Reducing welding nozzle for welding medium-thickness component and welding method

Abstract

The invention provides a variable-diameter welding nozzle for welding a medium-thickness component and a welding method. Aiming at the problems of poor quality, low efficiency and the like caused by defects during welding of the main force-bearing component of the aircraft landing gear, a straight tube welding nozzle is abandoned, a variable-diameter welding nozzle is redesigned, produced and verified, the welding accessibility is improved, and laminar flow layer shielding gas is formed. And a welding wire straightening mechanism is additionally arranged, so that the collimation of the welding wire is enhanced. The nozzle head is made of ceramic materials, adhesion and blocking of welding spatter are eradicated, and the protection effect is improved. A spin welding method is used, welding defects are eliminated, and welding quality is improved.

Description

Technical Field

[0001] The invention relates to the field of aviation welding, and in particular to a variable diameter welding nozzle and a welding method for welding medium-thickness components. Background Art

[0002] Aircraft use a large number of medium-thickness (δ18mm~δ42mm) cylindrical main load-bearing components, such as wheel trolley frames, landing gear shock absorber tubes and engine struts. The welding thickness exceeds 18mm, and the single weight of the smallest component exceeds 0.2 tons. The welding process requires special welding fixtures to support and rotate.

[0003] To increase weld penetration and minimize welding distortion, a V-shaped groove with a 2mm blunt edge and a 60° groove angle was machined in the joint area after comprehensive consideration of various factors. Furthermore, in accordance with HB / Z 5132-2014, "Ultra-High Strength Steel Fusion Welding Process and Quality Inspection," "preheating temperature before welding should be 250°C to 400°C. Throughout the welding process, the temperature of the weld and the surrounding area should be maintained at no less than 250°C."

[0004] Therefore, welding requires a groove and preheating to the appropriate temperature. Traditionally, this method involves manually operated arc welding with sticks. Continuous welding at high temperatures for extended periods of time makes it difficult to ensure weld quality meets project requirements, and weld defects of varying sizes and natures often occur. This necessitates repeated nondestructive testing, defect removal, rework, and repeated testing, severely impacting production efficiency and product quality.

[0005] With the development and advancement of aviation manufacturing technology, fully automated robotic welding systems are replacing manually operated arc welding techniques for the manufacture of medium-thickness cylindrical load-bearing components. To achieve high efficiency and quality welding, the robotic system utilizes a standard straight-tube welding nozzle—a cylindrical component made of carbon steel with a length of 70 mm, an outer diameter of 36 mm, and a wall thickness of 3 mm. The nozzle is mounted at the front end of the welding torch. Its movement is controlled by the robot's programming. The welding wire is ejected from the center of the nozzle, while shielding gas flows around the wire, protecting the weld pool and hot metal from air oxidation and contamination.

[0006] However, long, thick straight-tube welding nozzles are not suitable for welding medium-thick cylindrical load-bearing components in the aviation manufacturing industry. Instead, they are the root cause of poor weld accessibility, severe spatter, and increased defects such as lack of fusion and incomplete penetration. Due to the excessive outer diameter of straight-tube welding nozzles, they cannot penetrate deeply into the root of the V-groove to melt the blunt edge at the bottom of the groove, resulting in root incomplete penetration defects. Similarly, due to the excessive diameter of the welding nozzle, it often touches the groove surfaces on both sides during rotation, preventing the welding gun from rotating to melt the base material, resulting in lack of fusion defects on both sides of the weld groove.

[0007] To ensure the welding wire reaches the bottom and sides of the groove, the only option is to increase the wire stickout, compensating for the inherently poor reachability of straight welding nozzles and eliminating welding defects. However, the greater the wire stickout, the more severe the metal spatter. Some spatter adheres to the inner wall of the welding nozzle, blocking the flow of shielding gas and causing severe turbulence, which continuously deteriorates the shielding effect. As spatter accumulates on the inner wall of the carbon steel welding nozzle, it eventually completely blocks the nozzle's inner diameter, preventing the wire from being ejected smoothly and forcing the welding process to terminate.

