A method for multi-mode laser coupling additive manufacturing of aluminum alloy

Abstract

The present invention belongs to the field of laser processing technology, and in particular, relates to a method for multi-modal laser coupled additive manufacturing of aluminum alloys, the method comprising the steps of pre-treatment, construction of multi-modal coupled laser, additive process and strengthening treatment. The present invention shapes the laser light source into an annular flat-top laser through a laser shaping system and an optical path system, and uses an annular flat-top pulse laser to assist annular flat-top continuous laser for additive manufacturing, homogenizes the organizational structure of aluminum alloy parts, effectively improves the nucleation rate of the solidification process, and finally obtains refined grains, thereby enabling the workpiece to obtain excellent strength and plastic toughness. An annular flat-top pulse laser is used to strengthen the surface of the processed aluminum alloy, and the residual tensile stress generated by rapid laser solidification is changed into residual compressive stress, thereby obtaining an aluminum alloy workpiece with high strength and high fatigue resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser additive manufacturing, and in particular relates to a method for manufacturing aluminum alloy by multi-mode laser coupling additive manufacturing. Background Art

[0002] Laser additive manufacturing technology has been widely studied in industrial production as an energy-saving and environmentally friendly manufacturing technology, especially in the field of manufacturing and repairing complex aluminum alloy parts. Compared with traditional processing and manufacturing processes, laser additive manufacturing has a higher degree of design freedom and can realize the manufacturing of complex geometric shapes, including some internal structures and structures such as holes. Due to the high energy density of lasers, most known materials including metals and ceramics can be processed, which makes laser additive technology have a wide range of application scenarios. Laser additive manufacturing technology can respond quickly and customize and produce in small batches according to customer requirements. In addition, compared with traditional subtractive manufacturing processes, laser additive manufacturing technology produces almost no cutting waste, significantly reduces material waste, and has good economic benefits. These advantages have made laser additive manufacturing technology receive more and more attention.

[0003] Traditional laser additive manufacturing technology often uses a single-mode Gaussian light source as an energy source, and the temperature of the molten pool is generally high during laser additive manufacturing, which causes the aluminum alloy molten pool to form an oxide film on its surface after solidification, which is harmful to subsequent overlap. Since the functions that can be achieved by a single-mode laser light source are relatively simple, the existence of the oxide film is a pain point that traditional single-mode lasers cannot solve. In addition, the laser light source with Gaussian energy distribution will make the molten pool present a morphological feature of "high in the middle and low at both ends". The Gaussian weld bead is easy to make the surface of the overlapped aluminum alloy present an uneven wavy morphology when overlapping, and after the processing is completed, it is necessary to remove half of the material of the molten pool width from the edge of the part, which causes a great waste of materials. In addition, traditional laser additive manufacturing mostly uses optical external powder feeding technology to manufacture parts, which will cause part of the powder blown out by the powder feeder to fly and cannot enter the molten pool to participate in the forming of the parts, which greatly reduces the efficiency of additive manufacturing and causes material waste. From a microscopic perspective, due to the extremely fast solidification speed during the laser additive manufacturing process, it is easy to cause segregation of the structure of the manufactured aluminum alloy parts, resulting in uneven performance of the manufactured parts. Furthermore, since the molten pool presents a morphological feature of "high in the middle and low at both ends", its surface is heated unevenly in subsequent processing, which will aggravate the unevenness of the component composition. In addition, since the parts produced by laser additive manufacturing are not forged, their mechanical properties are often weaker than those produced by forging technology. These factors have greatly limited the development and application of laser additive manufacturing technology.

[0004] At present, the main method to reduce the component segregation and improve the performance of laser additively manufactured aluminum alloy parts is heat treatment strengthening after processing. However, the heat treatment method greatly prolongs the production cycle of parts and increases production costs. Summary of the invention

[0005] In order to solve the technical problem that the conventional laser additive manufacturing technology uses a single-mode Gaussian light source as an energy source to manufacture aluminum alloy parts with uneven morphology and component segregation, the present invention proposes an efficient and high-quality additive manufacturing method that utilizes multi-mode laser coupling and cooperates with a flat-top laser light source to obtain a uniform and flat surface morphology at the macro level and a stable and uniform aluminum alloy organizational structure at the micro level.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for multi-mode laser coupling additive manufacturing of aluminum alloy, comprising the following steps:

[0008] (1) using a continuous laser generator to emit a single-mode continuous Gaussian laser, using a laser beam shaping system to shape the single-mode continuous Gaussian laser into a single-mode continuous flat-top laser, and then using an optical element to shape the single-mode continuous flat-top laser into a single-mode continuous flat-top ring laser;

