A composite TIG welding method

Abstract

A composite TIG welding method, in which vibration wire feeding is used, and the welding wire is swung in a direction perpendicular to the weld, and the welding current is coupled with the oscillation frequency of the welding wire. When the welding wire swings to the maximum distance away from the center of the weld, the welding current reaches a peak value, and when the welding wire swings to the center of the weld, the welding current reaches a base value. This method can effectively improve the penetration ability and cladding effect in the TIG welding process, optimize the melt distribution in the weld, improve the welding quality and efficiency, and facilitate the realization of automated welding.

Description

Technical Field

[0001] The invention belongs to the field of welding, and in particular relates to a composite TIG vertical welding method. Background Art

[0002] During the construction of LNG cryogenic storage tanks, a large amount of internal tank welding work is required. 3 Taking the cryogenic storage tank as an example, the length of the vertical weld of the inner tank wall reaches about 900 meters. At present, the inner tank welding is mainly completed by manual arc welding, which has a large workload. Manual welding is easily affected by factors such as operating experience and techniques. When welding thick plates, problems such as insufficient cladding are prone to occur, resulting in poor welding quality. Automatic or semi-automatic inert gas welding (TIG welding) can effectively reduce labor losses during the welding process, but TIG welding is still prone to poor weld quality due to unreasonable distribution of the welding wire after melting during the vertical welding of thick plates. Therefore, a TIG welding method that improves penetration and cladding is provided, which has high practical value for improving the efficiency of LNG construction. Summary of the invention

[0003] The object of the present invention is to provide a composite TIG welding method to improve vertical welding penetration and cladding effect.

[0004] According to an embodiment of the present invention, a composite TIG welding method is provided, wherein during the welding process, the welding wire is fed in a vibration feeding manner, and the welding wire is swung in a direction perpendicular to the weld; the welding current is coupled to the frequency of the welding wire swinging, and the welding current reaches a peak value when the welding wire swings to the maximum distance away from the center of the weld, and the current reaches a base value when the welding wire swings to the center position of the weld.

[0005] By controlling the coupling of the wire oscillation frequency and the current frequency, the penetration ability and cladding effect during TIG welding can be effectively improved, the distribution of the melt in the weld can be optimized, and the welding quality and efficiency can be improved.

[0006] Furthermore, in some embodiments, the welding current is a square wave current. When welding magnetic steel plates, the square wave welding current can effectively suppress magnetic blow and improve welding quality.

[0007] Furthermore, in some embodiments, during the welding wire swinging process, the wire feeding speed when the welding current is at a peak value is greater than the wire feeding speed when the welding current is at a base value. The wire feeding speed is matched with the current change frequency to achieve the maximum whipping effect of the welding wire and improve the welding cladding efficiency.

[0008] Furthermore, in some embodiments, the positive polarity waveform accounts for no less than 85% of the welding current. Increasing the proportion of the positive polarity waveform in the working time can increase the welding penetration and the amount of base material melted, form a narrow and deep welding interface, and balance the penetration capacity and cladding efficiency.

[0009] Furthermore, in some embodiments, the composite TIG welding method is TIG vertical welding, which is a welding process widely used in large LNG storage tanks.

[0010] Furthermore, in some embodiments, the welding method includes a base welding step, a welding filling step and a welding capping step.

[0011] Furthermore, in some embodiments, in the base welding step, the welding current peak value is 150-180A, the base value is 80-90A, and the vibration wire feeding frequency is 3-5Hz; in the welding filling step, the welding current peak value is 200-260A, the base value is 100-130A, and the vibration wire feeding frequency is 4-8Hz; in the welding cover step, the welding current peak value is 240-280A, the base value is 120-140A, and the vibration wire feeding frequency is 4-8Hz.

[0012] Furthermore, in some embodiments, the tungsten pole tip used for welding is ground into a frustum shape, the frustum shape has an inclination angle of 30°-50°, and is ground longitudinally. The ground tungsten pole structure facilitates front end balling, and realizes rapid arc stabilization after AC arc starting.

[0013] Furthermore, in some embodiments, the shielding gas used in welding is argon gas with a purity of not less than 99.9%.

