Multi-laser composite scanning strategy and powder bed fusion forming method

Abstract

The invention relates to a multi-laser composite scanning strategy and a powder bed fusion forming method, and the multi-laser composite scanning strategy comprises the steps that Gaussian laser and Donout laser are used for double-laser scanning, and the Gaussian laser adopts an island scanning strategy; in each island, the Donut laser performs scanning in a mode of being perpendicular to the Gaussian laser and executes a short strip width scanning strategy; according to the double-laser scanning method, in an island, the Gaussian laser and the Donut laser start scanning at the same time and end scanning at the same time; after scanning of one island is completed, jumping to the next island and carrying out double-laser scanning again until all islands are scanned; the problems that in the LPBF forming technology, a large-area test piece is prone to warping and cracking, and hole-inclusion dilemma exists in the in-situ alloying process are effectively solved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of metal additive manufacturing, and in particular to laser powder bed fusion (LPBF) technology. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] Laser powder bed fusion (LPBF) forming technology is currently in its infancy, so it is very difficult to obtain high-quality pre-alloyed powders suitable for printing. To solve this problem, some research has turned to in-situ alloying methods to meet the needs of new alloys, which involves the processing of powder mixtures. However, in-situ alloying methods also have disadvantages, such as some component powders may evaporate excessively and cause failure, and some powder particles may not be completely melted due to their high melting points. In the high-speed thermal cycle of LPBF, especially when the input volume energy density is low, resulting in rapid cooling and insufficient element diffusion time, micro-analysis of elements may occur, which easily leads to the formation of inclusions in the final product. If the input volume energy density is high to improve the dissolution of alloying element particles in order to solve this problem, the temperature and pressure in the molten pool will increase due to the increase in energy density, resulting in more intense evaporation and vaporization of the material, which will inevitably produce pores after solidification. The above problems are the dilemma of pores-inclusions in the in-situ alloying process.

[0004] In addition, for specimens with larger areas, thermal stress problems are easily generated due to rapid cooling during the high-speed thermal cycle of LPBF, leading to warping and cracking.

[0005] At the same time, in traditional methods, LPBF uses a highly concentrated laser profile (Gaussian profile), which creates a small molten pool that cools rapidly, thereby limiting the diffusion of alloying elements; the highly concentrated Gaussian laser profile is also very likely to lead to a high aspect ratio molten pool, causing the formation of porosity and other problems.

[0006] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may contain information that does not constitute prior art. Summary of the invention

[0007] In view of this, the present disclosure provides a multi-laser composite scanning strategy and a powder bed fusion molding method to solve the problems of pore-inclusion dilemma during in-situ alloying and the problem of warping and cracking of large-area specimens in LPBF molding technology.

[0008] The inventive concept of the disclosed multi-laser composite scanning strategy is: Firstly, a high-power Gaussian laser is used in combination with a Donut laser for profile optimization, and then island scanning and fast short strip width scanning strategy (SSWSS) are combined to form a multi-laser composite scanning strategy (MLCSS). The interaction of the scanning trajectories of the two lasers produces a molten pool with a low aspect ratio and large geometric size. At the same time, the movement of the molten pool is slow, which solves the problem of inclusions that fail to diffuse due to rapid cooling. Then, through laser profile optimization, the Donut laser has low central energy and less metal evaporation, which effectively reduces the evaporation of the molten pool by high-power laser, solves the porosity problem caused by rapid evaporation, and effectively solves the dilemma of porosity and inclusions, significantly improving the uniformity of in-situ alloyed parts.

[0009] Secondly, by dividing the entire scanning area into multiple small areas (islands), each island is scanned separately, which significantly reduces thermal stress and prevents warping and cracking of large-area parts. Gaussian laser and Donut laser are used in combination, and Gaussian laser is used to perform linear scanning inside each island to quickly form the required molten pool, and then Donut laser is used for SSWSS scanning to provide uniform power input, promote interaction between scanning tracks, form a larger molten pool with low aspect ratio, and significantly improve the molding quality of parts.

