Flexible electrode in-line deformation electrical discharge cutting method

Abstract

A flexible electrode (2) in-line deformation electrical discharge cutting method. During machining of complex surfaces, such as blisks, a flexible electrode (2) is used as a tool electrode for electrical discharge machining, the surface of the flexible electrode (2) is used as a machining surface for performing cutting-type electrical discharge machining along a preset path, and, according to the curvature characteristics of the machined surfaces, the flexible electrode (2) undergoes in-line deformation, thereby completing the machining of complex surfaces. The flexible electrode (2) is made of a material having good electrical conductivity and elasticity, so as to ensure that the flexible electrode (2) can recover after deformation. Using the flexible electrode (2) for realizing electrical discharge cutting machining for three-dimensional complex surfaces can simplify a design process for the tool electrode and improve the electrical discharge machining efficiency.

Description

Flexible electrode on-line deformation electric spark cutting method TECHNICAL FIELD

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

[0005] In the patent "Maximum free movement trajectory search method for electric spark machining electrode of closed blisk" (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 spark 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 and overall machining efficiency of the electric spark machining.

[0007] In the patent "Pre-pore liquid pumping 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 pumping liquid 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 can be shortened, the electrode loss and the machining cost can be reduced, meanwhile, the machining precision can be ensured, the machining efficiency can be improved, and the electric spark machining with high efficiency and low cost is realized. SUMMARY

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

[0015] Firstly, the present application provides a flexible electrode on-line deformation electric spark cutting method, comprising:

[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 perform the cutting type electric spark machining along the set path; in the machining process, the machining gap between the flexible electrode and the machining 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.

[0017] Secondly, the flexible electrode on-line deformation electric spark cutting method is provided, comprising:

[0018] Step 1, according to the curvature variation characteristics of the standard profile of the machining 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:

[0019] Step 1-1, taking a standard profile line of the machining workpiece as an example, the function thereof can be expressed as: y=f(x)

[0020] In the formula, y''(x) is the second derivative, and y'(x) is the first derivative;

[0021] Step 1-2, according to the basic theory of the electric spark machining, the machining gap Δ is determined as: Δ=δ+a+d

[0022] In the formula, δ is the single-side initial 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 can be determined as: y=g(x)=f(x)+Δ+r-d

[0024] In the formula, r is the pipe diameter of the flexible electrode;

[0025] Step 1-4, the curvature p of the flexible electrode axis corresponding to the machined profile line can be expressed as:

[0026] Step 2, according to the curvature change 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:

[0027] Step 2-1, for the two-way bending of the flexible electrode, the following assumptions are made:

[0028] (1) In the longitudinal symmetry 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.

[0029] (2) There is only normal stress on the cross section of the flexible electrode, and there is no shear stress.

[0030] (3) There is no normal stress between the longitudinal line segments of the flexible electrode.

[0031] Step 2-2, according to the above assumptions, the strain e of any longitudinal line segment can be obtained:

[0032] 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.

[0033] 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 is:

[0034] Where E is the elastic modulus of the flexible electrode material.

[0035] Step 2-4, the bending moment M of the cross section of the flexible electrode can be obtained by force analysis:

[0036] Where A is the area of the cross section, and I z is the moment of inertia.

[0037] Step 3, according to the established mathematical model of the on-line deformation of the flexible electrode and the curvature change of the workpiece profile, the change of the curvature of the flexible electrode corresponding to the workpiece profile during machining is obtained, and then the change of the load borne by the flexible electrode during machining 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 of the machined workpiece standard profile in electric spark cutting machining.

