A full-band error converging laser reshaping method

Abstract

The application discloses a laser shaping method with full-band error convergence, and steps are as follows: firstly, based on the laser shaping simulation result, the pulse width range of densification-melting effect is determined, so that the shaping depth in the pulse width range is obtained; then, the initial surface shape value is extracted, a single laser point is gathered into a laser processing sub-region, the average value of the depths of points in the region is obtained, and a shaping average depth point graph is obtained; according to the relationship between the pulse width and the shaping depth, the shaping average depth point graph is converted into a pulse width point graph; then, an acousto-optic modulator signal is set, the overlapping scanning path of the laser processing sub-region is controlled, and high-precision shaping with full-band convergence is realized. The application does not need any additional cost, only needs to control the pulse width and scan according to the overlapping path, and full-band error convergence can be realized. The method expands the application scene of laser processing, and provides a new optical manufacturing method with high precision and low cost.

Description

Technical Field

[0001] This invention belongs to the field of optical processing, and in particular, it is a laser shaping method with full-band error convergence. Background Technology

[0002] With the development of modern optical technology, ultra-precision optical components are being used in an increasing number of fields. To meet the urgent processing needs of these components, laser polishing, with its non-contact processing characteristics and the absence of surface defects and polishing hydrolysis impurities, is a promising method for achieving high-precision processing. However, laser polishing leaves residual ripples on the surface, significantly degrading surface accuracy. Further reshaping of the components is necessary to meet imaging requirements. Therefore, it is essential to invent a method to remove these residual ripples. Laser reshaping is a relatively economical non-contact method, but current single-point scanning reshaping methods based on ablation principles cannot simultaneously guarantee the convergence of surface shape and roughness and introduce laser scanning ripples. Therefore, developing new theories and processes to achieve full-band error convergence of materials is of great significance to the development of the processing field. Summary of the Invention

[0003] The technical problem this invention aims to solve is that existing laser reshaping methods cannot guarantee simultaneous convergence of surface shape and roughness and introduce laser scanning ripples. Therefore, a laser reshaping method with full-band error convergence is proposed. This method combines the densification-melting effect with overlapping beam focusing technology. By simply controlling the pulse width and scanning according to the overlapping beam focusing process, full-band error convergence can be achieved. This method expands the application scenarios of laser reshaping and is of great significance for improving the manufacturing precision and efficiency of high-end optical components.

[0004] The technical solution of the present invention is as follows:

[0005] A laser reshaping method with convergent error across the entire frequency band is characterized by the following steps:

[0006] 1) Determining the width τ of the laser pulse at different times t based on the densification-melting effect p The formula is as follows:

[0007]

[0008] in

[0009] Where ρ0 is the density of the material to be shaped, and C p It is the specific heat capacity at constant pressure, K is the thermal conductivity, A is the absorptivity of the material to be shaped, P is the laser power, and v is the specific heat capacity at constant pressure. scan Here, r0 is the laser scanning speed, r0 is the laser spot radius, and T is the temperature of the material to be shaped. fτ is the virtual temperature of the material to be shaped, ΔH is the activation enthalpy, R is the ideal gas constant of 8.314 J / (mol·K), and x is the fitting coefficient; v Let be a relaxation function. This is the symbol for the gradient operator.

[0010] 2) Determine the shaping depth h corresponding to different laser pulse widths, using the following formula:

[0011]

[0012] Where h HAZ It refers to the thickness of the heat-affected zone.

[0013] 3) Extract the surface height data of the region to be reshaped. Set the lowest surface height position to 0. Points above this position need to be reshaped. The height above the lowest point is considered the reshaping depth. Then, extract the X-direction interval d sequentially. x Y-direction interval d y The reshaping depth of the points is then calculated; subsequently, the Gaussian laser points are bundled into laser processing sub-regions, and these sub-regions are used as a new removal function f(x,y) to calculate the average reshaping depth of the sub-regions, thereby obtaining a point map of the average reshaping depth.

[0014] 4) The average depth point map of the laser shaping Converted to laser pulse width dot plot

[0015]

[0016] in The pulse dwell time represents the laser processing sub-region. Represents the convolution symbol.

