A metal tube laser welding device with protective gas injection

Abstract

The application belongs to the technical field of metal pipe laser welding, and particularly relates to a metal pipe laser welding device with protective gas injection. The following scheme is proposed and comprises a base, a plurality of fixing sleeves are installed on the base, a ring frame is arranged on the base, the ring frame is rotationally arranged around a horizontal shaft, a laser is installed on the ring frame, a blowing pipe one is installed on the ring frame at both sides of the laser, the blowing pipe one is arranged perpendicularly to the laser, a spray head is rotationally connected to one end of the blowing pipe one which faces the center position of the ring frame, the end of the spray head which is away from the blowing pipe one is sealed, and a plurality of spray holes one which are arranged in a ring array are formed in the end of the spray head which is away from the blowing pipe one. The two blowing pipes one blow protective gas from the two sides of the pipe body welding position respectively, the spray head which is rotationally arranged at the end of the blowing pipe one and the ring-arranged spray holes one on the spray head improve the effectiveness of the protective gas in protecting the welding seam position, and the direct impact of the spray on the welding seam position is avoided.

Description

Technical Field

[0001] This invention relates to the field of metal tube laser welding technology, and more particularly to a metal tube laser welding apparatus with a protective gas jet. Background Technology

[0002] Laser welding is an advanced joining technology that uses a high-energy-density laser beam as a heat source to locally melt and fuse materials to form a weld. Laser welding technology for metal circular tube components is receiving increasing attention from the industry, especially in the fields of automobile exhaust pipes, precision medical device conduits, petrochemical pipelines, hydraulic system components, and the manufacturing of various thin-walled pipes, where increasingly higher requirements are being placed on weld quality.

[0003] In the laser welding process of metal round tubes, ensuring that the welding area is not disturbed by the external environment directly determines the internal quality and appearance of the weld. Therefore, shielding gas technology has become a crucial link in the laser welding process. In the existing technology, shielding gas is often sprayed directly onto the welding position through an external nozzle for protection. However, the direct spraying method is prone to causing strong mechanical impact on the molten pool due to the high-speed airflow, resulting in weld surface collapse, weld burn-through, deterioration of weld formation, or even complete failure. Summary of the Invention

[0004] Based on the technical problems in the background art, the present invention proposes a metal tube laser welding device with protective gas injection.

[0005] The present invention proposes a metal tube laser welding device with protective gas injection, comprising a base, on which multiple fixed sleeves are installed, and a ring frame is provided on the base. The ring frame is rotatably arranged around a horizontal axis and a laser is installed on the ring frame. A blowing tube is installed on both sides of the laser on the ring frame. The blowing tube is perpendicular to the laser. A nozzle is rotatably connected to one end of the blowing tube facing the center of the ring frame. The end of the nozzle away from the blowing tube is sealed. The end of the nozzle away from the blowing tube has a ring array of nozzle holes.

[0006] Preferably, mounting brackets are fixed at both ends of the ring frame on the base, and the mounting brackets have through slots. The ring frame is rotatably arranged between the two mounting brackets, and the ring frame is connected to a motor for transmission.

[0007] Preferably, a plurality of fan blades are fixed to the inner wall of one end of the nozzle, and a plurality of spray holes are opened on the outer circumference of the nozzle.

[0008] Preferably, a connecting ring is fixed to one end of the nozzle facing the blowing pipe, and the outer circumferential wall of the connecting ring is rotatably connected to the inner wall of the blowing pipe through a bearing. A baffle is fixed to the inner wall of the connecting ring at the position corresponding to the nozzle hole.

[0009] Preferably, a guide plate is provided on the inner wall of the ring frame above the blowing pipe, and the end of the guide plate near the blowing pipe is rotatably disposed between the ring frame and the guide plate. A spring is connected between the guide plate and the inner wall of the ring frame.

[0010] Preferably, the ring frame is equipped with a pressure sensor for detecting the compression force of the spring, and a non-contact speed sensor for detecting the rotation speed of the nozzle is provided on the inner wall of the ring frame near the circumference of the nozzle. The signal lines of the pressure sensor and the speed sensor are both led out to the controller through a conductive slip ring.

