Cooperative control titanium alloy laser welding defect control method and device

Abstract

The invention relates to the technical field of titanium alloy laser welding, in particular to a cooperative control titanium alloy laser welding defect control method and device, according to the method, asymmetric 8-shaped high-speed scanning is adopted in the welding direction, meanwhile, a double-pulse or sine pulse mode is adopted for laser power, and cooperation of the two modes is achieved; wherein in the front section scanning area stage, high power and large transverse swing are adopted for widening a molten pool and improving forming; and in the rear section scanning area stage, low power and small transverse swing are adopted, the existence time of the molten pool is prolonged, the secondary frequency of the double pulses or sine pulses is 10-50 times of the scanning frequency, strong stirring is generated on the molten pool, air hole escape is promoted, the mode is switched to the sine pulse mode during arc suppression, and smooth transition is achieved. By means of the method, the defects of air holes, poor forming and arc suppression in titanium alloy welding are effectively overcome, and high-quality welding is achieved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of titanium alloy laser welding, in particular to a titanium alloy laser welding defect control method and device. BACKGROUND

[0002] Titanium and titanium alloy are widely used in the fields of aerospace, ship and ocean engineering, nuclear power energy, electronic information, etc. due to their excellent specific strength and specific stiffness, high-quality corrosion resistance, and non-magneticity. Titanium alloy laser welding technology uses laser as a high-quality heat source (usually an optical fiber laser with a Gaussian distribution of beam cross-section energy density), uses its excellent energy density and directivity, and adopts a "heat conduction" or "keyhole" mode for welding, thereby having a series of advantages such as narrow weld width, small heat-affected zone and low welding deformation, and the use scenarios are continuously expanding, which has effectively promoted the development of titanium alloy welding technology.

[0003] However, the current titanium alloy laser welding technology, such as Figure 1 has certain technical bottlenecks, especially for medium-thin plate precision welding. Due to the large surface tension of liquid titanium alloy metal, the laser welding speed is fast, the pore escape condition is poor, and welding pores are easily formed; For a poor quality weld, it is difficult for the molten pool metal to form a supplement, and there are easy undercut or poor forming defects; 3) For a girth weld, the closing arc defect is difficult to control due to the existence of a closed arc.

[0004] Publication No. CN115812015A discloses a laser welding method and a laser welding device. Laser is scanned two-dimensionally while advancing in the X direction to irradiate the surface of the workpiece so as to weld the workpiece. The laser is scanned so that the first drawing pattern in the X direction located in front of the origin in the specified pattern is wider than the second drawing pattern located behind the origin with respect to the Y direction. The output of the laser is controlled so that the output of the laser in the drawing of the first drawing pattern is lower than that in the drawing of the second drawing pattern. However, only the problem of "obstacle" is solved, and the "molten pool metallurgical process" is not deeply regulated, so it is impossible to refine the grains and promote the pore escape.

[0005] Therefore, the development of titanium alloy laser precision welding technology is hindered, and it cannot be widely used in engineering applications. Therefore, a new titanium alloy laser welding defect control method and device are needed to solve the problems of titanium alloy laser welding of medium-thin plate precision welding pores, undercut or poor forming defects, and difficult control of the closing arc quality of the closed weld. SUMMARY

[0006] Therefore, the application aims to provide a titanium alloy laser welding defect control method and device with synergistic control, so as to solve the problems of porosity, undercut or poor forming defects in thin plate precision welding and difficult control of the closing weld arc quality in titanium alloy laser welding.

[0007] Traditional laser welding of titanium alloy usually adopts laser swing to realize optimization of the welding width and the molten pool cross-section shape during welding, to stir the molten pool, to increase the pore escape condition in liquid metal, and to reduce the porosity. However, the porosity in titanium alloy laser welding is a mixed porosity of "technological porosity" and "metallurgical porosity", the swing laser has certain effect on the "metallurgical porosity", but has no obvious effect on the "technological porosity"; at the same time, although the swing laser increases the welding width, it also has no ideal effect on eliminating the undercut or poor forming defects caused by the gap change between the assembly pairs. Therefore, for the thin plate precision welding of titanium alloy, when the assembly condition is not ideal (the gap between the assembly pairs cannot reach 0.1 times the plate thickness), there is still no better method to consider the internal quality and surface forming quality.

[0008] In order to solve the problems of porosity, undercut or poor forming defects in thin plate precision welding and difficult control of the closing weld arc quality in titanium alloy laser welding, the application provides a titanium alloy laser welding defect control method with synergistic control of scanning and pulse, which is based on titanium alloy laser welding, adopts asymmetric "∞" waveform scanning in the welding direction, simultaneously applies high-speed scanning in the welding direction, adopts double pulse or sine pulse mode for laser power to realize energy control, and realizes effective inhibition of porosity and poor forming in the titanium alloy welding process, avoids the arc defects, realizes high-quality titanium alloy welding, covers pure titanium and titanium alloy for welding material, covers plate welding seam, longitudinal weld seam and circumferential weld seam for weld seam type, can not only eliminate the porosity and incomplete fusion defects in the weld seam, but also has good improvement on the poor forming of the weld seam edge, and can realize thin plate precision high-quality welding in titanium alloy laser welding.

