Welding trajectory planning method for square tube K-TIG butt welding with dual robots

Abstract

The present invention relates to a welding trajectory planning method for K-TIG butt welding of square tubes by dual-robot collaboration, and belongs to the field of welding technology. The dual robots are a welding robot and a handling robot that can work collaboratively. The flange end of the welding robot is connected to a K-TIG welding gun, and the end of the handling robot is connected to a square tube structural member. The dual-machine collaborative operation and the K-TIG welding system are used to achieve the welding of the butt ring weld of the square tube structural member. The present invention plans the motion trajectory of the welding robot and the handling robot through position and speed constraints, so that the K-TIG welding gun is always located at a constant distance above the weld and aligned with the weld during the welding process, and the weld point is always in an ideal position, that is, the molten pool of the weld point is ensured to be as horizontal as possible. The influence of gravity on the molten pool during K-TIG welding is reduced, and the formation of welds in different local areas of the welded component is ensured to be consistent.

Description

Technical Field

[0001] The present invention relates to the field of welding technology, in particular to a welding technology combining a K-TIG welding technology and dual-machine collaboration, and more particularly to a welding trajectory planning method for K-TIG butt welding of square tubes using dual robots in collaboration. Background Art

[0002] K-TIG is a deep-penetrating, keyhole-type, non-melting inert gas (NIG) shielded welding method, classified as a high-current TIG welding technique. The arc pressure generated by the high current maintains a dynamic equilibrium with the gravity and surface tension of the liquid metal, forming a small, geometrically stable hole. This allows for single-sided welding and double-sided forming of medium-thick plates. K-TIG requires neither filler wire nor beveling for materials under 16 mm thick (such as ferritic, austenitic, duplex stainless steels, titanium alloys, and zirconium alloys), yet it boasts a 100-fold improvement in efficiency compared to traditional TIG welding. However, this welding method is more suitable for flat welding. Therefore, when welding curved workpieces (such as pipes), the pipe must be rotated to maintain a flat welding position relative to the welding path. Otherwise, vertical or overhead welding is more prone to weld defects such as dripping or melt damage caused by weld pool collapse. Existing solutions to this problem include pulsed welding capping and external axial magnetic field control, but both methods are highly inefficient and require extensive testing and evaluation.

[0003] Due to the complexity of welded workpiece structures and welding process combinations, traditional industrial control systems and single-robot-based production equipment have been unable to meet production requirements. Multi-robot collaborative systems significantly improve the flexibility and load capacity of industrial robot systems, and can quickly resolve the challenges posed by the complexity of welded workpiece structures and welding process combinations. Summary of the Invention

[0004] The purpose of the present invention is to provide a dual-robot collaborative square tube K-TIG butt welding trajectory planning method, which solves the problem of welding defects such as melting caused by the collapse of the K-TIG welding molten pool when the workpiece has a curved surface. The present invention plans the motion trajectory of the welding robot and the handling robot through position and speed constraints, so that the K-TIG welding gun is always located at a constant distance above the weld and aligned with the weld during the welding process. At the same time, the relative motion control of the welding robot and the handling robot keeps the K-TIG welding gun in a flat welding state relative to the welding trajectory and the welding speed remains unchanged. The influence of gravity on the molten pool during K-TIG welding is reduced, ensuring the consistent formation of welds in different local areas of the welded component.

