Method for high-quality and high-efficiency processing of inclined hole by ultrafast laser

Abstract

The application provides a method for high-quality and high-efficiency processing of inclined holes by ultrafast laser, and the method comprises the following steps: calculating the multi-pulse ablation threshold of an inclined workpiece by the results of ablation pits under different pulse energies, combining the energy density equation under different focal depths, and further obtaining the ablation depth equation at different focal depths on the inclined surface; designing different processing methods and processing parameters for the entrance, middle and exit stages of the inclined hole, and the feeding depth of each stage is calculated by the ablation depth equation at different focal depths and the number of scans. The method combines theoretical calculation with actual process, calculates the ablation depth equation at different focal depths on the inclined surface, establishes the ablation depth prediction model of the inclined hole processing process, and further determines the high-quality and high-efficiency processing method and processing parameters of the inclined hole. The three-stage processing selects different scanning modes and processing parameters for the entrance, middle and exit stages, which can effectively solve the problems of poor hole wall quality, poor process stability and low processing efficiency of the inclined hole.

Description

Technical Field

[0001] This invention relates to the field of special processing, and in particular to a method for high-quality and high-efficiency processing of oblique holes using ultrafast lasers. Background Technology

[0002] Modern manufacturing faces numerous challenges in machining oblique micro-holes, such as fuel injection holes in internal combustion engines, film cooling holes in aero-engine combustion chambers and guide vanes. This necessitates machining a large number of dense, discrete, small-diameter straight and oblique hole arrays on the walls of components made of high-generation single crystals and ceramic matrix composites. However, there are currently no high-quality and efficient technical solutions for the precision micromachining of micro-holes. With the development of laser technology, high-power, high-beam-quality ultrafast lasers have emerged. Due to their extremely short interaction time and extremely high light intensity density, they can significantly reduce thermal and mechanical damage during material processing, greatly improving laser processing quality. They are now widely used for precision micro-hole machining of various materials.

[0003] However, ultrafast lasers have precision issues such as taper and blind holes in the processing of oblique holes. Furthermore, the entry and exit points of oblique holes may experience processing damage such as cracking, chipping, local peeling, and poor quality of the entry and exit hole walls, resulting in low processing efficiency and poor processing stability. A method for laser-based oblique hole making is proposed in patent CN 110091083 A. This method involves using a spin-pulsed laser beam to perform circular motion at the workpiece's desired location to form a cutting ring. The cutting ring continues to move along a first direction of the workpiece until a hole is formed on the oblique workpiece. In this method, laser hole making is a non-contact process, which effectively reduces material damage compared to traditional machining. However, damage due to laser ablation still occurs at the hole's entrance and exit. Patent CN 112008262 A discloses an intelligent circular rotating laser method for machining irregularly shaped holes. This method involves intelligent 3D modeling based on the spatial structure of the hole, followed by control algorithm design and code generation to generate system control program code. Finally, an optical path module controls the spatial circular rotation of the laser beam to ensure the edge processing quality of the hole. However, this method only considers the optimization of the processing path and does not further modify the processing parameters to improve hole quality and efficiency.

[0004] The aforementioned problems severely limit the practical application of ultrafast laser processing technology for inclined small holes. Therefore, there is an urgent need for a high-quality and efficient method for ultrafast laser processing of inclined holes, which can minimize entry and exit damage, improve hole wall quality, and increase processing efficiency while maintaining high processing quality. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a high-quality and efficient ultrafast laser method for machining oblique holes. This invention enables high-quality laser machining of oblique small holes at different angles and curvatures on different materials. It employs a combination of theoretical calculations and practical processes, proposing a three-stage machining method for oblique holes. Different scanning methods and machining parameters are selected at the inlet, middle, and outlet stages of the oblique hole. This solves the problems of poor hole wall quality and poor process stability associated with oblique holes, and improves the machining quality and hole-making efficiency, while also exhibiting high machining stability and adaptability. The technical means employed in this invention are as follows:

[0006] A high-quality and efficient method for machining oblique holes using ultrafast lasers includes the following steps:

[0007] S1. Establish a predictive model for the ablation depth of an inclined workpiece, specifically including conducting multiple pulse ablation experiments on a workpiece with an inclination angle of θ, and using different pulse energies E. p The multi-pulse ablation threshold under the tilted workpiece was calculated based on the ablation pit results. The multi-pulse ablation threshold represents the critical value for material removal. Combined with the energy density equation at different focal depths, the ablation depth equation at different focal depths on the inclined plane is further obtained.

