method comprises the steps that a first laser beam and a plasma flow are coaxially output and act on a welded workpiece to form a penetrable welding seam, two identical beam splitting lasers act on the two sides of the penetrable welding seam to form a non-penetrable welding seam, the first laser beam and the beam splitting lasers conduct welding synchronously, the direction from the beam splitting lasers to the first laser beam is the welding direction, and the direction from the beam splitting lasers to the second laser beam is the non-penetrable welding seam. The laser power P of the first laser beam is 1-3.8 kW, and the sum of the laser power of the two split laser beams is 15%-25% of the laser power of the first laser beam; and the linear distance delta l between the first laser beam and the split laser is 3-26 mm. According to the method, the surface recesses on the two sides of the penetrable weld joint can be plastically deformed, so that the laser-plasma hybrid welding residual stress is effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a method and a device for reducing residual stress in laser-plasma composite welding. Background Art

[0002] Studies have shown that during the use of butt welded joints, the maximum stress acts on the joint area between the welding surface and the base material. The more dangerous deformation mode of the load on the weld is the transverse direction. Ultrasonic forging welds are used to reduce the residual stress level in the joint area between the welding surface and the base material. Mordyuk BN et al. proposed the use of surface ultrasonic forging method to improve the fatigue strength of carbon steel, stainless steel and titanium alloy welded joints. Knysh VV et al. also proposed the use of ultrasonic forging method to reduce the residual stress level of thin welded joints (2 to 3 mm) of aluminum alloys.

[0003] The method of ultrasonic forging applies a large mechanical impact to the welded structure, which may cause additional residual deformation. In addition, the forging process is carried out as a separate process operation after welding is completed, which significantly increases the manufacturing time of the welded structure and correspondingly reduces its production efficiency.

[0004] Research has shown that the use of metal cladding can reduce the residual stress of the weld to prevent the reduction of the fatigue strength of the base material. This method of welding deposited metal on the base material and reducing the residual stress includes two stages: the first stage is to weld the deposited metal to the base material; the second stage is to plastically deform the concave area of ​​the base material surface outside the deposited metal.

[0005] The method of metal cladding is a volume casting process that welds the deposited metal to the substrate. At the same time, unlike laser welding and plasma arc welding processes, this method does not have thermal localization. However, existing laser welding and plasma arc welding cannot effectively reduce the residual stress of laser-plasma hybrid welding.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The object of the present invention includes providing a method and a device for reducing residual stress in laser-plasma hybrid welding.

[0008] The embodiments of the present invention can be implemented as follows:

[0009] In a first aspect, the present invention provides a method for reducing residual stress in laser-plasma hybrid welding, which includes outputting a first laser beam and a plasma flow coaxially and acting on a workpiece to be welded to form a penetrating weld, acting two identical split laser beams on both sides of the penetrating weld to form a non-penetrating weld, the first laser beam and the split laser are welded synchronously, the direction from the split laser to the first laser beam is the welding direction, the laser power P of the first laser beam is 1-3.8kW, and the sum of the laser powers of the two split laser beams is 15%-25% of the laser power of the first laser beam; the straight-line distance Δl between the first laser beam and the split laser is 3-26mm.

[0010] In an optional embodiment, the calculation formula of the straight-line distance Δl is as follows: Δl = δ·e P+0.1·I / 0.1Vδ, where δ is the thickness of the workpiece to be welded, mm; P is the laser power of the first laser beam, kW; I is the plasma welding current, A; V is the welding speed, mm / s.

[0011] In an optional embodiment, the thickness δ of the welded workpiece is 1-10 mm;

[0012] And / or, the plasma welding current I is 0-150A, when the plasma welding current I is 0, that is, only the plasma flow is not used as a heat source for welding;

[0013] And / or, the welding speed V is 13-100 mm / s.

[0014] In an optional embodiment, the first laser beam is collimated and focused by a first collimator and a first focusing lens arranged in sequence in its emission direction, and the two split laser beams are focused by two second focusing lenses arranged in their emission direction.

