A laser manufacturing method with 2.5-dimensional periodic structure

Abstract

The present invention discloses a laser manufacturing method with a 2.5-dimensional periodic structure, which uses an ultrashort pulse laser to perform laser ablation on the surface of a metal substrate to be processed along multiple straight lines spaced at a certain distance, so that the wettability of the metal substrate surface changes. Synchronous powder feeding laser cladding is performed on the surface of a metal substrate with two different surface wettabilities spaced apart. After completing multiple passes of laser cladding, the laser cladding layer of each pass has the same absolute value of positive and negative height difference with the adjacent passes, and the cladding layer as a whole presents a 2.5-dimensional periodic structure. By repeatedly using this method in the laser additive manufacturing process, a densely packed multi-through hole type metal lightweight structure can be obtained. This structure has the advantages of lightweight, high strength, through holes, etc., and can be used in fields such as coolant flow cooling or hydrogen storage.

Description

Technical Field

[0001] The present invention relates to the field of laser manufacturing, and in particular to a laser manufacturing method with a 2.5-dimensional periodic structure. Background Art

[0002] Advanced structural technology is an emerging field of technology that studies the optimization of the design and fabrication of engineering structures to meet constraints and predetermined objectives (such as weight reduction and cost reduction). Design variables, objective functions, and constraints are the three key elements of structural optimization. Design variables are quantities that vary during the optimization process and are the direct targets of structural optimization. They can be categorized as simple variables, structural geometric variables, and material property variables. The objective function is a functional relationship that minimizes or maximizes the design variables according to a specific rule or method during the optimization process and serves as the basis for achieving the optimal solution. Constraints are the limiting conditions that must be met during structural design. Common examples include geometric constraints, stress constraints, displacement constraints, and stability constraints. Constraints serve as boundary conditions for optimizing the design variables. Structural optimization is generally divided into three levels based on the type of design variables: structural size optimization, shape optimization, and topology optimization. Currently, size optimization and shape optimization have been well developed, but both suffer from the limitation of not being able to modify the topological properties of the structure. Structural topology optimization is a recent branch of structural optimization research. Its basic idea is to transform the problem of finding the optimal topology of a structure into the problem of finding the optimal material distribution within a given design domain. Common topology optimization methods can be categorized into two main categories: degradation and evolution. Degeneration methods, as traditional topology optimization methods, typically seek the optimal topology by finding the zeros of the derivative of the objective function or through a series of iterative calculations. Evolutionary methods optimize overall performance through selection, crossover, and mutation, ultimately achieving a globally optimal solution.

[0003] Wettability, a key property of solid surfaces, plays a crucial role in many fields. In particular, during metal solidification, the wettability of the substrate surface determines the number of heterogeneous nucleation sites for the liquid metal on the substrate surface during the initial solidification phase. In-depth research on wettability has revealed that the microstructures created on metal surfaces significantly influence their wettability. Fabricating micro- and nanostructures on high-surface-energy metal substrates can achieve specific wetting states. Therefore, leveraging the superior mechanical properties of metal substrates to create extremely wettable functional surfaces on metal substrates holds significant promise for future applications.

[0004] Laser manufacturing of metal structures generally requires a melting process, which makes the construction and maintenance of topologically optimized configurations such as metal-based specific wettable functional surface microstructures a difficult-to-break technical bottleneck in the laser manufacturing of functional structures. Generally speaking, the selective laser melting (SLM) technology using a powder bed as a feeding method can produce certain topologically optimized parts that do not consider the surface functionalized microstructure, but the forming efficiency is low due to the limited thickness of the powder bed. In the field of laser cladding technology using synchronous powder feeding as a feeding method, although the construction efficiency is relatively high, the continuous delivery of powder and the precise control of the melting process are difficult to balance, resulting in extremely difficult manufacturing of topologically optimized parts. Summary of the Invention