[0008] S2. Determine the machining method and parameters for the inclined hole. Specifically, design different machining methods and parameters for the inlet, middle, and outlet stages of the inclined hole. Inlet stage: Use a lower pulse energy E. p1 1. Perform spiral surface scanning with fewer scans N1; 2. Intermediate stage: Use higher pulse energy E p2 1. Perform spiral surface scanning with a higher number of scans N2; 2. Use lower pulse energy E at the export stage. p3 Helical machining is performed; the feed depth at each stage is determined by the ablation depth equation for different coke depths and the number of scans.

[0009] Furthermore, after S2, S3 is also included, which involves testing and verifying the machining parameters of the inclined hole in three stages: the inlet, middle, and outlet of S2, and correcting the parameters. Finally, the overall inclined hole machining test is conducted. If the process and parameters are appropriate, actual machining can be carried out.

[0010] Furthermore, the multi-pulse ablation threshold under the tilted workpiece The calculation includes the following steps:

[0011] The laser was controlled to perform multiple pulse ablation experiments on an inclined workpiece by changing the laser single pulse energy E. p Measure the diameter D of the ablation pit under different laser energies in a multi-pulse operation;

[0012] The formula for the peak energy density within the tilted cross section of a Gaussian beam is as follows:

[0013]

[0014] In the formula, N is the number of pulses, and ω0 is the waist radius;

[0015] The relationship between the diameter of the laser ablation pit and the laser energy density is as follows:

[0016]

[0017] In the formula, Given the ablation threshold, the relationship between the multi-pulse energy and the diameter of the ablation pit can be derived from equations (1) and (2), as follows:

[0018]

[0019] Based on equation (3), a scatter plot of experimental data was drawn and linear fitting was performed. It was found that the logarithm of the multi-pulse energy and the square of the ablation pit diameter satisfy a linear relationship, and thus the multi-pulse ablation threshold was calculated.

[0020] Furthermore, the energy density equations for different focal depths are specifically determined by the energy density formula that follows a Gaussian function distribution along the radial direction and the determined spot radius size, that is, the energy density at a distance r from the spot center in the radial direction. Determined by the following formula:

[0021]

[0022] ω z Let ω be the beam radius. In a focused laser system, the beam radius changes continuously along the propagation direction. Any cross-section along the central axis exhibits a hyperbolic shape. The beam radius ω is the distance from the focal point z along the propagation direction. z Determined by the following formula:

[0023]

[0024] In the formula, R z The Rayleigh length of the laser system is determined by the following formula:

[0025]

[0026] In the formula, λ is the laser wavelength;

[0027] From equations (4), (5), and (6), the energy density equations for different focal depths can be obtained, as follows:

[0028]

[0029] Furthermore, the ablation depth equations at different focal depths on the inclined plane can be determined using the following logarithmic function based on the theoretical ablation depth at each location on the ablation surface irradiated by the laser, and are divided into negative defocus formulas and positive defocus formulas:

[0030]

[0031]

[0032] In the formula, ε f ε is the negative coke ablation depth coefficient. b The positive decoking depth coefficient is used. For laser energy density, The multi-pulse ablation threshold is defined, where the ablation depth coefficient is determined by measuring the ablation depth through positive and negative defocusing experiments, combined with the laser energy density. and multi-pulse ablation threshold Find the value. Since the laser energy follows a Gaussian distribution, the deepest processing depth for different focal depths is when r is 0, meaning the central axis position is the location of the deepest ablation depth within the spot area. Let this depth represent the ablation depth for different focal depths; the ablation depth equation can be simplified as follows:

[0033]

[0034]

[0035] Furthermore, S2 specifically refers to:

[0036] Entry stage: The laser focusing position is located at the intersection of the central axis of the circular hole and the inclined plane, using a fixed-focus, low-energy pulse E. p1 In spiral surface scanning with fewer scans N1, the machining depth varies depending on the inclined surface and the laser's focal depth. The angle between the bottom surface and the horizontal plane gradually decreases. When the rate of change of the angle is less than 10%, the focal point performs axial feed to a depth of a. p1 The size can be determined by the ablation depth equation at different coke depths and the number of scans N1. Then, the above steps are repeated, and after S1 feed operations, the bottom surface of the processed surface is nearly horizontal.

[0037] Intermediate stage: using higher pulse energy E p2 A spiral surface scanning process is performed with a high number of scans N2. When the ablation depth change rate is less than 5%, the focal point is axially fed to a depth of a. p2 A larger feed depth can improve processing efficiency while ensuring the quality of the hole wall. The size can be determined by the ablation depth equation for different coke depths and the number of scans N2. Then, repeat the above steps and perform S2 feed operations. When the bottom surface is about to be penetrated, the oblique hole exit part is reached.

[0038] Export stage: using lower pulse energy E p3 The spiral machining process is performed, and the pitch of the feed spiral is determined based on the equation for the ablation depth at different coke depths.

[0039] The present invention has the following advantages:

[0040] 1. This method proposes to combine theoretical calculation with actual process. By calculating the ablation depth equation at different coke depths on the inclined surface, an ablation depth prediction model for the inclined hole processing process is established, thereby further determining the high-quality and high-efficiency processing method and processing parameters for inclined holes.

[0041] 2. This method proposes a three-stage machining process for oblique micro-holes, selecting different scanning methods and machining parameters for the inlet, middle, and outlet stages. This can effectively solve the problems of poor hole wall quality, poor process stability, and low machining efficiency in oblique holes, and achieve high-quality oblique hole machining with a depth-to-diameter ratio greater than 10, while maintaining high machining stability and adaptability.

[0042] 3. The three-segment machining method for inclined holes proposed in this paper can produce inclined holes with different inclination angles and different curved surfaces with high depth-to-diameter ratios. This method can also be applied to the machining research of other inclined hole types such as rectangular holes, sieve holes, and cat ear-shaped holes. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a flowchart of the laser processing method for high-quality oblique holes provided by the present invention;

[0045] Figure 2 This is a schematic diagram showing the relationship between the logarithm of the multi-pulse energy and the square of the ablation pit diameter in this invention;

[0046] Figure 3 This is a schematic diagram of the positive and negative decoking and ablation depths on the inclined surface of the present invention;

[0047] Figure 4 This is a schematic diagram illustrating the division of the three-section machining method for oblique holes according to the present invention;

[0048] Figure 5 This is a schematic diagram of the three-section machining of the oblique hole of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] like Figure 1 As shown in the figure, this invention provides a high-quality and high-efficiency ultrafast laser machining method for oblique holes. This method enables high-quality laser machining of oblique circular holes at different angles and with different curvatures on different materials. It combines theoretical calculations with practical processes, proposing a three-stage machining method for oblique holes. Different scanning methods and machining parameters are selected for the inlet, middle, and outlet stages of the oblique hole. This solves the problems of poor hole wall quality and poor process stability in oblique holes, and improves the machining quality and hole-making efficiency, while also exhibiting high machining stability and adaptability. Specifically, it includes the following steps:

[0051] S1. Establish a predictive model for the ablation depth of an inclined workpiece, specifically including conducting multiple pulse ablation experiments on a workpiece with an inclination angle of θ, and using different pulse energies E. p The multi-pulse ablation threshold under the tilted workpiece was calculated based on the ablation pit results. The ablation pit results include 3D morphology, and the multi-pulse ablation threshold represents the critical value for material removal. Combined with the energy density equation at different focal depths, the ablation depth equation at different focal depths on the inclined plane is further obtained.