[0015] In an optional embodiment, the two split laser beams are the second laser beam split into two identical laser beams by a beam splitter, the second laser beam is independent of the first laser beam, or the second laser beam is obtained by reflecting the first laser beam by a flat plate beam splitter.

[0016] In an optional embodiment, the beam splitter is a polarization beam splitter 48BM-CC-B with a splitting ratio of 50:50.

[0017] In an optional embodiment, the flat plate beam splitter is set at 45°, and the ratio of refracted light to reflected light of the flat plate beam splitter is 3-6:1.

[0018] In an optional embodiment, when the second laser beam is independent of the first laser beam, the second laser beam is collimated by a second collimator arranged in the emission direction of the second laser beam.

[0019] In an optional embodiment, the first laser beam and the split laser beam are both protected by a shielding gas during welding.

[0020] In a second aspect, the present invention provides a device for implementing the method of reducing residual stress in laser-plasma hybrid welding as described in any of the aforementioned embodiments, comprising a first laser source for generating the first laser beam, a split laser source for generating the split laser, and a plasma arc generator for generating the plasma flow.

[0021] The beneficial effects of the method and device for reducing residual stress in laser-plasma hybrid welding provided by the embodiments of the present invention include:

[0022] The method for reducing residual stress of laser-plasma composite welding provided by the present invention is to form a penetrating weld by coaxially inputting a first laser beam and a plasma flow to the welded workpiece, and at the same time, two beam split lasers with a laser power lower than the first laser beam are used to simultaneously perform non-penetrating welding heat treatment on both sides of the penetrating weld. The heat treatment can plastically deform the surface depressions on both sides of the penetrating weld, thereby effectively reducing the residual stress of laser-plasma composite welding. During the welding process, the laser power of the first laser beam and the split laser and the straight-line distance Δl between the two have a significant effect on the reduction of residual stress. When the laser power of the split laser is too large, a penetrating weld is easily formed, and the effect of heat treatment of the penetrating weld of the first laser beam cannot be achieved. When the straight-line distance Δl is too large or too small, the formation time of the penetrating weld and the non-penetrating weld is too long or too short, which is not conducive to plastic deformation and easily leads to residual laser-plasma composite welding residual stress. The method for reducing residual stress of laser-plasma composite welding provided by the present invention is simple and easy to implement, and can effectively reduce the residual stress of laser-plasma composite welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A schematic diagram of the structure of the device for reducing residual stress in laser-plasma hybrid welding provided in this embodiment in the first case;

[0025] Figure 2 A schematic diagram of the structure of the device for reducing residual stress in laser-plasma hybrid welding provided in this embodiment in a second case;

[0026] Figure 3 A welding head device formed by combining a first laser source and a plasma arc generator in the device for reducing residual stress in laser-plasma hybrid welding provided in this embodiment;

[0027] Figure 4 It is a schematic diagram of the cross section of the two sides of the weld on the surface of the sample in Comparative Example 5 when no laser is used to act on the sample;

[0028] Figure 5 This is a schematic cross-sectional view of the case where a laser is used to act on both sides of the weld on the surface of the sample in Example 5.

[0029] Icons: 100-device for reducing residual stress in laser-plasma hybrid welding; 110-first laser source; 111-first collimator; 112-flat beam splitter; 113-first focusing lens; 120-second laser source; 121-splitting laser; 122-beam splitter; 123-second collimator; 124-second focusing lens; 130-plasma arc generator; 140-gas protection device; 150-penetrating molten pool; 160-non-penetrating molten pool; 200-workpiece to be welded. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0033] In the description of the present invention, it should be noted that if the terms "upper", "lower", "inside", "outside", etc. appear to indicate an orientation or position relationship, they are based on the orientation or position relationship shown in the accompanying drawings, or are the orientation or position relationship in which the product of the invention is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0034] In addition, the terms “first”, “second”, etc., if used, are merely used to distinguish between the descriptions and should not be understood as indicating or implying relative importance.

[0035] It should be noted that, in the absence of conflict, the features in the embodiments of the present invention may be combined with each other.