[0010] Based on the technical concept of the present invention, in order to achieve the above-mentioned invention object, in the first aspect, the multi-laser composite scanning strategy includes: Dual laser scanning is performed using a Gaussian laser and a Donut laser, wherein the Gaussian laser adopts an island scanning strategy; within each island, the Donut laser scans perpendicularly to the Gaussian laser and performs a short-strip width scanning strategy; The dual laser scanning method is that within an island, the Gaussian laser and the Donut laser start scanning and end scanning at the same time; after completing the scanning of one island, jump to the next island and perform the dual laser scanning again until all islands are completely scanned.

[0011] In the present disclosure and possible embodiments, the scanning paths of the Gaussian lasers are perpendicular to each other in the scanning directions of adjacent subareas.

[0012] In the present disclosure and possible embodiments, the Gaussian laser takes twice the spot diameter as the distance between scanning paths.

[0013] In the present disclosure and possible embodiments, the Donut laser power is 5% to 10% higher than the Gaussian laser power.

[0014] In the present disclosure and possible embodiments, the Gaussian laser scanning speed is greater than 300 mm / s.

[0015] In the present disclosure and possible embodiments, the size of the island is 5 mm×5 mm.

[0016] In a second aspect, the powder bed fusion molding method comprises: The multi-laser composite scanning strategy described in the first aspect is adopted for 3D printing.

[0017] In the present disclosure and possible embodiments, the raw material for 3D printing is additive manufacturing alloy powder.

[0018] In the present disclosure and possible embodiments, the additive manufacturing alloy powder includes but is not limited to iron-based powder, titanium-based powder, aluminum-based powder, nickel-based powder and magnesium-based powder; and / or, Before the 3D printing is performed, the additive manufacturing alloy powder is dried and the substrate is preheated.

[0019] In the present disclosure and possible embodiments, the 3D printing is performed under the protection of a protective gas.

[0020] The present invention has the beneficial effects: The multi-laser composite scanning strategy (MLCSS) disclosed in the present invention adopts the profile optimization of high-power Gaussian laser and Donut laser, combined with the strategy optimization of island scanning composite fast short strip width scanning strategy (SSWSS), so that the uniformity and forming quality of the in-situ alloyed parts are significantly improved through four means of block processing, low aspect ratio molten pool, laser profile optimization, and scanning trajectory interaction during the forming process, while effectively solving the porosity-inclusion dilemma and avoiding the problem of excessive thermal stress such as warping and cracking of large-area parts; in addition, through high-power laser and high scanning speed, the production efficiency is significantly improved and the production delivery time is shortened. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings herein are incorporated into the specification and constitute a part of the specification. These drawings illustrate embodiments consistent with the present disclosure and are used to illustrate the technical solutions of the present disclosure together with the specification.

[0022] FIG1 shows various laser scanning strategies, wherein (a), (b), (c), and (d) respectively show conventional scanning strategy, conventional island scanning strategy, conventional SSWSS scanning strategy, and island composite SSWSS scanning strategy; Figure 2 (a) and Figure 2 (b) are snapshots of the simulated temperature profiles of the melt pool evolution in a single layer during the laser scanning process, where Figure 2 (a) represents the conventional scanning method and Figure 2 (b) represents the MLCSS scanning method; Figure 3Schematic diagram of single track and single strip scanning when performing the island composite SSWSS scanning strategy; the black arrows indicate the laser scanning path and direction associated with each scanning type. DETAILED DESCRIPTION

[0023] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts that are not described in detail, those skilled in the art can also fully understand the present disclosure.

[0024] At the same time, unless the context clearly requires otherwise, the words "include", "comprises" and similar words throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0025] In order to solve the various problems of the current laser powder bed fusion forming (LPBF) technology described in the background technology, the present disclosure provides a multi-laser composite scanning strategy (MLCSS), which improves the forming quality and efficiency of the laser powder bed fusion forming (LPBF) technology through the following aspects: First, a high-power Gaussian laser is used in conjunction with a Donut laser for profile optimization, combined with island scanning and fast short strip width scanning strategy (SSWSS). The interaction of the scanning trajectories of the two lasers produces a molten pool with a low aspect ratio and large geometric dimensions, while making the molten pool move more slowly, solving the problem of inclusions that fail to diffuse due to rapid cooling. Then, through laser profile optimization, the Donut laser has lower central energy and less metal evaporation, which effectively reduces the evaporation of the molten pool by the high-power laser, solves the porosity problem caused by rapid evaporation, and thus effectively solves the dilemma of porosity and inclusions, significantly improving the uniformity of in-situ alloyed parts.

