A laser welding verification method

Abstract

The present invention discloses a laser welding verification method, comprising the following steps: S1: cleaning the surface of the welding area of ​​the end plate test piece and the side plate test piece; S2: pressing by welding tooling; S3: setting the positive spiral mode in the laser trajectory software, and performing the first round of welding on the end plate test piece and the side plate test piece; S4: determining the welding significant factor type of the welding test piece; screening the welding significant factors from the welds completed in the first round of welding; S5: determining the threshold range of each welding significant factor, and statistically delineating the welding parameter group range; respectively presetting the upper limit value and the lower limit value of the welding significant factor, and in the second round determining the actual upper and lower limit values ​​of the welding main factor through appearance, metallographic test and tensile test, finding the threshold range; and statistically calculating the parameter group range value of each welding significant factor. The beneficial effects of the present invention are: being able to efficiently find the optimal welding parameter group and determine the parameter range, making a surface coverage of the feasibility parameters, improving the welding strength, and having high verification efficiency, making accurate predictions on the mass production process capability, and providing greater compatibility with fluctuations in production process factors.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a laser welding method for end plates and side plates of a large module. Background Art

[0002] Lithium-ion batteries, with their high energy density, safety, pollution-free operation, long lifespan, and lack of memory effect, have been widely used in electric vehicles, energy storage, and portable electronics. In the power battery sector, battery pack design is constrained by energy density requirements and cost. The promotion of large-module solutions caters to current market demands. Due to their high energy density, excellent heat dissipation, and compact structure, they have attracted widespread attention in the lithium battery industry.

[0003] Laser welding plays a very important role in the production process of battery packs. Due to its advantages such as high welding strength, high energy, high speed, large depth, and small deformation, laser welding is widely used in the end-side plate welding process. In large modules, the end-side plate welding method is used to package the battery cells, and the modules are fixed to the box crossbeams through the end plates. As an important part affecting the structural strength of the battery pack, this packaging connection method has high requirements for weld strength. At this time, 5 series aluminum and 6 series aluminum need to be welded. Due to structural and weight restrictions, the end plates are only 2~3mm thick and need to reach a tensile force of more than 12KN after welding. Since it is easy to weld through when the thickness is 2mm, the strength still cannot meet the strength requirements when the penetration depth reaches 2mm. At this time, it is necessary to adjust the parameter ratio, increase the penetration width, and increase the welding strength.

[0004] Laser welding is an ideal method for connecting end panels due to its advantages, such as low heat input, minimal deformation, a stable weld pool, and low over-welding. However, existing technologies lack experience and methods for using laser welding to weld thin aluminum sheets (2mm) and achieve high tensile strength. This presents challenges in welding end panels in large modules, such as large lap weld gaps that prevent fusion and result in low strength, easily penetrating the thin bottom sheet. Furthermore, during the verification phase, it is impossible to predict the production process capability and pass rate. Traditional verification results are unable to accommodate fluctuations caused by production process factors, requiring repeated verification.

[0005] The information disclosed in this background section is only intended to enhance understanding of the overall background of the invention and should not be considered as an admission or any form of suggestion that the information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: how to solve the current problem of easy weld penetration and insufficient tensile strength in welding thinner aluminum sheets. There is an urgent need for a verification method that can obtain the horizontal coverage range of each major influencing factor and achieve point-to-surface coverage of the welding parameter group, thereby effectively improving the weld strength and welding yield.

[0007] The present invention solves the above technical problems through the following technical means:

[0008] A laser welding verification method comprises the following steps:

[0009] S1: Clean the welding area surfaces of the end plate specimen and the side plate specimen;

[0010] S2: Pressing by welding tooling;

[0011] S3: Set the forward rotation mode in the laser trajectory software and perform the first round of welding on the end plate specimen and the side plate specimen;

[0012] S4: Determine the welding significant factor type of the welding specimen; select the welding significant factors from the welds completed in the first round of welding;

[0013] S5: Determine the threshold range of each significant welding factor and statistically define the welding parameter group range;

[0014] The upper and lower limit values ​​of the significant welding factors are preset respectively. After the second round of welding is completed, the actual upper and lower limit values ​​of the main welding factors are determined through appearance, metallographic and tensile tests to find the threshold range; the parameter group range values ​​of each significant welding factor are counted.

[0015] The present invention can efficiently find the optimal welding parameter group and determine the parameter range, provide surface coverage of feasibility parameters, improve welding strength, increase verification efficiency, make accurate predictions on mass production process capabilities, and provide greater compatibility with fluctuations in production process factors.