[0036] The detailed steps, implementation principles and technical effects of the method for reducing residual stress in laser-plasma hybrid welding provided by the present invention, as well as the overall structure, working principle and technical effects of the corresponding device 100 for reducing residual stress in laser-plasma hybrid welding are described in detail below through examples and in combination with the accompanying drawings.

[0037] The present invention provides a method for reducing residual stress in laser-plasma composite welding, which comprises the following steps: coaxially outputting a first laser beam and a plasma flow and acting on a welded workpiece to form a penetrating weld, acting two identical split laser beams 121 on both sides of the penetrating weld to form a non-penetrating weld, the first laser beam and the split laser beam 121 are welded synchronously, the direction from the split laser beam 121 to the first laser beam is the welding direction, the laser power P of the first laser beam is 1-3.8 kW, the sum of the laser powers of the two split laser beams 121 is 15%-25% of the laser power of the first laser beam; and the straight-line distance Δl between the first laser beam and the split laser beam 121 is 3-26 mm.

[0038] In this embodiment, in terms of the movement direction of welding, the first laser beam and the split laser 121 serve as the front and rear laser beams respectively, wherein the first laser beam is mainly used as a heat source for welding to form a weld. When the energy of the first laser beam is insufficient, a plasma flow can be added to serve as a heat source for welding. The split laser 121 is located behind the first laser beam, and its laser power is significantly lower than that of the first laser beam. In addition, it only performs non-penetrating welding on the areas on both sides of the weld, thereby performing heat treatment on both sides of the weld. The two split laser beams 121 do not intersect, and therefore welding will not continue over the entire width of the weld, thereby effectively reducing the residual stress of the laser-plasma composite welding. It should be understood that the longitudinal axis of each non-penetrating weld passes through the transition zone from the penetrating weld metal to the substrate.

[0039] In this embodiment, the straight-line distance Δl between the first laser beam and the split laser beam 121 is clearly defined as 3-26 mm. The first laser beam and the split laser beam 121 need to be within the above range to achieve a good welding effect. When the straight-line distance Δl is too small or too large, it is not possible to effectively perform timely heat treatment on both sides of the weld. The straight-line distance Δl is related to welding parameters such as the thickness of the workpiece to be welded, the laser power of the first laser beam, the plasma welding current, and the welding speed.

[0040] Specifically, the calculation formula of the straight-line distance Δl is as follows: Δl = δ·e P+0.1·I / 0.1Vδ, where δ is the thickness of the workpiece to be welded, mm; P is the laser power of the first laser beam, kW; I is the plasma welding current, A; and V is the welding speed, mm / s.

[0041] Preferably, the thickness δ of the workpiece to be welded is 1-10 mm; and / or, the plasma welding current I is 0-150 A, when the plasma welding current I is 0, that is, only the plasma flow is not used as a heat source for welding; and / or, the welding speed V is 13-100 mm / s.

[0042] The first laser beam and the plasma flow are coaxially output through a common plasma forming nozzle, and there can be two or more electrodes for generating the plasma flow, and the electrode tip angle is an acute angle of 15-30°; wherein, the angle between the placement position of the electrode and the central axis of the first laser beam is 10-30°; when the first laser beam and the plasma flow are coaxially output, its nozzle is perpendicular to the workpiece to be welded or output at an angle of up to 20° vertically relative to the surface of the workpiece to be welded; the plasma arc generator 130 of the plasma flow is provided with a nozzle, and the diameter of the nozzle can be adjusted from 1 to 5 mm. When the first laser beam and the split laser beam 121 are welded, they are protected by a shielding gas. The shielding gas of the first laser beam is generated by the plasma arc generator 130, and the shielding gas includes argon or argon gas mixture. During the welding process, the plasma flow is covered by the external shielding gas, and the plasma flow and the shielding gas are output together. The shielding gas of the split laser beam 121 can be provided by a separate gas protection device 140. The focus of the first laser beam is located at a depth of 0-50% of the thickness of the workpiece; the first laser beam and the plasma flow can be continuous or pulsed; in the case of pulse modulation of the plasma flow, the pulse frequency is 10-40khz.

