Laser welding jig and welding method thereof

Abstract

The invention relates to the technical field of laser welding, in particular to a laser welding jig and a welding method thereof.The laser welding jig comprises a jig base used for containing a workpiece to be welded, a welding point position is arranged in the center of the jig base, and the welding jig further comprises a protective gas conveying mechanism, a laser welding mechanism and a laser welding mechanism, the annular air outlet discharges air to surround the welding point to form a protective air curtain; a smoke suction port of the smoke suction pipe extends into the protective air curtain; the negative pressure structure comprises an air inlet pipeline and a negative pressure base arranged on the jig base, the negative pressure pipeline is arranged in the negative pressure base, the air inlet pipeline is communicated with the negative pressure pipeline, an air inlet of the air inlet pipeline is formed over the annular air outlet, and a smoke suction opening of the smoke suction pipe sucks welding smoke generated by the welding point position under negative pressure. And the air pressure of the protective gas is positively correlated with the suction force generated by the negative pressure in the smoke suction pipe, so that the effect of balancing the absorption of the welding smoke and the injection of the protective gas without conflicts is achieved.

Description

Technical Field

[0001] This invention relates to the field of laser welding technology, and in particular to a laser welding fixture and its welding method. Background Technology

[0002] Laser welding, as a high-precision and high-efficiency modern joining technology, has been widely used in high-end manufacturing fields such as precision electronics, medical devices, and new energy vehicle batteries.

[0003] During laser welding, the molten metal evaporates and oxidizes rapidly, producing a large amount of welding fumes containing metal oxide particles. If these fumes are not removed in time, they will cause multiple hazards. Existing technologies typically employ two independent systems: one is a fume extraction system, which uses an external exhaust device to create negative pressure near the welding point to suck away the generated fumes; the other is a shielding gas system, which blows inert gases (such as argon or nitrogen) into the weld pool and its surrounding area to isolate the air, prevent high-temperature metal oxidation, and stabilize the plasma, thereby improving welding quality. However, this approach reveals a significant technical contradiction in practice: the suction generated by the fume extraction system and the airflow from the shielding gas system directly interfere with and clash with each other near the welding point. This causes the strong fume extraction airflow to quickly suck away the expensive shielding gas, resulting in the shielding gas curtain failing to stably cover the weld pool, making the weld prone to oxidation during laser welding. Summary of the Invention

[0004] Therefore, the purpose of this invention is to overcome the problem in the prior art that when treating welding fumes generated during laser welding, the protective gas at the welding point is also sucked in, reducing the protective ability of the protective gas. Therefore, a laser welding fixture is provided that uses the airflow generated by the protective gas to create suction and simultaneously inserts the fume extraction tube into the protective gas curtain. This allows for targeted fume extraction at the welding point, preventing the negative pressure absorption of welding fumes from affecting the shape of the protective gas curtain and reducing its protective effect. Thus, the fume extraction process and the protective gas injection process during laser welding are balanced.

[0005] To address the aforementioned technical problems, the present invention provides a laser welding fixture, including a fixture base for placing the workpiece to be welded, wherein a welding point is disposed at the center of the fixture base, and the welding fixture further includes: A protective gas delivery mechanism has an annular gas outlet, which is arranged around the welding point; the gas emitted from the annular gas outlet forms a protective gas curtain around the welding point. A smoking tube, the smoking port of which extends into the protective air curtain; The negative pressure structure includes an air inlet pipe and a negative pressure base disposed on the fixture base. The negative pressure base is provided with a negative pressure pipe. The air inlet pipe is connected to the negative pressure pipe. The air inlet of the air inlet pipe is located directly above the annular air outlet. The smoke pipe is connected to the negative pressure pipe. Wherein, the diameter of the air inlet pipe is at least twice the diameter of the negative pressure pipe. After the protective gas enters the air inlet pipe and flows through the negative pressure pipe, a negative pressure is formed in the smoke extraction pipe. The smoke extraction port of the smoke extraction pipe draws in the welding fumes generated at the welding point under the negative pressure. The pressure of the protective gas is positively correlated with the suction force generated by the negative pressure in the smoke extraction pipe.

