Electromagnetic field assisted laser brazing method

Abstract

The invention belongs to the technical field of laser brazing, and particularly relates to an electromagnetic field-assisted laser brazing method, which comprises the following steps of: firstly, cleaning before welding, then presetting mixed brazing filler metal powder, coating the mixed brazing filler metal powder in a groove of a test piece, clamping the dried test piece between two electromagnetic coils on an electromagnet above an argon shield cabin workbench, and then, carrying out electromagnetic field-assisted laser brazing. A current clamp of a direct-current power source I is clamped at the two ends of a welding seam of a test piece, the direction of Lorentz force generated when current at the position of the welding seam penetrates through an electromagnetic coil is downward, so that the brazing filler metal is downwards filled into the brazing seam, then an argon protection bin is vacuumized and filled with argon, and finally laser brazing is conducted. A laser heat source is used for heating and melting brazing filler metal, meanwhile, a steady-state electric field and a steady-state magnetic field are coupled to form an electromagnetic composite field, the brazing filler metal in the molten state downwards fills a brazing seam under the action of directional Lorentz force of the electromagnetic field, flowing of the brazing filler metal in gaps is promoted, formation of air holes and other defects in the brazing seam is reduced, and the welding quality is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of laser brazing, and in particular relates to an electromagnetic field-assisted laser brazing method. Background Art

[0002] In most cases, brazing utilizes the capillary phenomenon to allow the solder to flow into and remain in the joint gap. Therefore, the assembly gap of brazing is required to be kept within a small range, generally less than 0.15mm. However, in actual production, for some materials with complex structures or difficult processing, due to structural and processing accuracy limitations, it is inevitable that the joint gap will be too large. If the brazing gap is too large, there will be no capillary action in the gap, and the molten solder will be difficult to remain in the gap to form a complete joint. At this time, it is necessary to consider the use of large gap brazing technology.

[0003] At present, there are two main powder filling methods for large gap brazing technology: mixed powder method and pre-filled high melting point powder method. The mixed powder method is to mix the brazing material and high melting point powder and fill it into the weld gap. When the brazing temperature is reached, the low melting point component in the brazing material melts, wets the base material, and forms a viscous substance with the high melting point component, which stays in the gap and connects the parts. The pre-filled high melting point powder method is to first fill the high melting point powder into the weld gap, sinter it at high temperature into a metal skeleton, and then apply the brazing material to the outside of the joint. The molten brazing material fills between the sintered powders and stays in the gap to form a brazed joint. Vacuum brazing, laser brazing and other methods can be used for large gap brazing. They all use mixed powder or pre-filled high melting point powder to pre-place the brazing material and high melting point powder at the weld. The brazing material is heated by different heat sources, and the molten brazing material and high melting point powder fill the gap together to form a weld. However, both vacuum brazing and laser brazing have the following disadvantages: since there must be gaps between powders, although some of the gaps can be filled with brazing filler metal, they cannot be completely filled due to the small gaps and poor fluidity of the brazing filler metal; in addition, the liquid brazing filler metal will also shrink when solidifying, so shrinkage cavities in the joints are often unavoidable. Summary of the invention

[0004] In order to solve the problem of porosity defects in large gap brazed joints, the present invention proposes an electromagnetic field-assisted laser brazing method, in which the molten brazing filler metal fills the brazing seam downward under the action of the directional Lorentz force of the electromagnetic field, promotes the flow of the brazing filler metal, reduces the formation of defects such as porosity in the weld, and improves the brazing rate and welding quality.

