A method for improving the dynamic sharpness of machining tools

Abstract

The present invention proposes a method for improving the dynamic sharpness of a machining tool, comprising the following steps: (1) proposing an expression method for the dynamic sharpness of a tool; (2) establishing a correlation model between the dynamic sharpness of a tool and machining parameters; (3) adopting a method for ultrasonic vibration-assisted machining to improve the dynamic sharpness of a tool; (4) regulating the matching of machining parameters and ultrasonic vibration parameters to improve machining performance; (5) conducting an ultrasonic vibration grinding test, selecting the optimal model parameters, and improving the dynamic sharpness of the tool during machining. The machining method of the present invention is used to perform grinding on hard and brittle materials, which can effectively improve the sharpness of the tool, improve machining performance, reduce grinding force, and improve machining quality.

Description

Technical Field

[0001] The invention provides a method for improving the dynamic sharpness of a processing tool, and belongs to the technical field of grinding processing. Background Art

[0002] In grinding, the sharpness of the tool is related to the value of the tool rake angle. The smaller the actual rake angle, the smaller the grinding force and the sharper the tool ([1]Lu S, Li Z, Zhang J, Zhang C, Li G, Zhang H, et al. Coupled effect of tool geometry and tool-particle position on diamond cutting of SiC p / Al.Journal ofmaterials processing technology.2022;303:1). In traditional grinding, the tool often has a large negative rake angle, and the grinding force is large during the processing, which easily causes problems such as poor workpiece surface quality and low tool life ([2] Dai Chenwei. Research on topography evolution and abrasive cutting thickness distribution of single-layer brazed superabrasive grinding wheel [D]. Nanjing University of Aeronautics and Astronautics, 2017; [3] Ding Y, Shi G, Zhang H, Shi G, Han D. Analysis of critical negative rake angle and friction characteristics in orthogonal cutting of AL1060 and T2. Science progress (1916)). In order to improve the surface quality of the workpiece and increase the tool life, high-sharpness tools are required for processing. Ultrasonic vibration-assisted processing is an excellent processing technology that can effectively reduce grinding force and improve tool sharpness. Existing studies have shown that the effect of ultrasonic vibration decreases with the increase of grinding speed. At different grinding speeds, the effect of ultrasonic vibration is also different ([4]Chen J, An Q, Ming W, Chen M. Investigation on machined surface quality in ultrasonic-assisted grinding of Cf / SiC composites based on fracture mechanism of carbon fibers. International journal of advanced manufacturing technology. 2020; 109(5-6): 1583-99.).

[0003] Based on this, a method is needed to predict the tool sharpness during ultrasonic vibration-assisted grinding, and then match the ultrasonic parameters with the grinding parameters to improve the tool sharpness and achieve high-quality processing. Summary of the invention

[0004] Purpose of the invention: In view of the inadequacy of existing processing technology, the present invention proposes a method for improving the dynamic sharpness of grinding tools. Based on the technology of ordinary processing, the axial ultrasonic vibration processing technology is combined to establish a correlation model between the dynamic sharpness of the tool and the processing parameters. According to the different processing parameters, the corresponding ultrasonic vibration frequency is matched to meet the requirements of high dynamic sharpness processing. In the process of processing materials, this method can dynamically match the ultrasonic vibration parameters according to the different grinding parameters, thereby reducing the effective rake angle, improving the dynamic sharpness of the tool, reducing tool damage, and improving the processing quality.

[0005] Technical solution: In order to achieve the above-mentioned invention object, the present invention adopts the following technical solution:

[0006] A method for improving the dynamic sharpness of a machining tool, such as Figure 1 As shown, the steps are as follows:

[0007] Step 1: Propose an expression method for the dynamic sharpness of the tool;

[0008] Step 2: Establish the correlation model between tool dynamic sharpness and processing parameters;

[0009] Step 3: Using ultrasonic vibration assisted processing to improve the dynamic sharpness of the tool;

[0010] Step 4: Adjust the matching of processing parameters and ultrasonic vibration parameters to improve processing performance;

[0011] Step 5: Conduct ultrasonic vibration grinding tests to select the best model parameters and improve the dynamic sharpness of the tool during processing.

