A multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts

Abstract

The present invention belongs to the field of additive manufacturing technology, and in particular relates to a multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts, the method comprising steps such as part manufacturing planning, substrate pretreatment, construction of a multi-mode coupled laser, and additive manufacturing. The present invention uses a laser shaping system and an optical path system to shape the laser light source into a continuous flat-top ring laser, and uses a flat-top pulse laser and a flat-top oscillation laser to assist the continuous flat-top ring laser for additive manufacturing, thereby homogenizing the component's structure, effectively improving the nucleation rate of the solidification process, and ultimately obtaining refined grains; at the same time, it can achieve changes in the shape of the molten pool and the stress state, thereby improving the performance of the component. The use of multi-channel wire collaborative feeding to achieve a gradient change in the component composition enables the workpiece to obtain excellent strength and plastic toughness. At the same time, ceramic materials are used to strengthen the surface layer of the component, so that the part obtains extremely strong wear resistance, and ultimately obtains a high-strength, high-toughness, and high-wear-resistant part.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser additive manufacturing, and in particular relates to a multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts. Background Art

[0002] With the development of science and technology in my country, cutting-edge fields such as aerospace and marine vessels have occupied an increasingly important position. The facilities in these fields often need to work in extreme environments, which places increasingly higher demands on the various performances of the equipment used. Among them, the material composition and structure used in the equipment often determine the mechanical properties of the equipment. The two most common material structures in metal materials are the FCC structure with excellent plasticity and the BCC structure with high strength. The method of combining FCC structural materials with BCC structural materials in a layered structure has been proven to be an effective method to combine their excellent plasticity and strength. In addition, the method of surface modification using ceramic materials has also been proven to be able to further improve the service performance of the material. However, these methods all require a gradient change in the material composition of each layer, which is extremely difficult to achieve using traditional processing methods.

[0003] As an emerging manufacturing technology, additive manufacturing has garnered widespread attention and research since its introduction, particularly in the field of difficult-to-machine materials and structures. Additive manufacturing utilizes heat sources such as arcs and lasers to simultaneously melt metal wire / powder and a substrate, which then solidifies to form a predetermined structure. Compared to traditional subtractive manufacturing techniques such as casting, forging, and milling / turning, additive manufacturing can easily manufacture complex material structures and parts with complex geometries. Additive manufacturing also produces virtually no waste, significantly reducing material waste. Among the many additive manufacturing methods, laser additive manufacturing is widely used due to its high energy density and low thermal impact. Because lasers can process most known materials, including metals and ceramics, laser additive manufacturing holds enormous potential for application.

[0004] Traditional laser additive manufacturing (AM) technologies often use a single-mode Gaussian light source as the energy source and a single wire or powder as the material source. Single-mode laser sources offer limited functionality, and the residual thermal stresses caused by rapid solidification have long been a major pain point in AM. Furthermore, laser sources with a Gaussian energy distribution produce a melt pool with a "high center and low ends" morphology. This Gaussian weld bead can easily create an uneven, wavy surface on the overlapped part. After processing, half the width of the melt pool must be removed from the part edge, resulting in significant material waste. In addition to the shortcomings of the light source, the single wire feed method also undermines the flexibility of AM, limiting the production of parts to a single material composition. Microscopically, the extremely rapid solidification rate during laser AM can easily lead to microstructure segregation in the manufactured parts, resulting in uneven performance. Furthermore, due to the directional nature of the energy, the resulting solidification process often produces a columnar grain structure, which compromises the material's strength and plasticity and can also cause anisotropy. These factors have greatly restricted the development and application of laser additive manufacturing technology.

