A method for additive manufacturing of titanium alloys using silk-powder collaborative multimodal laser coupling

Abstract

The present invention belongs to the field of laser processing technology, and in particular relates to a method for additively manufacturing titanium alloys by using silk and powder in a coordinated multi-modal laser coupling method, the method comprising the steps of substrate pretreatment, construction of a multi-modal coupled laser, additive manufacturing, and surface strengthening. The present invention adopts a combination of wire feeding and powder feeding to transport materials, utilizes wire feeding to quickly manufacture structures with larger areas in parts, and utilizes powder materials to manufacture relatively fine structures, and can efficiently and accurately prepare titanium alloy parts. The additive manufacturing step adopts a multi-modal coupled annular laser, wherein the annular flat-top pulse laser can accelerate the flow of the liquid phase at the solidification front, thereby breaking the dendrite arms previously formed by solidification to form new crystal nuclei, and then forming an equiaxed crystal structure, thereby improving the strength and plasticity of the titanium alloy; the annular flat-top pulse laser can accelerate the stirring of the molten pool, increase the rate of heat and mass transfer inside the molten pool, reduce the element segregation phenomenon, and finally obtain a uniform and stable titanium alloy structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser additive manufacturing, and in particular relates to a method for additively manufacturing titanium alloys using silk powder and multi-modal laser coupling. Background Art

[0002] With the development of my country's aerospace industry, aerospace equipment needs to have the characteristics of high performance, long life, high reliability and low cost. Based on this development trend, metal components are required to have good mechanical properties and special functions such as heat protection, heat insulation, vibration reduction, and radiation resistance. Since the 1950s, titanium alloys have developed rapidly as an important structural metal. They are widely used in the aerospace field because of their high strength, excellent corrosion resistance, strong heat resistance and other excellent properties. However, since the structure of titanium alloy components used in the aerospace field is often more complex and titanium alloys themselves are difficult to process, it is difficult to use the traditional casting + machining method to efficiently and accurately prepare titanium alloy components that meet the design requirements.

[0003] Since its inception, additive manufacturing (AM) technology has attracted considerable attention for its efficiency and cost-effectiveness. Distinct from traditional subtractive machining methods involving material removal through cutting, the core concept of AM is to gradually build the desired three-dimensional part by stacking or adding material layer by layer. This process, simplified as "addition rather than removal," is applicable to the manufacture of complex titanium alloy components. There are two common feeding methods for AM: wire feeding and powder feeding. Wire feeding achieves near-100% wire utilization during the printing process, minimizing material waste. Wire is generally more economical than powder. Furthermore, wire feeding allows for continuous production, enabling uninterrupted production. However, because wire machining accuracy is affected by wire diameter, extremely thin sections of some parts are difficult to machine using wire feeding. Powder machining accuracy can be adjusted by adjusting the laser spot diameter. Furthermore, metal powders have a high laser energy absorption rate and excellent formability, making powder feeding a viable method for AM of extremely thin sections. Furthermore, powder feeding offers flexibility, facilitating the adjustment of powder composition and content. The additive manufacturing equipment in the existing technology can only adopt a single feeding method, which makes it difficult to efficiently and accurately process titanium alloy components with complex structures.

[0004] In addition to material feeding methods, additive manufacturing utilizes various heating energy sources, with arc and laser being common. Compared to arc AM, laser AM offers advantages such as a smaller heat-affected zone and higher precision, leading to its widespread research and application. Traditional laser AM techniques often utilize a single-mode Gaussian laser as the energy source. The resulting molten pool exhibits a "pointed ends and bulged center" morphology, which results in uneven heating of the previously solidified weld bead during subsequent processing. Furthermore, during the subsequent overlap process, this morphology creates a distinct curved overlap zone. The microstructure of this overlap zone differs from that of the non-overlap zone, leading to uneven performance in the final machined part. Furthermore, due to the extremely rapid solidification rate during laser AM, a high level of residual tensile stress often remains on the surface of the manufactured part, which can lead to cracking and hinder mechanical and fatigue performance. Summary of the Invention

[0005] In response to the technical problem that existing additive manufacturing technologies are difficult to efficiently and accurately process titanium alloy components with complex structures, the present invention proposes a method for additively manufacturing titanium alloys using silk powder and multimodal laser coupling, which can efficiently and accurately prepare titanium alloy components with complex structures that have uniform structure and good performance.

