Optimization method for laser drilling process parameters

Abstract

The invention relates to the technical field of carbon fiber composite material processing, and discloses a laser drilling process parameter optimization method, which is used for a carbon fiber composite material, and comprises the following steps: setting different laser parameters, processing in a coaxial annular filling mode, and obtaining the hole taper of a target through hole in the carbon fiber composite material and the width value of a heat affected zone; constructing a data set; laser parameters are used as factor variables, the width value and the hole taper of the heat affected zone are used as response variables, and an optimization model is constructed through a response surface method; and solving the optimization model by utilizing the data set to obtain numerical values of factor variables which simultaneously enable the width value and the hole taper of the heat affected zone to be minimum. According to the method, the optimal numerical values of the factor variables enabling the width value and the hole taper of the heat affected zone to be minimum at the same time are selected through the response surface curve method, the geometric accuracy of the hole and the damage degree of the material in the machining process can be effectively evaluated, therefore, technological parameters are optimized, the ideal hole shape is obtained, and heat damage is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fiber composite material processing, and in particular to a method for optimizing laser hole making process parameters. Background Art

[0002] Carbon fiber composites are high-performance composite materials that are flexible and adaptable engineering materials suitable for a variety of applications due to their excellent mechanical and physical properties, including high specific strength, high specific stiffness, excellent thermal stability and outstanding corrosion resistance. Due to these advantages, carbon fiber composites have become a promising alternative to traditional metal materials for a wide range of industrial fields that require structural materials with unique properties. In the aerospace field, carbon fiber composites are widely used in key satellite structures such as load-bearing cylinders, antennas and camera barrels to replace metals to achieve lightweight and high-strength designs. The typical thickness of carbon fiber composites used in satellites ranges from 0.4 mm to 2 mm, with skins or sheets with a thickness in the range of 0.8 mm becoming the main focus of processing and application.

[0003] Although carbon fiber composites are usually manufactured into near-net shapes through various forming processes, subtractive manufacturing such as cutting and drilling is still an inevitable part of most product manufacturing. Mechanical drilling has become a key operation for processing carbon fiber composites to meet connection requirements. However, traditional mechanical drilling is prone to defects such as delamination, burrs and cracks on the edge of the hole, while also causing severe tool wear and increasing processing costs. Reports show that delamination caused by traditional mechanical processing leads to the scrapping of up to 60% of carbon fiber composite parts during aircraft assembly. Among non-traditional processing methods, technologies such as electrospark machining, abrasive water jet machining, ultrasonic machining and laser machining show greater potential. However, non-traditional processing methods such as electrical discharge machining and ultrasonic machining are less efficient and produce more hole defects. The resonant frequency matching problem in ultrasonic machining also needs to be solved. Abrasive water jet machining causes the least thermal damage, but it is difficult to control the processing accuracy, resulting in high surface roughness and material delamination.

[0004] As an emerging processing technology, laser processing has the advantages of small scale, high controllability, environmentally friendly process, and non-contact processing. However, in the application of drilling carbon fiber composite materials, there are still problems of damage and low processing accuracy. Summary of the invention

[0005] The purpose of the present invention is to provide a method for optimizing laser hole making process parameters for carbon fiber composite materials, which can solve at least one of the above-mentioned technical problems. The specific solution is as follows: According to a specific embodiment disclosed in the present invention, the present invention provides a method for optimizing laser hole making process parameters, comprising: Setting different laser parameters, processing in a coaxial annular filling manner, obtaining the hole taper of the target through hole on the carbon fiber composite material and the width value of the heat affected zone, and constructing a data set; the laser parameters include: average power, scanning speed and filling times; The laser parameters are used as factor variables, the width of the heat-affected zone and the hole taper are used as response variables, and an optimization model is constructed by using the response surface method; The optimization model is solved using the data set to obtain the value of the factor variable that minimizes both the width of the heat affected zone and the hole taper.

[0006] Preferably, the hole is made in a coaxial annular filling manner to obtain the hole taper and the width value of the heat affected zone on the carbon fiber composite material, including: Using the coaxial annular filling method, a target through hole is machined in the carbon fiber composite material in a concentric circle scanning method from outside to inside; The hole taper is calculated by measuring the major and minor axes of the outlet position of the target through hole and the diameter of the inlet position of the target through hole by using an elliptical selection method; The average value of the diameter of the entrance position of the target through hole measured multiple times is used as the width value of the heat affected zone.

