A control method for lap joint of aluminum alloy tank plasma ring seam welding

Abstract

The application relates to the technical field of aluminum alloy welding, in particular to a plasma ring seam welding start-recovery arc lap joint control method for an aluminum alloy storage tank, which comprises the following steps: S1, providing ring-shaped cylinder segments, fixing two ring-shaped cylinder segments in a group to form a butt joint weld between the two ring-shaped cylinder segments, and performing pre-welding treatment on the butt joint weld; S2, performing plasma ring seam welding on the butt joint weld, and performing segmented control on welding parameters in the welding process, wherein the segmented control comprises a plurality of welding control segments arranged in sequence along the welding direction of the butt joint weld, and the plurality of welding control segments at least comprise a start arc segment, a piercing segment, a welding segment, an arc filling pit segment, a small hole recovery segment and a recovery arc segment. The application has the effect of improving the forming quality stability of the welding seam in the start-recovery arc lap joint area of the plasma ring seam welding of the aluminum alloy storage tank.

Description

Technical Field

[0001] This application relates to the technical field of aluminum alloy welding, and in particular to a method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks. Background Technology

[0002] Currently, aluminum alloy rocket propellant tanks are core structural components of launch vehicles, typically constructed by sequentially welding the front and rear tank bottoms and several cylindrical sections together using multiple circumferential butt welds. The quality of these circumferential butt welds directly affects the overall structural strength and flight safety of the propellant tank; therefore, reliable and robust welds, stable lap joint quality, uniform weld dimensions, and weld performance meeting standard requirements are all required.

[0003] Plasma arc welding, due to its high energy density and deep penetration, is widely used in the circumferential butt welding of aluminum alloy rocket propellant tank sections. However, during plasma circumferential welding, the weld transition quality in the lap area between the arc initiation and termination is unstable, and defects such as burn-through or incomplete fusion are prone to occur at the lap joint. This often requires milling and planing of this area for manual repair, which not only reduces welding efficiency but also affects the reliability of the joint.

[0004] Analysis revealed that the fundamental reason for the unstable weld formation quality in the arc initiation and termination lap joint area lies in the following: During the arc initiation stage, the welding current and ion gas flow rate need to increase rapidly to establish a plasma keyhole and achieve penetration. However, an excessively rapid increase in heat input can lead to overheating and burn-through of the base metal at the arc initiation point or turbulent molten pool. Conversely, during the arc termination stage, the heat input needs to be gradually reduced to close the keyhole and complete filling. However, an excessively rapid reduction in heat input can result in incomplete keyhole closure, leading to shrinkage cavities or incomplete fusion defects. In other words, there is a contradiction between the requirement for a "rapid increase" in heat input during the arc initiation stage and the need to "avoid burn-through," and a contradiction between the requirement for a "gradual decrease" in heat input during the arc termination stage and the need to "ensure keyhole closure." The requirements for heat input in the welding parameters during the arc initiation and termination stages are fundamentally contradictory.

[0005] Therefore, there is an urgent need for a method to control the start and end of the lap joint of plasma circumferential welding in aluminum alloy storage tanks. Summary of the Invention

[0006] To improve the forming quality stability of the weld in the lap joint area of ​​plasma circumferential welding of aluminum alloy tanks, this application provides a method for controlling the lap joint of plasma circumferential welding of aluminum alloy tanks.

[0007] This application provides a method for controlling the start and end of the lap joint during plasma circumferential welding of aluminum alloy storage tanks, which adopts the following technical solution:

[0008] A method for controlling the start and end of the lap joint in plasma circumferential welding of aluminum alloy storage tanks includes the following steps:

[0009] S1. Provide an annular cylindrical section, assemble and fix two annular cylindrical sections together so that a butt weld is formed between the two annular cylindrical sections, and perform pre-welding treatment on the butt weld;

[0010] S2. Perform plasma circumferential welding on the butt weld. During the welding process, the welding parameters are controlled in segments. The segmented control includes multiple welding control segments arranged sequentially along the welding direction of the butt weld. The multiple welding control segments include at least an arc initiation segment, a piercing segment, a welding segment, an arc filling segment, a small hole closing segment, and an arc closing segment. For each welding control segment, at least one of the parameters of welding current, plasma gas flow rate, welding speed, and wire feed speed is independently set.

[0011] In the arc-starting section, the welding current and ion gas flow rate are gradually increased from their initial values ​​to preheat the arc-starting point of the weld. In the perforation section, the welding current and ion gas flow rate continue to increase until the plasma pinhole penetrates the annular cylindrical section. The welding section maintains the main welding with preset parameters. In the arc-filling crater section, the welding current and / or ion gas flow rate are adjusted to achieve a smooth transition between the back-side penetration areas of the arc-starting section and the arc-ending section of the butt weld in the welding direction. In the pinhole-closing section, the plasma pinhole is closed by adjusting the welding current, welding speed, ion gas flow rate, and wire feed speed. The arc-ending section is reduced to the arc-extinguishing parameters, and its ion gas flow rate is less than that of the welding section.

[0012] By adopting the above technical solution, the complete welding process from arc initiation to arc extinguishing is divided into multiple independent welding control segments through segmented control of welding parameters. Each segment has independently set welding parameters, achieving segmented independent control and coordinated operation of key process parameters such as welding current, ion gas flow rate, welding speed, and wire feed speed. From the arc initiation segment to the piercing segment, the gradual increase of welding current and ion gas flow rate achieves smooth penetration of the plasma via, avoiding problems such as rapid penetration or molten pool turbulence. The welding segment maintains the main weld quality with stable parameters; from the arc filling crater segment to the via closing segment, the fine adjustment of parameters achieves a smooth transition between the beginning and end of the weld back penetration and the orderly closure of the plasma via, which is beneficial to maintaining the stability of the arc during the welding process; in the arc extinguishing segment, reducing the ion gas flow rate avoids defects such as shrinkage cavities and cracks in the weld, thereby improving the weld formation quality and reliability of the weld joint in the arc initiation and extinguishing overlap area.