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

[0007] A method for additively manufacturing titanium alloy using silk powder and multimodal laser coupling, comprising the following steps:

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

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

[0011] (4) A wire feeder and a powder feeder are provided at the same time, and the titanium alloy wire is fed to the multi-mode coupled laser nozzle through the wire feeder, and the titanium alloy powder is fed to the multi-mode coupled laser nozzle through the powder feeder;

[0012] (5) Structural division and path planning are performed based on the structural characteristics of the parts. The multi-modal coupled laser nozzle runs along the predetermined trajectory. During operation, the controller switches and controls the opening and closing of the conveying channels of the wire feeder and the powder feeder. Wire feeders or powder feeders are selectively used for raw material delivery according to the different structural parts of the titanium alloy parts. When printing the larger area of ​​the parts, the wire feeder is used to deliver the wire material to achieve efficient additive manufacturing. When printing the small and delicate parts, the powder feeder is used to deliver the powder material to achieve high-precision additive manufacturing. The additive manufacturing process of the titanium alloy parts is completed by continuous operation.

[0013] Preferably, the powder material and the wire material are both input from the hollow part of a single-mode pulse flat-top ring laser.

[0014] Preferably, in step (5), the power of the pulsed flat-top ring laser is 0.05-2 kW, and the power of the continuous flat-top ring laser is 2-10 kW.

[0015] Preferably, in step (5), a water cooling device is used to cool the multi-mode coupled laser nozzle, and a protective gas is introduced to prevent the flying powder from sticking to the laser nozzle and to prevent the molten pool from oxidizing.

[0016] Preferably, when conveying the powder in step (5), a powder feeding protective gas is introduced at the outlet of the powder feeder to ensure continuous and uniform conveying of the powder.

[0017] Preferably, the wire feeder includes a collimator, which ensures the continuity and stability of wire feeding.

[0018] Preferably, the optical element includes a toroidal mirror and a conical mirror.

[0019] Preferably, the method further includes a substrate pretreatment step, specifically, polishing the surface of the titanium alloy substrate to be flat and smooth, then performing shot peening to increase the roughness and thereby reduce the reflection loss of the laser, and finally using acetone cleaning to remove surface dirt.

[0020] Preferably, in step (5), the substrate is heated to 400° C. and kept at this temperature until the additive process is completed.

[0021] Preferably, step (5) includes a surface strengthening step, that is, when processing the final surface portion of the part, a powder feeder is used to deliver strengthening powder material, and the content of strengthening elements is added or increased in the strengthening powder material. Thereafter, the continuous flat-top ring laser is turned off, and the surface of the material is impact strengthened using a pulsed flat-top ring laser.

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

[0023] (1) The present invention adopts a combination of wire feeding and powder feeding to transport materials, which can combine the advantages of high efficiency and high utilization of wire feeding to quickly manufacture large-area structures in parts, and combine the advantages of high precision of powder feeding to perform high-precision manufacturing of relatively fine structures of parts.

[0024] (2) The annular flat-top pulse laser used in the present invention can accelerate the flow of the liquid phase at the solidification front when the titanium alloy solidifies, thereby breaking the dendrite arms formed by the previous solidification, thereby forming new crystal nuclei, which then grow into fine equiaxed crystal structures, ultimately improving the strength and plasticity of the titanium alloy.

[0025] (3) The annular flat-top pulse laser used in the present invention can accelerate the stirring of the molten pool, increase the rate of heat and mass transfer inside the molten pool, reduce the segregation of elements caused by rapid solidification, and ultimately obtain a uniform and stable titanium alloy structure.

[0026] (4) After the additive manufacturing process is completed, the surface of the material is impact strengthened by a circular flat-top pulse laser to regulate the residual stress state of the material surface, and the residual tensile stress generated by rapid solidification is converted into residual compressive stress to resist the formation of microcracks, thereby improving the fatigue resistance of the material.

[0027] (5) The annular continuous laser and annular pulsed laser used in the present invention are both processed by a beam shaping process to form a flat-top laser light source. During the additive process, the molten pool is affected by the laser energy distribution and exhibits a rectangular morphology, avoiding the problems of uneven heating and uneven microstructure caused by Gaussian welds.

[0028] (6) The present invention can use additional strengthening elements added to the powder material to achieve a gradient change in the component composition, and ultimately obtain a titanium alloy component that is "hard on the outside and tough on the inside". Moreover, due to the gradient change in the concentration of the strengthening elements, there is no problem of a fragile interface due to a sudden change in performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a process flow chart of the method for laser-coupled additive manufacturing of titanium alloys according to the present invention;

[0030] Figure 2 Schematic diagram of the structure of a titanium alloy impeller manufactured in an embodiment of the present invention;

[0031] Figure 3 Schematic diagram of a titanium alloy impeller main body manufactured by using a wire feeder to feed wire in an embodiment of the present invention;

[0032] Figure 4Schematic diagram of using a powder feeder to transport powder material to manufacture titanium alloy impeller blades in an embodiment of the present invention;

[0033] In the above figures: 1. Impeller body; 2. Impeller blades; 3. Titanium alloy substrate; 4. Continuous flat-top ring laser; 5. Pulsed flat-top ring laser; 6. Titanium alloy wire; 7. Titanium alloy powder. DETAILED DESCRIPTION

[0034] In order to better understand the present invention, the following is a detailed description with reference to the accompanying drawings and embodiments.