[0009] (2) using a pulse laser generator to emit a single-mode pulsed Gaussian laser, using a laser beam shaping system to shape the single-mode pulsed Gaussian laser into a single-mode pulsed flat-top laser, and then using an optical element to shape the single-mode pulsed flat-top laser into a single-mode pulsed flat-top ring laser;

[0010] (3) The single-mode continuous flat-top ring laser and the single-mode pulsed flat-top ring laser are respectively introduced into the multi-mode coupled laser nozzle, and the continuous flat-top ring laser is located within the light ring of the pulsed flat-top ring laser, thereby forming a multi-mode coupled ring laser;

[0011] (4) The aluminum alloy wire / powder is delivered from the center of the ring of the continuous flat-top ring laser through the wire / powder feeder, which avoids the powder splashing caused by the external powder delivery of the laser, improves the utilization rate of the powder, and improves the processing efficiency;

[0012] (5) The multi-mode coupled laser nozzle moves at a certain speed along a preset trajectory, so that the pulsed flat-top ring laser contacts the substrate first, and then the continuous flat-top ring laser contacts the substrate. The metal wire / powder melts and solidifies to form a weld bead, and the continuous operation finally completes the additive process of the entire part.

[0013] (6) After the molten pool is completely solidified to form a workpiece, the continuous flat-top ring laser is turned off, and the power of the pulsed flat-top ring laser is adjusted. The surface of the aluminum alloy workpiece is subjected to pulsed laser shock hardening without re-clamping. The additive process and the surface hardening process use the same set of laser equipment, avoiding errors caused by multiple clamping.

[0014] Preferably, the single-mode continuous flat-top ring laser is in the shape of a circular ring, and the single-mode pulsed flat-top ring laser is in the shape of an elliptical ring.

[0015] Preferably, the continuous flat-top ring laser is located inside the pulsed flat-top ring laser, the center of the continuous flat-top ring laser is located on the long axis of the pulsed flat-top ring laser and one side of the continuous flat-top ring laser is inscribed with the pulsed flat-top ring laser.

[0016] Preferably, in step (4), a water cooling device is used to cool the laser head while conveying the metal wire / powder, and a protective gas is used to prevent oxidation of the molten pool.

[0017] Preferably, the power of the pulsed flat-top ring laser is adjusted in step (6) to adjust the peak power density of the pulsed flat-top ring laser acting on the aluminum alloy to 5 GW / cm 2 , the spot diameter is adjusted to 2mm-4mm, so that the aluminum alloy surface reaches 10 7 / s strain rate.

[0018] Preferably, the method further includes a step of processing the aluminum alloy substrate, specifically, polishing the surface of the substrate to make it flat and smooth, and then cleaning with acetone to remove surface dirt.

[0019] Preferably, in the step (5) of material addition, the power of the pulsed flat-top ring laser is 0.05 kW to 6 kW, and the power of the continuous flat-top ring laser is 1 kW to 30 kW.

[0020] Compared with the prior art, the advantages and positive effects of the present invention are:

[0021] (1) The pulsed flat-top ring laser used in the present invention can improve the flow properties of the molten pool, accelerate the heat and mass transfer inside the molten pool, reduce the element segregation phenomenon caused by rapid laser solidification, and form a stable and uniform structure.

[0022] (2) The pulsed flat-top ring laser used in the present invention can act on the front of the solid-liquid interface when the aluminum alloy is solidifying, breaking up the dendrite arms generated by rapid solidification, increasing the nucleation rate during solidification, and inhibiting the growth of coarse dendrites. Ultimately, an extremely fine grain structure can be obtained, thereby improving the strength of the aluminum alloy workpiece.

[0023] (3) The pulsed flat-top ring laser used in the present invention can be used alone as a surface strengthening method. After the aluminum alloy parts are processed, the surface of the parts is laser impact strengthened to obtain residual compressive stress that is beneficial to resisting cracks, thereby improving the fatigue resistance of the material.

[0024] (4) The annular continuous laser light source and the annular pulsed laser light source used in the present invention are both flat-top light sources. During the additive process, the laser energy is evenly distributed to form a flat processing surface, thereby avoiding the Gaussian morphology feature of the molten pool surface being "high in the middle and low at both ends", thereby avoiding the Gaussian morphology feature from affecting the subsequent additive process.

