Method for suppressing machining taper by using trajectory non-uniform filling

Abstract

A method for suppressing machining cone angle by using trajectory non-uniform filling, step 1: using a Gaussian laser source to scan and etch the machining test piece, measuring the change relationship between the material pulse ablation threshold energy Fth(N) and the in-situ equivalent incident pulse number N on the machining test piece, and recording the material ablation threshold energy Fth(1) and the saturated material ablation threshold energy Fth(N0); Step 2: set the pulse energy density of the laser incident on the material surface; Step 3: considering the profile characteristics of the material to be removed area, according to the threshold incubation effect, set the machining parameters and plan the non-uniform filling trajectory, so that the in-situ equivalent incident pulse number N1 at the boundary shape control position is greater than the in-situ equivalent incident pulse number N2 of other filling areas; Step 4: machining test piece, test the machining cross section taper, if not satisfied, jump to step 2, reset the light parameters or plan the non-uniform filling trajectory, until the cross section taper meets the demand, and the output result is used for the manufacture of formal workpiece.

Description

Technical Field

[0001] This invention relates to the field of laser processing technology in special processing, particularly to high-precision subtractive processing of solid materials using ultrafast lasers, specifically to a method for optimizing the cone angle of the processing section and improving the quality of the section using trajectory planning of ultrafast lasers. Background Technology

[0002] The rapid development of modern science and technology, especially in aerospace, electronics, and weaponry, has led to an increasing demand for high-precision subtractive processing of solid materials. Ultrafast laser processing, with its narrow pulse width, high energy density, and extremely short material interaction time, offers advantages such as non-contact operation, strong material removal capability, high resolution, and a small heat-affected zone. It is an ideal method for achieving high-precision subtractive processing of solid materials, particularly difficult-to-machine materials like fiber-reinforced composites and ceramic matrix composites. Currently, ultrafast laser subtractive processing technology (ultrafast laser cutting and ultrafast laser milling) is widely used in the research and production of high-precision, difficult-to-machine parts and components in military industries such as aerospace and weaponry, as well as in civilian products such as computers, electronics, and chips, effectively ensuring and improving the key performance of products and assemblies. Typical examples include the widespread application of carbon fiber reinforced resin matrix composites processed by ultrafast lasers in the main load-bearing structures of satellites; and the widespread application of silicon carbide or diamond particle-reinforced metal matrix composites processed by ultrafast lasers in important fields such as miniature, highly stable structures for electronic and optical instruments and devices with extremely high heat flux densities.

[0003] Despite the many advantages of ultrafast laser processing, the high energy density of laser pulses results in a V-shaped groove formed after a single scan. During subsequent scans, some of the laser pulse energy acts on the inclined walls of the V-shaped groove, weakening its effective effect. This leads to a processing challenge where the processing depth gradually approaches saturation as the number of laser pulse strikes increases. Furthermore, when processing thick materials, a noticeable taper angle is formed in the kerf, a problem also present in other types of laser processing. This taper issue directly affects the structural accuracy and the processing limits.

[0004] Therefore, there is a need to develop a simple, high-precision, and low-cost method for taper suppression or even elimination, that is, a method that can achieve significant taper suppression or even elimination without beam shaping of the natural Gaussian beam or with the aid of a multi-axis linkage processing system. Summary of the Invention

[0005] The technical problem solved by this invention is: In the current technology, due to the Gaussian distribution of laser pulse energy in the radial direction, a V-shaped machining cone angle is inevitably generated when processing materials. Without the need for additional hardware costs such as radial homogenization of beam energy or multi-axis linkage oblique incidence cone elimination, a method is designed for high-precision products to eliminate or suppress the V-shaped machining cone angle by optimizing the machining trajectory.

[0006] The solution of this invention is: a method for suppressing machining cone angles using non-uniform trajectory filling, comprising:

[0007] Step 1: Use a Gaussian laser source to scan and etch the sample. Measure the relationship between the material pulse etch threshold energy Fth(N) and the in-situ equivalent incident pulse number N on the sample. Record the material etch threshold energy Fth(1) and the saturated material etch threshold energy Fth(N0) when the in-situ equivalent incident pulse number is 1.

[0008] Step 2: Set the optical parameters of the Gaussian laser source, and set the pulse energy density of the laser incident on the material surface according to the saturated material erosion threshold energy Fth(N0);

[0009] Step 3: Considering the contour features of the area to be removed, and based on the threshold hatching effect, plan a non-uniform filling trajectory so that the in-situ equivalent incident pulse number N1 at the boundary control point is greater than the in-situ equivalent incident pulse number N2 in other filling areas.