[0005] To address the difficulty in balancing continuous powder delivery and precise control of the melting process during laser cladding manufacturing of topologically optimized parts using synchronous powder feeding, the present invention provides a laser manufacturing method having a 2.5-dimensional periodic structure. The method comprises: periodically varying the wettability of a metal substrate surface at intervals of a certain distance, such that the wetting angles between the surface to be clad and the laser cladding powder melt in adjacent laser cladding passes are obtuse and acute, respectively. Synchronous powder feeding laser cladding is performed on a metal substrate surface having two different surface wettabilities spaced apart, such that the wetting angles between the metal surface and the laser cladding powder melt in adjacent laser cladding passes are obtuse and acute, respectively. Correspondingly, the cross-sectional profiles of the laser cladding layers in adjacent passes are superior and inferior arcs, respectively. Due to the equal mass of the cladding additive in each pass, after completing multiple laser cladding passes, the laser cladding layers in each pass have the same absolute value of positive and negative height differences with adjacent passes, resulting in the cladding layer exhibiting a 2.5-dimensional periodic structure as a whole. The method of the present invention is repeatedly implemented in multiple layers, and the grooves in the structure are filled and supported with high-melting-point powder. After the structure is completed, the unmelted high-melting-point powder is removed to construct a densely packed multi-through-hole metal-based lightweight structure.

[0006] The method comprises the following steps:

[0007] S1: Ablation hole processing: Using ultrashort pulse laser to ablate holes along multiple parallel straight lines at a certain interval on the surface of the metal substrate to be processed, a multi-line closely packed ablation hole lattice microstructure is formed on the surface of the metal substrate, and the holes are arranged parallel and staggered with the unablated interval areas;

[0008] S2: Laser cladding: Multi-pass synchronous feeding laser cladding is performed on the metal surface on which a close-packed ablation hole lattice microstructure has been formed, with an overlap rate of 0. Each cladding pass coincides with the linear close-packed ablation hole pass described in S1, or coincides with the interval described in S1, so that the cross-sectional profiles of the laser cladding layers of adjacent passes are respectively a superior arc and an inferior arc, and grooves to be filled are formed between adjacent cladding passes. The wetting angles between the metal surface of adjacent laser cladding passes and the laser cladding powder melt are respectively an obtuse angle and an acute angle;

[0009] S3: Fill the groove to be filled with tungsten carbide powder and compact it so that the upper surface of the tungsten carbide powder filling body is flush with the ridge of the cladding layer. At this time, the cladding layer and the surface of the tungsten carbide powder filling body form a new surface to be clad;

[0010] S4: preparing a cladding layer on the new surface to be clad described in S3 by multi-pass synchronous feeding laser cladding;

[0011] S5: using the cladding layer in S4 as the processing surface, repeating S1 to S4 multiple times until a three-dimensional structure is prepared;

[0012] S6: Separate the three-dimensional structure described in S5 and the metal matrix described in S1, remove the tungsten carbide powder in the groove to be filled in the three-dimensional structure, and perform ventilation, dust removal and cleaning to obtain a metal lightweight structure with multiple straight through holes, that is, a 2.5-dimensional periodic structure.

[0013] Furthermore, in S1, the pulse laser is any one of a femtosecond pulse laser, a picosecond pulse laser or a nanosecond pulse laser.

[0014] Furthermore, in S2, the laser spot used in laser cladding is circular.

[0015] Furthermore, the width of each linear closely packed ablation hole lattice microstructure region formed in S1 is equal to the width of the adjacent unprocessed spaced region, and is also equal to the diameter of the circular spot used in the laser cladding in S2.

[0016] Furthermore, in S1, the hole distance between two adjacent ablation holes in the linear close-packed ablation hole array microstructure is 5-15 microns.

[0017] Furthermore, in S2, the cladding layer completely covers the surface of the linear closely packed ablation hole lattice microstructure.

