A method for isotropic scanning in laser additive manufacturing of scanning galvanometers

Abstract

The present invention discloses an isotropic scanning method for laser additive manufacturing of a scanning galvanometer, comprising: dividing a processing surface into a number of small areas, filling a number of sinusoidal function curves in each small area as a scanning path, and equidistantly distributing adjacent sinusoidal function curves; performing laser scanning filling and synchronous remelting on a number of small areas planned by S1, and then scanning and synchronously remelting the next small area until the entire processing surface is scanned; after the entire processing surface is scanned, the entire processing surface is remelted, and then the next layer of additive manufacturing is performed, and the scanning path and remelting path filled in each small area of ​​the next layer are rotated 45° clockwise on the basis of the previous layer. The present invention uses curved path scanning and synchronous remelting, which disrupts the grain growth direction and allows the grains to be arranged in disorder, so that the overall mechanical properties of the additive manufacturing layer tend to be isotropic.

Description

Technical Field

[0001] The invention belongs to the field of additive manufacturing, and in particular relates to an isotropic scanning method for laser additive manufacturing of a scanning galvanometer. Background Art

[0002] Additive Manufacturing (AM) is the opposite of traditional subtractive processing. It uses high-energy-density lasers to melt materials point by point, deposit them layer by layer, and directly form them. Since its emergence, additive manufacturing has attracted widespread attention due to its advantages such as short processing cycle, high production efficiency, and high flexibility in production.

[0003] The emergence of high-power scanning galvanometer systems has greatly improved the speed and production efficiency of laser processing. The computer-controlled mechanical device drives the deflection of the X and Y reflected beams to realize the movement of the laser beam within the working range, and scans different graphics on the scanning field according to the established scanning route. Due to the good beam quality of the laser light source used, compared with other laser light sources, the working distance of the system is greatly increased when the focus spot size is the same, and the focus spot is greatly reduced when the working distance is the same. This feature enables the system to achieve higher processing efficiency and better processing quality in practical applications, and can achieve true rapid remote processing when used with a robot.

[0004] In the laser additive manufacturing process based on scanning galvanometers, due to the excessive cooling rate, large residual stresses and defects such as cracks and pores will be generated in the workpiece, affecting the performance of the additively manufactured workpiece. The general selective laser melting process only remelts the last formed layer (i.e., the outer surface) after the additive process is completed, which cannot well control the cumulative effect of the surface roughness between layers during the additive process. In addition, the bubbles generated during the additive process cannot fully overflow and remain in the additive manufacturing layer to form pore defects, which may eventually develop into crack sources. Therefore, designing a scanning method for synchronous remelting of galvanometer-type laser additive manufacturing is of great significance for improving the surface quality of the additive manufacturing layer and the isotropy of mechanical properties. Summary of the invention

[0005] The purpose of the present invention is to solve the problem of anisotropy of organizational properties in the process of scanning galvanometer laser additive manufacturing, and proposes a scanning method for synchronous remelting of scanning galvanometer laser additive manufacturing. This method can reduce the residual stress and porosity inside the additive manufacturing layer, reduce the cumulative effect of interlayer roughness, and improve the surface quality and isotropy of mechanical properties.

[0006] A laser additive manufacturing isotropic scanning method for a scanning galvanometer, comprising:

[0007] S1 divides the processing surface into several small areas, and fills several sine function curves in each small area as the scanning path, and the adjacent sine function curves are equidistantly distributed;

[0008] S2 performs laser scanning filling and synchronous remelting on several small areas planned by S1, and then scans and synchronously remelts the next small area until the entire processing surface is scanned;

[0009] After the entire processing surface of S3 is scanned, the entire processing surface is remelted, and then the next layer of additive manufacturing is carried out. The scanning path and remelting path for filling each small area in the next layer are rotated 45° clockwise based on the previous layer.

[0010] Furthermore, it is characterized in that the synchronous remelting in S2 is defined as: after each scanning of a small area is completed, the current small area is immediately remelted, the remelting path does not overlap with the scanning molding path, and then the next small area is scanned and remelted.

[0011] Furthermore, it is characterized in that the axes of the remelting path and the scanning forming path in S2 along the periodic direction are perpendicular to each other.

[0012] Furthermore, the remelting in S3 is performed twice, and the first and second remelting paths are perpendicular to each other.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention is used to optimize the scanning process of galvanometer laser additive manufacturing. Through the single-layer multi-directional laser scanning and synchronous remelting method, the grain growth direction is disturbed, the grains are arranged disorderly, and the overall mechanical properties of the additive manufacturing layer tend to be isotropic; and because the synchronous remelting is conducive to reducing the cumulative effect of interlayer surface roughness, the final surface roughness is reduced, and multiple remelting reduces the temperature gradient of the additive manufacturing layer, and reduces the residual stress caused by rapid cooling. In the additive process, since the two ends (i.e., the starting and ending ends) of each scanning path of the scanning layer have the fastest cooling speed and the shortest existence time of the molten pool, there are more pores distributed than in the middle part. When remelting, the straight line filled by the remelting layer is perpendicular to the axis of the scanning layer curve along the periodic direction, which can effectively increase the existence time of the molten pool at both ends of the scanning layer, allowing bubbles to fully escape and reduce porosity. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A flow chart of an isotropic scanning method for laser additive manufacturing of a scanning galvanometer according to the present invention;

