An automatic welding device and method for precast box girders

Abstract

This invention relates to the field of welding machine tool technology, specifically to an automatic welding device and method for precast box girders. The automatic welding device for precast box girders includes a frame, an upper welding assembly, a rebar fixing frame, and a lower welding assembly. The rebar fixing frame is used to hold the rebars to be welded. The upper welding assembly includes an upper welding head, and the lower welding assembly includes a lower welding head. The upper and lower welding heads can approach each other in a vertical direction to weld the rebars on the rebar fixing frame. The upper welding head includes an electrode rod extending in a vertical direction and an electrode head rotatably mounted on the electrode rod. The electrode head is used to contact and weld the rebars on the rebar fixing frame. When the upper welding head moves upward away from the rebar, the electrode head rotates around the electrode rod to prevent the electrode head from driving the rebar upward. This invention solves the technical problem in the prior art where the electrode head easily adheres to the rebar, and the rebar is easily pulled away from the rebar fixing frame.

Description

Technical Field

[0001] This invention relates to the field of welding machine tool technology, and specifically to an automatic welding device and method for precast box girders. Background Technology

[0002] The automatic welding device for precast box girders is used to weld multiple steel bars to form a steel frame. The automatic welding device for precast box girders mainly includes a frame, an upper welding assembly, a steel bar fixing frame, and a lower welding assembly. The upper and lower welding assemblies are arranged symmetrically. The steel bar fixing frame is located between the upper and lower welding assemblies. Before welding, multiple steel bars are placed in the positioning grooves of the steel bar fixing frame along the transverse and longitudinal directions, respectively. Then, the upper and lower welding assemblies clamp the intersection of the transverse and longitudinal steel bars from the upper and lower sides of the steel bar fixing frame, respectively. The electrode heads of the upper and lower welding assemblies are energized to weld the transverse and longitudinal steel bars together.

[0003] When welding the steel frame, the electrode heads of the upper and lower welding components of the precast box girder automatic welding device are prone to sticking to the steel bars after being energized. When the electrode head of the upper welding component rises, it can easily pull the steel bars out of the positioning groove of the steel bar fixing frame, which can lead to misalignment of the steel bars, affect the positioning of the steel bars, and reduce welding efficiency. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention proposes an automatic welding device and method for precast box girders, which solves the technical problems in the prior art where the electrode head easily sticks to the reinforcing bars, and the reinforcing bars are easily pulled out of the positioning groove of the reinforcing bar fixing frame by the electrode head, resulting in misalignment of the reinforcing bars and reduced welding efficiency.

[0005] The automatic welding device and method for precast box girders of the present invention adopts the following technical solution:

[0006] An automatic welding device and method for precast box girders includes a frame, an upper welding assembly, a rebar fixing frame, and a lower welding assembly. The rebar fixing frame is used to place the rebars to be welded. The upper welding assembly includes an upper welding head, and the lower welding assembly includes a lower welding head. The upper and lower welding heads can approach each other in a vertical direction to weld the rebars on the rebar fixing frame. The upper welding head includes an electrode rod extending in a vertical direction and an electrode head rotatably mounted on the electrode rod. The electrode head is used to contact and weld the rebars on the rebar fixing frame. When the upper welding head moves upward away from the rebars, the electrode head rotates around the electrode rod to prevent the electrode head from driving the rebars upward.

[0007] Furthermore, the end face of the electrode head that contacts the reinforcing bar is provided with two helical surfaces. Both helical surfaces extend circumferentially along the electrode head and have the same helical direction. The two helical surfaces are centrally symmetrical about the center of the electrode head. When the electrode head moves toward the reinforcing bar, the two helical surfaces slide against the reinforcing bar to drive the electrode head to rotate around the electrode rod in the first direction. A return torsion spring is provided between the electrode head and the electrode rod. When the electrode head moves away from the reinforcing bar, the return torsion spring drives the electrode head to rotate in the second direction and return to its original position. The second direction is opposite to the first direction.

[0008] Furthermore, the upper welding assembly includes a mounting plate, and the upper welding head is slidably mounted on the mounting plate in the left-right direction to adjust the left-right position of the upper welding head on the mounting plate. The mounting plate is provided with a locking mechanism for locking the upper welding head. After the left-right position of the upper welding head on the mounting plate is adjusted, the locking mechanism locks the upper welding head to prevent the upper welding head from moving left or right.