[0011] Preferably, before welding begins and with a stable supply of protective gas, the normal value of the spring compression force is obtained by acquiring the signal from the pressure sensor, and the normal value of the nozzle rotation speed is obtained by acquiring the signal from the speed sensor. During welding, the current spring compression force value and nozzle rotation speed value are acquired in real time, and the degree of pressure increase relative to the normal value and the degree of rotation speed decrease relative to the normal value are calculated respectively. The degree of pressure increase and the degree of rotation speed decrease are compared with the corresponding preset thresholds to determine whether the nozzle is blocked.

[0012] Preferably, when the pressure rises above a first pressure threshold and the rotational speed drops above a first rotational speed threshold, the system is determined to be in a state of slight blockage; when the pressure rises above a second pressure threshold and the rotational speed drops above a second rotational speed threshold, the system is determined to be in a state of moderate blockage; and when the pressure rises above a third pressure threshold and the rotational speed drops above a third rotational speed threshold, the system is determined to be in a state of severe blockage.

[0013] Preferably, a second blowing tube is installed on the ring frame, which is symmetrically arranged with the laser. The second blowing tube has two inclined tube heads.

[0014] Preferably, both ends of the ring frame are provided with ring plates, the outer diameter of the ring plates is smaller than the inner diameter of the slot on the mounting frame, and multiple springs are connected between the ring plates and the fixing sleeve.

[0015] The beneficial effects of this invention are as follows: In this invention, during welding operations, two blowing pipes blow protective gas from both sides of the pipe body being welded. Through the nozzles rotated at the ends of the blowing pipes and the annularly distributed nozzle holes on the nozzles, the airflow from the blowing pipes is dispersed out through the rotating nozzle holes, further dispersing the protective gas around the joint of the two pipe bodies. This improves the effectiveness of the protective gas in protecting the weld joint while avoiding direct impact on the weld joint from the direct spray, thereby effectively improving the effectiveness of the welding operation of the butt-jointed metal pipes, as well as improving welding quality and work efficiency.

[0016] In this invention, the nozzles on both sides of the laser eject protective gas from nozzle one and nozzle two, respectively. The upward-flowing portion of the protective gas impacts the inclined guide plate and bounces back to the weld surface at the welding position. This improves the protective gas coverage at the weld position while further reducing the impact force of the airflow to avoid damage to the weld.

[0017] In this invention, by combining the judgment of two characteristic parameters—the increase in spring compression force and the decrease in nozzle rotation speed—the problem of uneven distribution of protective gas caused by nozzle blockage can be accurately identified, and graded reminders can be given, thereby effectively ensuring the weld quality of laser welding of metal tubes. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of a metal tube laser welding device with protective gas injection proposed in this invention. Figure 2 This is a schematic diagram of the mounting frame structure of a metal tube laser welding device with protective gas injection proposed in this invention. Figure 3 This is a schematic diagram of the exploded structure of the ring frame position of a metal tube laser welding device with protective gas injection proposed in this invention; Figure 4 This is a schematic cross-sectional view of the ring frame structure of a metal tube laser welding device with protective gas injection proposed in this invention. Figure 5 This is a schematic diagram of the internal structure of the ring frame of a metal tube laser welding device with protective gas injection proposed in this invention. Figure 6 This is a schematic diagram of the distribution structure of blowpipe one, guide plate and blowpipe two of a metal tube laser welding device with protective gas injection proposed in this invention; Figure 7 This is a schematic diagram of the blowing tube structure of a metal tube laser welding device with protective gas injection proposed in this invention. Figure 8 This is a schematic diagram of the internal structure of the nozzle of a metal tube laser welding device with protective gas injection proposed in this invention.

[0019] In the diagram: 1. Base, 2. Fixing sleeve, 3. Ring frame, 4. Laser, 401 bracket one, 5. Blowing pipe one, 6. Nozzle, 601 nozzle one, 602 nozzle two, 7. Mounting bracket, 8. Positioning ring, 9. Slip ring, 10. Tooth ring, 11. Bracket two, 12. Motor, 13. Drive gear, 14. Ring plate, 15. Spring two, 16. Blowing pipe two, 16. Pipe head, 17. Connecting ring, 18. Fan blade, 19. Baffle plate, 20. Guide plate, 21. Rotating shaft, 22. Shaft seat, 23. Spring one. Detailed Implementation

