A laser-arc composite cleaning method for aluminum alloy oxide film

Abstract

The present invention discloses a laser-arc composite cleaning method for aluminum alloy oxide films, which relates to the field of aluminum alloy welding / additive manufacturing technology. The method first uses laser cleaning to remove the oxide film of uniform depth on the surface of the parent material / workpiece. Since the thickness of the surface oxide film / stains varies, the residual oxide film on the surface after laser cleaning will be distributed in the form of scattered points. This is followed by arc cathode cleaning, at which time the cathode spots will automatically search for the residual oxide film to achieve fixed-point cleaning of the oxide film. The present invention can remove the oxide film on the surface of the aluminum alloy to the greatest extent, the cleaning area can be freely adjusted, and will not cause obvious adverse effects on the parent material structure. It can be welded as soon as cleaning is completed, effectively preventing the regeneration of the oxide film, and significantly improving work efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum alloy welding / additive manufacturing, and more specifically, relates to a laser-arc composite cleaning method for aluminum alloy oxide films. Background Art

[0002] Traditional welding processes lack the cleaning process for oxide films. Brazing is the only process during which flux is used to remove oxide films from the base metal surface. Traditional additive manufacturing processes often rely on a single cleaning method to remove oxide films from the base metal. However, flux is corrosive, which not only harms the health of technicians but also reduces the service life of welded workpieces. Single cleaning methods often result in incomplete cleaning and are prone to secondary oxidation.

[0003] Laser cleaning of the motherboard is commonly used in welding / additive manufacturing processes. However, when the laser power is low, the main effect is that the gas and moisture in the streak holes on the aluminum alloy surface expand due to heat, generating a large explosive force, causing the oxide film to locally break and peel off. When the laser power is moderate, the main effect is that the oxide film is affected by the heat energy converted from light energy, causing it to expand due to heat, and the impact force generated is greater than the adhesion of the oxide film, causing the oxide film to peel off. When the laser power is too high, the oxide film is completely peeled off, and the heat energy converted from light energy is absorbed by the base material, causing the base material to over-melt and undergo secondary oxidation. In addition, during the additive manufacturing process, the change in the layer height of the deposited layer will cause the laser action point to no longer be the focus, and the laser energy density will vary significantly. At this time, the laser cleaning efficiency of the deposited layer surface will be greatly affected. The removal depth during the laser cleaning process can be approximately considered consistent, while the layer height distribution of stains and oxide films is often inconsistent. Therefore, single laser cleaning can easily result in inconsistent removal depth on the surface of the deposited layer, as well as insufficient removal depth or excessive removal depth, leading to re-oxidation.

[0004] Another cleaning method used in welding / additive manufacturing processes is arc cathode cleaning, where the base metal / workpiece is connected to the negative power supply and the tungsten electrode is connected to the positive power supply. The oxide film covering the aluminum alloy base metal has a low work function, so the cathode spot will primarily act on the oxide film. However, the movement of the cathode spot is irregular. When the oxide film and stains are present in the form of a pavement, the cathode spot's cleaning effect is random, resulting in a limited cleaning area. Furthermore, when the reverse polarity ratio (EP) is increased to a certain level, the cleaning area no longer increases in the same amount of time. Therefore, a single cathode cleaning method is prone to incomplete cleaning at the microscopic level.

[0005] Therefore, technicians are required to propose a cleaning method to overcome the shortcomings of the above-mentioned single cleaning method, better solve the problem of oxide film cleaning, reduce defects such as oxide film slag inclusion, pores and uneven molten droplet spreading during welding / additive manufacturing, and achieve better metallurgical bonding. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a laser-arc composite cleaning method for aluminum alloy oxide films. The basic principle is to use the characteristic of laser to remove the oxide film at a consistent depth to provide a precondition for arc cathode cleaning of the oxide film at a fixed point, and to combine the two cleaning methods to achieve high-quality oxide film cleaning. The present invention uses a moderate-power laser to act on the surface of the base material to remove the oxide film and stains at a fixed depth, and the remaining oxide film and stains are distributed in a lattice-like manner; followed by low-current arc cathode cleaning with inert gas protection. At this time, the cathode spots with extremely high current density in the arc will automatically search for the residual oxide film and evaporate and clean it. At the same time, the arc with extremely high temperature will isolate the oxygen in the air. Under the cover of the protective gas, the cleaned area has time and space for welding / additive work.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a laser-arc composite cleaning method for aluminum alloy oxide film. First, laser cleaning is used to remove the oxide film of consistent depth on the surface of the parent material / workpiece. Due to the different thicknesses of the surface oxide film / stains, the residual oxide film on the surface after laser cleaning will be distributed in the form of scattered points; then, arc cathode cleaning is used. At this time, the cathode spots will automatically search for the residual oxide film to achieve fixed-point cleaning of the oxide film. The two cleaning methods are combined to achieve a more effective cleaning effect and improve the quality of subsequent welding / additive manufacturing.