[0009] The technical scheme of the application is as follows: An object of the application is to disclose a titanium alloy laser welding defect control method with synergistic control, which comprises the following specific steps: S1: performing surface cleaning on the to-be-welded area of the titanium alloy workpiece to ensure the cleanliness of the welding interface; S2: assembling and fixing the workpiece to be welded to ensure that the assembly gap meets the welding requirements, then clamping the workpiece on a motion device, and adjusting the focal point position of the laser beam to a predetermined position on or below the surface of the workpiece; S3: setting welding process parameters in the control unit, the parameters at least including scanning path parameters, laser power parameters and motion parameters; The scanning path parameter is configured as an asymmetric "∞" shape, which includes a front scanning area and a rear scanning area along the welding direction, and the width of the front scanning area is greater than that of the rear scanning area. The laser power parameter is configured as a double pulse mode or a sine pulse mode. S4: starting the welding program, the laser outputs pulsed laser, the laser head or the motion device drives the laser beam to scan along the set asymmetric "∞" shape path, when the laser beam is in the front scanning area, the laser outputs high energy, and when the laser beam is in the rear scanning area, the laser outputs low energy; the scanning of the laser beam, the output of the laser power and the movement of the workpiece are coordinated. S5: during the welding process, the inert gas is continuously applied to the welding area to keep the molten pool in an inert atmosphere to prevent welding defects. S6: the welding is completed.

[0010] Further, in step S1, the titanium alloy includes pure titanium or TC4 titanium alloy, and the welding type includes a plate joint, a longitudinal joint or a circumferential joint.

[0011] Further, in step S3, the secondary pulse frequency of the double pulse mode or the sine pulse mode is 10 to 50 times the overall frequency of the "∞" shape scanning.

[0012] Further, in step S3, in the normal welding stage, the double pulse mode is used, the peak power peak value is 1.5 to 2.5 times the plate thickness, and the base power base value is 0.6 to 1.0 times the plate thickness.

[0013] Further, in step S3, in the circumferential joint arc closing stage, in the sine pulse mode, the peak power peak value is 2 to 2.5 times the plate thickness, and the base power base value is 0.8 to 1.5 times the plate thickness.

[0014] Further, in step S3, the front scanning area and the rear scanning area are both elliptical, the major axis H1 of the front scanning area is 3 to 5 mm, and the ratio of the major axis to the minor axis H1 / H2 of the front scanning area is 1.4 to 1.6.

[0015] Further, in step S3, the ratio of the minor axis H2 of the front scanning area to the major axis H3 of the rear scanning area is 0.8 to 1.2, and the ratio of the major axis to the minor axis of the rear scanning area is 1.4 to 1.6.

[0016] Further, in step S3, the overall frequency of the asymmetric "∞" shaped scanning is 50 to 120 Hz.

[0017] Further, in step S6, in the collection phase of the girth weld welding, the mode of the laser power is switched to a sinusoidal pulse mode, and an energy attenuation strategy is used for the collection.

[0018] Another object of the present application is to disclose a cooperatively controlled titanium alloy laser welding device, applied to any of the above-mentioned cooperatively controlled titanium alloy laser welding defect control methods, comprising: The laser is used to generate laser; The swing laser welding gun is used to receive the laser and control the scanning path of the laser on the workpiece surface; The control unit is connected with the laser and the swing laser welding gun, and is used to control the scanning path and output power of the laser.

[0019] Compared with the prior art, the cooperatively controlled titanium alloy laser welding defect control method and device have the following advantages: By introducing the cooperative control of the asymmetric "∞" shaped scanning path and the laser power pulse in the welding process, the front section of the scanning path has a larger lateral swing width, the rear section has a smaller lateral swing width, the laser power outputs high power in the front section scanning, and outputs low power in the rear section scanning, the formation and solidification process of the molten pool are accurately controlled in stages, the weld pool temperature field and the liquid metal are more uniform, the undercut, depression and other forming defects caused by insufficient energy of the molten pool and uneven gap between the groups are avoided, the asymmetric stirring of the molten pool can also be realized, the grain can be refined, and the weld performance can be improved, the gas pores and forming defects are effectively inhibited without changing the basic principle of laser welding, the welding efficiency can be ensured while the weld quality is significantly improved, and the multiple technical problems of high porosity in traditional constant parameter laser welding, sensitivity to gap between groups, easy to produce undercut or forming defects, and defects in collection are solved.

[0020] The present application combines the large swing of the front scanning area to expand the molten pool, overcome the gap between the groups and ensure the melting depth and width, with the high-power pulse to provide sufficient energy and realize efficient melting, and combines the small swing of the rear scanning area to prolong the residence time of the solidification front of the molten pool, with the low-power pulse to maintain the molten pool from solidifying immediately and reduce the solidification speed, cooperates with the secondary pulse, can not only stir the molten pool and facilitate the escape of pores, but also increases the duration of the molten pool and reduces the solidification speed of the molten pool, realizes the functional partition control of "front strong melting to overcome the gap between the groups and rear extension solidification to promote the escape of pores", effectively solves the fundamental problem of the large surface tension of the liquid metal of the titanium alloy and the difficulty of pore escape, and obtains a high-quality weld with internal compactness, beautiful appearance and smooth arc, and significantly improves the mechanical properties and service reliability of the welded joint.