[0007] Preferably, the expression of the hole taper is: ; in, The major axis and the minor axis of the ellipse respectively represent the entrance position; Respectively represent the major axis and minor axis of the ellipse of the exit position; d Indicates the thickness of the carbon fiber composite material target.

[0008] Preferably, the coaxial annular filling method is used, and the concentric circle scanning method is used from the outside to the inside. When the diameter of the unprocessed part in the central area is 10-15 times the filling spacing, the processing is stopped.

[0009] Preferably, the laser parameters are used as factor variables, the width of the heat affected zone and the hole taper are used as response variables, and an optimization model is constructed by response surface methodology, including: The central composite design in the response surface method was used to build the optimization model, and each of the response variables had 5 coding level values; The central composite design includes: 8 factor points, 6 axial points and 4 to 6 center points.

[0010] Preferably, the encoding level values ​​are: -2, -1, 0, 1, 2 respectively.

[0011] Preferably, the expression of the optimization model is: ; in, y represents the response variable, , x j represents factor variables; All represent regression coefficients; Indicates the error value.

[0012] Preferably, when the diameter of the target through hole on the carbon fiber composite material is 1.5 mm and the thickness is 0.8 mm, The optimization model expression of the hole taper of the target through hole is: ; The optimization model expression of the heat affected zone of the target through hole is: ;

[0013] in, P Indicates the average power, V Indicates the scanning speed, F Indicates the number of fills.

[0014] Preferably, the carbon fiber composite material has a fiber volume fraction of 60% and a thickness of 0.8 mm, and comprises: a top layer, a middle layer and a bottom layer; Wherein, the top layer and the bottom layer are cross-woven layers; The middle layers are layers of 0° and 9° unidirectional tapes arranged in sequence.

[0015] Preferably, the parameters of the laser include at least one of the following: Wavelength: 355nm, pulse width: 10ps, pulse frequency 500kHz, average power: 7W, scanning speed: 600mm / s, filling spacing: 40μm, filling times: 800N.

[0016] Compared with the prior art, the above solution of the embodiment disclosed in the present invention has at least the following beneficial effects: The present invention uses a coaxial annular filling method to make holes in carbon fiber composite materials, ensuring uniform removal and low damage of carbon fiber composite materials during processing. By characterizing and quantifying the hole taper and heat-affected zone, the optimal value of the factor variable that minimizes the width of the heat-affected zone and the hole taper is selected using the response surface curve method, which can effectively evaluate the geometric accuracy of the hole and the degree of damage to the material during the processing, thereby optimizing the process parameters, obtaining an ideal hole shape and reducing thermal damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings herein are incorporated into the specification and constitute a part of the specification, showing embodiments consistent with the disclosure of the present invention, and together with the specification, are used to explain the principles disclosed in the present invention. Obviously, the drawings described below are only some embodiments disclosed in the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings: Figure 1 A flow chart of a method for optimizing laser hole making process parameters provided by an embodiment of the present invention; Figure 2 A schematic diagram of the quantitative characterization of hole taper provided in an embodiment of the present invention; Figure 3 A schematic diagram of quantitative characterization of the heat-affected zone around a hole provided in an embodiment of the present invention; Figure 4 The experimental point distribution diagram of the three-factor central composite design provided by the embodiment of the present invention; Figure 5 A comparison diagram of the predicted value and the actual value of the hole taper optimization model provided in an embodiment of the present invention; Figure 6 A comparison diagram of the predicted value and the actual value of the heat affected zone optimization model provided in an embodiment of the present invention; Figure 7 A comparison diagram of the width of the heat-affected zone before and after treatment provided by an embodiment of the present invention; Figure 8 A comparison diagram of hole taper before and after optimization provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such product or device. In the absence of more restrictions, the elements defined by the sentence "comprises a" do not exclude the presence of other identical elements in the product or device including the elements.

[0020] The following is combined with Figure 1-8 Alternative embodiments of the present invention are described in detail.

[0021] Since the resin matrix strongly absorbs ultraviolet light, it can effectively reduce the phenomenon of incomplete resin decomposition. At the same time, the ultrashort pulse laser acts on the material in a very short time, so that the heat does not have time to diffuse inside the material, which can effectively avoid deformation, burning and other problems caused by overheating of the material. Therefore, the ultraviolet picosecond laser is used to cold process the nano carbon fiber material to obtain extremely small holes to meet the strict requirements of the material microstructure.

