Process for precisely machining rectangular diamond micro-channel in complex shape by pulse laser based on online monitoring

Abstract

The invention discloses a process for precisely machining a rectangular diamond micro-channel in a complex shape by pulse laser based on online monitoring. The method comprises the following steps: (1) carrying out a single-factor test, optimizing laser processing parameters, carrying out finite element simulation according to the type and depth requirements of a micro-channel, and selecting laser processing times; (2) determining the motion trail of the six-degree-of-freedom platform according to the complex micro-channel structure shape of the diamond workpiece to be machined; (3) micro-channel laser machining is conducted, linkage machining is conducted on the six-degree-of-freedom platform and a laser device, and the workpiece is always inclined in the direction perpendicular to the laser scanning path direction in the machining process; (4) after the micro-channel on one side is machined, laser machining is conducted on the micro-channel on the other side, and machining parameters are the same as those in the step (3); the inclination directions are opposite; and (5) after laser processing is finished, cleaning the surface of the diamond and measuring the perpendicularity of the groove. According to the method, a micro-channel structure with a complex shape can be efficiently processed, and the phenomenon that the side wall of the micro-channel is inclined due to non-uniform energy distribution in a Gaussian laser space is overcome.

Description

Technical Field

[0001] The present invention relates to the field of microstructure processing of hard and brittle materials such as diamond, and specifically to a process for precision processing of complex-shaped diamond rectangular microchannels using pulsed laser based on online monitoring. Background Art

[0002] Diamond is a typical hard and brittle material. Due to its properties such as high hardness, high wear resistance, high thermal conductivity, high breakdown voltage, high refractive index (n=2.4) and low thermal expansion coefficient, it is widely used in the fields of microelectronics, optical devices and aerospace. The extremely strong thermal conductivity of diamond makes diamond microchannels widely used in the field of efficient heat dissipation. However, the superhardness of diamond brings great difficulties to the high-precision processing of diamond products. Traditional mechanical processing methods have difficult-to-overcome problems such as slow processing speed, low processing efficiency and high processing cost when processing hard and brittle materials. There are great limitations in processing diamonds through mechanical processing methods. Laser processing is a new type of non-contact processing method. Its processing efficiency depends on the optical and thermal properties of the laser, and has nothing to do with the mechanical properties of the processing material. Therefore, it is very suitable for processing diamonds with high hardness and high wear resistance.

[0003] Due to the particularity of Gaussian laser energy distribution, the energy density at the edge of the laser spot is much lower than the energy density at the center of the spot, resulting in insufficient material removal at the edge during laser processing. The groove sidewalls obtained by laser processing are often inclined, and the groove cross-sectional profile is "V" shaped. This greatly affects the accuracy of laser processing micro-grooves. Although the Gaussian laser can be converted into a top-hat beam with uniform energy distribution through a beam shaper to ensure that the energy distribution in the diameter direction of the laser spot remains consistent, this method is expensive and cannot be applied to all lasers, and has certain limitations. At the same time, the repeatability and positioning accuracy of complex diamond microfluidic processing in traditional laser processing is poor. Calibration is done only by the naked eye before processing, and parameter changes cannot be handled intelligently and in real time during processing, resulting in poor batch processing stability and positioning accuracy.

[0004] Therefore, a trajectory control and process for pulsed laser precision machining of complex-shaped diamond rectangular microchannels based on online monitoring was proposed to improve the repeatability accuracy of laser machining and the verticality of the sidewalls of Gaussian laser-machined microchannels. Summary of the Invention

[0005] Purpose of the invention: In order to solve the problems of difficult repeated positioning, low processing precision stability and low processing quality of complex-shaped microchannels caused by uneven spatial distribution of Gaussian energy in traditional laser processing systems, the present invention provides a process for pulsed laser precision processing of complex-shaped diamond rectangular microchannels based on online monitoring. It can perform high-quality processing on complex diamond microchannels of different shapes, effectively improve the verticality of the side walls of laser-processed microgrooves, and ensure the accuracy of laser-processed microstructures.