[0013] Optionally, in multiple of the aforementioned welding control segments:

[0014] In the arc-starting section, the welding current gradually increases from the initial value, and the arc-starting ion gas flow rate is lower than that of the welding section to preheat the arc-starting point of the weld.

[0015] In the perforation section, the welding current, ion gas flow rate and welding speed are increased simultaneously to penetrate the annular cylindrical section and form a plasma aperture. Wire feeding begins after the plasma aperture is formed.

[0016] In the welding section, the main body of the butt weld is welded while maintaining preset welding parameters;

[0017] In the filler crater section, at least one of the welding current and the ion gas flow rate is greater than the corresponding parameter value in the welding section, so that the back penetration area of ​​the arc-starting section and the arc-ending section of the butt weld in the welding direction can be smoothly connected and transitioned.

[0018] In the narrowing section, the welding current, welding speed, and ion gas flow rate are reduced, while the wire feeding speed is increased to achieve the closure of the plasma aperture.

[0019] In the arc-extinguishing section, gas is supplied with a second ion gas flow rate and the welding current, welding speed, and wire feed speed are reduced until the arc is extinguished. The second ion gas flow rate is less than the ion gas flow rate in the welding section.

[0020] By adopting the above technical solution, the welding process is refined into six functionally distinct welding control sections, each with different parameter control strategies: the arc initiation section uses a small ion gas flow rate and a slowly increasing current to preheat the weld's arc initiation point, raising the base temperature and laying the foundation for subsequent smooth penetration; the piercing section uses a gradual increase in welding current, ion gas flow rate, and welding speed to achieve stable plasma aperture formation; the welding section maintains stable parameters to ensure the main welding quality of the entire circumferential weld; the crater filling section uses an appropriate increase in welding current or ion gas flow rate to achieve a smooth transition between the beginning and end of the circumferential weld back penetration; the aperture closing section uses a reduction in welding current and welding speed, a significant reduction in ion gas flow rate, and a rapid increase in wire feed speed to achieve rapid closure of the plasma aperture without affecting the weld's appearance and internal quality; the arc termination section uses a smaller ion gas flow rate to avoid plasma aperture formation and achieve slow arc extinguishing. The reasonable matching and coordinated cooperation of parameters between each section achieves smooth transition control of welding parameters for the lap joint of the circumferential weld.

[0021] Optionally, the welding current is applied using a variable polarity plasma method, and the ratio of the duration of the forward current to the duration of the reverse current remains the same in the arc initiation segment, the piercing segment, the welding segment, the arc filling segment, the small hole closing segment, and the arc closing segment.

[0022] By adopting the above technical solution and using variable polarity plasma welding, the positive current is used to achieve full penetration of the workpiece, and the reverse current is used to break the oxide film on the aluminum alloy surface and achieve cathode cleaning. The time ratio of positive current to reverse current is kept consistent in each welding control section, which is beneficial to improving the stability of the arc and the uniformity of the cathode cleaning effect during the welding process. It avoids the problem of inconsistent weld formation caused by changes in polarity ratio and is conducive to improving the uniformity of weld quality in the lap joint area.

[0023] Optionally, the duration of the perforation section is positively correlated with the wall thickness of the annular cylindrical section; the termination value of the welding current in the perforation section is the same as the welding current value in the welding section.

[0024] By adopting the above technical solution, the duration of the perforation section is positively correlated with the wall thickness, ensuring that annular cylinder sections of different wall thicknesses can obtain sufficient perforation time and achieve stable formation of plasma micro-holes; the termination value of the welding current in the perforation section is the same as the welding current value in the welding section, realizing a stepless smooth transition from the perforation section to the welding section, avoiding the problem of uneven weld morphology caused by sudden current changes, and helping to ensure the stability of weld formation quality in the lap joint area.

[0025] Optionally, in the narrowing section, within the same duration, the decrease in the ion gas flow rate is greater than the decrease in the welding current and the welding speed, and the increase in the wire feed speed is greater than the decrease in the welding current.

[0026] By adopting the above technical solution, the rate of decrease in ion gas flow in the small hole section is greater than the rate of decrease in welding current and welding speed, ensuring that the rapid decay of plasma penetration is faster than the rate of decrease in melting capacity, enabling the small hole to close quickly rather than collapse slowly. At the same time, the rate of increase in wire feed speed is greater than the rate of decrease in welding current, ensuring that the rapidly increasing wire feed can fully fill the fused and rapidly shrinking plasma small hole while the current still provides sufficient melting capacity. This achieves a reasonable match between small hole closure and weld filling, effectively avoiding defects such as shrinkage cavities and cracks during arc termination, while ensuring the penetration depth and appearance quality of the weld in the lap joint area.

[0027] Optionally, when the wall thickness of the annular cylindrical section reaches a thickness that would cause weld shrinkage defects if the transition from the closing hole section to the closing arc section were to occur directly after the closing hole section, an lap transition section is added between the closing hole section and the closing arc section. In the lap transition section, the welding current gradually decreases from the welding current value at the end of the closing hole section to the starting welding current value of the closing arc section, while the ion gas flow rate and welding speed remain unchanged.