[0006] In one embodiment of the present invention, the diameter of the air inlet pipe is three times the diameter of the negative pressure pipe.

[0007] In one embodiment of the present invention, an angle adjustment plate is provided at the annular air outlet to change the flow direction of the protective gas; the angle between the central axis of the annular air outlet and the vertical direction is an acute angle α, and the protective air curtain formed by the air outlet forms an upward cone shape.

[0008] In one embodiment of the invention, the welding fixture further includes a power controller for controlling the power of the laser welding head, the angle adjustment plate is connected to the power controller, and the power of the laser welding head is negatively correlated with the acute angle α.

[0009] In one embodiment of the present invention, the air inlet of the air inlet pipe is located within the protective air curtain, and the acute angle α is within the range of ±15°.

[0010] In one embodiment of the present invention, the air inlet pipe includes an air inlet section, a transfer section, and a guide section. The guide section is connected to the negative pressure pipe. The flow direction of the protective gas is opposite to that of the air inlet section and the guide section. Spiral guide vanes are provided at the air inlet of the air inlet section and the air inlet of the transfer section, which are used to guide the protective gas to enter from the air inlet and pass through the air inlet section-the transfer section-the guide section in sequence, thereby restricting the backflow of the protective gas.

[0011] In one embodiment of the present invention, the spiral guide vane is a continuous equidistant vane with a spiral angle ranging from 30° to 60°, and the rotation direction of the spiral guide vane matches the inflow direction of the protective gas.

[0012] In one embodiment of the present invention, a welding method is provided, based on a welding fixture, comprising: S1: The annular outlet sprays out protective gas, and the spray flow rate of the protective gas is the first flow rate, forming an initial protective gas curtain; S2: When laser welding begins, the flow rate of the shielding gas is gradually increased from the first flow rate to the second flow rate; S3: The protective gas flows through the air inlet pipe and enters the negative pressure pipe through the air inlet pipe. The aperture decreases instantaneously to form a Venturi effect. At this time, the pressure at the connection between the smoke pipe and the negative pressure pipe is less than the atmospheric pressure, forming a negative pressure. Under the negative pressure condition, the welding fumes generated by laser welding completely enter the smoke pipe. S4: During the laser welding process, maintain the second flow rate to ensure the continuity of the negative pressure state; S5: When the laser welding is finished, reduce the flow rate of the protective gas from the second flow rate to the first flow rate or turn it off.

[0013] In one embodiment of the present invention, a first time is set for the time delay from starting the protective fan to forming a stable negative pressure environment in the smoke extraction pipe, and a second time is set for the time delay from starting the protective fan to the start of laser welding, wherein the second time is greater than the first time.

[0014] In one embodiment of the present invention, at the initial start-up of the protective fan, it is operated for a short period of time at a flow rate of protective gas higher than the second flow rate.

[0015] Compared with the prior art, the above-described technical solution of the present invention has the following advantages: The laser welding fixture described in this invention changes the method of introducing the shielding gas, so that during the welding process, the shielding gas forms a cylindrical shielding gas curtain around the point to be welded. The welding nozzle of the laser welding is welded within the shielding gas curtain, and no oxidation reaction occurs. Furthermore, the pipe for absorbing welding fumes is extended into the shielding gas curtain to absorb the welding fumes generated at the welding point, preventing the shielding gas curtain from being affected by the suction of the absorbed welding fumes. The system includes an annular air outlet connected to a fan that injects inert gas. The gas is injected through the annular outlet to form a cylindrical, upward-facing protective air curtain. A fume extraction pipe extends into the protective air curtain, close to the welding point. It receives the protective airflow generated by the protective air curtain through a negative pressure structure. This airflow flows into the gas duct and, through the negative pressure duct, creates a Venturi effect. This Venturi effect creates negative pressure inside the fume extraction pipe, resulting in a linkage between the suction force within the pipe and the pressure of the protective gas. As the welding intensity and the amount of welding fumes produced by laser welding change, the suction force of the fume extraction pipe also changes accordingly. This prevents the suction force from being too high or too low, which could affect the protective efficiency of the gas, thus achieving a balance between the fume extraction and protective gas flow. Attached Figure Description