[0005] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0006] A dual-robot collaborative square tube K-TIG butt welding trajectory planning method is provided. A K-TIG welding gun and a square tube structural member are installed on a collaborative welding robot and a handling robot, respectively. The welding robot and the handling robot work together and cooperate with the K-TIG welding system to weld the butt girth weld of the square tube structural member. The method includes the following steps:

[0007] Step 1: Determine the K-TIG welding process parameters according to the material and thickness of the square tube structure;

[0008] Step 2: Determine the welding trajectory according to the structure of the square tube structure and the posture requirements of the welding point. The welding robot clamps the K-TIG welding gun and starts the arc from the arc starting point P0. After the arc is started, the K-TIG welding gun moves forward until it reaches the starting point P1 of the arc segment of the square tube structure. The movement speed of the K-TIG welding gun slowly decreases to 0. At this time, the handling robot grabs the square tube structure and rotates it around the center P2 of the arc segment to be welded. When the end point P3 of the arc segment of the square tube structure is used as the welding point, the K-TIG welding gun continues to move forward. The K-TIG welding gun performs the welding task of the straight section of the square tube structure. When it reaches the starting point of the next arc, it stops moving. At this time, the square tube structure rotates to perform the arc segment welding task of the square tube structure. This reciprocating process continues until the K-TIG welding gun completes the welding task of the square tube structure's circumferential weld and reaches the arc extinction point P4 to extinguish the arc. The motion trajectory of the dual robots during the welding process is constrained by the welding point to be welded, the posture requirements of the K-TIG welding gun, the height from the tungsten electrode to the workpiece surface, and the welding speed in the K-TIG welding process parameters.

[0009] Step 3: Divide the welding task into a straight segment welding task module and an arc segment welding task module based on the structural dimensions of the square tube structure. In different welding task modules, plan the K-TIG welding gun movement speed v and the angular velocity w of the square tube structure rotation based on the dimensional parameters of the square tube structure and the K-TIG welding process parameters.

[0010] The K-TIG welding process parameters are determined based on the material and thickness δ of the square tube structure, including the height d from the tungsten electrode to the workpiece surface, the welding speed v, and the welding current I. The welding current I ranges from 300 to 1000 A.

[0011] When performing the task of welding the straight section of a square tube structure, the welding robot clamps the K-TIG welding gun and moves in a straight line, and the handling robot remains stationary; when performing the task of welding the arc section of a square tube structure, the welding robot clamps the K-TIG welding gun and remains stationary, and the handling robot grabs the square tube structure and makes a rotational motion with the center of the arc section of the square tube structure as the center of the circle.

[0012] When performing the task of welding the straight section of a square tube structure, the welding speed v is equal to the movement speed of the K-TIG welding gun; when performing the task of welding the arc section of a square tube structure, the welding speed v is equal to the product of the angular velocity w of the square tube structure and the distance r from the node to be welded to the center of rotation.

[0013] When welding a straight section of a square tube, the total displacement of the K-TIG welding gun is 4a. When welding an arc section, the total length of the center's motion trajectory is Πb. When welding an arc section, the center of each arc section is located 45° above the center of the tube, at a distance b. The tube rotates at an angular velocity w = v / c, and the angle θ of rotation is 90°. a, b, and c are the shape parameters of the tube: a is the length of a straight section, b is the distance from the center of the tube to the center of rotation, and c is the radius of the arc section.

[0014] The beneficial effects of the present invention are:

[0015] 1. This invention uses K-TIG welding technology, which eliminates the need for beveling before welding and filler wire during welding. It can weld on one side and form on both sides, making it 100 times faster than traditional TIG welding technology. This saves costs and greatly improves welding efficiency.

[0016] 2. The dual-machine collaborative welding trajectory planning method proposed in this invention plans the motion trajectories of the welding robot and the handling robot using position and velocity constraints. This ensures that the K-TIG welding gun is always positioned a constant distance above and aligned with the weld seam during welding. Furthermore, the weld point is always in an ideal position, ensuring that the weld pool is as horizontal as possible. This reduces the impact of gravity on the weld pool during K-TIG welding, ensuring consistent weld formation across different regions of the square tube structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide further understanding of the present invention and constitute a part of this application. The illustrative examples of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0018] Figure 1 Schematic diagram of an embodiment of a square tube K-TIG butt welding operation using dual robots in collaboration according to the present invention;

[0019] Figure 2 This is a schematic diagram of the cross-sectional shape of a square tube according to the present invention;

[0020] Figure 3 A flowchart of welding tasks during the welding process of the present invention (the dotted lines represent three welding tasks that need to be performed during the welding process);

[0021] Figure 4 Schematic diagram of the relative motion trajectory of the tungsten electrode tip and the center of the workpiece of the present invention (the red dotted line represents the motion trajectory of the tungsten electrode tip of the K-TIG welding gun, and the blue dotted line represents the motion trajectory of the center of the square tube structure).

