Laser welding method based on waveform modulation

Abstract

The invention discloses a laser welding method based on waveform modulation, which comprises the following steps: step 1, pretreating the surface of a to-be-welded test plate to obtain a high-reflectivity to-be-welded test plate; and 2, performing power-modulated laser penetration fusion welding on the to-be-welded test plate made of the high-reflectivity material. According to the method, the optimized modulation process parameters capable of improving the heat efficiency and the stability in the welding process can be rapidly obtained for high-reflectivity materials with different reflectivity for infrared laser; according to the method, more accurate and efficient process guidance is provided for laser welding of high-reflectivity materials, and technical progress and industrial upgrading in related fields are promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of welding and relates to a laser welding method based on waveform modulation. Background Art

[0002] With the development of industrial technology, lightweight and high-strength metal materials such as magnesium alloys, aluminum alloys and copper alloys are increasingly used in aerospace, transportation, construction and electronics. These materials play an important role in structural lightweight design due to their excellent physical and mechanical properties. However, a major challenge encountered by these high-reflectivity materials during laser welding is their high reflectivity to the laser, which leads to the loss of laser energy, thus affecting the welding efficiency and weld quality.

[0003] When traditional laser welding technology is directly applied to high-reflectivity materials, a large amount of laser energy is reflected due to the high reflectivity of the material surface and cannot be effectively used in the welding process, resulting in low thermal efficiency. In addition, the energy loss caused by high reflectivity will also lead to unstable heat input during welding, thereby affecting the forming quality of the weld and the stability of the welding process. This instability often manifests itself as defects such as irregular weld shape, insufficient penetration, pores and spatter.

[0004] Although some studies have used power modulation technology to improve the laser welding process of high-reflectivity materials, these studies often lack a systematic analysis of the relationship between modulation parameters and material reflectivity. In current technology, there is no method that can clearly link the optimized power modulation parameters with the reflectivity of the material to achieve a simultaneous improvement in welding thermal efficiency and stability. Therefore, in practical applications, engineers often need to find the right welding parameters through a lot of trial and error, which is not only inefficient but also increases production costs.

[0005] To overcome these limitations, it is necessary to develop a new laser welding method to quickly determine the optimized power modulation parameters for high-reflectivity materials with different reflectivity to improve welding thermal efficiency and stability. Summary of the invention

[0006] In order to overcome the above problems, the present invention proposes a laser welding method based on waveform modulation. The method comprises: step 1, pre-treating the surface of the test plate to be welded to obtain a high reflectivity test plate to be welded; step 2, performing power-modulated laser deep penetration welding on the high reflectivity test plate to be welded. The method can quickly obtain optimized modulation process parameters that can improve the thermal efficiency and stability of the welding process for high reflectivity materials with different reflectivities to infrared lasers; the method provides more accurate and efficient process guidance for laser welding of high reflectivity materials, which helps to promote technological progress and industrial upgrading in related fields, thereby completing the present invention.

[0007] Specifically, the object of the present invention is to provide a laser welding method, the method comprising: Step 1, pre-treating the surface of the test plate to be welded to obtain a test plate to be welded with high reflectivity; Step 2: Perform power-modulated laser deep penetration welding on the high-reflectivity test plate to be welded.

[0008] In step 1, the pretreatment includes: removing oxides and impurities on the surface of the test plate to be welded.

[0009] In step 1, the material of the test plate to be welded is aluminum, aluminum alloy, magnesium, magnesium alloy, copper or copper alloy.

[0010] In step 1, the thickness of the test plate to be welded is ≥ 1 mm.

[0011] In step 1, the test plate to be welded has a reflectivity of more than 75% to an infrared laser with a wavelength of about 1 micron.

[0012] In step 2, the parameters of power modulation include modulation frequency, modulation amplitude and average power.

[0013] Among them, the modulation frequency satisfies: 100 Hz≤F≤700Hz, and F is the modulation frequency.

[0014] Among them, the modulation amplitude satisfies: 1 / 5≤A / P A ≤2 / 3, P A is the average power and A is the modulation amplitude.

[0015] In step 2, the welding speed is 0.1~10 m / min.

[0016] In step 2, the defocus amount is -5mm~5mm.

[0017] The present invention has the following beneficial effects: The laser welding method provided by the present invention clarifies the parameters of power modulation that can improve the thermal efficiency and stability of welding, establishes the relationship between the parameters of power modulation and the reflectivity of the material to be welded to the laser, provides a simple and convenient process selection for the actual operation of waveform modulated laser welding, avoids multiple trial and error tests of laser welding of different high reflectivity materials, and achieves the simultaneous improvement of the thermal efficiency and stability of the laser welding process of high reflectivity materials. It can be widely used in industrial production, is simple and convenient to operate, and has low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only used for the purpose of illustrating the preferred embodiments and are not considered to be limitations of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work.

