Laser stirring friction composite welding method for stainless steel special-shaped part

Abstract

The invention discloses a laser stirring friction composite welding method for stainless steel special-shaped parts. The method comprises the following steps that butt-joint grooves of a first stainless steel special-shaped part and a second stainless steel special-shaped part of a to-be-welded part and the positions near the two sides are cleaned; the pretreated first stainless steel special-shaped part and the pretreated second stainless steel special-shaped part are clamped and positioned; laser is used for positioned welding; laser preheating is carried out in front of a stirring head of a friction stir welding device, the preheating temperature range of the stainless steel special-shaped part is 400-450 DEG C, friction stir welding is carried out at the interval of 5-10 mm, and the speed of laser preheating and the speed of friction stir welding are kept the same. The effective melting point of stainless steel is reduced through laser preheating, high-precision and low-deformation space three-dimensional welding is achieved in combination with a six-connecting-rod type friction stir welding numerical control special machine, the method is applied to welding of a stainless steel guide rail supporting base and a barrel, and the production efficiency and reliability of a reusable launching barrel system are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of laser welding, and particularly relates to a laser friction stir composite welding method for stainless steel special-shaped parts. Background Art

[0002] The popularization and use of recyclable and reusable products is of great significance for aspects such as resource conservation, environmental protection, and sustainable development. At present, the recyclability and reusability of different types of products have penetrated into all walks of life. For example, SpaceX in the United States has made remarkable progress in rocket recycling, successfully achieving multiple rocket recycling and reuse, which has greatly promoted the progress of aerospace technology.

[0003] Major domestic key units are all carrying out the design and manufacturing work of recyclable and reusable products. For example, in the aerospace field, the launch tube system is an important part of missile weapon equipment. The launch tube system is mainly made of aluminum alloy materials, does not have the function of recyclability and reusability, and has a large production cost and a long production cycle. Stainless steel is an ideal material to replace aluminum alloy for manufacturing reusable launch tube systems due to its good corrosion resistance, high temperature resistance, heat resistance, and high strength. However, if stainless steel is used to manufacture the launch tube system, it will also face the three-dimensional space welding problem between the key functional components of the launch tube, namely the guide rail support seat and the cylinder body. Its weld seam is a typical stainless steel special-shaped part weld seam. At the same time, because the melting point and strength of stainless steel are far higher than those of aluminum alloy, and it also needs to meet the requirement of being reusable multiple times, its welding quality requirements are higher, resulting in greater welding difficulty, which has become the main bottleneck problem restricting its large-scale production. If the production continues to be carried out by manually drilling into the narrow special-shaped parts and using manual fusion welding methods such as TIG / MIG, not only the weld quality cannot be guaranteed, but also smoke, toxic gases, etc. will be generated, which will harm the physical and mental health of workers and the environment. At the same time, the high melting point of stainless steel also greatly limits the use of conventional friction stir welding. Therefore, there is an urgent need for an efficient, high-quality and green welding method to ensure the welding quality of stainless steel special-shaped parts.

[0004] The patent with the publication number CN116871660A proposes a three-dimensional friction stir welding method for welding a cylinder and a support seat in space. By using the retractable three-dimensional parallel friction stir welding method, it can solve the problem of three-dimensional welding in space between the key functional component of the aluminum alloy launch tube, the saddle-shaped guide rail support seat, and the cylinder, achieving the purpose of welding from the outside of the cylinder, thus replacing the conventional fusion welding method. However, this method is mainly for welding low-melting-point materials such as aluminum alloy, and essentially still belongs to the category of conventional friction stir welding. The melting point of stainless steel is much higher than that of aluminum alloy. If conventional friction stir welding is used, it will have a huge impact on equipment accuracy, tool wear, clamping force, etc., greatly shortening the service life of the equipment, accelerating the loss of the stirring tool and the clamping system. At the same time, since more heat is required to plasticize stainless steel during friction stir welding, its welding speed is much lower than that of welding low-melting-point materials such as aluminum alloy by friction stir welding, and the production efficiency will be greatly reduced, which is not suitable for the welding production of large-scale and batch products, and the production cost will also soar significantly. Moreover, due to the slow heat conduction of stainless steel itself, it is easy to cause heat accumulation, resulting in large welding deformation due to uneven heat distribution between the base material and the weld zone. At the same time, in the retractable three-dimensional parallel friction stir welding machine mentioned in this patent, the maximum tilt angle of the stirring head is 30°, which means that the three-dimensional space welding range is greatly limited, and it is impossible to weld the welds of many special-shaped parts that exceed the 30° tilt angle of the stirring head. Summary of the Invention