[0014] Furthermore, in some embodiments, during the welding process, a visual inspection system is used to monitor the weld pool state, and the weld image features are extracted through an image processing algorithm to control the weld quality. The visual inspection system can identify and locate areas that may not meet the welding quality requirements, which facilitates the subsequent direct and rapid grinding of the weld excess height. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the installation position of welding equipment in one embodiment;

[0016] Figure 2 This is a schematic diagram of a groove structure in one embodiment;

[0017] Figure 3a A pair of proportional metallographic photographs of the weld structure;

[0018] Figure 3b This is a metallographic photograph of the weld structure in one embodiment;

[0019] Figure 4 A schematic diagram of welding wire swing in one embodiment;

[0020] Figure 5a A graph of current-wire swing speed-wire feeding speed in one embodiment;

[0021] Figure 5b A graph of current-wire swing speed-wire feeding speed in another embodiment;

[0022] Figure 6a This is a photo of the weld surface morphology in another comparative example;

[0023] Figure 6b A photo of the weld surface morphology in one embodiment;

[0024] Figure 7a A photo of a weld with penetration of the back side of the primer in one embodiment;

[0025] Figure 7b A photo of a weld seam filled and formed in an embodiment;

[0026] Figure 7c A photo of a weld seam formed by a cover surface in an embodiment;

[0027] Figure 8a A scanning image of a weld surface in an embodiment;

[0028] Figure 8b Extraction of weld excess height contour in one embodiment;

[0029] Figure 8c It is a three-point curve drawn according to the weld reinforcement contour in one embodiment.

[0030] The purpose of the above drawings is to explain the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, but it is not intended to limit the present invention. For the sake of simplicity, the above drawings only schematically show the structure related to the technical features of the present invention, and do not strictly show the completed structure and all details according to the actual proportion. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0032] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The phrase appearing in various locations in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments herein may be combined with other embodiments without causing structural conflicts.

[0033] In the description of this article, the terms indicating the orientation or position relationship such as "upper", "lower", "left", "right", "lateral", "longitudinal", "height", "length", "width", etc. are intended to accurately describe the embodiments and simplify the description, but are not intended to limit the parts or structures involved to have a specific orientation, be installed or operate in a specific orientation, and should not be understood as limiting the embodiments of this article. In the description of this article, the meaning of "multiple" is at least two.

[0034] The inner tank welding of LNG cryogenic storage tank is a key process in the construction of LNG storage tank. In many engineering practices, the inner tank steel wall is made of 9% Ni steel, which is a magnetic material. It is easy to cause magnetic blow during arc welding, resulting in uneven fusion of molten pool droplets, resulting in defects such as incomplete fusion or incomplete penetration. The effect of automatic welding is poor. Therefore, the inner tank welding is currently highly dependent on manual arc welding. 2 Take the cryogenic storage tank as an example. The total length of the vertical welding seam of the inner tank wall can reach 900m. The overall welding workload is large. The large amount of smoke generated by manual welding leads to a bad working environment. At the same time, the welding quality is highly dependent on the operator's experience and the welding quality is unstable. A lot of root cleaning and grinding are required during the vertical welding process of arc welding. Especially for thick plate welding, the utilization rate of manual welding electrodes is lower, and the consumption of welding materials is large. In order to meet the requirements of weld excess height, a lot of grinding work is also required on the weld, which is time-consuming, labor-intensive and costly.

[0035] In order to solve the above problems, an embodiment of the present invention provides a composite TIG vertical welding method, which can achieve high-quality automatic welding in scenarios such as 9Ni steel, and improve the automatic welding penetration effect and cladding ability.

[0036] like Figure 1 As shown, the method can form a weld 1 between two plates to be welded (i.e., parent materials 2) by using an automatic welding device 3. Figure 4 During the welding process, the wire feeding mechanism 5 of the automatic welding device 3 adopts a vibration wire feeding method, so that the welding wire 8 vibrates back and forth in the direction of arrow 9 while the wire is being fed out; at the same time, the wire feeding mechanism 5 drives the welding wire 8 to swing in a direction perpendicular to the weld 1 (as shown by arrow 7), the center position of the weld pool 6 is B, and the maximum swing positions of the wire feeding mechanism 5 on both sides of B are A and C respectively, and the swing frequency of the wire feeding mechanism 5 is coupled with the welding current frequency. Combined with the welding current-wire swing speed-wire feeding speed spectrum Figure 5a, the vertical axis in the figure represents the current size / wire swing speed / wire feeding speed. During the swinging process, the wire feeding mechanism 5 briefly stops at positions A and C respectively (the speed is 0), and the welding current reaches the peak value; when the wire feeding mechanism 5 swings between A and C and passes through position B, the welding current reaches the base value. By coupling the swing frequency and the current frequency, the melt distribution in the molten pool 6 can be improved, so that the molten welding wire can be more effectively filled in the molten pool 6, thereby improving the welding quality and welding efficiency. In a preferred embodiment, the welding current uses a square wave current to better suppress magnetic blow. In other embodiments, for example, when welding non-ferromagnetic materials, welding currents of other waveforms such as a sine waveform can also be used.

