Full-position laser welding forming control method for circular seam of medium-thickness wall pipe

Abstract

The invention discloses a medium-thickness wall pipe circular seam all-position laser welding forming control method, and belongs to the technical field of laser welding. The problems that full-position laser deep penetration welding of the medium-thickness wall pipe lacks a systematic welding seam forming control method, and efficient and high-quality welding is difficult to achieve are solved. The method comprises the steps of 1, preparation before welding; 2, pre-calibrating a critical back fusion width threshold value; thirdly, inert gas protection flow control and initial welding parameter setting and execution are carried out; and 4, weld forming defect control. The method is used for the full-position laser welding forming control of the medium-thickness wall pipe circular seam.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of laser welding. BACKGROUND

[0002] In the field of high-end equipment manufacturing such as modern aerospace, energy power and petroleum chemical industry, the connection quality of medium-thick-walled pipe as the core component for conveying high-temperature and high-pressure medium is directly related to the safety of the system. In the manufacturing and assembly process of large equipment, the medium-thick-walled pipe often needs to complete the high-quality and reliable connection under the full-position welding condition.

[0003] At present, the butt joint of medium-thick-walled pipe mainly adopts argon arc welding, which usually needs to open a groove and fill multiple layers, and has the problems of large welding heat input, complex process, slow welding speed and low production efficiency. In comparison, laser welding technology, as an advanced manufacturing technology, uses high-energy density laser beam as heat source, has the advantages of large penetration, fast speed and small heat affected zone. It can realize the connection of medium-thick-walled pipe through one-time welding forming, greatly simplifying the process and improving the production efficiency. However, the full-position laser welding of medium-thick-walled pipe often has the problem of weld forming control: due to the large volume of molten pool and poor fluidity of molten metal, combined with the influence of gravity and surface tension, the weld forming at different welding positions is difficult to control, and defects such as weld collapse and back hump are easy to produce, which restricts the application of laser welding technology in this structure.

[0004] At present, the control method for weld forming mainly depends on customized tooling fixtures and welding equipment or relies on experience to optimize process parameters. The customized scheme often has poor universality, needs to be redesigned for different sizes of pipe, which is high in cost and complex; and relying on experience to optimize parameters needs to invest a lot of time and material cost. Therefore, there is an urgent need for a weld forming control method without improving equipment, with clear optimization strategy and strong universality. SUMMARY

[0005] The present application aims to solve the problem that the full-position laser deep penetration welding of medium-thick-walled pipe lacks a systematic weld forming control method and is difficult to realize efficient and high-quality welding, and further provides a medium-thick-walled pipe girth full-position laser welding forming control method.

[0006] A medium-thick-walled pipe girth full-position laser welding forming control method, which is carried out according to the following steps:

[0007] I. Pre-welding preparation:

[0008] Butt joint the medium-thick-walled pipe and fix it on the welding platform, and get the to-be-welded pipe by point fixing;

[0009] II. Pre-marking of critical back width threshold:

[0010] ① Marking of the first threshold:

[0011] The two plates with the same thickness and material as the pipe to be welded are butt-jointed to obtain a plate to be welded, and the plate to be welded is repeatedly laser welded by gradually reducing the welding heat input until the hump defect appears on the back of the weld, and the back width of the weld is measured as the first threshold value, that is, W b1 ;

[0012] ②Second threshold value calibration:

[0013] The two plates with the same thickness and material as the pipe to be welded are butt-jointed to obtain a plate to be welded, and the plate to be welded is repeatedly laser welded by gradually increasing the welding heat input until the collapse defect appears on the front of the weld, and the back width of the weld is measured as the second threshold value, that is, W b2 ;

[0014] Three, inert gas protection flow control and initial welding parameter setting and execution:

[0015] The inert gas is used as the protective gas, the welding side protective gas flow and the welding back protective gas flow of the pipe to be welded are set respectively, the initial welding parameters are set, and the all-position welding is performed along the outer wall of the pipe to be welded, and the laser power is linearly increased during the welding process to obtain an all-position weld;