[0016] Preferably, the step of cleaning the surface of the welding area of ​​the end plate specimen and the side plate specimen is: before welding begins, the surface of the end plate specimen and the side plate specimen needs to be magnetically polished or mechanically cleaned or repeatedly wiped with a dust-free cloth, and the surface flatness of the end plate specimen and the side plate specimen is 0.4~0.8μm / 100mm.

[0017] Cleaning the test piece and maintaining its flatness can reduce the occurrence of defective products such as cold solder joints;

[0018] Preferably, the welding fixture includes a base, a slide rail, a clamping block, and a quick-clamp wrench; a welding mounting frame is provided on one side of the base, a cross-shaped positioning groove is provided on the vertical surface of the welding mounting frame, and the end plate test piece and the side plate test piece are overlapped in the positioning groove;

[0019] The horizontal surface of the base is connected to the slide rail, the bottom of the pressing block is slidably connected to the slide rail, and the vertical end of the pressing block has a penetrating light hole, through which the laser passes to act on the side plate test piece and the end plate test piece;

[0020] The side of the pressing block close to the welding mounting frame is connected to the tooling pressure head, the top of the tooling pressure head is connected to the protective gas inlet valve, and an air outlet is arranged in the tooling pressure head.

[0021] The welding tooling can adapt to test pieces of different thicknesses and is easy to use and highly adaptable.

[0022] Preferably, in step S3, the shielding gas is introduced from the internal air passage of the tooling pressure head before welding begins and blown out from the air outlet with a flow rate of 15L / min~20L / min. The shielding gas is a mixture of one or more inert gases, wherein the purity of the shielding gas is greater than or equal to 99.99%.

[0023] Shielding gas can prevent oxidation during welding.

[0024] Preferably, the laser motion trajectory during welding adopts a positive rotation line mode, with a positive rotation density of 1 / mm to 3 / mm and an amplitude of 0.6 to 1.3 mm.

[0025] Preferably, in step S4, the significant factor types include at least two of power, speed, spacing, defocus and amplitude.

[0026] Preferably, in step S4, upper and lower limit values ​​are preset for the significant welding factors respectively, and the arrays with the maximum laser energy density and the minimum laser energy of the combined parameter group are found. Experiments are carried out respectively, and the parameter level thresholds are adjusted through weld appearance scoring, metallographic testing and tensile strength testing. After the actual upper and lower limit values ​​of each parameter are determined, the welding parameter group is delineated.

[0027] Preferably, the power variation of the laser welding process in steps S3 and S5 is:

[0028] The first section: from 0% to 8-12% of the welding path, the laser power is reduced from the set value AW to BW;

[0029] The second section: from 8-12% to 75-85% of the welding path, the laser power is set to BW;

[0030] The third stage: from 75-85% to 97-99% of the welding path, the laser power is gradually reduced from the set value of BW to CW;

[0031] The fourth stage: from 97-99% to 100% of the welding path, the laser power is reduced from the set value of CW to 0W;

[0032] The processes of power increase and power decrease are both linear changes.

[0033] In order to avoid welding explosion points and welding penetration, the welding process needs to accurately control the laser energy input. Therefore, the laser energy output in the welding process adopts a variable form and the energy output adopts a linear change.

[0034] Preferably, in steps S3 and S5, the laser movement speed is greater than or equal to 500 mm / s, and the defocus amount is -2 mm to +2 mm;

[0035] Laser wavelength: 500μm~1200μm;

[0036] The laser output modes include continuous and continuous;

[0037] The laser output energy distribution includes one of Gaussian distribution, annular distribution or Gaussian plus annular distribution. If Gaussian plus annular distribution is used, the Gaussian light intensity accounts for 60% to 95% of the total light intensity, and the annular light intensity accounts for 5% to 40% of the total light intensity.

[0038] Preferably, the welding laser is a fiber laser or a composite laser;

[0039] The welding laser is also connected to a galvanometer that oscillates on the X and Y axes. After the galvanometer focuses the laser beam, the beam waist cross-sectional area is less than or equal to 0.03 mm².

[0040] This embodiment uses a galvanometer and annular spot laser welding method to weld the end and side plates. By adjusting the laser welding parameter level, the purpose of improving the internal structure of the molten pool is achieved, and the spatter and bubble problems during the welding process can be effectively suppressed; when welding, the laser turns on the swing function, and the laser performs a positive rotation motion around the center line, which can effectively reduce the bubble formation rate and improve the gas escape efficiency, thereby helping to improve the mechanical properties of the weld.

