Laser welding hump defect suppression method

Abstract

The invention discloses a laser welding hump defect suppression method, which relates to the field of welding, and comprises the following steps: S1, processing a micro groove structure on a first welding surface of a first to-be-welded part and / or a second welding surface of a second to-be-welded part; filling alloy powder into each micro groove structure; and S2, the first welding face and the second welding face are welded together in a penetrating welding mode. The micro-groove structures are machined on the first welding face and / or the second welding face, the alloy powder is added into the micro-groove structures, the surface tension of liquid metal in the welding process is increased, the alloy powder can supplement the insufficient surface tension, humps are reduced or avoided, and the welding quality is improved. And the burning loss of beneficial alloy elements in the high-power laser welding process can be made up, the microstructure of the welding seam is regulated and controlled, and the mechanical property of the welding seam is optimized. According to the method, the hump defect can be restrained on the premise of not additionally arranging auxiliary equipment, and the weld joint which is attractive in shape and good in performance is obtained; and the application range is wide.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a method for suppressing hump defects in laser welding. Background Art

[0002] Thick plate welding is a key process in the manufacturing process of large-scale equipment such as aerospace, shipbuilding, rail transportation, and engineering machinery. Its quality directly determines the service performance and life of the equipment. With the continuous development of social needs and industrial technology, the structure and service environment of large-scale equipment are becoming more and more complex, which puts forward more stringent requirements for the welding and manufacturing of thick plates. In recent years, laser welding has been widely used in many fields such as aviation, micro-parts processing, and thin-walled material processing. Compared with traditional multi-layer and multi-pass arc welding, laser welding has the advantages of fast welding speed, high efficiency, low deformation and residual stress; compared with electron beam welding, laser welding has the advantages of not requiring a vacuum environment, easy to achieve welding of large and complex structures, and strong process adaptability; compared with stir friction welding, laser welding has the advantages of fast speed, high flexibility, strong adaptability, and no need for subsequent processing. Therefore, laser welding technology has its unique advantages in high efficiency, high quality, and high adaptability, and has become one of the important research directions in the field of thick plate welding in recent years.

[0003] Commonly used thick plate laser welding methods include laser multi-pass filling welding (arcing or not arcing with welding wire) and laser single-pass penetration welding. Laser multi-pass filling welding mainly fills the groove through the melting transition of the welding wire. Due to factors such as the amount of welding wire melting, the stability of the droplet transition and the flow of the molten pool, the filling thickness of single-pass welding is limited. Therefore, the use of laser filling welding method to achieve thick plate welding generally requires multiple welds. The difference is that laser penetration welding refers to a laser welding method in which the molten pool or keyhole completely penetrates the test plate during the welding process. Laser penetration welding relies on the high energy density and strong penetration of the laser. It can completely penetrate and melt the material without setting the groove and filling material, thereby realizing single-pass welding of thick plates. Compared with laser filling welding, the efficiency of laser penetration welding is significantly improved and the heat input is significantly reduced. Its application is of great significance for further shortening the manufacturing and maintenance cycle of large equipment and improving the service performance and life of large equipment.

[0004] However, in the process of laser penetration welding, hump defects are very likely to occur. Among them, hump refers to the uniformly distributed weld nodules that appear on the back of the weld. Since the metal gathers on the back of the weld to form weld nodules, the front of the weld is often accompanied by concave, resulting in the formation of derivative defects such as depressions and undercuts, which will lead to stress concentration and seriously weaken the joint performance. At present, the hump defect generated by laser penetration welding of thick plates has become an important obstacle to the application of this technology in related fields and needs to be broken through urgently. Existing studies have shown that in the process of ultra-high power laser welding of thick plates, the laser interacts violently with the material, the volume of the molten pool and the number of plumes increase sharply, and the surface tension of the molten pool is difficult to balance the downward gravity and the reaction force of the plume eruption. The force difference will drive the molten pool to flow to the back of the weld and gather, forming a hump defect. Therefore, an excessively large molten pool backflow driving force is a necessary condition for the generation of hump defects in the weld. Reducing the force difference on the molten pool is an effective way to suppress the hump. Among them, the molten pool backflow driving force refers to the force difference between the downward plume eruption reaction force and gravity and the upward surface tension.