[0043] Furthermore, in order to make the light source of the laser beam more concentrated, in this embodiment, the first laser beam is collimated and focused by a first collimator 111 and a first focusing lens 113 arranged in sequence in its emission direction, and the two split laser beams 121 are focused by two second focusing lenses 124 arranged in its emission direction.

[0044] In this embodiment, the two split laser beams 121 may have various sources, for example, they may be directly generated by two laser light sources, or the second laser beam may be split into two identical laser beams by a beam splitter 122, the second laser beam is independent of the first laser beam, the two split laser beams 121 are parallel to each other and to the first laser beam, or the second laser beam is obtained after the first laser beam is reflected by a flat beam splitter 112. When the second laser beam is independent of the first laser beam, the second laser beam is collimated by a second collimator 123 arranged in its emission direction.

[0045] The beam splitter 122 is a polarization beam splitter 48BM-CC-B, and the splitting ratio is 50:50. In this embodiment, the second laser beam can be split into two identical and parallel laser beams by the beam splitter 122, and the beam splitter 122 is commercially available. The flat beam splitter 112 is set at 45°, and the performance of the flat beam splitter 112 can be adjusted to make the ratio of the refracted and reflected light of the flat beam splitter 112 3-6:1.

[0046] Next, this embodiment describes in detail the two sources of the two split laser beams 121:

[0047] (1) When the two split laser beams 121 are the second laser beam split into two identical laser beams by the beam splitter 122, and the second laser beam is obtained by reflecting the first laser beam by the flat beam splitter 112, please refer to Figure 1 The specific structure of the device 100 for reducing residual stress in laser-plasma hybrid welding is as follows:

[0048] The device 100 for reducing residual stress in laser-plasma hybrid welding includes a first laser source 110 for generating a first laser beam, a split laser 121 source for generating a split laser 121, and a plasma arc generator 130 for generating a plasma flow, wherein the split laser 121 source is the second laser beam, and the second laser beam is obtained after the first laser beam is reflected by a flat-plate beam splitter 112. The first laser beam is collimated and focused by a first collimator 111 and a first focusing lens 113 sequentially arranged in its emission direction, and a flat-plate beam splitter 112 for refracting and reflecting the first laser beam is also arranged between the first collimator 111 and the first focusing lens 113, and the two split laser beams 121 are focused by two second focusing lenses 124 arranged in their emission direction.

[0049] The principle is as follows: the first laser beam generated by the first laser source 110 is introduced into the flat-plate beam splitter 112 through the optical fiber via the first collimator 111, and the flat-plate beam splitter 112 refracts and reflects the first laser beam, wherein the refracted laser is focused vertically downward through the first focusing lens 113, and finally acts on the surface of the workpiece 200 to be welded, and the refracted laser of the first laser beam and the plasma flow generated by the plasma arc generator 130 cooperate to form a penetrating molten pool 150 (penetrating welding) on ​​the workpiece to be welded. The reflected laser forms a second laser beam, which is further divided into two identical split laser beams 121 by a beam splitter. The two split laser beams 121 are focused on both sides of the weld on the surface of the workpiece 200 to be welded through two second focusing lenses 124 respectively. The straight-line distance between the split laser beam 121 and the first laser source 110 is Δl, forming a non-penetrating molten pool 160. In addition, when the split laser beam 121 is welding, the gas protection device 140 provides protective gas, so that the split laser beam 121 is welded under the action of the protective gas.

[0050] When the heat source provided by the first laser source 110 alone can meet the requirement, the plasma arc generator 130 may not generate a plasma flow but only provide a protective gas.

[0051] (2) When the two split laser beams 121 are the second laser beam split into two identical laser beams by the beam splitter 122, and the second laser beam is independent of the first laser beam, please refer to Figure 2 The specific structure of the device 100 for reducing residual stress in laser-plasma hybrid welding is as follows:

[0052] The device 100 for reducing residual stress in laser-plasma hybrid welding includes a first laser source 110 for generating a first laser beam, a split laser 121 source for generating a split laser 121, and a plasma arc generator 130 for generating a plasma flow, wherein the split laser 121 source is the second laser beam, the second laser beam is generated by the second laser source 120, the first laser beam is collimated and focused by a first collimator 111 and a first focusing lens 113 sequentially arranged in its emission direction, the second laser beam is collimated by a second collimator 123 sequentially arranged in its emission direction, and the two split laser beams 121 are focused by two second focusing lenses 124 arranged in their emission direction.

