Device and method for adjusting small spot laser energy distribution by using axicon

Abstract

The invention relates to a device and method for adjusting small light spot laser energy distribution by using axicon, and belongs to the field of 3D printing. The device comprises a focusing lens, a first axicon and a second axicon which are arranged on a parallel laser light path; the distance between the first axicon and the second axicon is adjusted based on the inclined plane angle of the first axicon, the inclined plane angle of the second axicon and the size of the needed small light spot, so that the distance between the first axicon and the second axicon meets the following formula: # imgabs0 #, D represents the size of the needed small light spot, and D represents the size of the needed small light spot. N represents the refractive indexes of glass materials of the first axicon and the second axicon, L represents the printing working distance, L represents the distance between the first axicon and the second axicon, and alpha and beta respectively represent the included angles between the inclined planes of the first axicon and the second axicon and the printing surface. The problem that the precision requirement of small-size light spot energy distribution adjustment cannot be met due to insufficient machining capacity is solved by adjusting the distance between the two axicon lenses.

Description

Technical Field

[0001] The present invention belongs to the technical field of 3D printing, and in particular relates to a device and method for adjusting small spot laser energy distribution by using an axicon. Background Art

[0002] Additive manufacturing, powder bed laser melting, or 3D metal printing selective laser melting SLM technology, has become the most accurate and important 3D metal printing technology. The laser beam scans the flat metal powder in sequence according to the path of each layer of the digital model to form a planar structure, which is stacked layer by layer to form a 3D structure.

[0003] In SLM technology, the industry currently uses Gaussian-distributed laser beams. The melt dynamics of the laser beams used to melt metal powders show that Gaussian beams have excessively strong local intensity, with about 86% of the incident wave power within the beam waist and near the axis. Repeated hot-cold cycles exacerbate this problem: the vaporization of the molten pool and the accumulation of recoil pressure in the bottom molten pool cause splashing and spoon-shaped molten pools; various defects, increased porosity and surface roughness; growth of columnar crystals and residual stresses, and anisotropic tendencies in mechanical properties; and a decrease in relative density, which greatly reduces the plasticity, impact toughness, and fatigue life of the printed product.

[0004] Due to the uneven distribution of laser energy, the energy density at the center of the spot is much greater than that at the edge of the spot, and accurate energy distribution cannot be achieved. When using Gaussian laser for production and processing, the laser utilization rate is low and the energy loss is large. As the power continues to increase, powder remelting occurs, which greatly reduces the quality of the printed product.

[0005] Based on the above problems, some solutions use a single axicon to shape the Gaussian beam. The shaped laser beam is a ring-shaped beam with low central energy, such as Figure 1 Assume that the focal length of the focusing lens is f, the glass refractive index of the axicon is n, the angle between the axicon and the bottom surface is α, the distance between the axicon and the focusing imaging surface is L, and the diameter of the annular spot at the imaging surface is D. When the angle α is very small, the following approximate formula is obtained:

[0006] , At this time, the laser focus spot on the imaging surface is a ring-shaped spot.

[0007] The laser spot size commonly used in 3D printing is 50~100um, and the galvanometer scanning working distance is more than 500mm. Taking the spot diameter D=100um, the working distance L=500mm, and the glass refractive index n=1.5 as an example, the angle α of the axicon is calculated as: α≈0.01°. Considering that in order to ensure the printing quality in 3D printing, the spot diameter change is required to be no more than ±3%, the accuracy requirement of the angle α is: α=0.01±0.0003°. The current cone angle processing accuracy of the axicon can only achieve ±0.01° at most, and the usual processing accuracy is ±0.05°. Under this processing accuracy, the error of the spot size at the final imaging surface is too large and far from meeting the use requirements. Therefore, using this solution, the angle accuracy requirement of the device far exceeds the limit of industrial processing capabilities. Therefore, the above solution can only ensure that the output laser beam maintains a ring beam on a macro scale. When the beam is focused into a small spot, its ring beam characteristics are difficult to maintain, and the size of the small spot cannot be guaranteed.

[0008] For an optical path shaping system composed of two axicon mirrors, such as the system described in the authorization announcement number CN115464154B, if it needs to meet the above-mentioned spot diameter D=100um and working distance L=500mm, the cone angle accuracy error of the two axicon mirrors is also required to be no more than ±0.0003°, which makes it only theoretically feasible to form a small annular spot by shaping the optical path with axicon mirrors, and it cannot be accurately realized in practice. In summary, in 3D printing, in order to reduce the splashing and keyhole caused by the excessive energy at the center of the high-speed beam, there are many ways to shape the beam energy distribution. All shaped beams only shape the macroscopic beam energy distribution itself. When the spot is focused, there is no such ability to shape the small spot on the order of tens of microns. Summary of the invention

[0009] The purpose of the present invention is to provide a device and method for adjusting the energy distribution of a small laser spot using an axicon mirror, so as to solve the problem that small spot shaping cannot be achieved due to the machining accuracy of the axicon mirror bevel during existing beam energy distribution shaping.