[0037] In a preferred embodiment, when the welding current reaches its peak value at positions A and C, the wire delivery speed of the wire feeding mechanism 5 also reaches its peak value; when the wire feeding mechanism 5 swings and passes through position B and the welding current reaches its base value, the wire delivery speed of the wire feeding mechanism 5 also reaches a low value. By coupling the change of the wire feeding speed of the wire feeding mechanism 5 with the swing frequency and the current frequency, the melting of the welding wire can be promoted, the maximum swing effect can be achieved, and the welding cladding efficiency can be improved. The spectrum of the swing speed, welding current, and wire feeding speed is shown in FIG. Figure 5a As shown, it can be seen that when the swing speed is 0, that is, when the wire feeding mechanism 5 is located at the A / C position, the current reaches a peak value and the wire feeding speed is the highest; when the swing speed is the highest, that is, when the wire feeding mechanism 5 swings between the A and C positions, the current reaches a base value and the wire feeding speed is the lowest.

[0038] In a preferred embodiment, the proportion of the positive polarity waveform in the welding current is not less than 85%, so as to increase the welding penetration and improve the melting amount of the base material, so as to help form a narrow and deep welding interface.

[0039] In a preferred embodiment, the welding process of composite TIG vertical welding of 9Ni steel plate is as follows:

[0040] First, if Figure 2 As shown, the base material 2 to be welded with an overall thickness of 10 mm is processed by groove processing: according to the U-shaped groove processing, the inclination angle of the U-shaped bevel α=8±1°, the radius r=1.6±0.25mm, the length of the horizontal section 4 L=2±0.25mm, the blunt edge thickness t=1.5±0.25mm, and the distance d between the lower edge of the horizontal section 4 and the top of the base material 2 is about 7mm.

[0041] The groove assembly is completed according to the assembly size requirements. The automatic welding device 3 self-melts 200mm, then moves 500mm in the air, controls the misalignment between the parent materials 2 to be ≤1mm, and the groove gap to be ≤1mm, checks the groove curvature, grinds the edges on both sides of the groove within 25mm to make it bright, and uses a brush and alcohol to further remove surface oil, rust and other impurities.

[0042] Before welding, a vertical welding back-gas protection device is suspended and adsorbed on the wall of the base material 2 to be welded, and a protective gas is filled into the protection device. In a preferred embodiment, the protective gas is argon with a purity of not less than 99.999%, stored in the form of liquid argon, and welding is started when the oxygen content is less than 0.1%. During the welding process, the vertical welding back-gas protection device protects the back of the weld, and the wall oxidation and insufficient penetration effect are achieved to achieve composite TIG vertical welding double-sided forming and avoid the root cleaning process.

[0043] In a preferred embodiment, the welding process includes a root welding step, a welding filling step and a welding capping step.

[0044] Specifically, in the base welding step, the peak welding current is 150-180A, and the base value is 80-90A; the welding speed is 90-100mm / min, the peak wire feeding speed is 1-1.4m / min, the low value of the wire feeding speed is about half of the peak speed, the vibration wire feeding frequency is 3Hz-5Hz, and the hot wire current is 40A-60A; the welding gas flow rate is 40-50L / min, and the back gas protection flow rate is 15-20L / min.

[0045] In the welding filling step, the peak value of the welding current is 200-260A and the base value is 100-130A;

[0046] The welding speed is 100-140mm / min, the wire feeding speed peak is 2-2.8m / min, the low value of the wire feeding speed is about half of the wire feeding speed peak, the vibration wire feeding frequency is 4-8Hz, the hot wire current is 40-60A; the welding gas flow is 40-50L / min, the back gas protection flow is 15-20L / min; the wire swing width is 4-6mm, and it stays at the A / C position on both sides of the molten pool 6 for 0.2s-0.5s in one swing cycle. When the welding thickness on one side of the plate wall is not less than 5mm, the back gas protection device can be turned off.

[0047] In the welding capping step, the peak value of the welding current is 240-280A, and the base value is 120-140A; the welding speed is 90-100mm / min, the peak value of the wire feeding speed is 2.8-3.2m / min, the low value of the wire feeding speed is about half of the peak value of the wire feeding speed, the vibration wire feeding frequency is 4-8Hz, and the hot wire current is 40-60A; the welding gas flow rate is 40-50L / min; the welding wire swing width is 6-8mm, and it stays at the A / C position on both sides of the molten pool 6 for 0.2-0.5s in one swing cycle.