[0008] Furthermore, excessively long welding wires wiggle freely within the hollow nozzle, causing arc combustion instability, erratic weld pool flow, and disruptive shielding gas flow direction and velocity. The combined effects of poor weld accessibility, weld pool instability, and shielding gas turbulence increase the uncontrollability of the welding process, ultimately leading to poor weld quality, increased defect rates, and reduced joint performance.

[0009] Therefore, solving the challenges of poor accessibility of straight welding nozzles during automated robotic welding, eliminating weld defects, and reducing spatter during welding become key issues in welding primary load-bearing structural components. At the same time, ensuring that the shielding gas flows laminarly into the weld area protects the molten pool from air contamination. Summary of the Invention

[0010] The present invention provides a variable-diameter welding nozzle and welding method for welding medium-thickness components. This relates to the welding of medium-thickness (δ18mm to δ42mm) cylindrical load-bearing components in the aviation manufacturing industry. The variable-diameter welding nozzle is used to weld thick, grooved, main load-bearing structural components. To address quality issues such as poor welding accessibility during automated robotic welding of medium-thickness cylindrical components, which can lead to severe spatter and welding defects, the invention employs measures such as optimizing the welding nozzle structure, modifying the welding method, and diverting the shielding gas flow to improve production efficiency, enhance product quality, and reduce the production rework rate.

[0011] A first aspect of the present invention provides a variable diameter welding nozzle for welding medium thickness components, comprising: a nozzle body 9 and a nozzle head 10;

[0012] The outer side of the welding gun electrode clamp 3 is threadedly connected to the nozzle body 9, and the inner side of the end of the nozzle body 9 is threadedly connected to the nozzle head 10. The nozzle head 10 is sleeved on the outer side of the wire outlet of the welding gun electrode clamp 3;

[0013] A thread hole 14 is provided at the center of the nozzle 10;

[0014] The nozzle body 9 and the nozzle head 10 are tapered in shape;

[0015] There is a gas mixing cavity between the nozzle body 9 and the welding gun electrode clamp 3. The middle cone part of the nozzle body 9 is surrounded by upper vent holes 11, which are connected to the gas mixing cavity.

[0016] The nozzle head 10 is provided with a middle layer vent hole 12 and a lower layer vent hole 13 along the axial direction;

[0017] One end of the middle vent hole 12 is arranged outside the middle cone of the nozzle head 10, and the other end is connected to the gas mixing cavity;

[0018] One end of the lower vent hole 13 faces the end of the welding gun electrode clamp 3 , and the other end is located at the outer end of the nozzle head 10 .

[0019] Optionally, the nozzle head 10 is made of ceramic material.

[0020] Optionally, the nozzle body 9 is made of copper.

[0021] Optionally, the diameters of the upper vent holes 11 , the middle vent holes 12 and the lower vent holes 13 are different.

[0022] Optionally, the diameter of the wire hole is 1.0 mm to 1.5 mm larger than the diameter of the welding wire.

[0023] Optionally, the nozzle body 9 has an overall length of 50 mm, an upper outer diameter of 36 mm, an inner diameter of 30 mm, a lower outer diameter of 18 mm, and a diameter of the upper vent hole 11 of 2.5 mm.

[0024] Optionally, the diameter of the middle layer ventilation hole 12 is 1.0 mm.

[0025] Optionally, the lower layer ventilation holes 13 are evenly distributed along the circumferential direction and have a diameter of 0.5 mm.

[0026] A second aspect of the present invention provides a welding method using the variable diameter welding nozzle according to any one of the first aspects, the welding method comprising:

[0027] The V-shaped groove is welded using the rotation method.

[0028] Optional welding methods include:

[0029] S1. Place the arc close to the root of the V-groove and rotate the medium-thick component to be welded to completely melt the blunt edge of the groove root and eliminate the incomplete penetration defect at the weld root;

[0030] S2. When welding the remaining part of the V-shaped groove, rotate the outer end of the reducer nozzle left and right, and use a continuous zigzag movement method to fully fill the wider weld in the middle of the V-shaped groove and eliminate interlayer defects.