[0010] In order to achieve the above object, the technical solution of the present invention is as follows: The present invention relates to a device for adjusting small spot laser energy distribution using an axicon mirror, which comprises a focusing lens, a first axicon mirror and a second axicon mirror arranged on a parallel laser light path, and the spacing between the first axicon mirror and the second axicon mirror is adjusted based on the bevel angle of the first axicon mirror, the bevel angle of the second axicon mirror and the required small spot size, so that the spacing between the first axicon mirror and the second axicon mirror satisfies the following formula: (1), Wherein, D represents the required small spot size, n represents the refractive index of the glass material of the first axicon and the second axicon, L represents the printing working distance, △L represents the spacing between the first axicon and the second axicon, and α and β represent the angles between the inclined surfaces of the first axicon and the second axicon and the printing surface, respectively.

[0011] Preferably, the first axicon is a concave axicon, the second axicon is a convex axicon, and the inclined surfaces of the first axicon and the second axicon are opposite.

[0012] Preferably, the first axicon mirror and the second axicon mirror are both concave axicon mirrors, and the inclined surfaces of the first axicon mirror and the second axicon mirror are opposite to each other.

[0013] Preferably, the first axicon and the second axicon are both located at the rear side of the focusing lens.

[0014] Preferably, the first axicon is located at the front side of the focusing lens, and the second axicon is located at the rear side of the focusing lens.

[0015] The present invention also relates to a method for adjusting the energy distribution of a small-spot laser using an axicon mirror, which is used to adjust the above-mentioned device for adjusting the energy distribution of a small-spot laser using an axicon mirror, and comprises the following steps: detecting the bevel angles of a first axicon mirror and a second axicon mirror, and adjusting the spacing between the first axicon mirror and the second axicon mirror according to the detection result and the required small-spot size, so that the spacing satisfies the following formula: (1), Wherein, D represents the required small spot size, n represents the refractive index of the glass material of the first axicon and the second axicon, L represents the printing working distance, △L represents the spacing between the first axicon and the second axicon, and α and β represent the angles between the inclined surfaces of the first axicon and the second axicon and the printing surface, respectively.

[0016] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: The present invention relates to a device and method for adjusting small spot laser energy distribution using an axicon mirror, which compensates for the inability to meet the precision requirement of small spot energy distribution adjustment due to insufficient processing capability by adjusting the spacing between two axicon mirrors. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of the optical path for shaping a Gaussian beam using an existing single axicon; FIG2 is a structural diagram of a device for adjusting small spot laser energy distribution using an axicon in Example 1; FIG3 is a structural diagram of a device for adjusting small spot laser energy distribution using an axicon in Example 2; FIG4 is a structural diagram of a device for adjusting small spot laser energy distribution using an axicon in Example 3; Among them, 1 is a focusing lens, 2 is a first axis conical mirror, and 3 is a second axis conical mirror. DETAILED DESCRIPTION

[0018] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with examples. The following examples are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0019] Example 1 Refer to the attached Figure 2 As shown, the present embodiment involves a device for adjusting the energy distribution of small-spot laser using an axicon mirror, comprising a focusing lens 1, a first axicon mirror 2 and a second axicon mirror 3 arranged on a parallel laser optical path, wherein the first axicon mirror 2 and the second axicon mirror 3 are both located at the rear side of the focusing lens 1. The first axicon mirror 2 is a concave axicon mirror, the second axicon mirror 3 is a convex axicon mirror, the inclined surfaces of the first axicon mirror 2 and the second axicon mirror 3 are opposite, the glass material refractive index of the first axicon mirror 2 and the second axicon mirror 3 is both n, the spacing between the first axicon mirror 3 and the second axicon mirror 3 is set to △L, and the angles between the inclined surfaces of the first axicon mirror 2 and the second axicon mirror 3 and the printing surface are α and β respectively. When the above device is used to adjust the energy distribution of small-spot laser, due to the limitation of the processing capacity of the first axicon mirror 2 and the second axicon mirror 3, the inclined surfaces of the first axicon mirror 2 and the second axicon mirror 3 cannot be accurately processed. When there is an error in the inclined surface angle of the first axicon mirror 2 and the second axicon mirror 3, the inclined surface angle error of the first axicon mirror 2 and the second axicon mirror 3 is compensated by the following method:

[0020] The bevel angles of the first axicon mirror 2 and the second axicon mirror 3 are detected, and the spacing between the first axicon mirror 2 and the second axicon mirror 3 is adjusted according to the detection result and the required small spot size so that the spacing satisfies the following formula: (1), Wherein, D represents the required small spot size, n represents the refractive index of the glass material of the first axicon and the second axicon, L represents the printing working distance (the vertical distance from the lens at the end of the optical path in the focusing lens 1, the first axicon 2 and the second axicon 3 to the printing working surface), △L represents the spacing between the first axicon and the second axicon, and α and β represent the angles between the inclined surfaces of the first axicon and the second axicon and the printing surface, respectively.