[0028] By adopting the above technical solution, when the wall thickness of the annular cylindrical section is large, the direct transition from the narrowing orifice section to the arc-closing section after the narrowing orifice section can cause a "waist-pinching" defect in the weld, i.e., the weld cross-section suddenly narrows. By adding an lap transition section between the narrowing orifice section and the arc-closing section, the welding current decreases slowly in this section, while the ion gas flow rate and welding speed remain unchanged. This achieves a smooth transition of the welding current from high to low values, effectively eliminating the "waist-pinching" problem of the weld between the narrowing orifice section and the arc-closing section under large wall thickness specifications, and ensuring the uniformity and consistency of the weld formation quality in the lap area of ​​thick plates.

[0029] Optionally, the perforated section may be provided with one or more perforated sub-stages connected in sequence, and the overlapping transition section may be provided with one or more transition sub-stages connected in sequence; the number of perforated sub-stages in the perforated section and the number of transition sub-stages in the overlapping transition section can be adjusted independently.

[0030] By adopting the above technical solution, the number of perforated sections and lap transition sections can be adjusted independently, so that the total number of welding control sections can be flexibly increased or decreased according to actual welding needs. This provides a larger parameter adjustment space for welding annular cylinder sections with different wall thicknesses and material combinations, further improving the versatility and adaptability of the lap control method, and enabling more precise control of arc start and end lap joints under different working conditions.

[0031] Optionally, when the wall thickness of the annular cylindrical section meets the set conditions and the lap transition section is added, the welding current value at the end of the narrowing section is equal to the welding current value at the beginning of the lap transition section, and the welding current value at the end of the lap transition section is equal to the welding current value at the beginning of the arc-closing section.

[0032] By adopting the above technical solution, the welding current between the small hole section, the lap transition section and the arc termination section is connected end to end and continuously transitioned, avoiding arc instability and weld formation defects caused by sudden current changes between sections. This ensures the continuity and stability of the current throughout the entire arc termination process after the introduction of the lap transition section, and further improves the weld formation quality of the lap area of ​​the large wall thickness specification.

[0033] Optionally, the filler crater segment is activated when welding reaches a preset distance from the arc initiation point. The preset distance is determined based on the wall thickness of the annular cylinder segment, and the weld areas covered by the filler crater segment, the closing hole segment, and the closing arc segment along the welding direction form an overlapping area with the weld area covered by the arc initiation segment.

[0034] By adopting the above technical solution, the starting time of the filler crater section is determined according to the wall thickness, ensuring that there is sufficient lap length under different wall thickness specifications to achieve a smooth connection of the back penetration area; the filler crater section, the small hole section, and the arc termination section form an overlapping lap area with the arc starting section, so that the welding heat input and filler metal on the arc termination side can fully cover the initial weld area of ​​the arc starting section, effectively eliminating defects such as incomplete fusion and pits at the lap joint, and improving the reliability of the lap joint.

[0035] Optionally, in the arc-starting section, the arc-starting ion gas flow rate is less than the ion gas flow rate in the perforation section and less than the ion gas flow rate in the welding section; the arc-starting section maintains a paused wire feeding state; the welding current gradually increases from its initial value, and the rate of increase of the welding current in the arc-starting section is lower than the rate of increase of the welding current in the perforation section.

[0036] By adopting the above technical solution, the arc-starting section uses a lower ion gas flow rate than the piercing section and the welding section, and the wire feeding is paused. A stable preheating arc is established at the arc-starting point of the weld without forming a plasma pinhole. This avoids the airflow turbulence and molten pool churning caused by excessive ion gas flow rate at the moment of arc-starting. The welding current increases slowly at a rate lower than that of the piercing section, so that the temperature of the base material at the arc-starting point gradually rises. This establishes a uniform temperature base for the rapid penetration of the piercing section and effectively prevents defects such as burn-through or lack of fusion at the arc-starting point.

[0037] In summary, this application includes at least one of the following beneficial technical effects:

[0038] 1. By implementing multi-segment precise control of welding parameters, each welding control segment independently sets parameters such as welding current, ion gas flow rate, welding speed, and wire feed speed, achieving precise and coordinated control of the entire process from arc initiation to arc extinguishing. This effectively solves the technical problem of unstable weld formation quality in the lap joint area and significantly improves the welding quality and efficiency of lap joints.

[0039] 2. The arc-starting section achieves preheating through a small ion gas flow rate and a slowly increasing current; the perforation section achieves smooth hole formation by gradually increasing parameters; the arc-filling crater section achieves a smooth connection between the beginning and end of the back-through weld by appropriately increasing parameters; and the hole-closing section achieves precise hole closure by rapidly decreasing the ion gas flow rate and rapidly increasing the wire feeding speed. The parameters of each section work together to ensure the penetration depth and appearance quality of the weld in the lap joint area.

[0040] 3. For thick-walled specifications, by adding an lap transition section between the narrowing section and the arc termination section and maintaining continuous welding current, the shrinkage defect of the weld section is effectively eliminated; by determining the start time of the filling crater section according to the wall thickness and forming an overlapping lap area, the smooth connection of the back penetration area of ​​the arc start and end is ensured; by coordinating the control of small ion gas flow rate, paused wire feeding and slow current rise in the arc start section, a uniform temperature foundation is established for subsequent piercing, further improving the weld formation quality and joint reliability in the lap area. Attached Figure Description

[0041] Figure 1 This is a process flow diagram of a method for controlling the start and end of the lap joint of plasma circumferential welding in an aluminum alloy storage tank according to an embodiment of this application.

[0042] Figure 2 This is a schematic diagram of the structure after the two annular cylinder segments are assembled in an embodiment of this application.

[0043] Figure 3 This is a schematic diagram of the control of multiple welding control segments in Embodiment 1 of this application.

[0044] Figure 4 This is a schematic diagram of the control of multiple welding control segments in Embodiment 2 of this application.