[0041] The advantages of the present invention are:

[0042] The present invention can efficiently find the optimal welding parameter group and determine the parameter range, provide surface coverage of feasibility parameters, improve welding strength, increase verification efficiency, make accurate predictions on mass production process capabilities, and provide greater compatibility with fluctuations in production process factors.

[0043] This embodiment effectively solves the problems of large module end and side plate welding, such as large lap weld gaps that prevent melting, low strength, and easy penetration of the bottom thin plate. The verification phase cannot predict the mass production process capability and pass rate, and a single verification result cannot cover fluctuations caused by production process factors, requiring repeated verification. This effectively improves weld strength and welding yield. It also expands the coverage of welding significant factor levels, achieving point-to-surface coverage of welding parameter groups, and increasing tolerance for errors caused by production line equipment fluctuations, assembly tolerances, and material tolerances.

[0044] In order to avoid welding explosion points and welding penetration, the laser energy input needs to be accurately controlled during the welding process. Therefore, the laser energy output during the welding process adopts a variable form, and the energy output adopts a linear change.

[0045] This embodiment uses a galvanometer and annular spot laser welding method to weld the end and side plates. By adjusting the laser welding parameter level, the purpose of improving the internal structure of the molten pool is achieved, and the spatter and bubble problems during the welding process can be effectively suppressed; when welding, the laser turns on the swing function, and the laser performs a positive rotation motion around the center line, which can effectively reduce the bubble formation rate and improve the gas escape efficiency, thereby helping to improve the mechanical properties of the weld. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 1 is a schematic structural diagram of a welding tool in a first embodiment of the present invention;

[0047] Figure 2 1 is a schematic structural diagram of the base and the slide rail in the first embodiment of the present invention;

[0048] Figure 3 Schematic diagram of the structure of the clamping block and the quick-clamp wrench in the first embodiment of the present invention;

[0049] Figure 4 is a cross-sectional view of the welding tool in Example 1 of the present invention;

[0050] Figure 5 Schematic diagram of the laser positive rotation line mode in Example 1 of the present invention;

[0051] Figure 6 This is a schematic diagram of a metallographic test in Example 1 of the present invention;

[0052] Figure 7 This is a schematic diagram of a tensile test in Example 1 of the present invention;

[0053] Figure 8 Schematic diagram of laser power variation in embodiment 1 of the present invention;

[0054] Figure 9 This is a schematic diagram of parameter group coverage in Example 1 of the present invention;

[0055] Figure 10 are the preset limit values ​​of the four significant welding factors in the second embodiment of the present invention;

[0056] Figure 11 This is a schematic diagram of the free combination of four significant welding factors in the second embodiment of the present invention;

[0057] Figure 12 This is a welding sample within the parameter range of the threshold range used in the second embodiment of the present invention;

[0058] Figure 13 This is a diagram showing the results of a tensile test on a welding sample in Example 2 of the present invention;

[0059] Figure 14 This is a diagram showing the metallographic test results of the welding sample in the second embodiment of the present invention;

[0060] Numbers in the figure:

[0061] 1. Base; 11. Welding mounting bracket; 12. Positioning groove;

[0062] 2. Slide rail; 3. Clamping block; 31. Light hole; 32. Tooling pressure head; 33. Protective gas inlet valve; 34. Air outlet; 4. Quick-clamp wrench; DETAILED DESCRIPTION

[0063] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with 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. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0064] Example 1:

[0065] A laser welding verification method comprises the following steps:

[0066] S1: Clean the welding area surfaces of the end plate specimen and the side plate specimen;

[0067] Specifically, in this embodiment, the types and thicknesses of laser welding materials for the end plate specimen and the side plate specimen include but are not limited to: the material of the end plate specimen is 6 series aluminum with a thickness of 3mm~5mm, and the material of the side plate specimen is 5 series aluminum with a thickness of 1.5mm~2mm. Before welding begins, the surfaces of the end plate specimen and the side plate specimen need to be magnetically polished, and the surface flatness is 0.4~0.8μm / 100mm.

[0068] The cleaning method can be mechanical cleaning, using 75% alcohol or acetone as the cleaning agent, and welding can be performed after the surface of the workpiece is dry; or a dust-free cloth can be used to repeatedly wipe the upper and lower surfaces of the side panels and end panels, and the welding area, and blow it dry with a compressed air gun.

