Method and device for laser welding of super-thick stainless steel plates

Abstract

The application provides a stainless steel super-thick plate laser welding method and device, which comprises the following steps: chamfering the end face of the super-thick stainless steel to be welded, the chamfering form is a combination of large blunt edge and U-shaped chamfering, one end of the chamfering is the first base material, and the other end is the second base material; placing the workpiece according to the corresponding welding method, closely butting the first base material and the second base material, and fixing them by a clamp, then cleaning the surface to be welded; adjusting the relative position of the laser beam and the protective gas cover to the base material according to the process required parameters, programming or teaching the welding path; setting the welding process parameters; opening the protective gas valve, starting the welding after waiting for the protective gas to fill the welding area, and carrying out front welding, back welding or front-back face welding. The application can be used for fusion welding of the super-thick stainless steel plate or backing welding of the super-thick plate with deep chamfering and thick blunt edge, can significantly improve the welding efficiency, reduce the welding deformation and reduce the post-welding machining allowance of high-precision products.

Description

Technical Field

[0001] This invention relates to the field of welding manufacturing technology, specifically to a laser welding method and apparatus for ultra-thick stainless steel plates. More particularly, it relates to an ultra-high power laser welding method for ultra-thick stainless steel plates used in nuclear power equipment. Background Technology

[0002] In recent years, human society has faced severe resource shortages, making the development of efficient, clean, safe, and environmentally compatible strategic and sustainable new energy sources an urgent priority. The development and utilization of nuclear fusion energy has sparked a global surge of attention. In the field of nuclear power equipment manufacturing, due to the large size and weight of the equipment, which cannot be integrally formed and must be assembled into multiple sections, numerous thick-plate welding applications are involved, placing stringent requirements on the welding quality and efficiency of the joints. Austenitic stainless steel, with its excellent room-temperature and low-temperature mechanical properties and corrosion resistance, is widely used in the nuclear power field.

[0003] For welding thick stainless steel plates, the current common practice is to use narrow-gap hot-wire TIG welding with multiple layers and passes. This method results in a large number of layers and passes, low welding efficiency, high heat input, large welding thermal deformation, large post-weld machining allowances, and difficulty in controlling dimensional accuracy. To improve welding efficiency and quality, other improved welding methods have been proposed.

[0004] Patent document CN102632330A discloses a submerged arc welding method for ultra-low carbon stainless steel thick plates. By employing high heat input and high interpass temperature, it can maintain sufficient melting within the molten pool, effectively avoiding the occurrence of microcrack defects, thereby obtaining a high-performance weld. This fundamentally breaks the process principles of not allowing preheating and requiring minimum heat input when welding stainless steel. Furthermore, the resulting weld's chemical composition, mechanical properties, internal defects, and resistance to intergranular corrosion all meet technical requirements. However, on the one hand, the use of high heat input leads to excessive heat input and softening of the heat-affected zone of the weld joint, which can easily adversely affect the joint's performance and service life. On the other hand, according to the data published in this invention, the maximum thickness for plate welding is no more than 20mm, which is insufficient to meet the increasing demands of the current manufacturing industry for plate welding thickness.

[0005] Patent document CN114226928A discloses a welding process and apparatus for thick titanium alloy plates, including a vacuum welding box to provide a vacuum environment for welding; a vacuum pump connected to the internal space of the vacuum welding box via a pipeline to extract air from the welding box and form a vacuum environment; a water-cooled argon-backed welding fixture arranged inside the vacuum welding box to support and fix the workpiece for welding; an argon inlet connected to the water-cooled argon-backed welding fixture via a pipeline to supply argon gas; and a cooling circulating water tank connected to the water-cooled argon-backed welding fixture via a pipeline to circulate circulating water for cooling. However, this method still requires a relatively deep bevel on the base material to be welded, a large amount of metal filling, and multiple filler wire weldings to fill the bevel. Furthermore, additional settings are required during the welding process to control the vacuum level of the welding environment and the heat dissipation of the workpiece and equipment, resulting in high welding difficulty and low welding efficiency. In addition, the vacuum welding box mentioned in this invention has limitations on the size of the base material to be welded, making it difficult to adapt to the welding of large-sized workpieces in actual production.

[0006] Patent document CN113732468A discloses a welding method for plates of 60mm and above with different specifications. The method includes pre-welding treatment: cleaning the welding surface using laser cleaning, simultaneously cleaning the area within 40mm of the weld seam, cutting a 45°–60° welding bevel, and preheating the area within 100mm of the weld seam to 200–300℃; welding operation: using a plasma welding machine to weld the root weld without filler wire; after the root weld is completed, gas shielded welding is used with welding parameters of 190–210A, voltage 22–24V, and welding speed of 24–28cm / min. The process involves hammering the weld bead between each weld layer, maintaining a preheating temperature of 200-400℃ if welding is discontinuous; submerged arc welding after gas shielded welding; post-weld treatment, where an infrared heater is used to heat the entire weld seam after completion, raising the temperature to 200-220℃, covering an area of ​​100mm on each side of the weld seam, measuring the temperature 50mm from the weld centerline; insulation cotton for one hour per 30mm of plate thickness after heating, removing the insulation cotton to allow natural cooling when the temperature drops to 150℃; and post-weld inspection. While this invention can weld plates thicker than 60mm, the operation is cumbersome and complex, resulting in excessive workload for welders, and the excessively large weld bevel angle severely impacts welding efficiency.