[0031] The present invention provides a variable diameter welding nozzle and a welding method for welding medium-thickness components, which have the following beneficial effects: 1) The welding nozzle is decomposed into two components, the nozzle body and the nozzle head, which are respectively made of copper material and ceramic material. High-temperature spatter will not adhere to the ceramic nozzle head, thereby preventing the disruption of the protective airflow and blocking the welding nozzle wire hole. 2) The welding nozzle has an overall conical structure, which can reach the root of the groove and improve the welding accessibility. 3) Air holes are opened in the circumferential, axial and longitudinal directions of the variable diameter welding nozzle to force the formation of a laminar flow layer of protective gas, thereby improving the protection effect. 4) A small-diameter wire hole is opened in the center of the nozzle head, and together with the electrode clamp, it constitutes a welding wire straightening mechanism to ensure the welding straightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of landing gear outer tube assembly and groove;

[0033] Figure 2 Schematic diagram of landing gear welding groove dimensions;

[0034] Figure 3 Schematic diagram of the matching position of the straight welding nozzle and the weldment;

[0035] Figure 4a Schematic diagram of the internal structure of the variable diameter welding nozzle;

[0036] Figure 4b Schematic diagram of the reduced diameter welding nozzle;

[0037] Figure 5a Schematic diagram of the mouth structure;

[0038] Figure 5b Schematic diagram of the mouth-body ventilation arrangement;

[0039] Figure 6a Schematic diagram of the internal structure of the mouth;

[0040] Figure 6b Schematic diagram of the ventilation structure on the upper part of the mouthpiece;

[0041] Figure 6c Schematic diagram of the nozzle's thread-passing hole and circumferential vent holes;

[0042] Figure 7 Schematic diagram of welding shielding gas layering;

[0043] Figure 8 Schematic diagram of the wire straightening mechanism and process;

[0044] Figure 9 Schematic diagram of groove bottom welding;

[0045] Figure 10 Schematic diagram of welding in the middle of the groove;

[0046] Figure 11a Schematic diagram of welding on the upper side of the groove;

[0047] Figure 11b Schematic diagram of welding in the middle part of the upper part of the groove;

[0048] Figure 11c Schematic diagram of welding on the other side of the upper part of the groove;

[0049] Description of reference numerals:

[0050] 1 bearing cylinder, 2 frame cylinder, 3 welding gun electrode clamp, 4 straight welding nozzle, 5 dry extension, 6 electrode clamp vent, 7 shielding gas, 8 welding wire, 9 nozzle body, 10 nozzle head, 11 upper vent, 12 middle vent, 13 lower vent, 14 wire hole, 15 upper shielding gas, 16 middle shielding gas, 17 lower shielding gas, 18 base weld, 19 reducing welding nozzle, 20 middle weld. DETAILED DESCRIPTION

[0051] The present application is further described in detail below in conjunction with welding examples of landing gear outer tubes and accompanying drawings.

[0052] The present invention mainly includes the following contents: 1) A variable diameter welding nozzle is used to replace the traditional straight tube welding nozzle, and the structure of the straight tube welding nozzle is decomposed into two components: a nozzle body with a variable diameter and a nozzle head with a small aperture. The overall structure is conical, which improves the accessibility of the welding nozzle; 2) The nozzle head adopts a long-length, small-aperture rod-shaped ceramic structure, which prevents spatter from adhering to the welding nozzle, and forms a long-distance lever mechanism together with the welding gun electrode clamp, which plays the role of straightening the welding wire, ensuring the straightness of the welding wire and reducing welding spatter; 3) The variable diameter welding nozzle adopts a form of large upper and small lower part, which can penetrate into the bottom of the groove, increases the side rotation function of the welding gun, can melt the metal on both sides of the groove, and eliminate defects such as incomplete welding and incomplete fusion; 4) A plurality of groups of ventilation holes are opened on the outer wall of the nozzle body and the end of the nozzle head. The protective gas flows through the ventilation holes to reach the weld area, forcing the formation of a stable laminar layer to protect the molten pool and high-temperature metal.

