Electromagnetic field-assisted laser brazing method

Abstract

The present invention belongs to the technical field of laser brazing, and particularly relates to an electromagnetic field-assisted laser brazing method. First, pre-welding cleaning is performed, and then mixed brazing material powder is pre-placed, and the mixed brazing material powder is coated on the groove of a specimen. The dried specimen is clamped between two electromagnetic coils on an electromagnet above a workbench in an argon protection chamber, and the current of a direct current power supply I is clamped at both ends of the weld of the specimen. The current at the weld passes through the electromagnetic coil and the Lorentz force generated is directed downward, so that the brazing material fills the brazing seam downward, and then the argon protection chamber is evacuated and filled with argon, and finally laser brazing is performed. The present invention pre-places the brazing material at the part to be welded, and in the protection of an argon atmosphere, heats and melts the brazing material with a laser heat source, and simultaneously couples a steady-state electric field and a magnetic field to form an electromagnetic composite field. The molten brazing material fills the brazing seam downward under the action of the directional Lorentz force of the electromagnetic field, promotes the flow of the brazing material in the gap, reduces the formation of defects such as pores in the weld, and improves the welding quality.

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 capillary action to allow the filler metal to flow into and remain within the joint gap. Therefore, the assembly gap for brazing is required to be kept within a relatively small range, generally less than 0.15 mm. However, in actual production, for some materials with complex structures or that are difficult to process, due to limitations in structure and processing accuracy, it is inevitable that the joint gap will be too large. If the brazing gap is too large, there will be no capillary action within the gap, and the molten filler metal will be difficult to remain in the gap to form a complete joint. In this case, it is necessary to consider adopting large gap brazing technology.

[0003] Currently, there are two main powder filling methods for wide-gap brazing: the mixed powder method and the pre-filled high-melting-point powder method. In the mixed powder method, a brazing filler metal and a high-melting-point powder are mixed and then filled into the weld gap. When the brazing temperature is reached, the low-melting-point component in the brazing material melts, wets the base metal, and forms a viscous mass with the high-melting-point component, which remains in the gap and connects the parts. In the pre-filled high-melting-point powder method, the high-melting-point powder is first filled into the weld gap and sintered at high temperature to form a metal skeleton. The brazing filler metal is then applied to the outside of the joint, where the molten filler metal flows between the sintered powder and remains in the gap, forming the brazed joint. Vacuum brazing and laser brazing are also available for wide-gap brazing. In both methods, the brazing filler metal and the high-melting-point powder are pre-placed at the weld joint using a mixed powder method or pre-filled high-melting-point powder method. The brazing filler metal is then heated using different heat sources, and the molten filler metal and the high-melting-point powder together fill the gap, forming the 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 solder, the gaps are small and the solder has poor fluidity and cannot be completely filled; in addition, the liquid solder will also shrink when solidifying, so shrinkage holes in the joint 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. The molten brazing material fills the brazing seam downward under the action of the directional Lorentz force of the electromagnetic field, promotes the flow of the brazing material, 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 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] Mixing nickel-based brazing filler metal with nickel-based high-temperature alloy powder, stirring thoroughly to make the powders uniformly mixed, and preparing mixed brazing filler metal powder for use; mixing the mixed brazing filler metal powder with a binder to form a paste, which is then loaded into a coater and coated on the groove of the test piece using the coater until the groove is completely filled with the brazing filler metal; and placing the coated test piece in 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 in the argon protection chamber. The direction of the weld at the groove is placed parallel to the two electromagnetic coils. The current clamp of DC power supply I is clamped at both ends of the weld of the specimen. The positive and negative poles of 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 DC power supply II to ensure that the Lorentz force generated by the current at the weld passing through the electromagnetic coil is directed downward.

[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 and fill the protection chamber with argon gas until the pressure in the argon gas protection chamber is 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 switches to energize the test piece and the electromagnet, adjust the laser head position to one end of the weld, turn on the laser, and use the controller to adjust the spot diameter according to the weld width to start welding. When welding is complete, turn off the laser, DC power supply I, and DC power supply II. After the test piece cools down, remove it from 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 inspected using a metallographic microscope.

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

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

[0020] In 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 500-2000 mT.

[0024] In step 5, the output power of the laser is set to 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 an argon atmosphere, heats and melts the solder with a laser heat source, while coupling a steady-state electric field and a 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 oxidation of the brazing material during the brazing process and the inability to wet the base material, which causes the defect of incomplete brazing. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the welding device of 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 cylinder; 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, 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, 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 brazing filler metal and the nickel-based high-temperature alloy powder were mixed in a weight ratio of 8:2, stirred thoroughly to make the powders uniformly mixed, and prepared into a mixed brazing filler metal powder for standby use; the mixed brazing filler metal powder was mixed with a binder in a weight ratio of 10:1, prepared into a paste, and loaded into an applicator. The paste brazing filler metal was applied to the groove of the test piece 5 using the applicator until the groove was completely filled with the brazing filler metal; the coated test piece was placed in a drying oven for drying;

[0036] Step 3: Test piece assembly

[0037] Open the door of the argon gas shielding 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 gas shielding chamber, and place the weld seam at the groove parallel to 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. Ensure that the Lorentz force generated by the current at the weld seam passing through the electromagnetic coil 4 is in the downward direction. Close the door of the argon gas shielding chamber 1;

[0038] Step 4: Vacuum and fill with argon

[0039] Turn on the vacuum pump 7 to discharge 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 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 maintain the magnetic field strength at 500-2000 mT. In this embodiment, the magnetic field strength is maintained at 1500 mT. Adjust the position of the laser head 11 to one end of the weld seam, turn on the laser 10, and adjust the spot diameter according to the weld seam width. Set the output power of the laser 10 to 500-1500 W and the welding speed to 0.5-2 m / min. In this embodiment, the output power of the laser 10 is set to 1400 W. Turn on the laser 10 to start welding. After welding is completed, 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, remove the test piece 5 from the argon gas protection chamber 1.

[0042] Step 6: Post-weld inspection

[0043] After welding, a visual inspection is performed to check whether the weld surface has defects such as cracks, inclusions, and incomplete penetration; 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 an argon atmosphere, heats and melts the solder with a laser heat source, while coupling a steady-state electric field and a 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 oxidation of the brazing material during the brazing process and the inability to wet the base material, which leads to incomplete penetration defects.

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 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 Mixing nickel-based brazing filler metal with nickel-based high-temperature alloy powder, stirring thoroughly to make the powders uniformly mixed, and preparing mixed brazing filler metal powder for use; mixing the mixed brazing filler metal powder with a binder to form a paste, which is then loaded into a coater and coated on the groove of the test piece using the coater until the groove is completely filled with the brazing filler metal; and placing the coated test piece in 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 in the argon protection chamber. The direction of the weld at the groove is placed parallel to the two electromagnetic coils. The current clamp of DC power supply I is clamped at both ends of the weld of the specimen. The positive and negative poles of 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 DC power supply II to ensure that the Lorentz force generated by the current at the weld passing through the electromagnetic coil is directed downward. 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 and fill the protection chamber with argon gas until the pressure in the argon gas protection chamber is 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 switches to energize the test piece and the electromagnet, adjust the laser head position to one end of the weld, turn on the laser, and use the controller to adjust the spot diameter according to the weld width to start welding. When welding is complete, turn off the laser, DC power supply I, and DC power supply II. After the test piece cools down, remove it from 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 inspected using 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 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 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 500-2000 mT.

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

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