[0005] At present, the methods for suppressing hump defects in thick plate laser welding mainly include vacuum method, magnetic field assisted method, air chamber assisted method, and bottom pad method. Among them, the vacuum method refers to placing the test plate in a vacuum chamber for low-pressure or vacuum welding. The welding effect is relatively ideal, but the vacuum chamber is complicated to build, the cost is high, the welding area is limited, and it basically remains in the laboratory stage; the magnetic field assisted method requires the establishment of electromagnetic field equipment, and the external magnetic field is used to compensate for the lack of surface tension to achieve hump defect suppression. The equipment of this method is complicated to build, the magnetic field effect is uneven, and it is difficult to obtain ideal results; the air chamber assisted method refers to setting an air chamber on the back of the test plate, and compensating for the lack of surface tension by air pressure to achieve hump defect suppression. This method has high requirements for air tightness and is not suitable for long and curved welds; the bottom pad method requires a metal sheet to be set on the back of the test plate to physically support the collapsed molten pool. The effect is not ideal and post-weld grinding is required.

[0006] Chinese patent CN111872551B provides a method for suppressing the hump defect on the back side of a laser welding weld. A high-speed transverse airflow is added above the molten pool through a special airflow nozzle, so that a pressure difference is formed above and below the molten pool due to the Bernoulli effect. The generated differential pressure acts on the molten pool, suppressing the flow of the molten pool to the back side of the weld, thereby suppressing the generation of the hump defect on the back side of the weld. The patent has the following defects: First, the patent generates a pressure difference by blowing air horizontally to form a Bernoulli effect to compensate for the lack of surface tension of the bottom molten pool. The effective pressure range that can be generated is within a small airflow range starting from the nozzle end. The airflow path is a horizontal path, which is only applicable to straight welds and difficult to apply to curved welds. For inclined welds (welds are inclined relative to the horizontal plane), due to the inclination of the molten pool, the gravity state of the molten pool changes. Whether the air pressure difference generated by the airflow can effectively suppress the hump remains to be verified. It is difficult to apply to inclined welds and its application range is limited. Second, in order to generate a sufficient pressure difference in the molten pool, the airflow velocity applied to the front weld is relatively large, and the high-speed airflow may directly act on the molten pool of the front weld, causing it to be impacted and causing the welding process to become unstable. Third, with the increase of plate thickness, the gravity of the molten pool and the recoil pressure it receives are greater, and the force difference generated by the airflow may be difficult to meet actual needs. Fourth, the force and flow state of the molten pool on the back of the weld are different. The force difference generated by this method is theoretically almost the same, and it is difficult to achieve uniform suppression of defects.

[0007] Chinese patent CN108406145A discloses a gas buoyancy assisted welding device and a welding method using the device. The basic principle is to form a closed air chamber under the weld through the auxiliary device and the workpiece, and the air chamber is filled with gas at a certain pressure. By controlling the flow rate of the outlet solenoid valve and the inlet solenoid valve 206, the air pressure in the air chamber is maintained stable, and a high-pressure atmosphere is created at the bottom of the weld. The pressure difference between the upper and lower surfaces of the weld is used to balance the gravity and dynamic pressure that cannot be balanced by the surface tension of the lower surface of the molten pool, so as to achieve the purpose of stabilizing the molten pool, eliminate welding defects such as collapse and humps, and thus improve the welding quality. This patent has the following defects: 1. This patent requires setting up an air chamber and controlling the gas flow rate, and the equipment is relatively complex; 2. The air chamber needs to fit tightly with the test plate to ensure airtightness, and the operation is complicated in actual production and has low adaptability; 3. During welding, the air chamber needs to be placed on the back of the weld and remain motionless. After completing local welding, it needs to be disassembled, repositioned, and reinstalled before the subsequent welding of a single long weld can be completed. The operation is complicated and the efficiency is low; if a customized design of a long length air chamber is used, the cost and working space will increase, which can hardly meet actual production; 4. It is difficult to customize the air chamber suitable for curved welds and oblique welds, it is difficult to ensure the airtightness of the air chamber, and it is difficult to apply to curved welds and oblique welds. Summary of the invention

[0008] The purpose of the present invention is to provide a method for suppressing hump defects in laser welding to solve the problems existing in the above-mentioned prior art, reduce or avoid the generation of humps, and obtain welds with beautiful shape and good performance; optimize the mechanical properties of the welds; and have a wide range of applications.

[0009] To achieve the above object, the present invention provides the following solutions:

[0010] The present invention provides a method for suppressing a laser welding hump defect, comprising the following steps:

[0011] S1, machining a micro-groove structure on a first welding surface of a first workpiece to be welded and / or a second welding surface of a second workpiece to be welded; and filling alloy powder into each of the micro-groove structures;

[0012] S2. Welding the first welding surface and the second welding surface together by penetration welding.

