Multimode laser coupling method for efficient and high-quality additive manufacturing of metal matrix composites

Abstract

The present invention belongs to the field of laser processing technology, and in particular, relates to a method for multi-mode laser coupling to efficiently and high-quality additively manufacture metal-based composite materials, the method comprising the steps of pre-treatment, substrate pre-treatment, construction of multi-mode coupled laser and additive manufacturing. The present invention uses a high-power pulsed laser as the main laser for energy supply to melt metal-based composite wires, while accelerating the flow of the molten pool, improving the nucleation rate, and realizing the processing of metal-based composite parts by additive manufacturing methods. A continuous laser is used to effectively slow down the cooling rate of the molten pool, greatly reducing the residual tensile stress generated in the component due to the rapid solidification of the molten pool. An oscillating laser is used to improve the molten pool morphology and reduce the number of lateral overlaps. The present invention utilizes multi-mode laser coupling and cooperates with a flat-top laser light source to obtain metal-based composite processing parts with a uniform and smooth surface morphology at the macro level and a stable and uniform organizational structure at the micro level.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser additive manufacturing, and in particular relates to a method for multi-mode laser coupling to efficiently and high-quality additively manufacture metal-based composite materials. Background Art

[0002] Metal matrix composites refer to materials that are artificially combined using metals and their alloys as the load-bearing matrix and reinforcing materials such as ceramics, carbon fibers, and intermetallic compounds as the reinforcing phase, including iron-based composites, titanium-based composites, and aluminum-based composites. Metal matrix composites have been widely studied in recent years because they often have excellent properties such as high specific strength, good wear resistance, strong fatigue resistance, and high fracture toughness. However, since metal matrix composites contain reinforcing phases of different properties, their physical and chemical properties are quite different from those of the metal substrate. Therefore, the traditional manufacturing process of metal matrix composites is often extremely complicated, with a long manufacturing process and high manufacturing costs.

[0003] Different from the traditional machining method of castings, laser additive manufacturing technology has been widely used in recent years due to its unique processing flow. It has significant advantages such as high manufacturing flexibility, simple production process, high manufacturing precision, high processing efficiency, high degree of intelligence, energy saving and environmental protection. It uses higher laser energy density to achieve extremely high energy concentration and can process most of the known high melting point materials (including ceramics, graphite, tungsten carbide, etc.). Therefore, laser additive manufacturing technology is suitable for processing metal-based composite components with complex structures.

[0004] Traditional laser additive manufacturing technology often uses a single-mode continuous Gaussian light source as an energy source. The functions it can achieve are relatively simple, and it is impossible to optimize the process specifically for the components of different properties inside the metal-based composite material. In addition, the energy distribution of the Gaussian laser is concentrated at the center of the spot and gradually weakens around it, which makes the molten pool prone to mountain-like morphological features, and it is easy to make the material have an uneven wavy morphology during the subsequent overlap process. This wavy morphology will cause the surface of the material to be heated unevenly during further processing, further aggravating the inhomogeneity of the material. From a microscopic point of view, due to the extremely fast solidification speed during the laser additive manufacturing process, it is easy to cause segregation of the organization of the manufactured metal-based composite component, resulting in uneven performance of the manufactured parts. In addition, since the density of the strengthening phase is different from that of the molten pool, it is easy to deposit at the bottom of the molten pool or float on the top of the molten pool during the solidification process, which weakens the strengthening effect of the strengthening phase on the component. From the perspective of manufacturing efficiency, since the direction of the laser is perpendicular to the surface of the component, it often causes the molten pool to have a deeper and narrower morphological feature, which causes a large part of the laser input energy to be wasted on the melting matrix, ultimately leading to a decrease in manufacturing efficiency. Therefore, it is necessary to develop a multi-modal laser coupled additive manufacturing technology based on beam shaping technology. Summary of the invention

[0005] In view of the technical problems that traditional laser additive manufacturing technology uses a single-mode Gaussian light source as an energy source to manufacture metal-based composite parts with uneven morphology, low laser energy utilization and component segregation in material organization, the present invention proposes a method for efficient and high-quality additive manufacturing of metal-based composite materials using multi-mode laser coupling and coordinated flat-top laser light source, which can obtain a uniform and flat surface morphology on a macro scale and a stable and uniform metal-based composite material organizational structure on a micro scale.

