A process for processing a large-power wind power generator with a roll-bending brazing copper ring

Abstract

The application discloses a processing technology of a roll-bending brazing copper ring for a high-power wind power generator, and comprises the following steps: S1, machining: machining both ends of a copper bar to obtain a half-thickness joint, wherein the half-thickness joint comprises a first inclined section, a horizontal section and a second inclined section from outside to inside, and two half-thickness joints are spliced with each other to form a lap joint section; S2, preliminary roll-bending; and S3, induction brazing: placing a silver-copper-nickel welding sheet on the horizontal section, and placing a silver-copper-zinc welding sheet on the first inclined section and the second inclined section. The copper ring prepared by the application has strength, hardness and toughness, and simultaneously has heat resistance and corrosion resistance, and can be safely used as the high-power wind power generator.

Description

TECHNICAL FIELD

[0001] The application relates to a brazing processing technology field, in particular to a rolling-bending brazing copper ring processing technology for a high-power wind generator. BACKGROUND

[0002] Brazing refers to a welding method that simultaneously heats a filler metal and a welding piece to a melting temperature of the filler metal, and then fills a gap of the solid welding piece with the liquid filler metal to connect the metals.

[0003] Induction brazing is a welding method that uses an alternating magnetic field formed by an alternating high-frequency, medium-frequency or power frequency power source and an induction coil to generate an induced current in the part, and uses the resistance heat generated by the current as a heat source. The workpiece is placed in the induction coil, the frequency and power of the coil are adjusted to generate appropriate induced current in the workpiece, thereby heating the workpiece.

[0004] The copper ring of a high-power wind generator (generally referring to a megawatt-level, especially a land-based and offshore wind turbine with a capacity of more than 3 MW) is a core component in a slip ring system, responsible for transmitting large current and signals between a rotating generator rotor and a stationary system, and its strength and reliability are crucial. At present, the copper ring part used on the stator and rotor of a high-power wind generator is generally formed into an open ring through a rolling-bending forming process from a copper bar or a copper busbar with a certain cross section, and then the joint of the open ring is welded through brazing. After welding, the circular ring is calibrated by a calibrating device to form a complete ring meeting the size requirements. For the joint brazing of the above open ring, there are two common joint forms: butt joint brazing joint and full-thickness lap joint brazing joint. However, the two brazing joints have the following respective problems:

[0005] Firstly, the butt joint brazing joint has a small brazing area, which can easily lead to low joint strength and unreliable welding.

[0006] Secondly, the full-thickness lap joint brazing joint has a bulky structure, which often brings inconvenience to the installation of the stator and rotor and affects the utilization rate of the internal space of the stator and rotor. SUMMARY

[0007] In view of the above problems, the application provides a rolling-bending brazing copper ring processing technology for a high-power wind generator.

[0008] The technical scheme of the application is as follows:

[0009] A rolling-bending brazing copper ring processing technology for a high-power wind generator, comprising the following steps:

[0010] S1, machining: according to the length of the finished copper ring to be machined, select a copper bar of the same length, machine both ends of the copper bar, and obtain a half-thickness joint, the half-thickness joint comprises, from outside to inside, a first inclined section, a horizontal section and a second inclined section, the first inclined section and the second inclined section have the same inclination angle and the same length, and the two half-thickness joints are spliced with each other to form a lap joint section;

[0011] S2, preliminary bending: place the machined copper bar in S1 on a bending device, and use a bending die to bend it to obtain an open copper ring, then place the lap joint section on a bending machine and perform flattening treatment;

[0012] S3, induction brazing: place a silver copper nickel soldering sheet on the horizontal section of one of the half-thickness joints with the position facing upwards, place a silver copper zinc soldering sheet on the first inclined section and the second inclined section, coat the silver copper nickel soldering sheet and the silver copper zinc soldering sheet on both sides with a flux, then splice and align the two half-thickness joints with each other, fix the lap joint section with a clamping tool, place the lap joint section on a mica plate, then place the mica plate on an induction coil of an induction heating device, press the lap joint section with a pneumatic press plate, keep the lap joint section, the mica plate and the induction coil fixed relative to each other, set the induction heating current to 90-120 A, start heating, heat until the soldering sheets in the lap joint section completely melt and fill the weld, stop heating, and obtain the bending brazed copper ring after water cooling.

