An axial point-ring multi-focus laser welding method

Abstract

The present invention discloses an axial point-ring multi-focus laser welding method, belonging to the technical field of laser welding. Compared with the situation in traditional welding methods where the focal plane of the central beam, the focal plane of the ring beam, and the beam combining plane of the point-ring laser beam usually coincide, in the present invention, the point-ring laser beam is coupled by a central beam with a waist-shaped distribution and a ring beam with an inverted conical distribution, and the focal plane of the central beam of the point-ring laser beam after being shaped by an optical element is located below the focal plane of the ring beam, and the central beam spot and the ring beam spot overlap at the beam combining plane below the focal plane of the central beam. In this way, the penetration depth is maintained by the beam combining plane spot, the central spot at the focal plane of the central beam penetrates the small hole and bubbles during collapse, the outer ring spot supports the middle of the small hole, and the ring spot at the focal plane of the ring beam maintains the opening of the small hole, which can effectively reduce the collapse frequency of the high-power laser welding small hole, stabilize the welding process, and suppress the weld porosity defect.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser welding, and more specifically, relates to an axial point-ring multi-focus laser welding method. Background Art

[0002] Thick-walled components of light alloys such as aluminum alloys, magnesium alloys, and titanium alloys have the advantages of low density, high specific strength, and good corrosion resistance, and are widely used in the fields of rail transit, aerospace, shipbuilding, and marine engineering. Compared with traditional arc welding and electron beam welding methods, laser beam welding has the advantages of high energy density, narrow fusion width, small heat affected zone, high welding efficiency, and less requirements for the welding environment, providing an effective means for welding thick-walled components of light alloys. During the high-power welding of thick light alloy plates, the laser beam acts on the workpiece surface to generate a huge vapor recoil pressure, forming an elongated small hole. Due to the physical properties of the light alloy plate itself, welding process instability, and the influence of plate thickness, the weld porosity defect is serious, significantly reducing the mechanical properties of the welded joint. Therefore, developing appropriate welding processes, suppressing weld porosity defects, and improving the mechanical properties of joints are key issues that need to be solved urgently.

[0003] In response to the above problems, existing research has shown that by using the laser stirring welding process, through the rapid stirring of the molten pool, the generated bubbles are stirred below the small hole, realizing the remelting of the small hole and the bubbles, thereby reducing the porosity defect in the weld. However, this method does not solve the generation of bubbles at the source, and moreover, due to the dispersion of energy, a greater energy heat input is required to form a small hole, which will also cause the weld to deviate. Some scholars have also adopted the adjustable annular beam welding process to stabilize the small hole by keeping the opening time of the small hole open. However, such research is mostly used to solve the spatter and porosity problems of light alloy thin plates or stainless steel thick plates, and has not been applied to solve the frequent occurrence of porosity defects caused by the instability of small holes in the laser welding of thick light alloy plates. Summary of the Invention

[0004] In view of the defects and improvement requirements of the prior art, the present invention provides an axial point-ring multi-focus laser welding method, aiming to solve the technical problem of serious weld porosity defects caused by the instability of small holes during the high-power laser welding of thick light alloy plates.

[0005] To achieve the above object, the present invention provides an axial point-ring multi-focus laser welding method, including:

[0006] The dot-ring laser beam emitted by the laser is subjected to multi-focus laser shaping through optical elements, so that the focal plane of the central beam of the shaped dot-ring laser beam is located below the focal plane of the ring beam, and the spot of the central beam overlaps with the spot of the ring beam at the beam combination surface below the focal plane of the central beam; wherein, the dot-ring laser beam is coupled by a central beam with a waist-shaped distribution and a ring beam with an inverted conical distribution; the distance between the focal plane of the ring beam and the beam combination surface is less than the penetration depth.

[0007] The shaped laser beam is used for welding.

[0008] Further, during the welding process, when the central beam acts on the workpiece to be welded, a small hole is generated. The central spot of the focal plane of the central beam melts and bridges the molten metal layer to penetrate the small hole and the bubble when it collapses. The outer ring spot supports the middle part of the small hole, the ring spot of the focal plane of the ring beam maintains the opening of the small hole, and the spot of the beam combination surface maintains the penetration depth.

[0009] Further, with the focal plane of the ring beam as the reference plane, zero defocus setting is performed.

[0010] Further, multi-focus laser shaping is performed through an aspherical mirror.

[0011] Further, the energies of both the central beam and the ring beam are Gaussian distributed.

[0012] Further, before welding, the surface of the workpiece to be welded is polished to remove the oxide layer, and the polished workpiece to be welded is wiped to remove oil stains and surface residues; the workpiece to be welded is fixed on the welding platform, and the welding head is deflected counterclockwise to form an angle of 0° to 15° with the vertical direction of the welding plane, and the welding path is set.