[0016] The initial welding parameters are specifically the starting laser power, the welding speed, the defocusing amount and the spot diameter;

[0017] Four, weld forming defect control:

[0018] ①Confirm the penetration of the all-position weld, when the weld is not fully penetrated, adjust the starting laser power in step three or the welding speed in step three, replace another pipe to be welded, and perform all-position welding along the outer wall of the pipe to be welded again;

[0019] ②Repeat step four ① until a fully penetrated all-position weld is obtained;

[0020] ③Measure the back width W b of the all-position fully penetrated weld at the 0° position of the flat position, when W b < W b1 or W b > W b2 , adjust the starting laser power in step four ②, the welding speed in step four ② or the spot diameter in step three, replace another pipe to be welded, and perform all-position welding along the outer wall of the pipe to be welded again;

[0021] ④Repeat step four ③ until W b1 < W b < W b2, and the final welding parameter is obtained, and the pipe to be welded is welded by using the final welding parameter, so that the full-position ring seam of the medium-thick wall pipe is obtained.

[0022] The beneficial effects of the present application are:

[0023] The present application is applied to the full-position welding of the medium-thick wall pipe, and realizes the “single-sided welding and double-sided forming”. This breaks through the process limitation of the traditional argon arc welding which must be opened to groove and multi-layer and multi-pass welding for the structure with a wall thickness of more than 3 mm due to the low energy density, and improves the welding efficiency while ensuring the welding quality.

[0024] The present application provides a systematic weld forming control strategy, which changes the traditional mode of relying on “trial and error method” to explore the process parameters by guiding the forming control with the aid of the control of the keyhole state and the molten pool geometry. This significantly shortens the process development cycle for the full-position laser welding of the medium-thick wall pipe, thereby reducing the time and material costs of research and development.

[0025] In view of the problem that the existing laser welding technology is limited in application due to the lack of effective forming control method, the present application provides a solution. This method effectively solves the problems of weld collapse and back hump in full-position welding, and does not need to modify the equipment, which is simple and easy to implement. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 FIG. 1 is a schematic view of the position of the full-position ring seam of the medium-thick wall pipe according to the present application, wherein 1 is a weld;

[0027] Figure 2 FIG. 3 is a schematic view of the direction of the back pressure of the surface tension fluid static pressure at the bottom surface of the weld at the welding angle θ according to the present application;

[0028] Figure 3 FIG. 4 is a forming effect diagram of the weld at the 90° position (vertical welding position) obtained under the final welding parameter of Example 1 according to the present application;

[0029] Figure 4 FIG. 5 is a forming effect diagram of the weld at the 90° position (vertical welding position) obtained under the final welding parameter of Example 2 according to the present application. DETAILED DESCRIPTION

[0030] DETAILED DESCRIPTION Figure 1 Specifically, the full-position laser weld forming control method for the medium-thick wall pipe ring seam according to the present embodiment is performed according to the following steps:

[0031] I. Preparation before welding:

[0032] The medium-thick wall pipe is butted and fixed on the welding platform, and is subjected to point fixing, so that the pipe to be welded is obtained.

[0033] II. Pre-marking of the critical back width threshold:

[0034] ① The first threshold value is calibrated:

[0035] Two plates with the same thickness and material as the pipe to be welded are butt jointed to obtain a plate to be welded. The laser welding is repeated on the plate to be welded by gradually reducing the welding heat input until the hump defect appears on the back of the weld. The back width of the weld is measured as the first threshold value, i.e. W b1 ;

[0036] ② The second threshold value is calibrated:

[0037] Two plates with the same thickness and material as the pipe to be welded are butt jointed to obtain a plate to be welded. The laser welding is repeated on the plate to be welded by gradually increasing the welding heat input until the collapse defect appears on the front of the weld. The back width of the weld is measured as the second threshold value, i.e. W b2 ;

[0038] Three, inert gas protection flow control and initial welding parameter setting and execution:

[0039] An inert gas is used as the protective gas, and the welding side protective gas flow and the welding back protective gas flow of the pipe to be welded are set. The initial welding parameters are set and full position welding is performed along the outer wall of the pipe to be welded. The laser power is linearly increased during the welding process to obtain a full position weld;

[0040] The initial welding parameters are specifically the starting laser power, the welding speed, the defocusing amount and the spot diameter;

[0041] Four, weld forming defect control:

[0042] ① Confirm the penetration of the full position weld. When the weld is not fully penetrated, adjust the starting laser power in step three or the welding speed in step three, replace another pipe to be welded, and perform full position welding along the outer wall of the pipe to be welded again;

[0043] ② Repeat step four ① until a full position fully penetrated weld is obtained;

[0044] ③ Measure the back width W b of the full position fully penetrated weld at the 0° position of the flat position. When W b < W b1 or W b > W b2 , adjust the starting laser power in step four ②, the welding speed in step four ② or the spot diameter in step three, replace another pipe to be welded, and perform full position welding along the outer wall of the pipe to be welded again;

[0045] ④ Repeat step four ③ until W b1 < W b < Wb2 The final welding parameters are obtained, and the pipe to be welded is welded by using the final welding parameters, so that the full-position girth welding of the medium-thick wall pipe is obtained.

[0046] In step two, the welding heat input is gradually reduced by reducing the laser power or increasing the welding speed, and the welding heat input is gradually increased by increasing the laser power or reducing the welding speed.

[0047] In step three, the weld surface and the back are protected by double inert gas protection during welding.

[0048] Weld surface protection: a drag cover device is used to continuously introduce high-purity argon into the welding area to prevent weld surface oxidation.

[0049] Weld back protection: before welding, the pipeline ends are sealed with airtight adhesive tape, and high-purity argon is continuously introduced into the pipeline to fully exhaust the residual air in the pipeline; during welding, internal gas protection is continuously performed, which can prevent weld back oxidation and improve the back forming effect.

[0050] In step three, the initial laser welding process parameters are set for full-position continuous laser welding; the initial welding parameters should have a high linear energy density, for example, the specific parameters can be: the initial laser power is 3kW~15kW, the initial welding speed is 0.5m / min~2.5m / min, the defocusing amount is 0mm~ -10mm, and the initial spot diameter is 0.1mm~0.5mm; for the difference in molten pool behavior caused by heat accumulation effect in different weld areas during full-position welding, the laser power is linearly increased during welding to compensate, thereby suppressing the forming defects caused by molten pool instability.

[0051] In step four, the weld forming characteristics are analyzed based on the molten pool mechanics balance theory to control the weld forming defects, which includes the following processes:

[0052] ① Confirm the penetration state:

[0053] First, confirm whether the full-position weld is fully penetrated. When the weld is not fully penetrated, increase the initial laser power in step three or reduce the initial welding speed in step three to increase the linear energy until a fully penetrated weld is obtained. When the weld is fully penetrated, proceed to the next step.

[0054] ② Measure the back width and determine the defect cause:

[0055] Measure the back width W at the 0° position of the flat position b Control the existing weld collapse, back hump and other defects.

[0056] In the laser welding process, the root cause of defects such as weld collapse and back hump is the imbalance between the surface tension (F σ ), recoil pressure (F R ) and hydrostatic pressure (F P ) of the liquid metal at the bottom of the molten pool.

[0057] Among them: surface tension (F σ ): inversely proportional to back weld width (W b ), the direction from the bottom of the weld to the surface of the weld, supporting the molten pool.

[0058] Hydrostatic pressure (F P ): related to material density and molten pool depth, always in the direction of gravity, and plays a role in collapsing the molten pool.

[0059] Recoil pressure (F R ): generated by metal vaporization, the direction from the surface of the weld to the bottom of the weld, is the key to forming and maintaining the keyhole.