[0021] The present application realizes the smooth transition and decrease of the welding energy through the integrated control strategy of the scanning path design + pulse power cooperation + arc collection mode switching, innovatively introduces the sinusoidal pulse mode in the arc collection stage to provide fluctuating and progressive energy reduction, avoids the sudden drop of energy, and superimposes energy attenuation to realize the smooth transition from the welding state to complete solidification, realizes the smooth transition and decrease of the welding energy, constructs the seamless connection process from normal welding to complete solidification, and effectively avoids the arc pit, crack and other arc collection defects. BRIEF DESCRIPTION OF DRAWINGS

[0022] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the present application illustrated in the drawings and their descriptions are used to explain the present application and are not intended to limit the present application unduly. Figure 1 It is a common defect diagram of titanium alloy laser welding; Figure 2 It is a schematic diagram of the laser welding device structure of the present application; Figure 3 It is a schematic diagram of the laser scanning and pulse cooperative control mode of the present application; Figure 4 It is a welding metallographic diagram of 3mm thick TA2 in example 2; Figure 5 It is an arc collection effect diagram of 1.5mm thick TC4 welded joint in example 3.

[0023] Explanation of the reference signs: 1, control unit; 2, laser control circuit; 3, welding gun swing signal control circuit; 4, laser pulse signal; 5, laser; 6, optical fiber; 7, laser swing signal; 8, laser swing signal editor; 9, swing laser welding gun; 10, laser beam; 11, workpiece; 12, positioner; 13, motion system control circuit. DETAILED DESCRIPTION

[0024] In order to make the technical means and purposes of the present application easy to understand, the embodiments of the present application are described in detail below in combination with specific drawings.

[0025] It should be noted that all the terms indicating direction and position in the present application, such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "inner", "outer", "top", "low", "transverse", "longitudinal", "center", etc., are only used to explain the relative position relationship, connection condition, etc. between components in a certain state, and are only for the convenience of describing the present application, and thus cannot be understood as a limitation on the present application. In addition, the description of "first", "second", etc. in the present application is only for the purpose of description, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features.

[0026] In the description of the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral connection; can be mechanical connection; can be direct connection, or indirect connection through an intermediate medium; can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0027] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "illustrative embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0028] The present application discloses a kind of synergic control's titanium alloy laser welding defect control method, by asymmetric scanning path and the time-space cooperation of pulse laser power, stage regulation and control molten pool behavior, effectively inhibit pore, forming bad and arc defect, to improve the comprehensive quality of titanium alloy weld. The method comprises the following steps: S1: the surface of titanium alloy workpiece 11 is cleaned to ensure the cleanliness of the welding interface; Specific operation: select the titanium alloy material to be tested, such as TA2, TC4 and other materials to process the required shape of the workpiece 11. Before welding, the surface within 20mm range on both sides of the weld and its surface is pretreated. First, acid pickling can be used HF-HNO3 mixed acid or other solutions to remove the surface oxide film; then use hard grinding head, hard grinding head can be silicon carbide grinding wheel, mechanical polishing on the weld area, further remove the residual oxide, oil, moisture and other pollutants. After cleaning, wipe the surface with anhydrous ethanol or acetone, and dry in a clean environment for standby.

[0029] Titanium alloy is extremely easy to react with oxygen, nitrogen, hydrogen and other gases at high temperature, generating brittle compounds, which seriously affects the performance of the welded joint. Surface cleaning is the first key process to prevent defects such as pores and cracks, and its purpose is to completely remove all possible impurities that may introduce pollution and ensure high cleanliness of the welding interface. The workpiece 11 cleaned effectively can significantly reduce the incidence of defects such as pores and incomplete fusion caused by surface pollution.

[0030] S2: the workpiece 11 to be welded is assembled and fixed, ensuring that the gap between the assembly meets the welding requirements, then the workpiece 11 is clamped on the motion device, and the focal point position of the laser beam 10 is adjusted to the predetermined position on the surface of the workpiece 11 or below the surface; Specific operation: accurately assemble the pretreated workpiece 11, and for butt weld, ensure that the assembly gap is ≤0.15 times the plate thickness, for example, 3mm plate thickness time gap ≤0.45mm. Use spot welding or special fixture to fix the workpiece 11 to prevent displacement during welding. The assembled workpiece 11 is firmly clamped on the motion device 12. The focal point position of the laser beam 10 is accurately adjusted by laser focusing instrument or trial welding method, usually set at 1-2mm below the surface of the workpiece 11.

[0031] Accurate assembly and clamping ensure the stability of the welding process, avoiding defects such as undercut and incomplete fusion caused by excessive gap or workpiece 11 movement. The adjustment of the focal point position directly affects the distribution of laser energy in the material, and the defocusing amount of 1-2mm below the surface is beneficial to form stable deep penetration keyhole and obtain sufficient penetration depth. This step ensures the geometric accuracy and stability of energy input in the welding process, which helps to achieve high quality and repeatable welding.

[0032] S3: set the welding process parameters in the control unit 1, including at least: scanning path parameters, laser power parameters and motion parameters; Among them, the scanning path parameter sets the scanning path of the laser beam 10 on the surface of the workpiece 11 as an asymmetric "∞" shape, which includes a front scanning area and a rear scanning area along the welding direction, and the transverse swing width of the front scanning area is greater than that of the rear scanning area. Preferably, the front scanning area and the rear scanning area are elliptical in shape. Alternatively, the front scanning area and the rear scanning area can be simply referred to as the "front ellipse" and the "rear ellipse," respectively.