[0006] Technical solution: The present invention achieves the above-mentioned purpose through the following technical solution:

[0007] A device for precision processing a complex-shaped diamond rectangular microchannel using pulsed laser based on online monitoring comprises a picosecond laser (1), a six-degree-of-freedom platform (4), and an online monitoring system; the online monitoring system comprises a CCD camera (3) with an infrared thermal imager; wherein the diamond piece (3) to be processed is horizontally placed on the six-degree-of-freedom platform (4) and fixed; the picosecond laser 1 and the CCD camera (2) with the infrared thermal imager are located above the platform, and the temperature of the workpiece surface is monitored in real time during the laser processing process; the motion trajectory of the six-degree-of-freedom platform is determined according to the shape of the complex microchannel, and is linked to the laser during the laser processing process.

[0008] Preferably, the six-degree-of-freedom platform has a movement accuracy of 20 nm and a rotation accuracy of arc-sec 0.1, and the laser used is a picosecond laser with a light source wavelength of 355 nm, a spot diameter of 10 μm, and a pulse width of 12 ps.

[0009] After the platform is tilted, the position of the workpiece changes. The six-degree-of-freedom platform follows the scanning trajectory of the laser to perform displacement and focal length compensation in the corresponding direction, thereby improving positioning accuracy and processing quality. The displacement compensation distance x' and focal length compensation distance z of the six-degree-of-freedom platform are calculated by formula (1) and formula (2):

[0010] x'=xx·c oθs (1)

[0011] z=x·sinθ (2)

[0012] X is the distance between the machining position and the center of the workpiece; θ is the inclination angle of the workpiece.

[0013] Based on the above device, a pulsed laser precision machining process for complex-shaped diamond rectangular microchannels based on online monitoring is described as follows:

[0014] Step 1: Conduct a single-factor experiment on picosecond laser processing of diamond microchannels, optimize the laser processing parameters, perform finite element simulation based on the type and depth requirements of the microchannel, and select the number of laser processing times.

[0015] In step 1, the laser energy density, scanning speed, and scanning spacing used in microchannel processing were selected through single-factor experiments. The principle of parameter selection is: for laser energy density, a higher laser energy density should be selected without causing deterioration of the laser processing surface quality and increase in the degree of graphitization; for scanning speed, a higher scanning speed should be selected without causing deterioration of the laser processing surface quality and increase in the degree of graphitization. The results of the single-factor experiment are as follows: Laser processing energy density 10.18J / cm 2 , laser frequency 400kHz, scanning speed 100mm / s, scanning spacing 5μm, scanning trajectory is a linear reciprocating trajectory; laser energy density is 10.18J / cm 2 When the material surface is processed, the degree of graphitization is low, which can effectively reduce the degree of damage to the material surface during processing.

[0016] In step 1, the steps for selecting the number of laser processing times through finite element simulation are as follows:

[0017] Step 1: Create a finite element model with a surface inclination angle of α1 and set it to state A. Simulate the evolution of the ablation area contour after different laser processing times on the model in state A. After the simulation is completed, export the ablation surface contour from COMSOL to a CAD file.

[0018] Step 2: Retain the upper surface profile of state A in step 1 and tilt it in the opposite direction by α2 = 2*α1. Re-import the profile information into COMSOL to construct a new initial state profile model, namely state B. Continue to simulate the groove profile evolution process with different laser processing times in state B, so as to control the inclination degree of the sidewalls on both sides of the groove, obtain the profile state at different times, and provide guidance for the selection of experimental parameters.

[0019] The surface inclination angle selected for state A is α1, which is 10°.

[0020] Step 2: Mount the diamond sheet to be processed on a six-degree-of-freedom platform, select the complex diamond microchannel structure to be processed, and determine the motion trajectory of the six-degree-of-freedom platform according to the shape of the complex microchannel.

[0021] Step 3: Use the parameters optimized by the single-factor experiment in step 1 and the laser processing times determined in step 2 to perform microchannel laser processing. First, use a CCD camera to assist the laser in focusing on the center of the diamond sheet, and use a six-degree-of-freedom platform to perform linked processing with the laser, so that during the picosecond laser processing, the workpiece is always tilted in the direction perpendicular to the laser scanning path.