[0060] To achieve stable formation, the surface tension (F σ ) must be able to resist the hydrostatic pressure (F P ), and at the same time the recoil pressure (F R ) must be able to be released through a stable penetrating keyhole. To achieve this mechanical balance, there are two key back weld width thresholds:

[0061] The first threshold (W b1 ) in step two ①: the back weld width corresponding to the keyhole that can just penetrate the molten pool stably.

[0062] The second threshold (W b2 ) in step two ②: the back weld width corresponding to the surface tension equal to the hydrostatic pressure.

[0063] The condition for stable formation is: W b1 <W b <W b2 .

[0064] According to the relationship between the weld width and the threshold, the parameters are optimized, and according to the measured back weld width (W b ), there are three cases and corresponding optimization strategies:

[0065] Case one: W b <W b1

[0066] Phenomenon: At this time, the keyhole is unstable or cannot penetrate the molten pool, and the recoil pressure cannot be released stably, resulting in back hump defects.

[0067] Optimization strategy: Increase the initial laser power in step 4.2 and decrease the initial welding speed in step 4.2 to increase the line energy, thereby increasing the back weld width and making W b Satisfy W b >W b1 .

[0068] Scenario 2: W b1 <W b <W b2

[0069] Phenomenon: At this point, the mechanical balance is maintained, the keyhole penetrates stably, the molten pool is effectively supported, and a defect-free and stable weld formation will be obtained.

[0070] Optimization strategy: This is the ideal state; maintain the current parameters.

[0071] Scenario 3: W b >W b2

[0072] Phenomenon: At this time, the molten pool is too wide, resulting in insufficient surface tension to resist the hydrostatic pressure of the fluid. The molten pool metal falls under the action of gravity, resulting in weld collapse defects.

[0073] Optimization strategy: The back weld width should be reduced by decreasing the initial laser power in step 4.2 or increasing the initial welding speed in step 4.2 to decrease the line energy, thereby reducing the back weld width and ensuring it meets the W requirement. b < W b2 .

[0074] like Figure 2 As shown, for all-position pipe welding, at any angle θ, the magnitude of the component of the hydrostatic pressure along the weld thickness is F. P •cosθ. In the non-flat welding position (θ≠0°), this component force is smaller than in the flat welding position (θ=0°). The decrease in hydrostatic pressure perpendicular to the weld means that the required surface tension to maintain weld stability is reduced. Therefore, as long as the weld width satisfies W in the flat welding position... b <W b2 Under these conditions, stable forming is more easily achieved in other welding positions (vertical welding, overhead welding), providing a theoretical guarantee for all-position welding.

[0075] Furthermore, the core of the weld width control lies in the control of the weld back width (W). b The control of the weld width on the back side and the weld width on the front side is stable under certain welding process parameters.

[0076] The beneficial effects of this specific implementation method are:

[0077] This specific implementation method is applied to all-position welding of medium-thick-walled pipes, achieving "single-sided welding with double-sided forming". This breaks through the process limitations of traditional argon arc welding, which requires beveling and multi-layer, multi-pass welding for structures with wall thicknesses of 3mm or more due to low energy density. It improves welding efficiency while ensuring weld quality.

[0078] This specific implementation provides a systematic weld formation control strategy that guides formation control by controlling the keyhole state and molten pool geometry, changing the traditional "trial and error" approach to exploring process parameters. This significantly shortens the process development cycle for all-position laser welding of medium-thick-walled pipes, thereby reducing R&D time and material costs.

[0079] This specific implementation method addresses the limitation of existing laser welding technology due to the lack of effective forming control methods. It provides a solution that effectively solves problems such as weld collapse and back hump in all-position welding, while requiring no equipment modification and being simple and easy to implement.

[0080] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the material of the medium-thick wall tube mentioned in step one is GH4169, and the wall thickness of the medium-thick wall tube is 3mm~15mm. Everything else is the same as in Specific Implementation Method One.

[0081] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the medium-thick wall pipe mentioned in step one is a pre-treated medium-thick wall pipe. Specifically, the pre-treatment involves machining the pipe's mating end face to a surface roughness Ra ≤ 3.2 μm, followed by cleaning, resulting in a medium-thick wall pipe with a smooth mating surface free of oil stains. Everything else is the same as in Specific Implementation Method One or Two.