[0026] Secondly, by dividing the entire scanning area into multiple small areas (islands), each island is scanned separately, which significantly reduces thermal stress and prevents warping and cracking of large-area parts. Gaussian laser and Donut laser are used in combination, and Gaussian laser is used to perform linear scanning inside each island to quickly form the required molten pool, and then Donut laser is used for SSWSS scanning to provide uniform power input, promote interaction between scanning tracks, form a larger molten pool with low aspect ratio, and significantly improve the molding quality of parts.

[0027] Thirdly, high laser scanning speed and power input are used to ensure that the time between adjacent single-track scans is short enough to achieve interaction between adjacent single-track molten pools, while increasing the construction rate of components and shortening production lead time.

[0028] Specifically, the present invention discloses a laser powder bed fusion (LPBF) technology based on a multi-laser composite scanning strategy, which specifically includes the following steps: S10: Preparation of alloy powder The method disclosed herein is not limited to a specific alloy powder, but is applicable to all types of alloy powders commonly used in additive manufacturing, including but not limited to iron-based powder, titanium-based powder, aluminum-based powder, nickel-based powder, and magnesium-based powder. In order to remove moisture and other possible volatile impurities in the powder and ensure the fluidity of the powder and the stability of the powder during the printing process, vacuum drying is preferably performed at 80°C for 8 hours before additive manufacturing.

[0029] S20: Configuration of printing equipment The disclosed method requires the use of a dual-laser 3D printer equipped with a Gaussian laser head and a Donut laser head. The printing chamber is filled with pure argon as a protective gas to prevent oxidation of the alloy material during high-temperature printing. In order to reduce thermal stress and deformation of the material during printing, the substrate is preferably preheated to 70°C~100°C. The specific substrate temperature depends on the selected alloy powder. Because different alloy powders require different printing temperatures, different substrate temperatures need to be selected to avoid an increase in thermal stress.

[0030] S30: Determination of printing parameters (1) Laser parameters: Preferably, in the method disclosed herein, the power setting range of the Gaussian laser is 70 W to 1000 W, which mainly depends on the type of alloy powder selected. For example, the laser power of titanium-based powder can be set at 500 W or above, but the power of magnesium-based powder should generally be less than 100 W.

[0031] The power of the donut laser should be slightly greater than that of the Gaussian laser because the movement speed of the donut laser head is faster than that of the Gaussian laser. It can be increased by 5% to 10% based on the power of the Gaussian laser. The specific laser power value can be selected as long as it can ensure the interaction between the trajectories, generate a relatively large and slow-moving molten pool with low thermal stress and low aspect ratio geometry, and no obvious defects are generated during scanning.

[0032] (2) Laser scanning speed: Preferably, in the method disclosed herein, the Gaussian laser scanning speed is greater than 300 mm / s, and the specific speed depends on the morphology of the molten pool and the maximum moving speed of the Donut laser head of the selected printer.

[0033] The scanning speed of the donut laser depends on the scanning speed of the Gaussian laser. It is required that the scanning speed of the donut laser can follow the moving speed of the Gaussian laser when adopting the SSWSS scanning strategy to keep the two lasers working together.

[0034] (3) Powder coating thickness and angle: Preferably, in the method disclosed herein, the thickness of each layer of powder is set to 0.02 millimeters (mm).

[0035] The scanning direction is preferably rotated 67° between every two adjacent layers to optimize the structural strength of the component and effectively reduce the material anisotropy caused by the printing direction.

[0036] S40: 3D Printing (1) Division of scanning area: Preferably, in the method disclosed herein, the scanning area is divided into a plurality of small areas (islands) of 5 mm×5 mm, and then each partition is scanned separately.

[0037] (2) Scanning within the island: Figure 1 shows the four scanning strategies, namely, conventional scanning strategy, island scanning strategy, SSWSS scanning strategy and island composite SSWSS, through (a), (b), (c) and (d), respectively.

