Multi-mode laser coupling additive manufacturing method for high-strength and high-toughness wear-resistant layered part

Abstract

The invention belongs to the technical field of additive manufacturing, and particularly relates to a multi-mode laser coupling additive manufacturing method for a high-strength and high-toughness wear-resistant layered part, which comprises the steps of part manufacturing planning, base material pretreatment, multi-mode coupling laser construction, additive manufacturing and the like. Through the laser shaping system and the light path system, the laser light source is shaped into the continuous flat-topped annular laser, the continuous flat-topped annular laser is assisted by the flat-topped pulse laser and the flat-topped oscillation laser for additive manufacturing, the organization structure of a component is homogenized, the nucleation rate in the solidification process is effectively increased, and finally refined crystal grains are obtained; meanwhile, the shape and stress state of the molten pool can be changed, and then the performance of the component is improved. Gradient changes of component components are achieved through cooperative feeding of multiple wires, a workpiece obtains excellent strength, plasticity and toughness, meanwhile, the surface layer of the component is strengthened through a ceramic material, the part obtains extremely high wear resistance, and finally the part with high strength, toughness and wear resistance is obtained.

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. Facilities in these fields often need to work in extreme environments, which puts higher and higher requirements on the performance 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 lamellar structure has been proven to be an effective method of combining 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 with traditional processing methods.

[0003] As an emerging manufacturing technology, additive manufacturing has received widespread attention and research since its advent, especially in the field of difficult-to-process materials and difficult-to-process structures. Additive manufacturing technology is a technology that uses heat sources such as arcs and lasers to melt metal wires / powders and substrates at the same time, and then solidifies to form a predetermined structure. Compared with traditional subtractive manufacturing technologies such as "casting-forging-milling / turning", additive manufacturing technology can easily realize the manufacture of complex material structures and complex geometric parts, and additive manufacturing technology produces almost no waste, which significantly reduces material waste and is in line with my country's green development strategy. Among the many additive manufacturing methods, laser additive manufacturing is widely used due to its high energy density and low thermal impact. Since lasers can process most known materials including metals and ceramics, laser additive manufacturing technology has a very broad application prospect.

[0004] Traditional laser additive manufacturing technology often uses a single-mode Gaussian light source as an energy source, and a single wire or powder as a material source. The functions that can be achieved by a single-mode laser light source are relatively single, and the residual thermal stress caused by rapid solidification has always been a major pain point in the field of additive manufacturing. In addition, a laser light source with Gaussian energy distribution will cause the molten pool to 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 parts present an uneven wavy morphology when overlapping, and after the processing is completed, it is necessary to remove half of the width of the molten pool from the edge of the part, which causes a great waste of materials. In addition to the shortcomings of the light source, the single wire feeding method also weakens the advantage of high flexibility of additive manufacturing, so that the manufactured parts can only be a single material component. From a microscopic point of view, due to the extremely fast solidification speed in the laser additive manufacturing process, it is easy to cause segregation of the organization of the manufactured parts, resulting in uneven performance of the manufactured parts. And due to the directional characteristics of energy, the grains produced in the solidification process are often columnar crystal structures, which are not conducive to the strength and plasticity of the material, and will make the material anisotropic. 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 gradient heterogeneous layered structures, high strength, high plasticity and toughness, and strong wear resistance, we need to invent an advanced additive manufacturing technology that combines 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, comprising the following steps:

[0009] (1) using a continuous laser generator to emit a continuous Gaussian laser, using a laser beam shaping system to shape the continuous Gaussian laser into a continuous flat-top laser, and then using an optical element to shape it into a continuous flat-top ring laser; using two groups of pulsed laser generators to respectively emit a pulsed Gaussian laser and an oscillating Gaussian laser, and using a laser beam shaping system 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) allowing the continuous flat-top ring laser, the oscillating flat-top laser and the pulsed flat-top laser to enter the multi-mode coupling laser nozzle, the oscillating flat-top laser and the pulsed flat-top laser to be located in 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, and under the action of the laser, the substrate and the wire melt simultaneously to form a molten pool; the oscillating flat-top laser irradiates into the molten pool from the rear side of the continuous flat-top ring laser, and under the action of the oscillating flat-top laser, the molten pool changes from a "deep and narrow" morphological feature to a "shallow and wide" morphological feature; the pulsed flat-top laser irradiates into the molten pool on the same side of the oscillating flat-top laser, and 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 will be 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 wire material includes FCC structure wire material, BCC structure wire material, and FCC+BCC structure dual-phase wire material;

[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 cored wire is used when manufacturing the first layer and the last layer of the part, wherein the outer layer of the 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, the step (4) further includes a substrate pretreatment step, specifically, grinding 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 adopts a pulsed flat-top ring laser as the main light source, which can improve the flow performance 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 optical wire feeding technology, and the sensor of the additive manufacturing equipment can directly detect the parameters of the laser and the molten pool, avoiding the interference of the optical wire feeding outside the sensor signal, making the subsequent feedback adjustment more accurate.