[0020] Example 1: Refer to Figures 1-8 A metal tube laser welding device with protective gas jet includes a base 1, on which multiple fixing sleeves 2 are installed. Two tubes to be welded are passed through the fixing sleeves 2 from both ends and joined together. The fixing sleeves 2 are used to fix the tubes. The fixing sleeves 2 used to limit the tubes are fixed by conventional means in the art or by directly using tube sleeves that match the tubes. This means is conventional in the art and will not be described in detail. A ring frame 3 is provided on the base 1. At least two sets of fixing sleeves 2 are provided at both ends of the ring frame 3. The ring frame 3 is rotatable about a horizontal axis and is coaxial with the fixing sleeves 2 and the tubes to be welded. The ring frame 3 is equipped with a laser 4, and a bracket 401 is fixed between the laser 4 and the ring frame 3. Two blowing pipes 5 are installed on both sides of the laser 4 on the ring frame 3, symmetrically arranged and perpendicular to the laser 4. The extension directions of the blowing pipes 5 and the laser 4 converge at the same point, meaning that when the laser 4 is directly above and welding vertically downwards, the two blowing pipes 5 are horizontally positioned precisely in the middle on both sides. A nozzle 6 is rotatably connected to one end of the blowing pipe 5 facing the center of the ring frame 3. The end of the nozzle 6 away from the blowing pipe 5 is sealed. One end of the blowing pipe 5 has a ring-shaped array of nozzles 601. During use, the two pipes to be welded are joined together at the center of the ring frame 3. Welding is performed using a laser 4 on the ring frame 3. The welding position is changed by rotating the ring frame 3 with the laser 4, and the blowing pipe 5 always rotates with the ring frame 3, ensuring that the two blowing pipes 5 are always positioned on either side of the laser 4. During welding, the two blowing pipes 5 blow protective gas from both sides of the pipe body to the welding position, allowing the protective gas to spread and flow along the circumference of the pipe body to the welding position, rather than... The gas flow is directly sprayed towards the welding position of the laser 4, avoiding damage to the welding position caused by the strong impact of the jet gas. Furthermore, through the nozzle 6, which is rotated at the end of the blower pipe 5, and the annularly distributed nozzle holes 601 on the nozzle 6, the gas flow sprayed by the blower pipe 5 is dispersed out from the multiple rotating nozzle holes 601, further dispersing the shielding gas around the joint position of the two pipes. This improves the effectiveness of the shielding gas in protecting the weld position, while further avoiding the impact of direct jet gas on the weld position. As a result, the effectiveness of the welding operation of the butt metal pipes is effectively improved, as well as the welding quality and work efficiency.

[0021] In this invention, mounting brackets 7 are fixed at both ends of the ring frame 3 on the base 1. The mounting brackets 7 have slots for placing the tube body, and the cross-section of the slots is much larger than the cross-section of the tube body. The ring frame 3 is rotatably arranged between the two mounting brackets 7. The ring frame 3 is connected to a motor 12. Specifically, a positioning ring 8 is fixed on the end face of the mounting bracket 7 facing the ring frame 3. Slip rings 9 are fixed at both ends of the ring frame 3. The end face of the slip ring 9 is provided with an annular groove. The inner wall of the annular groove slides in contact with the outer wall of the positioning ring 8. A toothed ring 10 is fixed on the outer wall of one of the slip rings 9. A bracket 11 is fixed between the motor 12 and the mounting bracket 7. The output shaft of the motor 12 is fixed with a drive gear 13 that meshes with the toothed ring 10. Thus, the rotation of the ring frame 3 is realized by the motor 12 to adjust the laser 4 to perform welding operations corresponding to different welding positions, and the stability of the ring frame 3 after rotation is also improved.

[0022] In this invention, a plurality of fan blades 18 are fixed to the inner wall of one end of the nozzle 6, and a plurality of nozzle holes 602 are provided on the outer circumferential wall of the nozzle 6, so that the airflow from the blowing pipe 5 toward the nozzle 6 impacts the fan blades 18, causing the nozzle 6 to rotate naturally. Through the plurality of nozzle holes 601 on the end face and the plurality of nozzle holes 602 in the circumferential direction, the protective gas can be effectively dispersed to the surrounding area of ​​the weld, ensuring the protective effect while effectively avoiding the impact of the airflow on the weld.