[0048] In a further preferred embodiment, in order to further improve the stirring effect of the molten pool and the fusion degree of the weld edge during welding, the wire feeding frequency of the wire feeding mechanism 5 is adjusted to be the same frequency as the swinging process. The wire is fed at the peak speed when the welding current reaches the peak value, and the wire is fed at a low speed when the welding current reaches the base value, so as to achieve the maximum swinging effect, assist the hot wire function, and greatly improve the welding cladding efficiency.

[0049] In a preferred embodiment, a visual inspection system is also used to monitor the molten pool status during the welding process, and the weld image features are extracted through an image processing algorithm. The maximum weld profile height is calculated using the vertical distance, the post-weld weld width size is analyzed, and the positions that may not meet the requirements are located and marked to facilitate rapid grinding of unqualified positions during subsequent grinding.

[0050] In a preferred embodiment, a 10 mm thick 9Ni steel plate is welded using a Φ=1 mm ERNiCrMo-4 welding wire, and the groove of the plate to be welded is processed to Figure 2 The structure shown adopts narrow gap groove and uses coating pulse welding. Before welding, the size is checked to control the U-shaped bevel α = 8 ± 1°, the radius r = 1.6 ± 0.1 mm, the length of the horizontal section 4 L = 2 ± 0.1 mm, and the blunt edge thickness t = 1.5 ± 0.1 mm.

[0051] The groove assembly is completed according to the assembly size requirements. The automatic welding device 3 self-melts 200mm, then moves 500mm in the air, controls the misalignment between the parent materials 2 to be ≤1mm, and the groove gap to be ≤1mm, checks the groove curvature, grinds the edges on both sides of the groove within 25mm to make it bright, and uses a brush and alcohol to further remove surface oil, rust and other impurities.

[0052] When welding the base, set the AC square wave parameters, the positive polarity waveform accounts for 90%, and the composite TIG vertical welding parameters are used, the welding peak current is 160-170A, the base current is 80A, the welding speed is 90mm / min, the wire feeding speed peak is 1.2m / min, the wire feeding speed is low value 0.6m / min, the vibration wire feeding frequency is 5HZ, the hot wire current is 40A, the welding gas flow is 50L / min, and the back gas protection flow is 20L / min; the synchronous pulse swing mode is used to achieve the same frequency and phase control of the current peak base value and the swing parameter, the swing width is 2mm, the swing time is 0.2S, and the dwell time on the left and right sides is 0.3S each. The surface morphology of the weld 1 obtained is as follows Figure 7a As shown in the figure. Among them, the swing time refers to Figure 4 As shown, the one-way time taken by the wire feeding mechanism 5 to move from position B to position A or C.

[0053] After the base is completed, welding filling is carried out, with a peak welding current of 220A, a base current of 110A, a welding speed of 100-mm / min, a peak wire feeding speed of 2.4m / min, a low wire feeding speed of 1.2m / min, a vibration wire feeding frequency of 6HZ, a hot wire current of 40A, a welding gas flow rate of L / min, a back gas shielding flow rate of 20L / min, a swing width of 4mm, a swing time of 0.2S, and a dwell time of 0.3S on both sides. The spectrum of the wire swing speed, welding current and wire feeding speed is collected during the welding process. Figure 5b The surface morphology of the weld 1 is shown in Figure 7b shown.

[0054] After the filling layer is completed, the back gas protection device is removed and the cover welding is carried out. The peak welding current is 260A, the base current is 120-130A, the welding speed is 90mm / min, the peak wire feeding speed is 3.0m / min, the low wire feeding speed is 1.5m / min, the vibration wire feeding frequency is 6HZ, the hot wire current is 40A, the welding gas flow is 50L / min, the swing width is 6-7mm, the swing time is 0.2S, and the dwell time on the left and right sides is 0.5S each.

[0055] After welding, the surface morphology of the weld 1 is as follows Figure 7c As shown, the weld microstructure is as follows Figure 3b As shown, a base welding is performed once to form welding area I, and then a filling welding is performed once to form filling layer II. Finally, a welding cap is performed once on both sides of the weld to form welding area III to complete the welding.

[0056] In a comparative example, the same plate and welding parameters as those in the above embodiment are used, except that the positive polarity waveform accounts for 50% of the AC square wave parameters. The obtained weld metallographic structure is as follows: Figure 3a As shown. Due to the low proportion of positive polarity waveforms, the penetration depth in each welding process in the comparative example is significantly less than that in the example. The thickness of the weld area I formed by a single base welding is relatively small, and a filling welding must be performed on both sides to form two filling layers II before the cap welding can be performed to form the weld area III. Therefore, the total working hours used for welding in the comparative example are significantly longer than those in the example. It can be seen that increasing the proportion of positive polarity waveforms can effectively improve the penetration depth and improve the welding efficiency.