[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 efficient and high-quality additive manufacturing of metal-based composite materials, 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) using an oscillating laser generator to emit a single-mode oscillating Gaussian laser, and using a laser beam shaping system to shape the single-mode oscillating Gaussian laser into a single-mode oscillating flat-top laser;

[0011] (4) allowing the single-mode continuous flat-top ring laser, the single-mode pulsed flat-top ring laser, and the single-mode oscillation flat-top laser to enter the multi-mode coupled laser nozzle respectively, and the light ring of the pulsed flat-top ring laser is located inside the continuous flat-top ring laser, and the single-mode oscillation flat-top laser is located at the rear of the single-mode continuous flat-top ring laser and the single-mode pulsed flat-top ring laser, so as to form a multi-mode coupled ring laser;

[0012] (5) delivering the metal matrix composite wire from the center of the pulsed flat-top ring laser through a wire feeder;

[0013] (6) The multi-mode coupled laser nozzle moves along a preset trajectory and continuously feeds the metal matrix composite wire at a certain speed. The metal matrix composite wire first contacts with the pulsed flat-top ring laser. After the metal matrix composite wire is melted, a molten pool is formed and contacts and combines with the substrate. Then, the molten pool contacts with the continuous flat-top ring laser for molten pool insulation treatment. Then, the single-mode oscillating flat-top laser contacts with the semi-solidified molten pool and continues to move, so that the originally narrow and deep molten pool becomes a wide and shallow molten pool. After that, the molten pool solidifies to form a weld bead. The multi-mode coupled laser nozzle continues to operate to finally complete the additive manufacturing process of the entire part.

[0014] Preferably, in step (5), a water cooling device is used to cool the laser head while conveying the metal matrix composite material wire, and a protective gas such as argon is used to prevent oxidation of the molten pool.

[0015] Preferably, the method further comprises a substrate processing step, specifically, grinding the surface of the substrate to make it flat and smooth, and then cleaning with acetone to remove surface dirt.

[0016] Preferably, in step (6), the pulse energy of the pulsed flat-top ring laser is 5-30 mJ, the frequency is 20-500 Hz, and the pulse width is 3-30 ns, the power of the continuous flat-top ring laser is 1000-30000 W, and the power of the oscillating flat-top laser is 200-2500 W, the oscillation frequency is 50-500 Hz, and the amplitude is 0.5-3 mm.

[0017] Compared with the prior art, the advantages and positive effects of the present invention are:

[0018] (1) The present invention adopts a high-power pulsed laser as the main energy supply laser, which can melt various substances with different physical and chemical properties in the metal-based composite material, and can process the metal-based composite material through the additive manufacturing method, thereby broadening the application scenarios of the laser additive manufacturing method.

[0019] (2) The present invention uses pulsed laser to accelerate the flow of the molten pool, promote 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. In addition, high-density or low-density strengthening phases can be evenly distributed inside the molten pool under strong stirring, avoiding local enrichment of the strengthening phase.

[0020] (3) The present invention uses a pulsed laser to produce an "explosion" effect at the front of the solid-liquid interface inside the molten pool, effectively breaking up the dendrite arms generated at the solidification front, increasing the number of crystal nuclei during solidification, and increasing the nucleation rate during the solidification process, ultimately obtaining a fine grain structure and excellent mechanical properties.

[0021] (4) The present invention uses continuous laser to effectively slow down the cooling rate of the molten pool, greatly reducing the residual tensile stress generated in the component due to the rapid solidification of the molten pool.

[0022] (5) The present invention uses an oscillating laser to change the molten pool morphology from "narrow and deep" to "wide and shallow", reducing the number of lateral overlaps and allowing more laser energy to act on the melting of the wire rather than the melting of the substrate.