[0033] Employing an asymmetric "∞" waveform, the "front ellipse" has a larger lateral swing width. Combined with higher laser power, this reduces the requirements for assembly, forming a stable molten pool cross-section and ensuring the depth and width of the molten pool. Simultaneously, it makes the weld pool more uniform, avoiding defects such as undercut and depressions caused by insufficient molten pool energy and uneven assembly gaps. The "back ellipse" has lower laser power, combined with smaller lateral swing and larger longitudinal swing, increasing the duration of the molten pool and reducing the solidification rate. Furthermore, the secondary pulse increases molten pool stirring, increasing the time for porosity to escape and enhancing the porosity boundary conditions, significantly reducing porosity. In sinusoidal pulse mode, the secondary pulse not only achieves molten pool stirring but also achieves more precise energy distribution across the molten pool width compared to dual-pulse coordination, resulting in a smoother arc termination.

[0034] The laser output power is set to pulse mode in the laser power parameters. Specific operation: Input the following key parameters into control unit 1, such as a PLC or dedicated welding control unit 1: Scanning path parameters: The scanning trajectory of laser beam 10 is set to an asymmetrical "∞" shape. The front and rear scanning areas are elliptical, and the path is formed by the connection of the "front ellipse" and the "rear ellipse" at the origin. Along the welding direction, the lateral swing width H1 of the "front ellipse" is greater than the lateral swing width H4 of the "rear ellipse". The major axis of the "front ellipse" is H1, and the minor axis is H2. The major axis of the "rear ellipse" is H3, and the minor axis is H4. Typical parameters are: H1 = 3~5mm, H1 / H2 = 1.4~1.6, H3 / H4 = 1.4~1.6, H2 / H3 = 0.8~1.2, and the overall scanning frequency f = 50~120Hz.

[0035] Laser power parameters: like Figure 3 As shown, after completing the scanning waveform parameter settings, the laser power is then set. During normal welding, a dual-pulse mode is usually used, with the peak stage being Pp and the base stage being Pb. The peak power of the Pp stage is Ppp = (1.5~2.5) × plate thickness mmKW, and Ppb = (0.1~0.3) × plate thickness mmKW. The peak power of the Pb stage is Pbp = (0.6~1.0) × plate thickness mmKW, and Pbb = (0.1~0.3) × plate thickness mmKW.

[0036] When the arc of the circumferential weld is made, in order to achieve more accurate energy control, a sinusoidal pulse mode can be used, with a peak phase Pp and a base phase Pb; the power peak Ppp in the Pp phase is (2-2.5) x plate thickness mm KW, and the Ppb is (0.1-0.3) x plate thickness mm KW; the peak Pbp in the Pb phase is (0.8-1.5) x plate thickness mm KW, and the Ppb is (0.1-0.3) x plate thickness mm KW.

[0037] In the process of high-speed swinging and pulse cooperation, the peak time Tp is the time consumed by the laser scanning "front ellipse", the base time Tb is the time consumed by the laser scanning "rear ellipse", the overall scanning frequency is f = 1 / (Tb+Tp) = 50-120 Hz, and the secondary pulse frequency (corresponding to the period T1) of the peak and base phases of the double pulse and the sinusoidal pulse is f1, which is 10-50 times of the overall scanning frequency f, i.e. f1 = (10-50) x f. The secondary pulse refers to the high-frequency and periodic pulsation of the laser power itself within one complete asymmetric "∞" shaped scanning cycle of the laser beam. In the double pulse mode, the high-frequency change is manifested as the rapid switching of the power between the "peak value in the peak phase Ppp" and the "base value in the peak phase Ppb", and between the "peak value in the base phase Pbp" and the "base value in the base phase Pbb". In the sinusoidal pulse mode, the power continuously changes in a sinusoidal waveform between the peak value and the base value. "Primary" refers to the scanning cycle: the time taken for the laser beam to scan a complete "∞" shape (including "front ellipse" and "rear ellipse"), which is called a scanning cycle (T = Tb+Tp). The frequency of this cycle is f = 1 / T, ranging from 50 to 120 Hz. "Secondary" refers to the power pulsation: within this scanning cycle (primary cycle), the laser power does not simply switch from high (peak Pp) to low (base Pb) once. Instead, within the "peak phase" and "base phase", the power itself also changes periodically at a higher frequency.

[0038] Motion parameters: set the relative motion speed of the workpiece 11 or the laser head, usually 800-1500 mm / min.

[0039] By pre-setting the parameters, the geometric characteristics of the scanning path are accurately associated with the time modulation of the laser power, providing instruction basis for subsequent cooperative control.

[0040] Preferably, the scanning direction of the "front ellipse" is counterclockwise, and the scanning direction of the "rear ellipse" is clockwise.

[0041] S4: start the welding program, the laser 5 outputs pulsed laser, the laser head or motion device drives the laser beam 10 to scan along the set asymmetric "∞" shaped path, in the period when the laser beam 10 is in the front scanning area, the laser 5 outputs high energy, in the period when the laser beam 10 is in the rear scanning area, the laser 5 outputs low energy; the scanning of the laser beam 10, the output of the laser power and the movement of the workpiece 11 are cooperated with each other; Specific operation: after starting the welding program, the control unit 1 synchronously sends out the scanning control signal and the power control signal. The galvanometer mirror of the swing laser welding gun 9 is driven by the scanning signal to make the laser beam 10 scan along the "∞" shaped path at high speed. At the same time, the laser 5 outputs the set peak power when the laser beam 10 scans the front ellipse and outputs the set base value power when the laser beam 10 scans the rear ellipse according to the power signal. The workpiece 11 is moved at a constant speed by the shifter 12.