[0005] An electromagnetic field-assisted laser brazing method comprises the following steps:

[0006] Step 1: Cleaning before welding

[0007] Use a grinder to remove the oxide on the surface of the specimen to be welded, and make a V-shaped or Y-shaped groove on the surface of the specimen. After making the groove, use a cleaning agent to remove the oil and debris on the surface of the specimen, blow it dry with compressed air, then clean the specimen with alcohol and blow it dry with compressed air;

[0008] Step 2: Pre-mix the solder powder

[0009] Mix the nickel-based brazing filler metal and the nickel-based high-temperature alloy powder, stir them thoroughly to make the powders evenly mixed, and prepare mixed brazing filler metal powder for standby use; mix the mixed brazing filler metal powder with a binder, prepare it into a paste, put it into a coater, and coat the paste brazing filler metal on the groove of the test piece with the coater to fill the groove with the brazing filler metal; put the coated test piece into a drying oven for drying;

[0010] Step 3: Test piece assembly

[0011] The dried specimen is clamped between the two electromagnetic coils on the electromagnet above the workbench of the argon protection chamber. The direction of the weld at the groove is placed parallel to the two electromagnetic coils. The current clamp of the DC power supply I is clamped at both ends of the weld of the specimen. The positive and negative poles of the DC power supply I are determined according to the magnetic field direction of the electromagnetic field generated by the electromagnetic coil on the electromagnet connected to the DC power supply II, ensuring that the current at the weld passes through the electromagnetic coil and the Lorentz force generated is in the downward direction;

[0012] Step 4: Vacuum and fill with argon

[0013] Turn on the vacuum pump to exhaust the gas in the argon protection chamber, and then turn off the vacuum pump; open the valve of the argon gas bottle, fill the protection chamber with argon gas, make the pressure in the argon protection chamber equal to the atmospheric pressure, and then stop filling the argon gas;

[0014] Step 5: Laser Brazing

[0015] Turn on the DC power supply I and DC power supply II to energize the test piece and the electromagnet, adjust the laser head position to one end of the weld, turn on the laser, and the controller adjusts the spot diameter according to the weld width to start welding. When welding is finished, turn off the laser, DC power supply I and DC power supply II. After the test piece cools down, take it out of the argon protection chamber;

[0016] Step 6: Post-weld inspection

[0017] After welding, a visual inspection is performed to check whether there are cracks, inclusions, or incomplete penetration on the weld surface; the test piece is dissected and the internal welding quality of the weld is checked under a metallographic microscope.

[0018] In step 1, the groove angle is between 30° and 60°.

[0019] In the step 2, the mass ratio of the nickel-based brazing filler metal to the nickel-based high-temperature alloy powder is 8:2.

[0020] In the step 2, the weight ratio of the mixed solder powder to the binder is 10:1.

[0021] In step 4, the argon gas is high-purity argon gas.

[0022] In step 4, the vacuum pump reduces the gas pressure in the argon protection chamber to 4×10 -2 Below Pa.

[0023] In step 5, the electromagnet changes the magnetic field strength by adjusting the current of the DC power supply II, and the magnetic field strength is maintained at 500-2000mT.

[0024] In step 5, the set output power of the laser is 500-1500W, and the welding speed is 0.5-2m / min.

[0025] The beneficial effects of the present invention are:

[0026] The present invention pre-places solder on the part to be welded, and in the protection of argon atmosphere, heats and melts the solder with a laser heat source, and simultaneously couples the steady-state electric field and magnetic field to form an electromagnetic composite field. The molten solder fills the brazing seam downward under the action of the directional Lorentz force of the electromagnetic field, promotes the flow of solder in the gap, reduces the formation of defects such as pores in the weld, and improves the brazing rate and welding quality.

[0027] An argon protection chamber is used to remove the air in the chamber and fill it with high-purity argon gas to avoid the incomplete penetration defect caused by oxidation of the brazing material during the brazing process and its inability to wet the base material. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of a welding device for the electromagnetic field-assisted laser brazing method of the present invention;

[0029] In the attached figure: 1. Argon protection chamber; 2. Workbench; 3. Electromagnet; 4. Electromagnetic coil; 5. Test piece; 6. DC power supply II; 7. Vacuum pump; 8. Argon gas bottle; 9. Controller; 10. Laser; 11. Laser head. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below with reference to the accompanying drawings.