[0019] In the attached picture: Figure 1 (a) shows a schematic diagram of the instantaneous power of an unmodulated laser; FIG1( b ) shows a schematic diagram of the instantaneous power variation waveform of a sinusoidally modulated laser; FIG2( a ) shows the top surface morphology of the weld in Comparative Example 1; FIG2( b ) shows the top surface morphology of the weld in Example 1; FIG3( a ) shows a metallographic image of a cross section of a weld in Comparative Example 1; FIG3( b ) shows a metallographic image of a cross section of a weld in Example 1; FIG4( a ) shows the top surface morphology of the weld in Comparative Example 2; FIG4( b ) shows the topography of the lower surface of the weld in Comparative Example 2; FIG5( a ) shows the top surface morphology of the weld in Example 2; FIG5( b ) shows the topography of the lower surface of the weld in Example 2; FIG6( a ) shows a metallographic image of a cross section of a weld in Comparative Example 3; FIG6( b ) shows a metallographic image of a cross section of a weld in Comparative Example 4; FIG7( a ) shows a metallographic image of a cross section of a weld in Comparative Example 5; FIG7( b ) shows a metallographic image of a cross section of a weld in Comparative Example 6. DETAILED DESCRIPTION

[0020] The specific embodiments of the present invention will be described in more detail below with reference to Figures 1(a) to 7(b). Although the specific embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0021] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0022] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "rear", etc. indicate positions or positional relationships based on the working state of the present invention, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying 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 limiting the present invention. In addition, the terms "first", "second", "third", and "fourth" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0023] To facilitate understanding of the embodiments of the present invention, further explanation will be given below by taking specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0024] According to a laser welding method based on waveform modulation provided by the present invention, the method comprises: Step 1, pre-treating the surface of the test plate to be welded to obtain a test plate to be welded with high reflectivity; Step 2: Perform power-modulated laser deep penetration welding on the high-reflectivity test plate to be welded.

[0025] The laser welding method based on waveform modulation is described in detail below.

[0026] Step 1: pretreat the surface of the test plate to be welded to obtain a test plate to be welded with high reflectivity.

[0027] In step 1, the pretreatment includes: removing oxides and impurities on the surface of the test plate to be welded. Preferably, the oxides and impurities on the surface of the test plate to be welded are removed by sandpaper grinding, and then rinsed in an organic solvent such as acetone.

[0028] Among them, removing oxides and impurities on the surface of the test plate to be welded helps to improve the absorption rate of the laser.

[0029] In step 1, the material of the test plate to be welded is aluminum, aluminum alloy, magnesium alloy, copper or copper alloy.

[0030] Among them, magnesium and magnesium alloys have the characteristics of low density, high specific strength and specific stiffness, excellent damping and thermal conductivity, and are widely used in metallurgy, building materials, aerospace and other fields; aluminum alloys have high specific strength and specific stiffness, good corrosion resistance, processing performance and mechanical properties, and have become an indispensable metal material for lightweight structural manufacturing in aerospace, shipbuilding and other transportation fields; copper alloys have excellent electrical conductivity, thermal conductivity, corrosion resistance and ductility, and are widely used in petrochemical, shipbuilding and power systems.

[0031] In step 1, the thickness of the test plate to be welded is ≥ 1 mm, preferably 1 to 10 mm.

[0032] Among other things, a certain thickness ensures effective deep penetration welding.

[0033] In step 1, the test plate to be welded has a reflectivity of more than 75% to an infrared laser with a wavelength of about 1 micron, that is, the reflectivity of the high-reflectivity test plate to be welded to the laser is not less than 75%.

[0034] Step 2: Perform power-modulated laser deep penetration welding on the high-reflectivity test plate to be welded.

[0035] In step 2, the parameters of power modulation include modulation frequency, modulation amplitude and average power.

[0036] Furthermore, the modulation frequency satisfies: 100 Hz≤F≤700 Hz, where F is the modulation frequency.

[0037] Furthermore, the modulation amplitude satisfies: 1 / 5≤A / P A ≤2 / 3, P A is the average power and A is the modulation amplitude.

[0038] Furthermore, the average power satisfies: P A <P0<P A +A, P0 is the critical laser power required for laser welding of the plate to be welded to form a certain penetration depth d, P A is the average power and A is the modulation amplitude.