[0053] A new variable-diameter welding nozzle has been redesigned, replacing the straight hollow welding nozzle with a variable-diameter welding nozzle to increase welding accessibility. The variable-diameter welding nozzle consists of two parts: a nozzle body with a variable diameter and a nozzle head with a small aperture. Made of copper and ceramic materials respectively, it increases the penetration length of the welding nozzle, diverts the airflow layer by layer, and forces the welding wire to be straightened. It overcomes the shortcomings of the straight welding nozzle, such as insufficient accessibility, poor protection effect, and inability to rotate. It improves welding accessibility, reduces welding defects, and reduces metal spatter. Using a variable-diameter welding nozzle, the welding wire is pushed deep into the root of the groove, completely melting the blunt edge of the groove to ensure complete penetration of the joint. The side-turn welding method is used to melt the material on both sides of the groove surface, reducing the incidence of defects. The layered shielding gas method is used to form a stable laminar layer to improve the protection effect.

[0054] The welding nozzle structure has been modified, replacing the traditional uniform-diameter tubular nozzle with a two-component nozzle body and nozzle tip. This provides ventilation, wire feeding, and alignment, with the nozzle body positioned closer to the welding gun and the nozzle tip closer to the weld pool. The nozzle body is a variable-diameter tubular structure, larger at the top and smaller at the bottom. Made of copper, the upper portion connects to the welding gun's electrode clamp via internal threads. The nozzle tip is mounted at the bottom of the nozzle body, closer to the weld pool. Made of ceramic, it prevents spatter from adhering to the nozzle and connects to the nozzle body via external threads.

[0055] The reducer welding nozzle features a tapered shape and is suitable for rotating in either direction, allowing for interchangeable nozzles depending on the weld groove configuration. Due to its significantly reduced diameter, the nozzle tip's outer diameter is only 8mm and its length is over 20mm. This significantly reduces the outer diameter of a conventional nozzle to 36mm, allowing for flexible penetration into the weld root, melting the blunt edge of the groove and eliminating incomplete penetration. Furthermore, due to its reduced size, the nozzle can be flexibly rotated between groove surfaces, completely melting the base material and eliminating incomplete penetration defects.

[0056] Ventilation holes of varying diameters are provided circumferentially and axially along the variable-diameter welding nozzle, forcing the shielding gas to flow in laminar layers, protecting different areas of the weld metal. Ventilation holes are provided on the nozzle's outer wall, allowing the shielding gas to flow through a laminar flow, protecting the upper and middle areas of the groove. Two sets of vent holes are located at the nozzle tip, which, together with the wire holes, form a three-layer shielding gas flow, ensuring that the shielding gas reaches the molten pool and the high-temperature metal area, forcing a protective gas layer.

[0057] The nozzle head is tubular and, in conjunction with the welding gun electrode clamp, forms a long-reach lever mechanism that aligns the welding wire and ensures wire straightness. Made of ceramic for improved wear resistance, it is mounted at the bottom of the nozzle body and features a large, small aperture. The center of the nozzle head features a wire hole 1.0mm to 1.5mm larger than the wire diameter. This hole, combined with the welding gun electrode clamp at the rear, forms the wire straightening mechanism, ensuring accurate alignment of the wire as it extends.

[0058] The landing gear outer tube assembly is welded from the bearing tube 1 and the frame tube 2. The welded joint thickness is 36mm. A single-sided V-shaped groove is opened in the welding area. The local structure of the weld is as follows: Figure 1 As shown. During welding, the outer cylinder assembly rotates and the corresponding welding nozzle moves forward to complete the welding of the circular weld. In order to ensure a full penetration of 36mm, a 60° single-sided V-shaped groove is opened in the welding area, and the root gap and blunt edge are both 2mm, as shown. Figure 2 shown.

