Flexible electrode on-line deformation electric spark cutting method

Abstract

The present application relates to a kind of flexible electrode on-line deformation electric spark cutting method, belong to electric processing technical field.The method features in: when carrying out the processing of complex surface such as blisk, flexible electrode is used as electric spark machining tool electrode, and its surface is used as processing surface to carry out cutting type electric spark machining along the set path, and according to the curvature characteristics of processing surface, make flexible electrode produce on-line deformation, to complete the processing of complex surface;Wherein, flexible electrode is prepared using material with good conductivity and elasticity, to ensure that flexible electrode can recover after deformation.The present application realizes three-dimensional complex surface electric spark cutting machining using flexible electrode, simplifies the design process of tool electrode, and improves electric spark machining efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to a flexible electrode on-line deformation electric spark cutting method, belonging to the technical field of electric processing. BACKGROUND

[0002] Blisk parts are one of the core components of aerospace engines. They integrate blades and disks into one, reducing the number of engine parts and weight, and significantly improving the thrust-to-weight ratio of the engine. With the continuous development of the aerospace industry, higher requirements are placed on the performance of aerospace engines. The structure of blisk parts is becoming increasingly complex, with blades becoming ultra-thin and twisted, and inter-blade passages becoming narrower. In addition, the application of closed blisks is also increasing. This poses a challenge to the machining and manufacturing of blisk parts.

[0003] Electric discharge machining technology has become one of the mainstream manufacturing processes for blisks due to its good accessibility, high machining precision, and absence of macroscopic cutting force.

[0004] In the patent "Multi-channel parallel machining electrode for rough machining of closed blisks" (Application No. 202011389263.8 Applicant Harbin Institute of Technology, Inventors Jia Yuchao Wang Zhenlong et al.), a multi-channel parallel machining electrode is proposed, which solves the problems of low efficiency, long equipment occupation time, and difficulty in designing arc machining electrodes for closed blisks with shroud in conventional electric discharge machining processes.

[0005] In the patent "Maximum free movement trajectory search method for electric discharge machining electrode of closed blisks" (Application No. 201510822228.3 Applicant Shanghai Jiaotong University, Inventors Kang Xiaoming Zhao Wansheng Liang Wei et al.), a trajectory search method is proposed. This method is suitable for various flow channel structures, has high success rate of trajectory search optimization, can realize multi-axis linkage, and has high machining efficiency.

[0006] In the patent "Six-axis linkage perturbation feeding method for electric discharge machining of closed blisks" (Application No. 201410336171.1 Applicant Shanghai Jiaotong University, Inventors Zhao Wansheng Kang Xiaoming Liang Wei et al.), a perturbation feeding method is proposed. Under the premise of ensuring no interference between the electrode and the final surface, additional perturbation movements are added to improve the discharge product discharge condition, improve the stability of the electric discharge machining, and improve the overall machining efficiency.

[0007] In the patent "Pre-pore liquid extraction and chip removal method for closed integral blade disk electric spark machining" (Application No. 201810899563.7, Applicant: Shanghai Jiaotong University, Inventors: Kang Xiaoming, Zhao Wansheng, Xu Haihua), the pre-pore parameter combination is designed according to the geometric model of the closed integral blade disk, and the pre-pore for liquid extraction is machined on the closed integral blade disk blank, thereby realizing effective discharge of the discharge product of the closed integral blade disk electric spark machining and improving the efficiency of the closed integral blade disk electric spark machining.

[0008] In the patent "Five-axis electric spark machining closed impeller trajectory planning method" (Application No. 201910126412.2, Applicant: Harbin Fenghua Co., Ltd., Aerospace Science and Technology, Inventors: Liu Zhonglu, Tang Boya, Guan Bowen, etc.), the electrode forming surface is solved by using the equal gap method, and the electrode trajectory is designed by using the conjugate method, thereby solving a series of problems such as tool accessibility caused by the use of multi-axis milling machining in the traditional machining method for closed integral turbine blade parts.