[0022] Therefore, the present invention provides a method for optimizing laser hole making process parameters for carbon fiber composite materials, comprising the following steps: Step S1, setting different laser parameters, processing in a coaxial annular filling manner, obtaining the hole taper of the target through hole on the carbon fiber composite material and the width value of the heat affected zone, and constructing a data set; the laser parameters include: average power, scanning speed and filling times.

[0023] Step S2: Taking the laser parameters as factor variables, the width value of the heat affected zone and the hole taper as response variables, an optimization model is constructed by using the response surface method.

[0024] Step S3: solving the optimization model using the data set to obtain the value of the factor variable that minimizes both the width of the heat affected zone and the hole taper.

[0025] This embodiment uses a coaxial ring method to process layer by layer, and the laser energy is evenly distributed, avoiding local thermal damage that may be caused by energy concentration at a single laser point, ensuring that the hole wall is flat, the hole diameter is accurate, and the taper of the hole is reduced.

[0026] By characterizing and quantifying the hole taper and heat-affected zone, and then using the response surface method to select the optimal quantitative standard, the geometric accuracy of the hole and the degree of damage to the material during the machining process can be effectively evaluated, thereby optimizing the process parameters, obtaining the ideal hole shape and reducing thermal damage.

[0027] In step S1, the laser parameters shown in Table 1 below are set to drill the carbon fiber composite material, and the hole taper of the target through hole and the width value of the heat affected zone under different parameters are obtained to form a data set.

[0028] The carbon fiber composite material has a fiber volume fraction of 60% and a thickness of 0.8 mm, and includes a top layer, a middle layer and a bottom layer. The top layer and the bottom layer are cross-woven layers, and the middle layer is a 0° and 9° unidirectional tape layer arranged in sequence.

[0029]

[0030] Furthermore, due to the effect of the laser Gaussian beam and the influence of factors such as sample thickness, there will be a certain diameter difference between the entrance and exit positions of the target through hole on the carbon fiber composite material, forming a hole taper.

[0031] When laser drilling carbon fiber composite materials, mechanical vibration and external interference may cause the path of the laser beam to deviate slightly, resulting in the cutting line not being able to follow the preset trajectory. At the same time, if the laser beam is not incident completely perpendicular to the material surface during processing, or deviates during the focusing process, it will cause uneven energy distribution, so that the entrance of the hole may not be a perfect circle but an ellipse.

[0032] Therefore, in this embodiment, an ellipse is used to simultaneously perform frame selection measurement on the entrance and exit positions of the hole to avoid the problem of over-expansion that covers unnecessary parts, or over-contraction that fails to fully cover the area that should be included.

[0033] like Figure 2 As shown, the hole taper T ellipse The expression is as follows: ; Among them, E in and E out represent the diameters of the ellipses at the hole entrance and exit positions, respectively; a in and b in represent the major and minor axes of the hole entrance ellipse, respectively; a out and b out Indicates the major and minor axes of the hole exit ellipse; d Indicates the thickness of the carbon fiber composite target.

[0034] Furthermore, the exposed fiber area is called the heat-affected zone, which is the most important defect in laser processing of carbon fiber composite materials. When quantifying the heat-affected zone around the target hole, the entrance position of the hole is used as the quantification object because the surface heat-affected zone contour at the entrance is clearer. Figure 3 As shown, the width of the heat affected zone is measured by analyzing the optical microscope image around the target hole. This embodiment selects 5 groups of data as samples, and records the width values ​​of the heat affected zone around each group of holes. In order to improve the reliability and representativeness of the measurement results, the final heat affected zone width uses the arithmetic mean of these 5 groups of data as the characterization result.

[0035] Furthermore, since the characteristic size of the holes made by picosecond ultraviolet pulse lasers in carbon fiber composite materials is usually in the micron level, it is difficult to achieve through-hole processing when performing a single scan at the focus position. In addition, since the energy is concentrated during a single scan, it is impossible to effectively remove the material, and it is easy to cause the expansion of the heat-affected zone, affecting the quality of the hole.