[0082] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step one, the butt joint gap of the pipe fittings to be welded is controlled to be less than 0.01mm; the spot fixing mentioned in step one is laser spot fixing. Everything else is the same as Specific Implementation Methods One to Three.

[0083] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: in step two ①, the average value of the weld width measured at different positions on the back of the weld is taken as the first threshold; in step two ②, the average value of the weld width measured at different positions on the back of the weld is taken as the second threshold. Everything else is the same as in Specific Implementation Methods One to Four.

[0084] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the inert gas mentioned in step three is argon; the flow rate of the shielding gas on the welding side of the pipe to be welded is set to 15L / min~25L / min in step three, and the flow rate of the shielding gas on the welding back side is set to 3L / min~5L / min; the initial welding parameters mentioned in step three are: initial laser power of 3kW~15kW, welding speed of 0.5m / min~2.5m / min, defocusing amount of 0mm~-10mm, and spot diameter of 0.1mm~0.5mm. Everything else is the same as in Specific Implementation Methods One to Five.

[0085] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that the linear increase in laser power described in step three is specifically performed according to the following formula: ;

[0086] in, The initial laser power, To terminate laser power, This represents the total increase in laser power, which is between 300W and 2000W. Everything else is the same as in embodiments one through six.

[0087] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: in step four①, when the weld is not fully penetrated, the initial laser power in step three is increased or the welding speed in step three is decreased, another pipe fitting to be welded is replaced, and all-position welding is performed again along the outer wall of the pipe fitting to be welded. Everything else is the same as in Specific Implementation Methods One to Seven.

[0088] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One through Eight in that: in step four ③, the average value of the weld width at different positions on the back side of the flat weld position at 0° in the fully penetrated weld is taken as W. b Everything else is the same as in specific implementation methods one through eight.

[0089] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One through Nine in that: in step four ③, when W... b <W b1 If necessary, increase the initial laser power in step four ②, decrease the welding speed in step four ②, or reduce the spot diameter in step three; replace the pipe fitting with another one to be welded, and re-perform all-position welding along the outer wall of the pipe fitting; in step four ③, when W b >W b2 If necessary, reduce the initial laser power in step four ② or increase the welding speed in step four ②, replace with another pipe fitting to be welded, and re-perform all-position welding along the outer wall of the pipe fitting. Other procedures are the same as in specific embodiments one through nine.

[0090] The beneficial effects of the present invention are verified using the following embodiments:

[0091] Example 1:

[0092] A method for controlling the formation of circumferential welds in medium-thick-walled pipes using all-position laser welding, comprising the following steps:

[0093] I. Pre-welding preparation:

[0094] Medium and thick-walled pipes are joined together, and the gap between the joints is controlled to be less than 0.01mm. Then, they are fixed to the welding platform with a clamp and tack-bonded to obtain the pipe fittings to be welded.

[0095] The medium-thick wall tube is made of GH4169, with a wall thickness of 10mm and an outer diameter of 150mm. The medium-thick wall tube is a pre-treated medium-thick wall tube. The pre-treatment specifically involves machining the pipe joint end face to a surface roughness Ra≤3.2μm and cleaning it with acetone to obtain a medium-thick wall tube with a smooth joint surface and no oil stains.

[0096] The spot fixation is laser spot fixation, and the laser spot fixation process parameters are: laser power of 4000W and light emission time of 300ms.