[0017] 5) Based on the laser pulse width dot plot By setting the timing signal to control the acousto-optic modulator of the laser, and controlling the overlapping scanning path of the laser processing sub-region through overlapping beam focusing, the laser shaping with full-band convergence can be achieved.

[0018] The laser pulse width needs to ensure that the material undergoes densification and melting processes, so as to utilize the densification-melting effect for processing; and individual Gaussian laser points need to be bundled into a new removal function and shaped according to the overlapping scanning path.

[0019] Compared with the prior art, the technical effects of the present invention are as follows:

[0020] 1) By employing the densification-melting effect, the inherent laser ablation subtractive shaping is broken, achieving simultaneous convergence of surface shape and roughness;

[0021] 2) Due to the use of overlapping clustering technology, intermediate frequency errors are not introduced and the amount of control data is reduced by three orders of magnitude;

[0022] 3) This invention only requires controlling the pulse width and scanning according to the overlapping beam process to achieve full-band error convergence, which is of great significance for improving processing efficiency and improving workpiece surface accuracy. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the densification-melting effect, where a is a schematic diagram of the material modification principle during laser irradiation, and b is a schematic diagram of the density change during the densification-melting process.

[0024] Figure 2 The diagram shows the bundled overlapping process in the experiment, where a is a schematic diagram of the overlapping bundled process and b is a schematic diagram of the region division and path planning.

[0025] Figure 3 The initial component results of the experimental workpiece in the embodiment are shown, where a is the initial surface shape, b is the roughness measured by the optical profilometer, and c is the roughness measured by the atomic force microscope.

[0026] Figure 4 The figures show the experimental results of the laser reshaping method with full-band error convergence in the embodiments, where a is the initial surface shape, b is the roughness measured by the optical profilometer, and c is the roughness measured by the atomic force microscope. Detailed Implementation

[0027] The laser shaping method of the present invention, which utilizes densification-melting effect and overlapping beam-gathering process to achieve full-band error convergence, will be described in detail below with reference to the accompanying drawings and embodiments. However, this should not be construed as limiting the scope of protection of the present invention.

[0028] In this embodiment, the parameters are set as follows: laser power is 26.5W, laser frequency is 95kHz, pulse spacing and path spacing are 25.5μm, beam radius is 150μm, and pulse width is between 39-51μs. The workpiece to be processed is a square fused silica flat workpiece with a side length of 30mm.

[0029] A laser reshaping method for achieving full-band error convergence by utilizing densification-melting effect and overlapping beam-gathering technology includes the following steps:

[0030] 1) First, based on the laser shaping simulation results, a finite element simulation model was established. Through finite element analysis, the thermodynamic temperature under different pulse widths was calculated. When the pulse width was controlled between 39μs and 51μs, the thermodynamic temperature was controlled within the range of 1875K-2200K. Within this temperature range, fused silica undergoes both volume shrinkage due to densification and surface smoothing due to melting. The material surface temperature does not reach the evaporation temperature. The principle is as follows: Figure 1 As shown, the pulse width is calculated as follows:

[0031]

[0032] in

[0033] Where ρ0 is the density of fused silica, which is known to be 2.201 g / cm³. 3 C p The specific heat capacity of fused silica at constant pressure is known to be 35.9360 J / (Kg·K), K is the thermal conductivity of fused silica, known to be 2.0504 (W / m·K), A is the absorptivity of fused silica, known to be 0.8, P is the laser power, known to be 26.5 W, and v scan The scanning speed is known to be 25.5 mm / s, r0 is the laser spot radius known to be 150 μm, and T... f The virtual temperature of the fused silica is known to be 1350 K, ΔH is the activation enthalpy known to be 457 KJ / mol, R is the ideal gas constant known to be 8.314 J / (mol·K), and x is the fitting coefficient known to be 0.9; τ v It is a relaxation function; is the gradient operator symbol; T is the temperature of the material to be shaped, which is measured experimentally.