[0036] Therefore, for the target through hole with a diameter of 1.5 mm and a thickness of 0.8 mm, this embodiment adopts a coaxial annular hole making method. This method distributes the laser energy by multiple concentric circle scanning from the outside to the inside, which can remove materials layer by layer and avoid excessive heat accumulation at a single focal point, thereby effectively controlling the growth of the aperture and the expansion of the heat-affected zone. This method can not only achieve precise processing of the hole, but also reduce the taper of the hole, improve the processing accuracy and consistency, and is particularly suitable for the processing needs of high-strength composite materials such as carbon fiber composites.

[0037] Furthermore, when performing concentric circle scanning processing, the filling spacing determines the line overlap rate of the laser beam, and the line overlap rate has a significant impact on the final processing effect. Reasonable filling spacing can effectively balance the accumulation of thermal effects and material removal efficiency, ensure a smooth and flat cutting surface, and accurate aperture, while avoiding problems such as thermal damage and uneven cutting. In this embodiment, when the filling spacing is set to L = 40 μm, the spot overlap can ensure uniform distribution of heat in the material. At this time, regardless of the scanning speed, number of fillings, or average power, the appearance of overheating areas can be effectively avoided, so that the hole taper and heat-affected zone of the carbon fiber composite material are minimized.

[0038] Furthermore, all through holes were processed by concentric circle filling from the outside to the inside, with a hole diameter of 1.5 mm, a filling spacing set to 40 μm, and a center area with an unprocessed portion with a diameter of 0.52 mm, in order to effectively control heat accumulation and reduce excessive expansion of the heat-affected zone.

[0039] In this embodiment, the average hole-making power is used as a variable, and the other laser parameters and hole-making parameters are kept consistent. It can be found that as the average hole-making power increases, the hole taper gradually decreases; while the heat-affected zone gradually expands with the increase of the average hole-making power. This is because high energy input leads to increased heat accumulation, especially under the action of high-frequency short pulses, the heat cannot be dissipated in time. The high thermal conductivity of carbon fiber promotes heat conduction, while the low thermal conductivity of resin leads to heat retention, which expands the heat-affected zone.

[0040] In this embodiment, the scanning frequency is used as a variable, and the other laser parameters and hole making parameters are kept consistent. The influence on the hole taper and heat affected zone is evaluated by introducing the key parameter of spot overlap rate. Among them, the spot overlap rate is related to the pulse frequency, scanning speed and laser beam diameter.

[0041] Spot overlap rate The calculation formula is as follows: ; in, f The laser pulse repetition frequency is 500kHz; r 0 is the laser focus spot diameter, r 0 = 30 μm; V s are the scanning speeds, which are 300 mm / s, 400 mm / s, 500 mm / s, 600 mm / s and 700 mm / s respectively.

[0042] It can be found that due to the different removal mechanisms and thermal response characteristics of carbon fiber and resin matrix, the uniformity of laser energy distribution is crucial to the quality of the hole wall. Carbon fiber has high strength and high thermal conductivity, but low laser absorption rate, and requires a higher spot overlap rate to improve the removal efficiency. As the scanning speed increases, the spot overlap rate is lower; however, the resin matrix has high laser absorption and low thermal conductivity, and it is easy to accumulate heat at a high spot overlap rate (such as 90%), resulting in an expansion of the heat affected zone. When the scanning speed is low (300 mm / s), the heat accumulation effect is aggravated and the heat affected zone increases; and as the scanning speed increases, the spot overlap rate decreases, the action time of the laser and the material is shortened, and the heat accumulation is reduced, thereby effectively reducing the width of the heat affected zone.

[0043] Therefore, during the processing, the spot overlap rate should be appropriately increased to reduce the hole taper and optimize the hole wall quality; at the same time, by controlling the spot overlap rate to reduce the range of the heat-affected zone, avoid material delamination or excessive thermal damage, and achieve efficient and high-quality laser processing goals.