[0097] II. Pre-calibration of the critical back width threshold:

[0098] ① Calibration of the first threshold:

[0099] Using a 10mm thick GH4169 butt plate, a flat workpiece to be welded was obtained. Laser welding was repeatedly performed on the workpiece by gradually reducing the welding heat input by decreasing the laser power, until laser welding was performed under the conditions of 8250W laser power, 0.9m / min welding speed, -5mm defocusing amount, and 0.3mm spot diameter. A hump defect began to appear on the back of the weld. The average of the weld width measured at three different locations on the back of the weld was taken as the first threshold, i.e., W. b1 =1.5mm;

[0100] ② Calibration of the second threshold:

[0101] Using a 10mm thick GH4169 butt plate, a flat plate to be welded was obtained. Laser welding was repeatedly performed on the flat plate by gradually increasing the welding heat input by increasing the laser power, until laser welding was performed under the conditions of 10250W laser power, 0.9m / min welding speed, -5mm defocusing amount, and 0.3mm spot diameter. At this point, collapse defects began to appear on the front side of the weld. The average of the weld width measured at three different locations on the back side was taken as the second threshold, i.e., W. b2 =3.5mm;

[0102] III. Inert gas protection flow control and initial welding parameter setting and execution:

[0103] ①Use a drag shield device to continuously introduce high-purity argon gas at a flow rate of 20L / min into the welding side of the pipe fitting to be welded;

[0104] ② Seal both ends of the pipe fitting to be welded with airtight tape, and then continuously introduce high-purity argon gas at a flow rate of 5L / min into the welding back of the pipe fitting;

[0105] ③ Set initial welding parameters and perform all-position welding along the outer wall of the medium-thick wall tube, and linearly increase the laser power during the welding process to obtain an all-position weld.

[0106] The initial welding parameters are as follows: initial laser power of 10kW, welding speed of 1.5m / min, defocusing amount of -5mm, and spot diameter of 0.3mm.

[0107] The linear increase in laser power is specifically performed according to the following formula: ;

[0108] in, The initial laser power, To terminate laser power, This represents the total increase in laser power, and the total increase in laser power is 1000W;

[0109] IV. Control of weld formation defects:

[0110] ① Confirm the penetration of the all-position weld in step three. The weld is fully penetrated, but there is a slight surface collapse defect.

[0111] ②Measure the weld width at three different locations on the back side of the flat weld position (0°) in a fully penetrated weld in all positions, and take the average value as W. b W b =3.9mm, that is W b >W b2 Reduce the initial laser power to 9750W, replace with another pipe fitting to be welded, and re-perform all-position welding along the outer wall of the pipe fitting. At this time, the back weld width at the 0° flat weld position in the weld is 2.2mm, which meets the W requirement. b1 <W b <W b2 That is, the final welding parameters are obtained, and the pipe fittings to be welded are welded using the final welding parameters to obtain the all-position circumferential seam of the medium-thick wall pipe.

[0112] The final welding parameters are as follows: initial laser power of 9750W, welding speed of 1.5m / min, defocusing amount of -5mm, spot diameter of 0.3mm, and total laser power increment of 1000W.

[0113] In Example 1, under the final welding parameters, the circumferential weld has good forming at all positions.

[0114] Example 2:

[0115] A method for controlling the formation of circumferential welds in medium-thick-walled pipes using all-position laser welding, comprising the following steps:

[0116] I. Pre-welding preparation:

[0117] Medium and thick-walled pipes are joined together, and the gap between the joints is controlled to be less than 0.01mm. Then, they are fixed to the welding platform with a clamp and tack-bonded to obtain the pipe fittings to be welded.

[0118] The medium-thick wall tube is made of GH4169, with a wall thickness of 9mm and an outer diameter of 135mm. The medium-thick wall tube is a pre-treated medium-thick wall tube. The pre-treatment specifically involves machining the pipe joint end face to a surface roughness Ra≤3.2μm and cleaning it with acetone to obtain a medium-thick wall tube with a smooth joint surface and no oil stains.

[0119] The spot fixation is laser spot fixation, and the laser spot fixation process parameters are: laser power of 3600W and light emission time of 300ms.