[0016] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0017] Figure 1 This is a schematic diagram of the structure of a laser welding fixture in a preferred embodiment of the present invention. Figure 1 ; Figure 2 This is a schematic diagram of the structure of a laser welding fixture in a preferred embodiment of the present invention. Figure 2 ; Figure 3 This is a schematic diagram of the angle adjustment plate portion in a preferred embodiment of the present invention; Figure 4 This is a schematic diagram of the negative pressure structure in a preferred embodiment of the present invention; Figure 5 This is a cross-sectional schematic diagram of the negative pressure structure portion in a preferred embodiment of the present invention; Figure 6 This is a schematic diagram of the gas flow direction in the negative pressure structure in a preferred embodiment of the present invention; Figure 7 This is a schematic diagram of the structure of a laser welding fixture in a preferred embodiment of the invention. Figure 3 .

[0018] Explanation of reference numerals on the accompanying drawings: 1. Fixture base; 11. Welding points; 12. Annular air outlet; 121. Angle adjustment plate; 122. Gas distribution chamber; 2. Negative pressure structure; 21. Smoke tube; 22. Negative pressure base; 221. Negative pressure pipe; 23. Air inlet pipe; 231. Air inlet section; 232. Transfer section; 233. Air guide section; 234. Spiral guide vane; 3. Acute angle α; D1: Protects the direction of gas flow. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0020] The purpose of this invention is to address the problem that during the fume extraction process of laser welding, the shielding gas at the welding point 11 is sometimes drawn in along with the fume, reducing the protective effect of the shielding gas. Therefore, a laser welding fixture is provided that utilizes the airflow generated by the shielding gas to create suction and simultaneously inserts the fume extraction tube 21 into the shielding gas curtain. This allows for targeted fume extraction at the welding point 11, preventing the negative pressure absorption of welding fumes from affecting the shape of the shielding gas curtain and reducing its protective effect. Thus, the fume extraction process and the shielding gas injection process during laser welding are balanced.

[0021] refer to Figure 1 , 2 As shown in Figure 4, specifically, a laser welding fixture is provided, including a fixture base 1 for placing the workpiece to be welded. A welding point 11 is located at the center of the fixture base 1. The welding fixture further includes: a protective gas delivery mechanism having an annular outlet 12 surrounding the welding point 11; the gas exiting the annular outlet 12 forms a protective gas curtain around the welding point 11; a fumigation pipe 21 with its fumigation port extending into the protective gas curtain; and a negative pressure structure 2, including an inlet pipe 23 and a negative pressure base 22 disposed on the fixture base 1. A negative pressure pipe 221 is installed inside the 22, and an air inlet pipe 23 is connected to the negative pressure pipe 221. The air inlet of the air inlet pipe 23 is located directly above the annular air outlet 12. The smoke extraction pipe 21 is connected to the negative pressure pipe 221. The diameter of the air inlet pipe 23 is at least twice the diameter of the negative pressure pipe 221. After the protective gas enters the air inlet pipe 23 and flows through the negative pressure pipe 221, a negative pressure is formed in the smoke extraction pipe 21. The smoke extraction port of the smoke extraction pipe 21 draws the welding fumes generated at the welding point 11 under the negative pressure. The pressure of the protective gas is positively correlated with the suction force generated by the negative pressure in the smoke extraction pipe 21.