[0045] Explanation of reference numerals in the attached figures:

[0046] 1. Annular cylindrical section; 2. Butt weld; 3. Arc initiation section; 4. Through-hole section; 5. Welding section; 6. Arc filling crater section; 7. Small hole closing section; 8. Arc closing section; 9. Overlap transition section. Detailed Implementation

[0047] The following is in conjunction with the appendix Figure 1-4 This application will be described in further detail.

[0048] This application discloses a method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks.

[0049] It should be noted that, in the description of this invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0050] Example 1: Refer to Figure 1 and Figure 2This embodiment takes an aluminum alloy annular cylinder section 1 with a wall thickness of 6mm as an example. A method for controlling the start and end of the lap joint of plasma circumferential welding in an aluminum alloy storage tank includes the following steps:

[0051] S1. Provide the annular cylinder segment 1 and assemble and fix it to form a butt weld 2, and perform pre-weld treatment on the butt weld 2. Specifically, install and fix the two annular cylinder segments 1 in their respective positions. During the installation process, it is necessary to ensure the coaxiality of the two annular cylinder segments 1. After the two annular cylinder segments 1 are joined, a butt weld 2 is formed between them. The pre-weld treatment includes the following sub-steps:

[0052] S11. Scrape and clean the blunt edges and the inner and outer 30mm range on both sides of the butt weld 2. Specifically, this includes: first, pre-wiping both sides of the weld with organic solvents such as acetone or anhydrous ethanol; after pre-wiping, scraping both sides of the butt weld 2 with a scraping tool; after scraping, cleaning the powder and debris generated by scraping with compressed air; after cleaning, wiping again with acetone or anhydrous ethanol.

[0053] S12. Adjust the assembly of the two annular cylinder sections 1 to ensure that the assembly gap and misalignment meet the welding requirements. In this embodiment, for annular cylinder section 1 with a wall thickness of 6mm, both the assembly gap and misalignment are less than 10% of the wall thickness (i.e., ≤0.6mm). The assembly gap must be determined to ensure sufficient penetration at the root of the butt weld 2 and to avoid burn-through. The misalignment must be determined to avoid arc blow and undercut defects.

[0054] During assembly, attention must be paid to the alignment of the four quadrants (0° / 90° / 180° / 270°) of the annular cylinder section 1 in the circumferential direction. The deviation must meet the requirements and be as small as possible. Axial feed is used for assembly and adjustment. After assembly, the position of the annular cylinder section 1 is fixed.

[0055] S13. After assembly, proceed with beveling, tack welding, and inspection and grinding in sequence. Specifically, beveling is performed using a special tool at a 100mm interval on both sides of the T-joint. The T-joint refers to the intersection of the longitudinal and circumferential seams of the annular cylinder section 1 (T-joint location). This location requires special reinforcement due to the intersection of two weld seams and the concentration of residual stress. Beveling can be performed at intervals of 150-300mm at other locations. The beveling depth is 1-2mm, approximately 30° on each side. This shallow beveling is used for manual tack welding to increase the penetration depth and ensure the welding quality. After completion, aluminum shavings are removed using compressed air.

[0056] After beveling, begin tack welding from a position near the quadrant with small or no gap. Before welding, preheat the welding area with a hot air gun to prevent defects at the weld point. In this embodiment, manual variable polarity argon arc welding with filler wire is used, with a welding current of 220A±10A. The filler wire needs to be preheated and dried, and the welding length is 30-50mm. The tungsten electrode extension length should be as short as possible during manual welding.

[0057] Inspection and Grinding. After the tack welds are completed, inspect the butt weld 2 and promptly address any issues such as misalignment or gaps. The gap and misalignment of the butt weld 2 must be controlled within 10% of the wall thickness of the annular section 1. Use a weld grinding device to grind the tack welds, taking care not to damage the base material. Leave a 0.2-0.5mm clearance during grinding to prevent damage to the base material and to prevent cracking during the welding process.

[0058] Reference Figure 2 and Figure 3 S2, Plasma circumferential welding. Specifically, before welding, check the nozzle diameter, tungsten electrode condition, ion gas and shielding gas reserves, and welding wire condition and reserves according to process requirements. In this embodiment, the welding torch is configured as follows: Φ3.2mm inner nozzle, 3.2mm tungsten electrode (pre-heated, tungsten electrode end face diameter 2.0mm), tungsten electrode inward reduction 2.8mm, overlap grinding length 40mm, high-purity argon gas as the shielding gas, and shielding gas flow rate 20-25 lpm.

[0059] Furthermore, a test plate must be welded before welding to verify the condition of the plasma welding torch. Simultaneously, the welding torch's operational status should be tested in advance according to the schedule to ensure that the torch and system meet the welding requirements. After preparation, plasma circumferential welding can be performed.

[0060] In this embodiment, the welding torch is fixed to the outside of the workpiece to be welded and welding is performed along the circumferential direction of the annular butt weld 2. The workpiece is placed on the positioner and rotated by the positioner.

[0061] During the welding process, welding parameters are controlled in segments. A multi-segment programming and control strategy is adopted to divide the complete welding process from arc ignition to arc extinguishing into multiple independent welding control segments. Each segment independently sets welding parameters to achieve segmented independent control and coordinated operation of key process parameters such as welding current, ion gas flow rate, welding speed and wire feed speed.

[0062] In this embodiment, the welding control section includes the arc initiation section 3, the piercing section 4, the welding section 5, the arc filling crater section 6, the small hole closing section 7, and the arc closing section 8. The parameter control principle of each section is as follows:

[0063] Arc Initiation Segment 3: Arc initiation segment 3 employs a stable plasma welding arc initiation. The welding current gradually increases from an initial value of 50A to 130A, while a relatively small initial ion gas flow rate (0.5 lpm) preheats the arc initiation point of the weld, thereby increasing the base temperature of the arc initiation point and laying the foundation for subsequent slow penetration. The welding speed increases from 80 mm / min to 150 mm / min without wire feeding. The duration of arc initiation segment 3 is set to 5 seconds, with a 3-second delay before reversing the direction of operation. In arc initiation segment 3, the ratio of the duration of the forward current to the reverse current (polarity ratio) is 19:4 (i.e., 19 ms for the positive half-wave and 4 ms for the negative half-wave). By applying welding current through a polarity-variable plasma method, the forward current achieves full penetration of the workpiece, while the reverse current breaks up the oxide film on the aluminum alloy surface and achieves cathodic cleaning.