[0005] Therefore, if we want to use additive manufacturing technology to manufacture parts with high strength, high plasticity and toughness and strong wear resistance with a gradient heterogeneous layered structure, we need to invent an advanced additive manufacturing technology with multi-modal laser coupling and multi-wire collaboration. Summary of the Invention

[0006] In response to the technical problem that the strength and plasticity of parts manufactured using existing additive manufacturing technologies are difficult to meet the requirements of special application fields, the present invention proposes an advanced additive manufacturing technology that utilizes multi-modal laser coupling and multi-wire collaboration to produce high-strength, high-toughness and wear-resistant metal-based composite layered parts.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts comprises the following steps:

[0009] (1) A continuous laser generator is used to emit a continuous Gaussian laser, and a laser beam shaping system is used to shape the continuous Gaussian laser into a continuous flat-top laser, which is then shaped into a continuous flat-top ring laser using an optical element; two sets of pulsed laser generators are used to respectively emit a pulsed Gaussian laser and an oscillating Gaussian laser, and a laser beam shaping system is used to shape the pulsed Gaussian laser and the oscillating Gaussian laser into a pulsed flat-top laser and an oscillating flat-top laser, respectively;

[0010] (2) The continuous flat-top ring laser, the oscillating flat-top laser, and the pulsed flat-top laser are all allowed to enter the multi-mode coupling laser nozzle, and the oscillating flat-top laser and the pulsed flat-top laser are located within the light ring of the continuous flat-top ring laser and away from the side of the forward direction of the multi-mode coupling laser nozzle, thereby forming a multi-mode coupling laser;

[0011] (3) Formulate the additive manufacturing path through structural division and path planning, and set the feeding sequence of different wires according to the material composition required for different layers;

[0012] (4) The multi-mode coupled laser nozzle moves at a certain speed along a preset trajectory, and at the same time, multiple wire feeders are used to feed wires of different compositions in each layer from the center of the continuous flat-top ring laser in a feeding order until the entire part is manufactured. In this process, the wire first contacts the continuous flat-top ring laser. Under the action of the laser, the substrate and the wire are melted simultaneously to form a molten pool; the oscillating flat-top laser is irradiated into the molten pool from the rear side of the continuous flat-top ring laser. Under the action of the oscillating flat-top laser, the molten pool changes from a "deep and narrow" morphology to a "shallow and wide" morphology; the pulsed flat-top laser is irradiated into the molten pool on the same side of the oscillating flat-top laser. Under the action of the pulsed flat-top laser, the columnar crystals inside the molten pool are broken to form fine equiaxed grains, and the residual tensile thermal stress generated by the rapid solidification of the laser is converted into residual compressive stress under the action of the pulsed flat-top laser.

[0013] Preferably, the continuous flat-top ring laser is in the shape of a circular ring, and the single-mode pulsed flat-top laser and the single-mode oscillation flat-top laser are located outside the diameter of the moving direction of the continuous flat-top ring laser, serving as auxiliary light sources.

[0014] Preferably, the oscillation mode of the oscillating flat-top laser is figure-8 oscillation.

[0015] Preferably, the filaments include FCC structure filaments, BCC structure filaments, and FCC+BCC structure dual-phase filaments;

[0016] Preferably, in step (4), different layers are conveyed in the order of FCC structure wire, FCC+BCC structure dual-phase wire, BCC structure wire, and FCC+BCC structure dual-phase wire.

[0017] Preferably, a flux-cored wire is used when manufacturing the first and last layers of the part, wherein the outer layer of the flux-cored wire is FCC structural metal and the inner core is ceramic particles.

[0018] Preferably, the pulse energy of the pulse laser is 5-30 mJ, the frequency is 20-500 Hz, and the pulse width is 3-30 ns; the oscillating laser power is 200-2500 W, the oscillation frequency is 50-500 Hz, and the amplitude is 0.5-3 mm; and the continuous laser power is 1000-30000 W.

[0019] Preferably, a water cooling device is used to cool the multi-mode coupled laser nozzle while conveying the wire, and a protective gas is used to prevent oxidation of the molten pool.

[0020] Preferably, the wire feeder includes a collimator to ensure uniform and stable feeding of the wire.

[0021] Preferably, step (4) further includes a substrate pretreatment step, specifically polishing the substrate surface to make it flat and smooth, and then cleaning with acetone to remove surface dirt.

[0022] Compared with the prior art, the advantages and positive effects of the present invention are:

[0023] (1) The present invention uses a pulsed flat-top ring laser as the main light source, which 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.