[0022] refer to Figure 1 , 2 As shown in Figure 4, the fixture base 1 is typically made of a high-temperature resistant metal (such as stainless steel or aluminum alloy), and its top forms a flat bearing surface for positioning and placing the workpiece to be welded. The central area of ​​the bearing surface is defined as the welding point 11, where the laser welding head will approach and emit a laser beam for welding. refer to Figure 1 , 2 As shown in Figures 4 and 7, to protect the laser welding point 11 and prevent high-temperature oxidation of the welding molten metal, an external protective gas delivery device is required. This device is used to introduce protective gas during welding. The protective gas delivery mechanism is integrated inside or outside the fixture base 1. Its core is an annular gas distribution chamber 122, which is connected to an inert protective gas source via an external pipeline. Above or inside the distribution chamber, a continuous ring of slits forms an annular outlet 12. This annular outlet 12 is precisely positioned around the welding point 11. When a protective gas (such as argon) is introduced, it flows out evenly from the annular outlet 12, forming a columnar or slightly conical protective gas curtain that extends downwards around the welding point 11. The main function of this gas curtain is to isolate air, prevent oxidation of the weld pool, and disperse plasma that may interfere with the laser.

[0023] refer to Figure 1 , 2As shown in Figures 4 and 6, an integrated fumigation system consisting of a negative pressure structure 2 and a fumigation pipe 21 is also provided. The negative pressure structure 2 includes a negative pressure base 22 mounted on the fixture base 1. A negative pressure pipe 221 is machined inside the negative pressure base 22. An air inlet pipe 23 is also provided, with one end of the air inlet facing downwards and directly above the annular air outlet 12. The other end of the air inlet pipe 23 bends downwards and connects to the inlet of the negative pressure pipe 221. The protective gas enters the air inlet pipe 23 and flows into the negative pressure pipe 221 in the direction of D1. The fumigation pipe 21 is typically a long, thin metal tube with its fumigation port horizontal, slightly raised, or lowered and extending through the protective air curtain, terminating near the welding point 11 (e.g., 3-10 mm from the workpiece surface) to optimally capture the initially generated welding fumes. The outlet end of the smoking pipe 21 is connected to the outlet end of the negative pressure pipe 221, thus forming a "T"-shaped confluence flow path. Regarding the pipe diameter settings of the inlet pipe 23 and the negative pressure pipe 221, the core design parameter is that the diameter of the inlet pipe 23 is at least twice the diameter of the negative pressure pipe 221. After the protective gas is ejected from the annular outlet 12 to form a protective air curtain, most of its airflow does not directly dissipate into the environment, but enters the inlet of the inlet pipe 23 and flows along the extension direction of the inlet pipe 23, finally entering the negative pressure pipe 221. Since the diameter of the inlet pipe 23 is much larger than the diameter of the negative pressure pipe 221, when this mainstream of the protective gas enters the inlet pipe 23 and flows towards the negative pressure pipe 221, where the cross-section decreases sharply, according to the continuity equation in fluid mechanics (Q = ... When the flow rate Q remains essentially constant, the velocity v of the protective gas increases sharply as it flows through the small-section negative pressure pipe 221. As the fluid velocity increases in the narrow pipe, its static pressure decreases. Therefore, based on this principle, a local low-pressure zone (i.e., negative pressure) is formed in the throat or the entire narrow section of the negative pressure pipe 221. This local low-pressure zone acts directly on the fumigation pipe 21 through the connected pipe. Since the fumigation port of the fumigation pipe 21 is exposed to the normal pressure welding area, and the inside of the pipe is connected to the negative pressure zone, a pressure difference is generated at the fumigation port from the outside to the inside of the pipe, creating suction. This suction continuously draws the welding fumes generated at the welding point 11 into the fumigation pipe 21. refer to Figure 1 , 2As shown in Figure 4, the welding fumes are drawn into the negative pressure pipe 221, where they instantly mix with the high-speed flowing shielding gas. The shielding gas acts as a carrier, carrying the fumes and dust out of the outlet of the negative pressure pipe 221. The outlet of the negative pressure pipe 221 can be installed on the welding fixture and can enter the subsequent filtration system or exhaust duct. Furthermore, the supply pressure of the shielding gas directly determines the gas flow rate and initial kinetic energy entering the inlet pipe 23. The higher the pressure, the more gas flows in, the higher the flow velocity generated in the negative pressure pipe 221, and the stronger the negative pressure and suction force of the smoke inlet. Therefore, the pressure of the shielding gas and the suction force generated by the negative pressure in the smoke inlet 21 are positively correlated. The operator only needs to adjust the total pressure of the shielding gas to control the shielding effect and smoke intensity synchronously and in the same direction. The two no longer need to be adjusted independently and do not interfere with each other, but achieve a dynamic and matched effect.