[0005] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a laser friction stir composite welding method for stainless steel special-shaped parts, which reduces the effective melting point of stainless steel by laser preheating and realizes high-precision and low-deformation three-dimensional welding in space by combining a six-link friction stir welding numerical control special machine. This method is applied to the welding of stainless steel guide rail support seats and cylinders, significantly improving the production efficiency and reliability of the reusable launch tube system, and can be extended to fields such as aerospace and high-end equipment manufacturing.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions: The present invention provides a laser friction stir composite welding method for stainless steel special-shaped parts, including the following steps: S1. Pretreatment: Clean the butt joint groove and the vicinity on both sides of the first stainless steel special-shaped part and the second stainless steel special-shaped part of the workpiece to be welded; S2. Clamping: Clamp and position the first stainless steel special-shaped part and the second stainless steel special-shaped part after pretreatment; S3. Laser tack welding: Use laser for tack welding; S4, laser stir friction welding: firstly, laser preheating is performed in front of the stirring head of the stir friction welding device. The preheating temperature range of stainless steel special-shaped parts is 400-450°C, and then stir friction welding is performed at a distance of 5-10mm. The laser preheating and stir friction welding are kept at the same speed.

[0007] In the present invention, when selecting the preheating temperature before friction stir welding of stainless steel special-shaped parts, it is considered that stainless steel has 475°C embrittlement phenomenon, especially the brittle temperature range of chromium-nickel austenitic stainless steel is generally 450-850°C. When the temperature exceeds the brittle temperature range, the toughness and plasticity of chromium-nickel austenitic stainless steel will be reduced, and cracks, fractures and other damages will occur easily; at the same time, the temperature range in which stainless steel is prone to intergranular corrosion is also 450-850°C. In this temperature range, the chromium element in stainless steel is easy to combine with carbon to form chromium carbide, resulting in the chromium content near the grain boundary being high. The amount of chromium is reduced, forming a chromium-depleted area, thereby causing intergranular corrosion; the melting point of general stainless steel is usually between 1400 and 1500°C. In order to lower its melting point in disguise, soften the stainless steel material better, and also minimize the temperature difference between the weld and the parent material in the vicinity after welding, and minimize the deformation after welding, the present invention has finally determined through experiments that the ideal preheating temperature range is 400 to 450°C. If the preheating temperature is too high, the stainless steel will produce problems such as embrittlement and intergranular corrosion. If the preheating temperature is too low, the effects of lowering the melting point in disguise, softening the material and reducing the deformation after welding cannot be achieved.

[0008] After many tests, the present invention finally determined that the distance between laser preheating and friction stir welding is 5 to 10 mm to ensure a good preheating effect. If the distance is too small, there will be a certain interference between laser preheating and friction stir welding. At the same time, due to the poor thermal conductivity of stainless steel, the preheating temperature will not be able to expand to the entire friction stir welding area in time, and the preheating effect cannot be achieved. If the distance is too large, the preheating temperature may have dropped before friction stir welding, and the preheating effect cannot be achieved either.

[0009] Furthermore, in step S4, before laser preheating, a laser preheating test is carried out using a first stainless steel test piece and a second stainless steel test piece that are made of the same material and have a similar structure to the first stainless steel special-shaped piece and the second stainless steel special-shaped piece, and an infrared thermometer is used to measure the preheating temperature in the laser preheating test to ensure that the measured preheating temperature range is between 400 and 450° C., and then the laser power and scanning speed at the measured temperature are recorded, and the heat input of laser welding is calculated according to the following formula: Q=ηP / v, where η is the thermal efficiency coefficient, which ranges from 0.8 to 0.85. When welding stainless steel, its value is generally 0.8. It is calculated that the heat input range of laser welding is about 5 to 9 KJ / cm.

[0010] Further, in the step S4, the welding speed of friction stir welding is 80 - 100 mm / min. Then, according to the heat input of laser welding calculated in the laser preheating test, the laser preheating power range is calculated to be 1000 - 1500 W according to the formula Q = ηP / v.

[0011] Further, in the step S4, the laser scanning speed is the same as the moving speed of the stirring head, which is 80 - 100 mm / min.