[0039] The inventors have found that when the above modulation frequency, modulation amplitude and power changes are met, the thermal efficiency and stability of laser welding of high-reflectivity test plates to be welded can be improved.

[0040] In step 2, in order to obtain a penetration depth not less than that of unmodulated laser welding, the average power P A , the modulation amplitude A and the reflectivity α of the material to be welded to the laser satisfy: ; And the modulation frequency F, modulation amplitude A and the reflectivity α of the material to be welded to the laser satisfy:

[0041] In step 2, the input of laser energy is controlled by adopting appropriate power modulation to reduce reflection loss, improve thermal efficiency, increase penetration depth, and reduce defects such as spatter and pores; since the high-reflectivity test plate to be welded is prone to aggravate the imbalance of laser energy distribution in the hole depth direction when the reflectivity is large, the volume of the lower part of the small hole is excessively expanded, which leads to unstable laser welding small holes and molten pools and poor welding quality. The inventors obtain a penetration depth not lower than that of unmodulated laser welding by establishing a relationship between the parameters of power modulation and the reflectivity α of the material to be welded to the laser; the relationship between the above-mentioned power modulation parameters and the reflectivity α of the laser realizes the simultaneous improvement of thermal efficiency and stability during laser welding of reflective plates, and can quickly obtain optimized modulation process parameters for improving thermal efficiency and stability of the welding process for materials with different reflectivities.

[0042] In step 2, the welding speed is 0.1-10 m / min, preferably 1-8 m / min, and more preferably 1-4 m / min.

[0043] Among them, too slow welding speed may cause excessive melting and affect the quality of the weld; the faster the welding speed, the shorter the laser irradiation time on the high reflectivity test plate to be welded, and the higher the power density, but too fast welding speed may lead to insufficient penetration. The above welding speed can obtain materials with excellent weld quality.

[0044] In step 2, the defocus amount is -5 mm to 5 mm, preferably 0 to 5 mm, and more preferably 0 to 2 mm.

[0045] The smaller the defocus, the more focused the laser beam, the higher the energy density, and the greater the possible melting depth, but it will also lead to excessive melting; on the contrary, the larger the defocus, the more dispersed the laser beam, the lower the energy density, and the insufficient melting depth. The above defocus is more appropriate.

[0046] In step 2, the modulation waveform can be a sine wave or a triangle wave. These waveforms can provide stable power changes and help improve the stability of the welding process.

[0047] In step 2, since the absorption rate of infrared laser on the high reflectivity test plate to be welded is relatively low, it is preferred to perform power-modulated laser deep penetration welding on the high reflectivity test plate to be welded by using an infrared laser source.

[0048] The present invention is further described below through specific examples, but these examples are merely exemplary and do not constitute any limitation to the scope of protection of the present invention.

[0049] Example 1

[0050] Take a 100mm×30mm×8mm AZ31 magnesium alloy test plate with a reflectivity of about 85% (α=0.85). Use sandpaper to remove the oxide film and oil on the surface of the test plate to expose the fresh metal. Use acetone to clean the surface to be welded and the butt surface of the test plate. Then fix and clamp it on the workbench. Use a modulation frequency F of 100Hz, a modulation amplitude A of 1150W, and an average power P A The power of the welding machine was 2100 W, and a sine wave as shown in Figure 1 (b) was used. The welding speed was 4 m / min, and the defocus was 2 mm (at this welding speed and defocus, the critical laser power P0 required for laser welding to form a penetration of d=1.5Dc was 2400 W). The upper surface morphology of the weld formed at the end of welding is shown in Figure 2 (b), and the metallographic image of the weld cross section is shown in Figure 3 (b).

[0051] Example 2

[0052] Take a 100mm×30mm×1.5mm T2 copper test plate with a reflectivity of about 98% (α=0.98). Use sandpaper to remove the oxide film and oil on the surface of the test plate to expose the fresh metal. Use acetone to clean the surface to be welded and the butt joint surface of the test plate. Then fix and clamp it on the workbench. Use a modulation frequency F of 100Hz, a modulation amplitude A of 1500W, and an average power P A The power source is 2500 W, a sine wave as shown in FIG1 (b) is used, the welding speed is 1 m / min, and the defocus is 0 mm (the weld in this embodiment is a full penetration weld, so the penetration depth d is the plate thickness, i.e., 1.5 mm. At this welding speed and defocus, the critical laser power P0 required for laser welding to form a penetration depth of d=1.5 mm is 2600 W). The upper surface morphology of the weld formed at the end of welding is shown in FIG5 (a), and the lower surface morphology is shown in FIG5 (b).