[0044] In this embodiment, the change in the number of fillings can reflect the different degrees of energy accumulation and material removal during the processing. The number of fillings is taken as a variable, the other laser parameters and hole making parameters are kept consistent, and the measured hole taper and heat affected zone width data are fitted. It can be found that the increase in the number of fillings makes the laser energy distribution more uniform, the single input energy is reduced, and the total heat distribution tends to be smooth, thereby reducing the thermal damage to the resin matrix and carbon fiber caused by local heat accumulation, and significantly reducing the range of the heat affected zone. At the same time, filling circle by circle provides enough time for heat dissipation, making the thermal effect more controllable, and improving the thermal stability of the hole wall and the overall processing quality. For the hole taper, the increase in the number of fillings gradually optimizes the material removal through more processing trajectories, reduces the unevenness of the hole wall and the difference between the inlet and outlet apertures, makes the hole wall closer to the ideal cylindrical shape, and significantly reduces the hole taper. This shows that by increasing the number of fillings, not only can the heat affected zone be effectively reduced, but also a higher precision aperture shape can be obtained, and the overall processing results can be optimized.

[0045] Therefore, in step S2, multi-factor optimization is performed by response surface method. When constructing the optimization model, average power, scanning speed and filling times are used as factor variables, and the width value of the heat affected zone and hole taper are used as response variables. The optimization model is constructed by response surface method and experimental analysis is performed. The ultimate goal is to achieve the simultaneous minimization of the heat affected zone and hole taper in laser processing through the optimal parameter combination to improve the processing quality and efficiency.

[0046] Specifically, this embodiment uses the central composite design (CCD) in the response surface method to study and optimize the laser processing technology. Compared with another Box-Behnken design (BBD) in the response surface method, the central composite design has a stronger response surface fitting ability and is particularly suitable for modeling complex nonlinear relationships.

[0047] The central composite design is a second-order design, with average power, scanning speed and filling times as factor variables, and the expression of the second-order optimization model to be fitted is: ; in, y represents the response variable, , x j represents factor variables.

[0048] All represent regression coefficients; Indicates the error value.

[0049] In this embodiment, the response variables are the width value of the heat affected zone and the hole taper, and the number of factor variables is 3.

[0050] like Figure 4 As shown, a central composite design consists of three parts: 1. Factor points: Factor points refer to all experimental points in a two-level factorial design, which are used to estimate linear and interactive effects. The total number of factor points is 2. 3 =8, where 3 is the number of factor variables; the factor levels are coded as +1 and -1.

[0051] 2. The center point is the median point of all factor ranges. In Design-expert, its factor level is coded as 0. It is used to evaluate experimental errors and enhance model fitting. The center point is usually repeated 4-6 times to improve the accuracy of error evaluation, that is, the number of center points is 4~6.

[0052] 3. Axis point refers to the +α or -α level of a factor code. The position of the axis point is determined by the principles of rotatability and orthogonality. It is used to capture quadratic nonlinear effects and ensure prediction accuracy and factor independence. The α value of the axis point is determined by the principles of rotatability and orthogonality: rotatability ensures that the prediction model has consistent errors within the same range from the center point, while orthogonality ensures that each experimental factor combination is independent of each other to avoid correlation interference.

[0053] Generally, the α value of the axis point is chosen between 1 and between( n is the number of factor variables, and this embodiment has 3 factor variables P, V, F), so that the axis point and the center point are located on the same sphere. The total number of axis points in this embodiment is 2*3=6. The factor level coding of the axis point is usually higher than that of the ordinary factor point, so as to provide more information to fit the quadratic regression model. In this embodiment, -2 and +2 are selected as the axis point level coding to ensure a larger axis point range, so that the quadratic model can be better fitted and the nonlinear relationship between the factor and the response variable can be captured. And the axis points are placed at the edge of the factor space, which helps to provide more data points, improve the model prediction accuracy, and ensure accurate prediction within the experimental range.

[0054] Therefore, in this embodiment, based on the response surface method, the central composite design model (CCD) in Design Expert 13.0 software was used to design a three-factor five-level experiment. The average power (P), scanning speed (V) and filling times (F) were used as optimization variables, and the hole taper and heat affected zone were used as response variables. A total of 20 groups of experiments were conducted, including 14 groups of axial points and 6 groups of center points.

[0055] The true parameter values ​​of the selected factor level codes are shown in Table 2. In order to avoid systematic errors, the experiment was conducted in a random arrangement. The specific experimental parameters and variable results are shown in Table 3.

[0056]

[0057]

[0058] The hole taper results were calculated based on the data in Table 3. The hole taper and process parameters were fitted with polynomials using response surface analysis to obtain the hole taper-process parameter regression prediction model. The first-order terms (P, V) and the second-order terms (P 2 、F 2 ) have p values ​​less than 0.05, which are significant terms in the regression equation. The optimization model expression of the hole taper of the target through hole is obtained as follows:

[0059] The obtained optimization model of hole taper was subjected to variance analysis and significance test, as shown in Table 4.