[0053] The principle is as follows: the first laser beam generated by the first laser source 110 is introduced through the optical fiber via the first collimator 111 and focused by the first focusing lens 113, and finally acts on the surface of the workpiece 200 to be welded. The first laser beam and the plasma flow generated by the plasma arc generator 130 act in combination to form a penetrating molten pool 150 (penetrating welding) on ​​the workpiece to be welded. The second laser beam generated by the second laser source 120 is collimated by the optical fiber via the second collimator 123, and then further divided into two identical split laser beams 121 by a beam splitter. The two split laser beams 121 are focused by two second focusing lenses 124 and act on both sides of the weld seam on the surface of the workpiece 200 to be welded. The linear distance between the split laser beam 121 and the first laser source 110 is Δl, forming a non-penetrating molten pool 160. In addition, when the split laser beam 121 is welding, the gas protection device 140 provides protective gas, so that the split laser beam 121 is welded under the action of the protective gas.

[0054] When the heat source provided by the first laser source 110 alone can meet the requirement, the plasma arc generator 130 may not generate a plasma flow but only provide a protective gas.

[0055] Comparative Example

[0056] In this comparative example, only the first laser beam and the plasma flow are used to simultaneously act on the same or similar positions of the workpieces to be welded to form a penetrating weld, and the laser is not used to act on both sides of the weld on the surface of the sample.

[0057] Experimental Example 1

[0058] In order to verify the feasibility of the method and device for reducing residual stress in laser-plasma hybrid welding, an experiment was conducted to verify that the scheme of the present application and the scheme of comparative example 1 were selected to carry out research and experiments. During the experiment, the same welding head equipment was used for laser-plasma hybrid welding. The equipment was as follows: Figure 3 As shown. The welding head is fixed on the robot and moves at the relative speed required for welding the workpiece. When welding penetrating welds, a MFSC-4000W fiber laser (Max Photonics, China) is used, with a laser power of up to 4.0KW, and is equipped with a Cebora TIG AC-DC Evo 450 / T Robot arc welder with an output current of up to 400A and a plasma module (Cebora, Italy). When welding non-penetrating welds, a MFSC-1000W fiber laser (Max Photonics, China) is used, with a laser power of up to 1.0KW. The welding base material is AISI 304 stainless steel plate with a size of 200mm×100mm×δmm, where the thickness δ is 0.5~12.0mm. Corresponding to the welding of 304 stainless steel of different thicknesses, as shown in Table 1, continuous laser radiation and compressed DC arc are used in the welding process.

[0059] When butt welding is performed by using a method in which the laser acts on both sides of the weld on the surface of the sample, the distance Δl between the focal axis of the front laser beam and the two beams separated by the rear laser beam depends on the thickness δ of the welded plate, the power P1 of the first laser beam, and the welding current. The power of the second laser beam is P2.

[0060] Table 1. Main parameters of AISI 304 stainless steel welding mode in the examples and comparative examples (δ = 0.5 ~ 12mm)

[0061]

[0062] Laser-plasma hybrid welding of 304 stainless steel was performed in a butt joint mode. After welding, the welded samples were metallographically processed and then inspected using an optical microscope. Figure 4 and Figure 5 The cross section of a 4 mm thick 304 stainless steel laser-plasma hybrid welded joint is shown. Figure 4 In Comparative Example 5, the two sides of the weld seam on the surface of the sample were not acted on by laser. Figure 5 In Example 5, laser was used to act on both sides of the weld on the surface of the sample. Figure 4 and Figure 5 It can be seen that Figure 5 There are obvious traces of non-penetrating molten pools on both sides of the penetrating weld.