[0007] In summary, current welding methods for ultra-thick stainless steel plates suffer from low efficiency, shallow penetration depth in a single pass, large thermal deformation, and complex processes, making them unsuitable for the rapid development of nuclear power technology. Furthermore, the literature review indicates that no welding method using ultra-high power lasers for direct, deep-penetration welding of stainless steel thicker than 20mm has been found. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a method and apparatus for laser welding ultra-thick stainless steel plates.

[0009] A laser welding method for ultra-thick stainless steel plates according to the present invention includes:

[0010] Step S1: Perform beveling on the ultra-thick stainless steel end face to be welded. The beveling form is a combination of a large blunt edge and a U-shaped beveling. The beveling forms the dividing line, with one end as the first base material and the other end as the second base material.

[0011] Step S2: Place the workpiece according to the corresponding welding method, and tightly butt the first base material and the second base material together and fix them with a clamp, and then clean the surface to be welded;

[0012] Step S3: Adjust the relative positions of the laser beam and protective gas shield to the base material according to the parameters required by the process, and program or teach the welding path;

[0013] Step S4: Set welding process parameters;

[0014] Step S5: Open the protective gas valve, wait for the protective gas to fill the welding area, and then start welding to perform front welding, back welding, or front and back cover welding.

[0015] Preferably, the U-shaped bevel angle is 0-12 degrees, and the bevel angle on one side is 0-6 degrees;

[0016] The width of the U-shaped bevel is 4-14mm, excluding 14mm;

[0017] The filling depth of the U-shaped bevel is determined by the remaining plate thickness.

[0018] Preferably, the thickness of the ultra-thick stainless steel base material is 30-300 mm;

[0019] For single-sided root pass welding, the blunt edge thickness should be above 12mm; for double-sided root pass welding, the blunt edge thickness should be above 20mm.

[0020] Preferably, when the thickness of the weld plate far exceeds the maximum penetration depth of the ultra-high power laser, ultra-high power ultra-deep penetration welding is selected as the root welding for ultra-thick components, and a shallow groove is opened above the root weld.

[0021] The shallow groove is used to fill the weld metal that expands during the initial welding.

[0022] Preferably, the welding method includes flat welding, horizontal welding, or vertical welding;

[0023] The parameters required for the process include defocusing amount and welding torch angle;

[0024] Welding is performed by tilting the laser beam backward or forward by 5 to 10 degrees, with a laser defocusing amount of -5 to -40 mm.

[0025] The protective gas shield is located behind the laser beam, 4-12 mm away from the laser beam, and 1-12 mm away from the surface of the base material.

[0026] Preferably, the welding process parameters include laser power, welding speed, shielding gas flow rate, whether the laser beam oscillates, oscillation mode, and oscillation parameters;

[0027] The laser power is 20–60 kW, the laser spot diameter is 0.40–0.8 mm, and the welding speed is 0.3–1.6 m / min.

[0028] The oscillation frequency is 50-200Hz, and the oscillation amplitude is 1.0-6.0mm, which stirs the molten pool through oscillation;

[0029] The protective gas is nitrogen, and the gas flow rate is 40-100 L / min.

[0030] Preferably, the protective gas valve is opened, and after the protective gas fills the welding area, welding is started. A high-power laser is projected onto the center of the bevel, and the base material is rapidly melted, evaporated, and vaporized to form a keyhole for deep penetration welding. At the same time, the welding torch moves forward to achieve deep penetration welding on the front or back of the base material.

[0031] The front and back cover welding includes the following steps: before welding, the root pass is cleaned, and then the cover weld is performed using CMT cold metal transfer or laser-CMT composite welding. Similarly, if the remaining filling thickness after the back root is completed can be used to complete the cover weld, then the cover weld can be performed directly; otherwise, filling is required before the cover weld can be performed.

[0032] Preferably, the penetration depths of the two welds overlap within the base material.

[0033] Preferably, if the thickness of the weld plate is within the range of ultra-high power laser deep penetration welding, then the cover plate can be directly welded after deep penetration welding;

[0034] The laser power for cap welding is 0–10000 W; the welding speed is 0.3–1.6 m / min.

[0035] The wire feed speed for CMT cover welding is 4–11 m / min; the shielding gas is a mixture of 98% argon and 2% carbon dioxide, with a gas flow rate of 15–40 L / min.