[0018] Furthermore, in S4, the overlap rate of the laser cladding is 40%-60%.

[0019] Furthermore, in S3, the tungsten carbide powder is compacted mechanically; in S6, the three-dimensional structure is removed and turned over with the side facing downward, and mechanical vibration is applied to it to clear the unmelted tungsten carbide powder in the three-dimensional structure, and all the through holes are ventilated, dusted and cleaned to complete the forming of the three-dimensional metal lightweight structure.

[0020] Furthermore, in S3, the tungsten carbide powder is bonded to the groove to be filled by using an inorganic binder or an organic binder. In S6, the inorganic binder or the organic binder is removed by heating to clean the tungsten carbide powder.

[0021] Beneficial effects of the present invention:

[0022] The present invention utilizes an ultrashort pulse laser to perform laser ablation drilling on the surface of a metal substrate to be processed along multiple spaced-apart straight lines, creating a densely packed lattice of ablated holes on the metal surface. The depth of the ablated holes is greater than the penetration depth of the subsequent laser cladding on the metal substrate surface. The densely packed microporous structure formed by ultrashort pulse ablation is spaced apart from the original, unablated surface, causing periodic changes in the wettability of the metal substrate surface. Synchronous powder-feeding laser cladding is performed on the surface of a metal substrate with two different surface wettabilities spaced apart. The wetting angles between the metal surface and the laser cladding powder melt in adjacent laser cladding passes are obtuse and acute, respectively. Correspondingly, the cross-sectional profiles of the laser cladding layers in adjacent passes are superior and inferior arcs, respectively. Due to the equal mass of the cladding additive in each pass, after completing multiple passes of laser cladding, the laser cladding layers in each pass have the same absolute value of positive and negative height differences with the adjacent passes, resulting in a 2.5-dimensional periodic structure. By repeatedly applying this method during laser additive manufacturing, a densely packed, multi-through-hole metal lightweight structure can be obtained. This structure offers advantages such as lightweight, high strength, and through-holes, and can be used in applications such as coolant flow cooling and hydrogen storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The surface of the metal substrate to be processed after the step S1 in the embodiment of the present invention is as follows Figure 1 Schematic diagram shown;

[0024] Figure 2 Schematic diagram of the cross section of the metal substrate to be processed after the S2 step in the embodiment of the present invention;

[0025] Figure 3 Schematic diagram of the cross section of the metal substrate to be processed after the S4 step in the embodiment of the present invention;

[0026] Figure 4 Schematic diagram of the cross section of the metal substrate to be processed after step S6 in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] 1. Determine the ultrashort pulse laser ablation trajectory and continuous laser cladding trajectory on the surface of the selected metal substrate A;

[0029] 2. Based on the above trajectory information, use a computer to generate the ultrashort pulse laser ablation path and a computer to generate the continuous laser cladding path;

[0030] 3. Using a femtosecond pulse laser, deep laser ablation is performed along a straight line on the surface of the metal substrate A to be processed, so that a densely packed ablation hole lattice microstructure is generated on the surface of the metal substrate. The distance between each modified area is 3 mm, the depth of the ablation hole is greater than 100 microns, the center distance between adjacent ablation holes is less than 10 microns, and the width of each pass of the unablated area on the metal substrate surface and the microstructure area are equal and adjacent;

[0031] 4. Fill and compact all grooves of the completed 2.5D structure cladding layer with high melting point powder WC, so that the upper surface of the tungsten carbide powder filling body is at the same height as the ridge of the 2.5D structure cladding layer, so that the upper surface of the filled cladding layer becomes a plane;

[0032] 5. Using the upper surface of the cladding layer described in step 4 as the new substrate surface, perform synchronous powder feeding laser cladding with an overlap rate of 50%. After cladding is completed, a new upper surface of the cladding layer is formed;

[0033] 6. Using the upper surface of the new cladding layer in step 5 as the new substrate surface, repeat steps 2-4 multiple times until the three-dimensional structure is completed;

[0034] 7. Remove the three-dimensional structure and turn it over with the side facing downward, apply mechanical vibration to it, empty the unmelted tungsten carbide powder in the three-dimensional structure, and ventilate, dust and clean all the through holes to complete the formation of the three-dimensional metal lightweight structure. The three-dimensional metal lightweight structure is a 2.5-dimensional periodic structure.