[0009] For the above-mentioned electric spark machining of the integral blade disk, a forming electrode is used for machining, and the forming electrode design is difficult and difficult to prepare, which affects the efficiency of the electric spark machining. In recent years, flexible electrodes with simple shape and good comprehensive performance have been applied in the electrochemical machining of integral blade disks.

[0010] In the patent "Flexible electrode dynamic deformation electrochemical machining method and application" (Application No. 202110860375.5, Applicant: Nanjing University of Aeronautics and Astronautics, Inventors: Zhu Di, Xu Zhengyang, Liu Lin), a tubular or rod-shaped metal with a certain rigidity but can be bent and deformed when a corresponding load is applied is used as an electrochemical machining tool electrode, and complex surfaces such as closed integral blade disks are machined, thereby improving the electrochemical machining efficiency and ensuring the machining precision.

[0011] In the patent "Flexible electrode dynamic deformation electrochemical machining device and method for multi-leaf cascade of integral component" (Application No. 202210497135.8, Applicant: Nanjing University of Aeronautics and Astronautics, Inventors: Xu Zhengyang, Liu Lin), the electrode design process is simplified, and multiple electrodes are used for simultaneous machining, thereby greatly improving the machining efficiency. In addition, the number and distribution position of the flexible electrodes can be adjusted according to the actual integral blade disk model to adapt to different machining requirements.

[0012] In the patent "Flexible electrode dynamic deformation double-electrode electrochemical machining device and method" (Application No. 202210499138.5, Applicant: Nanjing University of Aeronautics and Astronautics, Inventors: Xu Zhengyang, Liu Lin), a simple electrode is used to realize the simultaneous machining of two complex surfaces through one clamping, thereby greatly improving the machining efficiency.

[0013] Both the electric spark machining and the electrolytic machining belong to non-contact machining, if the flexible electrode with good comprehensive performance is applied to the electric spark machining of the blisk, the period of design and preparation of the tool electrode will be shortened, the electrode loss and machining cost are reduced, meanwhile, the machining precision is ensured, the machining efficiency is improved, and the electric spark machining with high efficiency and low cost is realized. SUMMARY

[0014] The present application aims to provide a flexible electrode on-line deformation electric spark cutting method, and is applied to the machining of the blisk.

[0015] A flexible electrode on-line deformation electric spark cutting method, characterized in that:

[0016] In the machining of the complex profile such as the blisk, the flexible electrode is used as the tool electrode of the electric spark machining, and the surface thereof is used as the machining surface to cut the electric spark machining along the set path; in the machining process, the machining gap between the flexible electrode and the machined workpiece is ensured to be less than the spark discharge limit distance, the electric spark working fluid fills the machining gap, so that the spark discharge always exists in the machining gap, the workpiece material is removed by the instantaneous high temperature melting effect generated by the spark discharge, and the flowing electric spark working fluid timely takes away the electric spark machining products and heat; meanwhile, according to the curvature characteristics of the machining profile, the flexible electrode is deformed on-line in the machining process, so as to complete the machining of the three-dimensional complex profile; the flexible electrode is prepared by using the material with good conductivity and elasticity, and the flexible electrode can be restored after deformation; the specific process is as follows:

[0017] Step 1, according to the curvature variation characteristics of the standard profile of the machined workpiece, the relationship between the on-line deformation of the flexible electrode and the profile curvature of the workpiece is established, and the mathematical model is established as follows:

[0018] Step 1-1, taking a standard profile line of the machined workpiece as an example, the function thereof can be expressed as:

[0019] y=f(x)

[0020] Step 1-2, according to the basic theory of the electric spark machining, the machining gap Δ is determined as:

[0021] Δ=δ+a+d

[0022] In the formula, δ is the single-side starting discharge gap, a is the single-side discharge removal amount, and d is the single-side electrode loss amount;

[0023] Step 1-3, the function of the flexible electrode axis after deformation is determined as:

[0024] y=g(x)=f(x)+Δ+r-d

[0025] In the formula, r is the pipe diameter of the flexible electrode;

[0026] Step 1-4, the curvature p of the flexible electrode axis corresponding to the machining profile line can be expressed as:

[0027]

[0028] In the formula: g"(x) is the second derivative, g'(x) is the first derivative;

[0029] Step 2, according to the curvature change characteristics of the deformed flexible electrode, the relationship between the online deformation of the flexible electrode and the machining load is established, and the mathematical model is established as follows:

[0030] Step 2-1, for the two-way bending of the flexible electrode, the following assumptions are made:

[0031] (1) In the longitudinal symmetry plane of the flexible electrode, a pair of force couples with equal size and opposite direction make the flexible electrode bend purely.

[0032] (2) There is only normal stress on the cross section of the flexible electrode, and there is no shear stress.

[0033] (3) There is no normal stress between the longitudinal line segments of the flexible electrode.

[0034] Step 2-2, according to the above assumptions, the strain e of any longitudinal line segment can be obtained:

[0035]

[0036] Where p is the radius of curvature of the neutral layer, and z is the distance from the longitudinal line segment to the neutral layer.

[0037] Step 2-3, because there is no normal stress between the longitudinal line segments, each line segment is unidirectional stretching or compression. When the stress is less than the proportional limit, according to Hooke's law, the normal stress s of any longitudinal line segment:

[0038]

[0039] Where E is the elastic modulus of the flexible electrode material.

[0040] Step 2-4, the bending moment M of the cross section of the flexible electrode can be obtained by force analysis:

[0041]

[0042] Where A is the area of the cross section, and I z is the moment of inertia.

[0043] Step 3, according to the established mathematical model of the on-line deformation of the flexible electrode and the change of the curvature of the workpiece surface, the change of the curvature of the flexible electrode corresponding to the workpiece surface in the machining process is obtained, and then the change of the load borne by the flexible electrode in the machining process is obtained according to the relationship between the on-line deformation of the flexible electrode and the machining load; the calculated load is combined with the two models to make the flexible electrode realize on-line deformation in the electric spark cutting machining, so as to realize the on-line deformation of the flexible electrode in the electric spark cutting machining.

[0044] The on-line deformation electric spark cutting method of the flexible electrode has the characteristics that the pulse power source used has the characteristics that:

[0045] For the machining object with a long and narrow surface, a high and low voltage composite pulse power source is used, wherein the high voltage pulse is used for breaking the gap, and the low voltage pulse provides the machining energy to make the discharge gap larger. This mode is beneficial to chip removal, stable machining, and high pulse utilization rate, and is very beneficial to the electric spark machining of the long and narrow surface.

[0046] For the machining object with high surface quality requirements, a comb-shaped wave pulse power source with high frequency short pulse and low frequency long pulse is used, wherein the high frequency and high peak current are the basic pulse, and the low frequency and low peak current pulse is superimposed below. The power source has the characteristics of high frequency short pulse, good roughness, low frequency long pulse, high machining speed and low electrode loss.

[0047] The on-line deformation electric spark cutting method of the flexible electrode has the characteristics that:

[0048] According to the heat transfer effect and heat conduction theory, in order to meet the low loss use requirement of the flexible electrode, the low loss condition of the electrode needs to be met:

[0049]

[0050] Wherein, t i is the discharge time, is the discharge current amplitude, θ m is the melting point of the electrode material, λ is the thermal conductivity of the electrode material, C is the specific heat capacity of the electrode material, and ρ is the density of the electrode material.

[0051] Compared with the prior art, the present application has the following advantages.

[0052] (1) A flexible electrode on-line deformation electric spark cutting method is provided. In the machining of complex surfaces such as integral blisks, a flexible electrode is used as a tool electrode for electric spark machining, and the surface thereof is used as a machining surface to perform cutting type electric spark machining along a set path, and the flexible electrode is deformed on-line according to the curvature characteristics of the machining surface, so as to complete the machining of the complex surface.