[0023] In this invention, a connecting ring 17 is fixed to one end of the nozzle 6 facing the blowing pipe 5. The outer circumferential wall of the connecting ring 17 is rotatably connected to the inner wall of the blowing pipe 5 through a bearing. A baffle 19 is fixed to the inner wall of the connecting ring 17 at the position corresponding to the nozzle 601. By setting the baffle 19, the jet airflow of the blowing pipe 5 can be prevented from directly passing through the nozzle 601 and impacting the weld position, thereby further improving the protection of the weld, especially the protection effect on the newly welded position when the ring frame 3 is rotated and repositioned.

[0024] In this invention, a guide plate 20 is provided on the inner wall of the ring frame 3 above the blowpipe 5. The guide plate 20 is positioned between the blowpipe 5 and the laser 4. A rotating shaft 21 is fixed to one end of the guide plate 20 near the blowpipe 5. Both ends of the rotating shaft 21 are rotatably connected to bearing seats 22. The bearing seats 22 are fixed to the inner wall of the ring frame 3. A spring 23 is connected between the guide plate 20 and the inner wall of the ring frame 3. During the welding operation, the nozzles 6 on both sides of the laser 4 spray protective gas from the nozzle 601 and nozzle 602 respectively. The upward-flowing protective gas impacts the inclined guide plate 20 and rebounds to the weld surface at the welding position. This improves the protective gas protection at the weld position while further reducing the airflow impact force to avoid damage to the weld.

[0025] In this invention, a second blowing pipe 16 is installed on the ring frame 3, symmetrically arranged with the laser 4. The second blowing pipe 16 has two inclined pipe heads 161. When in use, the second blowing pipe 16 also blows protective gas. The blowing direction of the pipe head 161 is tangential to the outer wall of the pipe to be welded. Since the second blowing pipe 16 is symmetrically arranged with the laser 4, the second blowing pipe 16 is located away from the laser 4. The blowing of the pipe head 161 along the tangential direction of the pipe will not damage the overheated weld. Furthermore, the negative pressure formed by the blowing of the pipe head 161 in the tangential direction can guide the airflow blown by the nozzles 6 on both sides to converge towards the weld position. This can avoid blowing directly towards the overheated weld while ensuring that the protective gas flows towards the weld position, thereby improving the welding operation effect.

[0026] In this invention, ring plates 14 are provided at both ends of the ring frame 3. The ring plates 14 are located between the mounting frame 7 and the fixing sleeve 2. The outer diameter of the ring plates 14 is smaller than the inner diameter of the groove on the mounting frame 7. Multiple springs 15 are connected between the ring plates 14 and the fixing sleeve 2. Through the ring frame 3 and the ring plates 14 at both ends, a relatively independent welding chamber can be formed inside during welding operations, reducing the flow of external ambient air into the chamber. Furthermore, as the protective gas flows through the internal chamber, the ring plates 14 at both ends can be moved with the airflow changes, so that the airflow can be guided to flow and disperse axially in the tube body through the moving ring plates 14, further improving the protective effect of the protective gas.

[0027] Example 2: Refer to Figures 1-8 A metal tube laser welding device with protective gas injection, based on embodiment 1, in order to determine the blockage status of the nozzle 6, a pressure sensor for measuring the compressive force of spring-23 is installed on the inner wall of the ring frame 3. The pressure sensor can be a miniature resistance strain gauge pressure sensor with a range of 0-50N, an accuracy of ±0.5%FS, and an operating temperature range of -40℃ to 150℃. The pressure sensor is fixed to the connection end between the back of the guide plate 20 and the spring-23, so that the compressive force of the spring-23 acts directly on the force-bearing surface of the sensor. The signal line of the pressure sensor runs along the inner wall of the ring frame 3 and is led out to an external controller through a conductive slip ring installed on the end face of the slip ring 9. The controller has a built-in analog-to-digital conversion module.