[0024] refer to Figure 1 , 2 As shown in Figure 4, in another embodiment, fluid simulation and experimental testing revealed that when the diameter of the air inlet pipe 23 is three times the diameter of the negative pressure pipe 221, the system can achieve a better balance between energy consumption, negative pressure intensity, and airflow stability. Under this ratio, the cross-sectional shrinkage ratio is large enough that its area ratio is 9:1, which can generate a sufficiently strong Venturi effect, form a significant negative pressure, and ensure sufficient suction power for smoking.

[0025] refer to Figure 1 , 2 As shown in Figures 3 and 4, in another embodiment, an angle adjustment plate 121 is provided at the annular air outlet 12 to change the flow direction of the protective gas; the angle between the angle adjustment plate 121 and the vertical direction is an acute angle α, and the protective gas curtain formed by the air outlet forms an upward cone shape; the welding fixture also includes a power controller, which is used to control the power of the laser welding head, the angle adjustment plate 121 and the power controller are connected, and the power of the laser welding head is negatively correlated with the acute angle α.

[0026] refer to Figure 1 , 2As shown in Figures 3 and 4, the protective gas delivery mechanism is improved to enhance its adaptability to different welding conditions. An angle adjustment plate 121 is added at the annular gas outlet 12. The angle adjustment plate 121 can be a ring of independent small blades arranged around the annular gas outlet 12, or it can be a continuous annular skirt that can be elastically or hingedly deformed. Each blade or skirt section can be driven by a micro stepper motor, shape memory alloy actuator, or manual fine-tuning mechanism to change its angle with the horizontal plane. By adjusting the angle adjustment plate 121, the direction of the protective gas ejection can be changed. Specifically, by making the angle adjustment plate 121 form an acute angle α with the vertical direction, the protective gas flowing out of the outlet is not vertically downward, but has a certain horizontal radial component. When the airflow direction of all outlets is adjusted to be inclined inward or outward, the converging airflow will form an upward conical protective gas curtain. When α makes the airflow direction slightly inward to tilt towards the central axis of the welding point 11, a converging conical gas curtain is formed, which can more effectively protect the weld pool and has a higher gas utilization rate. It is particularly suitable for deep penetration welding or materials with extremely high protection requirements (such as titanium alloys). When α makes the airflow direction slightly outward, a diffuse conical gas curtain is formed. This mode has a wider coverage area, helps to dilute and block the entrainment of surrounding air in advance, and has a pre-gathering effect on smoke and dust in a slightly larger area, making it easier for the smoke extraction pipe 21 to draw it in.

[0027] refer to Figure 1 , 2As shown in Figures 3 and 4, the welding fixture also includes a power controller. This power controller can be a built-in controller module of the welding power supply or an external PLC or industrial computer. The power controller is electrically connected to the control terminal of the laser welding head, enabling it to acquire or set the laser welding power in real time. Simultaneously, the power controller is signal-connected to the actuator (such as a motor driver) of the drive angle adjustment plate 121. When performing high-power welding: the laser energy input is large, resulting in a large amount of welding fumes with fine particles and a fast jet speed, and severe disturbance in the molten pool, requiring a stronger fume extraction capability. Furthermore, high power may generate stronger plasma, requiring a more concentrated protective gas curtain for suppression. At this time, the power controller will reduce the angle α at high power. A smaller α means the airflow is closer to vertical downwards, and a more vertical airflow can be more effectively controlled by the upper air inlet pipe 2. 3. Capture, thereby generating a stronger airflow velocity and a larger smoke negative pressure in the negative pressure pipe 221 to cope with large amounts of smoke. At this time, the air curtain is more concentrated, and the protection of the high-energy welding pool is more direct and effective. When performing low-power welding: the amount of smoke generated is small and the molten pool is relatively calm. At this time, the power controller adjusts the angle α according to the lower power. The larger α makes the protective airflow direction more inclined, and the formed conical air curtain is more diffused. This can provide sufficient protection range, and because the horizontal component of the airflow increases, some gas may interact with the smoke area earlier, achieving gentle and effective smoke control, while avoiding waste of protective gas or excessive cooling of the molten pool due to excessive suction.