[0120] II. Pre-calibration of the critical back width threshold:

[0121] ① Calibration of the first threshold:

[0122] Using a 9mm thick GH4169 butt plate, a flat plate to be welded was obtained. Laser welding was repeatedly performed on the flat plate by gradually reducing the welding heat input by decreasing the laser power, until laser welding was performed under the conditions of 7500W laser power, 0.9m / min welding speed, -4.5mm defocusing amount, and 0.3mm spot diameter. A hump defect began to appear on the back of the weld. The average of the weld width measured at three different locations on the back of the weld was taken as the first threshold, i.e., W. b1 =1.4mm;

[0123] ② Calibration of the second threshold:

[0124] Using a 9mm thick GH4169 butt plate, a flat plate to be welded was obtained. Laser welding was repeatedly performed on the flat plate by gradually increasing the welding heat input by increasing the laser power, until laser welding was performed under the conditions of 9750W laser power, 0.9m / min welding speed, -4.5mm defocusing amount, and 0.3mm spot diameter. At this point, collapse defects began to appear on the front side of the weld. The average of the weld width measured at three different locations on the back side was taken as the second threshold, i.e., W. b2 =3.3mm;

[0125] III. Inert gas protection flow control and initial welding parameter setting and execution:

[0126] ① A drag-cover device is used to continuously supply high-purity argon gas at a flow rate of 20L / min to the welding side of the pipe fitting to be welded;

[0127] ② Seal both ends of the pipe fitting to be welded with airtight tape, and then continuously introduce high-purity argon gas at a flow rate of 5L / min into the welding back of the pipe fitting;

[0128] ③ Set initial welding parameters and perform all-position welding along the outer wall of the medium-thick wall tube, and linearly increase the laser power during the welding process to obtain an all-position weld.

[0129] The initial welding parameters are as follows: initial laser power of 9000W, welding speed of 1.2m / min, defocusing amount of -4.5mm, and spot diameter of 0.3mm.

[0130] The linear increase in laser power is specifically performed according to the following formula: ;

[0131] in, The initial laser power, To terminate laser power, This represents the total increase in laser power, and the total increase in laser power is 1000W;

[0132] IV. Control of weld formation defects:

[0133] ① Confirm the penetration status of the all-position weld in step three. The weld is fully penetrated, and there are surface collapse defects and back weld bead defects.

[0134] ②Measure the weld width at three different locations on the back side of the flat weld position (0°) in a fully penetrated weld in all positions, and take the average value as W. b , obtain W b =4.6mm, i.e. W b >W b2 Increase the welding speed to 1.8 m / min, replace the pipe fitting with another medium-thick wall pipe, and re-perform all-position welding along the outer wall of the medium-thick wall pipe. At this time, the back weld width at the 0° flat weld position in the weld is 2 mm, which meets W. b1 <W b <W b2 That is, the final welding parameters are obtained, and the pipe fittings to be welded are welded using the final welding parameters to obtain the all-position circumferential seam of the medium-thick wall pipe.

[0135] The final welding parameters are as follows: initial laser power of 9000W, welding speed of 1.8m / min, defocusing amount of -4.5mm, spot diameter of 0.3mm, and total laser power increment of 1000W.

[0136] In Example 2, under the aforementioned final welding parameters, the circumferential weld has good forming at all positions.

[0137] Figure 3 The figure shows the forming effect of the weld at a 90° position (vertical welding position) obtained under the final welding parameters in Example 1. As can be seen from the figure, the double-sided forming is good, with no collapse or hump.

[0138] Figure 4 This is a diagram showing the weld formation effect at a 90° angle (vertical welding position) obtained under the final welding parameters in Example 2. As can be seen from the diagram, the weld is uniformly formed on both sides, and defects are eliminated.