[0028] In this invention, a non-contact speed sensor is installed on the inner wall of the ring frame 3 near the circumferential surface of the nozzle 6. The speed sensor is a Hall effect sensor. At the same time, a miniature permanent magnet is attached to the outer circumferential wall of the nozzle 6. The air gap between the Hall sensor and the permanent magnet is adjusted to 1-3mm to ensure that a pulse signal is generated in each cycle when the nozzle 6 rotates. The signal line of the Hall sensor is also connected to the pulse counting port of the external controller through a conductive slip ring.

[0029] In this invention, before the welding operation begins, an initial calibration procedure is performed. Specifically, the control device introduces protective gas at standard working pressure, causing the blower pipe 5 to supply gas to the nozzle 6. The nozzle 6 rotates stably under the drive of the airflow, and the guide plate 20 compresses the spring 23 after being impacted by the airflow. The controller continuously collects the force signal from the pressure sensor and the pulse signal from the speed sensor. The sampling frequency is set to 20Hz, and 30 sampling points are continuously recorded. The average value of the pressure signal is calculated and recorded as F0. The speed pulse frequency is calculated, converted to revolutions per minute, and the average value is recorded as n0. At the same time, the standard deviations σF and σn of each parameter are recorded. During the calibration process, the laser 4 is not activated, and the pipe to be welded is not placed.

[0030] After calibration, the two pipes to be welded are passed through the fixing sleeve 2, ensuring the butt weld is located in the center plane of the ring frame 3. The shielding gas supply is then activated. Once the pressure and rotation speed signals stabilize within the ranges of F0±5% and n0±5%, respectively, the laser 4 is activated, and the motor 12 drives the ring frame 3 to rotate for welding. During welding, the controller collects the current pressure value F and rotation speed value n in real time and calculates the relative deviation. .

[0031] The controller has three preset blockage levels, corresponding to minor blockage, moderate blockage, and severe blockage. Each level is judged using two deviation thresholds: pressure deviation thresholds denoted as AF1, AF2, and AF3, and speed deviation thresholds denoted as AN1, AN2, and AN3, all satisfying the condition 0. <AF1<AF2<AF3,0<AN1<AN2<AN3; The specific method for determining the threshold values ​​is as follows: With the nozzle 6 in a brand new, unclogging state, an air-jet test is conducted using standard protective gas pressure. The typical fluctuation ranges of ΔF and Δn under normal conditions are recorded. Then, a simulated experiment of partial clogging of different degrees is conducted on the nozzle 6 orifices using a manual method: 10%, 20%, and 40% of the total number of orifices are sealed sequentially with high-temperature solder or heat-resistant tape, corresponding to slight, moderate, and severe clogging, respectively. For each degree of clogging, the test is repeated more than three times, and the corresponding stable values ​​of ΔF and Δn are recorded. The lower limit of ΔF under each degree of clogging is subtracted from the upper limit of normal fluctuation as AF1, AF2, and AF3; the lower limit of Δn under each degree of clogging is subtracted from the upper limit of normal fluctuation as AN1, AN2, and AN3; the above threshold values ​​are written into the non-volatile memory of the controller.

[0032] In this invention, during the welding process, the controller updates the status judgment every 0.5 seconds: if ΔF ≥ AF1 and Δn ≥ AN1 are satisfied simultaneously, and this state lasts for more than 1 second, it is judged as a slight blockage; if ΔF ≥ AF2 and Δn ≥ AN2 are satisfied simultaneously, and this state lasts for more than 1 second, it is judged as a moderate blockage; if ΔF ≥ AF3 and Δn ≥ AN3 are satisfied simultaneously, and this state lasts for more than 1 second, it is judged as a severe blockage; if only one side of the deviation is satisfied while the other side of the deviation does not reach the corresponding threshold, the previous judgment result is maintained to avoid misjudgment due to instantaneous noise.

[0033] When a minor blockage is detected, the controller displays "Minor blockage of the nozzle, it is recommended to clean the nozzle after this welding is completed" on the display screen. At the same time, the green indicator light stays on, indicating that the working condition is normal but attention is required. When a moderate blockage is detected, the controller illuminates a yellow indicator light and makes it flash at a frequency of 1Hz. At the same time, it drives the buzzer to emit short intermittent beeps, and the display shows "Moderate blockage of nozzle, uneven distribution of protective gas, please stop the machine and clean it as soon as possible"; When a severe blockage is detected, the red indicator light will remain on, the buzzer will sound continuously, and the display screen will show "The nozzle is severely blocked, and the protective gas is seriously insufficient. Please clean the nozzle immediately."