[0013] Further, welding is performed in a surfacing form, and 99.99% argon is used as the welding protection gas.

[0014] Generally speaking, through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0015] Compared with the situation where the focal plane of the central beam, the focal plane of the ring beam, and the beam combination surface of the dot-ring laser beam usually coincide in the traditional welding method, in the present invention, the dot-ring laser beam is coupled by a central beam with a waist-shaped distribution and a ring beam with an inverted conical distribution, and the focal plane of the central beam of the dot-ring laser beam shaped by optical elements is located below the focal plane of the ring beam, and the spot of the central beam overlaps with the spot of the ring beam at the beam combination surface below the focal plane of the central beam. In this way, the penetration depth is maintained by the spot of the beam combination surface, the central spot of the focal plane of the central beam penetrates the small hole and the bubble when it collapses, the outer ring spot supports the middle part of the small hole, and the ring spot of the focal plane of the ring beam maintains the opening of the small hole, which can effectively reduce the collapse frequency of the high-power laser welding small hole, stabilize the welding process, and suppress the weld porosity defect. Brief Description of the Drawings

[0016] Figure 1 Schematically shows a schematic diagram of the laser optical path setting;

[0017] Figure 2 Schematically shows a schematic diagram of the axial spatial energy distribution of the dot-ring multi-focus;

[0018] Figure 3 Schematically shows a normalized diagram of the energy distribution of three special planes;

[0019] Figure 4 Schematically shows a schematic diagram of the focus - small hole - molten pool - workpiece during the high-power laser welding process of the dot-ring multi-focus;

[0020] Figure 5 Schematically shows a schematic diagram of the bridging molten metal layer between the small hole and the bubble on the central focal plane when the small hole collapses during the welding process. Detailed Embodiments

[0021] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] In the present invention, terms such as "first", "second", etc. (if any) in the present invention and the drawings are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence.

[0023] The present invention obtains a multi-focus beam with an axial distribution through optical element shaping. The laser optical path setting is shown in Figure 1 as shown, and the spatial energy distribution is shown in Figure 2 as shown in (a) therein. It is composed of a central beam with a waist-shaped Gaussian distribution (which can also be called a dot beam) and an outer ring beam with an inverted conical Gaussian distribution. The energy distribution of the two beams is central energy: outer ring energy = 6:4. The focal plane of the central beam is 3 mm below the focal plane of the outer ring beam. The light spots of the two beams overlap at the beam combination plane 3 mm below the focal plane of the central beam and converge into a light spot, and the energy distribution is Gaussian. The molten depth is maintained through the light spot at the beam combination plane. The central light spot at the focal plane of the central beam penetrates the small hole and the bubble when the small hole collapses. The outer ring light spot supports the middle part of the small hole, and the ring light spot at the focal plane of the ring beam maintains the opening of the small hole, which can effectively reduce the collapse frequency of the high-power laser welding small hole, stabilize the welding process, and suppress the weld porosity defect. At present, there are few reports on lasers with such a spatial distribution obtained through beam shaping, and the welding process and its optimization scheme are still blank.

[0024] In this embodiment, aluminum alloy is taken as an example, and its process plan is as follows:

[0025] Use a 2024 aluminum alloy plate with a length of 200 mm, a width of 100 mm, and a thickness of 8 mm as the welding base material; before welding, gently polish the surface of the aluminum alloy plate with a grinding machine to remove the oxide layer, and wipe the polished aluminum alloy plate with alcohol to remove oil stains, surface residues, etc.; fix the plate to be welded on the welding platform with a fixture, deflect the welding head counterclockwise to form an angle of 10° with the perpendicular direction of the welding plane, and set the welding path. The YMM-10000 fiber laser is subjected to multi-focus laser shaping through an aspherical mirror. The fiber core diameter is 100 μm, the central wavelength is 1080 ± 10 nm, the beam divergence angle is 0.1 rad, and the maximum power of the laser is 10000 W.

[0026] Use the beam after laser shaping for welding. The total power of laser welding is 9000 W, the power of the central beam is 5400 W, and the power of the ring beam is 3600 W. At the focal plane of the ring beam, the spot radius of the central beam is 0.15 mm, the inner diameter of the ring beam spot is 0.265 mm, and the outer diameter is 0.435 mm; at the focal plane of the central beam, the spot radius of the central beam is 0.085 mm, and the total spot radius is 0.27 mm; at the beam combination surface, the total spot radius is 0.24 mm.

[0027] Taking the focal plane of the ring beam as the reference plane, perform zero defocus setting, then the spot of the central beam shows a negative defocus effect; perform welding in a surfacing form, and the welding speed is 60 mm / s; the welding shielding gas uses 99.99% pure argon, and its flow rate is 25 L / min. The diameter of the shielding gas pipe is 30 mm, ensuring that the pipe area is significantly larger than the molten pool area to achieve good protection for the molten pool.