[0035] Example: Figure 1 As shown, a method for additively manufacturing titanium alloy using silk powder and multi-modal laser coupling includes the following steps:

[0036] 1. Program settings

[0037] According to Figure 2 The structural characteristics of the titanium alloy impeller shown are used to perform typical structural division and additive path planning, and the set program is input into the controller.

[0038] 2. Substrate pretreatment

[0039] The titanium alloy substrate, which supports the additively manufactured titanium alloy impeller, undergoes surface treatment. Specifically, the surface of the titanium alloy substrate 3 is polished to maintain a smooth and flat surface. Shot peening is then used to increase the surface roughness and maximize the laser's absorption rate. After shot peening, the surface is cleaned with acetone to remove as much dirt as possible. The titanium alloy substrate 3 is then preheated to 400°C on a heating device and maintained at this temperature until the process is complete.

[0040] 3. Constructing multi-mode coupled lasers

[0041] The first laser generator is turned on to emit a single-mode continuous Gaussian laser. After beam shaping, the light source energy is reconstructed in the spatial scale to form a single-mode continuous flat-top laser. The single-mode continuous flat-top laser passes through the optical path system containing optical elements such as a ring mirror and a conical mirror to form a Figure 3 The continuous flat-top ring laser 4 is shown.

[0042] The second laser generator is turned on to emit a single-mode pulsed Gaussian laser. After beam shaping, the light source energy is reconstructed in the spatial scale to form a single-mode pulsed flat-top laser. The single-mode pulsed flat-top laser passes through the optical path system containing optical elements such as a ring mirror and a conical mirror to form a Figure 3 The pulsed flat-top ring laser 5 is shown.

[0043] A single-mode continuous flat-top ring laser 4 and a single-mode pulsed flat-top ring laser 5 simultaneously enter the multi-mode coupled laser nozzle, forming a multi-mode coupled laser. The pulsed flat-top ring laser 5 is located within the continuous flat-top ring laser 4. In this embodiment, the ring diameter of the continuous flat-top ring laser 4 is smaller than that of the pulsed flat-top ring laser 5, and the two rings are concentric.

[0044] 4. Additive Manufacturing

[0045] like Figure 2 As shown, the impeller body 1 is a relatively simple component, manufactured efficiently using wire-feed additive manufacturing. The multi-modal coupled laser nozzle moves at a predetermined speed along a preset trajectory. The wire feeder controls the titanium alloy wire 6 to be fed to the center of the multi-modal coupled laser nozzle at a predetermined speed, where it is conveyed under the control of a controller. During this process, circulating cooling water is introduced into the multi-modal coupled laser nozzle through a water-cooling device to cool the device. A shielding gas is also introduced to prevent flying powder from adhering to the laser nozzle. The shielding gas also prevents oxidation of the molten pool.

[0046] Under the action of the continuous flat-top ring laser 4 and the single-mode pulsed flat-top ring laser 5, the titanium alloy wire 6 is completely melted and combined with the titanium alloy substrate 3 to form a molten pool. Once the molten pool is formed, the pulsed flat-top ring laser 5 located in the inner ring accelerates the flow of the molten pool, promoting the diffusion of elements within the molten pool. Furthermore, the pulsed flat-top ring laser 5 impacts the dendrites forming at the solidification front, breaking the dendrite arms and forming new nuclei. This in turn increases the nucleation rate and enhances the strength of the impeller body 1.

[0047] After the impeller body 1 is manufactured, the impeller body 1 is used as a new load-bearing additive matrix, and the impeller blades 2 are additively manufactured on its side, such as Figure 3 As shown in the figure, the impeller blades 2 are a more complex component, manufactured with high precision using powder-feed additive manufacturing. A multi-modal coupled laser nozzle moves at a predetermined speed along a pre-set trajectory. A powder feeder controls the titanium alloy powder 7, which is fed to the center of the multi-modal coupled laser nozzle at a predetermined speed and conveyed under the control of a controller. During this process, a protective powder feeding gas is introduced, surrounding the output metal powder to ensure continuous and uniform powder delivery.

[0048] As the titanium alloy powder 7 falls, it interacts with the continuous flat-top ring laser 4 and the single-mode pulsed flat-top ring laser 5, forming small molten droplets that combine with the impeller body 1 to form a molten pool. Once the molten pool is formed, the pulsed flat-top ring laser 5 located in the inner ring accelerates the flow of the molten pool, promoting the diffusion of elements within the molten pool. Furthermore, the pulsed flat-top ring laser 5 impacts the dendrites forming at the solidification front, breaking the dendrite arms and forming new nuclei. This increases the nucleation rate and enhances the strength of the impeller blades 2.