[0010] Step 4: Process the test piece according to the planned non-uniform filling trajectory based on the determined optical parameters. Test the taper of the processed section. If it does not meet the requirements, jump to Step 2, reset the optical parameters or plan the non-uniform filling trajectory until the section taper meets the requirements, and use the output results for the manufacturing of the formal workpiece.

[0011] Preferably, the materials of the processing test piece and the final workpiece are solid materials.

[0012] Preferably, the Gaussian laser source emits pulsed laser light, with a single pulse width and duration of less than 100 ps.

[0013] Preferably, the optical parameters of the Gaussian laser source are set to keep the pulse width and wavelength of the Gaussian laser source constant during the scanning etching process in steps 1 to 4.

[0014] Preferably, the pulse energy density F0 of the laser incident material surface is F0 = k·Fth(N0), and the dimensionless constant k is set to a value range of 5. <k<20。

[0015] Preferably, step 3 is implemented in the following ways:

[0016] Determine the estimation formula for the in-situ equivalent pulse number N;

[0017] By reducing the laser scanning speed at the boundary control point or increasing the trajectory filling density at the boundary control point, the in-situ equivalent pulse number N1 corresponding to the boundary control point is determined according to the estimation formula, such that N1 > N2.

[0018] Preferably, when the focused spot is a Gaussian spot, the in-situ equivalent pulse number N is estimated using the following formula:

[0019]

[0020] Where S is the spot area, f is the pulse repetition frequency, v is the laser scanning speed, and Ls(x,y) is the trajectory filling density distribution at coordinates (x,y).

[0021] Preferably, in step 3, at boundary control point N1, Fth(N1) satisfies Fth(N1)>[Fth(1)+Fth(N0)] / 2, and Fth(N2) satisfies Fth(N2)<[Fth(1)+Fth(N0)] / 2.

[0022] A laser processing apparatus, characterized in that the laser processing apparatus is used to perform the laser processing method described above. It is applicable to laser subtractive manufacturing, which includes laser cutting, laser milling, and laser rotary drilling.

[0023] The advantages of this invention compared to the prior art are:

[0024] (1) The present invention provides a method for suppressing processing taper by using non-uniform trajectory filling. Compared with traditional methods such as energy radial distribution homogenization after beam spatial shaping and multi-axis linkage oblique incidence taper elimination, it does not require the use of photoelectric devices to flatten the top of the spatial Gaussian beam, nor does it require a four-axis or more-axis linkage processing system. It is an economical method.

[0025] (2) The present invention provides a method for suppressing processing taper by using non-uniform trajectory filling. It is a method that uses the in-situ equivalent pulse number N1 of the boundary control area manufactured by non-uniform trajectory to be greater than that of other filling areas N2. According to the "threshold incubation effect", the material removal threshold of the boundary control area is lower than that of other areas, thereby enhancing the material removal rate of the boundary control area and realizing taper suppression.

[0026] (3) The present invention provides a method for suppressing processing taper by non-uniform trajectory filling, and provides quantitative calculation formulas for adjusting the in-situ equivalent incident pulse number N1 at the boundary shape control position and the in-situ equivalent incident pulse number N2 in other regions. The proposed method is applicable to a variety of laser subtractive manufacturing methods such as laser cutting, laser milling, and laser rotary cutting for hole making, and the taper suppression method is universal for different material types, and the degree of taper compensation can be flexibly adjusted as required. Therefore, the present method is also a flexible and universal method. Description of Drawings

[0027] Figure 1 is a flowchart illustrating the method for suppressing processing taper by non-uniform trajectory filling of the present invention.

[0028] Figure 2 is a micrograph of a near-zero taper structure cross-section when a groove with a processing depth of 0.5 mm is milled by laser after adopting the present invention. Detailed Description of Embodiments

[0029] The present invention will be further described below with reference to embodiments.