[0036] Preferably, it includes a first base material, a second base material, and a protective gas shield;

[0037] After beveling the ultra-thick stainless steel end face to be welded, one end is the first base material and the other end is the second base material, with the bevel as the dividing line. The protective gas cover is located behind the laser beam.

[0038] The workpieces are placed according to the corresponding welding method, and the first and second base materials are tightly joined together and fixed with a clamp. Then the surface to be welded is cleaned.

[0039] Adjust the relative positions of the laser beam and protective gas shield to the base material according to the parameters required by the process, and program or teach the welding path.

[0040] According to the set welding process parameters, open the protective gas valve, wait for the protective gas to fill the welding area, and then start welding to perform front welding, back welding, or front and back cover welding.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. This invention uses ultra-high power laser for deep penetration welding, with a single-sided penetration depth ≥20mm and a double-sided penetration depth ≥30mm. It can achieve direct penetration of 40-120mm (single-sided or double-sided), significantly reducing the amount of filler metal in the weld. The welding efficiency is more than 10 times that of the currently mature narrow-gap hot wire TIG welding, the deformation is less than 1 / 5 of that of narrow-gap hot wire TIG multi-layer multi-pass welding, and the machining allowance is less than 1 / 5 of that of traditional welding methods, significantly improving welding efficiency and product quality.

[0043] 2. When using ultra-high power laser for deep penetration welding, the present invention employs a negative defocus welding method, which allows the focal position with the highest energy density to penetrate into the groove, increasing the penetration depth. At the same time, it helps to reduce spatter and improve weld formation.

[0044] 3. Depending on the plate thickness, this invention can be used for direct welding or as a root pass welding for ultra-thick plates. When the plate thickness is within the penetration depth range of the ultra-high power laser (including penetration on both sides), only ultra-high power root pass welding and capping are needed for direct forming. When the welding depth far exceeds the penetration depth range of the ultra-high power laser, this method can be used for root pass welding, and the remaining part can be filled by narrow-gap hot wire TIG multi-layer multi-pass welding, or by (oscillating) laser-cold / hot wire multi-layer filling. When used for root pass welding of ultra-thick plates, the extremely small heat input of the ultra-high power laser allows the total thermal deformation to be controlled to about 1mm, while the high rigidity constraint of the ultra-thick deep penetration root pass ensures that the subsequent multi-layer filling is basically free from deformation, significantly reducing the difficulty of subsequent weld planning and parameter adjustment, significantly improving the efficiency of filling welding, the consistency of welding quality, and the dimensional accuracy of the product.

[0045] 4. When using ultra-high power for ultra-thick root pass welding, this invention can achieve uniform mass and heat transfer by oscillating and stirring the molten pool with the laser beam, thereby reducing residual welding stress and lowering the risk of shrinkage cavities or cracks at the bottom or center of the weld. Furthermore, by oscillating the laser beam to stabilize and increase the keyhole opening, the welding process is stabilized, and the generation of process porosity is suppressed, which is quite important for root pass welding of ultra-thick plates.

[0046] 5. The present invention provides a method for creating a shallow groove above the root pass of ultra-thick plates, which facilitates the direct filling of the shallow groove with the weld metal expanded from the root pass welding. This reduces the amount of pre-weld grinding work for ultra-thick plate filler welding, lowers the workload, and reduces the preparation time before filler welding. In addition, the shallow groove method can constrain and reduce the generation of plasma to a certain extent, ensuring the stability of the weld penetration depth.

[0047] 6. The 4-14mm U-shaped bevel in this invention is narrower, has fewer filler passes, consumes less welding wire, and has higher welding efficiency compared to the traditional multi-layer, multi-pass filling bevel of more than 14mm. This significantly reduces economic and time costs. Attached Figure Description

[0048] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0049] Figure 1 This is a schematic diagram of the beveling of the first and second base materials for single-sided full penetration welding of ultra-thick stainless steel plates.

[0050] Figure 2 This is a schematic diagram of an ultra-high power laser welding device for ultra-thick stainless steel plates.

[0051] Figure 3 This is a schematic diagram of the beveling of the first and second base materials for double-sided welding of ultra-thick stainless steel plates.

[0052] Figure 4 This is a schematic diagram of the beveling of the first and second base materials for single-sided root pass welding of ultra-thick stainless steel plates.

[0053] Figure 5 This is a schematic diagram of the beveling of the first and second base materials for double-sided root welding of ultra-thick stainless steel plates.

[0054] Figure 6 A schematic diagram of the beveling and shallow groove of the first and second base materials for double-sided root welding of ultra-thick stainless steel plates.