[0064] Perforation Section 4: Perforation section 4 is the first critical stage for controlling the plasma aluminum alloy circumferential seam overlap. By gradually increasing the welding current from 130A to 180A, the ion gas flow rate from 0.5lpm to 1.3lpm, and the welding speed from 150mm / min to 200mm / min, the plasma pinholes penetrating the annular section 1 are achieved.

[0065] The duration of the perforation section 4 is set to 20 seconds. For other wall thickness specifications, the duration of the perforation section 4 increases with the increase of wall thickness, for example, 20 seconds for 7mm wall thickness, 30 seconds for 8mm wall thickness, 30 seconds for 9mm wall thickness, 40 seconds for 9.5mm wall thickness, and 50 seconds for 12mm wall thickness, to ensure that the annular cylindrical section 1 of different wall thickness specifications can obtain sufficient perforation time.

[0066] Once the operator visually confirms plasma pinhole penetration by observing the molten pool (methods for determining pinhole completion include, but are not limited to, visual observation by the operator, arc voltage monitoring, or molten pool image recognition), the wire is fed at a speed of 1700 mm / min, and the welding segment control immediately enters welding segment 5. The termination value of the welding current (180A) in pinhole segment 4 is the same as the welding current value (180A) in welding segment 5, achieving a stepless and smooth transition from pinhole segment 4 to welding segment 5.

[0067] Welding Segment 5: When the set perforation completion conditions are met, switch to welding segment parameters and enter the welding process. Welding segment 5 maintains stable welding parameters to perform the main welding of the entire circumference butt weld 2. In this embodiment, the welding current of welding segment 5 is 180A (forward current) and 190A (reverse current), the ion gas flow rate is 1.3 lpm, the welding speed is 200 mm / min, and the wire feed speed is 1700 mm / min. The polarity ratio is maintained at 19:4.

[0068] Arc-filling crater section 6: When welding reaches a preset distance from the arc-starting point (200-400mm in this embodiment), the arc-filling crater lap control stage begins. This section requires single-sided welding with double-sided forming, and is the weld connection stage for achieving post-weld penetration and through-hole penetration of the butt weld 2. It directly affects the subsequent X-ray inspection results. This preset distance is determined based on the wall thickness of the annular cylinder section 1; the greater the wall thickness, the larger the preset distance.

[0069] In this embodiment, the welding current of the filler crater section 6 remains constant at 180A (forward current) and 190A (reverse current), the ionizing gas flow rate increases from 1.3 lpm to 1.4 lpm, the welding speed remains at 200 mm / min, and the wire feed speed remains at 1700 mm / min. The duration of the filler crater section 6 is set to 4 seconds. The welding current or ionizing gas flow rate in this section is slightly higher than the corresponding parameter values ​​in the welding section 5, in order to ensure a smooth transition between the arc-starting section 3 and the back penetration area of ​​the arc-ending section 8 in the welding direction of the butt weld 2.

[0070] Narrowing section 7: In this section, the welding current is gradually reduced from 180A to 160A, the welding speed is gradually reduced from 200mm / min to 160mm / min, the ion gas flow rate is significantly reduced from 1.4lpm to 0.5lpm, and the wire feed speed is rapidly increased from 1500mm / min to 3000mm / min. The duration of narrowing section 7 is set to 12 seconds.

[0071] The control principle for the pinhole closing section 7 is as follows: the welding current and welding speed are gradually reduced, and within the same duration, the decrease in ion gas flow rate is greater than the decrease in welding current and welding speed, while the increase in wire feed speed is greater than the decrease in welding current. This achieves rapid closure of the plasma pinhole while ensuring uniform fusion of the weld appearance, without affecting the weld's appearance or internal quality. In this section, the slowly decreasing welding current can still fully melt the rapidly increasing wire feed rate, and the melted wire feed rate can fully fill the rapidly shrinking plasma pinhole, thus achieving closed control of the plasma pinhole.

[0072] The rapid increase in wire feeding speed allows the wire to quickly fill the molten pool cavity, which gradually shrinks due to the decrease in ion gas flow rate. The timely replenishment of filler metal prevents shrinkage defects caused by insufficient molten pool metal during the orifice closure process, thus achieving the simultaneous completion of orderly orifice closure and weld filling.

[0073] Arc Extinguishing Phase 8: This phase is the slow extinguishing stage of the plasma arc. In this embodiment, the welding current in Arc Extinguishing Phase 8 is reduced from 160A to 50A, the welding speed from 160mm / min to 100mm / min, and the wire feed speed from 3000mm / min to 500mm / min. The duration of Arc Extinguishing Phase 8 is set to 8 seconds, including a 7-second downhill section, a 1-second arc extinguishing phase, a 7.5-second stop delay, and a 7-second wire feed delay. A second ion gas flow rate is used in this phase, maintained at 0.5 lpm, to prevent plasma pinholes in the weld and to rapidly reduce the welding current, welding speed, and wire feed speed until the arc is extinguished.

[0074] In this embodiment, the welding current of each welding control segment is applied by a variable polarity plasma method. In all segments, the time ratio (variable polarity ratio) of the positive current to the reverse current is 19:4, that is, 19ms for the positive half-wave and 4ms for the negative half-wave. This constant ratio helps to maintain the stability of the arc and the uniformity of the cathode cleaning effect during the welding process.