[0022] In the figure: 10, welding robot; 11, handling robot; 12, K-TIG welding gun; 13, square tube structural component; 14, butt girth weld of square tube structural component. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0024] See also Figures 1 to 4 As shown, the dual-robot collaborative square tube K-TIG butt welding welding trajectory planning method of the present invention, the robots that can work collaboratively are a welding robot 10 and a handling robot 11, wherein the flange end of the welding robot is connected to the K-TIG welding gun 12, and the end of the handling robot is connected to the square tube structure 13, and the dual-robot collaborative operation and the K-TIG welding system are used to achieve high-quality welding of the square tube structure butt ring weld 14 of the square tube structure 13. This method plans the motion trajectory of the welding robot 10 and the handling robot 11 through position and speed constraints, so that the K-TIG welding gun is always located at a constant distance above the weld and aligned with the weld during the welding process, and the weld point is always in an ideal posture, that is, the molten pool of the weld point is ensured to be as horizontal as possible. Reduce the influence of gravity on the molten pool during K-TIG welding, and ensure that the weld formation of different local areas of the welded component is consistent. Specifically comprising the following steps:

[0025] Step 1: Determine reasonable K-TIG welding process parameters based on the material and thickness of the square tube structural parts.

[0026] Step 2: The welding trajectory is determined based on the special structure of the square tube structure and the required position of the weld point. The welding robot clamps the K-TIG welding gun and starts the arc from the arc starting point P0. After the arc is started, the K-TIG welding gun moves forward a certain distance until it reaches the starting point P1 of the square tube structure's arc segment. The K-TIG welding gun's movement speed slowly decreases to 0. At this time, the handling robot grabs the square tube structure and rotates it around the center of the arc segment to be welded, P2. When the end point P3 of the square tube structure's arc segment is the weld point, the K-TIG welding gun continues to move forward to weld the straight segment of the square tube structure. When it reaches the next arc starting point, the K-TIG welding gun stops moving. At this time, the square tube structure rotates to perform the arc segment welding task. This reciprocating process continues until the K-TIG welding gun completes the welding task of the square tube structure's circumferential weld and reaches the arc extinction point P4 to extinguish the arc. The motion trajectory of the dual robots during the welding process is constrained by the posture requirements of the welding point and the K-TIG welding gun, and the height from the tungsten electrode to the workpiece surface and the welding speed in the K-TIG welding process parameters.

[0027] Step 3: Based on the structural dimensions of the square tube, the welding task is divided into two modules: welding straight segments and arc segments. Within each module, the K-TIG welding gun speed and the angular velocity of the square tube's rotation are adjusted based on the tube's dimensional parameters and K-TIG welding process parameters.

[0028] Furthermore, to ensure K-TIG welding quality in step 1, the K-TIG welding process parameters must be determined based on the material and thickness δ of the workpiece being welded. These parameters include the height d from the tungsten electrode to the workpiece surface, the welding speed v, and the welding current I. The welding current range is 300–1000 A.

[0029] Furthermore, step 2 determined that the arc starting position (P0) was located at the center of the straight segment of the square tube structure, the arc extinction point (P4) was located near the arc starting point (P0), and the welding trajectory. The motion trajectory of the dual robots during welding was constrained by the required position of the weld point and the K-TIG welding process parameters, including the height from the tungsten electrode to the workpiece surface and the welding speed.