[0012] The method for improving the dynamic sharpness of the machining tool is to install the ultrasonic vibration device on the machine tool and apply axial ultrasonic vibration on the basis of ordinary machining. Figure 2 , so that the tool motion trajectory and grinding speed direction change, see Figure 3 The change in grinding speed changes the processing form from two-dimensional cutting to three-dimensional cutting. In three-dimensional cutting, the dynamic sharpness of the tool is determined by the actual rake angle, see Figure 4 , 5 According to different machining parameters in ultrasonic vibration assisted grinding, the tool edge inclination angle λ is calculated using formula (1). s :

[0013]

[0014] Where A is the vibration amplitude of the tool, f is the vibration frequency of the tool, and v s is the grinding speed.

[0015] Based on the obtained tool edge inclination angle, the actual rake angle γ in the grinding process is calculated using formula (2): e

[0016]

[0017] It can be seen from the above formula that the introduction of ultrasonic vibration reduces the actual rake angle of the tool and improves the sharpness of the tool.

[0018] Based on this, an expression method for tool dynamic sharpness is proposed, a correlation model between tool dynamic sharpness and processing parameters is established, a control strategy of processing parameters on tool dynamic sharpness is proposed, and processing parameters are optimized according to experimental results to improve tool dynamic sharpness. The specific steps are as follows:

[0019] Step 1: Propose a method to express the dynamic sharpness of the tool

[0020] The actual rake angle of the tool in the grinding process is used to describe the dynamic sharpness of the tool, and the grinding force in the process is used to characterize the dynamic sharpness.

[0021] Step 2: Establish a correlation model between tool dynamic sharpness and grinding parameters and vibration parameters

[0022] According to the set processing parameters, the average single abrasive grain cutting thickness is calculated using formula (3):

[0023]

[0024] In the formula, a p is the grinding depth, b is the workpiece width, v is the grinding depth, w is the feed speed, n d is the number of abrasive particles, l is the length of the motion trajectory, and n is the spindle speed.

[0025] According to the different angles of the abrasive particles, the plastic deformation force is calculated using formula (4)(5), and the elastic deformation force is calculated using formula (6)(7)(8)(9).

[0026]

[0027] In the formula, σ y is the yield strength of the material, A(a c ) is the shear surface area, β is the friction angle, φ is the shear angle, k1 is the proportionality coefficient, μ is the friction coefficient, E is the elastic modulus, ρ is the radius of the tool tip arc, and a c is the single-grain cutting thickness, and ε is a parameter related to the back angle.

[0028] The grinding force is calculated using formulas (9) and (10).

[0029]

[0030] In the formula, k1 and k2 are model parameters, F n 、F t are the normal force and the tangential force, respectively. are the normal force components, are the tangential force components respectively, which are equations about the rake angle and cutting thickness.

[0031] Step 3: Method of using ultrasonic vibration assisted processing to improve the dynamic sharpness of the tool

[0032] Step 4: Adjust the processing parameters and ultrasonic vibration parameters to match and improve processing performance

[0033] When the grinding speed remains unchanged, the dynamic sharpness of the tool shows an upward trend with the increase of ultrasonic frequency and amplitude; when the ultrasonic vibration frequency and amplitude remain unchanged, the dynamic sharpness of the tool decreases with the increase of grinding speed; too low grinding speed will increase the cutting thickness of a single abrasive grain and increase the grinding force.

[0034] Based on this, the present invention proposes a control strategy for the dynamic sharpness of the tool: in ultrasonic vibration-assisted grinding, the ultrasonic frequency is increased to increase the dynamic sharpness of the tool. Under the premise of ensuring a high grinding speed, for different grinding speeds, matching ultrasonic vibration frequencies and amplitudes are used to meet the needs of high tool dynamic sharpness processing.

[0035] Step 5: Conduct ultrasonic vibration grinding tests to select the best model parameters and improve the dynamic sharpness of the tool during processing:

[0036] Combined with the data obtained from experimental measurements, the regression analysis method is used to select the best model parameters k1 and k2.

[0037] Using the established tool sharpness prediction model and taking the reduction of grinding force as the optimization target, the matching relationship between grinding parameters and ultrasonic parameters is obtained, and the optimal ultrasonic vibration parameter f is determined using formulas (11)(12).