[0053] (2) Simplifies the design process of the tool electrode, improves the machining flexibility and the EDM efficiency. The flexible electrode is made of a material with good conductivity and elasticity. Compared with the shaped electrode, the flexible electrode has a simple shape and a short preparation period. In addition, the flexible electrode can be restored after deformation, and can be used multiple times under the condition of ensuring low electrode loss.

[0054] (3) Wide application range. The machining load can be adjusted and the online deformation of the flexible electrode can be controlled according to different machining objects. In addition to being applicable to the machining of the whole blisk with a complex profile, the flexible electrode can also be applied to the machining of the blisk ring type part with high solidity and dense blades. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 Flexible electrode online deformation EDM schematic diagram

[0056] Figure 2 Flexible electrode online deformation EDM schematic diagram

[0057] Label name in the figure: 1, machining workpiece, 2, flexible electrode, 3, working liquid inlet, 4, EDM product, 5, bubble, 6, spark discharge, 7, working liquid outlet, 8, working liquid, 9, initial profile, 10, load, 11, deformed profile. DETAILED DESCRIPTION

[0058] The specific implementation process of the present application will be described in detail below with the spiral tube electrode as an example of the flexible electrode.

[0059] The spiral tube electrode is made of a metal material with good conductivity and elasticity. The spiral tube electrode has spiral gaps on the side wall.

[0060] For the machining object with a long and narrow profile, a high and low voltage composite pulse power source is used, in which the high voltage pulse is used to break the gap, and the low voltage pulse provides the machining energy to make the discharge gap larger. For the machining object with high surface quality requirements, a comb wave pulse power source with high frequency short pulse and low frequency long pulse is used, in which the high frequency and high peak current is the basic pulse, and the low frequency and low peak current pulse is superimposed on the basic pulse.

[0061] For example, the flexible electrode is a spiral tube electrode, and the machining object is a whole blisk with a complex profile. Figure 1As shown, the processing workpiece 1 is connected to the positive pole of the pulse power supply, and the flexible electrode 2 is connected to the negative pole of the pulse power supply. During processing, the pulse power supply is turned on, the flexible electrode 2 is fed along the cutting direction, the working liquid 8 flows into the processing gap through the gap of the flexible electrode 2 from the working liquid inlet 3 at both ends of the flexible electrode 2, while ensuring that the processing gap between the flexible electrode 2 and the processing workpiece 1 is less than the limit distance of the spark discharge 6. The material of the processing workpiece 1 is removed by the instantaneous high temperature melting effect generated by the spark discharge 6. The process of single discharge mainly includes ionization preparation stage, discharge thermal erosion stage and ionization elimination stage. The product 4 and the bubble 5 generated by the electric discharge machining flow out through the working liquid outlet 7 along with the working liquid 8. At the beginning of processing, the flexible electrode 2 has not yet been deformed under load, so the shape of the initial profile 9 after processing is straight, and as the load 10 is applied, the flexible electrode 2 is deformed in line, and when the processing is terminated, the shape of the deformed profile 11 after processing becomes curved. Through the above process, the processing of the complex profile is completed.