[0013] Further, in S1, the length of the horizontal section is 1.5-2 times the thickness of the copper bar.

[0014] Description: By constraining the length of the horizontal section and the thickness of the copper bar, the welding is ensured to be firm.

[0015] Further, in S1, the length L of the copper bar is π(r1+r2) / 2+L ＇ , wherein L ＇ is the length of the lap joint section, r1 is the outer diameter of the finished copper ring, and r2 is the inner diameter of the finished copper ring.

[0016] Description: By determining the length of the copper bar in advance when selecting materials, the error can be reduced, and the prepared copper ring can be ensured to be the same as the requirements of the drawing.

[0017] Further, in S1, the inclination angle of the first inclined section and the second inclined section is determined according to the tensile strength of the copper bar material, and the calculation formula is as follows:

[0018] ;

[0019] , wherein is the included angle between the first inclined section and the second inclined section and the horizontal section, and the unit is °; Rm is the tensile strength of the copper bar material, and the unit is MPa.

[0020] Description: By optimizing the inclination angles of the first and second inclined sections, the balance of strength, hardness and toughness is achieved.

[0021] Further, in S2, the roll bending die comprises an upper limiting ring and a lower limiting ring, an upper backing ring below the upper limiting ring, a lower backing ring above the lower limiting ring, and an intermediate backing ring between the upper and lower backing rings, and the intermediate backing ring is in butt joint with the copper bar.

[0022] Description: By providing a dedicated roll bending die, the roll bending precision is improved, and at the same time, it is ensured that the roll bending process will not cause surface damage to the copper bar.

[0023] Further, in S3, the silver-copper-nickel solder sheet is GB / T 10046 BAg56CuNi, the silver-copper-zinc solder sheet is GB / T 10046 BAg45CuZn, BAg50CuZn or BAg60CuZn, the thickness of the silver-copper-nickel solder sheet and the silver-copper-zinc solder sheet is 0.2mm±0.05mm, the silver-copper-nickel solder sheet and the silver-copper-zinc solder sheet abut each other when placed, and the flux is QJ102 flux.

[0024] Description: By selecting appropriate silver solder sheets as brazing filler metals at different positions, the prepared copper ring can have strength, hardness and toughness.

[0025] Further, in S3, the pressure of the pneumatic pressing plate on the lap joint section is 0.4-0.6MPa.

[0026] Description: By reasonably controlling the pressure of the pneumatic pressing plate, it can be ensured that the brazing part always remains firm.

[0027] Further, in S3, the clamping tool comprises a main body, fastening clamps on both sides of the upper surface of the main body, the fastening clamps are fixedly connected with the main body through fastening bolts and fastening nuts, a placing groove for placing the copper bar is arranged on the upper surface of the main body below the fastening clamps, and the mica plate is fixedly arranged in the groove arranged in the middle of the main body.

[0028] Description: By the clamping tool, the overall stability of the lap joint section during brazing is maintained.

[0029] Further, it further comprises a step S4:

[0030] S4, roll bending and shaping: the welding flash, welding slag and excess welding height at the welded joint are polished flat with an angle grinder, the lap joint section is placed on a roll bending equipment, and the lap joint section in a flat state is roll bent to a required arc state of the copper ring by the roll bending die from inside to outside.

[0031] Description: By the shaping ensure that the final drawing need big power wind turbine with copper ring.

[0032] The beneficial effects of the present application are:

[0033] (1) The present application optimizes the structure of the butt joint part of the copper bar, so that the processing butt joint part of the copper ring for high-power wind turbine is smoother, and the induction brazing process can complete the welding in a short time, wherein two different silver soldering sheets are preferred as the welding materials of the inclined section and the horizontal section, so as to further improve the welding strength, the lower brazing temperature of the silver copper zinc soldering sheet can make it melt into the internal gap of the lap joint section first, then the silver copper nickel soldering sheet melts, and the lower fluidity of the silver copper nickel soldering sheet improves the strength and hardness of the lap joint section, so that the prepared copper ring has strength, hardness and toughness, and has heat resistance and corrosion resistance, and can be safely used as a high-power wind turbine;