[0009] Furthermore, a movable sleeve is fitted on the electrode rod above the electrode head. The movable sleeve can move up and down along the axial direction of the electrode rod. The lower end of the movable sleeve and the upper end of the electrode head are respectively provided with a pushing curved surface. The pushing curved surface at the lower end of the movable sleeve abuts against the pushing curved surface at the upper end of the electrode head. When the electrode head rotates in the first direction, the electrode head pushes the movable sleeve upward. When the electrode head rotates in the second direction, the movable sleeve moves downward.

[0010] Furthermore, a slide block is fixed to the upper end of the electrode rod, and the electrode rod is slidably suspended on the mounting plate via the slide block. The movable sleeve is connected to a sliding plate via a connecting rod, and the sliding plate is slidably mounted on the slide block via a guide rod. When the movable sleeve moves up and down along the axis of the electrode rod, the movable sleeve drives the sliding plate to slide left and right via the connecting rod. A telescopic spring is connected between the sliding plate and the slide block. When the electrode head rotates in the second direction, the movable sleeve moves downward under the action of the telescopic spring.

[0011] Furthermore, two upper welding heads are slidably disposed on the mounting plate, and the two upper welding heads are spaced apart and symmetrically arranged in the left-right direction.

[0012] Furthermore, the upper welding assembly includes an upper support arm, which is fixed on the frame. The upper support arm is provided with a lifting drive mechanism, and the mounting plate is connected to the lifting drive mechanism. The lifting drive mechanism drives the mounting plate and the upper welding head to move up and down.

[0013] Furthermore, the lifting drive mechanism includes a telescopic cylinder, which is mounted on the upper support arm. The telescopic cylinder has a telescopic rod extending in the vertical direction. A mounting base is fixed to the lower end of the telescopic rod. A transition rod extending in the vertical direction is connected to one side of the mounting base. The mounting plate is connected to the lower end of the transition rod.

[0014] Furthermore, the upper support arm extends in the front-rear direction, the front end of the upper support arm is fixed on the frame, and two sets of the lifting drive mechanisms are spaced apart along the front-rear direction on the upper support arm. Each set of lifting drive mechanisms is connected to the mounting plate, and each mounting plate is provided with an upper welding head.

[0015] An automatic welding method for precast box girders is disclosed. This method utilizes the aforementioned automatic welding device for precast box girders. During welding, multiple reinforcing bars to be welded together are sequentially placed on a reinforcing bar fixing frame. The upper welding head moves downwards, and the lower welding head moves upwards. The electrode heads of the upper and lower welding heads respectively contact the reinforcing bars on the reinforcing bar fixing frame and weld them. After one welding operation is completed, the upper welding head moves upwards, and the lower welding head moves downwards. Simultaneously, the electrode head rotates to prevent the upper welding head from driving the reinforcing bars upwards.

[0016] The beneficial effects of the present invention are as follows: In the automatic welding device and method for precast box girders of the present invention, when the upper welding head moves upward away from the reinforcing bar, the electrode head of the automatic welding device for precast box girders will rotate around the electrode rod. In this way, even if the electrode head and the reinforcing bar stick together during welding, the electrode head will separate from the reinforcing bar due to the rotation when the electrode head leaves the reinforcing bar, thereby preventing the electrode head from driving the reinforcing bar upward and avoiding the reinforcing bar from detaching from the reinforcing bar fixing frame and losing its positioning function, thus ensuring welding quality and improving welding efficiency.

[0017] Furthermore, the electrode head of this invention is provided with a helical curved surface. This helical curved surface abuts against the reinforcing bar, thereby pushing the electrode head to rotate. When the electrode head abuts against the reinforcing bar, the helical curved surface of the electrode head abuts against and slides relative to the surface of the reinforcing bar, which can scrape away impurities adhering to the surface of the helical curved surface, thus ensuring reliable contact and fit between the electrode head and the reinforcing bar, guaranteeing welding reliability. In addition, because the electrode head end face is provided with a helical curved surface, after the electrode head abuts against the reinforcing bar, its rotation will cause the lower end of the electrode head to cover both sides of the reinforcing bar. This can block some of the sparks generated during welding, reducing the amount of sparks flying outwards. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Those skilled in the art should understand that these drawings are not necessarily drawn to scale.