[0069] S2: Perform the first pressing and welding using welding tooling;

[0070] Specifically, such as Figure 1 、 Figure 2 、 Figure 3 、 Figure 4As shown, the welding tool in this embodiment includes a base 1, a slide rail 2, a clamping block 3, and a quick-clamp wrench 4; a welding mounting frame 11 is provided on one side of the base 1, and a cross-shaped positioning groove 12 is provided on the vertical surface of the welding mounting frame 11. The end plate test piece and the side plate test piece can be overlapped in the positioning groove 12. In this embodiment, the side plate test piece is placed horizontally and the end plate test piece is placed vertically, and the two are overlapped at the center position. During welding, the laser acts on the side plate test piece through the light hole, melts part of the base material of the side plate test piece, and connects it with the end plate test piece.

[0071] The horizontal surface of the base 1 is connected to the slide rail 2. The clamping block 3 has a roughly L-shaped structure. The horizontal portion of the clamping block 3 is slidably connected to the slide rail. The vertical end of the clamping block 3 can be moved toward the welding mount to be clamped against the side panel test piece and the end panel test piece. The vertical end of the clamping block 3 has a through-hole 31, through which the laser can pass and act on the side panel test piece and the end panel test piece. The side of the clamping block 3 near the welding mount is connected to the tooling pressure head 32. The top of the tooling pressure head 32 is connected to the shielding gas inlet valve 33. The tooling pressure head 32 is provided with an outlet hole 34. The shielding gas inlet valve 33 is connected to an external gas source, and the gas source can be blown out through the outlet hole, thereby providing gas protection during welding.

[0072] Before welding begins, the shielding gas is introduced from the internal air passage of the tooling pressure head and blown out from the air outlet with a flow rate of 15L / min~20L / min. The shielding gas is a mixture of one or more inert gases, and the purity of the shielding gas is greater than or equal to 99.99%.

[0073] The quick-clamp wrench 4 is connected to the right end of the clamping block 3, and the bottom of the quick-clamp wrench 4 is connected to the right end of the base 1. By operating the quick-clamp wrench 4, the tooling pressure head 32 of the clamping block can be pressed on the side plate test piece and the end plate test piece. The quick-clamp position 4 can be flexibly adjusted according to the thickness requirements of the verification test piece, and the side plate test piece and the end plate test piece are installed in the positioning groove 12. During the rotation of the quick-clamp wrench 4, the clamping block 3 is pushed to clamp the test piece. The shielding gas enters the cavity of the tooling pressure head 32 through the shielding gas inlet valve 33, and is then blown out through the air outlet 34 to disperse the plasma gas generated during the welding process. The slide rail 2 ensures that the clamping module moves forward and backward smoothly. The tooling realizes that the first inspection welding mode of verification and mass production is consistent with mass production, and vertical welding.

[0074] During a single welding, pre-lighting is required (a low-energy beam that will not cause damage), and the position of the test piece is adjusted and confirmed each time the welding is performed. In this embodiment, a red light preview is performed, and the side panel test piece is offset 0.5mm along the overlap line of the side panel test piece and the end panel test piece. Alternatively, CCD detection is added before welding to identify and locate the overlap position of the end panel test piece and the side panel test piece, thereby overcoming the error caused by the overlap position after assembly, and adopting the overlap welding method, the weld is offset 0.5mm from the upper plate of the side panel, thereby avoiding the problem of unqualified strength caused by poor penetration after welding deviation.

[0075] The laser oscillation function should be turned on during welding, and protective gas should be introduced to protect the molten pool.

[0076] Due to the long weld seam of the end and side plates, the large welding area, and poor positioning consistency, but the thickness of the end plate welding area is relatively thin, there are many difficulties in welding the end and side plates. The main problems are: the same weld has two undesirable conditions: cold welding and weld penetration. The reason is: there are gaps in some areas of the side and end plate welding areas after assembly, and the gaps are randomly distributed; first, on the equipment, the clamping force detection has a tolerance of ±50N, and the mechanical displacement tolerance of the laser lens is ±0.3mm, which is not conducive to eliminating the gap between materials and finding the focus. Secondly, in terms of materials, there is a flatness tolerance of ±0.2mm / m on the surface of the side plate and the end plate, and the two sides of the side plate are bent and covered on the upper surface of the end plate. There is an angle tolerance of ±2° at the bending point, and a tolerance of ±0.3mm in the folding edge length. Again, in terms of the positioning of the pressure head and tooling, the flatness of the tooling surface is ±0.5mm / m, and the verticality of the pressure head is ±0.2mm. The tolerances of various production-related factors are accumulated in the welding assembly area and need to be solved at the process method end. The welding parameter level and combination mode are maximally compatible with the errors caused by assembly. By reducing the speed, power and density, increasing the defocus, and adjusting the amplitude, the main effect factors can be freely combined into multiple parameter groups within the threshold range to achieve point-to-surface coverage of the parameter group. The optimal solution is found to expand the gap compatibility range to 0.8mm, the 3mm end plate weld penetration is controlled between 1~2.8mm, and the 2mm end plate weld penetration is controlled between 1~1.8mm.