[0024] (2) The present invention uses a pulsed flat-top laser as an auxiliary light source to irradiate from the rear side of the main light source, acting on the front edge of the solid-liquid interface to break up the dendrite arms generated during the solidification process, thereby increasing the nucleation rate of the solidification process and improving the nucleation efficiency of fine equiaxed crystals.

[0025] (3) The present invention uses a pulsed flat-top laser to effectively change the stress state of the material surface, converting the residual tensile stress generated by rapid solidification into residual compressive stress that is beneficial to improving the life of the material.

[0026] (4) The oscillating flat-top laser used in the present invention can control the shape of the molten pool, so that the "deep and narrow" molten pool morphology is changed to a "wide and shallow" morphology, thereby reducing the impact of remelting on the previous weld.

[0027] (5) The present invention adopts the technology of internal optical wire feeding. The sensor of the additive manufacturing equipment can directly detect the parameters of the laser and the molten pool, avoiding the interference of external optical wire feeding on the sensor signal, making the subsequent feedback adjustment more accurate.

[0028] (6) The present invention uses a multi-channel wire feeder for material transportation, and different layers transport wires of different compositions, which can adjust the material composition of different layers in situ, thereby greatly improving the efficiency of additive manufacturing. The wire materials used are FCC structure wires, BCC structure wires, and FCC+BCC structure two-phase wires, taking into account the high strength characteristics of the BCC structure and the high plasticity advantages of the FCC structure, so that the final parts can achieve good strength and plasticity synergy. There is a BCC+FCC two-phase structure layer between the BCC structure layer and the FCC structure layer, which makes the layered structure composition show a gradient change trend, avoids the interface mismatch problem caused by phase mutation, and thus reduces the probability of material cracking.

[0029] (7) The present invention manufactures a layer of FCC phase + ceramic phase structure on the outermost layer of the part, so that the surface layer of the part can have extremely high wear resistance while retaining strong plasticity and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a process flow chart of the additive manufacturing method of the present invention;

[0031] Figure 2 Schematic diagram of the multi-mode laser working condition in the additive process according to an embodiment of the present invention;

[0032] Figure 3 Schematic diagram of the traditional Gaussian oscillation laser shaping molten pool;

[0033] Figure 4 Schematic diagram of molten pool shaping in an embodiment of the present invention;

[0034] Figure 5 Schematic diagram of the effect of pulsed laser on the solidification front of the molten pool in an embodiment of the present invention;

[0035] Figure 6 Schematic diagram of the effect of pulsed laser on residual stress on the surface of a material in an embodiment of the present invention;

[0036] In the above figures: 1. FCC+ceramic composite layer; 2. FCC structural layer; 3. FCC+BCC structural layer; 4. BCC structural layer; 5. Substrate; 6. BCC phase metal wire; 7. FCC phase metal wire; 8. FCC+BCC structural wire; 9. FCC+ceramic phase cored wire; 10. Annular continuous flat-top laser; 11. Pulsed flat-top laser; 12. Oscillating flat-top laser; 13. Top of molten pool; 14. Bottom of molten pool; 15. Molten pool after shaping; 16. Solid-liquid interface at the solidification front; 17. Columnar crystal; 18. Broken crystal arm; 19. Equiaxed crystal. DETAILED DESCRIPTION

[0037] In order to better understand the present invention, the following is a detailed description with reference to the accompanying drawings and embodiments.

[0038] Example: Figure 1 As shown, a multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts includes the following steps:

[0039] 1. Parts manufacturing planning

[0040] Slice the parts according to their structural features, such as Figure 2As shown, in this embodiment, the part is divided into seven layers, with the outermost and bottommost layers both consisting of an FCC structure + ceramic composite layer 1. The interior of the part comprises metal layers, specifically alternating FCC and BCC layers 2 and 4. A layer of FCC + BCC dual-phase structure 3 is sandwiched between the FCC and BCC layers to ensure a uniform transition between the phases. The wire controller is designed based on the structural characteristics of the part and its layered structure to control the coordinated feed speed of multiple wires.