[0060] The F distribution test statistic of the removal rate is 10.8. The P value test is used to determine whether the model is reliable. Generally, P < 0.05 is considered significant. In this embodiment, P < 0.0001 of the hole taper, so the reliability of the established model is significant.

[0061] The signal-to-noise ratio of the removal rate model is 12.8696>4. It is generally believed that a signal-to-noise ratio greater than 4 indicates that the model is reliable and the fit R 2 =0.9067. The closer the value is to 1, the better the model fits.

[0062] Prediction fitting coefficient Pred.R 2 =0.4297 and the corrected fitting coefficient Adj.R 2 =0.8227 is a good fit. The lack-of-fit value of the model is not significant, which is 0.1001.

[0063] Therefore, the optimization model of the hole taper of this embodiment is well fitted.

[0064]

[0065] Furthermore, the hole taper optimization model obtained by fitting is used to calculate the predicted value of the hole taper, and the calculated result is compared with the actual value. Figure 5 As shown in the figure. From the comparison results, we can see that the data points are distributed around the fitting line, indicating that the optimization model of hole taper has a high degree of fit, which proves the accuracy of the model. Based on the above analysis, the regression model is significant, has a high degree of fit, and has reliable prediction ability.

[0066] The optimization model of the heat affected zone of the target through hole is established by using the same method as the hole taper optimization model. According to the experimental results, the heat affected zone regression model is obtained by fitting and analyzing 20 sets of data. The first-order terms (V, F), cross terms (PV, PF, VF) and quadratic terms (V 2 、F 2 ) have p values ​​less than 0.05, which are significant terms in the regression equation. The heat affected zone optimization model expression of the target through hole is:

[0067] The variance analysis method was used to perform a significance test on the constructed heat affected zone optimization model, and the test results are shown in Table 5.

[0068]

[0069] By analyzing Table 5, the following results can be obtained: the F value in the variance analysis is 119.10, the P value is <0.0001, and the regression model has a strong significance; the P value of the lack of fit term is 0.1558>0.05, which is not significant. The P value results of the model and the lack of fit term show that this regression model is reliable. The signal-to-noise ratio of the heat affected zone model is 35.1585>4, and the goodness of fit R 2 =0.9908. The closer the value is to 1, the better the model fits. Prediction fitting coefficient Pred.R 2 =0.9445 and the corrected fitting coefficient Adj.R 2 =0.9824 is very consistent. This proves that the regression prediction model is reasonable and can be used for data simulation.

[0070] The reliability of the constructed heat affected zone optimization model is verified. Figure 6 This is a graph of the actual value and predicted value of the heat affected zone optimization model. It can be seen from the figure that the data points are evenly distributed around the fitting line, and there are no abnormal data points, indicating that the regression model has a high degree of fit and reliable prediction ability.

[0071] In step S3, based on the data in Table 2, with the goal of minimizing the two parameters of hole taper and heat affected zone, multi-objective optimization is performed within the research range of the laser hole making parameters of this embodiment to obtain the optimization criteria and weights shown in Table 6.

[0072]

[0073] Furthermore, the combination of factor variables and response variables is verified to determine the feasibility of the optimized laser hole making process parameters. The error calculation formula is shown in formula (3):

[0074] Wherein, H0 is the predicted value of the measured target through hole; H1 is the true value of the measured target through hole and the relative error of the measured target through hole.

[0075] The experimental results and error rates are shown in Table 7. Although there is a certain error between the experimental results and the predicted results, it is within the allowable error range (the error may come from machine tool error, model error, measurement error and material property error). In addition, the experimental values ​​and predicted values ​​are basically consistent, indicating that the data error is small and the constructed optimization model is reliable.

[0076]

[0077] In this embodiment, the three-factor 0 level in the response surface method is used as a comparative test, and the average power is set to 6W, the scanning speed is 500mm / s, and the filling number is 1000N. Figure 7-Figure 8The comparison of heat affected zone width before and after optimization and the comparison of hole taper before and after optimization are shown.

[0078] contrast Figure 7 (a) and Figure 7 (b) It can be seen that the width of the heat affected zone becomes smaller, compared with Figure 8 (a) and Figure 8 (b) It can be seen that the diameter of the ellipse at the through-hole exit becomes larger and the hole taper becomes smaller.