[0038] (g(0)-g(f)) / g(0)<α (12)

[0039] (g(0)-g(f)) / g(0)<α (13)

[0040] Where α is the reduction amplitude of grinding force, and g(0) is the grinding force when the frequency is 0.

[0041] Beneficial effects: The method for improving the dynamic sharpness of a processing tool of the present invention has the following advantages:

[0042] 1. Good processing quality: Based on the optimal processing parameters, the actual rake angle of the abrasive can be effectively reduced, thereby reducing the grinding force and the depth of sub-surface damage, and the processing quality is good.

[0043] 2. Long tool life: Reducing grinding force can effectively reduce tool wear and increase tool life. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the process of the present invention.

[0045] Figure 2 It is a schematic diagram of an ultrasonic vibration device.

[0046] Figure 3 It is a schematic diagram of ultrasonic vibration grinding.

[0047] Figure 4 This is the trajectory diagram of abrasive particle movement (left: conventional processing; right: ultrasonic processing).

[0048] Figure 5 This is a schematic diagram of processing (left: conventional processing; right: ultrasonic processing).

[0049] Figure 6 This is a schematic diagram of the tool rake angle (left: conventional machining; right: ultrasonic machining).

[0050] Figure 7 It is the experimental data power and model calculation power of the present invention.

[0051] Description of main reference numerals: 1-machine tool, 2-machine tool feeding system, 3-spindle, 4-primary coil, 5-ultrasonic tool holder, 6-brazed diamond tool, 7-workpiece to be processed, 8-fixture, 9-cable, 10-ultrasonic power supply, 11-tool base, 12-diamond abrasive grains, 13-normal processing track. 14-ultrasonic processing track, 15-base surface. DETAILED DESCRIPTION

[0052] The present invention is further described in detail below through specific examples:

[0053] Example 1

[0054] A method for improving the dynamic sharpness of a machining tool. The ultrasonic vibration system primary coil 4 and ultrasonic tool holder 5 need to be installed on the spindle 3 of a machine tool 1 in advance, and connected to an ultrasonic power supply 10 through a cable 9. The ultrasonic power supply converts the mains electricity into a high-frequency oscillating electrical signal, which is transmitted to the brazed diamond tool 6 through the ultrasonic tool holder 5, so that the diamond abrasive grains 12 on the tool base 11 perform high-frequency mechanical vibration and contact the workpiece 7 to be machined installed on the fixture 8, thereby machining the workpiece. This ultrasonic vibration effect changes the abrasive grain trajectory from the ordinary machining trajectory 13 to the ultrasonic machining trajectory 14 ( Figure 3 ), and the grinding speed direction is changed, the tool rake face and the tool base surface 15 produce a deflection angle, thereby improving the dynamic sharpness of the tool and improving the processing quality. Specifically comprising the following steps:

[0055] Step 1: Propose a method to express the dynamic sharpness of the tool

[0056] The actual rake angle of the tool in the grinding process is used to describe the dynamic sharpness of the tool, and the grinding force in the process is used to characterize the dynamic sharpness of the tool.

[0057] Step 2: Establish a correlation model between tool dynamic sharpness and grinding parameters and vibration parameters

[0058] According to different machining parameters in ultrasonic vibration-assisted grinding, the tool edge inclination angle λ is calculated using formula (1): s :

[0059]

[0060] Where A is the vibration amplitude of the tool, f is the vibration frequency of the tool, and v s is the grinding speed.

[0061] Based on the obtained tool edge inclination angle, the actual rake angle γ in the grinding process is calculated using formula (2): e

[0062]

[0063] In the formula, γ n is the static rake angle of the tool, its value is -35°, and the calculation results are shown in Table 1.

[0064] Table 1 Actual rake angle values

[0065]

[0066]

[0067] According to the set processing parameters, the average single abrasive grain cutting thickness is calculated using formula (3):

[0068]

[0069] In the formula, a p is the grinding depth, b is the workpiece width, v is the grinding depth, w is the feed speed, n d is the number of abrasive particles, l is the length of the motion trajectory, and n is the spindle speed.