[0028] refer to Figure 1 , 2 As shown in Figures 3 and 4, in order to ensure that the kinetic energy of the protective air curtain is used efficiently, the air inlet of the air inlet pipe 23 must be within the coverage of the protective air curtain. That is, the conical airflow ejected from the annular air outlet 12 should be able to directly impact or wrap around the edge of the air inlet, ensuring that most of the kinetic energy of the protective gas can be input into the negative pressure generating system with almost no waste. Therefore, the angle range of the acute angle α is specifically limited to: between ±15°, i.e., -15° ≤ α ≤ +15°.

[0029] refer to Figure 5 As shown, in another embodiment, the air inlet pipe 23 includes an air inlet section 231, a transfer section 232, and a guide section 233. The guide section 233 is connected to the negative pressure pipe 221. The flow direction of the protective gas in the air inlet section 231 and the guide section 233 is opposite. Spiral guide vanes are provided at the air inlet of the air inlet section 231 and the air inlet of the transfer section 232. These vanes are used to guide the protective gas to enter from the air inlet and pass through the air inlet section 231-transfer section 232-guide section 233 in sequence, thus restricting the backflow of the protective gas. The spiral guide vanes are continuous equidistant vanes with a spiral angle between 30° and 60°. The rotation direction of the spiral guide vanes matches the inflow direction of the protective gas.

[0030] refer to Figure 5 As shown, in the use of the air inlet pipe 23, the protective gas enters from the air inlet of the air inlet pipe 23 under the drive of air pressure. Due to the shape limitation of the air inlet pipe 23, the protective gas may flow back, resulting in a decrease in the efficiency of airflow within the air inlet pipe 23. Therefore, the air inlet pipe 23 is configured to include, specifically, an air inlet section 231, a transfer section 232, and a guide section 233 connected in sequence. The end of the guide section 233 is connected to the negative pressure pipe 221. Importantly, the protective gas enters through the air inlet section 231. The flow direction is opposite to that in the air guide section 233. The gas flows from bottom to top in the air inlet section 231, and after completing a 180-degree turn in the transfer section 232, it flows from top to bottom in the air guide section 233 and then enters the negative pressure pipe 221. In this flow channel with a sudden change in direction, local backflow or eddies are more likely to occur under pressure fluctuations, thereby disturbing or even destroying the stability of the smoking negative pressure. Therefore, spiral guide vanes are provided. Specifically, the first set of spiral guide vanes is provided at the air inlet of the air inlet section 231. When the protective air curtain enters the air inlet, the spiral guide vanes guide the gas from axial flow to a rotating spiral flow. Since the rotating airflow has angular momentum, its inertia helps to suppress reverse flow, and the pre-swirl allows the gas to adapt more smoothly to subsequent flow direction changes. At the inlet of the transfer section 232, a second set of spiral guide vanes is set. The design direction of this set of vanes is coordinated with the first set. It is used to sort out the airflow after the turn, reorganize the potentially chaotic airflow into an orderly rotating flow, and ensure that the airflow can smoothly enter the air guide section 233 and rush towards the negative pressure pipe 221. This prevents the generation of backflow vortices due to flow separation at this critical node. Through the cooperation of these two sets of spiral guide vanes, the backflow of protective gas in the complex pipe can be effectively limited, maintaining the stability of negative pressure generation and the continuity of smoke suction.