[0055] The markings in the above figures represent: 1-first parent material, 2-second parent material, 3-laser beam, 4-protective gas shield. Detailed Implementation

[0056] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0057] This invention utilizes ultra-high power lasers for single-sided or double-sided deep penetration welding of the materials to be welded. It can be used for penetration welding of ultra-thick stainless steel plates or root pass welding of ultra-thick plates with deep bevels and thick blunt edges. The process includes beveling, assembly and cleaning, welding path teaching, setting welding process parameters, front welding, and also includes back welding and front and back cover welding. It can significantly improve welding efficiency, reduce welding deformation, and decrease post-weld machining allowances for high-precision products.

[0058] Example 1

[0059] A laser welding method for ultra-thick stainless steel plates according to the present invention includes the following steps:

[0060] Step S1: Beveling. Beveling is performed on the weldable end face of the extra-thick stainless steel. The beveling method is a combination of a large blunt edge and a U-shaped beveling. The U-shaped beveling angle is 0-12 degrees, with a single-sided beveling angle of 0-6 degrees. The U-shaped beveling width is 4-14mm (excluding 14). The U-shaped beveling filling depth is determined by the remaining plate thickness, typically requiring a depth greater than 2-12mm. The base material is 304 or 316 stainless steel with a thickness of 30-300mm or more. For single-sided root pass welding, the blunt edge thickness is 12mm or more, such as 15mm or 20mm. For double-sided root pass welding, the blunt edge thickness can be 20mm or more, such as 22mm or 25mm.

[0061] When the thickness of the weld plate far exceeds the maximum penetration depth of ultra-high power lasers, ultra-high power ultra-deep penetration welding can be used for the root pass welding of ultra-thick components. In this case, a shallow groove is further opened above the root pass weld to fill the weld metal that expands during the root pass welding. This reduces the amount of pre-weld grinding work required for ultra-thick plate filler welding, lowers the workload of workers, and reduces the preparation time before filler weld welding. The method of opening a shallow groove above the root pass weld of ultra-thick plates facilitates the direct filling of the shallow groove by the weld metal that expands during the root pass welding. Furthermore, the shallow groove method, to a certain extent, constrains and reduces plasma generation, ensuring the stability of the weld penetration depth.

[0062] Step S2: Assembly and Cleaning. Place the workpiece according to the corresponding welding method, and tightly butt the first and second base materials together and fix them with clamps. Then clean the surfaces to be welded, removing oil, dust, etc. from the surfaces and bevels. The welding methods include flat welding, horizontal welding, or vertical welding.

[0063] Step S3: Welding path programming or teaching. Adjust the relative positions of the laser beam and shielding gas hood to the base material according to the process requirements, such as the defocus amount and welding torch angle, and program or teach the welding path. Weld the laser beam by tilting it backward or forward by 5-10°, with a laser defocus amount of -5 to -40mm. The shielding gas hood is located behind the laser beam, 4-12mm away from the laser beam, and 1-12mm away from the surface of the base material.

[0064] Step S4: Set welding process parameters. These parameters include laser power, welding speed, shielding gas flow rate, whether the laser beam oscillates, the oscillation mode, and oscillation parameters. The laser power is 20–60 kW, the laser spot diameter is 0.40–0.8 mm, and the welding speed is 0.3–1.6 m / min. During the root pass welding, the laser beam oscillation mode can use various modes such as: "|" (horizontal oscillation perpendicular to the welding direction), "○" (circular oscillation), "8" (figure-eight oscillation perpendicular to the welding direction), and "∞" (∞ oscillation parallel to the welding direction). The oscillation frequency is 50–200 Hz, and the oscillation amplitude is 1.0–6.0 mm. Oscillation stirs the molten pool, achieving homogenization of mass and heat transfer, reducing residual welding stress, and increasing the keyhole opening to ensure welding stability. The shielding gas is nitrogen, with a flow rate of 40–100 L / min.

[0065] Step S5: Open the protective gas valve and wait for the protective gas to fill the welding area before starting welding. Perform front welding, back welding, or front and back cover welding. Depending on the thickness of the base material and the laser power, single-sided or double-sided welding combined with cover welding can be selected to complete the welding directly. For example, for ultra-thick stainless steel plates of 48mm or 88mm and above, a 25-30kW laser beam can be used for single-sided and double-sided welding respectively. It can also be used only for root pass welding of workpieces with a plate thickness far exceeding the maximum penetration depth of ultra-high power. For example, for ultra-thick stainless steel plates with blunt edges of 48mm or 88mm and above, a 25-30kW laser beam can be used for single-sided and double-sided root pass welding respectively to improve welding efficiency and control welding deformation.

[0066] Front welding. Open the shielding gas valve and wait for the shielding gas to fill the welding area before starting welding. The high-power laser is projected onto the center of the bevel, and the base material quickly melts, evaporates, and vaporizes to form a keyhole for deep penetration welding. At the same time, the welding torch moves forward to achieve deep penetration welding on the front side of the base material.