[0041] 2. Substrate pretreatment

[0042] The substrate 5 carrying the additive part is surface treated. Specifically, the surface of the substrate 5 is polished to make the surface of the substrate 5 flat and smooth. Then, the roughness of the substrate surface is increased by shot blasting to reduce the reflection of the laser on the substrate surface. Finally, the surface of the substrate 5 is cleaned with a solvent such as acetone or anhydrous ethanol to remove as much stain as possible.

[0043] 3. Constructing multi-mode coupled lasers

[0044] The first, second and third laser generators are turned on at the same time to generate single-mode continuous Gaussian laser, single-mode pulsed Gaussian laser and single-mode oscillation Gaussian laser respectively. After being shaped by the laser beam shaping system, the energy of the single-mode continuous Gaussian laser, single-mode pulsed Gaussian laser and single-mode oscillation Gaussian laser is redistributed in space to form continuous single-mode flat-top laser, single-mode pulsed flat-top laser 11 and single-mode oscillation flat-top laser 12. After the continuous flat-top laser passes through the optical path system including optical elements such as the ring mirror and the conical mirror, it forms the following Figure 2 The continuous flat-top ring laser 10 is shown. The continuous flat-top ring laser, oscillating flat-top laser, and pulsed flat-top laser are all introduced into the multi-mode coupled laser nozzle. The oscillating flat-top laser and pulsed flat-top laser are located within the ring of the continuous flat-top ring laser and away from the direction of travel of the multi-mode coupled laser nozzle, forming a multi-mode coupled laser. In this embodiment, the single-mode pulsed flat-top laser and the single-mode oscillating flat-top laser are located outside the diameter of the continuous flat-top ring laser's direction of movement. The single-mode pulsed flat-top laser 11 and the single-mode oscillating flat-top laser 12 are transmitted from the side of the ring continuous flat-top laser 10 as auxiliary light sources in a paraxial manner. This minimizes the complexity of the optical path and laser head structure while achieving multi-mode laser functionality.

[0045] 4. Additive Manufacturing

[0046] Based on the structural characteristics of the part, BCC metal wire 6, FCC metal wire 7, FCC+BCC structure wire 8, and FCC+ceramic cored wire 9 with appropriate compositions are selected. After passing through a collimator, all four wires are fed into the laser ring of a continuous flat-top ring laser 10. A controller coordinates the feeding of these multiple wires according to the desired composition of the part.

[0047] The multi-mode coupled laser nozzle moves at a predetermined speed along a preset trajectory, while BCC metal wire 6, FCC metal wire 7, FCC+BCC structure wire 8, and FCC+ceramic cored wire 9 are alternately fed downward from the interior of a continuous flat-top ring laser 10 at specific speeds. During this process, a shielding gas is delivered to the continuous flat-top ring laser 10 and its vicinity through the multi-mode coupled laser nozzle, forming a protective zone near the continuous flat-top ring laser 10 to prevent rapid oxidation of the molten pool at high temperatures.

[0048] If conventional continuous Gaussian ring laser is used for additive manufacturing, a "deep and narrow" molten pool will be formed after the wire is melted. The molten pool consists of a molten pool bottom 14 and a molten pool top 13. The molten pool bottom 14 is formed after the substrate 5 is partially melted. In this embodiment, due to the influence of the oscillating flat-top laser 12 on the shape of the molten pool, the "deep and narrow" molten pool changes to a "shallow and wide" molten pool, such as Figure 3 As shown. At the same time, due to the reconstruction of the laser energy in the spatial scale, the molten pool morphology is further changed to a square molten pool. The shaped molten pool 15 solidifies in the subsequent additive process to form a new matrix for carrying the next layer of material, as shown Figure 4 shown.