[0022] In step three, the tilt angle of the six-degree-of-freedom platform is determined as follows: the tilt angle of the six-degree-of-freedom platform is gradually increased from 0° to 20° to explore the evolution of the ablation area profile under different sample tilt angles; the platform tilt angle is selected to be 10° based on the groove cross-sectional profile and depth and width changes. When the tilt angle is 10°, the depth and width of the laser-processed groove are less affected by the tilt angle, and the effect on the laser ablation rate is small.

[0023] Step 4: After laser processing of one side of the microchannel in step 3, the six-degree-of-freedom platform and the laser are linked again, and the tilt direction of the six-degree-of-freedom platform is opposite to the tilt direction in step 3, and the microchannel on the other side is laser processed. The processing parameters are the same as those in step 3, and the number of laser scans should be less than the number of scans in step S2 to ensure the symmetry of the two sides of the microgroove.

[0024] Step 5: After laser processing, clean the diamond surface and measure the verticality of the groove.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention uses an online monitoring system to monitor the temperature and posture of the material during the processing in real time, thereby reducing errors in the processing process and improving the shape accuracy and position accuracy of complex-shaped microfluidic channel processing.

[0027] (2) The present invention uses a high-precision six-degree-of-freedom platform and laser for linkage processing, and performs focal length and displacement compensation through the six-degree-of-freedom platform, thereby improving the positioning accuracy and processing efficiency of complex-shaped diamond microchannel processing.

[0028] (3) The present invention uses finite element simulation to determine the number of laser scans before laser processing. Finite element simulation can effectively optimize parameters, save time, and improve processing efficiency.

[0029] (4) The present invention solves the problem of insufficient material removal at the groove sidewall caused by uneven spatial energy distribution of Gaussian laser by symmetrically tilting the material processing method, thereby improving the processing accuracy of the micro-groove. This method provides a new idea for subsequent research on laser precision microstructure processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of a process for precision machining of complex-shaped diamond rectangular microchannels using pulsed lasers based on online monitoring according to the present invention;

[0031] Figure 2 This is an example diagram of a complex-shaped diamond rectangular microfluidic channel;

[0032] Figure 3This is a schematic diagram of the processing process of pulsed laser precision machining trajectory control and technology of complex-shaped diamond rectangular micro-channels based on online monitoring of the present invention;

[0033] Figure 4 The temperature monitoring of the workpiece surface during laser processing; (a) is the temperature distribution of the workpiece surface before laser processing, and (b) is the temperature distribution of the workpiece surface during laser processing;

[0034] Figure 5 1 is a graph showing the results of a single-factor experiment in Example 1 of the present invention, wherein (a) shows the effect of laser energy density on the depth and width of the microchannel, (b) shows the effect of laser scanning speed on the depth and width of the microchannel, and (c) shows the effect of laser scanning spacing on the depth and width of the microchannel;

[0035] Figure 6 1 is a graph showing the cross-sectional profile, depth, and width of the grooves processed at different surface inclination angles in Example 1 of the present invention;

[0036] Figure 7 It is a finite element simulation process diagram of the present invention.

[0037] Figure 8 Result diagrams of finite element simulation optimization parameters of Example 1 of the present invention are shown, showing the change in groove depth caused by different scan times in the finite element simulation step 1, where the scan times in (a) are 20, (b) are 30, (c) are 40, and (d) are 60.

[0038] Figure 9 1 is a comparison diagram of the processing effects of Example 1 of the present invention, wherein (a) is a diagram showing the processing results of vertical laser processing of diamond, and (b) is a diagram showing the processing results of tilt processing by the laser and the six-degree-of-freedom platform of the present invention.

[0039] Figure 2 Middle: 1-Picosecond laser, 2-CCD camera with infrared thermal imager, 3-Diamond wafer to be processed, 4-Six-degree-of-freedom platform. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0041] In the description of the present invention, unless otherwise clearly specified and limited, the term "installation" should be understood in a broad sense. For example, it can be either fixed installation or detachable installation, direct installation or indirect installation through an intermediate medium. For ordinary technicians in this field, the specific meaning of the above terms in the present invention can be understood according to the specific circumstances.