[0077] S3: Set the positive rotation mode in the laser trajectory software;

[0078] Specifically, the laser motion trajectory is drawn on the laser trajectory motion drawing software to draw the forward rotation welding trajectory and calibrate the trajectory position to coincide with the required welding position.

[0079] When welding, the laser motion trajectory uses the positive spiral mode (such as Figure 5 ), the positive rotation density is 1 / mm~3 / mm, the amplitude is 0.6~1.3mm, and the welding process develops from bottom to top.

[0080] S4: Determine the welding significant factor type of the welding test piece

[0081] It should be noted that there are multiple types of welding factors that affect welds. Assuming there are 10 factors (including power, speed, spacing, density, defocus, line shape, amplitude, machine, shielding gas velocity, and dust removal velocity, a total of 10 factors), during the first round of welding, a partial factor DOE experiment can be performed. All factors and their results can be entered into Mintab software. The P value of each factor can be checked through grouping, setting center points, and variance analysis. If the P value is greater than 0.05, the factor is screened out. If it is less than 0.05, it is considered a significant welding factor. The weld appearance can also be combined to perform the first round of significant welding factor screening. In this example, only four welding factors (power, speed, amplitude, and defocus) are confirmed to have a significant impact on the weld, so these four are considered significant welding factors.

[0082] Among them, power is the energy of the laser beam per unit time; speed is the linear velocity or focal velocity, here it refers to linear velocity; spacing is the distance between the peaks of the sine wave; density is the number of sine waves within a length range of 1 mm; defocus is the distance between the welding surface and the beam focus.

[0083] In the above S4, the types of lasers used include but are not limited to green light to infrared light, with a wavelength of 500μm~1200μm; the laser output modes include but are not limited to CW (continuous wave) and QCW (quasi-continuous wave); the laser output energy distribution forms include but are not limited to Gaussian distribution, annular distribution or one of Gaussian plus annular distribution; if Gaussian distribution light intensity plus annular distribution is used, the Gaussian light intensity accounts for 60%~95% of the total light intensity, and the annular light intensity accounts for 5%~40% of the total light intensity.

[0084] In order to guide the laser to perform a forward-rotating welding trajectory and achieve beam swing during the welding process, a galvanometer is required, and the galvanometer needs to have the ability to swing on the X and Y axes; after the galvanometer focuses the laser beam, the beam waist cross-sectional area is less than or equal to 0.03mm² (which can be measured by a beam profiler);

[0085] This embodiment uses a galvanometer and annular spot laser welding method to weld the end and side plates. By adjusting the laser welding parameter level, the purpose of improving the internal structure of the molten pool is achieved, and the spatter and bubble problems during the welding process can be effectively suppressed; when welding, the laser turns on the swing function, and the laser performs a positive rotation motion around the center line, which can effectively reduce the bubble formation rate and improve the gas escape efficiency, thereby helping to improve the mechanical properties of the weld.

[0086] Laser power needs to be adjusted based on material thickness; the laser speed should be greater than or equal to 500 mm / s, and the defocus should be between -2 mm and +2 mm. Fiber lasers or hybrid lasers should be used as welding lasers, preferably fiber lasers, with a fiber diameter requirement of 10 μm to 20 μm.

[0087] Among them, in order to avoid welding explosion points and welding through, the welding process needs to accurately control the laser energy input, so the laser energy output in the welding process adopts a variable form, and the energy output adopts a linear change. In the above S4, the total welding energy waveform is set in the waveform preview (such as Figure 8 As shown in the figure), the first section: from 0% to 10% of the welding path, the laser power drops from the set value of 6000W to 4900W; the second section: from 10% to 80% of the welding path, the laser power drops from the set value of 4900W; the third section: from 80% to 98% of the welding path, the laser power drops from the set value of 4900W to 3700W; the fourth section: from 98% to 100% of the welding path, the laser power drops from the set value of 3700W to 0W. All power increase and decrease processes are linear changes.