[0019] Figure 1 This is a three-dimensional schematic diagram of a first embodiment of an automatic welding device for precast box girders according to the present invention;

[0020] Figure 2 This is a partial perspective view of a first embodiment of an automatic welding device for precast box girders according to the present invention;

[0021] Figure 3 This is a side view of a first embodiment of an automatic welding device for precast box girders according to the present invention;

[0022] Figure 4 This is a three-dimensional schematic diagram of the upper welding assembly in the first embodiment of the automatic welding device for precast box girders of the present invention;

[0023] Figure 5 This is an exploded view of the upper welding assembly in the first embodiment of the automatic welding device for precast box girders of the present invention;

[0024] Figure 6 This is a front view of a first embodiment of an automatic welding device for precast box girders according to the present invention (with the steel bar fixing frame removed).

[0025] Figure 7 for Figure 6 A magnified schematic diagram of part A in the middle;

[0026] Figure 8 for Figure 7 Another state diagram.

[0027] In the diagram: 100, frame; 200, upper welding assembly; 201, upper support arm; 202, telescopic cylinder; 203, mounting base; 204, mounting plate; 205, electrode rod; 206, electrode head; 207, moving sleeve; 208, retaining ring; 209, connecting rod; 210, sliding plate; 211, telescopic spring; 212, locking mechanism; 213, upper welding head; 300, rebar fixing frame; 400, lower welding assembly; 401, lower support arm; 402, lower welding head; 500, rebar. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The serial numbers assigned to components in this document, such as "first," "second," etc., are merely used to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages). In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0030] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first and second features are in direct contact, or that they are in indirect contact through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0031] An embodiment of the automatic welding device for precast box girders of the present invention, such as... Figures 1 to 8As shown, the automatic welding device for precast box girders includes a frame 100, an upper welding assembly 200, a rebar fixing frame 300, and a lower welding assembly 400. The rebar fixing frame 300 is a frame structure. For ease of explanation, the length extension direction of the rebar fixing frame 300 is set to the left-right direction. The rebar fixing frame 300 is used to place the rebars 500 to be welded. The upper welding assembly 200 includes multiple upper welding heads 213, and the lower welding assembly 400 includes multiple lower welding heads 402. The upper welding heads 213 and lower welding heads 402 can approach each other in the vertical direction to weld the rebars 500 on the rebar fixing frame 300. In this embodiment, the upper welding assembly 200 and the lower welding assembly 400 have the same structure and are arranged symmetrically vertically. The structure of the upper welding assembly 200 will be described below; the structure of the lower welding assembly 400 can be referred to that of the upper welding assembly 200.

[0032] In this embodiment, the upper welding assembly 200 includes an upper support arm 201, which extends in a front-to-back direction and has its front end fixed to the frame 100. The upper support arm 201 is equipped with a lifting drive mechanism. In this embodiment, two sets of lifting drive mechanisms are spaced apart in the front and back. Each set of lifting drive mechanisms is connected to a mounting plate 204, which is rectangular and extends horizontally. Each mounting plate 204 has two upper welding heads 213, which are spaced apart horizontally and symmetrically arranged, resulting in a total of four upper welding heads 213. In other embodiments, the number of lifting drive mechanisms, mounting plates 204, and upper welding heads 213 can be set according to welding requirements. In this embodiment, the lifting drive mechanism includes a telescopic cylinder 202, which is mounted on the upper support arm 201. The telescopic cylinder 202 has a telescopic rod extending in the vertical direction, and a mounting base 203 is fixed to the lower end of the telescopic rod. A transition rod extending in the vertical direction is connected to one side of the mounting base 203, and the mounting plate 204 is connected to the lower end of the transition rod. During operation, the lifting drive mechanism drives the mounting plate 204 and the upper welding head 213 to move up and down to weld the reinforcing bar 500.

[0033] The upper welding head 213 includes an electrode rod 205 extending in the vertical direction, and an electrode head 206 rotatably mounted on the electrode rod 205. The electrode head 206 is used to abut against and weld the reinforcing bar 500 on the reinforcing bar fixing frame 300. It should be noted that the electrode rod 205 and electrode head 206 are conductive structures in this invention, and there is a conductive connection between them. The electrode rod 205 is connected to a wire (not shown in the figure). During welding, the electrode rod 205 and electrode head 206 are energized, thereby welding the reinforcing bar 500. In this invention, when the upper welding head 213 moves upward away from the reinforcing bar 500, the electrode head 206 rotates around the electrode rod 205. In this way, even if the electrode head 206 and the reinforcing bar 500 stick together during welding, the electrode head 206 rotates away from the reinforcing bar 500, causing the electrode head 206 to separate from the reinforcing bar 500. This prevents the electrode head 206 from driving the reinforcing bar 500 upward, avoiding the reinforcing bar 500 from detaching from the reinforcing bar fixing frame 300 and losing its positioning function, thereby ensuring welding quality and improving welding efficiency.