[0035] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A laser manufacturing method having a 2.5-dimensional periodic structure, characterized in that: The following steps are involved: S1: Ablation hole processing: Using an ultrashort pulse laser, ablation holes are processed along multiple parallel straight lines on the surface of the metal substrate to be processed at a certain interval. Multiple linear close-packed ablation hole lattice microstructures are formed on the surface of the metal substrate, and are arranged parallel to the unablated interval areas. The hole spacing between two adjacent ablation holes in the linear close-packed ablation hole lattice microstructure is 5-15 microns; S2: Laser cladding: Multi-pass synchronous feeding laser cladding is performed on the metal surface on which a close-packed ablation hole lattice microstructure has been formed, with an overlap rate of 0. Each cladding pass coincides with the linear close-packed ablation hole pass described in S1, or coincides with the interval described in S1, so that the cross-sectional profiles of the laser cladding layers of adjacent passes are respectively a superior arc and an inferior arc, and grooves to be filled are formed between adjacent cladding passes. The wetting angles between the metal surface of adjacent laser cladding passes and the laser cladding powder melt are respectively an obtuse angle and an acute angle; S3: Fill the groove to be filled with tungsten carbide powder and compact it so that the upper surface of the tungsten carbide powder filling body is flush with the ridge of the cladding layer. At this time, the cladding layer and the surface of the tungsten carbide powder filling body form a new surface to be clad; S4: preparing a cladding layer on the new surface to be clad described in S3 by multi-pass synchronous feeding laser cladding; S5: using the cladding layer in S4 as the processing surface, repeatedly performing S1-S4 until a three-dimensional structure is prepared; S6: Separate the three-dimensional structure described in S5 and the metal matrix described in S1, remove the tungsten carbide powder in the groove to be filled in the three-dimensional structure, and perform ventilation, dust removal and cleaning to obtain a metal lightweight structure with multiple straight through holes, that is, a 2.5-dimensional periodic structure.

2. The laser manufacturing method having a 2.5-dimensional periodic structure according to claim 1, characterized in that: In S1, the ultrashort pulse laser is any one of a femtosecond pulse, a picosecond pulse or a nanosecond pulse laser.

3. The laser manufacturing method having a 2.5-dimensional periodic structure according to claim 1, characterized in that: In S2, the laser spot used in laser cladding is circular.

4. The laser manufacturing method having a 2.5-dimensional periodic structure according to claim 1, characterized in that: The width of each linear closely packed ablation hole lattice microstructure region formed in S1 is equal to the width of the adjacent unprocessed spaced region, and is also equal to the diameter of the circular spot used in laser cladding in S2.

5. The laser manufacturing method having a 2.5-dimensional periodic structure according to claim 1, characterized in that: In S2, the cladding layer completely covers the surface of the linear closely packed ablation hole lattice microstructure.

6. The laser manufacturing method having a 2.5-dimensional periodic structure according to claim 1, characterized in that: In S3, the tungsten carbide powder is compacted mechanically.

7. The laser manufacturing method having a 2.5-dimensional periodic structure according to claim 1, characterized in that: In S4, the overlap rate of laser cladding is 40%-60%.

8. The laser manufacturing method having a 2.5-dimensional periodic structure according to claim 1, characterized in that: In S3, the tungsten carbide powder is bonded to the groove to be filled by using an inorganic binder or an organic binder; in S6, the inorganic binder or the organic binder is removed by heating to clean the tungsten carbide powder.

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