[0008] Preferably, a 3D scanning unit is used to obtain the current layer surface height, and the height is fed back to the laser cleaning unit in real time, so that the laser energy density in the laser cleaning action area is consistent.

[0009] Preferably, the relative positions of the laser light outlet and the tungsten electrode remain unchanged, and the relative positions of the laser action point and the arc action point are closely spaced and do not overlap.

[0010] Preferably, the tungsten electrode is connected to the negative power supply, and the parent metal / workpiece is connected to the positive power supply. The arc current is 30-60A. When the aluminum alloy parent metal / workpiece serves as the cathode, i.e., during the EP phase, electrons are primarily emitted by field emission, and the arc cannot be sustained and stable. Therefore, the arc is an AC arc with an AC frequency of 10-50Hz, with the EP phase accounting for 40-80% of the arc current.

[0011] Preferably, the arc gun muzzle is elliptical, and the arc cross section is also elliptical. Compared with a circular shape, it can achieve a larger cleaning width under low current conditions and reduce the possibility of interference between hardware.

[0012] Preferably, the laser cleaning width is larger than the arc cleaning width, and the arc cleaning width is larger than the welding / additive width to ensure the correct implementation of the cleaning method.

[0013] Preferably, during the arc cleaning process, a small current and a high EP ratio are used to reduce the arc heat input and prevent the surface of the parent material / workpiece from melting.

[0014] Preferably, the laser action area and the low current arc action area are always within the protection range of the inert gas during operation to avoid secondary oxidation after cleaning.

[0015] Preferably, the shielding gas flow rate has a significant impact on the size of the cleaning area. The shielding gas flow rate can be changed according to the subsequent welding / additive width requirements to adjust the cleaning area. The gas flow rate range is 3 to 15 L / min.

[0016] The beneficial effect produced by the above technical solution is that: the present invention combines the characteristics of the two cleaning methods, adopts laser cleaning first, and then adopts low-current arc cathode cleaning to achieve the removal of stains and oxide films on the surface of the parent material. The focal length of the laser cleaning spot in the present invention is regulated by the layer height profile data returned by the 3D scanning unit, so that the laser energy density at the point of action is consistent when the laser cleans the oxide film. After laser cleaning, the residual oxide film on the surface of the parent material will exist in a scattered distribution. At this time, cathode cleaning can achieve fixed-point cleaning. At the same time, the high-temperature area provided by the arc will isolate the oxygen in the air in the form of ionization. Adding protective gas to this area can effectively prevent re-oxidation after cleaning, and the size of the cleaning area can be freely adjusted by changing the protective gas flow rate. Therefore, the present invention can better solve the problem of oxide film cleaning, and also provide sufficient oxide film-free time and space to achieve cleaning and welding, which can reduce defects such as oxide film slag inclusion, pores and uneven droplet spreading in the welding / additive process, and achieve better metallurgical bonding. In summary, the present invention can remove the oxide film on the surface of aluminum alloy to the greatest extent, the cleaning area can be freely adjusted, and will not cause obvious adverse effects on the parent material structure. It can be welded as soon as the cleaning is completed, effectively preventing the regeneration of the oxide film, and significantly improving work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the uncleaned parent material surface;

[0018] Figure 2 Schematic diagram of the base material surface after laser cleaning;

[0019] Figure 3 Schematic diagram of the base material surface after laser-arc composite cleaning;

[0020] Figure 4 Schematic diagram of the laser-arc action area. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0022] The laser-arc composite cleaning method for aluminum alloy oxide film first uses laser cleaning to remove the oxide film of uniform depth on the surface of the parent material / workpiece. Due to the different thickness of the surface oxide film / stains (such as Figure 1 As shown), the residual oxide film on the surface after laser cleaning will be distributed in the form of scattered points (as shown Figure 2 (As shown). A 3D scanning unit is used to determine the current layer surface height, which is fed back to the laser cleaning unit in real time, ensuring consistent laser energy density across the cleaning area. The relative position of the laser exit and tungsten electrode remains unchanged, and the laser and arc action points are closely spaced and non-overlapping.