[0034] In this embodiment, the end face of the electrode head 206 that contacts the reinforcing bar 500 is provided with two helical surfaces. Both helical surfaces extend circumferentially along the electrode head 206 and have the same helical direction, and are centrally symmetrical about the center of the electrode head 206. During the movement of the electrode head 206 toward the reinforcing bar 500, the two helical surfaces press against and slide against the reinforcing bar 500, respectively, to drive the electrode head 206 to rotate around the electrode rod 205 in a first direction. Specifically, as follows... Figure 7 and Figure 8 As shown, when the electrode head 206 is not in contact with the reinforcing bar 500, the electrode head 206 is in its initial position, such as... Figure 7 As shown; when the electrode head 206 moves downward to a certain position, the electrode head 206 and the reinforcing bar 500 begin to abut against each other. Since the position of the reinforcing bar 500 is restricted and cannot move, under the action of the helical curved surface, the reinforcing bar 500 will push the electrode head 206 to rotate, as shown. Figure 8 As shown, the electrode head 206 on the right rotates clockwise (viewed from below), while the electrode head 206 on the left rotates counterclockwise. During the rotation of the electrode head 206, the helical surface of the electrode head 206 abuts against and slides relative to the surface of the reinforcing bar 500, which can scrape off impurities adhering to the surface of the helical surface, thereby ensuring reliable contact and fit between the electrode head 206 and the reinforcing bar 500, and ensuring welding reliability.

[0035] In this embodiment, a reset torsion spring (not shown in the figure) is provided between the electrode head 206 and the electrode rod 205. When the upper welding head 213 moves away from the rebar 500, the reset torsion spring will drive the electrode head 206 to rotate in the second direction and reset, thereby preventing the electrode head 206 from driving the rebar 500 to move upward, and preventing the rebar 500 from detaching from the rebar fixing frame 300 and losing its positioning function for the rebar 500. It should be noted that the first direction can be clockwise or counterclockwise, and the first direction and the second direction are opposite, which means that the same electrode head 206 will rotate in opposite directions when moving upward and downward, respectively.

[0036] In this embodiment, the upper welding head 213 is slidably mounted on the mounting plate 204 in the left-right direction to adjust its left-right position on the mounting plate 204. Specifically, each mounting plate 204 has sliding grooves extending in the left-right direction on its front and rear sides. Each upper welding head 213 has a U-shaped sliding block fixed to the upper end of its electrode rod 205. The inner side of the sliding block has protrusions that fit the sliding grooves. The sliding block engages with the mounting plate 204 from either the left or right end, allowing the protrusions inside the sliding block to insert into the sliding grooves, thereby enabling the electrode rod 205 to be slidably suspended on the lower side of the mounting plate 204. The mounting plate 204 is provided with a locking mechanism 212 for locking the upper welding head 213. After the left-right position of the upper welding head 213 on the mounting plate 204 is adjusted, the locking mechanism 212 locks the upper welding head 213 to prevent it from moving left or right. In this embodiment, the locking mechanism 212 includes a telescopic push rod. When the telescopic push rod is extended, it presses against the slide at the upper end of the electrode rod 205, thereby fixing the slide on the mounting plate 204 to prevent the slide from moving left and right on the mounting plate 204.

[0037] In this embodiment, a movable sleeve 207 is fitted over the electrode head 206 on each electrode rod 205. The movable sleeve 207 can move up and down along the axial direction of the electrode rod 205. The lower end of the movable sleeve 207 and the upper end of the electrode head 206 are respectively provided with pushing surfaces, and the pushing surface at the lower end of the movable sleeve 207 abuts against the pushing surface at the upper end of the electrode head 206. When the electrode head 206 rotates in a first direction, it pushes the movable sleeve 207 upwards; when the electrode head 206 rotates in a second direction, the movable sleeve 207 moves downwards.