[0034] (2) The present application optimizes the internal length of the lap joint section according to the thickness of the copper ring, and optimizes the angle of the inclined section according to the different materials of the copper ring. When the tensile strength of the material is low, the angle of the inclined section is reduced as much as possible to avoid the length of the inclined section being too long, so as to appropriately reduce the coverage area of the silver copper zinc soldering sheet and ensure the overall strength of the copper ring. The materials with high strength can appropriately increase the angle and length of the inclined section to improve the toughness, so as to balance the strength, hardness and toughness;

[0035] (3) The present application also provides a rolling bending die and a clamping tool, so as to provide protection for the rolling bending and brazing of the copper ring, and provide technical support for the development of the induction brazing processing technology of the copper ring for high-power wind turbine. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a schematic view of the overall structure of the copper ring after processing;

[0037] Figure 2 is a side view of the copper ring after processing;

[0038] Figure 3 is a front view of the half-thickness joint;

[0039] Figure 4 is a top view of the half-thickness joint;

[0040] Figure 5 is a schematic view of the structure of the rolling bending die;

[0041] Figure 6 is a schematic view of the structure of the open copper ring after preliminary rolling bending and the lap joint section after flattening treatment;

[0042] Figure 7 is a schematic view of the structure of the clamping tool;

[0043] Figure 8 is a structural diagram of an induction coil;

[0044] Figure 9 is a schematic diagram of the lap joint after roll bending and sizing;

[0045] Figure 10 is a photo of the lap joints of each group in the experimental example;

[0046] Figure 11 is a brazing RT photo of the lap joints of each group in the experimental example;

[0047] Figure 12 is a brazing copper ring lap joint RT photo in the experimental example.

[0048] Wherein, 1-copper bar, 2-half-thickness joint, 21-first inclined section, 22-horizontal section, 23-second inclined section, 3-roll bending die, 31-limit ring, 32-upper gasket ring, 33-lower gasket ring, 34-intermediate gasket ring, 4-clamping tool, 41-main body, 42-fastening clamping plate, 43-fastening bolt, 44-fastening nut, 45- placement groove, 46-groove, 5-mica plate, 6-induction coil, 7-pneumatic pressing plate. DETAILED DESCRIPTION

[0049] Embodiment 1: A roll bending and brazing copper ring processing technology for high-power wind turbines, comprising the following steps:

[0050] S1, machining: according to the length of the finished copper ring to be machined, select a copper bar 1 with the same length, machine both ends of the copper bar 1 to obtain a half-thickness joint 2, as shown in Figure 3 and Figure 4 , the half-thickness joint 2 includes a first inclined section 21, a horizontal section 22 and a second inclined section 23 from outside to inside, the first inclined section 21 and the second inclined section 23 have the same inclination angle and the same length, two half-thickness joints 2 are spliced to form a lap joint, the length of the horizontal section 22 is 1.8 times the thickness of the copper bar 1, and the length L of the copper bar 1 is π(r1+r2) / 2+L ＇ , wherein L ＇ is the length of the lap joint, r1 is the outer diameter of the finished copper ring, and r2 is the inner diameter of the finished copper ring, the inclination angle of the first inclined section 21 and the second inclined section 23 is determined according to the tensile strength of the copper bar 1 material, and the calculation formula is as follows:

[0051] ;

[0052] , wherein is the included angle between the first inclined section 21 and the second inclined section 23 and the horizontal section 22, and the unit is °; Rm is the tensile strength of the copper bar 1 material, and the unit is MPa;

[0053] S2, preliminary bending: as shown in Figure 5 , the copper bar 1 after machining in S1 is placed on the bending equipment, and the bending die 3 is used for bending to obtain an open copper ring, and then the lap joint is placed on the bending machine for flattening treatment, as shown in Figure 6 , the bending die 3 includes upper and lower limiting rings 31, an upper gasket ring 32 below the upper limiting ring 31, a lower gasket ring 33 above the lower limiting ring 31, and an intermediate gasket ring 34 between the upper gasket ring 32 and the lower gasket ring 33, and the intermediate gasket ring 34 is butted against the copper bar 1;