[0023] (6) The multi-mode lasers used in the present invention are all flat-top light sources. During the additive process, the laser energy is evenly distributed, which can form a smooth processing surface and avoid the molten pool surface presenting a Gaussian morphology feature of "high in the middle and low at both ends", thereby avoiding the Gaussian morphology feature from affecting the subsequent additive process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The process flow chart of the method for laser additive manufacturing of metal-based composite materials of the present invention;

[0025] 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;

[0026] Figure 3 A schematic diagram of the shape of the molten pool during the additive manufacturing process in an embodiment of the present invention;

[0027] In the above figures: 1. substrate; 2. solidified material; 3. rear end of molten pool; 4. oscillating flat-top laser; 5. continuous flat-top ring laser; 6. metal matrix composite wire; 7. pulsed flat-top ring laser; 8. front end of molten pool. DETAILED DESCRIPTION

[0028] In order to better understand the present invention, a detailed description is given below in conjunction with the accompanying drawings and embodiments.

[0029] Example: Figure 1 As shown, a method for multi-mode laser coupling efficient and high-quality additive manufacturing of metal matrix composite materials comprises the following steps:

[0030] 1. Pre-treatment

[0031] According to the morphological features of the workpiece to be processed, the slicing plan is carried out and the moving trajectory of the multi-mode coupled laser nozzle is set.

[0032] 2. Substrate pretreatment

[0033] The substrate 1 that supports the additive metal-based composite material part 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, it is cleaned with acetone to remove the dirt on the surface of the substrate 1 as much as possible.

[0034] 3. Constructing multi-mode coupled laser

[0035] The first laser generator, the second laser generator and the third laser generator are turned on at the same time to generate single-mode continuous Gaussian laser, single-mode pulsed Gaussian laser and single-mode oscillating Gaussian laser respectively. After being shaped by the laser beam shaping system, the energy of the single-mode continuous Gaussian laser, the single-mode pulsed Gaussian laser and the single-mode oscillating Gaussian laser is redistributed to form continuous single-mode flat-top laser, single-mode pulsed flat-top laser and single-mode oscillating flat-top laser 4. After the continuous flat-top laser and the pulsed flat-top laser pass through the optical path shaping system including optical elements such as a ring mirror and a conical mirror, they are formed as follows: Figure 2 The continuous flat-top ring laser 5 and the pulsed flat-top ring laser 7 are shown. The single-mode continuous flat-top ring laser 5, the single-mode pulsed flat-top ring laser 7 and the single-mode oscillation flat-top laser 4 are respectively made to enter the multi-mode coupling laser nozzle, and the pulsed flat-top ring laser 7 is located in the light ring of the continuous flat-top ring laser 5, and the single-mode oscillation flat-top laser 4 is located at the rear side of the single-mode continuous flat-top ring laser 5 and the single-mode pulsed flat-top ring laser 7 (i.e., the side opposite to the moving direction of the multi-mode coupling laser nozzle), forming a multi-mode coupling ring laser.

[0036] 4. Additive Manufacturing Process

[0037] 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 Figure 2 The rear end 3 of the middle molten pool points to the direction of the front end 8 of the molten pool. The pulse energy of the controlled pulse flat-top ring laser is 5-30mJ, the frequency is 20-500Hz, and the pulse width is 3-30ns. The power of the continuous flat-top ring laser is 1000-30000W, and the power of the oscillating flat-top laser is 200-2500W, the oscillation frequency is 50-500Hz, and the amplitude is 0.5-3mm.