[0067] Reverse welding. Decide whether to perform reverse welding as needed. If reverse welding is performed, repeat steps three and four: welding path programming and process parameter setting, and then weld. Similarly, first open the shielding gas valve, and after the shielding gas fills the welding area, start welding while simultaneously moving the welding torch forward to achieve deep penetration welding on the reverse side of the base material. To ensure sufficient strength, the penetration depth of the two welds must overlap within the base material to ultimately achieve complete penetration of both the first and second base materials.

[0068] Cover welding is performed on both sides. Whether or not to perform cover welding depends on the requirements. If the plate thickness is within the range of ultra-high power laser deep penetration welding, cover welding can be performed directly after deep penetration welding. Before welding, clean the root pass with a grinding wheel and alcohol, then perform cover welding using CMT (Cold Metal Transfer) or laser-CMT hybrid welding. Similarly, if the remaining filler thickness after the reverse root pass can be completed with cover welding, then proceed directly with cover welding; otherwise, filler welding is required before cover welding. For cover welding, the preferred laser power is 0–10000W; the welding speed is 0.3–1.6 m / min. The wire feed speed for CMT in cover welding is 4–11 m / min. The shielding gas is a mixture of 98% argon and 2% carbon dioxide, with a flow rate of 15–40 L / min. Depending on the material, structure, stress level, etc., the laser parameters used for welding on both sides do not necessarily need to be exactly the same, meaning the penetration depth on both sides does not need to be exactly equal.

[0069] This method is applicable to various welding methods, including flat welding, horizontal welding, and vertical welding. To ensure proper weld formation on both sides and reduce spatter, horizontal or vertical welding generally yields better welding results.

[0070] This invention aims to fundamentally solve the problems of low efficiency, large metal filling amount, large heat input, excessively wide heat-affected zone, and excessive post-weld machining allowance when welding thick plates using traditional welding processes.

[0071] Furthermore, in conjunction with the instruction manual appendix Figures 1 to 6 The laser welding method for ultra-thick stainless steel plates of the present invention will be further described in detail with specific embodiments.

[0072] Example 2: A method for ultra-high power laser single-sided penetration welding of 316 stainless steel ultra-thick plates with a thickness of 48mm or more, which is carried out according to the following steps:

[0073] Step 1: Beveling. The welded end face of the extra-thick stainless steel is beveled. The beveling method is a large blunt edge + U-shaped bevel, with a blunt edge of 44mm, a single-sided groove of 2-4mm x 4mm (0-degree angle), and a 1mm diameter chamfer at the bottom. Figure 1 As shown, a represents the bevel width, b represents the bevel depth, and H represents the blunt edge thickness.

[0074] Step 2: Assembly and Cleaning. Using a flat welding method, place the workpiece flat, then tightly butt the first base material 1 and the second base material 2 together and fix them with clamps. Clean the surfaces to be welded, removing oil, dust, and other contaminants from the surfaces and bevels.

[0075] Step 3: Welding Path Teaching. Adjust the relative positions of the laser beam 3 and the protective gas shield 4 with the base material, and teach the welding path, such as... Figure 2 As shown; the laser beam 3 is located in front of the protective gas cover 4, and the guiding spot of the laser beam 3 is located in the center of the shallow groove, 4-6 mm away from the front end of the protective gas cover 4; the bottom end of the protective gas cover 4 is 1-2 mm away from the surface of the base material.

[0076] Step 4: Set welding process parameters. Set the power of laser beam 3 to 25-30kW, the defocusing amount to -10--20mm, the laser beam tilt to 8°, the welding speed to 0.6m / min, the shielding gas to nitrogen, and the shielding gas flow rate to 80L / min.

[0077] Step 5: Laser Welding. Open the shielding gas valve and wait for the shielding gas to fill the welding area. Then turn on the laser and start welding. The high-power laser beam 3 is projected onto the center of the bevel, while the welding torch moves forward to achieve deep penetration welding of the base material.

[0078] Step Six: Cover Welding. Whether or not to perform cover welding depends on the needs (if the test plate consistency is good, cover welding is not required; however, during product welding, due to gaps and misalignments, it is difficult to ensure the cover weld formation, so cover welding is usually necessary). Before welding, clean the root pass with a grinding wheel and alcohol, then perform cover welding using CMT (Cold Metal Transfer) or laser-CMT hybrid welding. The laser power is 0–3000W, the welding speed is 0.6 m / min, the wire feed speed is 8–10 m / min, and the shielding gas is a mixture of 98% argon and 2% carbon dioxide.

[0079] The above method can achieve high-quality and high-efficiency welding of 48mm thick 316LN stainless steel plates on one side.

[0080] Example 3: A method for ultra-high power laser double-sided penetration welding of 316 stainless steel ultra-thick plates with a thickness of 88mm or more, performed according to the following steps:

[0081] Step 1: Beveling. The ultra-thick stainless steel end face to be welded is beveled. The beveling method is a large blunt edge + U-shaped bevel, with a blunt edge thickness of 80mm. The single-sided groove size is 4mm x 4-6mm, the bevel angle is 0 degrees, and the bottom diameter chamfer is 1mm. Figure 3 As shown.