Claims

1. A flexible electrode on-line deformation electric spark cutting method, characterized in that: In the processing of complex surfaces such as blisks, a flexible electrode is used as the tool electrode for electric spark machining, and its surface is used as the machining surface to perform cutting-type electric spark machining along a set path; during the machining process, the machining gap between the flexible electrode and the workpiece is ensured to be smaller than the spark discharge limit distance, and the electric spark working fluid fills the machining gap, so that spark discharge always exists in the machining gap; the workpiece material is removed by the instantaneous high-temperature melting effect generated by the spark discharge, and the flowing electric spark working fluid timely carries away the electric spark machining products and heat; at the same time, according to the curvature characteristics of the machining surface, the flexible electrode is deformed on-line during the machining process, thereby completing the machining of the three-dimensional complex surface; the flexible electrode is made of a material with good electrical conductivity and elasticity, and the flexible electrode can be restored after deformation; the specific process is as follows: Step 1, according to the curvature variation characteristics of the standard surface of the workpiece, the relationship between the on-line deformation of the flexible electrode and the curvature of the workpiece surface is established, and the mathematical model is established as follows: Step 1-1, taking a standard surface line of the workpiece as an example, its function can be expressed as: y = f(x) Step 1-2, combined with the basic theory of electric spark machining, the machining gap Δ is determined as: Δ = δ + a + d In the formula: δ is the single-sided initial discharge gap, a is the single-sided discharge removal amount, and d is the single-sided electrode loss amount; Step 1-3, thus the function of the flexible electrode axis after deformation can be determined as: y = g(x) = f(x) + Δ + r - d In the formula: r is the pipe diameter of the flexible electrode; Step 1-4, therefore, the curvature p of the flexible electrode axis corresponding to the machining surface line can be expressed as: In the formula: g″(x) is the second derivative, and g′(x) is the first derivative; Step 2, according to the curvature variation characteristics of the deformed flexible electrode, the relationship between the on-line deformation of the flexible electrode and the machining load is established, and the mathematical model is established as follows: Step 2-1, for the two-way bending of the flexible electrode, the following assumptions are made: (1) In the longitudinal symmetrical plane of the flexible electrode, a pair of force couples with equal size and opposite direction are applied to make the flexible electrode bend purely; (2) There is only normal stress on the cross section of the flexible electrode, and there is no shear stress; (3) There is no normal stress between the longitudinal line segments of the flexible electrode; Step 2-2, according to the above assumptions, the strain ε of any longitudinal line segment is obtained: Wherein, p is the curvature radius of the neutral layer, and z is the distance from the longitudinal line segment to the neutral layer; Step 2-3, because there is no normal stress between the longitudinal line segments, each line segment is stretched or compressed in one direction; when the stress is less than the proportional limit, according to Hooke's law, the normal stress σ of any longitudinal line segment is: Wherein, E is the elastic modulus of the flexible electrode material; Step 2-4, by analyzing the stress on the cross section of the flexible electrode, the bending moment M is obtained: where A is the area of the cross section, I z is the moment of inertia; Step 3, according to the established mathematical model of the flexible electrode online deformation and the change of the workpiece surface curvature, the change of the flexible electrode curvature corresponding to the workpiece surface in the machining process is obtained, and then the change of the load borne by the flexible electrode in the machining process is obtained from the relationship between the flexible electrode online deformation and the machining load; the calculated load is combined with the two models to make the flexible electrode realize online deformation in the electric spark cutting machining to fit the standard surface of the workpiece.

2. The flexible electrode online deformation electric spark cutting method according to claim 1, characterized in that: For the long and narrow surface machining object, a high and low voltage composite pulse power source is used, wherein the high voltage pulse is used for breaking the gap, and the low voltage pulse provides the machining energy to make the discharge gap larger; this method is beneficial to chip removal, stable machining, and high pulse utilization rate, and is very beneficial to the electric spark machining of the long and narrow surface; For the machining object with high surface quality requirement, a comb wave pulse power source with high frequency short pulse and low frequency long pulse is used, wherein the high frequency and high peak current is the basic pulse, and the low frequency and low peak current pulse is superimposed below it; this power source has the characteristics of high frequency short pulse with good roughness and low frequency long pulse with high machining speed and low electrode loss.

3. The flexible electrode online deformation electric spark cutting method according to any one of claims 1 to 2, characterized in that: According to the heat transfer effect and heat conduction theory, in order to meet the low loss use requirement of the flexible electrode, the electrode low loss condition needs to be met: where t i is the discharge time, is the discharge current amplitude, θ m is the electrode material melting point, λ is the electrode material thermal conductivity, C is the electrode material specific heat capacity, and ρ is the electrode material density.

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