[0052] S2. Determine the machining method and parameters for the inclined hole. Specifically, design different machining methods and parameters for the inlet, middle, and outlet stages of the inclined hole. Inlet stage: Use a lower pulse energy E. p1 1. Perform spiral surface scanning with fewer scans N1; 2. Intermediate stage: Use higher pulse energy E p2 1. Perform spiral surface scanning with a higher number of scans N2; 2. Use lower pulse energy E at the export stage. p3 Helical machining is performed; the feed depth at each stage is determined by the ablation depth equation at different coke depths and the number of scans.

[0053] S3. Conduct machining parameter tests and verifications for the three stages of the inclined hole in S2: inlet, middle, and outlet. Correct the parameters and finally conduct overall inclined hole machining tests and verifications. If the process and parameters are appropriate, actual machining can proceed.

[0054] like Figure 2 As shown, the multi-pulse ablation threshold under the tilted workpiece The calculation includes the following steps:

[0055] The laser was controlled to perform multiple pulse ablation experiments on an inclined workpiece by changing the laser single pulse energy E. p Measure the diameter D of the ablation pit under different laser energies in a multi-pulse operation;

[0056] The formula for the peak energy density within the tilted cross section of a Gaussian beam is as follows:

[0057]

[0058] In the formula, N is the number of pulses, and ω0 is the waist radius;

[0059] The relationship between the diameter of the laser ablation pit and the laser energy density is as follows:

[0060]

[0061] In the formula, Given the ablation threshold, the relationship between the multi-pulse energy and the diameter of the ablation pit can be derived from equations (1) and (2), as follows:

[0062]

[0063] Based on equation (3), a scatter plot of experimental data was plotted and linear fitting was performed. It was found that the logarithm of the multi-pulse energy and the square of the ablation pit diameter satisfy a linear relationship. Thus, the multi-pulse ablation threshold was calculated. The ablation threshold is the critical value for material removal. When the energy is greater than this value, the material will begin to be removed.

[0064] like Figure 3 As shown, when the surface to be processed is located before laser focusing (the focused spot is inside the material), material removal only occurs at the surface, generating plasma. However, when the surface to be processed is located after laser focusing (the focused spot is on the upper surface of the material), the air at the focal point is broken down by the pulsed laser, generating plasma and consuming some pulse energy. Therefore, the actual pulse energy reaching the surface for material removal is reduced, resulting in a greater actual processing depth for negative defocusing than for positive defocusing. The pre-focus ablation depth H... f ablation depth H after coking b The calculation is as follows:

[0065] Establish energy density equations for different focal depths. On a light spot with a defined radius, the energy density distribution along the radial direction of the light spot follows a Gaussian function formula, that is, the energy density at a distance r from the center of the light spot in the radial direction. Determined by the following formula:

[0066]

[0067] ω zLet ω be the beam radius. In a focused laser system, the beam radius changes continuously along the propagation direction. Any cross-section along the central axis exhibits a hyperbolic shape. The beam radius ω is the distance from the focal point z along the propagation direction. z Determined by the following formula:

[0068]

[0069] In the formula, R z The Rayleigh length of the laser system is determined by the following formula:

[0070]

[0071] In the formula, λ is the laser wavelength;

[0072] From equations (4), (5), and (6), the energy density equations for different focal depths can be obtained, as follows:

[0073]

[0074] The ablation depth equations for different focal depths on the inclined plane can be determined using the following logarithmic function based on the theoretical ablation depth at each location on the ablation surface irradiated by the laser. These equations are divided into negative defocus formulas and positive defocus formulas:

[0075]

[0076]

[0077] In the formula, ε f ε is the negative coke ablation depth coefficient. b The positive decoking depth coefficient is used. For laser energy density, The multi-pulse ablation threshold is defined, where the ablation depth coefficient is measured through positive and negative defocusing experiments. The ablation depth differs depending on whether the material is under positive or negative defocusing; therefore, the ablation depth coefficient is introduced to differentiate between them. This is combined with the laser energy density. and multi-pulse ablation threshold Find the value. Since the laser energy follows a Gaussian distribution, the deepest processing depth for different focal depths is when r is 0, meaning the central axis position is the location of the deepest ablation depth within the spot area. Let this depth represent the ablation depth for different focal depths; the ablation depth equation can be simplified as follows:

[0078]

[0079]

[0080] like Figure 4 , Figure 5 As shown, S2 specifically refers to:

[0081] Entry stage: The calculation in this stage involves the positive defocus and negative defocus mentioned above. As the number of scans increases, the tilt angle of the processed bottom surface becomes smaller and smaller. When the change rate of the tilt angle relative to the tilt angle after the previous scan is less than 10%, the focus begins to move down (feed depth).

[0082] Specifically, the laser focusing position is located at the intersection of the central axis of the circular hole and the inclined plane, using a fixed-focus, low-energy pulse E. p1 In spiral surface scanning with fewer scans N1, the machining depth varies depending on the inclined surface and the laser's focal depth. The angle between the bottom surface and the horizontal plane gradually decreases. When the rate of change of the angle is less than 10%, the focal point performs axial feed to a depth of a. p1 The size can be calculated by the ablation depth equation at different coke depths and the number of scans N1. Then, repeat the above steps and perform S1 feeds to achieve a near-horizontal bottom surface, i.e., when the inclination angle is 0. Based on the above design, low damage at the entrance, hole wall quality and dimensional accuracy can be guaranteed. Using spiral surface sweeping can provide conditions for subsequent processing steps to achieve high depth-to-diameter ratio oblique hole processing.

[0083] Intermediate stage: using higher pulse energy E p2 A spiral surface scanning process is performed with a high number of scans N2. When the ablation depth change rate is less than 5%, the focal point is axially fed to a depth of a. p2 A larger feed depth can improve processing efficiency while ensuring hole wall quality. The size can be determined using the ablation depth equation for different coke depths and the number of scans N2. Then, the above steps are repeated. After S2 feed cycles, the hole reaches the oblique hole exit section when the bottom surface is about to be penetrated. The ablation depth variation rate here applies to fixed-coke processing. As the number of scans increases, the processing depth decreases. When the variation rate of the depth relative to the previous scan depth is less than 5%, the focal point begins to shift downwards (feed depth).

[0084] Exit Stage: At the hole exit point after the intermediate stage, because the material is inclined and the machining bottom surface is flat, one side will be machined first, which is the exit stage. A lower pulse energy E is used. p3 By performing helical machining and determining the pitch of the feed helix based on the ablation depth equation for different coke depths, high-quality hole walls can be achieved at the exit of the inclined hole. Furthermore, helical machining can further improve hole-making efficiency.