[0070] According to the different angles of the abrasive particles, the plastic deformation force is calculated using formula (4)(5), and the elastic deformation force is calculated using formula (6)(7)(8)(9).

[0071]

[0072] In the formula, σ y is the yield strength of the material, A(a c ) is the shear surface area, β is the friction angle, φ is the shear angle, k1 is the proportionality coefficient, μ is the friction coefficient, E is the elastic modulus, ρ is the tool tip arc radius, a c is the single-grain cutting thickness, and ε is a parameter related to the back angle.

[0073] The grinding force is calculated using formulas (10) and (11).

[0074]

[0075] In the formula, k1 and k2 are model parameters, F n 、F t are the normal force and the tangential force, respectively. are the normal force components, are the tangential force components respectively, which are equations about the rake angle and cutting thickness.

[0076] Step 3: Method of using ultrasonic vibration assisted processing to improve the dynamic sharpness of the tool

[0077] Step 4: Adjust the processing parameters and ultrasonic vibration parameters to match and improve processing performance

[0078] When the grinding speed remains unchanged, the dynamic sharpness of the tool shows an upward trend with the increase of ultrasonic frequency and amplitude; when the ultrasonic vibration frequency and amplitude remain unchanged, the dynamic sharpness of the tool decreases with the increase of grinding speed; too low grinding speed will increase the cutting thickness of a single abrasive grain and increase the grinding force.

[0079] Based on this, the present invention proposes a control strategy for the dynamic sharpness of the tool: in ultrasonic vibration-assisted grinding, the ultrasonic frequency is increased to increase the dynamic sharpness of the tool. Under the premise of ensuring a high grinding speed, for different grinding speeds, matching ultrasonic vibration frequencies and amplitudes are used to meet the needs of high tool dynamic sharpness processing.

[0080] Step 5: Conduct ultrasonic vibration grinding tests to select the best model parameters and improve the dynamic sharpness of the tool during processing

[0081] The selected processing parameters are: spindle speed 8000-30000r / min, ultrasonic vibration frequency 24, 40, 60kHz, ultrasonic vibration amplitude 5μm; the selected tool parameters are: tool diameter 6mm, abrasive particle size 40 / 45 mesh, abrasive particles are arranged in an orderly manner, the matrix material is 45 steel, the binder is silver-copper-titanium binder, and the test results are shown in Table 2.

[0082] Table 2 Grinding force experimental values

[0083]

[0084]

[0085] Combined with the data obtained from experimental measurements, the regression analysis method was used to select the best model parameters k1 and k2, and the final grinding force data were obtained as shown in Table 3.

[0086] Table 3 Theoretical values ​​of grinding force

[0087]

[0088] Using the established tool sharpness prediction model and taking the reduction of grinding force as the optimization target, the matching relationship between grinding parameters and ultrasonic parameters is obtained, and the optimal ultrasonic vibration parameter f is determined using formulas (12) and (13).

[0089] (g(0)-g(f)) / g(0)<α (12)

[0090] (g(0)-g(f)) / g(0)<α (13)

[0091] In the formula, α is the reduction amplitude of grinding force, α is taken as 15%, g(0) is the grinding force when the frequency is 0, and the recommended ultrasonic amplitude under different processing parameters is shown in Table 4.

[0092] Table 4 Recommended ultrasonic vibration parameters

[0093] Serial number Spindle speed n(rpm) Optimal ultrasonic amplitude f(kHz) 1-1 8000 >20 1-2 16000 >32 1-3 30000 >60

[0094] According to the optimized processing parameters, combined with the existing frequency ultrasonic tool holder, 24, 40 and 60kHz ultrasonic vibration tool holders were used to carry out conventional grinding and ultrasonic vibration assisted grinding experiments under different processing parameters. The experimental parameter settings are shown in Table 5.

[0095] Table 5 Verification experiment parameters surface

[0096] Serial number Spindle speed n(rpm) Optimal ultrasonic amplitude f(kHz) 1-1 8000 24 1-2 16000 40 1-3 30000 60

[0097] The selected tool parameters are: tool diameter 6 mm, abrasive grain size 40 / 45 mesh, abrasive grains arranged in an orderly manner, matrix material 45 steel, binder silver copper titanium binder, and the grinding force in the experiment was measured. The results are shown in Table 6.