[0054] S3, induction brazing: as shown in Figure 7 and Figure 8 , silver copper nickel soldering sheet is placed on the horizontal section 22 of the one half-thickness joint 2 with the position upward, silver copper zinc soldering sheet is placed on the first inclined section 21 and the second inclined section 23, flux is coated on both sides of the silver copper nickel soldering sheet and the silver copper zinc soldering sheet, then the two half-thickness joints 2 are aligned and spliced with each other, the lap joint is fixed by the clamping tool 4, the lap joint is placed on the mica plate 5, the mica plate 5 is placed on the induction coil 6 of the induction heating equipment, the lap joint is pressed down by the pneumatic pressing plate 7, the pressure of the pneumatic pressing plate 7 pressing down the lap joint is 0.5 MPa, the relative fixation of the lap joint, the mica plate 5 and the induction coil 6 is maintained, the induction heating current is set to 100 A, heating is started, the soldering sheet in the lap joint is completely melted and fills the weld after heating, heating is stopped, and the bending brazing copper ring is obtained after water cooling, and the appearance of the weld is checked, the silver copper nickel soldering sheet is GB / T10046 BAg56CuNi, the silver copper zinc soldering sheet is GB / T 10046 BAg50CuZn, the thickness of the silver copper nickel soldering sheet and the silver copper zinc soldering sheet is 0.2 mm, the silver copper nickel soldering sheet and the silver copper zinc soldering sheet abut against each other when placed, and the flux is QJ102 flux;

[0055] The clamping tool 4 includes a main body 41, fastening clamps 42 on both sides of the upper surface of the main body 41, the fastening clamps 42 are fixedly connected with the main body 41 through fastening bolts 43 and fastening nuts 44, the upper surface of the main body 41 below the fastening clamps 42 is provided with a placing groove 45 for placing the copper bar 1, and the mica plate 5 is fixedly arranged in the recess 46 arranged in the middle of the main body 41;

[0056] S4, bending and shaping: as shown in Figure 9 , the welding flash, welding slag and excess welding height at the welded joint after welding are polished flat by an angle grinder, the lap joint is placed on the bending equipment, and the lap joint in the flat state is bent to the required circular arc state of the copper ring from inside to outside by the bending die 3, as shown in Figure 1 and Figure 2 , the diameter of the lap joint circular ring after bending is checked.

[0057] The welded copper ring is placed on a specially-made ring diameter inspection tool, which is generally made of ordinary carbon steel plate through processes such as plasma cutting, leveling, quenching heat treatment, and machining of ring grooves. The carbon steel plate is quenched to ensure that the steel hardness is within the range of HRC 45-50. The ring groove diameter on the inspection tool is specially designed according to the diameter of the finished copper ring and its tolerance requirements. The depth of the ring groove is generally 2 / 3 of the width of the copper ring.

[0058] If the welded copper ring can be smoothly placed into the ring groove on the inspection tool, it is considered that the diameter, roundness, and other dimensions of the welded copper ring meet the drawing requirements and do not need further shaping. If the welded copper ring cannot be smoothly placed into the ring groove on the inspection tool, it is considered that the diameter, roundness, and other dimensions of the welded copper ring do not meet the drawing requirements and need to be further shaped by knocking with a rubber hammer or other tools.

[0059] The shaped welded copper ring is further polished to remove surface defects such as scratches and pits using a pneumatic polishing device. Then, a hundred-grit cloth is used to clean the surface of the welded copper ring, removing oxides and oil stains, as shown in FIG. 4B. Figures 10-12

[0060] Example 2: The difference between this example and Example 1 is that in S1, the length of the horizontal section 22 is 1.5 times the thickness of the copper bar 1.

[0061] Example 3: The difference between this example and Example 1 is that in S1, the length of the horizontal section 22 is 2 times the thickness of the copper bar 1.

[0062] Note: The length of the horizontal section 22 should be controlled at an appropriate length and is proportional to the thickness. The thicker the thickness, the longer the length of the horizontal section 22 should be increased.

[0063] Example 4: The difference between this example and Example 1 is that in S3, the pressure of the pneumatic pressing plate 7 pressing the lap joint section is 0.4 MPa, which keeps the lap joint section, the mica plate 5, and the induction coil 6 relatively fixed. The induction heating current is set to 90 A.

[0064] Example 5: The difference between this example and Example 1 is that in S3, the pressure of the pneumatic pressing plate 7 pressing the lap joint section is 0.6 MPa, which keeps the lap joint section, the mica plate 5, and the induction coil 6 relatively fixed. The induction heating current is set to 120 A.

[0065] Note: The pressing pressure of the pneumatic pressing plate and the induction heating current can be reasonably adjusted within the range given in the present application.