[0038] In the above flexible electrode on-line deformation electric spark cutting method, the pulse power source used is:

[0039] For the machining object with long and narrow profile, a high and low voltage composite pulse power is used, wherein the high voltage pulse is used for breaking the gap, and the low voltage pulse provides the machining energy, so as to increase the discharge gap. This mode is beneficial to chip removal, stable machining, and high pulse utilization rate, and is very beneficial to the EDM of long and narrow profile;

[0040] For the machining object with high surface quality requirement, a comb wave pulse power 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 the basic pulse. This power has the characteristics of good roughness of high frequency short pulse and high machining speed, low electrode loss of low frequency long pulse.

[0041] The flexible electrode on-line deformation EDM method has the characteristics that:

[0042] According to the heat transfer effect and heat conduction theory, in order to meet the low loss requirement of the flexible electrode, the low loss condition of the electrode needs to be met:

[0043] 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 p is the density of the electrode material.

[0044] Compared with the prior art, the embodiment scheme of the present application has the following obvious advantages:

[0045] (1) The flexible electrode on-line deformation EDM method disclosed in the embodiment uses a flexible electrode as a tool electrode for EDM when machining a complex profile such as a blisk, uses its surface as a machining surface to perform cutting type EDM along a set path, and deforms the flexible electrode on-line according to the curvature characteristics of the machining profile, so as to complete the machining of the complex profile.

[0046] (2) The design process of the tool electrode is simplified, and the machining flexibility and EDM efficiency are improved. The flexible electrode is prepared from a material with good conductivity and elasticity, and compared with a 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 low electrode loss.

[0047] (3) Wide application range, the machining load can be adjusted and the on-line deformation of the flexible electrode can be controlled according to different machining objects. In addition to machining the blisk with a complex profile, the present application can also be applied to the blisk ring type parts with large density and dense blades. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 is a flexible electrode in-line deformation electric spark cutting schematic diagram;

[0049] Figure 2 is a flexible electrode in-line deformation electric spark cutting schematic diagram;

[0050] Figure label name: 1, processing workpiece, 2, flexible electrode, 3, working fluid inlet, 4, electric spark processing product, 5, bubble, 6, spark discharge, 7, working fluid outlet, 8, working fluid, 9, initial profile, 10, load, 11, deformed profile. DETAILED DESCRIPTION

[0051] The following will be combined with the spiral tube electrode as a flexible electrode as an example, the specific implementation process of the present application is described in detail.

[0052] The spiral tube electrode is made of metal material with good conductivity and elasticity, and the spiral tube electrode has spiral gaps on the side wall.

[0053] For the processing object with long and narrow profile, 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 processing energy to make the discharge gap larger. For the processing object with high surface quality requirement, a comb wave pulse power source with high frequency short pulse and low frequency long pulse is used, and the high frequency and high peak current are the basic pulse, and the low frequency and low peak current pulse is superimposed below.

[0054] As shown in Figure 1 and Figure 2, the processing workpiece 1 is connected to the positive pole of the pulse power source, and the flexible electrode 2 is connected to the negative pole of the pulse power source. During processing, the pulse power source is turned on, the flexible electrode 2 is fed along the cutting direction, the working fluid 8 flows into the processing gap through the gap of the flexible electrode 2 from the working fluid inlet 3 at both ends of the flexible electrode 2, and at the same time, the processing gap between the flexible electrode 2 and the processing workpiece 1 is ensured to be less than the limit distance of the spark discharge 6. The material of the processing workpiece 1 is removed by using 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 electric spark processing flow out through the working fluid outlet 7 along with the working fluid 8. At the beginning of processing, since the flexible electrode 2 has not yet been deformed under load, the shape of the initial profile 9 after processing is straight, and with the application of load 10, 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 complex profile is completed.