[0015] Figure 2 It is a schematic diagram of scanning forming and remelting paths in an isotropic scanning method for laser additive manufacturing of a scanning galvanometer according to the present invention;

[0016] In the figure, 1-partition scanning forming path, 2-partition synchronous remelting path, 3-region boundary line, 4-overall remelting path. DETAILED DESCRIPTION

[0017] In the description of the present invention, it is necessary to understand that the terms "one end", "the other end", "outside", "upper", "inside", "horizontal", "coaxial", "center", "end", "length", "outer end" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0018] The present invention will be further described below in conjunction with the accompanying drawings.

[0019] Embodiment 1

[0020] A laser additive manufacturing isotropic scanning method for a scanning galvanometer is used, comprising the following steps:

[0021] (1) Set the processing surface size to 100×100 mm and the size of each small area to 4×4 mm;

[0022] (2) A small area is uniformly filled with a sine curve as the scanning path. The amplitude of the sine function curve is 1 mm, the period is 2π, and the initial phase angle is 0°. Two adjacent sine curves are equidistantly distributed with a distance of 0.03 mm. A straight line is uniformly filled as the remelting path. Two adjacent straight lines are equidistantly distributed with a distance of 0.03 mm. The remelting path and the scanning path are perpendicular to each other along the periodic direction.

[0023] (3) Perform laser scanning filling and synchronous remelting along the scanning path and remelting path planned in step (2), with a laser power of 600 W and a scanning speed of 500 mm / s; after scanning, perform two overall remeltings on the additive manufacturing layer, with the two remelting paths being perpendicular to each other, with a laser power of 600 W and a scanning speed of 500 mm / s.

[0024] Embodiment 2

[0025] The present invention is used to repair the cavitation part of the turbine blade, the light cavitation area of ​​the blade is polished and the surface oil is removed with acetone, and the size of the area to be repaired is measured to be 15×30 mm and the depth is 1 mm.

[0026] Perform penetrant testing on the area to be repaired to confirm that the cavitation area has been completely removed.

[0027] A Co-based alloy powder was selected as the repair material, and its composition is as follows:

[0028]

[0029] The area of ​​the blade to be repaired is a curved surface, and 6% sodium silicate solution is selected as the adhesive. It is mixed with the alloy powder in a weight ratio of 1:5 and stirred into a paste. Then, it is applied to the area to be repaired and compacted. Then, a 0.2mm feeler gauge is placed on both sides of the powder. The powder is scraped flat with a scraper and left to stand for 5 minutes to wait for the adhesive to dry.

[0030] Adjust the focal length of the galvanometer laser additive manufacturing system, divide the area to be repaired into several 5×5mm small areas, and use sine curves to evenly fill the small areas as the scanning path. The amplitude of the sine function curve is 0.8mm, the period is 2π, and the initial phase angle is 0°. Two adjacent sine curves are equidistantly distributed with a distance of 0.05mm; use straight lines to evenly fill as the remelting path, and two adjacent straight lines are equidistantly distributed with a distance of 0.05mm. The remelting path and the scanning path are perpendicular to each other along the axis of the periodic direction.

[0031] The laser power is determined to be 600W, the scanning speed is 300mm / s, and the laser power and scanning speed of the forming scan and remelting are the same. The divided small areas are laser scanned and remelted synchronously in sequence. After the repair area is scanned, the additive manufacturing layer is remelted as a whole to reduce the residual stress and remove the boundary line of the small area, and then the next layer of additive manufacturing is carried out.

[0032] After the additive manufacturing process is completed, the additive manufacturing layer is polished, acetone is used to remove oil stains, and then penetrant testing is performed to check whether there are defects such as pores and cracks in the repair area to verify whether the repair quality is qualified.

[0033] The above embodiments are only preferred embodiments of the present invention and are not limitations of the technical solutions of the present invention. Any technical solution that can be implemented on the basis of the above embodiments without creative work should be deemed to fall within the scope of protection of the patent of the present invention.

Claims

1. A method for isotropic scanning of laser additive manufacturing for scanning galvanometers, characterized in that: include: S1 divides the processing surface into several small areas, and fills several sine function curves in each small area as the scanning path, and the adjacent sine function curves are equidistantly distributed; S2 performs laser scanning filling and synchronous remelting on several small areas planned by S1, and then scans and synchronously remelts the next small area until the entire processing surface is scanned. The definition of synchronous remelting is: after each small area is scanned, the current small area is immediately remelted, and the remelting path and the axis of the scanning molding path along the periodic direction are perpendicular to each other, and then the next small area is scanned and remelted; After the entire processing surface of S3 is scanned, the entire processing surface is remelted, and then the next layer of additive manufacturing is carried out. The scanning path and remelting path for filling each small area in the next layer are rotated 45° clockwise on the basis of the previous layer; In S3, remelting is performed twice, and the first and second remelting paths are perpendicular to each other.

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