[0031] like Figure 1 As shown, an electromagnetic field assisted laser brazing method comprises the following steps:

[0032] Step 1: Cleaning before welding

[0033] Use a grinder to remove the oxide on the surface of the specimen 5 to be welded, and make a V-shaped 45° groove on the surface of the specimen 5. The groove angle should not be too large, and should be between 30° and 60°. After making the groove, use a cleaning agent to remove oil and debris on the surface of the specimen 5, blow it dry with compressed air, and then clean the specimen 5 with alcohol and blow it dry with compressed air.

[0034] Step 2: Pre-mix the solder powder

[0035] The nickel-based solder and the nickel-based high-temperature alloy powder are mixed in a mass ratio of 8:2, and stirred thoroughly to make the powders evenly mixed, and the mixed solder powder is prepared for standby use; the mixed solder powder is mixed with the binder in a weight ratio of 10:1, and prepared into a paste, which is loaded into a coater, and the paste solder is coated on the groove of the test piece 5 by the coater, and the solder fills the groove; the coated test piece is placed in a drying oven for drying;

[0036] Step 3: Test piece assembly

[0037] Open the door of the argon protection chamber 1, clamp the dried test piece 5 between the two electromagnetic coils 4 on the electromagnet 3 above the workbench 2 of the argon protection chamber, and place the weld seam at the groove in parallel with the two electromagnetic coils 4. Clamp the current clamp of the DC power supply I at both ends of the weld seam of the test piece 5. The positive and negative poles of the DC power supply I are determined according to the magnetic field direction of the electromagnetic field generated by the electromagnetic coil 4 on the electromagnet 3 connected to the DC power supply II 6, to ensure that the current at the weld seam passes through the electromagnetic coil 4 and the Lorentz force generated is in the downward direction, and close the door of the argon protection chamber 1;

[0038] Step 4: Vacuum and fill with argon

[0039] Turn on the vacuum pump 7 to exhaust the gas in the argon protection chamber 1. Wait until the gas pressure in the argon protection chamber 1 drops to 4×10 -2 Pa, turn off the vacuum pump 7, open the valve of the argon gas bottle 8, fill the argon gas into the argon gas protection chamber 1, make the gas pressure in the argon gas protection chamber 1 equal to the atmospheric pressure, and stop filling the argon gas;

[0040] Step 5: Laser Brazing

[0041] Turn on the DC power supply I and DC power supply II 6 switches to energize the test piece 5 and the electromagnet 3, and keep the magnetic field strength at 500-2000mT. In this embodiment, the magnetic field strength is maintained at 1500mT; adjust the position of the laser head 11 to one end of the weld, turn on the laser 10, and the controller 9 adjusts the spot diameter according to the weld width. The output power of the laser 10 is set to 500-1500W, and the welding speed is 0.5-2m / min. In this embodiment, the output power of the laser 10 is set to 1400W. Turn on the laser 10 to start welding. After welding, turn off the laser 10, turn off the DC power supply I and DC power supply II 6, and after the test piece 5 cools down, take the test piece 5 out of the argon protection chamber 1;

[0042] Step 6: Post-weld inspection

[0043] After welding, a visual inspection is performed to check whether the weld has cracks, inclusions, incomplete penetration and other defects; the test piece is dissected and the internal welding quality of the weld is checked under a metallographic microscope to ensure that it is in good condition.

[0044] The present invention pre-places solder on the part to be welded, and in the protection of argon atmosphere, heats and melts the solder with a laser heat source, and simultaneously couples the steady-state electric field and magnetic field to form an electromagnetic composite field. The molten solder fills the brazing seam downward under the action of the directional Lorentz force of the electromagnetic field, promotes the flow of solder in the gap, reduces the formation of defects such as pores in the weld, and improves the brazing rate and welding quality.