[0023] Then, use arc cathode cleaning, at this time the cathode spot will automatically find the residual oxide film, to achieve the fixed point cleaning of the oxide film, the two cleaning methods are combined to achieve a more effective cleaning effect (such as Figure 3 As shown), the subsequent welding / additive manufacturing quality is improved. Among them, the tungsten electrode is connected to the negative pole of the power supply, and the base material / workpiece is connected to the positive pole of the power supply. The arc current is 30~90A. When the aluminum alloy base material / workpiece is used as the cathode, that is, the EP stage, the electron emission mode is mainly field emission, and the arc cannot exist continuously and stably, so the arc is an AC arc with an AC frequency of 10-50Hz, and the EP stage accounts for 40~80%. The muzzle of the arc gun is elliptical, and the arc cross-section is also elliptical. Compared with the circular shape, it can achieve a larger cleaning width under low current conditions, while reducing the possibility of interference between hardware. The laser cleaning width is greater than the arc cleaning width, and the arc cleaning width is greater than the welding / additive manufacturing width to ensure the correct implementation of the cleaning method. During the arc cleaning process, the small current and high EP ratio adopted have a small arc heat input, which will not cause the surface of the base material / workpiece to melt. As Figure 4 As shown, the laser active area and the low-current arc active area remain within the inert gas shielding area during operation, preventing secondary oxidation after cleaning. The shielding gas flow rate has a significant impact on the size of the cleaning area. The shielding gas flow rate can be adjusted based on the subsequent welding / additive manufacturing width requirements to achieve the desired cleaning area. The gas flow rate range is 3 to 15 L / min.

[0024] A specific embodiment of the present invention is as follows:

[0025] Step 1: Turn on the 3D scanning unit to indicate the infrared light, turn on the laser cleaning unit to indicate the infrared light, and keep the 3D scanning area, laser area and arc area as Figure 2 As shown. The base material is connected to the positive pole of the power supply, the tungsten electrode is connected to the negative pole of the power supply, and the distance between the tungsten electrode and the base material is 2mm;

[0026] Step 2: Adjust the laser frequency to 10kHz, pulse width to 30ns, power to 20W, and scanning width to 50mm;

[0027] Step 3: Adjust the power supply EN stage current amplitude to 30A, EP stage current amplitude to 30A, EP stage accounting for 60%, AC frequency to 40Hz, current waveform to rectangular wave, and shielding gas flow rate to 5L / min.

[0028] Step 4: Start the arc and turn on the laser. The relative position of the arc and the laser action area remains unchanged, and the relative movement speed with the base material is 200 mm / min.

[0029] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A laser-arc composite cleaning method for aluminum alloy oxide film, characterized in that: First, laser cleaning is used to remove a layer of oxide film of uniform depth on the surface of the parent material / workpiece. The thickness of the surface oxide film / stains varies. After laser cleaning, the residual oxide film on the surface of the parent material / workpiece will be distributed in the form of scattered points; then, arc cathode cleaning is used to remove the residual oxide film in the form of scattered points on the surface of the parent material / workpiece. At this time, the cathode spots will automatically search for the residual oxide film to achieve targeted cleaning of the oxide film.

2. The laser-arc hybrid cleaning method for aluminum alloy oxide film according to claim 1, characterized in that: The 3D scanning unit is used to obtain the current surface height of the oxide layer and feed it back to the laser cleaning unit in real time, so that the laser energy density in the laser cleaning area is consistent.

3. The laser-arc hybrid cleaning method for aluminum alloy oxide film according to claim 1, characterized in that: The relative positions of the laser light outlet and the tungsten electrode remain unchanged, and the relative positions of the laser action point and the arc action point are closely spaced and do not overlap.

4. The laser-arc hybrid cleaning method for aluminum alloy oxide film according to claim 1, characterized in that: The tungsten electrode is connected to the negative pole of the power supply, and the base material / workpiece is connected to the positive pole of the power supply. When the aluminum alloy base material / workpiece acts as the cathode, it is the EP stage; when the aluminum alloy base material / workpiece acts as the anode, it is the EN stage. The switching frequency between the EN and EP stages is 10-50Hz.

5. The laser-arc hybrid cleaning method for aluminum alloy oxide film according to claim 1, characterized in that: The arc gun muzzle is elliptical, and the arc cross section is also elliptical.

6. The laser-arc hybrid cleaning method for aluminum alloy oxide film according to claim 1, characterized in that: The laser cleaning width is greater than the arc cleaning width, and the arc cleaning width is greater than the welding / additive cleaning width.

7. The laser-arc hybrid cleaning method for aluminum alloy oxide film according to claim 4, characterized in that: During the arc cleaning process, a small current is adopted, and the small current range is 30~90A; a high EP ratio is adopted, and the EP stage time accounts for 40~80% of a single cycle.

8. The laser-arc hybrid cleaning method for aluminum alloy oxide film according to claim 1, characterized in that: The laser action area and the low current arc action area are always within the protection range of inert gas during operation to avoid secondary oxidation after cleaning.

9. The laser-arc hybrid cleaning method for aluminum alloy oxide film according to claim 1, characterized in that: The shielding gas flow rate is changed according to the subsequent welding / additive width requirements to adjust the cleaning area. The gas flow rate range is 3 to 15 L / min.

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