[0042] The "high energy + large swing" of the front part provides sufficient heat input, strongly melts the base material, expands the molten pool, effectively overcomes the gap between the groups, guarantees the penetration and the width of the molten pool, solves the problem of poor forming; the "low energy + small swing" of the rear part reduces the heat input, prolongs the solidification time of the molten pool, creates favorable conditions for the escape of pores, at the same time, the small swing has a "compaction" effect on the tail of the molten pool, improves the appearance of the weld. Through the function partition control, the porosity inside the weld is significantly reduced, the density of the weld is improved, at the same time, the weld with uniform and beautiful appearance is obtained, and the problem that the porosity and the forming are difficult to be considered in the welding of titanium alloy is solved.

[0043] Preferably, in the double pulse mode, the power peak value of the peak power is 1.5 to 2.5 times the plate thickness, and the power base value of the base power is 0.6 to 1.0 times the plate thickness.

[0044] The peak power Pp is the main energy source in the welding process, which is used to realize the rapid melting of the base material and form a stable deep molten pool. The peak power is set to 1.5 to 2.5 times the plate thickness, unit: kW, which provides sufficient energy density for the laser beam 10, guarantees the minimum effective melting, ensures that the specified plate thickness of the material can be completely penetrated under normal process parameters, prevents excessive evaporation of the material caused by excessive energy input, and produces spatter or unstable molten pool. At the same time, too high power may cause the heat affected zone to be too large, which affects the joint performance. It is ensured that stable and controllable penetration and width can be obtained under different plate thicknesses, effectively overcoming the defects such as incomplete fusion and undercut caused by slightly large or uneven gap between groups, guaranteeing the geometric integrity and carrying capacity of the weld.

[0045] The base power Pb is output in the "post-ellipse" scanning phase, which is not for main melting, but for maintaining the molten pool in liquid or semi-liquid state, and reducing the cooling rate of the molten pool. The base power is set to 0.6 to 1.0 times of the plate thickness, in units of kW, to provide a moderate and continuous heat input. The base power of 0.6 times of the plate thickness is sufficient to offset part of the heat dissipation, effectively prolonging the solidification time of the molten pool and creating a sufficient time window for the bubbles to float out of the viscous liquid metal. The upper limit of 1.0 times of the plate thickness prevents the base power from being too high, avoiding excessive expansion, collapse or new pores of the molten pool caused by continuous high energy input in the "post-ellipse" phase. The moderate base power combined with the small swing of the "post-ellipse" plays a role of "compaction" and "smoothing" for the tail of the molten pool, which helps to improve the surface forming of the weld.

[0046] In the "pre-ellipse" phase, high power + large swing realizes strong melting, solving the problems of penetration and forming; in the "post-ellipse" phase, medium power + small swing realizes delayed solidification and pore discharge, and this coordinated control strategy makes the utilization of laser energy more efficient and accurate, solving the contradiction between penetration and pore-free in titanium alloy welding.

[0047] S5: During the welding process, inert gas protection is continuously applied to the welding area, so that the molten pool is in an inert atmosphere, preventing the occurrence of welding defects; preferably, the inert gas is argon.

[0048] Specific operation: From the beginning of arc striking to the end of arc stopping, high-purity argon with a purity of ≥99.99% is continuously delivered to the welding area. A drag cover type or side blowing type protection device is usually used to ensure that the molten pool, high-temperature weld and heat-affected zone are always in an argon protective atmosphere during the entire cooling process.

[0049] Titanium alloy starts to absorb gas above 400℃, and reacts with O, N, H and other elements in the air to form brittle phases. Inert gas protection is a necessary measure to prevent weld oxidation, nitriding and hydrogen embrittlement. Effective gas protection can significantly improve the plasticity and toughness of the weld, avoid brittle cracks and mechanical property degradation caused by pollution, and ensure the quality of the weld.

[0050] Step S6: When the girth weld welding is carried out to the end point, switch the control mode of the laser power, adopt the pulse mode of the sine waveform and superimpose the energy attenuation strategy, realize the smooth transition and decrease of the welding energy, complete the defect-free arc stopping, and the welding is finished; Preferably, in the sinusoidal pulse mode, the laser power periodically varies between the peak phase and the base phase in a sinusoidal waveform, and in the arc collection process, the power peak of the peak phase and the power base of the base phase are both linearly attenuated according to a preset attenuation rate. By letting the peak power and the base power linearly attenuate at the same time according to the preset rate, the overall trend of energy reduction is ensured to be smooth and continuous, avoiding sudden changes in energy, reducing the cooling speed and temperature gradient of the molten pool, effectively relieving the concentration of thermal stress, fundamentally inhibiting the generation of arc pits and cracks caused by thermal shock, and improving the structural integrity of the joint.

[0051] Specific operation: when the welding program detects that the end point is about to be reached, especially the closed part of the circular weld, the control mode is automatically switched. The control of the laser power is switched from the double pulse mode to the sinusoidal pulse mode, that is, the laser power periodically varies between the set peak and base in a sinusoidal waveform. At the same time, the energy attenuation program is started, so that the peak power and the base power are both linearly attenuated according to a preset attenuation rate, such as 5W / ms, until the energy is reduced to zero and the welding process is completed.