[0045] At the same time, an argon protection chamber is used to remove the air in the chamber and fill it with high-purity argon gas to avoid the incomplete penetration defect caused by oxidation of the brazing material during the brazing process and the inability to wet the base material.

Claims

1. An electromagnetic field-assisted laser brazing method, characterized in that: The following steps are involved: Step 1: Cleaning before welding Use a grinder to remove the oxide on the surface of the specimen to be welded, and make a V-shaped or Y-shaped groove on the surface of the specimen. After making the groove, use a cleaning agent to remove the oil and debris on the surface of the specimen, blow it dry with compressed air, then clean the specimen with alcohol and blow it dry with compressed air; Step 2: Pre-mix the solder powder Mix the nickel-based brazing filler metal and the nickel-based high-temperature alloy powder, stir them thoroughly to make the powders evenly mixed, and prepare mixed brazing filler metal powder for standby use; mix the mixed brazing filler metal powder with a binder, prepare it into a paste, put it into a coater, and coat the paste brazing filler metal on the groove of the test piece with the coater to fill the groove with the brazing filler metal; put the coated test piece into a drying oven for drying; Step 3: Test piece assembly The dried specimen is clamped between the two electromagnetic coils on the electromagnet above the workbench of the argon protection chamber. The direction of the weld at the groove is placed parallel to the two electromagnetic coils. The current clamp of the DC power supply I is clamped at both ends of the weld of the specimen. The positive and negative poles of the DC power supply I are determined according to the magnetic field direction of the electromagnetic field generated by the electromagnetic coil on the electromagnet connected to the DC power supply II, ensuring that the current at the weld passes through the electromagnetic coil and the Lorentz force generated is in the downward direction; Step 4: Vacuum and fill with argon Turn on the vacuum pump to exhaust the gas in the argon protection chamber, and then turn off the vacuum pump; open the valve of the argon gas bottle, fill the protection chamber with argon gas, make the pressure in the argon protection chamber equal to the atmospheric pressure, and then stop filling the argon gas; Step 5: Laser Brazing Turn on the DC power supply I and DC power supply II to energize the test piece and the electromagnet, adjust the laser head position to one end of the weld, turn on the laser, and the controller adjusts the spot diameter according to the weld width to start welding. When welding is finished, turn off the laser, DC power supply I and DC power supply II. After the test piece cools down, take it out of the argon protection chamber; Step 6: Post-weld inspection After welding, a visual inspection is performed to check whether there are cracks, inclusions, or incomplete penetration on the weld surface; the test piece is dissected and the internal welding quality of the weld is checked under a metallographic microscope.

2. The electromagnetic field-assisted laser brazing method according to claim 1, characterized in that: In step 1, the groove angle is between 30° and 60°.

3. The electromagnetic field-assisted laser brazing method according to claim 1, characterized in that: In the step 2, the mass ratio of the nickel-based brazing filler metal to the nickel-based high-temperature alloy powder is 8:

2.

4. The electromagnetic field-assisted laser brazing method according to claim 1, characterized in that: In the step 2, the weight ratio of the mixed solder powder to the binder is 10:

1.

5. The electromagnetic field-assisted laser brazing method according to claim 1, characterized in that: In step 4, the argon gas is high-purity argon gas.

6. The electromagnetic field-assisted laser brazing method according to claim 1, characterized in that: In step 4, the vacuum pump reduces the gas pressure in the argon protection chamber to 4×10 -2 Below Pa.

7. The electromagnetic field-assisted laser brazing method according to claim 1, characterized in that: In step 5, the electromagnet changes the magnetic field strength by adjusting the current of the DC power supply II, and the magnetic field strength is maintained at 500-2000mT.

8. The electromagnetic field-assisted laser brazing method according to claim 1, characterized in that: In step 5, the set output power of the laser is 500-1500W, and the welding speed is 0.5-2m / min.

Images