[0075] After welding, the lap joint can be ground down. The grinding length varies depending on the parameters and wall thickness. In this embodiment, the lap grinding length is 40mm. Welding parameters need to be fine-tuned during the welding process according to the actual situation. After welding, X-ray and visual inspections are performed. X-ray inspection meets the requirements for Class I welds, and the inspection is qualified; the appearance meets visual and dimensional requirements, and the inspection is qualified.

[0076] In this application, "overlapping position" refers to the overlapping connection area near the arc initiation point on the circumferential butt weld 2. Along the welding direction, the arc initiation segment 3 starts at the arc initiation point, the through-hole segment 4 follows immediately after the arc initiation segment 3, the welding segment 5 covers the main body of the circumferential weld, the arc filling crater segment 6 starts at a preset position before returning to the arc initiation point after one round of welding, and the small hole closing segment 7 and the arc closing segment 8 are connected sequentially after the arc filling crater segment 6. The weld of the overlapping area is the overlapping part of the area covered by the arc filling crater segment 6, the small hole closing segment 7, and the arc closing segment 8 and the area covered by the arc initiation segment 3.

[0077] For annular cylinder section 1 with different wall thicknesses, the steps are as follows: S1 Pre-welding treatment The operation method is the same as in the above embodiments, the main difference lies in the process parameters of S2 plasma circumferential welding, the specific parameters are shown in the table below:

[0078] Table of plasma circumferential welding parameters for the 6mm annular section 1:

[0079] Starting arc segment 5 seconds 50→130 100→150 19:4 0.5→0.5 80→150 No silk feeding Startup with a 3-second delay, reverse perforated section 20 seconds 130→180 150→190 19:4 0.5→1.3 150→200 1700 Wire feeding after perforation Welding section Manual 180 190 19:4 1.3 200 1700 Manually switch parameter segments Filling the arch crater section 4sec 180→180 190→190 19:4 1.3→1.4 200→200 1700 Cut into segments after reaching the set position. Small hole section 12sec 180→160 190→170 19:4 1.4→0.5 200→160 1500→3000 — closing arc segment 8sec 160→50 170→80 19:4 0.5→0.5 160→100 3000→500 Downhill section: 7 seconds; Arc extinguishing: 1 second; Stopping delay: 7.5 seconds; Wire feeding delay: 7 seconds.

[0080] Table of plasma circumferential welding parameters for the 7mm annular section 1:

[0081] Starting arc segment 5 seconds 50→130 100→150 19:4 0.5→0.5 80→150 No silk feeding Startup with a 3-second delay, reverse perforated section 20 seconds 130→190 150→190 19:4 0.5→1.3 150→170 1800→2000 Wire feeding after perforation Welding section Manual 190 190 19:4 1.3 170 1800 / 2000 Manually switch parameter segments Filling the arch crater section 4sec 190→190 190→190 19:4 1.3→1.4 170→170 1800 / 2000 Cut into segments after reaching the set position. Small hole section 12sec 190→175 190→170 19:4 1.4→0.5 170→150 1500→3500 — closing arc segment 8sec 175→50 170→80 19:4 0.5→0.5 150→100 3500→500 Downhill section: 7 seconds; Arc extinguishing: 1 second; Stop delay: 7.5 seconds; Wire feeding delay: 6.5 seconds.

[0082] Table of plasma circumferential welding parameters for the 8mm annular section 1:

[0083] Starting arc segment 5 seconds 50→160 120→180 19:4 0.5→0.5 80→130 No silk feeding Startup with a 3-second delay, reverse perforated section 30 seconds 160→230 180→250 19:4 0.5→2.0 130→150 2000 Wire feeding after perforation Welding section Manual 230 250 19:4 2.0 150 2000 Manually switch parameter segments Filling the arch crater section 4sec 230→230 250→250 19:4 2.0→2.1 150→150 2000 Cut into segments after reaching the set position. Small hole section 12sec 230→200 250→230 19:4 2.1→0.5 150→130 2000→4000 — closing arc segment 8sec 200→50 230→70 19:4 0.5→0.5 130→80 4000→500 Downhill section: 7 seconds; Arc extinguishing: 1 second; Stop delay: 7.5 seconds; Wire feeding delay: 6.8 seconds.

[0084] Table of plasma circumferential welding parameters for the 9mm annular section 1:

[0085] Starting arc segment 5 seconds 50→160 120→180 19:4 0.5→0.5 80→100 No silk feeding Startup with a 3-second delay, reverse perforated section 30 seconds 160→230 180→250 19:4 0.5→2.0 100→130 1800 Wire feeding after perforation Welding section Manual 230 250 19:4 2.0 130 1800 Manually switch parameter segments Filling the arch crater section 4sec 230→230 250→250 19:4 2.0→2.1 130→130 1800 Cut into segments after reaching the set position. Small hole section 12sec 230→200 250→230 19:4 2.1→0.5 130→100 1800→4000 — closing arc segment 8sec 200→50 230→70 19:4 0.5→0.5 100→80 4000→500 Downhill section: 7 seconds; Arc extinguishing: 1 second; Stop delay: 7.5 seconds; Wire feeding delay: 6.8 seconds.