[0063] After welding with the above welding parameters, the welded sample was examined by metal microscope and the residual stress was measured. The displacement caused by stress relaxation was measured by comparing the speckle interferometer images before and after drilling the welded sample, and the residual stress was calculated using the measured displacement.

[0064] The speckle interferometry method for measuring residual stresses is based on the application of an interferometer optical scheme in which the studied part of the object under test is illuminated symmetrically from two directions at the same angle, allowing the determination of the in-plane components of the displacement vector characterizing the deformation of the object. The displacements caused by the relaxation of residual stresses in bulk materials induced by the drilling of blind holes were measured using the ESPI method. The measurements were carried out in the following sequence: the device was placed on the surface of the object, and the reflected speckle pattern, characterizing the initial state before the drilling of the controlled part, was stored in the computer memory using a CCD camera. A second speckle pattern of the reflection, after stress relief after drilling a blind hole with a diameter and depth of about 0.4-1.0 mm, was also stored in the computer.

[0065] By computer processing of the fringe pattern, the displacements and residual stresses in the irradiated area can be calculated.The developed program provides for measurements with the help of speckle interferometry of the displacement component ux at a constant distance from the hole center (eg r=2,50r0).

[0066] In this case, the stress σ xx , σ yy and τ xy The measured displacement u caused by relaxation x The dependency is expressed by the following formula:

[0067] u x (θ)=F(θ)σ xx +G(θ)σ yy +H(θ)τ xy

[0068] Where F(θ), G(θ), H(θ) are functions that depend on the mechanical properties of the material, the distance from the center of the hole and its diameter. The angle θ determines the coordinates (x=2,5r0 cos(θ); Y=2,5r0 sin(θ)), i.e. the point where the displacement is measured.

[0069] Using the provided method, the determination of residual stresses is achieved in the following stages:

[0070] Select different angles θ relative to the illumination axis and points at 2.5r0 from the center of the drill hole with a radius of r0; use the speckle interferometer to measure the displacement ux(θ) of the selected point; the component σ xx , σ yy and τ xy The least square method is used to calculate Eq.1; the values ​​of principal stresses σ1, σ2 and principal angles are determined.

[0071] Table 2 lists the measurement results of equivalent residual stress of welded joints obtained by hybrid welding in the embodiments and comparative examples. While keeping other parameters the same, the maximum equivalent stress in the heat affected zone and the average equivalent stress along the welded joint were measured.

[0072] Table 2. Residual equivalent stress values ​​when welding AISI 304 stainless steel according to the embodiments and comparative examples (δ = 0.5-12 mm)

[0073] Example Maximum residual equivalent stress, MPa Average residual equivalent stress, MPa Example 1 360 140 Comparative Example 1 360 140 Example 2 360 140 Comparative Example 2 400 150 Example 3 380 150 Comparative Example 3 430 170 Example 4 390 150 Comparative Example 4 460 170 Example 5 400 160 Comparative Example 5 490 180 Example 6 420 170 Comparative Example 6 490 180 Example 7 440 170 Comparative Example 7 500 190 Example 8 480 180 Comparative Example 8 500 190 Example 9 510 200 Comparative Example 9 520 200

[0074] As can be seen from Table 2, the results show that for 304 stainless steel welded joints with a thickness not exceeding 1.0 mm, the solution of the embodiment of the present application has no significant effect on the value of residual stress, which may be due to the thin thickness. For welded joints with a thickness exceeding 10.0 mm, the solution of the embodiment of the present application has little effect on the value of residual stress, which may be due to the larger distance Δl and the cooling of the weld metal to below the phase transition temperature. The study of the residual equivalent stress level showed that the proposed method resulted in a reduction of the maximum (peak) stress value by 12% to 18%, which shows that the proposed method has acceptable effectiveness.