[0028] After welding is completed, use X-rays to test the pore distribution of the weld.

[0029] When welding with the shaped laser beam used in the present invention, multiple process parameters can be changed. The process parameters mentioned in this embodiment are only one of them, and the process parameters can be selected according to the welding effect to be achieved. At the same time, it should be noted that when it is clear in the present invention that the focal plane of the central beam of the shaped point-ring laser beam is located below the focal plane of the ring beam, and the spot of the central beam overlaps with the spot of the ring beam at the beam combination surface below the focal plane of the central beam, it is not difficult for those skilled in the optical field to implement how to achieve the above shaping through optical elements. Generally speaking, the process plan conceived by the present invention mainly has the following effects:

[0030] (1) The spatial energy distribution of the dot-ring laser beam adopted in the present invention is extremely special. It has three special positions in the direction perpendicular to the welding surface (i.e., along the beam propagation direction), and these three positions play a decisive role in the dynamic behavior of the keyhole. The first special position is the ring focal plane, where the light spot is a center-ring light spot, as shown in (b) of Figure 2 . The energy density of the ring light spot is larger than that of other positions, and the light spot is larger, as shown in (c) of Figure 2 , acting on the workpiece surface; the second special position is the focal plane of the central beam, where the light spot is a center-ring light spot, and the size of the light spot is smaller than that of the ring focal plane, as shown in (d) of Figure 2 . The energy is more concentrated, and the energy density of the central beam light spot reaches the maximum among all positions, as shown in (e) of Figure 2 ; the third special position is the beam combination plane 3 mm below the focal plane of the central beam, where the light spot is a circular Gaussian light spot formed by the superposition of two beams, as shown in (f) of Figure 2 . Its energy distribution is as shown in (g) of Figure 2 . In order to more intuitively compare the energy distribution sizes of the three planes, they are normalized, as shown in Figure 3 .

[0031] (2) During the welding process, the ring light spot located on the workpiece surface has the functions of melting the surface metal of the workpiece, keeping the keyhole open and preheating the base material, reducing the energy required for the central beam to penetrate the workpiece surface; when the central beam acts on the base material, an elongated keyhole is generated, and the bottom position of the keyhole is greater than the position of the beam combination plane. At this time, the single Gaussian light spot maintains the penetration depth, as shown in Figure 4 . When the energy distribution on the keyhole wall is uneven and necking occurs and then collapses, the center-ring light spot located at the focal plane position of the central beam will quickly melt and bridge the molten metal layer, inhibit the collapse of the keyhole, and its ring beam will further support the keyhole wall at this position, maintain the stability of the keyhole, avoid generating bubbles, and thus reduce the formation of pores in the weld seam, as shown in Figure 5 .

[0032] It is easy for those skilled in the art to understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An axial point-ring multi-focus laser welding method, characterized in that, it includes: Performing multi-focus laser shaping on the point-ring laser beam emitted by the laser through an optical element, so that the focal plane of the central beam of the shaped point-ring laser beam is located below the focal plane of the ring beam, and the spot of the central beam overlaps with the spot of the ring beam at the beam combination surface below the focal plane of the central beam; wherein, the point-ring laser beam is coupled by a central beam with a waist-shaped distribution and a ring beam with an inverted conical distribution; the distance between the focal plane of the ring beam and the beam combination surface is less than the penetration depth; Using the shaped laser beam for welding.

2. The axial point-ring multi-focus laser welding method according to claim 1, characterized in that, During the welding process, when the central beam acts on the workpiece to be welded, a small hole is generated. The central spot of the focal plane of the central beam melts and bridges the molten metal layer to penetrate the small hole and bubbles when collapsing. The outer ring spot supports the middle part of the small hole, the ring spot of the focal plane of the ring beam maintains the opening of the small hole, and the spot of the beam combination surface maintains the penetration depth.

3. The axial point-ring multi-focus laser welding method according to claim 1, characterized in that, Taking the focal plane of the ring beam as the reference plane, zero defocus setting is carried out.

4. The axial point-ring multi-focus laser welding method according to claim 1, characterized in that, Performing multi-focus laser shaping through an aspherical mirror.

5. The axial point-ring multi-focus laser welding method according to claim 1, characterized in that, The energies of both the central beam and the ring beam are Gaussian distributed.

6. The axial point-ring multi-focus laser welding method according to claim 1, characterized in that, Before welding, the surface of the workpiece to be welded is polished to remove the oxide layer, and the polished workpiece to be welded is wiped to remove oil stains and surface residues; the workpiece to be welded is fixed on the welding platform, the welding head is deflected counterclockwise to form an angle of 0° to 15° with the vertical direction of the welding plane, and the welding path is set.

7. The axial point-ring multi-focus laser welding method according to claim 1, characterized in that, Welding is carried out in a surfacing form, and 99.99% argon is used as the welding protection gas.

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