[0049] like Figure 5 As shown, a pulsed flat-top laser 11 is irradiated in the shaped molten pool 15. During the solidification process of the molten pool, the shaped molten pool 15 is violently stirred, thereby breaking the coarse columnar crystals 17 at the solid-liquid interface 16 at the solidification front. The broken crystal arms 18 will serve as new nucleation sites to reduce the nucleation energy of the molten pool and promote the formation of fine equiaxed crystals 19 in the molten pool. Furthermore, due to the violent stirring inside the shaped molten pool 15, the elements and ceramic particles inside the molten pool will be evenly distributed inside the molten pool, which will improve the uniformity of the manufactured parts. Furthermore, due to the fast solidification speed of the laser additive process, residual thermal tensile stress that is harmful to the performance of the workpiece is easily formed on the surface of the workpiece, such as Figure 6 As shown in Figure 1, under the impact of the pulsed flat-top laser 11, the residual tensile stress on the material surface is transformed into residual compressive stress that is beneficial to the material properties, thereby improving the service life of the parts.

[0050] The multi-mode coupled laser head cycles the above process according to a predetermined trajectory, and finally completes the additive process of the entire metal matrix composite laminar part.

[0051] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any person skilled in the art may utilize the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes for application in other fields. However, any simple modification, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts, characterized in that: The following steps are involved: (1) A continuous laser generator is used to emit a continuous Gaussian laser, and a laser beam shaping system is used to shape the continuous Gaussian laser into a continuous flat-top laser, which is then shaped into a continuous flat-top ring laser using an optical element; two sets of pulsed laser generators are used to respectively emit a pulsed Gaussian laser and an oscillating Gaussian laser, and a laser beam shaping system is used to shape the pulsed Gaussian laser and the oscillating Gaussian laser into a pulsed flat-top laser and an oscillating flat-top laser, respectively; (2) The continuous flat-top ring laser, the oscillating flat-top laser, and the pulsed flat-top laser are all allowed to enter the multi-mode coupling laser nozzle, and the oscillating flat-top laser and the pulsed flat-top laser are located within the light ring of the continuous flat-top ring laser and away from the side of the forward direction of the multi-mode coupling laser nozzle, thereby forming a multi-mode coupling laser; (3) Formulate the additive manufacturing path through structural division and path planning, and set the feeding sequence of different wires according to the material composition required for different layers of the part; (4) The multi-modal coupled laser nozzle moves at a certain speed along a preset trajectory, and at the same time, multiple wire feeders deliver wires of different compositions in each layer in a feeding sequence from the center of the continuous flat-top ring laser until the entire part is manufactured.

2. The multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts according to claim 1, characterized in that: The continuous flat-top ring laser is in the shape of a circular ring, and the single-mode pulse flat-top laser and the single-mode oscillation flat-top laser are located outside the diameter of the moving direction of the continuous flat-top ring laser.

3. The multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts according to claim 1, characterized in that: The oscillation mode of the oscillation flat-top laser is figure-8 oscillation.

4. The multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts according to claim 1, characterized in that: The filaments include FCC structure filaments, BCC structure filaments and FCC+BCC structure dual-phase filaments.

5. The multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts according to claim 1, characterized in that: In step (4), different layers are conveyed in the order of FCC structure wire, FCC+BCC structure dual-phase wire, BCC structure wire, and FCC+BCC structure dual-phase wire.

6. The multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts according to claim 4, characterized in that: When manufacturing the first and last layers of the part, a flux-cored wire is used. The flux-cored wire has a hollow structure, an outer layer of FCC structural metal, and an inner core of ceramic particles.

7. The multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts according to claim 1, characterized in that: The pulse energy of the pulse laser is 5-30 mJ, the frequency is 20-500 Hz, and the pulse width is 3-30 ns; the oscillation laser power is 200-2500 W, the oscillation frequency is 50-500 Hz, and the amplitude is 0.5-3 mm; and the continuous laser power is 1000-30000 W.

8. The multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts according to claim 1, characterized in that: While conveying the wire, a water cooling device is used to cool the multi-mode coupled laser nozzle, and a protective gas is used to prevent oxidation of the molten pool.

9. The multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts according to claim 1, characterized in that: The wire feeder includes a collimator.

10. The multi-mode laser coupled additive manufacturing method for high-strength, high-toughness, and wear-resistant layered parts according to claim 1, characterized in that: Before step (4), a substrate treatment step is also included, specifically, the substrate surface is polished to make it flat and smooth, and after polishing, acetone is used to clean and remove surface dirt.

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