[0038] The disclosed method adopts the island composite SSWSS scanning strategy of FIG. 1 (d), specifically, the Gaussian laser and the Donut laser start scanning at the same time, wherein the scanning strategy of the Gaussian laser is to perform parallel line scanning in each partition, and preferably the scanning directions of adjacent partitions are perpendicular to each other. Figure 3 As shown: During the specific scanning, in each island, the Gaussian laser scans in a straight line scanning manner. Each scanning path goes from one end of the island to the other end, moving in the same direction. The distance between the two scanning paths depends on the diameter of the laser spot. Usually, twice the spot diameter is taken as the distance between the scanning paths.

[0039] The Donut laser performs reciprocating scanning according to the SSWSS scanning strategy. Specifically, it starts scanning the track along the scanning direction perpendicular to the Gaussian laser. After scanning the first track, it moves a distance twice the spot diameter to scan the second track in the opposite direction.

[0040] (3) Scan the entire area After completing the scanning of one island according to the island composite SSWSS scanning strategy, jump to the next island and repeat the above island scanning process until all islands in the entire area are scanned.

[0041] S50: Post-printing processing The molded parts are subjected to stress relief annealing, excess powder and support structures are removed, and grinding and polishing are performed.

[0042] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples. In the disclosed embodiments, the specific process of in-situ alloying of Al-Mg-Si-Ni alloy by the powder bed fusion forming method based on the multi-laser composite scanning strategy MLCSS of the present invention is as follows: 1. Alloy material preparation The Al-Mg-Si-Ni alloy of the disclosed embodiment has a composition ratio of 5.0% Mg, 2.2% Si, 1.7% Ni, and the balance is Al. Alloy powder with a particle size of 15-53 microns (μm) and a median particle size of about 28 microns is selected to meet the needs of fine printing. At the same time, the metal powder is dried, specifically vacuum dried at 80°C for 8 hours, in order to remove moisture and other possible volatile impurities in the powder to ensure the fluidity of the powder and stability during the printing process.

[0043] 2. Printing device configuration In the disclosed embodiment, a dual laser 3D printer equipped with laser powder bed fusion (LPBF) technology is used, and a Gaussian laser head and a Donut profile laser head are also used. The printing chamber is filled with pure argon gas, which is used as a protective gas to prevent oxidation of the alloy material during high-temperature printing. The substrate is preheated to 70°C, which helps to reduce thermal stress and deformation of the material during printing and optimize the structural integrity of the printed product.

[0044] 3. Printing parameter settings 1. Laser parameters: The Gaussian laser power was set to 350 watts (W).

[0045] The Gaussian laser scanning speed was set to 900 millimeters per second (mm / s).

[0046] The Donut laser power was set to 300 watts (W).

[0047] The Donut laser scanning speed was set to 1600 mm / s.

[0048] 2. Powder thickness and angle: Set the thickness of each layer of powder to 0.02 mm.

[0049] The scanning direction is rotated 67° between each adjacent layer to optimize the structural strength of the component and effectively reduce the material anisotropy caused by the printing direction.

[0050] 4. Printing process The 3D printing is performed using the Multi-Laser Combined Scanning Strategy (MLCSS) disclosed in the present invention. The MLCSS adopts high-power Gaussian laser and Donut laser, and is formed by island scanning combined with a fast short strip width scanning strategy (SSWSS). Therefore, the entire printing process first performs island scanning, divides the entire area into multiple islands, and then scans each island separately. After each island is scanned, the next island is scanned until all islands are scanned.

[0051] 1. Division of scanning area: The island scanning strategy divides the scanning area into multiple small areas (islands) of 5 mm x 5 mm. Each island is scanned separately to reduce thermal stress and prevent component warping and cracking.

[0052] 2. Scanning within the island: In the embodiment of the present disclosure, the Gaussian laser and the Donut laser are started to scan at the same time, wherein the scanning strategy of the Gaussian laser is to perform parallel line scanning in each partition in the same direction, the scanning directions of adjacent partitions are perpendicular to each other, and the directions of adjacent scanning paths in each partition are the same or opposite. The Gaussian laser scanning power is set to 350 watts (W), the laser scanning speed is set to 900 millimeters / second (mm / s), and twice the spot diameter is taken as the distance between the scanning paths; the scanning trajectory moves along a straight line, and after scanning the first trajectory, the second trajectory is scanned until the first island is scanned, and then the subsequent islands are scanned in the same way.