[0088] S5: Determine the threshold range of each significant welding factor and statistically define the welding parameter group range;

[0089] The upper and lower limit values ​​of the welding significant factors are preset respectively. The second round of appearance and metallographic tests (such as Figure 7 as shown) and tensile tests (as Figure 8 (as shown) determine the actual upper and lower limit values ​​of the welding main factors and find the threshold range.

[0090] Since the factors interact and affect the energy density of the welding surface, the upper and lower limit values ​​of the welding significant factors are preset to find the maximum and minimum arrays of laser energy density of the combined parameter group. All low-level values ​​are used as the minimum laser energy density array, and all high-level values ​​are used as the maximum laser energy density array.

[0091] The specific implementation is to first weld with the preset maximum energy density parameters, adjust the power and speed ratio until 3mm> penetration> 2.8mm, and obtain the highest threshold parameter group of each parameter within the experimental range. On the contrary, if the preset density is too large and welding penetration occurs, adjust the power and speed ratio until 3mm> penetration> 2.8mm; similarly, find the minimum array of combined parameters, first weld with the preset minimum energy density parameters, adjust the power and speed ratio until the penetration is about 5mm, and obtain the lowest threshold parameter group of each parameter within the experimental range. On the contrary, if the preset density is too small and cold welding occurs, adjust the power and speed ratio until the penetration> 5mm; finally, lock the parameter range, and the parameters can be freely combined within the range, and the welding is all qualified.

[0092] In this embodiment, power and speed change synchronously. If only power is increased while speed remains unchanged, the power will be too high and energy will be concentrated. If speed cannot keep up, biting will easily occur. Therefore, there is a matching ratio between power and speed.

[0093] like Figure 9As shown in the figure, each significant welding factor can be freely combined into multiple parameter groups within the threshold range, so that the parameter group can be covered from point to surface.

[0094] The welding parameter group was identified, and finally the optimal parameters under the current 5M1E (man-machine-material-method-environmental-measurement) conditions were determined through experiments within the qualified area.

[0095] This embodiment can efficiently find the optimal welding parameter group and determine the parameter range, provide surface coverage of feasibility parameters, improve welding strength, increase verification efficiency, make accurate predictions of mass production process capabilities, and provide greater compatibility with fluctuations in production process factors.

[0096] This embodiment effectively solves the problems of welding the end and side plates of large modules, such as the large gap between lap welds that cannot be melted, low strength, easy welding through of the bottom thin plate, inability to predict the mass production process capability and pass rate during the verification phase, inability of a single verification result to cover the fluctuations caused by production process factors, repeated verification, etc., and effectively improves the weld strength and welding yield; at the same time, it expands the coverage range of welding significant factor levels, realizes point-to-surface coverage of welding parameter groups, and expands the tolerance of errors caused by production line equipment fluctuations, assembly tolerances, and material tolerances.

[0097] Example 2:

[0098] like Figure 10 、 Figure 11 As shown, the difference between this embodiment and the first embodiment is that: since the interaction between density and power is very obvious, the density and spacing are set to fixed values, or if they are found to be in a relatively satisfactory range in a round of experiments, then the significant welding factors of this embodiment can be selected as power, speed, defocus and amplitude.

[0099] S1: Clean the welding area surfaces of the end plate specimen and the side plate specimen;

[0100] Clean the upper and lower surfaces of the welding area of ​​the side plate test piece and the end plate test piece. The cleaning solvent is alcohol. The specific cleaning steps are as follows: Use a dust-free cloth to repeatedly wipe the upper and lower surfaces of the side plate and the end plate, as well as the welding area, and blow them dry with a compressed air gun;

[0101] The material types and thicknesses of the end plate and side plate specimens selected for laser welding in this embodiment are: the end plate material is: 5-series aluminum plate (5083-H111), material thickness 1.5mm, and the end plate is: 6-series aluminum plate (6063-T6), material thickness 3mm. The surface of the specimens needs to be cleaned before welding.