[0013] Preferably, S1 comprises: after filling the alloy powder into each of the micro-groove structures, compacting the alloy powder in the micro-groove structures.

[0014] Preferably, S1 includes: the micro-groove structure includes a plurality of first micro-grooves arranged in a lattice, and the first welding surface and the second welding surface are rectangular surfaces.

[0015] Preferably, the opening of each of the first microgrooves is circular.

[0016] Preferably, S1 includes: before filling the alloy powder into each of the micro-groove structures, obtaining the required mass of the alloy powder by formula 1, and formula 1 is as follows:

[0017] M=ρVat / mn Formula 1

[0018] Among them, M is the mass of the alloy powder required for each of the micro-groove structures; ρ is the density of the alloy powder; V is the volume of each of the first micro-grooves; a and b are the length and width of the rectangular surface, respectively; m is the distance between the centers of two adjacent first micro-grooves of each of the micro-groove structures along the length direction of the rectangular surface; n is the distance between the centers of two adjacent first micro-grooves of each of the micro-groove structures along the width direction of the rectangular surface.

[0019] Preferably, S1 includes: each of the micro-groove structures includes a plurality of strip-shaped second micro-grooves, and the plurality of the second micro-grooves of each of the micro-groove structures are staggered and arranged in a mesh shape.

[0020] Preferably, each of the second microgrooves is a rectangular groove.

[0021] Preferably, S1 includes: before filling the alloy powder into each of the micro-groove structures, obtaining the required mass of the alloy powder by formula 2, where formula 1 is as follows:

[0022] M=[atH-(ls)*(ks)*(t / l)*(a / k)]ρ Formula 2

[0023] Among them, H is the depth of each second microgroove; the center line of each second microgroove along the length direction of the rectangular surface is the first center line, the center line of each second microgroove along the width direction of the rectangular surface is the second center line, l is the distance between two adjacent first center lines of each microgroove structure, k is the distance between two adjacent second center lines of each microgroove structure; s is the width of each second microgroove.

[0024] Preferably, S1 includes: a method for obtaining the first welding surface includes: performing milling processing on the first workpiece to be welded to obtain the flat first welding surface; a method for obtaining the second welding surface includes: performing milling processing on the second workpiece to be welded to obtain the flat second welding surface.

[0025] Preferably, S1 includes: machining a micro-groove structure on the first welding surface and / or the second welding surface using a pulsed laser.

[0026] Compared with the prior art, the present invention has achieved the following technical effects:

[0027] The present invention provides a method for suppressing hump defects in laser welding, which includes machining a micro-groove structure on a first welding surface of a first part to be welded and / or a second welding surface of a second part to be welded; filling alloy powder into each micro-groove structure; and welding the first welding surface and the second welding surface together by penetration welding. The present invention increases the surface tension of the liquid metal in the subsequent welding process by machining a micro-groove structure on the first welding surface and / or the second welding surface, and adding alloy powder into the micro-groove structure. The alloy powder can not only supplement the lack of surface tension and reduce or avoid the generation of humps, but also compensate for the burning of beneficial alloy elements in the high-power laser welding process, regulate the weld microstructure, and optimize the mechanical properties of the weld. The present invention can suppress hump defects without the need for additional auxiliary equipment, and obtain a weld with beautiful shape and good performance; it has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 A schematic diagram of a method for suppressing a laser welding hump defect provided by the present invention;

[0030] Figure 2 A schematic diagram of a rectangular surface processed with a first micro groove provided by the present invention;

[0031] Figure 3 for Figure 2 A magnified view of middle;

[0032] Figure 4 for Figure 3 Sectional view of the middle QQ;

[0033] Figure 5 A schematic diagram of a rectangular surface processed with a second micro groove provided by the present invention;

[0034] Figure 6 for Figure 5 Enlarged view of middle B;

[0035] Figure 7 for Figure 6 A cross-sectional view of XX;

[0036] In the figure: 1. first part to be welded; 2. second part to be welded; 3. rectangular surface; 4. laser beam; 5. protective gas nozzle. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0038] The purpose of the present invention is to provide a method for suppressing hump defects in laser welding to solve the problems existing in the above-mentioned prior art, reduce or avoid the generation of humps, and obtain welds with beautiful shape and good performance; optimize the mechanical properties of the welds; and have a wide range of applications.