[0052] Traditional linear or stepwise attenuation is easy to cause the energy of the molten pool to drop suddenly, resulting in arc pits, shrinkage holes or cracks. The sinusoidal pulse mode provides a fluctuating and gradual energy drop, avoiding sudden energy drops, while the continuous pulses can still produce stirring effects on the molten pool in the arc collection area, promoting gas discharge and stress release. This arc collection strategy realizes the smooth transition of welding energy, effectively prevents arc pit, crack and other arc collection defects, and obtains a smooth, dense and defect-free arc collection end, which is especially suitable for automatic welding of circular welds with high quality requirements for arc collection, and significantly improves the overall quality and reliability of the welded joint.

[0053] Preferably, in step S6, the secondary pulse frequency of the sinusoidal pulse mode is 10 to 50 times the overall frequency of the "∞" shape scanning.

[0054] The "∞" shape scanning frequency f determines the time period of the ellipse + ellipse before the laser beam 10 completes a complete scanning cycle near the arc collection point. Setting the secondary pulse frequency f1 of the sinusoidal pulse to 10 to 50 times the scanning frequency, i.e. f1=(10-50)×f, means that during the laser beam 10 completes a complete "∞" shape scanning path, the laser power will complete 10 to 50 sinusoidal waveform periodic changes between the peak and the base. The higher the secondary pulse frequency, the more "disturbances" to the molten pool per unit time, and the stronger the dynamic stirring effect. The range of 10 to 50 times ensures that there are enough energy fluctuations to continuously stir the molten pool in each scanning cycle.

[0055] The setting ensures that the period of energy modulation is strictly aligned with the period of spatial scanning. Regardless of the position of the laser beam 10 in the scanning path, the corresponding power modulation is continuous, stable and predictable, avoiding energy output disorder or control out of step due to frequency mismatch, ensuring the stability and repeatability of the process.

[0056] The method has the following advantages: 1. Asymmetric "∞" waveform is adopted, the "front ellipse" has a larger lateral swing width, which can reduce the requirements for the group pair, form a stable molten pool section, ensure the depth and width of the molten pool, and the scanning waveform can homogenize the molten pool, so that the weld pool temperature field and the liquid metal are more uniform, and the undercut, depression and other forming defects caused by insufficient energy of the molten pool and uneven gap between the group pairs are avoided; 2. The "rear ellipse" has a lower laser power, a smaller lateral swing and a larger longitudinal swing, and is coordinated with the second pulse, which can not only stir the molten pool and facilitate the escape of pores, but also increase the duration of the molten pool, reduce the solidification speed of the molten pool, increase the pore escape time, increase the pore escape boundary conditions, and greatly reduce the porosity; 3. During the arc closing process of the closed loop weld, the sine pulse mode is adopted, and the second pulse not only realizes the stirring of the molten pool, but also realizes the more accurate energy distribution of the energy in the molten pool width compared with the double pulse, so that a smoother arc closing can be realized; 4. The asymmetric "∞" waveform can not only reduce the forming defects and porosity, but also realize the asymmetric stirring of the molten pool, refine the grains and improve the performance of the weld.

[0057] As shown in Figure 2 The application discloses a titanium alloy laser welding device with cooperative control, which is applied to the titanium alloy laser welding defect control method with cooperative control and comprises the following components. A laser 5 is used for generating laser; A swing laser welding gun 9 is used for receiving the laser and controlling the scanning path of the laser on the surface of a workpiece 11; A control unit 1 is connected with the laser 5 and the swing laser welding gun 9 and is used for controlling the scanning path and the output power of the laser.

[0058] The disclosed synergic control titanium alloy laser welding device realizes automation and intellectualization of the welding process by organically integrating the laser 5, the swing laser welding gun 9 and the control unit 1, integrating the complex control logic in the control unit 1 and accurately coordinating the actions of the two by the control unit 1. The operator only needs to input corresponding process parameters such as scanning frequency, pulse parameters and welding speed in the control unit 1, and the device can automatically execute the entire synergic control process, thereby ensuring the stability and repeatability of the welding quality. Meanwhile, by adjusting the parameters, the device can be suitable for titanium alloy materials of different thicknesses and different types and various joint forms such as plate splicing, longitudinal seam and girth seam, has wide applicability and good process adaptability, can realize any synergic control titanium alloy laser welding defect control method and fundamentally optimizes the welding metallurgical process of titanium alloy and realizes comprehensive and effective control of blowhole, poor forming and arc receiving defects.

[0059] Specifically, the control unit 1 is configured to: generate a scanning control signal for driving the swing laser welding gun 9 to form an asymmetric “∞” shaped scanning path; generate a power control signal for controlling the laser 5 to output double pulses or sinusoidal pulses; wherein the power control signal is synchronized with the scanning control signal in time to realize synergic control of the scanning path and the laser power.