[0059] When using the straight welding nozzle 4 to weld the landing gear outer tube assembly (including the bearing tube 1 and the frame tube 2), the welding gun is located at the upper part of the welding groove, as shown in the figure. Figure 3As shown. The straight welding nozzle 4 is a standard straight hollow tube form, which is installed at the lower end of the welding gun electrode clamp 3. During welding, the shielding gas 7 flows out from top to bottom through the electrode clamp vent 6 to reach the molten pool and its vicinity, protecting the molten pool and the high-temperature metal. In view of the fact that the outer diameter of the straight welding nozzle 4 is 36mm, the welding nozzle cannot penetrate into the bottom of the groove, and the dry extension length 5 of the welding wire 8 must be increased to 20mm~25mm in order to melt the blunt edge and ensure that the 2mm thickness is completely melted through. Excessive dry extension length causes the alignment of the welding wire 8 to deteriorate and serious spatter occurs, which ultimately leads to the inability to completely melt the blunt edge of the root of the groove, resulting in an incomplete penetration defect at the bottom of the weld. Similarly, because the outer diameter of the straight welding nozzle 4 is too large, the welding gun cannot rotate left and right, and cannot completely melt both sides of the groove, resulting in unfused defects on both sides of the weld.

[0060] The present invention decomposes the straight welding nozzle 4 into two components, the nozzle body 9 and the nozzle head 10, and redesigns their respective structures. Figure 4a As shown in the figure, the nozzle body 9 is connected to the welding gun electrode clamp 3 with internal threads at the top, and the nozzle head 10 is located at the bottom, close to the molten pool. The welding wire 8 passes through the welding gun electrode clamp 3, the nozzle body 9, and the nozzle head 10 from the center, and finally exits the nozzle head 10 with a small dry extension. Shielding gas enters from the top, passes through the vent 6 in the welding gun electrode clamp 3, forms a protective atmosphere inside and around the nozzle body 9 and nozzle head 10, and reaches the welding area.

[0061] The assembly shape of the variable diameter welding nozzle 19 (the assembly general name of the nozzle body 9 and the nozzle head 10 two components) is as follows Figure 4b As shown, the overall appearance is a tapered structure with varying diameters. The diameter at the top remains unchanged and is still assembled with the original welding gun electrode holder 3, while the diameter gradually decreases downwards. To form a multi-layer shielding gas flow, an upper vent hole 11 is circumferentially provided in the middle portion of the nozzle body 9, while a middle vent hole 12 and a lower vent hole 13 are provided in the middle portion and end portion of the nozzle head 10, respectively.

[0062] Mouth body 9 overall structure as Figure 5a As shown, it has an overall length of 50mm and is made of copper to prevent spatter and adhesion. Both the upper and lower sections are straight cylindrical, with a tapered middle section. An upper vent hole 11 with a diameter of 2.5mm is provided in the tube wall. The upper section has an outer diameter of 36mm and an inner diameter of 30mm, and is internally threaded to connect to the welding gun electrode clamp 3. The lower section has an outer diameter of 18mm and is internally threaded to connect to the nozzle head 10.

[0063] The upper vent holes 11 are opened on the conical wall, the number of which is 8 and evenly distributed along the circumference. The structure is as follows Figure 5b The angle between the conical portion and the straight tube is 145°, with the larger diameter tube at the top gradually transitioning to the smaller diameter tube at the bottom. The copper material is used to reduce the adhesion of welding spatter and prevent it from blocking the upper ventilation hole 11.

[0064] The overall structure of the nozzle 10 is as follows Figure 6a As shown, the nozzle tip is essentially cylindrical and made of ceramic. Because it is located near the high-temperature molten pool, ceramic is used to prevent splashes from the hot liquid metal from adhering to the tip and hindering the welding process. The upper portion is externally threaded and connected to the nozzle body 9, forming a reduced-diameter welding nozzle 19 assembly. The overall outer diameter is much smaller than that of the straight welding nozzle 4. A middle vent hole 12, a lower vent hole 13, and a wire hole 14 are provided along the length of the nozzle tip for passage of shielding gas 7 and welding wire 8, respectively.

[0065] The middle layer vent holes 12 are made in the circumferential direction of the outer surface of the nozzle head 10, the number of which is 4 and evenly arranged along the circumferential direction. Figure 6b The middle vent holes 12 have a diameter of 1.0 mm and extend throughout the length of the welding process. During welding, the shielding airflow passes through the middle vent holes 12 to form a middle shielding airflow, protecting the metal material in the high-temperature zone from oxidation and contamination by the air.