[0039] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] like Figures 1 to 7 As shown, the present invention provides a method for suppressing laser welding hump defects, comprising the following steps:

[0041] S1, machining a micro-groove structure on a first welding surface of the first workpiece to be welded 1 and / or a second welding surface of the second workpiece to be welded 2; and filling alloy powder into each micro-groove structure;

[0042] S2. Welding the first welding surface and the second welding surface together by penetration welding.

[0043] The present invention processes a micro-groove structure on the first welding surface and / or the second welding surface, and adds alloy powder to the micro-groove structure, so that the surface tension of the liquid metal in the subsequent welding process is increased. The alloy powder can not only make up for the lack of surface tension and reduce or avoid the generation of humps, but also make up for the burnout of beneficial alloy elements in the high-power laser welding process, regulate the weld microstructure, and optimize the mechanical properties of the weld. The present invention can suppress hump defects without the need for additional auxiliary equipment, and obtain a weld with beautiful shape and good performance. The present invention is to add alloy powder to the part to be welded. This method is not limited by the type of weld and can be applied to a variety of weld types such as straight welds, curved welds and oblique welds, and has a wide range of applications.

[0044] In the present invention, S1 includes: after filling the alloy powder into each micro-groove structure, compacting the alloy powder in the micro-groove structure.

[0045] As a feasible implementation method, Figure 2 As shown, S1 includes: the micro-groove structure includes a plurality of first micro-grooves arranged in a lattice, and the first welding surface and the second welding surface are rectangular surfaces 3. The regular distribution of the micro-groove structure can reduce or avoid the segregation of powder in the molten pool.

[0046] In the present invention, the opening of each first microgroove is circular.

[0047] In the present invention, S1 includes: before filling the alloy powder into each micro-groove structure, obtaining the required mass of the alloy powder by formula 1, and formula 1 is as follows:

[0048] M=ρVat / mn Formula 1

[0049] Wherein, M is the mass of alloy powder required for each micro-groove structure; ρ is the density of alloy powder; V is the volume of each first micro-groove, V is determined by the diameter d and the depth h of each first micro-groove; a and t are the length and width of the rectangular surface 3 respectively; m is the distance between the centers of two adjacent first micro-grooves of each micro-groove structure along the length direction of the rectangular surface 3; n is the distance between the centers of two adjacent first micro-grooves of each micro-groove structure along the width direction of the rectangular surface 3. By changing the arrangement spacing m and n of the first micro-grooves in the z and x directions, as well as the volume V of a single first micro-groove, quantitative control of filling powder can be achieved.

[0050] As another feasible implementation, Figure 3 As shown, S1 includes: each micro-groove structure includes a plurality of strip-shaped second micro-grooves, and the plurality of second micro-grooves of each micro-groove structure are staggered and arranged in a mesh shape. The regular distribution of the micro-groove structure can reduce or avoid the segregation of powder in the molten pool.

[0051] In the present invention, each second micro groove is a rectangular groove.

[0052] In the present invention, S1 includes: before filling the alloy powder into each micro-groove structure, obtaining the required mass of the alloy powder by formula 2, where formula 1 is as follows:

[0053] M=[atH-(ls)*(ks)*(t / l)*(a / k)]ρ Formula 2

[0054] Wherein, H is the depth of each second microgroove; the center line of each second microgroove along the length direction of the rectangular surface 3 is the first center line, the center line of each second microgroove along the width direction of the rectangular surface 3 is the second center line, l is the distance between two adjacent first center lines of each microgroove structure, k is the distance between two adjacent second center lines of each microgroove structure; s is the width of each second microgroove. By changing the arrangement spacing m and n of the grid-like second microgroove in the z and x directions, as well as the depth H of the second microgroove, quantitative control of the filling powder can be achieved.

[0055] In the present invention, S1 includes: a method for obtaining a first welding surface includes: performing milling processing on a first workpiece 1 to be welded to obtain a flat first welding surface; a method for obtaining a second welding surface includes: performing milling processing on a second workpiece 2 to be welded to obtain a flat second welding surface.

[0056] It should be noted that the micro-groove structure of the present invention is not limited to the two feasible implementation forms mentioned above, and can also be other micro-structure forms that can be filled with metal powder.

[0057] In the present invention, S1 includes: using pulsed laser to process a micro-groove structure on the first welding surface and / or the second welding surface.