[0012] Further, the process parameter range of friction stir welding is as follows: the rotation speed of the stirring head is 600 - 700 r / min, the welding speed is 80 - 100 mm / min, the penetration depth is 0.1 - 0.2 mm, and the front angle of the main shaft of the friction stir welding device is about 2°.

[0013] Since the high melting point of stainless steel is reduced after laser preheating, but it is still higher than that of light metals such as aluminum alloy, slightly more heat is required. Therefore, the rotation speed of the stirring head is slightly higher than that for welding light metals such as aluminum alloy, and the welding speed is slightly lower. Compared with the friction stir welding of stainless steel without preheating, the rotation speed of the stirring head is greatly reduced.

[0014] Further, the friction stir welding device is a six - link type friction stir welding numerical control special machine.

[0015] The laser - six - link type friction stir composite welding technology can effectively solve the problem of three - dimensional welding of stainless steel special - shaped parts in space, including solving the three - dimensional space welding problem of two special - shaped parts, namely the stainless steel guide rail support seat and the stainless steel cylinder. It successfully meets the requirements of the reusable stainless steel special - shaped part launch system. The six - link type friction stir welding numerical control special machine, compared with the existing retractable three - dimensional parallel friction stir welding equipment, is based on the design of a multi - degree - of - freedom hybrid robot configuration, establishes a hybrid robot structure stiffness model based on the structure matrix method, and at the same time uses the principle of virtual work to establish a hybrid robot dynamics model. It adopts a synchronous double - drive six - link structure form, and both the upper and lower ends of each link are connected to the slider and the moving platform through spherical pairs respectively. On the basis of classical PID control, it integrates the motor control algorithm of ADRC (active disturbance rejection control) to realize the rotation and tilt of the moving platform, and the maximum tilt angle can reach 90°, so as to drive the tilt angle of the stirring head to also reach 90°, far exceeding 30°. Therefore, the welding of special - shaped parts in the three - dimensional space range is almost not restricted. At the same time, its equipment has a high degree of automation and good welding quality consistency. It can not only weld thin plates but also medium - thick plates, which can make up for the problem of insufficient rigidity of the robot friction stir welding of medium - thick plates.

[0016] Furthermore, in the step S3, when laser tack welding is performed on the first stainless steel special-shaped part and the second stainless steel special-shaped part using a laser, the tack welding interval is 40 to 50 mm, and the tack welding seam length is 10 to 15 mm.

[0017] The main purpose of laser positioning welding is to prevent the deformation of stainless steel special-shaped parts during stir friction welding. Since the thermal conductivity of stainless steel is low and the linear expansion coefficient is 40% larger than that of carbon steel, the deformation after welding is larger than that of carbon steel. At the same time, stir friction welding has high requirements for assembly accuracy. Therefore, laser positioning welding must ensure a certain weld penetration depth. Specifically, the specific process parameters of laser positioning welding are: laser power of 1500~2000W, welding speed of 1.0~1.2m / min, defocus of +2~+5mm, shielding gas flow of 15~20L / min, the purity of shielding gas argon is ≥99.999%, and the laser deflection angle is 8°.

[0018] Furthermore, in step S2, the first stainless steel shaped part and the second stainless steel shaped part to be welded are clamped by using an internal support tool and an external clamp respectively, and the butt clearance between the first stainless steel shaped part and the second stainless steel shaped part after clamping is ≤0.15mm, and the misalignment between the first stainless steel shaped part and the second stainless steel shaped part is ≤0.15mm.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts laser preheating technology, and determines the ideal preheating temperature range (400-450°C) through experiments, so as to avoid embrittlement and intergranular corrosion of stainless steel and reduce the deformation resistance of the material. The laser energy is used for preheating before friction stir welding, and the material with a high melting point, such as stainless steel, can be successfully welded. The reason is that preheating to a certain temperature before welding is equivalent to lowering the melting point of the welded material in disguise, reducing the deformation resistance, which is conducive to friction stir welding; preheating to an ideal temperature before welding can also effectively reduce the temperature difference between the parent material and the weld after welding, thereby achieving the purpose of reducing welding deformation and improving the accuracy of the welded product; preheating before welding can also reduce the clamping force and driving force, reduce wear, greatly extend the service life of equipment and tools, increase the welding speed, and facilitate the large-scale and mass production of products.