[0049] 5. Surface strengthening

[0050] Since the surface of a part is often the most likely source of cracks, the titanium alloy composition used on the surface of the part is different from that inside. When the part is processed to the final surface, the controller adjusts the content of strengthening elements in the titanium alloy powder fed into the multi-modal coupled laser nozzle, and feeds a powder material with gradually increasing amounts of strengthening elements until the surface of the part is processed. Due to the extremely fast cooling rate of the laser additive manufacturing process, residual tensile stress is easily formed on the surface of the part. Therefore, after processing is completed, the continuous flat-top ring laser 4 is turned off, and the pulsed flat-top ring laser 5 is used to impact strengthen the surface of the material, converting the residual tensile stress into residual compressive stress that helps resist crack formation. Finally, the process is repeated to complete the strengthening of the entire 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 method for additive manufacturing of titanium alloy using silk powder and multimodal laser coupling, characterized in that: The following steps are involved: (1) Using a continuous laser generator to emit a single-mode continuous Gaussian laser, a laser beam shaping system is used to shape the single-mode continuous Gaussian laser into a single-mode continuous flat-top laser, and then an optical element reconstructs 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 reconstruct the single-mode pulsed flat-top laser into a single-mode pulsed flat-top ring laser; (3) allowing the single-mode continuous flat-top ring laser and the single-mode pulsed flat-top ring laser to enter the multi-mode coupled laser nozzle respectively, and the single-mode pulsed flat-top ring laser is located within the light ring of the single-mode continuous flat-top ring laser, thereby forming a multi-mode coupled ring laser; (4) Setting a wire feeder and a powder feeder to deliver titanium alloy wire or powder to the multi-mode coupled laser nozzle; (5) The multi-mode coupled laser nozzle runs along a predetermined trajectory. During operation, the opening and closing of the conveying channels of the wire feeder and the powder feeder are controlled by switching the controller. When printing a larger area of ​​a component, the wire feeder is used to convey the wire material, and when printing a smaller area, the powder feeder is used to convey the powder material. The continuous operation completes the additive manufacturing process of the titanium alloy parts.

2. The method for additive manufacturing of titanium alloy using silk powder and multimodal laser coupling according to claim 1, characterized in that: The powder material and the wire material are both input from the hollow part of a single-mode pulse flat-top ring laser.

3. The method for additive manufacturing of titanium alloy using silk powder and multimodal laser coupling according to claim 1, characterized in that: In step (5), the power of the pulsed flat-top ring laser is 0.05-2kW, and the power of the continuous flat-top ring laser is 2-10kW.

4. The method for additive manufacturing of titanium alloy using silk powder and multimodal laser coupling according to claim 1, characterized in that: In step (5), a water cooling device is used to cool the multi-mode coupled laser nozzle, and a protective gas is introduced to prevent the flying powder from sticking to the laser nozzle and to prevent the molten pool from oxidizing.

5. The method for additive manufacturing of titanium alloy using silk powder and multimodal laser coupling according to claim 1, characterized in that: When conveying the powder in step (5), a powder feeding protective gas is introduced at the outlet of the powder feeder to ensure continuous and uniform conveying of the powder.

6. The method for additive manufacturing of titanium alloy using silk powder and multimodal laser coupling according to claim 1, characterized in that: The wire feeder includes a collimator.

7. The method for additive manufacturing of titanium alloy using silk powder and multimodal laser coupling according to claim 1, characterized in that: The optical elements include a toroidal mirror and a conical mirror.

8. The method for additive manufacturing of titanium alloy using silk powder and multimodal laser coupling according to claim 1, characterized in that: The process also includes a substrate pretreatment step, specifically grinding the surface of the titanium alloy substrate to be flat and smooth, followed by shot blasting to increase the roughness, and finally using acetone cleaning to remove surface dirt.

9. The method for additive manufacturing of titanium alloy using silk powder and multimodal laser coupling according to claim 1, characterized in that: In step (5), the substrate is heated to 400° C. and kept at this temperature until the additive process is completed.

10. The method for additive manufacturing of titanium alloy using silk powder and multi-modal laser coupling according to claim 1, characterized in that: The step (5) includes a surface strengthening step, that is, when processing the final surface portion of the part, a powder feeder is used to deliver strengthening powder material, and the content of strengthening elements is added or increased in the strengthening powder material. Thereafter, the continuous flat-top ring laser is turned off, and the surface of the material is impact strengthened using a pulsed flat-top ring laser.

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