[0034] By using the method described in this embodiment, the problem of uneven distribution of protective gas caused by nozzle blockage can be accurately identified by combining two characteristic parameters: the increase of spring compression force and the decrease of nozzle speed. The method can also provide graded warnings, thereby effectively ensuring the weld quality of laser welding of metal tubes.

[0035] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A metal tube laser welding device with protective gas jetting, comprising a base (1) and a plurality of fixing sleeves (2) mounted on the base (1), characterized in that, A ring frame (3) is provided on the base (1). The ring frame (3) is rotatably arranged around a horizontal axis. A laser (4) is installed on the ring frame (3). A blowpipe (5) is installed on both sides of the laser (4) on the ring frame (3). The blowpipe (5) is perpendicular to the laser (4). A nozzle (6) is rotatably connected to one end of the blowpipe (5) facing the center of the ring frame (3). The nozzle (6) is sealed at one end away from the blowpipe (5). A ring array of nozzle holes (601) is opened at the other end of the nozzle (6) away from the blowpipe (5). Mounting brackets (7) are fixed at both ends of the ring frame (3) on the base (1). The mounting brackets (7) are provided with through slots. The ring frame (3) is rotatably arranged between the two mounting brackets (7). The ring frame (3) is connected to the drive A motor (12) is connected to the nozzle (6). Multiple fan blades (18) are fixed on the inner wall of one end of the nozzle (6). Multiple nozzle holes (602) are opened on the outer circumference of the nozzle (6). A guide plate (20) is set on the inner wall of the ring frame (3) above the blowing pipe (5). The end of the guide plate (20) near the blowing pipe (5) is rotatably set between the ring frame (3). A spring (23) is connected between the guide plate (20) and the inner wall of the ring frame (3). A pressure sensor for detecting the compression force of the spring (23) is set on the ring frame (3). A non-contact speed sensor for detecting the rotation speed of the nozzle (6) is set on the inner wall of the ring frame (3) near the circumference of the nozzle (6). The signal lines of the pressure sensor and the speed sensor are led out to the controller through a conductive slip ring. Before welding begins and with a stable supply of protective gas, the normal value of the spring compression force is obtained by collecting the signal from the pressure sensor, and the normal value of the nozzle rotation speed is obtained by collecting the signal from the speed sensor. During the welding process, the spring compression force value and nozzle rotation speed value are collected in real time, and the degree of pressure increase and the degree of rotation speed decrease relative to the normal value are calculated respectively. The degree of pressure increase and the degree of rotation speed decrease are compared with the corresponding preset thresholds to determine whether the nozzle (6) is blocked. When the degree of pressure increase exceeds the first pressure threshold and the degree of rotation speed decrease exceeds the first rotation speed threshold, it is determined to be a slight blockage state. When the degree of pressure increase exceeds the second pressure threshold and the degree of rotation speed decrease exceeds the second rotation speed threshold, it is determined to be a moderate blockage state. When the degree of pressure increase exceeds the third pressure threshold and the degree of rotation speed decrease exceeds the third rotation speed threshold, it is determined to be a severe blockage state.

2. The metal tube laser welding apparatus with protective gas injection according to claim 1, characterized in that, The nozzle (6) is fixed with a connecting ring (17) at one end facing the blowing pipe (5). The outer circumference of the connecting ring (17) is rotatably connected to the inner wall of the blowing pipe (5) through a bearing. A baffle (19) is fixed at the position corresponding to the nozzle hole (601) on the inner wall of the connecting ring (17).

3. A metal tube laser welding apparatus with protective gas injection according to any one of claims 1 to 2, characterized in that, The ring frame (3) is equipped with a second blowing tube (16) symmetrically arranged with the laser (4), and the second blowing tube (16) has two inclined tube heads (161).

4. A metal tube laser welding apparatus with protective gas injection according to any one of claims 1 to 2, characterized in that, Both ends of the ring frame (3) are provided with ring plates (14). The outer diameter of the ring plate (14) is smaller than the inner diameter of the groove on the mounting frame (7). Multiple springs (15) are connected between the ring plate (14) and the fixing sleeve (2).

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