[0031] refer to Figure 5 As shown, the spiral guide vanes are preferably continuous equidistant blades, thus their spacing is constant, ensuring uniform and continuous guidance of the airflow and avoiding sudden changes in flow velocity and additional turbulence caused by pitch variations. The helix angle of the blades is set between 30° and 60°. In actual testing, when the helix angle of the blades is close to 30°, the blades are relatively "gentle," with a mild rotational acceleration effect on the airflow and low flow resistance, making them suitable for applications requiring low pressure loss and high flow rate. When the helix angle of the blades is close to 60°, the blades are relatively "steep," exerting a strong rotational effect on the airflow and generating high swirling intensity, resulting in excellent backflow prevention and guidance capabilities. However, the flow resistance also increases accordingly, making them adaptable to different operating conditions. Furthermore, the rotation direction of the spiral guide vanes must match the inflow direction of the protective gas, and its rotation direction needs to be consistent with the pipeline layout and the guidance requirements of the next stage blades to ensure that the airflow is guided in the desired direction and that no countercurrent occurs.

[0032] To utilize programmed control of shielding gas flow rate to synchronously drive and dynamically adjust the welding protection and fume removal processes, a laser welding method is established, comprising: S1: The annular outlet 12 ejects protective gas. At this time, the ejection flow rate of the protective gas is the first flow rate. The first flow rate is a relatively low reference flow rate. Its value is usually set to the minimum flow rate required to stably form the initial protective gas curtain around the welding point 11, thus forming the initial protective gas curtain. S2: When laser welding begins, the flow rate of the shielding gas is gradually increased from the first flow rate to the second flow rate. The second flow rate is the working flow rate during the welding process, which is much greater than the first flow rate. The duration of the increase process is usually 0.5 to 2 seconds. This avoids the sudden change in flow rate causing a violent impact on the already formed weak shielding gas curtain and the flow field inside the pipe, and ensures a smooth transition of the system from "standby state" to "working state". S3: The protective gas flows through the inlet pipe 23 and enters the negative pressure pipe 221 through the inlet pipe 23. The aperture decreases instantaneously to form the Venturi effect. At this time, the pressure at the connection between the smoke pipe 21 and the negative pressure pipe 221 is less than the atmospheric pressure, forming a negative pressure. Under the negative pressure condition, the welding fumes generated by laser welding completely enter the smoke pipe 21. S4: During laser welding, maintain the second flow rate to ensure the continuity of the negative pressure state, so that the protective gas curtain G maintains a stable shape and coverage effect, and continuously provides anti-oxidation protection for the molten pool; S5: When laser welding ends, reduce the flow rate of the shielding gas from the second flow rate to the first flow rate or turn it off. When it is reduced to the first flow rate, the working condition is when multiple points need to be welded continuously or welding is required at short time intervals. At this time, reducing and maintaining the first flow rate can maintain a basic inert environment and prevent the weld from being oxidized during the high-temperature cooling stage. When it is turned off directly, it is suitable for a single welding operation to be completed and the equipment is about to enter the idle state.

[0033] In another embodiment, to avoid welding orientation deviation caused by smoke pollution at the moment of arc initiation / welding, a first time is set from the start of the protective fan to the formation of a stable negative pressure environment in the smoke extraction pipe 21, and a second time is set from the start of the protective fan to the start of laser welding, with the second time being greater than the first time.

[0034] Since any fluid system has inertia, establishing flow from a static state requires overcoming resistance such as pipe wall friction and the viscosity of the gas itself. Therefore, at the beginning of the shielding gas supply, it does not immediately operate at the first flow rate, but at a third flow rate that is significantly higher than the welding working flow rate for a very short period of time. Then it is quickly reduced to and stabilized at the first flow rate before proceeding to the subsequent S2 step. At this time, the short-term impact energy of the third flow rate allows the gas flow to quickly fill the entire flow channel, greatly shortening the time from zero flow to the formation of the initial flow field. This can shorten the entire welding cycle and improve production efficiency.