[0038] In this embodiment, each movable sleeve 207 is connected to a sliding plate 210 via a connecting rod 209. The sliding plate 210 is slidably mounted on the slide block via a guide rod. The two sliding plates 210 on each mounting plate 204 are located between the two electrode rods 205. When the movable sleeve 207 moves up and down along the axis of the electrode rod 205, the movable sleeve 207 drives the sliding plate 210 to slide left and right via the connecting rod 209. When the movable sleeve 207 moves upward, the two sliding plates 210 on the same mounting plate 204 move closer to each other. When the movable sleeve 207 moves downward, the two sliding plates 210 on the same mounting plate 204 move further apart. A telescopic spring 211 connects the sliding plate 210 to the slide block. The telescopic spring 211 is sleeved on the guide rod. When the electrode head 206 rotates in the second direction, the movable sleeve 207 moves downward under the action of the telescopic spring 211. In this embodiment, each movable sleeve 207 has a retaining ring 208 on its periphery. One end of the connecting rod 209 is hinged to the sliding plate 210, and the other end is hinged to the retaining ring 208.

[0039] In this embodiment, the lower welding assembly 400 includes a lower support arm 401 and a lower welding head 402. The structure of the lower welding assembly 400 is the same as that of the upper welding assembly 200, and will not be described in detail here. In other embodiments, the structure of the lower welding assembly 400 may be different from that of the upper welding assembly 200.

[0040] The present invention utilizes the welding method of the aforementioned precast box girder automatic welding device. During welding, multiple reinforcing bars 500 to be welded together are first placed sequentially on the reinforcing bar fixing frame 300. The left and right positions of the two upper welding heads 213 on each mounting plate 204 are adjusted, and then the upper welding heads 213 are fixed to the mounting plate 204 using the locking mechanism 212. After the preparation work is completed, the lifting drive mechanism is started, thereby driving the mounting plate 204 and the upper welding heads 213 on the mounting plate 204 to gradually approach the reinforcing bars 500 on the reinforcing bar fixing frame 300. Specifically, the upper welding heads 213 move downward and the lower welding heads 402 move upward. The electrode heads 206 of the upper welding heads 213 and the lower welding heads 402 respectively contact the reinforcing bars 500 on the reinforcing bar fixing frame 300 and weld the reinforcing bars 500. Taking the welding head 213 as an example, after the motor head of the upper welding head 213 abuts against the reinforcing bar 500, the upper welding head 213 continues to move downward. Due to the sliding fit between the reinforcing bar 500 and the spiral curved surface of the electrode head 206, the reinforcing bar 500 will push the electrode head 206 to rotate. Figure 8As shown, the electrode head 206 on the right rotates clockwise (viewed from below), and the electrode head 206 on the left rotates counterclockwise. After one welding operation is completed, the telescopic rod of the lifting drive mechanism retracts, causing the upper welding head 213 to move upward and the lower welding head 402 to move downward. When the upper welding head 213 moves upward, under the action of the return torsion spring between the electrode head 206 and the electrode rod 205, the electrode head 206 rotates to prevent the upper welding head 213 from driving the reinforcing bar 500 upward. During the next welding operation, after the electrode head 206 abuts against the reinforcing bar 500, the helical surface of the electrode head 206 abuts against and slides relative to the surface of the reinforcing bar 500, which can scrape off impurities adhering to the surface of the helical surface, thereby ensuring reliable contact and cooperation between the electrode head 206 and the reinforcing bar 500 and ensuring welding reliability. In addition, since the electrode head 206 has a spiral curved surface on its end face, after the electrode head 206 comes into contact with the steel bar 500, the lower end of the electrode head 206 will cover both sides of the steel bar 500 after the electrode head 206 rotates. This can block some of the sparks generated during welding and reduce the amount of sparks flying outward.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An automatic welding device for precast box girders, comprising a frame, an upper welding assembly, a rebar fixing frame, and a lower welding assembly, wherein the rebar fixing frame is used to place the rebars to be welded, the upper welding assembly includes an upper welding head, the lower welding assembly includes a lower welding head, and the upper and lower welding heads are capable of approaching each other in a vertical direction to weld the rebars on the rebar fixing frame, characterized in that: The upper welding head comprises an electrode rod extending in the up-down direction, and an electrode head rotatably arranged on the electrode rod, the electrode head being used to contact and weld the steel bars on the steel bar fixing frame, and when the upper welding head moves away from the steel bars upward, the electrode head rotates around the electrode rod to prevent the electrode head from moving upward with the steel bars; The end face of the electrode head, which is in contact with the steel bars, is provided with two spiral curved surfaces, the two spiral curved surfaces extend along the circumference of the electrode head and have the same spiral direction, and the two spiral curved surfaces are centrally symmetric about the center of the electrode head, during the movement of the electrode head towards the steel bars, the two spiral curved surfaces are respectively in sliding fit with the steel bars to drive the electrode head to rotate around the electrode rod in a first direction, after the electrode head abuts against the steel bars, the spiral curved surface of the electrode head abuts against and slides relative to the surface of the steel bars, and after the rotation of the electrode head, the lower end of the electrode head is covered on both sides of the steel bars, the electrode head and the electrode rod are provided with a reset torsional spring, and when the electrode head moves away from the steel bars, the reset torsional spring drives the electrode head to rotate in a second direction and reset, the second direction being opposite to the first direction. A moving sleeve is sleeved on the electrode rod at a position above the electrode head, the moving sleeve can move up and down along the axial direction of the electrode rod, the lower end of the moving sleeve and the upper end of the electrode head are respectively provided with a pushing curved surface, the pushing curved surface of the lower end of the moving sleeve and the pushing curved surface of the upper end of the electrode head abut against each other, when the electrode head rotates in the first direction, the electrode head pushes the moving sleeve to move upward, and when the electrode head rotates in the second direction, the moving sleeve moves downward. The upper end of the electrode rod is fixed with a sliding seat, the electrode rod is hung on the mounting plate through the sliding seat, the moving sleeve is connected with a sliding plate through a connecting rod, and the sliding plate is slidably arranged on the sliding seat through a guide rod, when the moving sleeve moves up and down along the axial direction of the electrode rod, the moving sleeve drives the sliding plate to slide left and right through the connecting rod, and the sliding plate and the sliding seat are connected with an extension spring, and when the electrode head rotates in the second direction, the moving sleeve moves downward under the action of the extension spring.