[0030] The posture requirement of the weld point is to ensure that the molten pool of the weld point is as horizontal as possible. The posture requirement of the K-TIG welding gun is that the K-TIG welding gun is always located at a constant distance above the weld and aligned with the weld.

[0031] Furthermore, in step 3, the welding task is divided into two modules, one for welding straight segments and one for welding arc segments, based on the structural dimensions of the square tube. Within each module, the K-TIG welding torch velocity v and the angular velocity w of the square tube's rotation are planned based on the dimensional parameters of the square tube and the K-TIG welding process parameters.

[0032] When welding a straight section of a square tube, the welding robot holds the K-TIG torch and moves linearly, while the handling robot remains stationary. When welding an arc section of a square tube, the welding robot holds the K-TIG torch and remains stationary, while the handling robot grasps the square tube and rotates around the center of the arc.

[0033] When welding a straight section of a square tube, the welding speed v is equal to the torch's speed. When welding an arc, the welding speed v is equal to the product of the tube's angular velocity w and the distance r from the node to be welded to the center of rotation.

[0034] When performing the straight segment welding task of the square tube structure, the total displacement of the K-TIG welding gun is 4a. When performing the arc segment welding task of the square tube structure, the total length of the motion trajectory of the center of the square tube structure is Πb.

[0035] When performing the arc segment welding task of the square tube structural member, the center of the arc segment of the square tube structural member is located 45° above the center of the square tube structural member and the distance is b.

[0036] When performing arc segment welding of a square tube structural member, the angular velocity of the square tube structural member is w=v / c, and the rotation angle θ is 90°.

[0037] a, b, and c are shape parameters of the square tube structure, that is, a is the distance of a straight segment of the square tube structure, b is the distance from the center of the square tube structure to the rotation center, and c is the radius of the arc segment of the square tube structure.

[0038] The K-TIG welding system includes: K-TIG welding gun, K-TIG welding power source, K-TIG second generation control panel, cooling water tank and square tube structural parts. Example

[0039] Taking the butt girth weld of a square tube as an example, the structural dimensions of the square tube divide the welding task into two modules: straight-segment welding and arc-segment welding. Within each module, the K-TIG welding gun's speed and the tube's rotational angular velocity are adjusted based on the tube's dimensional parameters and K-TIG welding process parameters. The specific implementation steps are as follows:

[0040] A K-TIG welding system was integrated into a collaborative welding robot and handling robot, connecting a K-TIG welding gun and a square tube component. The square tube component's base material was 14mm thick TC4 titanium alloy, and the K-TIG welding process was used. The welding current (I) was 600A, the welding speed was 220mm / min, the shielding gas was 25L / min of pure Ar, the tungsten electrode extended 12.5mm, the tip angle was 60 degrees, and the distance to the workpiece surface was 1.5mm. The square tube component was pre-polished for gap-free joint assembly.

[0041] like Figure 3 As shown, the K-TIG welding gun first strikes the arc at the midpoint P0 of the straight segment of the square tube structure, and the current climbs for 5 seconds to ensure stable perforation of the workpiece. After 5 seconds, the K-TIG welding gun starts to weld the straight segment of the square tube structure at a walking speed of 220 mm / min until it reaches the starting point P1 of the circular arc segment of the square tube structure. The movement speed of the K-TIG welding gun slowly decreases to 0. At this time, the handling robot grabs the square tube structure and rotates it with the center P2 of the circular arc segment to be welded as the center of the circle. After the center of the square tube structure rotates 90 degrees counterclockwise at an angular velocity w=220 / c, that is, when the end point P3 of the circular arc segment of the square tube structure is used as the point to be welded, the K-TIG welding gun continues to move forward to weld the straight segment of the square tube structure. When it reaches the next arc starting point, the K-TIG welding gun stops moving. At this time, the square tube structure rotates to perform the circular arc segment welding task of the square tube structure. This process repeats until the K-TIG gun completes a full circumference weld of the square tube and reaches the arc above P4, where the arc is extinguished. The current decreases within 5 seconds, completing the welding task.