[0020] (2) Laser positioning welding is first used to prevent deformation of stainless steel special-shaped parts during friction stir welding. Subsequently, the interval between laser preheating and friction stir welding is controlled at 5 to 10 mm. The two move and operate synchronously (speed 80 to 100 mm / min) to avoid thermal interference and ensure the preheating effect. Laser preheating reduces energy demand and the welding speed is increased to 80 to 100 mm / min, which is suitable for mass production. The tensile strength of the welded joint is more than 95% of the base material, the welding deformation is extremely small, the weld surface is well formed, and no defects such as flash and surface peeling are observed.

[0021] (3) Compared with the fusion welding method, the laser-friction stir composite welding has the process characteristics of low stress and small deformation, which can improve the precision of the welded product. At the same time, there is no smoke, dust and spatter during the welding process, the noise is low, it is green and environmentally friendly, the environment is basically pollution-free, the working environment is good, and it has basically no harm to the physical and mental health of workers. Specific embodiments

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] Embodiment 1 A laser-friction stir composite welding method for stainless steel special-shaped parts includes the following steps: S1. Laser preheating test: The first stainless steel test piece and the second stainless steel test piece similar to the first stainless steel special-shaped part and the second stainless steel special-shaped part are cut by wire cutting respectively. The first stainless steel test piece and the second stainless steel test piece are clamped, and then the laser beam is aligned with the butt joint groove for preheating. At the same time, an infrared thermometer is used to measure the temperature of the preheating area. The infrared thermometer moves closely following the laser beam, and the moving speeds of the two are the same. When the temperature measured by the infrared thermometer is 400 °C, record the laser power and laser scanning speed of the preheating laser beam at this temperature, and calculate the heat input of laser welding according to the following formula: Q = ηP / v, where η is the thermal efficiency coefficient, generally taken as 0.8 when welding stainless steel. After calculation, the heat input of laser welding is about 5 KJ / cm.

[0024] S2. Pretreatment: Clean the butt joint groove and the area 15 - 30 mm on both sides of the first stainless steel special-shaped part and the second stainless steel special-shaped part of the workpiece to be welded, removing burrs, surface protrusions, oil stains and rust.

[0025] S3. Clamping: The first stainless steel special-shaped part and the second stainless steel special-shaped part of the workpiece to be welded are clamped respectively by using an internal support tooling and an external fixture, ensuring that the butt joint gap between the first stainless steel special-shaped part and the second stainless steel special-shaped part after clamping ≤ 0.15 mm, and the misalignment between the first stainless steel special-shaped part and the second stainless steel special-shaped part ≤ 0.15 mm.

[0026] S4. Laser tack welding: Use a laser beam to perform tack welding on the first and second stainless steel special-shaped parts after clamping. The tack welding spacing is 40 mm, and the length of the tack weld is 10 mm.

[0027] The specific process parameters of laser tack welding are as follows: the laser power is 1500 W, the welding speed is 1.0 m / min, the defocus amount is +4 mm, the shielding gas flow rate is 18 L / min, the purity of the shielding gas argon is ≥99.999%, and the laser deflection angle is 8°.

[0028] After the tack welding is completed, clean the tack weld to remove spatter, dirt, etc. on the surface and vicinity of the weld.

[0029] S5. Laser friction stir welding: During laser friction stir composite welding, first perform laser preheating, and then use a six-link friction stir welding numerical control special machine to perform friction stir welding. The laser preheating and friction stir welding maintain the same speed. At the starting point, first turn on the laser beam for laser preheating and stay for 0.5 - 1 s. After reaching the predetermined preheating temperature, move along the path trajectory of the butt joint groove for preheating. After the laser beam moves 5 mm along the path trajectory of the butt joint groove, start the six-link friction stir welding numerical control special machine and also move along the path trajectory of the butt joint groove to start welding; in laser friction stir composite welding, the laser preheating power is 1000 W, the laser scanning speed is the same as the moving speed of the stirring head, which is 100 mm / min. At the end point, first turn off the laser beam, and turn off the six-link friction stir welding numerical control special machine when it welds to this point.

[0030] The main process parameter range of friction stir welding is as follows: the rotation speed of the stirring head is 700 r / min, the welding speed is 100 mm / min, the penetration depth is 0.2 mm, and the front inclination angle of the main shaft of the six-link friction stir welding machine is about 2°.