[0042] Example 1

[0043] like Figure 3 As shown, an apparatus for pulsed laser precision machining of complex-shaped rectangular diamond microchannels based on online monitoring includes a picosecond laser 1, a six-degree-of-freedom platform 4, and an online monitoring system. The online monitoring system includes a CD camera 2 with an infrared thermal imager. A diamond wafer 3 to be machined is horizontally placed and fixed on the six-degree-of-freedom platform 4. The picosecond laser 1 and the CD camera 2 with an infrared thermal imager are located above the platform and monitor the workpiece surface temperature in real time during laser machining. The motion trajectory of the six-degree-of-freedom platform is determined by the shape of the complex microchannel and is linked to the laser during the machining process.

[0044] During laser processing, the temperature change of the material surface is an important factor affecting the processing quality. By using an infrared thermal imager to reflect the instantaneous temperature of the laser irradiation area in real time, the laser parameters can be efficiently controlled, the degree of graphitization of the diamond surface can be reduced, and the surface quality of the microchannel can be improved.

[0045] Figure 2 This is an example of a complex-shaped diamond rectangular microchannel. In this embodiment, a picosecond laser is used to process a wavy ( Figure 2 Taking the rectangular microchannel array shown in (b) as an example, the processing technology includes the following steps:

[0046] Step 1: Conduct a single-factor experiment on picosecond laser processing of diamond microchannels, optimize laser processing parameters, perform finite element simulation based on the type and depth requirements of the microchannel, and select the number of laser processing times;

[0047] (1) Before processing the diamond wavy array rectangular microchannel, a single factor experiment was conducted to determine the laser energy density, scanning speed, and scanning spacing used in processing the microchannel. The principle of parameter selection is: for laser energy density, a larger laser energy density should be selected without causing the laser processing surface quality to deteriorate and the degree of graphitization to increase; for scanning speed, a higher scanning speed should be selected without causing the laser processing surface quality to deteriorate and the degree of graphitization to increase.

[0048] The results of the single factor test are as follows Figure 5 As shown. Based on the results of single factor test, the laser processing energy density is 10.18J / cm 2, laser frequency 400kHz, scanning speed 100mm / s, scanning spacing 5μm, scanning trajectory is a linear reciprocating trajectory; laser energy density is 10.18J / cm 2 When the material surface is processed, the degree of graphitization is low, which can effectively reduce the degree of damage to the material surface during processing.

[0049] (2) Perform finite element simulation based on the type and depth requirements of the microchannel to determine the number of laser scans. The steps of finite element simulation are as follows:

[0050] Step 2-1, determine the inclination angle of the six-degree-of-freedom platform: gradually increase the inclination angle α of the six-degree-of-freedom platform from 0° to 20°, and explore the evolution of the ablation area profile under different sample inclination angles; the greater the inclination of the sample surface, the better the verticality of one side of the groove. As the inclination of the sample surface increases, the width of the groove gradually increases, while the depth of the groove decreases. The cross-sectional profile, depth, and width of the groove processed at different surface inclination angles are shown in the figure below. Figure 6 Considering factors such as the groove width and the sidewall inclination, the platform inclination angle α1 is selected to be 10°. When the inclination angle is 10°, the depth and width of the laser-processed groove are less affected by the inclination angle, and the effect on the laser ablation rate is also small.

[0051] Step 2-2: Create a finite element model with a sample surface tilt angle of α1 = 10° and set it to state A. Simulate the evolution of the ablated area profile after different laser processing times on the model in state A. After the simulation, export the ablated surface profile from COMSOL as a CAD file.