[0075] In summary, the method for reducing the residual stress of laser-plasma hybrid welding provided by the present invention forms a penetrating weld by simultaneously acting the first laser beam and the plasma flow on the same or similar position of the welded workpiece, and simultaneously performs non-penetrating welding heat treatment on both sides of the penetrating weld with two beam split lasers 121 with a laser power lower than the first laser beam. The heat treatment can plastically deform the surface depressions on both sides of the penetrating weld, thereby effectively reducing the residual stress of the laser-plasma hybrid welding. During the welding process, the laser power of the first laser beam and the beam split laser 121 and the straight-line distance Δl between the two have a significant effect on the reduction of the residual stress. When the laser power of the beam split laser 121 is too large, a penetrating weld is easily formed, and the effect of heat treatment of the penetrating weld of the first laser beam cannot be achieved. If the straight-line distance Δl is too large or too small, the formation time of the penetrating weld and the non-penetrating weld will be too long or too short, which is not conducive to plastic deformation and easily leads to residual laser-plasma hybrid welding residual stress. The method for reducing the residual stress of laser-plasma composite welding provided by the present invention is simple and easy to implement, and can effectively reduce the residual stress of laser-plasma composite welding.

[0076] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for reducing residual stress in laser-plasma hybrid welding, characterized in that: The method comprises the following steps: coaxially outputting a first laser beam and a plasma flow and acting on a workpiece to be welded to form a penetrating weld, and acting two identical split laser beams on both sides of the penetrating weld to form a non-penetrating weld. The first laser beam and the split laser beam are welded synchronously, and the direction from the split laser beam to the first laser beam is the welding direction. The laser power P of the first laser beam is 1-3.8 kW, and the sum of the laser powers of the two split laser beams is 15%-25% of the laser power of the first laser beam. The straight-line distance Δl between the first laser beam and the split laser beam is 3-26 mm.

2. The method for reducing residual stress in laser-plasma hybrid welding according to claim 1, characterized in that: The calculation formula of the straight-line distance Δl is as follows: Δl=δ·eP+0.1·I / 0.1Vδ, Wherein, δ is the thickness of the workpiece to be welded, mm; P is the laser power of the first laser beam, kW; I is the plasma welding current, A; V is the welding speed, mm / s.

3. The method for reducing residual stress in laser-plasma hybrid welding according to claim 2, characterized in that: The thickness δ of the welded workpiece is 1-10 mm; And / or, the plasma welding current I is 0-150A, when the plasma welding current I is 0, that is, only the plasma flow is not used as a heat source for welding; And / or, the welding speed V is 13-100 mm / s.

4. The method for reducing residual stress in laser-plasma hybrid welding according to claim 1, characterized in that: The first laser beam is collimated and focused by a first collimator and a first focusing lens arranged in sequence in the emission direction of the first laser beam, and the two split laser beams are focused by two second focusing lenses arranged in the emission direction of the first laser beam.

5. The method for reducing residual stress in laser-plasma hybrid welding according to claim 1, characterized in that: The two split laser beams are the second laser beam split into two identical laser beams by a beam splitter, the second laser beam is independent of the first laser beam, or the second laser beam is obtained by reflecting the first laser beam by a flat beam splitter.

6. The method for reducing residual stress in laser-plasma hybrid welding according to claim 5, characterized in that: The beam splitter is a polarization beam splitter 48BM-CC-B with a splitting ratio of 50:

50.

7. The method for reducing residual stress in laser-plasma hybrid welding according to claim 5, characterized in that: The flat plate beam splitter is set at 45 degrees, and the ratio of the refracted light to the reflected light of the flat plate beam splitter is 3-6:

1.

8. The method for reducing residual stress in laser-plasma hybrid welding according to claim 5, characterized in that: When the second laser beam is independent of the first laser beam, the second laser beam is collimated by a second collimator arranged in an emission direction of the second laser beam.

9. The method for reducing residual stress in laser-plasma hybrid welding according to claim 1, characterized in that: When the first laser beam and the split laser beam are used for welding, they are both protected by protective gas.

10. A device for implementing the method for reducing residual stress in laser-plasma hybrid welding as claimed in any one of claims 1 to 9, characterized in that: The invention comprises a first laser source for generating the first laser beam, a split laser source for generating the split laser beam, and a plasma arc generator for generating the plasma flow.

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