[0038] The metal matrix composite wire 6 is fed downward from the hollow part of the pulse flat-top ring laser 7 at a certain attack speed, and it contacts the pulse flat-top ring laser 7 before the pulse flat-top ring laser 7. Under the action of the pulse flat-top ring laser 7, the metal matrix composite wire 6 will melt. The remaining energy of the pulse flat-top ring laser 7 contacts the substrate 1, causing the surface of the substrate 1 to partially melt, and combines with the melted liquid metal of the metal matrix composite wire 6 to form a narrow and deep molten pool front end 8. At the same time, Figure 1 The shielding gas shown in the figure is delivered to the front end 8 of the molten pool and its vicinity through a multi-modal coupling laser nozzle, forming a protection area near the front end 8 of the molten pool to prevent the front end 8 of the molten pool from being rapidly oxidized at high temperatures. After the front end 8 of the molten pool is formed, as the multi-modal laser moves, the continuous flat-top ring laser 5 contacts the molten pool, which can deliver a certain amount of heat to the molten pool and reduce the cooling rate of the molten pool to avoid the generation of thermal cracks. As the multi-modal coupling laser nozzle moves, the oscillating flat-top laser 4 contacts the front end 8 of the molten pool. Under the action of the oscillating flat-top laser 4, the front end 8 of the molten pool is violently stirred, so that the dendrites generated during solidification are broken, and the dendrite arms after the break form new crystal nuclei, which grow and finally solidify; in addition, under the action of the violent stirring inside the front end 8 of the molten pool, the elements and strengthening particles inside the molten pool can be evenly distributed in the molten pool. Furthermore, under the action of the oscillating flat-top laser 4, the molten pool morphology becomes wider and shallower, and finally forms Figure 2 as well as Figure 3 The morphology of the rear end 3 of the molten pool. The rear end 3 of the molten pool subsequently solidifies to form a solidified molding material 2, and its surface serves as a new additive receiving surface for the next additive processing. The multi-mode coupled laser nozzle continues to operate according to the predetermined trajectory, looping the above process, and finally completing the additive manufacturing process of the entire metal matrix composite part.

[0039] 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 efficient and high-quality additive manufacturing of metal matrix composite materials, comprising the following steps: (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) using an oscillating laser generator to emit a single-mode oscillating Gaussian laser, and using a laser beam shaping system to shape the single-mode oscillating Gaussian laser into a single-mode oscillating flat-top laser; (4) allowing the single-mode continuous flat-top ring laser, the single-mode pulsed flat-top ring laser, and the single-mode oscillation flat-top laser to enter the multi-mode coupling laser nozzle respectively, and the light ring of the pulsed flat-top ring laser is located inside the continuous flat-top ring laser, and the single-mode oscillation flat-top laser is located behind the single-mode continuous flat-top ring laser and the single-mode pulsed flat-top ring laser, so as to form a multi-mode coupling laser; (5) delivering the metal matrix composite wire from the center of the pulsed flat-top ring laser through a wire feeder; (6) The multi-mode coupled laser nozzle moves along a preset trajectory, continuously delivering metal matrix composite wire. The metal matrix composite wire contacts the pulsed flat-top ring laser to form a molten pool, which contacts and combines with the substrate. The molten pool then contacts the continuous flat-top ring laser for molten pool insulation treatment. After that, the single-mode oscillating flat-top laser contacts the semi-solidified molten pool, turning the originally narrow and deep molten pool into a wide and shallow molten pool. The molten pool then solidifies to form a weld, and the multi-mode coupled laser nozzle continues to move to complete the additive manufacturing of the entire part.

2. The method for high-efficiency and high-quality additive manufacturing of metal-based composite materials by multi-mode laser coupling according to claim 1, characterized in that: In step (5), a water cooling device is used to cool the laser head while conveying the metal matrix composite material wire, and a protective gas is used to prevent oxidation of the molten pool.

3. The method for high-efficiency and high-quality additive manufacturing of metal-based composite materials by multi-mode laser coupling according to claim 1, characterized in that: The method also includes a substrate pretreatment step, specifically, grinding the substrate surface to make it flat and smooth, and then using acetone to clean and remove surface dirt.

4. The method for high-efficiency and high-quality additive manufacturing of metal-based composite materials by multi-mode laser coupling according to claim 1, characterized in that: In step (6), the pulse energy of the pulsed flat-top ring laser is 5-30 mJ, the frequency is 20-500 Hz, and the pulse width is 3-30 ns. The power of the continuous flat-top ring laser is 1000-30000 W. The power of the oscillating flat-top laser is 200-2500 W, the oscillation frequency is 50-500 Hz, and the amplitude is 0.5-3 mm.

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