2. The automatic precast box girder welding device according to claim 1, characterized in that: The upper welding assembly comprises a mounting plate, the upper welding head is slidably arranged on the mounting plate in the left-right direction to adjust the left-right position of the upper welding head on the mounting plate, and the mounting plate is provided with a locking mechanism for locking the upper welding head, when the adjustment of the left-right position of the upper welding head on the mounting plate is completed, the locking mechanism locks the upper welding head to prevent the upper welding head from moving left and right.

3. The automatic precast box girder welding device according to claim 2, characterized in that: Two upper welding heads are slidably arranged on the mounting plate, and the two upper welding heads are arranged in a spaced and left-right symmetrical manner in the left-right direction.

4. The automatic precast box girder welding device according to claim 2, characterized in that: The upper welding assembly comprises an upper support arm, the upper support arm is fixed on the rack, the upper support arm is provided with a lifting driving mechanism, the mounting plate is connected with the lifting driving mechanism, and the lifting driving mechanism drives the mounting plate and the upper welding head to move up and down.

5. The automatic precast box girder welding device according to claim 4, characterized in that: The lifting driving mechanism comprises a telescopic cylinder, the telescopic cylinder is mounted on the upper support arm, the telescopic cylinder has a telescopic rod extending in the up-down direction, the lower end of the telescopic rod is fixed with a mounting seat, one side of the mounting seat is connected with a connecting rod extending in the up-down direction, and the mounting plate is connected with the lower end of the connecting rod.

6. The automatic precast box girder welding device of claim 4, wherein: The upper support arm extends in the front-rear direction, the front end of the upper support arm is fixed on the rack, two groups of lifting driving mechanisms are arranged on the upper support arm in a spaced manner in the front-rear direction, each group of lifting driving mechanisms is connected with a mounting plate, and each mounting plate is provided with an upper welding head.

7. A method for automatic welding of a precast box girder, characterized by: The method uses the prefabricated box girder automatic welding device of any one of claims 1-6, and when welding, the multiple steels to be welded together are placed on the steel fixing frame in sequence, the upper welding head is moved downward, the lower welding head is moved upward, the electrode head of the upper welding head and the electrode head of the lower welding head are in contact with the steels on the steel fixing frame respectively, and the steels are welded; after completing the welding once, the upper welding head is moved upward, the lower welding head is moved downward, and the electrode head is rotated to prevent the upper welding head from moving the steels upward.

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