[0053] Comparative Example 1 A 100mm×30mm×8mm AZ31 magnesium alloy test plate with a reflectivity of about 85% (α=0.85) was taken. The oxide film and oil stains on the surface of the test plate were removed by sandpaper grinding to expose the fresh metal. The surface to be welded and the butt surface of the test plate were cleaned with acetone. Then, it was fixed and clamped on the workbench. The normal power shown in Figure 1 (a) was used for unmodulated welding. The normal power was 2100 W, the welding speed was 4 m / min, and the defocus was 2 mm. The surface morphology of the weld formed at the end of welding is shown in Figure 2 (a), and the metallographic image of the weld cross section is shown in Figure 3 (a).

[0054] From Figures 3 (a) and 3 (b), we can see the weld penetration depths obtained in Comparative Example 1 and Example 1, respectively. By analyzing Figures 2 (a) and 2 (b), Figures 3 (a) and 3 (b), we can find that: 1) the weld surface formation of the power modulated laser welding in Example 1 is smoother and more uniform than the weld of the non-modulated welding in Comparative Example 1, indicating that the stability of the welding process in Example 1 is improved; 2) the cross-sectional penetration depth of the weld by the power modulated laser welding in Example 1 is about 1.5 times that of the non-modulated weld cross-sectional penetration depth in Comparative Example 1, and the thermal efficiency of the welding process is significantly improved. The weld penetration depth is significantly improved by power modulation under the parameters.

[0055] Comparative Example 2 A 100 mm × 30 mm × 1.5 mm T2 copper test plate with a reflectivity of about 98% (α = 0.98) was taken. The oxide film and oil stains on the surface of the test plate were removed by sandpaper grinding to expose fresh metal. The surface to be welded and the butt surface of the test plate were cleaned with acetone. Then, it was fixed and clamped on the workbench. The normal power shown in Figure 1 (a) was used for unmodulated welding. The normal power was 2500 W, the welding speed was 1 m / min, and the defocus was 0 mm. The upper surface morphology of the weld formed at the end of welding is shown in Figure 4 (a), and the lower surface morphology is shown in Figure 4 (b).

[0056] By analyzing Figures 4 (a), 4 (b), 5 (a) and 5 (b), we can see that: 1) In the unmodulated laser welding of Comparative Example 2, the 1.5 mm thick copper plate cannot be welded with a deep penetration at a laser power of 2.5 kW, and only a very shallow molten layer is formed on the surface of the sample. 2) In the modulated laser welding of Example 2, a full penetration weld is obtained at a modulation frequency of 300 Hz under an average power of 2.5 kW and a modulation amplitude of 500 W. There are no holes or weld nodules caused by spatter in the weld, and the quality of weld formation is significantly improved, indicating that the weld penetration can be significantly improved by power modulation under the parameters in Example 2.

[0057] Comparative Example 3 A 100 mm × 30 mm × 8 mm AZ31 magnesium alloy test plate with a reflectivity of about 85% (α = 0.85) was taken. The oxide film and oil stains on the surface of the test plate were removed by sandpaper grinding to expose fresh metal. The surface to be welded and the butt surface of the test plate were cleaned with acetone. Then, it was fixed and clamped on the workbench. The normal power shown in Figure 1 (a) was used for unmodulated welding. The normal power was 2400 W, the welding speed was 4 m / min, and the defocus was 2 mm. The metallographic image of the cross-section of the weld is shown in Figure 6 (a), and the penetration depth is about 4.8 mm.

[0058] Comparative Example 4 Take a 100mm×30mm×8mm AZ31 magnesium alloy test plate with a reflectivity of about 85% (α=0.85). Use sandpaper to remove the oxide film and oil on the surface of the test plate to expose the fresh metal. Use acetone to clean the surface to be welded and the butt surface of the test plate. Then fix and clamp it on the workbench. Use a modulation frequency F of 1000Hz, a modulation amplitude A of 450W, and an average power P A The power is 2400 W, a sine wave as shown in Figure 1 (b) is used, the welding speed is 4 m / min, the defocus is 2 mm, and the metallographic image of the weld cross section is shown in Figure 6 (b), with a penetration depth of about 3.3 mm.