[0066] Example 6: The difference between this example and Example 1 is that in S3, the silver copper zinc soldering sheet is GB / T 10046 BA45CuZn, and the thickness of the silver copper nickel soldering sheet and the silver copper zinc soldering sheet is 0.15 mm.​

[0067] Example 7: The difference between this example and Example 1 is that in S3, the silver copper zinc solder sheet is GB / T 10046 BAg60CuZn, and the thickness of the silver copper nickel solder sheet and the silver copper zinc solder sheet is 0.25 mm.

[0068] Description: The three kinds of silver copper zinc solder sheets given in the present application are general-purpose brazing filler metals, and the thickness of the silver copper nickel solder sheet and the silver copper zinc solder sheet can be reasonably adjusted within the range given in the present application according to the comprehensive cost and material strength requirements.

[0069] Experimental Example: In order to verify the actual effect of the method of the present application, several groups of comparative experiments were designed for comparative analysis. Comparative Example 1 is a copper ring prepared by a butt joint brazed joint method, Comparative Example 2 is a copper ring prepared by a full-thickness lap joint brazed joint method, Comparative Example 3 uses a continuous whole piece of silver copper nickel solder sheet to press and braze in the inclined section and the horizontal section, Comparative Example 4 uses a continuous whole piece of silver copper zinc solder sheet GB / T 10046 BAg50CuZn to press and braze in the inclined section and the horizontal section, and in Comparative Example 5, no inclined section and horizontal section are divided, but a pre-processed arc-shaped transition section is used at the position where the original inclined section and horizontal section overlap, and then a continuous whole piece of silver copper zinc solder sheet GB / T 10046 BAg50CuZn is used to press and braze. The rest of the steps in Comparative Examples 3 to 5 are the same as in Example 1, and the final test results are shown in Table 1.

[0070] Table 1 Performance table of copper rings prepared by different methods

[0071] ;

[0072] From the data in the above table, it can be seen that in the three groups of examples of the present application, good tensile strength and toughness are achieved, and the structure integrity and performance stability can be better maintained when subjected to external force impact;

[0073] In Comparative Examples 1 and 2, the butt joint brazed joint is prone to low joint strength, poor welding reliability and other problems due to its small brazing area. The full-thickness lap joint brazed joint has a bulky structure, which often brings inconvenience to the installation of the stator and rotor and affects the utilization rate of the internal space of the stator and rotor, so the tensile strength and toughness of both are relatively low.

[0074] In Comparative Examples 3 and 4, a continuous whole piece of silver solder sheet is used. When a silver copper nickel solder sheet is selected, the tensile strength is relatively high, but the temperature required for brazing is also relatively high, requiring relatively high power and time, and the toughness is generally low. When a silver copper zinc solder sheet is selected, the temperature required is relatively low, but the tensile strength and toughness are both generally low, which may be due to the fact that brittle phases are easily precipitated in the inclined section and the horizontal section.

[0075] The arc-shaped smooth transition in Comparative Example 5 can achieve a technical effect close to that of Example 1, but the arc-shaped smooth transition section requires high machining during the machining process, thereby prolonging the overall working time.

[0076] In addition, the inclination angles of the first inclined section 21 and the second inclined section 23 are determined according to the tensile strength of the copper bar 1 material. For example, when the material of the copper bar 1 is chromium-zirconium copper, and the tensile strength is 480 MPa, then = 90 + 0.05 x 480 = 114°;

[0077] When the material of the copper bar 1 is aluminum bronze, and the tensile strength is 700 MPa, then = 90 + 0.05 x 700 = 125°;

[0078] When the material of the copper bar 1 is tellurium copper, and the tensile strength is 350 MPa, then = 90 + 0.05 x 350 = 107.5°;

[0079] When the material of the copper bar 1 is pure copper, and the tensile strength is 200 MPa, then = 90 + 0.05 x 200 = 100°.