[0086] Table of plasma circumferential welding parameters for the 9.5mm wall thickness of annular section 1:

[0087] Starting arc segment 5 seconds 50→230 120→210 19:4 0.5→0.5 60→100 No silk feeding Startup with a 3-second delay, reverse perforated section 40 seconds 230→270 210→270 19:4 0.5→2.0 100→130 1800 Wire feeding after perforation Welding section Manual 270 270 19:4 2.0 130 1800 Manually switch parameter segments Filling the arch crater section 4sec 270→270 270→270 19:4 2.0→2.1 130→130 1800→1900 Cut into segments after reaching the set position. Small hole section 12sec 270→250 270→240 19:4 2.1→0.5 130→110 1900→3000 — Overlapping transition section 6sec 250→230 250→240 19:4 0.5→0.5 110→110 3000→3000 Solve the problem of the weld seam pinching between the narrow hole section and the arc section. closing arc segment 13 seconds 230→80 240→80 19:4 0.5→0.5 110→80 3000→500 Downhill section 12 seconds, arc extinguishing 1 second, stop delay 10 seconds, wire feeding delay 8 seconds.

[0088] Table of plasma circumferential welding parameters for the wall thickness of 12mm annular section 1:

[0089] Starting arc segment 8sec 50→260 120→210 19:4 0.5→0.5 60→100 No silk feeding Startup with a 3-second delay, reverse perforated section 50 seconds 260→320 210→280 19:4 0.5→2.8 100→120 1500 Wire feeding after perforation Welding section Manual 320 280 19:4 2.8 120 1500 Manually switch parameter segments Filling the arch crater section 6sec 320→320 280→280 19:4 2.8→2.9 120→120 1500→1800 Cut into segments after reaching the set position. Small hole section 15 seconds 320→270 280→240 19:4 2.9→0.5 120→100 1800→3000 — Overlapping transition section 8sec 270→230 240→220 19:4 0.5→0.5 100→100 3000→3000 Solving the problem of pinching waist closing arc segment 15 seconds 230→80 240→80 19:4 0.5→0.5 100→80 3000→500 Downhill section 12 seconds, arc extinguishing 1 second, stop delay 10 seconds, wire feeding delay 10 seconds.

[0090] Example 2:

[0091] Reference Figure 2 and Figure 4 The difference between this embodiment and Embodiment 1 is that when the wall thickness of the annular cylinder section 1 reaches a thickness that would cause weld shrinkage defects if the transition directly from the closing section 7 to the closing section 8 were to occur, an lap transition section 9 is added between the closing section 7 and the closing section 8. In the lap transition section 9, the welding current gradually decreases from the welding current value at the end of the closing section 7 to the initial welding current value of the closing section 8, while the ion gas flow rate and welding speed remain unchanged.

[0092] The welding current value at the end of the small hole section 7 is equal to the welding current value at the beginning of the lap transition section 9, and the welding current value at the end of the lap transition section 9 is equal to the welding current value at the beginning of the arc-closing section 8, ensuring a continuous and smooth connection of current between each section.

[0093] Taking the 9.5mm wall thickness embodiment as an example, the welding current of the lap transition section 9 is gradually reduced from 250A to 230A, the ion gas flow rate is kept constant at 0.5lpm, the welding speed is kept constant at 110mm / min, and the duration is set to 6 seconds.

[0094] Taking the 12mm wall thickness embodiment as an example, the welding current of the lap transition section 9 is gradually reduced from 270A to 230A, the ion gas flow rate is kept constant at 0.5lpm, the welding speed is kept constant at 100mm / min, and the duration is set to 8 seconds.

[0095] When the wall thickness of the annular section 1 is large, the direct transition from the narrowing section 7 to the arc-closing section 8 after the narrowing section 7 will cause a "waist-pinching" defect in the weld, that is, the weld cross-section suddenly shrinks and narrows. By adding an lap transition section 9 between the narrowing section 7 and the arc-closing section 8, the welding current is gradually reduced in this section, while the ion gas flow rate and welding speed remain unchanged. This achieves a smooth transition of the welding current from high to low value, effectively eliminating the "waist-pinching" problem of the weld between the narrowing section 7 and the arc-closing section 8 under large wall thickness specifications, and ensuring the uniformity and consistency of the weld formation quality in the lap area of ​​thick plates.

[0096] The perforation section 4 can be equipped with one or more perforation sub-stages connected in sequence, and the lap transition section 9 can be equipped with one or more transition sub-stages connected in sequence; the number of perforation sub-stages and the number of transition sub-stages can be adjusted independently, so that the total number of welding control sections can be flexibly increased or decreased according to actual welding needs.

[0097] Example 3:

[0098] Reference Figure 2 and Figure 4 The difference between this embodiment and Embodiment 1 is that, taking an annular cylindrical section 1 with a wall thickness of 8mm as an example, different current increase strategies are adopted for the arc initiation section 3 and the perforation section 4. In the arc initiation section 3, the welding current gradually increases from an initial value of 50A to 100A, the duration of the arc initiation section 3 is set to 30 seconds, and the welding current increase rate is approximately 1.7A / s; at the same time, the arc initiation point of the weld is preheated with an arc initiation ion gas flow rate of 0.4lpm. The arc initiation ion gas flow rate is less than the ion gas flow rate of the perforation section 4 (1.5lpm) and less than the ion gas flow rate of the welding section 5 (1.5lpm). The wire feeding is paused throughout the arc initiation section 3.

[0099] In the piercing section 4, the welding current is increased from 100A to 230A, the ion gas flow rate is increased from 0.4lpm to 1.5lpm, the welding speed is increased from 80mm / min to 180mm / min, the duration of the piercing section 4 is set to 30 seconds, and the welding current increase rate is approximately 4.3A / s.

[0100] Therefore, the welding current rise rate of arc initiation section 3 (approximately 1.7 A / s) is lower than that of piercing section 4 (approximately 4.3 A / s), which makes the preheating of arc initiation section 3 more gradual and sufficient. This is beneficial for the thick-walled annular cylindrical section 1 to establish a stable molten pool foundation before piercing, and avoids arc instability and poor arc initiation point formation caused by excessive current rise.