[0030] As shown in Figure 1 , a method for suppressing processing taper by non-uniform trajectory filling comprises

[0031] Step 1: Turn on the laser energy of the processing system, adjust the relative positions and postures of each component of the processing system, use a Gaussian laser source to perform scanning etching on a test piece, use a metallographic microscope to observe and collect data on the experimental etching depth of laser scanning, use the theoretical formula of the area epitaxy method to measure the variation relationship between the material pulse ablation threshold energy Fth(N) and the in-situ equivalent incident pulse number N on a processing test piece, and record the material ablation threshold energy Fth(1) when the in-situ equivalent incident pulse number is 1 and the saturated material ablation threshold energy Fth(N0)

[0032] Step 2: Set optical parameters: According to F0=k·Fth(N0), the value range of the dimensionless constant k is set as 5<k<20, and the incident energy density of the pulsed laser is set. The optical parameters further include spot repetition frequency and laser scanning speed v;

[0033] Step 3: For the profile to be processed of the test piece, use the proposed formula to plan the non-uniform filled laser trajectory according to the in-situ equivalent incident pulse number N1 at the boundary shape control position and the in-situ equivalent incident pulse number N2 in other regions, so that N1>N2; and set processing parameters to start processing until the preset operation is completed, wherein the in-situ equivalent pulse number N is estimated by the following formula:

[0034]

[0035] Where S is the spot area, v is the laser scanning speed, f is the pulse repetition frequency, and L... s (x,y) represents the trajectory filling density distribution at coordinates (x,y).

[0036] When the focused spot in step 3 is another type of spot, the equivalent pulse number N is estimated according to the conventional algorithm in the field.

[0037] Meanwhile, the erosion thresholds Fth(N1) and Fth(N2) for N1 and N2 must meet the following adjustment range:

[0038] Fth(N1)>[Fth(1)+Fth(500)] / 2Fth(N2)<[Fth(1)+Fth(500)] / 2

[0039] Step 4: Based on the dimensions and precision of the structure, select an optical microscope, vernier calipers, or other measuring methods to check whether the taper of the target structure of the test piece meets the requirements. If it does not meet the requirements, skip to Step 2 and modify the laser scanning speed v or the trajectory fill density until the cross-sectional taper meets the requirements. Use the output results for the manufacturing of the actual workpiece.

[0040] Specifically, according to formula (1), L is... s (x, y) are adjustable parameters to control the in-situ equivalent pulse number N; according to the well-known formula in the field:

[0041]

[0042] Where D is the material removal diameter when the applied pulse energy density F0 is applied, and w is the spot diameter (1 / e). 2 (Type definition). For the material etch threshold Fth(N1) corresponding to N1 at the boundary control point, which is significantly smaller than the material etch threshold Fth(N2) corresponding to N2 in other regions, the material etch diameter D(N1) will be greater than D(N2), thus producing a significant cone-suppressing effect. This invention also limits the applied pulse energy density F0 to ensure that the applied pulse energy density does not enter the saturation region, providing a good parameter selection range.

[0043] Of course, the present invention can also adopt another processing method. According to formula (1), keeping other parameters unchanged, v is used as an adjustable parameter to realize the control of the in-situ equivalent pulse number N; by making the scanning speed at the boundary control point lower than that in other areas, N1 can be greater than N2. Based on the principle above, the cone suppression effect can be obtained.

[0044] The following is a further explanation with reference to specific embodiments:

[0045] The material to be processed is high volume fraction aluminum-based silicon carbide with a thickness of 1.5mm and a size of 20×20mm. A circular groove with an inner diameter of 10mm, an outer diameter of 12mm, and a depth of 0.5mm needs to be laser-milled on it.

[0046] The laser in CNC laser processing equipment can emit a Gaussian beam with a center wavelength of 532nm. After optical path transmission and focusing by the scanning head lens, it is projected onto the workpiece surface, generating a single-pulse sequence with a duration of 10ps and an adjustable pulse frequency of 0.1MHz to 2MHz. The peak flux of the generated spatial Gaussian spot can reach up to 10J / cm². 2 Press "1 / e" 2 The diameter of the focused spot defined by the "-type Gaussian spot diameter" is approximately 30 μm.

[0047] First, the relationship between the material etch threshold energy Fth(N) and the in-situ equivalent incident pulse number N was measured on the processed test piece, and Fth(1) and Fth(500) were recorded.

[0048] Secondly, based on F0=k·Fth(500), with the dimensionless constant k taking the value of 8, the incident energy density of the pulsed laser is calculated to be 12.8 J / cm². 2 .