[0052] Keep the upper surface contour of state A in step 1 and tilt it in the opposite direction by 10° (α2 = 20°), and re-import the contour information into COMSOL to construct a new initial state contour model, namely state B, as shown in Figure 7 As shown. In state B, the evolution of the groove profile with different laser processing times is simulated to control the inclination of the sidewalls on both sides of the groove, obtain the profile state at different times, and provide guidance for the selection of test parameters. The finite element simulation results are shown in Figure 8 According to the results of finite element simulation, the number of scans is selected as 60.

[0053] Step 2: Determine the motion trajectory of the six-degree-of-freedom platform based on the complex microchannel shape, so that the six-degree-of-freedom platform follows the laser scanning trajectory to perform displacement and focal length compensation in the corresponding direction, realizing the coordinated processing of the six-degree-of-freedom platform and the laser. Based on the distance x between the processing position and the center of the workpiece and the angle θ of the workpiece tilt, the displacement compensation distance x' and the focal length compensation distance z of the six-degree-of-freedom platform are calculated using equations (1) and (2):

[0054] x'=xx·c oθs (1)

[0055] z=x·sinθ (2)

[0056] In this embodiment, a square, defect-free CVD diamond with a side length of 15 mm and a thickness of 1 mm was selected and mounted at the center of a six-degree-of-freedom platform. A picosecond laser with a light source wavelength of 355 nm, a spot diameter of 10 μm, and a pulse width of 12 ps was used to focus on the center of the CVD diamond sheet with the assistance of a CCD camera. The processing type was selected as a wavy microchannel.

[0057] Step 3: Use a CCD camera to assist the laser in focusing on the center of the diamond sheet, and use the processing parameters determined by the single factor test results in step 1 to perform micro-channel processing. The processing parameters are an energy density of 10.18 J / cm 2 , laser frequency 400kHz, scanning speed 100mm / s, scanning spacing 5μm, and scanning times 60 times. During the processing, the six-degree-of-freedom platform is controlled to be linked with the laser so that the workpiece is always tilted 10° in the direction perpendicular to the laser scanning path.

[0058] Step 4: After the laser processing in step 3 is completed, the six-degree-of-freedom platform is controlled so that the workpiece is always tilted 10° in the opposite direction of the tilt direction in step 3, and laser processing is performed again with the same processing parameters as in step 3.

[0059] Among them, in step 3 and step 4, the diamond surface processing status is monitored in real time by a CCD camera with an infrared thermal imager during the laser processing process to provide guidance for parameter selection.

[0060] Step 5: After the processing is completed, the processed CVD diamond is ultrasonically cleaned, and the micro-groove morphology and verticality after processing are measured and recorded, such as Figure 9 As shown in (b), it can be seen that compared with the laser vertical processing diamond processing results Figure 9 (a) The microchannel processed by the present invention can effectively avoid the formation of a "V"-shaped structure on the side wall, greatly improving the verticality of the microchannel side wall, and the verticality is close to 90°.

[0061] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the inventive concept, which all fall within the scope of protection of the present invention.

Claims

1. A device for precision machining of complex-shaped diamond rectangular microchannels using pulsed lasers based on online monitoring, characterized in that: The invention comprises a picosecond laser (1), a six-degree-of-freedom platform (4), and an online monitoring system; the online monitoring system comprises a CCD camera (3) with an infrared thermal imager; wherein the diamond sheet (3) to be processed is horizontally placed on the six-degree-of-freedom platform (4) and fixed; the picosecond laser (1) and the CCD camera (2) with an infrared thermal imager are located above the platform, and the surface temperature of the workpiece is monitored in real time during the laser processing process; the motion trajectory of the six-degree-of-freedom platform is determined according to the shape of the complex microchannel, and is linked with the laser during the laser processing process.

2. The device for pulsed laser precision machining of complex-shaped diamond rectangular microchannels based on online monitoring according to claim 1, characterized in that: After the platform is tilted, the position of the workpiece changes. The six-degree-of-freedom platform follows the scanning trajectory of the laser to perform displacement and focal length compensation in the corresponding direction, thereby improving positioning accuracy and processing quality. The displacement compensation distance and focal length compensation distance z of the six-degree-of-freedom platform are calculated by formula (1) and formula (2): (1) (2) x is the distance between the processing position and the center of the workpiece; q is the inclination angle of the workpiece.