[0025] (5) The aluminum alloy powder used in the present invention is transported from the inside of the hollow continuous flat-top ring laser, which avoids the powder splashing caused by the external delivery of the laser, improves the powder utilization rate, improves the processing efficiency, and avoids the interference of the aluminum alloy powder on the sensor signal. The additive process and the surface strengthening process use the same set of laser equipment, which avoids the errors caused by multiple clamping, shortens the overall processing flow of the aluminum alloy workpiece, and further improves the processing efficiency.

[0026] (6) The optical powder / wire feeding technology adopted in the present invention enables the sensor to directly detect the parameters of the laser and the molten pool, avoiding the interference of aluminum alloy powder on the sensor signal, making the subsequent feedback adjustment more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The process flow chart of the laser additive manufacturing method for aluminum alloy of the present invention;

[0028] Figure 2 It is a schematic diagram of the working condition of the multi-mode laser in the additive process in an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the pulse laser working condition during the strengthening process in an embodiment of the present invention;

[0030] In the above figures: 1. substrate; 2. continuous flat-top ring laser; 3. pulsed flat-top ring laser; 4. workpiece; 5. molten pool. DETAILED DESCRIPTION

[0031] In order to better understand the present invention, a detailed description is given below in conjunction with the accompanying drawings and embodiments.

[0032] Example: Figure 1 As shown, a method for multi-mode laser coupling additive manufacturing of aluminum alloy comprises the following steps:

[0033] 1. Pre-treatment

[0034] According to the morphological features of the workpiece 4, the slicing plan is made and the moving trajectory of the laser head is set. The substrate that carries the additive aluminum alloy parts is surface treated, specifically, the surface of the substrate 1 is polished to keep the surface of the substrate 1 flat and smooth, and after polishing, acetone is used for cleaning to remove as much dirt as possible from the surface of the substrate 1.

[0035] 2. Constructing multi-mode coupled laser

[0036] The first laser generator and the second laser generator are turned on at the same time to generate single-mode continuous Gaussian laser and single-mode pulsed Gaussian laser respectively. After being shaped by the laser beam shaping system, the energy of the single-mode continuous Gaussian laser and the single-mode pulsed Gaussian laser is redistributed to form continuous single-mode flat-top laser and single-mode pulsed flat-top laser. After the continuous flat-top laser and the pulsed flat-top laser pass through the optical path system including optical elements such as the ring mirror and the conical mirror, they are formed as follows: Figure 2 The continuous flat-top ring laser 2 and the pulsed flat-top ring laser 3 are shown. The single-mode continuous flat-top ring laser 2 and the single-mode pulsed flat-top ring laser 3 are respectively made to enter the multi-mode coupled laser nozzle, and the continuous flat-top ring laser 2 is located in the light ring of the pulsed flat-top ring laser 3 to form a multi-mode coupled ring laser. In this embodiment, the left side of the pulsed flat-top ring laser 3 (i.e., the side of region A) is a certain distance away from the continuous flat-top ring laser 2, and the right side of the pulsed flat-top ring laser 3 (i.e., the side of region C) is tangent to the continuous flat-top ring laser 2.

[0037] 3. Additive process

[0038] The multi-mode coupled laser nozzle moves at a certain speed along a preset trajectory. In this embodiment, the moving direction of the multi-mode laser is as follows: Figure 2 As shown. The left side of the pulsed flat-top ring laser 3 preferentially contacts the unprocessed substrate 1 during the initial addition, removing the dirt and oxides remaining on the initial surface of the substrate 1. As the multi-modal laser moves, the surface of the substrate 1 after the oxide film is removed contacts the high-power continuous flat-top ring laser 2. The aluminum alloy wire or powder material for addition is transported to the hollow part of the continuous flat-top ring laser 2. The metal wire or powder material is melted under the action of the continuous flat-top ring laser 2 and forms a molten pool 5 in area B; at the same time, Figure 1The shielding gas shown in the figure is delivered to region B and its vicinity through a multi-modal coupled laser nozzle, forming a protection area near region B to prevent the molten pool 5 from rapid oxidation at high temperature. After the molten pool 5 is formed in region B, as the multi-modal laser moves, the right side of the pulsed flat-top ring laser 3 irradiates into the molten pool 5. Under the action of the pulsed flat-top ring laser 3, violent agitation occurs inside the molten pool 5, causing the dendrites generated during solidification to break, and the dendrite arms after the breakage to form new crystal nuclei, which then grow and finally solidify. In the subsequent additive process, the weld bead formed by solidification is used as a new substrate, and the next additive process is performed above the surface of the formed workpiece 4. The above process is repeated according to a predetermined trajectory, and the additive process of the entire aluminum alloy part is finally completed.