[0066] The lower layer vent hole 13 and the wire hole 14 are made in the circumferential direction and the center position of the nozzle head 10 respectively. Figure 6c As shown, the lower layer of ventilation holes 13 are evenly distributed along the circumference, with a diameter of 0.5 mm and a number of four. During welding, shielding gas passes through the lower layer of ventilation holes 13 to the upper part of the molten pool, achieving the purpose of protecting the molten pool. The wire hole 14 is centrally located, concentric with the nozzle head 10, and has a diameter of 2.0 mm. Its main function is to ensure smooth passage of the welding wire 8. The gap between the welding wire 8 and the wire hole 14 allows a small amount of shielding gas to pass through, helping to protect the welding pool.

[0067] During welding, the welding wire 8 passes through the center of the welding gun and reaches the root of the groove formed by the bearing tube 1 and the frame tube 2. After the arc is ignited, the blunt edge at the bottom of the groove will be completely melted to eliminate the incomplete welding defect, such as Figure 7 As shown. Thanks to the use of a variable-diameter welding nozzle 19, welding accessibility is greatly improved, allowing the welding wire to reach the root of the groove. Shielding gas 7 enters the variable-diameter welding nozzle 19 through the welding gun electrode clamp 3 and forms an upper shielding gas layer 15 through the nozzle body 9, protecting the outermost area of the weld. Continuing through the middle-layer vent holes 12 and lower-layer vent holes 13 of the nozzle head 9, it forms a middle-layer shielding gas 16 and a lower-layer shielding gas 17, protecting the high-temperature metal and the weld pool, respectively. The nozzle head 10 is made of ceramic material, preventing welding spatter from adhering to the surrounding area of the nozzle head 10 or the interior of the wire hole 14, thus ensuring a smooth welding process.

[0068] The variable diameter welding nozzle 19 has the function of straightening the welding wire 8. Figure 8As shown, the welding gun electrode clamp 3 and nozzle head 10 form a wire straightening mechanism. The length exceeds 70 mm, and the inner diameter of the wire hole 14 exceeds the wire diameter by 1.0 mm to 1.5 mm. This provides long-range wire restraint, preventing wire swing during feeding. This ensures the wire 3 is aligned when it exits the nozzle head 10, reducing arc spatter.

[0069] Taking advantage of the good accessibility of the variable diameter welding nozzle 19, the blunt edge of the root of the groove is melted, such as Figure 9 To reduce welding deformation in the landing gear assembly, a V-shaped groove is created at the welded ends of the support tube 1 and the frame tube 2. A reducing welding nozzle 19 is moved linearly near the root of the groove, melting the root to form a base weld 18. During the welding process, the reducing welding nozzle 19 moves linearly, creating a stable and controllable arc combustion, completely melting the metal at the root of the groove, eliminating incomplete penetration defects, and forming a satisfactory weld.

[0070] After the bottom weld 18 is completed, the upper area is welded by rotating left and right. The process is as follows: Figure 10 As the base weld 18 is completed, the weld area gradually widens, and continuing with the straight-line welding method can no longer cover the entire weld area. Taking advantage of the small outer diameter and operational flexibility of the variable-diameter welding nozzle 19, the welding method is changed to a left-right rotation method. The variable-diameter welding nozzle 19 is required to simultaneously move forward within the plane and rotate left and right, forming a continuous "Z"-shaped welding path, forming the middle weld 20.

[0071] The method of rotating the variable diameter welding nozzle 19 left and right is used to continue welding the weld with a larger width, and fully melt the metal on both sides of the groove to eliminate the unfused defects. The process is as follows Figure 11a 、 Figure 11b and Figure 11c As shown. Since the outer diameter of the straight welding nozzle 4 is too large, it has disadvantages such as poor accessibility and inability to rotate, which makes it impossible to fuse the metal on both sides of the groove, and easily forms unfused defects. The variable diameter welding nozzle 19 adopts a variable diameter design, which greatly improves flexibility and has a rotation function.