[0034] 2) Calculate the shaping depth corresponding to different pulse widths. Based on the results obtained in step 1), the material density, compacted region mass, and volume corresponding to different pulse widths can be obtained, thus yielding the shaping depth h corresponding to different laser pulse widths between 39μs and 51μs, as shown in the following formula:

[0035]

[0036] Where h HAZ It refers to the thickness of the heat-affected zone, which ranges from 6.6 μm to 8.8 μm.

[0037] 3) Use surface shape inspection equipment to detect surface shape errors in the workpiece, and use MATLAB software to extract the X-direction interval d sequentially based on the detection results. x Y-direction interval d yThe height is determined by using the lowest point as a reference to obtain the shaping depth information for each point. Then, individual Gaussian laser points are clustered into laser processing sub-regions. These sub-regions are used as a new removal function f(x,y). The average shaping depth of each extracted point within the sub-region is calculated to obtain the average shaping depth point map of the sub-region.

[0038] 4) Calculate the pulse width corresponding to each sub-region using the Princeton equation, and then refine the average depth point map. Convert to pulse width dot plot The calculation method is as follows:

[0039]

[0040] in Represents the length of stay. Represents the convolution symbol.

[0041] 5) Based on the pulse width dot plot Set the timing signal to control the acousto-optic modulator; control the overlapping scanning path of the laser processing sub-region, such as... Figure 2 As shown, high-precision shaping with convergence across the entire frequency band is ultimately achieved.

[0042] Laser reshaping is performed according to the above steps. The results before and after processing are as follows: Figure 3 and Figure 4 As shown in the figure, the laser shaping method, which utilizes densification-melting effect and overlapping beam-gathering technology to achieve full-band error convergence, significantly reduces the surface PV (0.049λ-0.024λ) and RMS (0.009λ-0.003λ) of the workpiece. No obvious laser scanning ripples are observed on the surface, and the micron-scale roughness (0.447nm-0.453nm) and nanoscale roughness (0.290nm-0.269nm) remain intact. In summary, the processing results observed in the examples demonstrate the significant practical effectiveness of this invention.

Claims

1. A laser reshaping method with convergent error across the entire frequency band, characterized in that, include: S1. Determination of laser pulse width τ at different times t based on densification-melting effect p The formula is as follows: in Where ρ0 is the density of the material to be shaped, and C p It is the specific heat capacity at constant pressure, K is the thermal conductivity, A is the absorptivity of the material to be shaped, P is the laser power, and v is the specific heat capacity at constant pressure. scan Here, r0 is the laser scanning speed, r0 is the laser spot radius, and T is the temperature of the material to be shaped. f τ is the virtual temperature of the material to be shaped, ΔH is the activation enthalpy, R is the ideal gas constant of 8.314 J / (mol·K), and x is the fitting coefficient; v Let be a relaxation function. This is the gradient operator symbol; S2. Determine the shaping depth h corresponding to different laser pulse widths, using the following formula: Where h HAZ It is the thickness of the heat-affected zone; S3. Extract the surface height data of the area to be reshaped. Set the lowest surface height position to 0. Points above this position need to be reshaped. The height above the lowest point is considered the reshaping depth. Extract the X-direction interval d sequentially. x Y-direction interval d y The reshaping depth of each point is determined; subsequently, the Gaussian laser points are clustered into laser processing sub-regions, and these sub-regions are used as a new removal function f(x,y). The average reshaping depth of each point within the sub-region is then calculated to obtain the average reshaping depth of each sub-region, thus yielding a point map of the average reshaping depth. S4. Map the average depth of the laser shaping point. Converted to laser pulse width dot plot The conversion formula is as follows: in The pulse dwell time represents the laser processing sub-region. Represents the convolution symbol; S5. According to the laser pulse width dot plot By setting the timing signal to control the acousto-optic modulator of the laser, and controlling the overlapping scanning path of the laser processing sub-region through overlapping beam focusing, the laser shaping with full-band convergence can be achieved.

2. The laser shaping method with full-band error convergence as described in claim 1, characterized in that, The laser pulse width needs to ensure that the material undergoes densification and melting processes, thereby utilizing the densification-melting effect for processing; and individual laser points need to be bundled into a new removal function and shaped according to the overlapping scanning path to avoid the generation of laser scanning ripples.

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