[0057] In another comparative example, the welding wire swing frequency and the welding current frequency are not coupled, and the welding results are as follows: Figure 6a As shown in FIG. 1 , it can be seen that the profile of the weld 1 in region IV is obviously distorted and unevenly distributed, indicating that the cladding effect in this region is poor, the weld structure is unevenly distributed, the weld quality is poor, and the post-weld grinding workload is also large. Figure 6bAs shown, the boundary of weld 1 is uniform and straight as a whole, indicating that the cladding effect is good and the subsequent grinding workload is also low.

[0058] In a preferred embodiment, the weld pool is monitored by a visual inspection system during welding, and the visual inspection system can be integrated into the automatic welding device 3 or set separately. Figure 8a As shown, the visual inspection system performs line scanning on the weld 1 to form a scanning line 10, and extracts the contour features of the weld 1 on the scanning line 10 through an image processing algorithm, such as Figure 8b As shown. Further, based on the contour feature results of the weld 1, a three-point curve is established, including the lowest points D1 and D2 on both sides of the weld 1 and the highest point D3 of the weld 1, thereby calculating the weld residual height value and weld width at the position of the scanning line 10. As the visual inspection system traverses the entire weld 1, the complete residual height value and weld width distribution of the weld 1 can be obtained, thereby controlling the weld quality. During the scanning process, points that may not meet the weld quality requirements are identified and located, and unqualified areas can be quickly located and polished efficiently during the post-weld polishing process.

[0059] It should be understood that the groove structure and welding parameters provided in the above embodiments are not unique. In other embodiments, the groove structure can be scaled in appropriate proportions according to the specific size of the workpiece to be welded, and the welding parameters can be reasonably and adaptively adjusted.

[0060] The purpose of the above embodiments is to further explain the present invention in detail in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Based on the embodiments of the present invention, the method steps involved are optimized or equivalently replaced, and the implementation methods in different embodiments are combined without conflicting structures and principles, which all fall within the protection scope of the present invention.

Claims

1. A composite TIG welding method, characterized in that: During the welding process, the wire feeding method of the welding wire is vibration feeding, and the welding wire is swung in a direction perpendicular to the weld; the welding current is coupled with the frequency of the welding wire swing, and the welding current reaches a peak value when the welding wire swings to the maximum distance away from the center of the weld, and the current reaches a base value when the welding wire swings to the center of the weld; During the wire swinging process, the wire feeding speed is coupled with the swinging frequency and the current frequency. When the welding current is at a peak value, the wire feeding speed is greater than the wire feeding speed when the welding current is at a base value. When the welding current reaches a peak value, the wire feeding speed reaches a peak value, and when the welding current reaches a base value, the wire feeding speed reaches a low value.

2. The hybrid TIG welding method according to claim 1, characterized in that: The welding current is a square wave current.

3. The hybrid TIG welding method according to claim 1 or 2, characterized in that: The positive polarity waveform accounts for no less than 85% of the welding current.

4. The hybrid TIG welding method according to claim 1 or 2, characterized in that: The composite TIG welding method is TIG vertical welding.

5. The hybrid TIG welding method according to claim 1 or 2, characterized in that: It includes a base welding step, a welding filling step and a welding capping step.

6. The hybrid TIG welding method according to claim 5, characterized in that: In the base welding step, the welding current peak value is 150-180A, the base value is 80-90A, and the vibration wire feeding frequency is 3-5Hz; in the welding filling step, the welding current peak value is 200-260A, the base value is 100-130A, and the vibration wire feeding frequency is 4-8Hz; in the welding cover step, the welding current peak value is 240-280A, the base value is 120-140A, and the vibration wire feeding frequency is 4-8Hz.

7. The hybrid TIG welding method according to claim 1 or 2, characterized in that: The extreme end of the tungsten used for welding is ground into a frustum shape, the inclination angle of the frustum is 30°-50°, and longitudinal grinding is adopted.

8. The hybrid TIG welding method according to claim 1 or 2, characterized in that: The shielding gas used in welding is argon with a purity of not less than 99.999%.

9. The hybrid TIG welding method according to claim 1 or 2, characterized in that: During the welding process, a visual inspection system is used to monitor the weld pool status, and the weld image features are extracted through image processing algorithms to control the weld quality.

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