[0031] Example 2 A laser friction stir composite welding method for stainless steel special-shaped parts, including the following steps: S1. Laser preheating test: Use wire cutting to cut out the first and second stainless steel test pieces similar to the first and second stainless steel special-shaped parts respectively. Clamp the first and second stainless steel test pieces, and then align the laser beam with the butt joint groove for preheating. At the same time, use an infrared thermometer to measure the temperature of the preheating area. The infrared thermometer closely follows the movement of the laser beam, and the two move at the same speed. When the temperature measured by the infrared thermometer is 450 °C, record the laser power and laser scanning speed of the preheating laser beam at each temperature, and calculate the heat input of laser welding according to the following formula: Q = ηP / v, where η is the thermal efficiency coefficient, generally taken as 0.8 when welding stainless steel. After calculation, the heat input range of laser welding is 9 KJ / cm.

[0032] S2. Pretreatment: Clean the butt joints and the 15 - 30 mm areas on both sides of the first and second stainless steel shaped parts of the workpieces to be welded, removing burrs, surface protrusions, oil stains, rust, etc.

[0033] S3. Clamping: Clamp the first and second stainless steel shaped parts of the workpieces to be welded respectively using an internal support tooling and an external fixture, ensuring that the butt joint gap between the first and second stainless steel shaped parts after clamping is ≤ 0.15 mm, and the misalignment between the first and second stainless steel shaped parts is ≤ 0.15 mm.

[0034] S4. Laser tack welding: Use a laser beam to perform tack welding on the clamped first and second stainless steel shaped parts. The tack welding spacing is 50 mm, and the tack weld length is 15 mm.

[0035] The specific process parameters of laser tack welding are: laser power is 2000 W, welding speed is 1.0 m / min, defocus amount is +3 mm, shielding gas flow rate is 20 L / min, the purity of shielding gas argon is ≥ 99.999%, and the laser deflection angle is 8°.

[0036] After tack welding, clean the tack welds, removing spatter, dirt, etc. on the weld surface and nearby.

[0037] S5. Laser friction stir welding: When performing laser friction stir composite welding, first perform laser preheating, and then use a six - link friction stir welding CNC special machine to perform friction stir welding. The laser preheating and friction stir welding maintain the same speed. At the starting point, first turn on the laser beam for laser preheating, stay for 0.5 - 1 s, and then move along the path of the butt joint for preheating after reaching the predetermined preheating temperature. After the laser beam moves 10 mm along the path of the butt joint, start the six - link friction stir welding CNC special machine and also move along the path of the butt joint to start welding; in laser friction stir composite welding, the laser preheating power is 1500 W, the laser scanning speed is the same as the stirring head moving speed, which is 80 mm / min. At the end point, first turn off the laser beam, and turn off the six - link friction stir welding CNC special machine when it welds to this point.

[0038] The main process parameter range of friction stir welding is as follows: the rotational speed of the stirring head is 600 r / min, the welding speed is 80 mm / min, the penetration depth is 0.1 mm, and the front angle of the main shaft of the six-link friction stir welding machine is about 2°.

[0039] Example 3 A laser friction stir composite welding method for stainless steel special-shaped parts includes the following steps: S1. Laser preheating test: Use wire cutting to cut out the first stainless steel test piece and the second stainless steel test piece similar to the first stainless steel special-shaped part and the second stainless steel special-shaped part respectively. Clamp the first stainless steel test piece and the second stainless steel test piece, and then aim the laser beam at the butt joint groove for preheating. At the same time, use an infrared thermometer to measure the temperature of the preheating area. The infrared thermometer closely follows the movement of the laser beam, and the two move at the same speed. When the temperature measured by the infrared thermometer is 420 °C, record the laser power and laser scanning speed of the preheating laser beam at each temperature, and calculate the heat input of laser welding according to the following formula: Q = ηP / v, where η is the heat efficiency coefficient, generally taken as 0.8 when welding stainless steel. After calculation, the heat input of laser welding is 6.4 KJ / cm.

[0040] S2. Pretreatment: Clean the butt joint groove and the area 15 - 30 mm on both sides of the first stainless steel special-shaped part and the second stainless steel special-shaped part of the workpiece to be welded, removing burrs, surface protrusions, oil stains, rust and so on.