3. A process for pulsed laser precision machining of complex-shaped diamond rectangular microchannels based on online monitoring, characterized in that: Here are the steps: Step 1: Conduct a single-factor experiment on picosecond laser processing of diamond microchannels, optimize laser processing parameters, perform finite element simulation based on the type and depth requirements of the microchannel, and select the number of laser processing times; Step 2: Mount the diamond sheet to be processed on a six-degree-of-freedom platform, select the complex diamond microchannel structure to be processed, and determine the motion trajectory of the six-degree-of-freedom platform according to the shape of the complex microchannel; Step 3: Using the parameters optimized by the single-factor experiment in Step 1 and the laser processing times determined in Step 2, microchannel laser processing is performed. A CCD camera is first used to assist the laser in focusing on the center of the diamond sheet. A six-degree-of-freedom platform is then used to perform linked processing with the laser, ensuring that the workpiece is always tilted perpendicular to the laser scanning path during picosecond laser processing. Step 4: After laser processing one side of the microfluidic channel in step 3, the six-degree-of-freedom platform and laser are linked again, and the six-degree-of-freedom platform is tilted in the opposite direction to that in step 3 to perform laser processing on the other side of the microfluidic channel. The processing parameters are the same as in step 3. Step 5: After laser processing, clean the diamond surface and measure the verticality of the groove.

4. The process for pulsed laser precision machining of complex-shaped diamond rectangular microchannels based on online monitoring according to claim 3, characterized in that: In step 1, the laser energy density, scanning speed, and scanning spacing used in microchannel processing are selected through single-factor experiments. The principle of parameter selection is: for laser energy density, a larger laser energy density should be selected without causing deterioration of the laser processing surface quality and increase in the degree of graphitization; for scanning speed, a higher scanning speed should be selected without causing deterioration of the laser processing surface quality and increase in the degree of graphitization.

5. The process for pulsed laser precision machining of complex-shaped diamond rectangular microchannels based on online monitoring according to claim 4, characterized in that: The results of the single factor test are as follows: Laser processing energy density is 10.18 J / cm 2 , laser frequency 400kHz, scanning speed 100mm / s, scanning spacing 5μm, scanning trajectory is a linear reciprocating trajectory; laser energy density is 10.18 J / cm 2 When the material surface is processed, the degree of graphitization is low, which can effectively reduce the degree of damage to the material surface during processing.

6. The process for pulsed laser precision machining of complex-shaped diamond rectangular microchannels based on online monitoring according to claim 3, characterized in that: In step three, the tilt angle of the six-degree-of-freedom platform is determined as follows: the tilt angle of the six-degree-of-freedom platform is gradually increased from 0° to 20° to explore the evolution of the ablation area profile under different sample tilt angles; the platform tilt angle is selected to be 10° based on the groove cross-sectional profile and depth and width changes. When the tilt angle is 10°, the depth and width of the laser-processed groove are less affected by the tilt angle, and the effect on the laser ablation rate is small.

7. The process for pulsed laser precision machining of complex-shaped diamond rectangular microchannels based on online monitoring according to claim 3, characterized in that: In step 1, the steps for selecting the number of laser processing times through finite element simulation are as follows: Step 1: Create a finite element model with a surface inclination angle of α1 and set it to state A. Simulate the evolution of the ablation area contour after different laser processing times on the model in state A. After the simulation is completed, export the ablation surface contour from COMSOL to a CAD file. Step 2: Retain the upper surface profile of state A in step 1 and tilt it in the opposite direction by α2=2*α1. Re-import the profile information into COMSOL to construct a new initial state profile model, namely state B. Continue to simulate the groove profile evolution process with different laser processing times in state B, so as to control the inclination degree of the sidewalls on both sides of the groove, obtain the profile state at different times, and provide guidance for the selection of experimental parameters.

8. The process for pulsed laser precision machining of complex-shaped diamond rectangular microchannels based on online monitoring according to claim 7, characterized in that: The surface inclination angle selected for state A is α1, which is 10°.

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