[0021] Taking the spot diameter D = 100um, the working distance L = 500mm, and the glass refractive index n = 1.5 as an example, α = β = 1°, according to formula (1), the distance between the two axicon lenses can be obtained as ΔL = 0.573mm.

[0022] If the accuracy requirement of the spot diameter D is 100±1um, the ΔL dimensional accuracy satisfies: ΔL=0.573±0.006mm is sufficient.

[0023] When an error occurs in the angle processing of the axicon, for example, the angle a is processed from 1° to 1.01°, the final spot on the imaging surface is required to be D=100±1um. According to formula (1), we can get:

[0024] ΔL=0.723±0.007mm; That is, when an error occurs in the angular machining of the axicon, the light spot at the final imaging surface can be corrected to a standard value by adjusting the value of ΔL.

[0025] Therefore, when using the technical solution of this embodiment, the small annular light spot required for printing can be accurately achieved under the existing processing conditions. By adjusting the spacing between the two axis cone mirrors and controlling the accuracy of the spacing, the light spot at the printing work surface can be adjusted to the theoretical standard value with sufficiently high accuracy to meet the printing requirements.

[0026] Example 2 like Figure 3 As shown, the present embodiment is different from the embodiment 1 in that the first axicon mirror 2 and the second axicon mirror 3 in the present embodiment are both concave axicon mirrors, and the inclined surfaces of the first axicon mirror 2 and the second axicon mirror 3 are opposite.

[0027] The adjustment method of the device for adjusting the energy distribution of a small-spot laser using an axicon mirror in this embodiment is the same as that in Embodiment 1, and will not be elaborated in detail in this embodiment.

[0028] Example 3 like Figure 4 As shown, the difference between this embodiment and Embodiment 1 is that the first axicon 2 and the second axicon 3 in this embodiment are respectively located in front of and behind the focusing lens 1 .

[0029] The adjustment method of the device for adjusting the energy distribution of a small-spot laser using an axicon mirror in this embodiment is the same as that in Embodiment 1, and will not be elaborated in detail in this embodiment.

[0030] The adjustment method of the device for adjusting the energy distribution of a small-spot laser using an axicon mirror in this embodiment is the same as that in Embodiment 1, and will not be elaborated in detail in this embodiment.

[0031] The present invention is described in detail above in conjunction with the embodiments, but the contents described are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of application of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A device for adjusting the energy distribution of a small spot laser using an axicon, characterized in that: The invention comprises a focusing lens, a first axicon and a second axicon arranged on a parallel laser light path, and the spacing between the first axicon and the second axicon is adjusted based on the bevel angle of the first axicon, the bevel angle of the second axicon and the required small spot size, so that the spacing between the first axicon and the second axicon satisfies the following formula: （1）， Wherein, D represents the required small spot size, n represents the refractive index of the glass material of the first axicon and the second axicon, L represents the printing working distance, △L represents the spacing between the first axicon and the second axicon, and α and β represent the angles between the inclined surfaces of the first axicon and the second axicon and the printing surface, respectively.

2. The device for adjusting small spot laser energy distribution using an axicon according to claim 1, characterized in that: The first axicon is a concave axicon, the second axicon is a convex axicon, and the inclined surfaces of the first axicon and the second axicon are opposite.

3. The device for adjusting small spot laser energy distribution using an axicon according to claim 1, characterized in that: The first axicon mirror and the second axicon mirror are both concave axicon mirrors, and the inclined surfaces of the first axicon mirror and the second axicon mirror are opposite to each other.

4. The device for adjusting small spot laser energy distribution using an axicon according to claim 1, characterized in that: The first axicon and the second axicon are both located at the rear side of the focusing lens.

5. The device for adjusting small spot laser energy distribution using an axicon according to claim 1, characterized in that: The first axicon is located at the front side of the focusing lens, and the second axicon is located at the rear side of the focusing lens.

6. A method for adjusting the energy distribution of a small-spot laser using an axicon mirror, used to adjust the device for adjusting the energy distribution of a small-spot laser using an axicon mirror as claimed in claim 1, characterized in that: It includes the following steps: Detect the bevel angles of the first axicon mirror and the second axicon mirror, and adjust the distance between the first axicon mirror and the second axicon mirror according to the detection result and the required small spot size so that the distance satisfies the following formula: （1）， Wherein, D represents the required small spot size, n represents the refractive index of the glass material of the first axicon and the second axicon, L represents the printing working distance, △L represents the spacing between the first axicon and the second axicon, and α and β represent the angles between the inclined surfaces of the first axicon and the second axicon and the printing surface, respectively.

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