[0049] Again: For the profile to be processed on the specimen, a region 0.18 mm from the boundary is preset as the shape control boundary area. Using the adjustment ranges that the etch thresholds Fth(N1) and Fth(N2) for N1 and N2 mentioned above must satisfy: Fth(N1) > [Fth(1) + Fth(500)] / 2, Fth(N2) < [Fth(1) + Fth(500)] / 2, based on the measured relationship curve between the material etch threshold energy Fth(N) and the in-situ equivalent incident pulse number N, N1 = 40 and N2 = 8 are set. Using the formula: With a preset velocity v of 1 m / s and a current f of 0.2 MHz, the scanning trajectory for the control boundary region and other regions is planned. Experimental processing with non-uniform filling of constant velocity trajectories is then conducted.

[0050] Finally, an optical microscope was used to inspect whether the taper of the target structure of the test piece met the requirements. Observation revealed that the most probable taper of the cross-section was only 2°, meaning the machined structural section was very close to vertical, fully meeting the product's manufacturing requirements, and requiring no further iterative refinement to eliminate the taper. Therefore, the output results were used for the manufacturing of the final workpiece. A partial view of the machined component is shown below. Figure 2 As shown.

[0051] As a common method, the present invention provides a method for suppressing machining cone angles by using non-uniform trajectory filling, which obviously has good universality: by using the method that the trajectory filling density distribution in the boundary control area is higher than that in other areas, it quantitatively compensates for the under-machining at the boundary caused by the Gaussian beam. It can be seen that the present invention also has the characteristics of simplicity, reliability and good operability. It can directly use existing general equipment conditions without adding any additional hardware conditions to suppress or even eliminate cone angles, realize high-precision subtractive processing of materials, and is an economical and easy-to-implement method.

[0052] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

[0053] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A method for suppressing machining cone angles using non-uniform trajectory filling, characterized in that... include: Step 1: Use a Gaussian laser source to scan and etch the sample. Measure the relationship between the material pulse etch threshold energy Fth(N) and the in-situ equivalent incident pulse number N on the sample. Record the material etch threshold energy Fth(1) and the saturated material etch threshold energy Fth(N0) when the in-situ equivalent incident pulse number is 1. Step 2: Set the optical parameters of the Gaussian laser source, and set the pulse energy density of the laser incident on the material surface according to the saturated material erosion threshold energy Fth(N0); Step 3: Considering the contour features of the area to be removed, and based on the threshold hatching effect, plan a non-uniform filling trajectory so that the in-situ equivalent incident pulse number N1 at the boundary control point is greater than the in-situ equivalent incident pulse number N2 in other filling areas. Step 4: Process the test piece according to the planned non-uniform filling trajectory based on the determined optical parameters, and test the taper of the processed section. If it does not meet the requirements, jump to Step 2, reset the optical parameters or plan the non-uniform filling trajectory until the section taper meets the requirements, and use the output results for the manufacturing of the formal workpiece. The specific implementation methods for step 3 include: Determine the estimation formula for the in-situ equivalent pulse number N; when the focused spot is a Gaussian spot, the in-situ equivalent pulse number N is estimated according to the following formula: Where S is the spot area, f is the pulse repetition frequency, v is the laser scanning speed, and L... s (x,y) represents the trajectory filling density distribution at coordinates (x,y); By reducing the laser scanning speed at the boundary control point or increasing the trajectory filling density at the boundary control point, the in-situ equivalent pulse number N1 corresponding to the boundary control point is determined according to the estimation formula, so that N1 > N2. The pulse energy density of the laser incident on the material surface is F0 = k·Fth(N0), and the dimensionless constant k is set to a value within the range of 5. <k<20。 2. The method according to claim 1, characterized in that: The materials used for processing test pieces and final workpieces are solid materials.

3. The method according to claim 1, characterized in that: The Gaussian laser source emits pulsed laser light, with a single pulse width and duration of less than 100 ps.

4. The method according to claim 1, characterized in that: The optical parameters of the Gaussian laser source are set to keep the pulse width and wavelength of the Gaussian laser source constant during the scanning and etching process in steps 1 to 4.

5. The method according to claim 1, characterized in that: In step 3, the in-situ equivalent incident pulse number N1 at the boundary control point is such that Fth(N1) satisfies Fth(N1)>[Fth(1)+ Fth(N0)] / 2, and Fth(N2) satisfies Fth(N2)<[Fth(1)+Fth(N0)] / 2.

6. A laser processing device, characterized in that, The laser processing equipment is used to perform the laser processing method as described in any one of claims 1 to 5.

7. The laser processing equipment according to claim 6, characterized in that... It is applicable to laser subtractive manufacturing, which includes laser cutting, laser milling, and laser rotary cutting for hole making.

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