[0082] Step Two: Assembly and Cleaning. The workpiece is placed horizontally using a horizontal welding method. Then, the first base material 1 and the second base material 2 are tightly joined together and fixed with clamps. The surfaces to be welded are cleaned to remove oil, dust, and other contaminants from the surfaces and bevels.

[0083] Step 3: Welding path teaching. Adjust the relative positions of the laser beam 3 and the protective gas shield 4 with the base material, and program or teach the welding path; the laser beam 3 is located in front of the protective gas shield 4, and the guiding spot of the laser beam 3 is located at the center of the shallow groove, 4-6 mm away from the front end of the protective gas shield 4; the bottom end of the protective gas shield 4 is 1-2 mm away from the surface of the base material.

[0084] Step 4: Set welding process parameters. Set the power of laser beam 3 to 25-30kW, the defocusing amount to -10 to -30mm, the laser beam tilt to 8°, the welding speed to 0.6m / min, the shielding gas to nitrogen, and the shielding gas flow rate to 80L / min.

[0085] Step 5: Front welding. Open the shielding gas valve and wait for the shielding gas to fill the welding area before starting welding. The high-power laser beam 3 is projected onto the center of the bevel, while the welding torch moves forward to achieve deep penetration welding of the base material on the front side.

[0086] Step Six: Reverse Welding. Repeat Steps Three and Four, open the shielding gas valve, wait for the shielding gas to fill the welding area, then turn on the laser and start welding. The high-power laser beam 3 is projected onto the center of the bevel, while the welding torch moves forward to achieve deep penetration welding on the reverse side of the base material. To ensure sufficient strength, the penetration depth of the two welds must overlap within the base material to ultimately achieve complete penetration of the first base material 1 and the second base material 2.

[0087] Step 7: Cover welding on both sides. Whether or not to perform cover welding depends on the needs (if the test plate has good consistency, cover welding is not necessary; however, during product welding, due to gaps and misalignments, it is difficult to ensure the cover weld is formed, so cover welding is usually required). Before welding, clean the root pass with a grinding wheel and alcohol, then perform cover welding using CMT (Cold Metal Transfer) or laser-CMT hybrid welding. The laser power is 0–3000W, the welding speed is 0.6 m / min, the wire feed speed is 8–10 m / min, and the shielding gas is a mixture of 98% argon and 2% carbon dioxide.

[0088] The above method can achieve high-quality and high-efficiency welding of 88mm thick 316LN stainless steel plates on both sides.

[0089] Example 4: A method for ultra-high power laser single-sided root pass welding of 134mm 316 stainless steel ultra-thick plate, which is carried out according to the following steps:

[0090] Step 1: Beveling. The ultra-thick stainless steel end face to be welded is beveled. The beveling method is a large blunt edge + U-shaped bevel. The blunt edge thickness is 40mm, the U-shaped bevel angle is 4-8 degrees (2-4 degrees per side), the bottom width of the bevel is 14mm, the radius (R) is 5mm, and the fill depth is 94mm. Figure 4 As shown, H represents the total thickness of the ultra-thick stainless steel plate to be welded, h represents the thickness of the blunt edge, A represents the width of the bottom of the U-shaped bevel, B represents the depth of the U-shaped bevel, R represents the radius of the chamfer at the bottom of the U-shaped bevel, and γ represents the angle of one side of the U-shaped bevel.

[0091] Step Two: Assembly and Cleaning. The workpiece is placed horizontally using a horizontal welding method. The first base material 1 and the second base material 2 are tightly butt-jointed and fixed with clamps. The surfaces to be welded are cleaned to remove oil, dust, and other contaminants from the surfaces and bevels.

[0092] Step 3: Welding path programming or teaching. Adjust the relative positions of the laser beam 3 and the protective gas shield 4 with the base material, and teach the welding path; the laser beam 3 is located in front of the protective gas shield 4, and the guiding spot of the laser beam 3 is located at the center of the bevel, 4-6 mm away from the front end of the protective gas shield 4; the bottom end of the protective gas shield 4 is 5-10 mm away from the bottom of the bevel.

[0093] Step 4: Set welding process parameters. Set the power of laser beam 3 to 25-30kW, the defocusing amount to -10 to -30mm, the laser beam tilt to 8°, the welding speed to 0.6m / min, the shielding gas to nitrogen, and the shielding gas flow rate to 80L / min.

[0094] Step 5: Laser welding. Open the shielding gas valve and wait for the shielding gas to fill the welding area before starting welding. The high-power laser beam 3 is projected onto the center of the bevel, while the welding torch moves forward to achieve full penetration welding of the base material.