[0059] From Figure 6 (a) and Figure 6 (b), we can see that when the modulation amplitude A is less than the average power P A When the modulation frequency F is 1000 Hz, the cross-sectional penetration depth of the weld of AZ31 magnesium alloy laser welding in Example 4 after power modulation is less than the cross-sectional penetration depth of the weld in Example 3 without laser modulation. Under this parameter, the weld penetration depth cannot be increased by power modulation.

[0060] Comparative Example 5 A 100 mm × 30 mm × 8 mm AZ31 magnesium alloy test plate with a reflectivity of about 85% was taken. The oxide film and oil stains on the surface of the test plate were removed by sandpaper grinding to expose fresh metal. The surface to be welded and the butt surface of the test plate were cleaned with acetone. Then, it was fixed and clamped on the workbench. The normal power shown in Figure 1 (a) was used for unmodulated welding. The normal power was 2100 W, the welding speed was 8 m / min, and the defocus was 0 mm. The metallographic image of the cross-section of the weld was shown in Figure 7 (a), and the penetration depth was about 3.25 mm.

[0061] Comparative Example 6 Take a 100mm×30mm×8mm AZ31 magnesium alloy test plate with a reflectivity of about 85%. Use sandpaper to remove the oxide film and oil on the surface of the test plate to expose the fresh metal. Use acetone to clean the surface to be welded and the butt surface of the test plate. Then fix and clamp it on the workbench. Use a modulation frequency of 700Hz, a modulation amplitude of 450W, and an average power of P A The critical laser power P0 required for laser welding to form a penetration depth of d = 2.8 mm is 2100 W (at this welding speed and defocus, the critical laser power P0 required for laser welding to form a penetration depth of d = 2.8 mm is 1500 W). A sine wave as shown in Figure 1 (b) is used, the welding speed is 8 m / min, the defocus is 0 mm, and the metallographic image of the cross-section of the weld is shown in Figure 7 (b), with a penetration depth of about 2.8 mm.

[0062] By analyzing Figure 7 (a) and Figure 7 (b), we can find that: modulation amplitude A, modulation frequency F, average power P AAlthough the parameter conditions of power modulation are met, the average power P is not met. A , the relationship between the modulation amplitude A and the reflectivity α of the material to be welded to the laser, as well as the relationship between the modulation frequency F, the modulation amplitude A and the reflectivity α of the material to be welded to the laser. After power modulation in Example 6, the cross-sectional penetration depth of the weld of AZ31 magnesium alloy laser welding is still less than the cross-sectional penetration depth of the weld of the unmodulated laser welding in Example 5. Under this parameter, the weld penetration depth cannot be increased by power modulation, that is, the unoptimized modulation parameters not only cannot increase the penetration depth, but will lead to a decrease in the penetration depth, and a concave defect will be formed on the weld surface.

[0063] The present invention is described in detail above in combination with preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are only illustrative explanations of the present invention and do not constitute any limitation on the protection scope of the present invention. Without exceeding the spirit and protection scope of the present invention, various improvements, equivalent substitutions or modifications may be made to the technical content of the present invention and its embodiments, which all fall within the protection scope of the present invention. The protection scope of the present invention shall be subject to the attached claims.

Claims

1. A laser welding method, characterized in that: The method comprises: Step 1, pre-treating the surface of the test plate to be welded to obtain a test plate to be welded with high reflectivity; Step 2: Perform power-modulated laser deep penetration welding on the high-reflectivity test plate to be welded.

2. The method according to claim 1, characterized in that Preferably, in step 1, the pretreatment includes: removing oxides and impurities on the surface of the test plate to be welded.

3. The method according to claim 1, characterized in that In step 1, the material of the test plate to be welded is aluminum, aluminum alloy, magnesium, magnesium alloy, copper or copper alloy.

4. The method according to claim 1, characterized in that In step 1, the thickness of the test plate to be welded is ≥ 1 mm.

5. The method according to claim 1, characterized in that In step 1, the test plate to be welded has a reflectivity of more than 75% to an infrared laser with a wavelength of about 1 micron.

6. The method according to claim 1, characterized in that In step 2, the parameters of power modulation include modulation frequency, modulation amplitude and average power.

7. The method according to claim 6, characterized in that The modulation frequency satisfies: 100 Hz≤F≤700Hz, where F is the modulation frequency.

8. The method according to claim 6, characterized in that Modulation amplitude satisfies: 1 / 5≤A / P A ≤2 / 3, P A is the average power and A is the modulation amplitude.

9. The method according to claim 1, characterized in that In step 2, the welding speed is 0.1~10 m / min.

10. The method according to claim 1, characterized in that In step 2, the defocus amount is -5mm~5mm.

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