[0039] 4. Strengthening treatment

[0040] Due to the fast solidification speed of the laser additive process, residual tensile stress that is harmful to the performance of the workpiece 4 is easily formed on the surface of the workpiece 4, such as Figure 3 As shown, the area D that has not been strengthened by the pulse flat-top ring laser 3 is a residual tensile stress area. Therefore, in this embodiment, after the additive process is completed, the continuous flat-top ring laser 2 is turned off, and the power of the pulse flat-top ring laser 3 is adjusted, and the multi-mode coupling laser nozzle is controlled to move so that the pulse flat-top ring laser 3 gradually moves to the left. Under the impact of the pulse flat-top ring laser 3, the residual tensile stress on the surface of the workpiece 4 is converted into residual compressive stress, and a residual compressive stress area E is formed that is beneficial to improving the fatigue resistance of the workpiece 4. Finally, the process is repeated to complete the strengthening of the entire workpiece 4.

[0041] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for multi-mode laser coupling additive manufacturing of aluminum alloy, characterized in that: The following steps are involved: (1) using a continuous laser generator to emit a single-mode continuous Gaussian laser, using a laser beam shaping system to shape the single-mode continuous Gaussian laser into a single-mode continuous flat-top laser, and then using an optical element to shape the single-mode continuous flat-top laser into a single-mode continuous flat-top ring laser; (2) using a pulse laser generator to emit a single-mode pulsed Gaussian laser, using a laser beam shaping system to shape the single-mode pulsed Gaussian laser into a single-mode pulsed flat-top laser, and then using an optical element to shape the single-mode pulsed flat-top laser into a single-mode pulsed flat-top ring laser; (3) The single-mode continuous flat-top ring laser and the single-mode pulsed flat-top ring laser are respectively introduced into the multi-mode coupled laser nozzle, and the continuous flat-top ring laser is located within the light ring of the pulsed flat-top ring laser, thereby forming a multi-mode coupled ring laser; (4) Aluminum alloy wire / powder is delivered from the center of the ring of the continuous flat-top ring laser through a wire / powder feeder; (5) The multi-mode coupled laser nozzle moves along a preset trajectory, so that the pulsed flat-top ring laser contacts the substrate first, and then the continuous flat-top ring laser contacts the substrate. The metal wire / powder melts and solidifies to form a weld bead, and the continuous operation finally completes the additive process of the entire part. (6) After the molten pool is completely solidified to form a workpiece, the continuous flat-top ring laser is turned off, the power of the pulsed flat-top ring laser is adjusted, and the surface of the aluminum alloy workpiece is subjected to pulsed laser shock strengthening treatment without re-clamping.

2. The method for multi-modal laser coupling additive manufacturing of aluminum alloy according to claim 1, characterized in that: The single-mode continuous flat-top ring laser is in the shape of a circular ring, and the single-mode pulse flat-top ring laser is in the shape of an elliptical ring.

3. The method for multi-modal laser coupling additive manufacturing of aluminum alloy according to claim 2, characterized in that: The continuous flat-top ring laser is located inside the pulsed flat-top ring laser, the center of the continuous flat-top ring laser is located on the long axis of the pulsed flat-top ring laser and one side of the continuous flat-top ring laser is inscribed with the pulsed flat-top ring laser.

4. The method for manufacturing aluminum alloy by multi-mode laser coupling additive manufacturing according to claim 1, characterized in that: In step (4), a water cooling device is used to cool the laser head while conveying the metal wire / powder, and a protective gas is used to prevent oxidation of the molten pool.

5. The method for multi-modal laser coupling additive manufacturing of aluminum alloy according to claim 1, characterized in that: In step (6), the power of the pulsed flat-top ring laser is adjusted to adjust the peak power density of the pulsed flat-top ring laser acting on the aluminum alloy to 5 GW / cm 2 , the spot diameter is adjusted to 2mm-4mm, so that the aluminum alloy surface reaches 10 7 / s strain rate.

6. The method for multi-mode laser coupling additive manufacturing of aluminum alloy according to claim 1, characterized in that: The method also includes an aluminum alloy substrate processing step, specifically, grinding the surface of the substrate to make it flat and smooth, and then using acetone to clean and remove surface dirt.

7. The method for multi-mode laser coupling additive manufacturing of aluminum alloy according to claim 1, characterized in that: In step (5), the power of the pulsed flat-top ring laser is 0.05 kW to 6 kW, and the power of the continuous flat-top ring laser is 1 kW to 30 kW.

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