Claims

1. A process for manufacturing a roll-bending brazing copper ring for a high-power wind power generator, characterized in that, The method comprises the following steps: S1, machining: according to the length of the finished copper ring to be machined, a copper bar (1) with the same length is selected, and both ends of the copper bar (1) are machined to obtain a half-thickness joint (2), the half-thickness joint (2) comprises a first inclined section (21), a horizontal section (22) and a second inclined section (23) from outside to inside, the first inclined section (21) and the second inclined section (23) have the same inclination angle and the same length, and two half-thickness joints (2) are spliced with each other to form a lap joint section; S2, preliminary bending: the copper bar (1) machined in S1 is placed on a bending device, and is bent by a bending die (3) to obtain an open copper ring, and then the lap joint section is placed on a bending machine for flattening treatment; S3, induction brazing: a silver copper nickel soldering sheet is placed on the horizontal section (22) of the half-thickness joint (2) with the position facing upward, a silver copper zinc soldering sheet is placed on the first inclined section (21) and the second inclined section (23), and a flux is coated on both sides of the silver copper nickel soldering sheet and the silver copper zinc soldering sheet, then the two half-thickness joints (2) are spliced and aligned with each other, the lap joint section is fixed by a clamping tool (4), the lap joint section is placed on a mica plate (5), the mica plate (5) is placed on an induction coil (6) of an induction heating device, the lap joint section is pressed down by a pneumatic pressing plate (7), the relative positions of the lap joint section, the mica plate (5) and the induction coil (6) are kept fixed, the induction heating current is set to 90-120 A, heating is started, the soldering sheets in the lap joint section are completely melted and the weld is filled after heating, and the rolled and brazed copper ring is obtained after water cooling.

2. A process for processing a roll-bending brazing copper ring for a high-power wind power generator according to claim 1, characterized in that, In S1, the length of the horizontal section (22) is 1.5-2 times the thickness of the copper bar (1).

3. A process for processing a roll-bending brazing copper ring for a high-power wind power generator according to claim 1, characterized in that, In S1, the length L of the copper bar (1) = π(r1+r2) / 2+L ＇ wherein L ＇ is the length of the overlap section, r1 is the outer diameter of the finished copper ring, and r2 is the inner diameter of the finished copper ring.

4. The process for processing roll-bending brazing copper ring for high-power wind power generator according to claim 1, characterized in that, In S1, the inclination angles of the first inclined section (21) and the second inclined section (23) are determined according to the tensile strength of the copper bar (1), and the calculation formula is as follows: ； wherein, is the included angle between the first inclined section (21) and the second inclined section (23) and the horizontal section (22), in °; Rm is the tensile strength of the copper bar (1) material, in MPa.

5. The process for processing roll-bending brazing copper ring for high-power wind power generator according to claim 1, characterized in that, In S2, the bending die (3) comprises two limiting rings (31) at the upper and lower parts, an upper gasket ring (32) below the limiting ring (31) at the upper part, a lower gasket ring (33) above the limiting ring (31) at the lower part, and an intermediate gasket ring (34) between the upper gasket ring (32) and the lower gasket ring (33), and the intermediate gasket ring (34) is in abutment with the copper bar (1).

6. A process for manufacturing a roll-bending brazing copper ring for a high-power wind turbine generator according to claim 1, characterized in that, In S3, the thickness of the silver copper nickel soldering sheet and the silver copper zinc soldering sheet is 0.2 mm±0.05 mm, the silver copper nickel soldering sheet and the silver copper zinc soldering sheet abut each other when placed, and the flux is QJ102 flux.

7. A process for manufacturing a roll-bending brazing copper ring for a high-power wind turbine generator according to claim 1, characterized in that, In S3, the pressure of the pneumatic pressing plate (7) pressing the lap joint section is 0.4-0.6 MPa.

8. A process for manufacturing a roll-bending brazing copper ring for a high-power wind turbine generator according to claim 1, characterized in that, In S3, the clamping tool (4) comprises a main body (41), fastening clamping plates (42) on both sides of the upper surface of the main body (41), and the fastening clamping plates (42) are fixedly connected with the main body (41) through fastening bolts (43) and fastening nuts (44), a placing groove (45) for placing the copper bar (1) is arranged on the upper surface of the main body (41) below the fastening clamping plates (42), and the mica plate (5) is fixedly arranged in a recess (46) arranged in the middle of the main body (41).

9. The process for processing roll-bending brazing copper ring for high-power wind power generator according to claim 1, characterized in that, Also comprising step S4: S4, roll bending and shaping: the welding of the completed weld, welding slag and excess welding height with an angle grinder to polish flat, put the lap joint section on the roll bending equipment, use the roll bending die (3) from inside to outside, roll the lap joint section in flat state to the required arc state of the copper ring.

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