[0041] S3. Clamping: Clamp the first stainless steel special-shaped part and the second stainless steel special-shaped part of the workpiece to be welded respectively with an internal support tooling and an external fixture, ensuring that the butt joint gap between the first stainless steel special-shaped part and the second stainless steel special-shaped part after clamping ≤ 0.15 mm, and the misalignment amount between the first stainless steel special-shaped part and the second stainless steel special-shaped part ≤ 0.15 mm.

[0042] S4. Laser tack welding: Use the laser beam to perform tack welding on the clamped first stainless steel special-shaped part and the second stainless steel special-shaped part. The tack welding spacing is 45 mm, and the length of the tack weld is 12 mm.

[0043] The specific process parameters of laser tack welding are as follows: the laser power is 1800 W, the welding speed is 1.2 m / min, the defocus amount is +2 mm, the shielding gas flow rate is 16 L / min, the purity of the shielding gas argon ≥ 99.999%, and the laser deflection angle is 8°.

[0044] After the tack welding is completed, clean the tack weld, removing the spatter, dirt, etc. on the weld surface and nearby.

[0045] S5, Laser Friction Stir Welding: During laser friction stir composite welding, first perform laser preheating, and then use a six-link friction stir welding numerical control special machine to perform friction stir welding. The laser preheating and friction stir welding maintain the same speed. At the starting point, first turn on the laser beam for laser preheating and stay for 0.5 - 1 s. After reaching the predetermined preheating temperature, move along the path trajectory of the butt joint groove for preheating. After the laser beam moves 8 mm along the path trajectory of the butt joint groove, start the six-link friction stir welding numerical control special machine and also move along the path trajectory of the butt joint groove to start welding; in laser friction stir composite welding, the laser preheating power is 1200 W, and the laser scanning speed is the same as the moving speed of the stirring head, which is 90 mm / min. At the end point, first turn off the laser beam, and turn off the six-link friction stir welding numerical control special machine when it welds to this point.

[0046] The main process parameter range of friction stir welding is: the rotation speed of the stirring head is 650 r / min, the welding speed is 90 mm / min, the penetration depth is 0.17 mm, and the front inclination angle of the main shaft of the six-link friction stir welding machine is about 2°.

[0047] Example 4 A laser friction stir composite welding method for stainless steel special-shaped parts includes the following steps: S1, Laser preheating test: Use wire cutting to cut out the first stainless steel test piece and the second stainless steel test piece similar to the first stainless steel special-shaped part and the second stainless steel special-shaped part respectively. Clamp the first stainless steel test piece and the second stainless steel test piece, then align the laser beam with the butt joint groove for preheating, and at the same time use an infrared thermometer to measure the temperature of the preheating area. The infrared thermometer closely follows the movement of the laser beam, and the two move at the same speed. When the temperature measured by the infrared thermometer is 430 °C, record the laser power and laser scanning speed of the preheating laser beam at each temperature, and calculate the heat input of laser welding according to the following formula: Q = ηP / v, where η is the thermal efficiency coefficient, generally taken as 0.8 when welding stainless steel. After calculation, the heat input of laser welding is 7.2 KJ / cm.

[0048] S2, Pretreatment: Clean the butt joint groove and the 15 - 30 mm area on both sides of the first stainless steel special-shaped part and the second stainless steel special-shaped part of the workpiece to be welded, removing burrs, surface protrusions, oil stains, rust and other substances.

[0049] S3, Clamping: The first stainless steel special-shaped part and the second stainless steel special-shaped part to be welded are clamped by an internal support tooling and an external fixture respectively, ensuring that the butt joint gap between the first stainless steel special-shaped part and the second stainless steel special-shaped part after clamping is ≤0.15 mm, and the misalignment amount between the first stainless steel special-shaped part and the second stainless steel special-shaped part is ≤0.15 mm.

[0050] S4. Laser positioning welding: Use a laser beam to perform positioning welding on the clamped first stainless steel special-shaped part and the second stainless steel special-shaped part. The spacing of the positioning welds is 40 mm, and the length of the positioning weld is 10 mm.

[0051] The specific process parameters of the laser positioning welding are: laser power is 1500 W, welding speed is 1.0 m / min, defocus amount is +2 mm, shielding gas flow rate is 16 L / min, the purity of the shielding gas argon is ≥99.999%, and the laser deflection angle is 8°.

[0052] After the positioning welding is completed, clean the positioning welds to remove spatter, dirt, etc. on the surface and near the welds.