[0035] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A laser welding fixture, comprising a fixture base for placing a workpiece to be welded, wherein a welding point is disposed at the center of the fixture base, characterized in that: The welding fixture also includes: A protective gas delivery mechanism has an annular gas outlet, which is arranged around the welding point; the gas emitted from the annular gas outlet forms a protective gas curtain around the welding point. A smoking tube, the smoking port of which extends into the protective air curtain; The negative pressure structure includes an air inlet pipe and a negative pressure base disposed on the fixture base. The negative pressure base is provided with a negative pressure pipe. The air inlet pipe is connected to the negative pressure pipe. The air inlet of the air inlet pipe is located directly above the annular air outlet. The smoke pipe is connected to the negative pressure pipe. Wherein, the diameter of the air inlet pipe is at least twice the diameter of the negative pressure pipe. After the protective gas enters the air inlet pipe and flows through the negative pressure pipe, a negative pressure is formed in the smoke extraction pipe. The smoke extraction port of the smoke extraction pipe draws in the welding fumes generated at the welding point under the negative pressure. The pressure of the protective gas is positively correlated with the suction force generated by the negative pressure in the smoke extraction pipe.

2. The laser welding fixture according to claim 1, characterized in that: The diameter of the air inlet pipe is three times that of the negative pressure pipe.

3. The laser welding fixture according to claim 1, characterized in that: An angle adjustment plate is provided at the annular air outlet to change the flow direction of the protective gas; the angle between the angle adjustment plate and the vertical direction is an acute angle α, and the protective air curtain formed by the air outlet forms an upward cone shape.

4. A laser welding fixture according to claim 3, characterized in that: The welding fixture also includes a power controller for controlling the power of the laser welding head. The angle adjustment plate is connected to the power controller, and the power of the laser welding head is negatively correlated with the acute angle α.

5. A laser welding fixture according to claim 4, characterized in that: The air inlet of the air inlet pipe is located within the protective air curtain, and the acute angle α is within the range of ±15°.

6. A laser welding fixture according to claim 1, characterized in that: The air inlet pipe includes an air inlet section, a transfer section, and an air guide section. The air guide section is connected to the negative pressure pipe. The flow direction of the protective gas is opposite to that of the air inlet section and the air guide section. Spiral guide vanes are provided at the air inlet of the air inlet section and the air inlet of the transfer section, which are used to guide the protective gas to enter from the air inlet and pass through the air inlet section-the transfer section-the air guide section in sequence, thereby restricting the backflow of the protective gas.

7. A laser welding fixture according to claim 6, characterized in that: The spiral guide vanes are continuous equidistant vanes with a spiral angle ranging from 30° to 60°. The rotation direction of the spiral guide vanes matches the inflow direction of the protective gas.

8. A laser welding method, based on a laser welding fixture according to any one of claims 1-7, characterized in that: The welding method includes: S1: The annular outlet sprays out protective gas, and the spray flow rate of the protective gas is the first flow rate, forming an initial protective gas curtain; S2: When laser welding begins, the flow rate of the shielding gas is gradually increased from the first flow rate to the second flow rate; S3: The protective gas flows through the air inlet pipe and enters the negative pressure pipe through the air inlet pipe. The aperture decreases instantaneously to form a Venturi effect. At this time, the pressure at the connection between the smoke pipe and the negative pressure pipe is less than the atmospheric pressure, forming a negative pressure. Under the negative pressure condition, the welding fumes generated by laser welding completely enter the smoke pipe. S4: During the laser welding process, maintain the second flow rate to ensure the continuity of the negative pressure state; S5: When the laser welding is finished, reduce the flow rate of the protective gas from the second flow rate to the first flow rate or turn it off.

9. A laser welding method according to claim 8, characterized in that: The time delay from starting the protective fan to forming a stable negative pressure environment inside the smoke extraction pipe is set as a first time, and the time delay from starting the protective fan to the start of laser welding is set as a second time, wherein the second time is greater than the first time.

10. A laser welding method according to claim 8, characterized in that: When the protective fan is started, it is operated for a short period of time at a flow rate of protective gas higher than the second flow rate.

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