[0102] S2: Perform the first pressing and welding using welding tooling;

[0103] Fix the workpiece to be welded on the welding fixture, and use the pressing fixture to tightly fit the side plate test piece and the end plate test piece;

[0104] S3, draw the laser motion trajectory on the laser trajectory motion drawing software to draw the forward rotation welding trajectory (such as Figure 5 ) and calibrate the trajectory position to coincide with the required welding position;

[0105] S4. Welding test pieces to determine the type of welding significant factors and find the threshold value;

[0106] This embodiment selects: IPG laser (4000 / 2000) laser because of its good ring beam quality and energy distribution that is beneficial to the escape of plasma gas generated during welding, which can meet welding requirements. Therefore, IPG laser is selected, and the fiber diameter is 27μm. To meet the requirements of efficient and fast welding, the laser output mode is CW (continuous) and the laser output energy distribution form is Gaussian distribution. To achieve the guidance of the laser to perform a positive rotation welding trajectory and the beam swing during the welding process, this embodiment requires the use of a galvanometer, and the galvanometer has the function of swinging on the X and Y axes. The beam analyzer measures that after the galvanometer focuses the laser beam, the beam waist cross-section is circular with a cross-sectional area of ​​0.02mm².

[0107] In this embodiment, the laser welding parameters are determined based on the thickness of the side plate and end plate and the selected laser equipment. After a round of conventional welding appearance screening, the density standard is determined to be 5.28 pieces / mm, the outer ring power standard is 960W, and the types of significant influencing factors are identified: center power, speed, defocus amount and amplitude. The upper and lower limit values ​​of the significant welding factors are preset (such as Figure 10 ).

[0108] In this embodiment, in order to avoid welding explosion points and weld penetration, the welding process needs to accurately control the laser energy input. Therefore, the laser energy output in the welding process adopts a variable form, and the energy output adopts a linear change. Specifically, the first section: from 0% to 10% of the welding path, the laser power is reduced from the set value of 6000W to 4900W; the second section: from 10% to 80% of the welding path, the laser power is reduced from the set value of 4900W; the third section: from 80% to 98% of the welding path, the laser power is gradually reduced from the set value of 4900W to 3700W; the fourth section: from 98% to 100% of the welding path, the laser power is reduced from the set value of 3700W to 0W. All power increase and decrease processes are linear changes.

[0109] In this embodiment, the shielding gas is introduced from the internal gas pipe of the tooling pressure head before welding begins, with a flow rate of 12 L / min. The shielding gas type is Ar, and the shielding gas purity is measured to be greater than 99.99%;

[0110] In order to increase the welding area and improve the end side plate weld tolerance to the assembly error in the Y-axis direction, the amplitude is increased to increase the weld width. In order to control the penetration depth within the qualified range and improve the end side plate tolerance to the assembly error in the X-axis direction, the center power, speed and defocus are adjusted to achieve the purpose of controlling the penetration depth. The parameter levels of the virtual weld and the weld penetration are determined by metallographic testing to determine the threshold value ( Figure 10 ), and then conduct orthogonal experiments to verify that the parameter levels within the range can be freely combined ( Figure 11 ), the welding trajectory is set to a positive spiral curve as ( Figure 5 ), the welding process develops from bottom to top.

[0111] S5. Statistically identify the optimal welding parameter group.

[0112] Each significant welding factor can be freely combined into multiple parameter groups within the threshold range (see Figure 11 ), realize the parameter group coverage from point to surface.

[0113] The welding parameter group is delineated and the optimal parameters under the current 5M1E (man-machine-material-environmental) conditions are finally determined within the qualified area. Specifically, multiple groups of parameters within the threshold range are selected for welding. After welding is completed, the welding samples are as follows: Figure 12 High-frame video recording of the welding process was conducted for analysis: almost no spatter occurred during the welding process, and the movement of the molten pool remained stable during the welding process;

[0114] After welding, the samples were subjected to welding peeling force test. Shear force test was carried out by 180 degree tensile test. 19 groups of samples were tested using standard tensile testing machine. The maximum tensile force when the peeling process broke was recorded. All the 30mm weld tensile test results were qualified (see Figure 12 .The tensile strength values ​​are all above 6037N), and the metallographic test results are all qualified (see Figure 13 , the penetration depth is above 0.532cm, Figure 14 , weld width is above 2.020cm), process capability level ≥1.33, predicted mass production welding first pass rate ≥99.97%, target achieved.

[0115] Comparative Example:

[0116] S1-S4 of the above-mentioned embodiment 1 or embodiment 2 can be adopted; the difference from embodiment 1 is that the verification parameter is a single factor change, and the single factor change means that in step S5, the power and speed of embodiment 1 change synchronously, and this embodiment refers to only a single factor change, such as finding the optimal power when the speed, defocus amount, and amplitude are unchanged; finding the optimal speed when the power, defocus amount, and amplitude are unchanged; this test process has a large workload and is easy to miss the optimal parameter group, and the final result of the verification is a set of parameters, which has weak ability to cope with fluctuations in production factors in mass production.