[0053] S5. Laser friction stir welding: When performing laser friction stir composite welding, first perform laser preheating, and then use a six-link friction stir welding numerical control special machine to perform friction stir welding. The laser preheating and the friction stir welding maintain the same speed. At the starting point, first turn on the laser beam for laser preheating and stay for 0.5 - 1 s. After reaching the predetermined preheating temperature, move along the path trajectory of the butt joint groove for preheating. After the laser beam moves 6 mm along the path trajectory of the butt joint groove, start the six-link friction stir welding numerical control special machine and also move along the path trajectory of the butt joint groove to start welding; in the laser friction stir composite welding, the laser preheating power is 1500 W, the laser scanning speed is the same as the moving speed of the stirring head, which is 100 mm / min. At the end point, first turn off the laser beam, and turn off the six-link friction stir welding numerical control special machine when it welds to this point.

[0054] The main process parameter range of the friction stir welding is: the rotation speed of the stirring head is 630 r / min, the welding speed is 100 mm / min, the penetration depth is 0.15 mm, and the front inclination angle of the main shaft of the six-link friction stir welding machine is about 2°.

[0055] Comparative Example 1 Comparative Example 1 is a comparative test example of Example 3, and the difference between it and Example 3 is: In Comparative Example 1, the stainless steel special-shaped part is not preheated. The specific steps are as follows: S1. Pretreatment: Clean the butt joints and the 15 - 30 mm areas on both sides of the first and second stainless - steel special - shaped parts to be welded, removing burrs, surface protrusions, oil stains, and rust and scale, etc.

[0056] S2. Clamping: Clamp the first and second stainless - steel special - shaped parts to be welded respectively using an internal support tooling and an external fixture, ensuring that the butt joint gap between the first and second stainless - steel special - shaped parts after clamping is ≤ 0.15 mm, and the misalignment amount between the first and second stainless - steel special - shaped parts is ≤ 0.15 mm.

[0057] S3. Laser positioning welding: Use a laser beam to perform positioning welding on the clamped first and second stainless - steel special - shaped parts. The spacing of the positioning welds is 45 mm, and the length of the positioning welds is 12 mm.

[0058] The specific process parameters of laser positioning welding are as follows: laser power is 1800 W, welding speed is 1.2 m / min, defocus amount is +2 mm, shielding gas flow rate is 16 L / min, the purity of shielding gas argon is ≥ 99.999%, and the laser deflection angle is 8°.

[0059] After the positioning welding is completed, clean the positioning welds, removing spatter, dirt, etc. on the weld surface and nearby.

[0060] S4. Friction stir welding: Directly perform friction stir welding along the butt joint. The main process parameter range of friction stir welding is as follows: the rotational speed of the stirring head is 1200 r / min, the welding speed is 30 mm / min, the penetration depth is 0.1 mm, and the front - tilt angle of the main shaft of the six - link friction stir welding machine is about 2°.

[0061] Comparative example 2 Comparative example 2 is a comparative test example of Example 3. The difference between it and Example 3 is that: In comparative example 2, during the laser - friction stir composite welding process, the preheating temperature is controlled at 380 °C, and the laser preheating power is 800 W. Other steps and parameter settings are the same as those in Example 3.

[0062] Comparative example 3 Comparative example 3 is a comparative test example of Example 3. The difference between it and Example 3 is that: In comparative example 3, during the laser - friction stir composite welding process, the preheating temperature is controlled at 470 °C, and the laser preheating power is 1600 W. Other steps and parameter settings are the same as those in Example 3.

[0063] Experimental performance test: The welded joints of the first and second stainless steel special-shaped parts in Examples 1-4 and Comparative Examples 1-3 were observed to observe the degree of welding deformation and the forming effect of the weld surface (whether there are defects such as flash burrs, surface peeling, surface depressions, and oxidation and blackening at the weld), and three groups of mechanical property tests were respectively carried out on the welded joints and the base materials of the stainless steel special-shaped parts at room temperature, and the test average values were obtained. The test results are shown in Table 1.

[0064] Table 1 As can be seen from Table 1, in Examples 1-4, the tensile strength of the welded joint specimens of the special-shaped parts reached more than 95% of the tensile strength of the base material specimens of the special-shaped parts, indicating that the welding quality achieved the expected effect. Moreover, after laser-friction stir composite welding, the welding deformation was small, the weld surface formed well, and no flash burrs, surface peeling and other defects were seen.