[0095] The above method enables high-quality and high-efficiency root pass welding of 316LN stainless steel ultra-thick plates with a single-sided thickness of 134mm and a blunt edge thickness of 40mm. The large blunt edge ensures sufficient rigidity, and the deformation after root pass welding is only about 1mm, which can significantly reduce the thermal deformation of the workpiece, improve welding efficiency, and lay the foundation for subsequent layer-by-layer filling.

[0096] Example 5: A method for ultra-high power laser double-sided root pass welding of 268mm 316 stainless steel ultra-thick plates, performed according to the following steps:

[0097] Step 1: Beveling. The ultra-thick stainless steel end face to be welded is beveled. The beveling method is a large blunt edge + U-shaped bevel. The blunt edge thickness is 80mm, the U-shaped bevel angle is 4-8 degrees (2-4 degrees on one side), the width is 14mm, the bottom chamfer R=5mm, and the filling depth on one side is 94mm. Figure 5 As shown.

[0098] Step Two: Assembly and Cleaning. The workpiece is placed horizontally using a horizontal welding method. The first base material 1 and the second base material 2 are tightly butt-jointed and fixed with clamps. Then, the surfaces to be welded are cleaned to remove oil, dust, and other contaminants from the surfaces and bevels.

[0099] Step 3: Welding path programming or teaching. Adjust the relative positions of the laser beam 3 and the protective gas shield 4 with the base material, and teach the welding path; the laser beam 3 is located in front of the protective gas shield 4, and the guide spot of the laser beam 3 is located at the center of the bevel, 4-6 mm away from the front end of the protective gas shield 4; the bottom end of the protective gas shield 4 is 5-10 mm away from the bottom of the bevel.

[0100] Step 4: Set welding process parameters. Set the power of laser beam 3 to 25-40kW, the defocusing amount to -10-30mm, the laser beam tilt to 8°, the welding speed to 0.6m / min, the shielding gas to nitrogen, and the shielding gas flow rate to 80L / min;

[0101] Step 5: Front welding. Open the shielding gas valve and wait for the shielding gas to fill the welding area before starting welding. The high-power laser beam 3 is projected onto the center of the bevel, while the welding torch moves forward to achieve deep penetration welding of the base material on the front side.

[0102] Step Six: Reverse Welding. Repeat Steps Three and Four, open the shielding gas valve, and wait for the shielding gas to fill the welding area before starting welding. The high-power laser beam 3 is projected onto the center of the bevel, while the welding torch moves forward to achieve deep penetration welding on the reverse side of the base material. To ensure sufficient strength, the penetration depth of the two welds must overlap within the base material to ultimately achieve complete penetration of the first base material 1 and the second base material 2.

[0103] The above method enables high-quality and high-efficiency root pass welding of ultra-thick 316LN stainless steel plates with a total thickness of 268mm on both sides and a blunt edge thickness of 80mm. The large blunt edge ensures sufficient rigidity, and the deformation after root pass welding is only about 1mm, which can significantly reduce the thermal deformation of the workpiece, improve welding efficiency, and lay the foundation for subsequent layer-by-layer filling.

[0104] Example 6: A method for ultra-high power laser double-sided root pass welding of ultra-thick 316 stainless steel plates, performed according to the following steps:

[0105] Step 1: Beveling. The ultra-thick stainless steel end face to be welded is beveled. The beveling pattern is a large blunt edge + U-shaped bevel + shallow groove at the bottom center. The blunt edge is 40-80mm, the U-shaped bevel angle is 4-8 degrees (2-4 degrees on one side), the width is 14mm, the bottom chamfer R=5mm, the filling depth on one side is 94mm, and a shallow groove of 4-6mm width and 2-4mm depth is machined at the bottom center of the bevel. Figure 6 As shown.

[0106] Step Two: Assembly and Cleaning. The workpiece is placed horizontally using a horizontal welding method. The first base material 1 and the second base material 2 are tightly butt-jointed and fixed with clamps. Then, the surfaces to be welded are cleaned to remove oil, dust, and other contaminants from the surfaces and bevels.

[0107] Step 3: Welding path programming or teaching. Adjust the relative positions of the laser beam 3 and the protective gas shield 4 with the base material, and teach the welding path; the laser beam 3 is located in front of the protective gas shield 4, and the guiding spot of the laser beam 3 is located at the center of the shallow groove at the bottom of the bevel, 4-6 mm away from the front end of the protective gas shield 4; the bottom end of the protective gas shield 4 is 5-10 mm away from the bottom of the bevel.

[0108] Step 4: Set welding process parameters. Set the power of laser beam 3 to 20-40kW, the defocusing amount to -10-30mm, the laser beam tilt to 8°, the welding speed to 0.6m / min, the shielding gas to nitrogen, and the shielding gas flow rate to 80L / min.

[0109] Step 5: Front welding. Open the shielding gas valve and wait for the shielding gas to fill the welding area before starting welding. The high-power laser beam 3 is projected onto the center of the bevel, while the welding torch moves forward to achieve deep penetration welding of the base material on the front side.