[0117] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A laser welding verification method, characterized in that: The following steps are involved: S1: Clean the welding area surfaces of the end plate specimen and the side plate specimen; S2: Pressing by welding tooling; S3: Set the forward rotation mode in the laser trajectory software and perform the first round of welding on the end plate specimen and the side plate specimen; S4: Determine the welding significant factor type of the welding specimen; select the welding significant factors from the welds completed in the first round of welding; S5: Determine the threshold range of each significant welding factor and statistically define the welding parameter group range; The upper and lower limit values ​​of the significant welding factors are preset respectively. After the second round of welding is completed, the actual upper and lower limit values ​​of the main welding factors are determined through appearance, metallographic and tensile tests to find the threshold range; the parameter group range values ​​of each significant welding factor are counted.

2. A laser welding verification method according to claim 1, characterized in that: The steps for cleaning the welding area surface of the end plate specimen and the side plate specimen are as follows: before welding begins, the surfaces of the end plate specimen and the side plate specimen need to be magnetically polished or mechanically cleaned or repeatedly wiped with a dust-free cloth, and the surface flatness of the end plate specimen and the side plate specimen is 0.4~0.8μm / 100mm.

3. The laser welding verification method according to claim 1, characterized in that: The welding fixture includes a base, a slide rail, a clamping block, and a quick-clamp wrench; a welding mounting frame is provided on one side of the base, and a cross-shaped positioning groove is provided on the vertical surface of the welding mounting frame, and the end plate test piece and the side plate test piece are overlapped in the positioning groove; The horizontal surface of the base is connected to the slide rail, the bottom of the pressing block is slidably connected to the slide rail, and the vertical end of the pressing block has a penetrating light hole, through which the laser passes to act on the side plate test piece and the end plate test piece; The side of the pressing block close to the welding mounting frame is connected to the tooling pressure head, the top of the tooling pressure head is connected to the protective gas inlet valve, and an air outlet is arranged in the tooling pressure head.

4. A laser welding verification method according to claim 3, characterized in that: In step S3, before welding begins, the shielding gas is introduced from the internal air passage of the tooling pressure head and blown out from the air outlet with a flow rate of 15L / min~20L / min. The shielding gas is a mixture of one or more inert gases, and the purity of the shielding gas is greater than or equal to 99.99%.

5. The laser welding verification method according to claim 1, characterized in that: During welding, the laser motion trajectory adopts the positive rotation mode, the positive rotation density is 1 / mm~3 / mm, and the amplitude is 0.6~1.3mm.

6. A laser welding verification method according to claim 1, characterized in that: In step S4 , the significant factor types include at least two of power, speed, spacing, defocus amount, and amplitude.

7. The laser welding verification method according to claim 1, characterized in that: In step S4, upper and lower limit values ​​are preset for the significant welding factors respectively, and the combination parameter group with the maximum laser energy density and the minimum laser energy array is found. Experiments are carried out respectively, and the parameter level threshold is adjusted through weld appearance scoring, metallographic testing and tensile strength testing. After determining the actual upper and lower limit values ​​of each parameter, the welding parameter group is delineated.

8. The laser welding verification method according to claim 1, characterized in that: The power variation of the laser welding process in steps S3 and S5 is: The first section: from 0% to 8-12% of the welding path, the laser power is reduced from the set value AW to BW; The second section: from 8-12% to 75-85% of the welding path, the laser power is set to BW; The third stage: from 75-85% to 97-99% of the welding path, the laser power is gradually reduced from the set value of BW to CW; The fourth stage: from 97-99% to 100% of the welding path, the laser power is reduced from the set value of CW to 0W; The processes of power increase and power decrease are both linear changes.

9. The laser welding verification method according to claim 1, characterized in that: In steps S3 and S5, the laser movement speed is greater than or equal to 500 mm / s, and the defocus amount is -2 mm to +2 mm; Laser wavelength: 500μm~1200μm; The laser output modes include continuous and continuous; The laser output energy distribution includes one of Gaussian distribution, annular distribution or Gaussian plus annular distribution. If Gaussian plus annular distribution is used, the Gaussian light intensity accounts for 60% to 95% of the total light intensity, and the annular light intensity accounts for 5% to 40% of the total light intensity.

10. The laser welding verification method according to claim 1, characterized in that: The welding laser is a fiber laser or a composite laser; The welding laser is also connected to a galvanometer that oscillates on the X and Y axes. After the galvanometer focuses the laser beam, the beam waist cross-sectional area is less than or equal to 0.03 mm².

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