[0065] In Comparative Example 1, since the stainless steel special-shaped parts were not preheated, the welding deformation was slightly larger, there were traces of oxidation and blackening on the weld surface, the weld surface became concave, and incomplete penetration / incomplete fusion occurred at the bottom of the weld.

[0066] In Comparative Example 2, due to the low preheating temperature, a small amount of oxidation black spots appeared on the weld surface, and a small amount of incomplete penetration / incomplete fusion occurred on the back of the weld.

[0067] In Comparative Example 3, due to the too high preheating temperature, some crack traces appeared in the joint area, and the weld surface forming was slightly rough.

[0068] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirits of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A laser stir friction composite welding method for stainless steel special-shaped parts, characterized in that: The following steps are involved: S1. Pretreatment: Clean the butt joint groove and the vicinity of both sides of the first stainless steel special-shaped part and the second stainless steel special-shaped part to be welded; S2, clamping: clamping and positioning the first stainless steel special-shaped part and the second stainless steel special-shaped part after pretreatment; S3, laser positioning welding: using laser for positioning welding; S4, laser stir friction welding: firstly, laser preheating is performed in front of the stirring head of the stir friction welding device. The preheating temperature range of stainless steel special-shaped parts is 400-450°C, and then stir friction welding is performed at a distance of 5-10mm. The laser preheating and stir friction welding are kept at the same speed.

2. The laser stir friction hybrid welding method for stainless steel special-shaped parts according to claim 1, characterized in that: In step S4, before laser preheating, a laser preheating test is carried out using a first stainless steel test piece and a second stainless steel test piece that are made of the same material and have a similar structure to the first stainless steel special-shaped piece and the second stainless steel special-shaped piece, and an infrared thermometer is used to measure the preheating temperature in the laser preheating test to ensure that the measured preheating temperature range is between 400 and 450° C. Then, the laser power and scanning speed at the measured temperature are recorded, and the heat input of laser welding is calculated according to the following formula: Q=ηP / v, where η is the thermal efficiency coefficient, which is 0.8, P is the laser power, and v is the laser scanning speed. The heat input range of laser welding is calculated to be 5 to 9 KJ / cm.

3. The laser stir friction hybrid welding method for stainless steel special-shaped parts according to claim 2, characterized in that: In step S4, the welding speed of the friction stir welding is 80-100 mm / min, and the laser preheating power range is calculated to be 1000-1500 W according to the heat input of the laser welding calculated in the laser preheating test.

4. The laser stir friction hybrid welding method for stainless steel special-shaped parts according to claim 3, characterized in that: In step S4, the laser scanning speed is the same as the moving speed of the stirring head, which is 80-100 mm / min.

5. The laser stir friction hybrid welding method for stainless steel special-shaped parts according to claim 3 or 4, characterized in that: The process parameter range of stir friction welding is: stirring head rotation speed is 600-700r / min, welding speed is 80-100mm / min, and pressing depth is 0.1-0.2mm.

6. The laser stir friction hybrid welding method for stainless steel special-shaped parts according to claim 5, characterized in that: The friction stir welding device is a six-link type friction stir welding CNC machine.

7. The laser stir friction hybrid welding method for stainless steel special-shaped parts according to claim 1, characterized in that: In the step S3, when laser tack welding is performed on the first stainless steel special-shaped part and the second stainless steel special-shaped part by laser, the tack welding interval is 40 to 50 mm, and the tack welding seam length is 10 to 15 mm.

8. The laser stir friction hybrid welding method for stainless steel special-shaped parts according to claim 7, characterized in that: The specific process parameters of laser positioning welding are: laser power is 1500~2000W, welding speed is 1.0~1.2m / min, defocus is +2~+5mm, shielding gas flow is 15~20L / min, the purity of shielding gas argon is ≥99.999%, and the laser deflection angle is 8°.

9. The laser stir friction hybrid welding method for stainless steel special-shaped parts according to claim 1, characterized in that: In the step S2, the first stainless steel shaped part and the second stainless steel shaped part to be welded are clamped by using an inner support tool and an outer clamp respectively, and the butt clearance between the first stainless steel shaped part and the second stainless steel shaped part after clamping is ≤0.15mm, and the misalignment between the first stainless steel shaped part and the second stainless steel shaped part is ≤0.15mm.

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