[0058] The present invention can be applied to the welding of thick plates. In the figure, the x direction is the welding direction, and the z direction is the thickness direction of the welded parts. The length of the first welded part 1 or the second welded part 2 is a, the width is b, and the thickness is t; a micro-groove structure is machined on the first welding surface of the first welded part 1 and the second welding surface of the second welded part 2, and then the two parts are butt-jointed and welded along the welding direction. It should be noted that the present invention can also be applied to the welding of other welding seams, such as curved and oblique welds.

[0059] During welding, a laser beam 4 may be used for welding, and a shielding gas may be sprayed at the welding point through a shielding gas nozzle 5. The angle between the laser beam 4 and the vertical plane is 5°.

[0060] In the present invention, the selection principles of alloy powder include: 1. It can increase the surface tension of the molten pool; 2. Try not to have a negative impact on the structure and performance of the weld. Taking 316L as an example, the surface tension of the molten pool can be increased by adding a small amount of elements such as silicon or molybdenum; silicon can also improve the oxidation resistance of the metal, and molybdenum can also enhance the stability of the metal at high temperatures, but the addition of these elements must be controlled within an appropriate range to avoid the loss of other properties. It should be noted that the filling amount of the alloy powder can be obtained by experiments and other means, which will not be elaborated here.

[0061] The present invention can be applied to all penetration welding facing the hump defect problem, such as laser penetration welding, laser arc composite penetration welding, and the first welding lock bottom welding in arc welding.

[0062] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for suppressing hump defects in laser welding, characterized in that: The steps include: S1, machining a micro-groove structure on a first welding surface of a first workpiece to be welded and / or a second welding surface of a second workpiece to be welded; and filling alloy powder into each of the micro-groove structures; S2. Welding the first welding surface and the second welding surface together by penetration welding.

2. The method for suppressing laser welding hump defects according to claim 1, characterized in that: S1 includes: After the alloy powder is filled into each of the micro-groove structures, the alloy powder in the micro-groove structures is compacted.

3. The method for suppressing laser welding hump defects according to claim 1, characterized in that: S1 includes: The micro-groove structure includes a plurality of first micro-grooves arranged in a lattice, and the first welding surface and the second welding surface are rectangular surfaces.

4. The method for suppressing laser welding hump defects according to claim 3, characterized in that: The opening of each of the first microgrooves is circular.

5. The method for suppressing laser welding hump defects according to claim 3, characterized in that: S1 includes: Before filling the alloy powder into each of the micro-groove structures, the required mass of the alloy powder is obtained by formula 1, which is as follows: M=ρVat / mn Formula 1 Among them, M is the mass of the alloy powder required for each of the micro-groove structures; ρ is the density of the alloy powder; V is the volume of each of the first micro-grooves; a and b are the length and width of the rectangular surface, respectively; m is the distance between the centers of two adjacent first micro-grooves of each of the micro-groove structures along the length direction of the rectangular surface; n is the distance between the centers of two adjacent first micro-grooves of each of the micro-groove structures along the width direction of the rectangular surface.

6. The method for suppressing laser welding hump defects according to claim 1, characterized in that: S1 includes: Each of the micro-grooves structures comprises a plurality of strip-shaped second micro-grooves, and the plurality of second micro-grooves of each of the micro-grooves structures are staggered and arranged in a mesh shape.

7. The method for suppressing laser welding hump defects according to claim 6, characterized in that: Each of the second microgrooves is a rectangular groove.

8. The method for suppressing laser welding hump defects according to claim 7, characterized in that: S1 includes: Before filling the alloy powder into each of the micro-groove structures, the required mass of the alloy powder is obtained by formula 2, and formula 1 is as follows: M=[atH-(ls)*(ks)*(t / l)*(a / k)]ρ Formula 2 Among them, H is the depth of each second microgroove; the center line of each second microgroove along the length direction of the rectangular surface is the first center line, the center line of each second microgroove along the width direction of the rectangular surface is the second center line, l is the distance between two adjacent first center lines of each microgroove structure, k is the distance between two adjacent second center lines of each microgroove structure; s is the width of each second microgroove.

9. The method for suppressing laser welding hump defects according to claim 1, characterized in that: S1 includes: The method for obtaining the first welding surface includes: performing milling processing on the first workpiece to be welded to obtain the flat first welding surface; the method for obtaining the second welding surface includes: performing milling processing on the second workpiece to be welded to obtain the flat second welding surface.

10. The method for suppressing laser welding hump defects according to claim 1, characterized in that: S1 includes: A micro groove structure is processed on the first welding surface and / or the second welding surface by using a pulse laser.

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