[0098] Table 6 Grinding force of conventional grinding and ultrasonic grinding

[0099]

[0100]

[0101] The above results show that the use of recommended parameters for ultrasonic vibration assisted grinding tests can effectively reduce the grinding force, thereby effectively reducing the sub-surface damage depth and improving the processing quality. At the same time, the reduction of grinding force also effectively reduces tool wear. Compared with ordinary processing, the tool life of ultrasonic processing under the recommended parameters is generally increased by more than 50%.

Claims

1. A method for improving the dynamic sharpness of a processing tool, characterized in that: The following steps are involved: Step 1: Propose a method to express the dynamic sharpness of the tool According to the characteristics of grinding, the effective rake angle of the tool in grinding is used to describe the dynamic sharpness of the tool, and the grinding force in processing is used to verify the dynamic sharpness of the tool; Step 2: Establish the correlation model between tool dynamic sharpness and grinding parameters and vibration parameters According to different machining parameters in ultrasonic vibration-assisted grinding, the tool edge inclination angle λ is calculated using formula (1): s : Where A is the vibration amplitude of the tool, f is the vibration frequency of the tool, and v s is the grinding speed; Based on the obtained tool edge inclination angle, the effective rake angle γ in grinding is calculated using formula (2): e : In the formula, γ n is the static rake angle of the tool; According to the set processing parameters, the average single abrasive grain cutting thickness is calculated using formula (3): In the formula, a p is the grinding depth, b is the workpiece width, v is the grinding depth, w is the feed speed, n d is the number of abrasive particles, l is the length of the motion trajectory, n is the spindle speed, and θ is the semi-cone angle of the abrasive particles; According to the different angles of the abrasive particles, the plastic deformation force is calculated using formulas (4) and (5), and the elastic deformation force is calculated using formulas (6), (7), (8), and (9): In the formula, σ y is the yield strength of the material, A(a c ) is the shear surface area, β is the friction angle, φ is the shear angle, k1 is the proportionality coefficient, μ is the friction coefficient, E is the elastic modulus, ρ is the tool tip arc radius, a c is the single-chip cutting thickness, ε is a parameter related to the back angle, H is the material hardness, and γ is the tool rake angle; The grinding force is calculated using formula (10) (11): In the formula, k1 and k2 are model parameters, F n 、F t are the normal force and the tangential force, respectively. are the normal force components, are the tangential force components, which are equations about the rake angle and the cutting thickness; Step 3: Using ultrasonic vibration assisted processing to improve the dynamic sharpness of the tool; Step 4: Adjust the matching of processing parameters and ultrasonic vibration parameters to improve processing performance; In ultrasonic vibration-assisted grinding, the ultrasonic frequency is increased to increase the dynamic sharpness of the tool. Under the premise of ensuring the grinding speed, the matching ultrasonic vibration frequency and amplitude are used for different grinding speeds to meet the needs of high tool dynamic sharpness processing; Step 5: Conduct ultrasonic vibration grinding tests to select the best model parameters and improve the dynamic sharpness of the tool during processing; Combined with the data obtained from experimental measurements, the regression analysis method is used to select the best model parameters k1 and k2; Using the established tool sharpness prediction model and taking the reduction of grinding force as the optimization target, the matching relationship between grinding parameters and ultrasonic parameters is obtained, and the optimal ultrasonic vibration parameter f is determined using formula (12)(13): (g(0)-g(f)) / g(0)<α (12) (g(0)-g(f)) / g(0)<α (13) In the formula, α is the reduction amplitude of grinding force, and g(0) is the grinding force when the frequency is 0.

2. A method for improving the dynamic sharpness of a machining tool according to claim 1, characterized in that: In step five, the processing parameters selected for the ultrasonic vibration assisted grinding test are: spindle speed 8000-30000r / min, ultrasonic vibration frequency 24, 40 or 55kHz, ultrasonic vibration amplitude 5μm; the selected tool parameters are: tool diameter 6mm, abrasive grain size 40 or 45 mesh, abrasive grains arranged in order, matrix material 45 steel, and binder silver-copper-titanium binder.

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