[0101] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks, characterized in that, Includes the following steps: S1. Provide an annular cylindrical section (1), assemble and fix two annular cylindrical sections (1) together so that a butt weld (2) is formed between the two annular cylindrical sections (1), and perform pre-welding treatment on the butt weld (2); S2. Plasma circumferential welding is performed on the butt weld (2). During the welding process, the welding parameters are controlled in segments. The segment control includes multiple welding control segments arranged sequentially along the welding direction of the butt weld (2). The multiple welding control segments include at least an arc-starting segment (3), a piercing segment (4), a welding segment (5), an arc-filling crater segment (6), a small hole closing segment (7), and an arc-closing segment (8). For each welding control segment, at least one of the parameters of welding current, ion gas flow rate, welding speed, and wire feeding speed is independently set. In the arc-starting section (3), the welding current and ion gas flow rate are gradually increased from their initial values ​​to preheat the arc-starting point of the weld; in the perforation section (4), the welding current and ion gas flow rate continue to increase until the plasma pinhole penetrates the annular cylinder section (1); the welding section (5) maintains the main body welding with preset parameters; in the arc-filling crater section (6), the welding current and / or ion gas flow rate are adjusted to achieve a smooth transition between the back penetration area of ​​the arc-starting section (3) and the arc-ending section (8) of the butt weld (2) in the welding direction; in the pinhole-closing section (7), the plasma pinhole is closed by adjusting the welding current, welding speed, ion gas flow rate and wire feeding speed; the arc-ending section (8) is reduced to the arc-extinguishing parameter, and its ion gas flow rate is less than that of the welding section (5).

2. The method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks according to claim 1, characterized in that: In the multiple welding control sections mentioned above: In the arc-starting section (3), the welding current gradually increases from the initial value, and the arc-starting ion gas flow rate is lower than that of the welding section (5) to preheat the arc-starting point of the weld. In the perforated section (4), the welding current, ion gas flow rate and welding speed are increased simultaneously to penetrate the annular cylindrical section (1) and form a plasma aperture. Wire feeding begins after the plasma aperture is formed. In the welding section (5), the main body of the butt weld (2) is welded while maintaining the preset welding parameters; In the arc-filling crater section (6), at least one of the welding current and the ion gas flow rate is greater than the corresponding parameter value in the welding section (5), so that the back penetration area of ​​the arc-starting section (3) and the arc-ending section (8) of the butt weld (2) in the welding direction is smoothly connected and transitioned. In the closed-hole section (7), the welding current, welding speed and ion gas flow rate are reduced, while the wire feeding speed is increased to achieve the closure of the plasma aperture; In the arc-extinguishing section (8), the second ion gas flow rate is used to supply gas and reduce the welding current, welding speed and wire feeding speed until the arc is extinguished. The second ion gas flow rate is less than the ion gas flow rate of the welding section (5).

3. The method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks according to claim 2, characterized in that: The welding current is applied using a variable polarity plasma method. In the arc initiation segment (3), the piercing segment (4), the welding segment (5), the arc filling segment (6), the small hole closing segment (7), and the arc closing segment (8), the ratio of the duration of the forward current to the duration of the reverse current remains the same.

4. The method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks according to claim 2, characterized in that: The duration of the perforation section (4) is positively correlated with the wall thickness of the annular cylindrical section (1); the termination value of the welding current in the perforation section (4) is the same as the welding current value in the welding section (5).

5. The method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks according to claim 2, characterized in that: In the narrowing section (7), within the same duration, the decrease in the ion gas flow rate is greater than the decrease in the welding current and the welding speed, and the increase in the wire feeding speed is greater than the decrease in the welding current.

6. The method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks according to claim 1, characterized in that: When the wall thickness of the annular section (1) reaches a thickness that would cause weld shrinkage defects if the direct transition from the closing section (7) to the closing section (8) after the closing section (7) is terminated, an lap transition section (9) is added between the closing section (7) and the closing section (8). In the lap transition section (9), the welding current gradually decreases from the welding current value at the end of the closing section (7) to the starting welding current value of the closing section (8), while the ion gas flow rate and welding speed remain unchanged.

7. The method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks according to claim 6, characterized in that: The perforated section (4) may be provided with one or more perforated sub-stages connected in sequence, and the overlapping transition section (9) may be provided with one or more transition sub-stages connected in sequence; the number of perforated sub-stages in the perforated section (4) and the number of transition sub-stages in the overlapping transition section (9) may be adjusted independently.

8. The method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks according to claim 6, characterized in that: When the wall thickness of the annular cylinder section (1) meets the set conditions and the overlapping transition section (9) is added, the welding current value at the end of the closing hole section (7) is equal to the welding current value at the beginning of the overlapping transition section (9), and the welding current value at the end of the overlapping transition section (9) is equal to the welding current value at the beginning of the arc closing section (8).

9. The method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks according to claim 2, characterized in that: The filling crater section (6) is activated when the welding reaches a preset distance from the arc starting point. The preset distance is determined according to the wall thickness of the annular cylinder section (1). The weld area covered by the filling crater section (6), the closing hole section (7), and the closing arc section (8) along the welding direction forms an overlapping area with the weld area covered by the arc starting section (3).

10. The method for controlling the start and end of arc lap joints in plasma circumferential welding of aluminum alloy storage tanks according to claim 1 or 2, characterized in that: In the arc-starting section (3), the arc-starting ion gas flow rate is less than the ion gas flow rate of the perforation section (4) and less than the ion gas flow rate of the welding section (5); the arc-starting section (3) maintains a wire feeding paused state; the welding current gradually increases from the initial value, and the welding current increase rate of the arc-starting section (3) is lower than the welding current increase rate of the perforation section (4).

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