[0079] In summary, the present invention uses ultraviolet picosecond lasers to make holes. Lasers with ultraviolet wavelengths (such as 355nm) have higher absorption rates in carbon fiber composite material (CFRP) processing, especially for epoxy resins, which improves processing quality and reduces thermal damage. Ultraviolet light has a short wavelength and concentrated energy, and can act on the surface of the material more accurately, reduce the heat conduction effect, and reduce the size of the heat affected zone (HAZ). Picosecond lasers release high peak power in a very short time through ultrashort pulses, directly vaporize materials or generate plasma, reduce the heat absorbed by the matrix material, and further reduce the HAZ. With characteristics close to "cold processing", picosecond lasers effectively reduce heat accumulation problems and provide higher precision in fine processing. The response surface curve method is used to optimize the laser parameters to achieve the minimum heat affected zone and hole taper under these parameters.

[0080] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other. For the system or device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0081] The above embodiments are only used to illustrate the technical solutions disclosed in the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments disclosed in the present invention.

Claims

1. A method for optimizing laser hole making process parameters for carbon fiber composite materials, characterized in that: include: Set different laser parameters, process in a coaxial ring filling mode, obtain the hole taper of the target through hole on the carbon fiber composite material and the width value of the heat affected zone, and construct a data set; The laser parameters include: average power, scanning speed and filling times; The laser parameters are used as factor variables, the width of the heat-affected zone and the hole taper are used as response variables, and an optimization model is constructed by using the response surface method; The optimization model is solved using the data set to obtain the value of the factor variable that minimizes both the width of the heat affected zone and the hole taper.

2. The method according to claim 1, characterized in that The method of making holes in a coaxial annular filling manner to obtain the hole taper and the width value of the heat affected zone on the carbon fiber composite material includes: Using the coaxial annular filling method, a target through hole is machined in the carbon fiber composite material in a concentric circle scanning method from outside to inside; The hole taper is calculated by measuring the major and minor axes of the outlet position of the target through hole and the diameter of the inlet position of the target through hole by using an elliptical selection method; The average value of the diameter of the entrance position of the target through hole measured multiple times is used as the width value of the heat affected zone.

3. The method according to claim 2, characterized in that The expression of the hole taper is: ， in, The major axis and the minor axis of the ellipse respectively represent the entrance position; Respectively represent the major axis and minor axis of the ellipse of the exit position; d Indicates the thickness of the carbon fiber composite material target.

4. The method according to claim 2, characterized in that: By using the coaxial annular filling method, in a concentric circle scanning method from outside to inside, the processing is stopped when the diameter of the unprocessed part in the central area is 10-15 times the filling spacing.

5. The method according to claim 1, characterized in that The optimization model is constructed by using the response surface method with the laser parameters as factor variables, the width value of the heat affected zone and the hole taper as response variables, including: The central composite design in the response surface method was used to build the optimization model, and each of the response variables had 5 coding level values; The central composite design includes: 8 factor points, 6 axial points and 4 to 6 center points.

6. The method according to claim 5, characterized in that The encoding level values ​​are: -2, -1, 0, 1, 2 respectively.

7. The method according to claim 6, characterized in that The expression of the optimization model is: ； in, y represents the response variable, , x j represents factor variables; All represent regression coefficients; Indicates the error value.

8. The method according to claim 7, characterized in that When the diameter of the target through hole on the carbon fiber composite material is 1.5 mm and the thickness is 0.8 mm, The optimization model expression of the hole taper of the target through hole is: ； The optimization model expression of the heat affected zone of the target through hole is: ； in, P Indicates the average power, V Indicates the scanning speed, F Indicates the number of fills.

9. The method according to claim 8, characterized in that The carbon fiber composite material has a fiber volume fraction of 60% and a thickness of 0.8 mm, and includes: a top layer, a middle layer and a bottom layer; Wherein, the top layer and the bottom layer are cross-woven layers; The middle layers are layers of 0° and 9° unidirectional tapes arranged in sequence.

10. The method according to claim 8, characterized in that The parameters of the laser include at least one of the following: Wavelength: 355nm, pulse width: 10ps, pulse frequency 500KHz, average power: 7w, scanning speed: 600mm / s, filling spacing: 40μm, number of fillings: 800.

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