[0028] (6) The present invention uses a multi-channel wire feeder for material transportation. Different layers transport wires of different compositions, and the material composition of different layers can be adjusted in situ, thereby greatly improving the efficiency of additive manufacturing. The wires selected are FCC structure wires, BCC structure wires, and FCC+BCC structure dual-phase wires, which take 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-plasticity synergy. There is a BCC+FCC dual-phase structure layer between the BCC structure layer and the FCC structure layer, so that the layered structure components show a gradient change trend, avoiding the interface mismatch problem caused by phase mutation, thereby reducing 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 working condition of multi-mode laser in the additive process in an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of the conventional Gaussian oscillation laser shaping molten pool;

[0033] Figure 4 This is a schematic diagram of the 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, a detailed description is given below in conjunction with 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 comprises 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 7 layers, of which the top layer and the bottom layer are both FCC structure + ceramic composite layer 1; the interior of the part is a metal layer, specifically, FCC structure layer 2 and BCC structure layer 4 are alternately present, and a layer of FCC + BCC dual-phase structure layer 3 is sandwiched between the FCC structure layer 2 and the BCC structure layer 4 to ensure a uniform transition of the physical phase structure. The program of the wire controller is designed according to the structural characteristics of the part and the layered structure to control the coordinated feeding 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 keep the surface of the substrate 5 flat and smooth, and then the roughness of the substrate surface is increased by shot peening to reduce the reflection of the laser on the substrate surface, and finally the surface of the substrate 5 is cleaned with a solvent such as acetone or anhydrous ethanol to remove stains on the substrate surface as much as possible.

[0043] 3. Constructing multi-mode coupled laser

[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, the single-mode pulsed Gaussian laser and the 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 a ring mirror and a conical mirror, it forms a continuous single-mode flat-top laser. Figure 2 The continuous flat-top ring laser 10 shown. 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. The oscillating flat-top laser and the pulsed flat-top laser are located in the halo of the continuous flat-top ring laser and away from the side of the multi-mode coupling laser nozzle to form a multi-mode coupling 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 moving direction of the continuous flat-top ring laser. 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-shaped continuous flat-top laser 10 as auxiliary light sources in a paraxial manner, so as to reduce the complexity of the optical path and the laser head structure as much as possible while realizing the multi-mode laser function.

[0045] 4. Additive Manufacturing

[0046] According to the structural characteristics of the parts, BCC phase metal wire 6, FCC phase metal wire 7, FCC+BCC structure wire 8 and FCC+ceramic phase core wire 9 with appropriate composition are selected. After passing through the collimator, all four wires are passed into the laser ring of the continuous flat-top ring laser 10, and under the action of the controller, multiple wires are fed in a coordinated manner according to the composition required by the parts.

[0047] The multi-mode coupled laser nozzle moves at a certain speed along a preset trajectory, and at the same time, the BCC phase metal wire 6, the FCC phase metal wire 7, the FCC+BCC structure wire 8, and the FCC+ceramic phase core wire 9 are alternately fed downward from the inside of the continuous flat-top ring laser 10 at a specific speed. In this process, the shielding gas is delivered to the continuous flat-top ring laser 10 and its vicinity through the multi-mode coupled laser nozzle, forming a protection area near the continuous flat-top ring laser 10 to prevent the molten pool from rapid oxidation at high temperature.

[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 agitated, so that the coarse columnar crystals 17 at the solid-liquid interface 16 at the solidification front are broken. 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 the figure, under the impact of the pulsed flat-top laser 11, the residual tensile stress on the material surface will be transformed into residual compressive stress that is beneficial to the material performance, 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 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 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) using a continuous laser generator to emit a continuous Gaussian laser, using a laser beam shaping system to shape the continuous Gaussian laser into a continuous flat-top laser, and then using an optical element to shape it into a continuous flat-top ring laser; using two groups of pulsed laser generators to respectively emit a pulsed Gaussian laser and an oscillating Gaussian laser, and using a laser beam shaping system 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) allowing the continuous flat-top ring laser, the oscillating flat-top laser and the pulsed flat-top laser to enter the multi-mode coupling laser nozzle, the oscillating flat-top laser and the pulsed flat-top laser to be located in 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-mode 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 is 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 wires include FCC structure wires, BCC structure wires and FCC+BCC structure dual-phase wires.

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 parts, a cored wire is used. The cored wire is a hollow structure, the outer layer of which is FCC structural metal, and the inner core is 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 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.

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 surface of the substrate is polished to make it flat and smooth, and after polishing, acetone is used to clean and remove surface dirt.

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