[0053] The Donut laser scans back and forth according to the SSWSS strategy. It starts scanning the track along the scanning direction perpendicular to the Gaussian laser. After scanning the first track, it moves 0.1mm and moves in the opposite direction to scan the second track. The above process is repeated from the starting point to the end point to form a scanning track parallel to the Gaussian laser scanning track. The two tracks are merged into the first scanning strip. The Donut laser scanning power is set to 380 watts (W) and the scanning speed is set to 1600 mm / s (mm / s).

[0054] In the embodiments of the present disclosure, a basic molten pool is first formed quickly by linear scanning using a Gaussian laser, and at the same time, a Donut laser is scanned according to the SSWSS strategy. The two laser scanning strategies are used alternately to promote the interaction between the scanning trajectories and form a larger molten pool with a low aspect ratio, thereby improving the uniformity and quality control of the parts.

[0055] By comparing FIG2 (a) and FIG2 (b), it can be seen that in the multi-laser composite scanning strategy (MLCSS) disclosed in the present invention, two beam mode lasers start scanning at the same time. Since the Gaussian laser scans along a straight line trajectory, the scanning distance is short and it will reach the end of the first path first. Although the scanning distance of the Donut laser is longer than that of the Gaussian laser, because it has a faster scanning speed, it will heat the scanning path again after the Gaussian laser, thereby further expanding the molten pool to slow down the cooling rate and ensure the diffusion of the metal components.

[0056] In the embodiments of the present disclosure, high laser scanning speed and power input are used to ensure that the time between adjacent single-track scans is short enough to achieve interaction between adjacent single-track molten pools, while increasing the construction rate of parts and shortening production lead time.

[0057] 3. Overall area scan: After completing the scan of one island, jump to the next island and repeat the above island scanning process until all islands in the entire area are scanned, that is, the entire scan of the area is completed.

[0058] The embodiments of the present disclosure have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A multi-laser composite scanning strategy, characterized in that: include: Dual laser scanning is performed using a Gaussian laser and a Donut laser, wherein the Gaussian laser adopts an island scanning strategy; within each island, the Donut laser scans perpendicularly to the Gaussian laser and performs a short-strip width scanning strategy; The dual laser scanning method is that within an island, the Gaussian laser and the Donut laser start scanning and end scanning at the same time; after completing the scanning of one island, jump to the next island and perform the dual laser scanning again until all islands are completely scanned.

2. The multi-laser composite scanning strategy according to claim 1, characterized in that: The scanning paths of the Gaussian lasers are perpendicular to each other in the scanning directions of adjacent subareas.

3. The multi-laser composite scanning strategy according to claim 1 or 2, characterized in that: The Gaussian laser takes twice the spot diameter as the distance between scanning paths.

4. The multi-laser composite scanning strategy according to claim 3, characterized in that: Donut laser power is 5%~10% higher than Gaussian laser power.

5. The multi-laser composite scanning strategy according to claim 4 is characterized in that: The Gaussian laser scanning speed is greater than 300 mm / s.

6. The multi-laser composite scanning strategy according to claim 5, characterized in that: The island has a size of 5 mm×5 mm.

7. A powder bed fusion molding method, characterized in that: include: 3D printing is performed using the multi-laser composite scanning strategy described in any one of claims 1 to 6.

8. The powder bed fusion molding method according to claim 7, characterized in that: The raw material for the 3D printing is additive manufacturing alloy powder.

9. The powder bed fusion molding method according to claim 8, characterized in that: The additive manufacturing alloy powder includes but is not limited to iron-based powder, titanium-based powder, aluminum-based powder, nickel-based powder and magnesium-based powder; and / or, Before the 3D printing is performed, the additive manufacturing alloy powder is dried and the substrate is preheated.

10. The powder bed fusion molding method according to any one of claims 7 to 9, characterized in that: The 3D printing is performed under the protection of a protective gas.

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