Claims

1. A method of forming control for circumferential full position laser welding of a medium wall thickness pipe, characterized by It is carried out in the following steps: I. Preparation before welding: The butt joint of the medium-thick wall pipe is fixed on the welding platform, and the point solidification is carried out to obtain the pipe to be welded; II. Pre-marking of critical back melt width threshold: ① Marking of the first threshold: Two plates with the same thickness and material as the pipe to be welded are butt-jointed to obtain a plate to be welded, and the plate to be welded is repeatedly laser welded by gradually reducing the welding heat input until hump defects appear on the back of the weld, and the back of the weld is measured to obtain the first threshold value, i.e. W b1 ; ② Marking of the second threshold: Two plates with the same thickness and material as the pipe to be welded are butt-jointed to obtain a plate to be welded, and the plate to be welded is repeatedly laser welded by gradually increasing the welding heat input until the front of the weld begins to collapse, and the back of the weld is measured to be the second threshold value, i.e. W b2 ; III. Inert gas protection flow control and initial welding parameter setting and execution: An inert gas is used as the protective gas, and the welding side protective gas flow and the welding back protective gas flow of the pipe to be welded are set respectively, the initial welding parameters are set, and full-position welding is carried out along the outer wall of the pipe to be welded, and the laser power is linearly increased during the welding process to obtain a full-position weld; The initial welding parameters are specifically the starting laser power, the welding speed, the defocusing amount and the spot diameter; IV. Weld forming defect control: ① Confirm the full-position weld penetration, when the weld is not fully penetrated, adjust the starting laser power in step III or the welding speed in step III, replace another pipe to be welded, and re-perform full-position welding along the outer wall of the pipe to be welded; ② Repeat step 4 ① until a full-position fully penetrated weld is obtained; iii. measuring the back width W at the 0° position of the flat position in the full position fully penetrated weld b when W b < W b1 or W b > W b2 adjusting the starting laser power in step four ii, the welding speed in step four ii, or the spot diameter in step three, replacing another pipe to be welded, and re-performing the full position welding along the outer wall of the pipe to be welded. IV. Repeat step IV. iii until W b1 W b W b2 The final welding parameters are obtained, and the pipe fittings to be welded are welded by using the final welding parameters, i.e. the full-position girth welding of the medium-thick wall pipe is obtained.

2. A method of full position laser welding of a pipe girth according to claim 1, characterized in that The material of the medium-thick wall pipe in step I is GH4169, and the wall thickness of the medium-thick wall pipe is 3mm-15mm.

3. The method of claim 1, wherein The medium-thick wall pipe in step I is a pretreated medium-thick wall pipe, and the pretreatment specifically includes mechanically processing the pipe butt joint end face to a surface roughness Ra≤3.2μm, and then cleaning to obtain a smooth and oil-free butt joint surface.

4. The method of claim 1, wherein The butt joint gap of the pipe to be welded in step I is controlled to be less than 0.01mm; the point solidification in step I is laser point solidification.

5. The method of claim 1, wherein The average value of the melt width at different positions of the weld back in step 2 ① is the first threshold; the average value of the melt width at different positions of the weld back in step 2 ② is the second threshold.

6. The method of claim 1, wherein The inert gas in step III is argon; the welding side protective gas flow of the pipe to be welded in step III is 15L / min-25L / min, and the welding back protective gas flow is 3L / min-5L / min; the initial welding parameters in step III are specifically that the starting laser power is 3kW-15kW, the welding speed is 0.5m / min-2.5m / min, the defocusing amount is 0mm- -10mm, and the spot diameter is 0.1mm-0.5mm.

7. The method of claim 1, wherein The linear increase of the laser power in step three is specifically done according to the following formula: ; wherein, is a start laser power, is an end laser power, is a total laser power increment, and the total laser power increment is 300 W to 2000 W.

8. The method of claim 1, wherein When the weld is not fully penetrated in step 4 ①, the starting laser power in step III is increased or the welding speed in step III is decreased, another pipe to be welded is replaced, and full-position welding is re-performed along the outer wall of the pipe to be welded.

9. The method of claim 1, wherein The average of the back different position weld width at the 0° position of the flat position in the full position full penetration weld measured in Step Four ③ is W b .

10. The method of claim 1, wherein when W b < W b1 , increase the initial laser power in step four ②, decrease the welding speed in step four ② or reduce the spot diameter in step three, replace another pipe to be welded, and perform full position welding along the outer wall of the pipe to be welded again; when W b > W b2 , decrease the initial laser power in step four ② or increase the welding speed in step four ②, replace another pipe to be welded, and perform full position welding along the outer wall of the pipe to be welded again.

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