[0110] Step Six: Reverse Welding. Repeat Steps Three and Four, open the shielding gas valve, and wait for the shielding gas to fill the welding area before starting welding. The high-power laser beam 3 is projected onto the center of the bevel, while the welding torch moves forward to achieve deep penetration welding on the reverse side of the base material. To ensure sufficient strength, the penetration depth of the two welds must overlap within the base material to ultimately achieve complete penetration of the first base material 1 and the second base material 2.

[0111] The above method allows the weld metal that expands during the root pass to directly fill the shallow groove, reducing the amount of pre-weld grinding work for ultra-thick plate filler welding, lowering the workload, and reducing the pre-weld preparation time. In addition, the shallow groove method can also constrain and reduce plasma generation to a certain extent, ensuring the stability of the weld penetration depth.

[0112] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0113] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A laser welding method for ultra-thick stainless steel plates, characterized in that, include: Step S1: Perform beveling on the ultra-thick stainless steel end face to be welded. The beveling form is a combination of a large blunt edge and a U-shaped beveling. The beveling forms the dividing line, with one end as the first base material and the other end as the second base material. Step S2: Place the workpiece according to the corresponding welding method, and tightly butt the first base material and the second base material together and fix them with a clamp, and then clean the surface to be welded; Step S3: Adjust the relative positions of the laser beam and protective gas shield to the base material according to the parameters required by the process, and program or teach the welding path; Step S4: Set welding process parameters; Step S5: Open the protective gas valve, wait for the protective gas to fill the welding area, then start welding to perform front welding, back welding, or front and back cover welding. The parameters required for the process include defocusing amount and welding torch angle; Welding is performed by tilting the laser beam backward or forward by 5 to 10 degrees, with a laser defocusing amount of -5 to -40 mm. The welding process parameters include laser power; The laser power is 20–60 kW, and the laser spot diameter is 0.40–0.8 mm. The U-shaped bevel angle is 0-12 degrees, and the bevel angle on one side is 0-6 degrees; The width of the U-shaped bevel is 4-14mm, excluding 14mm; The filling depth of the U-shaped bevel is determined by the remaining plate thickness; The thickness of the ultra-thick stainless steel base material is 30-300 mm; For single-sided root pass welding, the blunt edge thickness should be above 12mm; for double-sided root pass welding, the blunt edge thickness should be above 20mm.

2. The laser welding method for ultra-thick stainless steel plates according to claim 1, characterized in that, When the thickness of the weld plate far exceeds the maximum penetration depth of the ultra-high power laser, ultra-high power ultra-deep penetration welding is selected as the root welding for ultra-thick components, and a shallow groove is opened above the root weld. The shallow groove is used to fill the weld metal that expands during the initial welding.

3. The laser welding method for ultra-thick stainless steel plates according to claim 1, characterized in that, The welding method includes flat welding, horizontal welding, or vertical welding; The protective gas shield is located behind the laser beam, 4-12 mm away from the laser beam, and 1-12 mm away from the surface of the base material.

4. The laser welding method for ultra-thick stainless steel plates according to claim 1, characterized in that, The welding process parameters also include welding speed, shielding gas flow rate, whether the laser beam oscillates, oscillation mode, and oscillation parameters; The welding speed is 0.3–1.6 m / min; The oscillation frequency is 50-200Hz, and the oscillation amplitude is 1.0-6.0mm, which stirs the molten pool through oscillation; The protective gas is nitrogen, and the gas flow rate is 40-100 L / min.

5. The laser welding method for ultra-thick stainless steel plates according to claim 1, characterized in that, Open the protective gas valve, wait for the protective gas to fill the welding area, start welding, and the high-power laser is projected onto the center of the bevel. The base material quickly melts, evaporates, and vaporizes to form a keyhole for deep penetration welding. At the same time, the welding torch moves forward to achieve deep penetration welding on the front or back of the base material. The front and back cover welding includes the following steps: before welding, the root pass is cleaned, and then the cover weld is performed using CMT cold metal transition laser-CMT composite welding. Similarly, if the remaining filling thickness after the back root pass is completed is sufficient to complete the cover weld, then the cover weld can be performed directly; otherwise, filling is required before the cover weld can be performed.

6. The laser welding method for ultra-thick stainless steel plates according to claim 5, characterized in that, The penetration depth of the two welds overlaps within the base material.

7. The laser welding method for ultra-thick stainless steel plates according to claim 5, characterized in that, If the thickness of the weld plate is within the range of ultra-high power laser deep penetration welding, then the cover plate can be directly welded after deep penetration welding. The laser power for cap welding is 0–10000 W; the welding speed is 0.3–1.6 m / min. The wire feed speed for CMT cover welding is 4–11 m / min; the shielding gas is a mixture of 98% argon and 2% carbon dioxide, with a gas flow rate of 15–40 L / min.

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