[0042] Through the dual-robot collaborative square tube K-TIG butt welding welding trajectory planning method of the present invention, the obtained square tube structural part annular butt weld is continuous and has a very uniform width. The weld surface appears bright silver or silver-yellow and no obvious defects such as spatter, pores and cracks are observed.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements to the present invention are intended to fall within the scope of protection of the present invention.

Claims

1. A dual-robot collaborative square tube K-TIG butt welding trajectory planning method, characterized by: A K-TIG welding gun and a square tube structure are installed on a collaborative welding robot and a handling robot, respectively. The welding robot and the handling robot work together and cooperate with the K-TIG welding system to weld the butt girth weld of the square tube structure, including the following steps: Step 1: Determine the K-TIG welding process parameters according to the material and thickness of the square tube structure; Step 2: Determine the welding trajectory according to the structure of the square tube structure and the posture requirements of the welding point. The welding robot clamps the K-TIG welding gun and starts the arc from the arc starting point P0. After the arc is started, the K-TIG welding gun moves forward until it reaches the starting point P1 of the arc segment of the square tube structure. The movement speed of the K-TIG welding gun slowly decreases to 0. At this time, the handling robot grabs the square tube structure and rotates it around the center P2 of the arc segment to be welded. When the end point P3 of the arc segment of the square tube structure is used as the welding point, the K-TIG welding gun continues to move forward. The K-TIG welding gun performs the welding task of the straight section of the square tube structure. When it reaches the starting point of the next arc, it stops moving. At this time, the square tube structure rotates to perform the arc segment welding task of the square tube structure. This reciprocating process continues until the K-TIG welding gun completes the welding task of the square tube structure's circumferential weld and reaches the arc extinction point P4 to extinguish the arc. The motion trajectory of the dual robots during the welding process is constrained by the welding point to be welded, the posture requirements of the K-TIG welding gun, the height from the tungsten electrode to the workpiece surface, and the welding speed in the K-TIG welding process parameters. Step 3: Divide the welding task into a straight segment welding task module and an arc segment welding task module based on the structural dimensions of the square tube structure. In each welding task module, plan the K-TIG welding gun movement speed and the angular velocity w of the square tube structure according to the dimensional parameters of the square tube structure and the K-TIG welding process parameters. When performing the task of welding the straight section of a square tube structure, the welding robot clamps the K-TIG welding gun and performs linear motion, while the handling robot remains stationary. When performing the task of welding the circular section of a square tube structure, the welding robot clamps the K-TIG welding gun and remains stationary, while the handling robot grabs the square tube structure and performs rotational motion with the center of the circular section of the square tube structure as the center. When welding a straight section of a square tube, the welding speed v is equal to the K-TIG torch's movement speed. When welding an arc section of a square tube, the welding speed v is equal to the product of the square tube's angular velocity w and the distance from the node to be welded to the center of rotation. When welding a straight section of a square tube, the total displacement of the K-TIG welding gun is 4a. When welding an arc section of a square tube, the total length of the motion trajectory of the center of the tube is πb. When welding an arc section of a square tube, the center of the arc is located 45° above the center of the tube and at a distance b. a, b, and c are shape parameters of the square tube structure, that is, a is the distance of a straight segment of the square tube structure, b is the distance from the center of the square tube structure to the rotation center, and c is the radius of the arc segment of the square tube structure.

2. The dual-robot collaborative square tube K-TIG butt welding trajectory planning method according to claim 1 is characterized by: The K-TIG welding process parameters are determined according to the material and thickness δ of the square tube structure, including the height d from the tungsten electrode to the workpiece surface, the welding speed v, and the welding current I.

3. The dual-robot collaborative square tube K-TIG butt welding trajectory planning method according to claim 2 is characterized in that: The welding current I has a value range of 300~1000A.

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