[0060] The scanning control signal generated by the control unit 1 accurately defines the motion trajectory of the laser beam 10 on the surface of the workpiece 11, i.e. the asymmetric “∞” shaped path, which divides the welding process into two stages of different functions, i.e. “front ellipse” and “rear ellipse” in space. Meanwhile, the power control signal generated by the control unit 1 is synchronized with the scanning path in time, so that the high-power peak value is accurately corresponding to the “front ellipse” scanning period and the low-power base value is accurately corresponding to the “rear ellipse” scanning period. Integrating the two key functions of scanning path generation and laser power modulation in the same control unit 1 and realizing the accurate synchronization of the two by the built-in algorithm avoids using multiple independent control units 1 or external synchronization devices, which simplifies the system structure, reduces the equipment cost and failure rate. The operator only needs to input or call the preset process program on the user interface of the control unit 1 to start the entire synergic control process by one key, which greatly reduces the operation difficulty and improves the production efficiency and process repeatability.

[0061] The control unit 1 of the application can be an industrial computer, a single-chip microcomputer, a PC, a PLC or a DSP, mainly for setting laser power, matching welding parameters and setting welding motion device parameters. The laser 5 is a fiber laser, the swing laser welding gun 9 is a laser welding head capable of two-axis swing and the laser swing signal editor 8 is used for welding head control.

[0062] In operation, the laser power, swing parameters, welding speed and other parameters are input into the control unit 1, the control unit 1 connects the laser 5 through the laser control line 2, connects the laser swing signal editor 8 through the welding gun swing signal control line 3, and the control unit 1 generates the laser pulse signal 4, the laser swing signal 7, and the motion control signal; the laser pulse signal 4 is input into the laser 5 through the laser control line 2, the laser 5 inputs the generated pulse laser into the swing laser welding gun 9 through the optical fiber 6, and the laser beam 10 scans the workpiece 11; the laser swing signal editor 8 compiles the laser swing signal 7 to generate the required laser swing waveform for driving the two-axis swing of the swing laser welding gun 9; at the same time, the motion control signal realizes the movement of the workpiece 11, which can be the movement of the welding gun head or the cooperation of both, and the three can realize the welding effect of the present application after cooperation.

[0063] Specifically, it also includes: The motion platform is used to carry and move the workpiece 11 or the swing laser welding gun 9. The gas protection device is used to provide a protective gas atmosphere in the welding area.

[0064] The motion platform is used to carry the workpiece 11 to be welded and accurately move according to the predetermined welding track, such as a straight line, a ring, etc. In some embodiments, the motion platform can also be used to move the swing laser welding gun 9, while the workpiece 11 remains stationary, and its movement is accurately controlled by the control unit 1 according to the preset welding path and speed, which can maintain consistent process parameters throughout the entire weld length, thereby obtaining a uniform and high-quality continuous weld.

[0065] The gas protection device is used to continuously deliver inert protective gas, such as argon, to the welding pool area during the welding process, forming a local, air-insulating protective atmosphere. The device usually includes a gas source, a flowmeter, a solenoid valve and a nozzle, and its work is started by the control unit 1 at the beginning of welding and stopped after the end of welding. Because titanium alloy has extremely strong chemical activity at high temperatures, it is extremely easy to react with oxygen, nitrogen, hydrogen and other elements in the air, resulting in the embrittlement of the weld, the generation of pores and cracks. The gas protection device provides a pure inert gas atmosphere, effectively isolates the air, prevents oxidation and pollution of the high-temperature molten pool and heat-affected zone, and helps to ensure the mechanical properties, corrosion resistance and internal quality of the titanium alloy weld.

[0066] The moving speed of the motion platform and the start-stop of the gas protection device can be coordinated and controlled by the same control unit 1. For example, the control unit 1 sends a moving instruction to the motion platform and opens the electromagnetic valve of the gas protection device at the same time when starting the laser scanning and power modulation, so as to realize the full automation and high integration of the welding process, simplify the operation process, reduce human errors, ensure the stability and repeatability of the whole welding process, and significantly improve the intelligent level and production efficiency of the system.

[0067] Preferably, the motion platform can be a positioner 12, and the motion platform is connected with the control unit 1 through a motion system control line 13. Embodiment

[0068] The specific implementation process of the present application is as follows, taking welding of a 3mm thick TA2 ring joint as an example: S1: The workpiece 11 is pickled, and then the area near the weld joint within 20mm is cleaned by a hard grinding head; S2: The workpiece 11 is assembled and spot welded, and the assembly gap is ≤0.15 times the plate thickness; S3: The workpiece 11 is installed on the positioner 12, and the position of the beam focal point is adjusted to be about 1-2mm below the surface of the workpiece 11; S4: Start welding, the laser 5 outputs pulsed laser, and the laser welding head scans according to the asymmetric “∞” waveform, the “front ellipse” time domain is the laser peak value, and the “rear ellipse” time domain is the laser base value, which can realize effective control welding of defects in cooperation with the motion system; the swing “∞” waveform parameters are input in the control unit 1: the major axis H1 of the “front ellipse” is 4mm; H1 / H2=1.5; H2 / H3=1; H3 / H4=1.5; the overall scanning frequency of the “∞” is f=100Hz; the laser parameters are input in the control unit 1: Ppp=6KW, Ppb=0.3KW; Pbp=1.8KW, Pbb=0.3KW; f1=1000Hz; the welding speed V is input in the control unit 1: 1000-1500mm / min; S5: From the start of welding to the end of welding, the welding position is protected by argon, so that the weld joint area, heat affected zone and the like should be in an argon atmosphere; S6: After reaching the welding end point, the arc is collected by using a sine pulse in cooperation with attenuation, and the welding is completed. Embodiment