[0085] Specifically, due to the differences between the laser and the material being processed, the required energy and the number of scans also differ. Therefore, the specific criteria for dividing the three stages can be adjusted according to the actual application scenario.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for high-quality and high-efficiency machining of oblique holes using ultrafast lasers, characterized in that, Includes the following steps: S1. Establish a predictive model for the ablation depth of an inclined workpiece, specifically including conducting multiple pulse ablation experiments on a workpiece with an inclination angle of θ, and using different pulse energies E. p The ablation pit results were used to calculate the multi-pulse ablation threshold for the tilted workpiece. The multi-pulse ablation threshold represents the critical value for material removal. Combined with the energy density equation at different focal depths, the ablation depth equation at different focal depths on the inclined plane is further obtained. S2. Determine the machining method and parameters for the inclined hole. Specifically, design different machining methods and parameters for the inlet, middle, and outlet stages of the inclined hole. Inlet stage: Use a lower pulse energy E. p1 1. Perform spiral surface scanning with fewer scans N1; 2. Intermediate stage: Use higher pulse energy E p2 1. Perform spiral surface scanning with a higher number of scans N2; 2. Use lower pulse energy E at the export stage. p3 Helical machining is performed; the feed depth at each stage is determined by the ablation depth equation at different coke depths and the number of scans. The multi-pulse ablation threshold under the tilted workpiece The calculation includes the following steps: The laser was controlled to perform multiple pulse ablation experiments on an inclined workpiece by changing the laser single pulse energy E. p Measure the diameter D of the ablation pit under different laser energies in a multi-pulse operation; The formula for the peak energy density within the tilted cross section of a Gaussian beam is as follows: In the formula, Where N is the peak energy density on the surface; and N is the number of pulses. The waist radius; The relationship between the diameter of the laser ablation pit and the laser energy density is as follows: In the formula, Given the ablation threshold, the relationship between the multi-pulse energy and the diameter of the ablation pit can be derived from equations (1) and (2), as follows: Based on equation (3), a scatter plot of experimental data was drawn and linear fitting was performed. It was found that the logarithm of the multi-pulse energy and the square of the ablation pit diameter satisfy a linear relationship, and thus the multi-pulse ablation threshold was calculated. The energy density equations for different focal depths are specifically determined by the energy density formula that follows a Gaussian function distribution along the radial direction and the predetermined spot radius, i.e., the energy density at a distance r from the spot center in the radial direction. Determined by the following formula: Let be the beam radius. In a focused laser system, the beam radius changes continuously along the propagation direction. Any cross-section along the central axis exhibits a hyperbolic shape. The beam radius at the distance z from the focal point in the propagation direction is... Determined by the following formula: In the formula, The Rayleigh length of the laser system is determined by the following formula: In the formula, The wavelength of the laser; From equations (4), (5), and (6), the energy density equations for different focal depths can be obtained, as follows: The ablation depth equations for different focal depths on the inclined plane can be determined using the following logarithmic function based on the theoretical ablation depth at each location on the ablation surface irradiated by the laser. These equations are divided into negative defocus formulas and positive defocus formulas: In the formula, H f , H b These represent the ablation depth under negative and positive defocusing conditions, respectively, and are used to predict the processing depth under different defocusing states. The negative coke ablation depth coefficient. The positive decoking depth coefficient is used. For laser energy density, The multi-pulse ablation threshold is defined, where the ablation depth coefficient is determined by measuring the ablation depth through positive and negative defocusing experiments, combined with the laser energy density. and multi-pulse ablation threshold The laser energy follows a Gaussian distribution. The deepest processing depth for different focal depths is when r is 0, i.e., the central axis position is the position with the deepest ablation depth within the spot area. Let this depth be the ablation depth for different focal depths, and the ablation depth equation can be simplified as follows:

2. The method for high-quality and high-efficiency machining of oblique holes using ultrafast lasers according to claim 1, characterized in that, S2 also includes: S3. Conduct machining parameter tests and verifications for the three stages of the inclined hole in S2: inlet, middle, and outlet. Correct the parameters and finally conduct overall inclined hole machining tests and verifications. If the process and parameters are appropriate, actual machining can proceed.

3. The method for high-quality and high-efficiency machining of oblique holes using ultrafast lasers according to claim 1, characterized in that, Specifically, S2 is: Entry stage: The laser focusing position is located at the intersection of the central axis of the circular hole and the inclined plane, using a fixed-focus, low-energy pulse E. p1 In spiral surface scanning with fewer scans (N1), the machining depth varies depending on the inclined surface and the laser's focal depth. The angle between the bottom surface and the horizontal plane gradually decreases. When the rate of change of the angle is less than 10%, the focal point performs axial feed to a depth of a. p1 The size can be determined by the ablation depth equation at different coke depths and the number of scans N1. Then, the above steps are repeated, and after S1 feed operations, the bottom surface of the processed surface is nearly horizontal. Intermediate stage: using higher pulse energy E p2 A spiral surface scanning process is performed with a high number of scans N2. When the ablation depth change rate is less than 5%, the focal point is axially fed, with a feed depth of a. p2 The size can be determined by the ablation depth equation at different coke depths and the number of scans N2. Then, repeat the above steps and perform S2 feed operations. When the bottom surface is about to be penetrated, the oblique hole exit part is reached. Export stage: using lower pulse energy E p3 The spiral machining process is performed, and the pitch of the feed spiral is determined based on the ablation depth equation for different coke depths.

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