[0072] When the welding area is too large, first rotate the reducing welding nozzle 19 to the groove surface on one side of the bearing cylinder 1, add welding wire 8 to form a weld, such as Figure 11a Secondly, in the middle part, the arc melts the welding wire 8 and the previous layer of weld to form the weld in the middle part, as shown in FIG. Figure 11b Finally, keep the arc from going out, continue to rotate the variable diameter welding nozzle 19 to the groove surface on one side of the frame tube 2, and continue to add welding wire 8 to continue to form the weld. Figure 11c Following the above procedure, continuous work is performed in both the length and height directions to finally complete the welding of the landing gear assembly.

[0073] The present invention boasts significant technical and economic benefits. It is not only suitable for welding medium-thickness load-bearing components such as wheel trolley frames, landing gear shock absorbers, and engine struts, but can also be applied to welding medium- and heavy-thickness flat-plate main load-bearing frame beams, significantly improving welding quality. Furthermore, it can be extended to the manufacture of medium- and heavy-thickness components in other industries, achieving the goals of improving welding quality, increasing manufacturing efficiency, and reducing manufacturing costs.

Claims

1. A variable diameter welding nozzle for welding medium thickness components, characterized in that: include: Mouth body (9) and mouth head (10); The outer side of the welding gun electrode clamp (3) is threadedly connected to the nozzle body (9), the inner side of the end of the nozzle body (9) is threadedly connected to the nozzle head (10), and the nozzle head (10) is sleeved on the outer side of the wire outlet of the welding gun electrode clamp (3); A thread hole (14) is provided at the center of the nozzle (10); The outer shapes of the nozzle body (9) and the nozzle head (10) are tapered; A gas mixing cavity is provided between the nozzle body (9) and the welding gun electrode clamp (3); upper vent holes (11) are provided around the central cone portion of the nozzle body (9); and the upper vent holes (11) are communicated with the gas mixing cavity; The nozzle head (10) is provided with a middle layer vent hole (12) and a lower layer vent hole (13) along the axial direction; One end of the middle-layer vent hole (12) is arranged outside the middle cone of the nozzle head (10), and the other end is connected to the air mixing cavity; One end of the lower vent hole (13) faces the end of the welding gun electrode clamp (3), and the other end is located at the outer end of the nozzle head (10).

2. The variable diameter welding nozzle for welding medium thickness components according to claim 1, characterized in that: The mouthpiece (10) is made of ceramic material.

3. The variable diameter welding nozzle for welding medium thickness components according to claim 1, characterized in that: Mouth body (9) adopts copper material.

4. The variable diameter welding nozzle for welding medium thickness components according to claim 1, characterized in that: The diameters of the upper layer vent holes (11), the middle layer vent holes (12) and the lower layer vent holes (13) are different.

5. The variable diameter welding nozzle for welding medium thickness components according to claim 1, characterized in that: The diameter of the wire hole is 1.0mm to 1.5mm larger than the diameter of the welding wire.

6. The variable diameter welding nozzle for welding medium thickness components according to claim 1, characterized in that: The nozzle body (9) has an overall length of 50 mm, an upper outer diameter of 36 mm, an inner diameter of 30 mm, a lower outer diameter of 18 mm, and an upper vent hole (11) with a diameter of 2.5 mm.

7. The variable diameter welding nozzle for welding medium thickness components according to claim 1, characterized in that: The diameter of the middle layer vent hole (12) is 1.0 mm.

8. The variable diameter welding nozzle for welding medium thickness components according to claim 1, characterized in that: The lower layer vent holes (13) are evenly distributed along the circumferential direction and have a diameter of 0.5 mm.

9. A welding method using the variable diameter welding nozzle according to any one of claims 1 to 8, characterized in that: Welding methods include: The V-shaped groove is welded using the rotation method.

10. The welding method according to claim 9, characterized in that: include: S1. Place the arc close to the root of the V-groove and rotate the medium-thick component to be welded to completely melt the blunt edge of the groove root and eliminate the incomplete penetration defect at the weld root; S2. When welding the remaining part of the V-shaped groove, rotate the outer end of the reducer nozzle left and right, and use a continuous "Z"-shaped movement method to fully fill the wider weld in the middle of the V-shaped groove and eliminate interlayer defects.

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