[0069] TA2 butt weld with 3mm, "pre-ellipse" long axis H1=4mm; H1 / H2=1.5; H2 / H3=1; H3 / H4=1.5; "∞" overall scanning frequency f=100Hz; Ppp=6KW, Ppb=0.3KW; Pbp=1.8KW, Pbb=0.3KW; f1=1000Hz. Welding speed V=1000mm / min; the weld cross section after welding is shown in Figure 4 Fig. 1, and after welding, no defects such as incomplete fusion and porosity are found according to NB / T 47013 radiographic testing Class I. Embodiment

[0070] TC4 ring weld with 1.5mm, in order to avoid the arc defects, the present scheme is adopted, "pre-ellipse" long axis H1=3mm; H1 / H2=1.5; H2 / H3=1; H3 / H4=1.5; welding speed V=800mm / min; "∞" overall scanning frequency f=50Hz; Ppp=3KW, Ppb=0.15KW; Pbp=1.5KW, Pbb=0.15KW; f1=500Hz; the weld after welding is shown in Figure 5 Fig. 2, it can be seen that the arc transition is smooth, uniform and beautiful, and there is no arc defect; after welding, the penetration is Class I according to NB / T 47013.

[0071] The above is only the preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for synergistically controlling defects in laser welding of titanium alloys, characterized by, The method comprises the following specific steps: S1: surface cleaning of the titanium alloy workpiece (11) to be welded to ensure the cleanliness of the welding interface; S2: the workpiece (11) to be welded is assembled and fixed to ensure that the assembly gap meets the welding requirements, and then the workpiece (11) is clamped on the motion device, and the focal point position of the laser beam (10) is adjusted to a predetermined position on the surface of the workpiece (11) or below the surface; S3: set the welding process parameters in the control unit (1), the parameters at least including: scanning path parameters, laser power parameters and motion parameters; Wherein, the scanning path parameters set the scanning path of the laser beam (10) on the surface of the workpiece (11) as an asymmetric "∞" shape, which includes a front scanning area and a rear scanning area along the welding direction, the transverse swing width of the front scanning area is greater than that of the rear scanning area; The laser power parameter sets the laser output power to adopt a double pulse mode or a sinusoidal pulse mode; S4: start the welding program, the laser (5) outputs pulsed laser, the laser head or the motion device drives the laser beam (10) to scan along the set asymmetric "∞" shape path, when the laser beam (10) is in the front scanning area, the laser (5) outputs high energy, when the laser beam (10) is in the rear scanning area, the laser (5) outputs low energy; the scanning of the laser beam (10), the output of the laser power and the motion of the workpiece (11) are cooperated; S5: during the welding process, inert gas protection is continuously applied to the welding area to make the molten pool in an inert atmosphere to prevent the occurrence of welding defects; S6: the welding is completed.

2. The synergistically controlled titanium alloy laser welding defect control method of claim 1, wherein, In step S1, the titanium alloy includes pure titanium or TC4 titanium alloy, and the welding type includes plate joint weld, longitudinal weld or circumferential weld.

3. The synergistically controlled titanium alloy laser welding defect control method of claim 1 or 2, wherein, In step S3, the frequency of the secondary pulse of the double pulse mode or the sinusoidal pulse mode is 10 to 50 times of the overall frequency of the "∞" shape scanning.

4. The synergistically controlled titanium alloy laser welding defect control method of claim 1, wherein, In step S3, in the normal welding stage, the double pulse mode is adopted, the power peak value of the peak power is 1.5 to 2.5 times of the plate thickness, and the power base value of the base power is 0.6 to 1.0 times of the plate thickness.

5. The synergistically controlled titanium alloy laser welding defect control method of claim 1, wherein, In step S3, in the ring weld arc closing stage, in the sinusoidal pulse mode, the power peak value of the peak power is 2 to 2.5 times of the plate thickness, and the power base value of the base power is 0.8 to 1.5 times of the plate thickness.

6. The synergistically controlled titanium alloy laser welding defect control method of claim 1, wherein, In step S3, the front scanning area and the rear scanning area are both elliptical, the major axis H1 of the front scanning area is 3 to 5 mm, and the ratio of the major axis to the minor axis H1 / H2 of the front scanning area is 1.4 to 1.

6.

7. The synergistically controlled titanium alloy laser welding defect control method of claim 6, wherein, In step S3, the ratio of the minor axis H2 of the front scanning area to the major axis H3 of the rear scanning area is 0.8 to 1.2, and the ratio of the major axis to the minor axis of the rear scanning area is 1.4 to 1.

6.

8. The synergistically controlled titanium alloy laser welding defect control method of claim 1, wherein, In step S3, the overall frequency of the asymmetric "∞" shape scanning is 50 to 120 Hz.

9. The synergistically controlled titanium alloy laser welding defect control method of claim 1, wherein, In step S6, the mode of the laser power is switched to a sinusoidal pulse mode in the arc collection phase of the girth weld welding, and an energy attenuation strategy is matched.

10. A synergistically controlled titanium alloy laser welding apparatus, characterized by, The titanium alloy laser welding defect control method applied to the synergic control of any one of claims 1-9 comprises: The laser (5) is used to generate laser; The swing laser welding gun (9) is used to receive the laser and control the scanning path of the laser on the surface of the workpiece (11); The control unit (1) is connected with the laser (5) and the swing laser welding gun (9), and is used to control the scanning path and output power of the laser.

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