Claims

1. A flexible electrode online deformation electric spark cutting method, characterized by: When processing complex surfaces such as integral blades, a flexible electrode is used as the tool electrode for EDM, and its surface is used as the processing surface for cutting-type EDM along the set path. During the processing, the processing gap between the flexible electrode and the workpiece is ensured to be less than the spark discharge limit distance, and the EDM working fluid fills the processing gap so that spark discharge always exists in the processing gap. The instantaneous high-temperature melting effect generated by the spark discharge is used to erode the workpiece material, and the flowing EDM working fluid promptly takes away the EDM products and heat. At the same time, according to the curvature characteristics of the processing surface, the flexible electrode is deformed online during the processing, thereby completing the processing of three-dimensional complex surfaces. The flexible electrode is made of materials with good conductivity and elasticity to ensure that the flexible electrode can recover after deformation.

2. The flexible electrode online deformation electric spark cutting method according to claim 1, characterized in that: Step 1: Based on the curvature variation characteristics of the standard surface of the workpiece, the relationship between the online deformation of the flexible electrode and the curvature of the workpiece surface is established. The mathematical model establishment process is as follows: Step 1-1, taking the processing of a standard surface line of a workpiece as an example, its function can be expressed as: y=f(x) Where: y″(x) is the second-order derivative, y′(x) is the first-order derivative; Step 1-2: Combine the basic theory of EDM and determine the machining gap Δ: Δ=δ+a+d Where: δ is the unilateral initial discharge gap, a is the unilateral discharge erosion amount, and d is the unilateral electrode loss; Steps 1-3: From this, the function after the flexible electrode axis is deformed can be determined as: y=g(x)=f(x)+Δ+rd Where: r is the diameter of the flexible electrode; Steps 1-4, so the curvature ρ of the flexible electrode axis corresponding to the processed profile line can be expressed as: Step 2: Based on the curvature change characteristics of the flexible electrode after deformation, the relationship between the online deformation of the flexible electrode and the processing load is established. The mathematical model establishment process is as follows: Step 2-1: For the bidirectional bending of the flexible electrode, make the following assumptions: (1) In the longitudinal symmetry plane of the flexible electrode, a pair of force couples with equal magnitude and opposite directions are applied, causing the flexible electrode to bend purely. (2) There is only normal stress but no shear stress on the cross section of the flexible electrode. (3) There is no positive stress between the longitudinal segments of the flexible electrode. Step 2-2: Based on the above assumptions, obtain the strain ε of any longitudinal segment: Where ρ is the radius of curvature 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 longitudinal segments, each segment is in unidirectional tension or compression. When the stress is less than the proportional limit, Hooke's law shows that the normal stress σ of any longitudinal segment is: Where E is the elastic modulus of the flexible electrode material. Step 2-4: Perform force analysis on the cross section of the flexible electrode to obtain the bending moment M: Where A is the area of ​​the cross section, I z is the moment of inertia. Step 3. Based on the established mathematical model of the online deformation of the flexible electrode and the change in the curvature of the workpiece surface, the change in the curvature of the workpiece surface corresponding to the flexible electrode during the processing is obtained. Then, based on the relationship between the online deformation of the flexible electrode and the processing load, the change in the load borne by the flexible electrode during the processing is obtained. The applied load is calculated by combining the two models, so that the flexible electrode can achieve online deformation to fit the standard surface of the workpiece during the electrospark cutting process.

3. The flexible electrode online deformation electric spark cutting method according to claim 1, characterized in that: For machining objects with narrow and long surfaces, a high- and low-voltage composite pulse power supply is used, where the high-voltage pulse is used to break down the gap, while the low-voltage pulse provides machining energy, increasing the discharge gap. This method facilitates chip removal, stabilizes machining, and has a high pulse utilization rate, making it very beneficial for EDM machining of narrow and long surfaces. For machining objects requiring high surface quality, a comb-wave pulse power supply is used, combining high-frequency short pulses with low-frequency long pulses. High-frequency, high-peak current pulses serve as the basic pulses, with low-frequency, low-peak current pulses superimposed underneath. This power supply offers excellent roughness with high-frequency short pulses and high machining speeds and low electrode loss with low-frequency long pulses.

4. The flexible electrode online deformation electric spark cutting method according to any one of claims 1 to 3, characterized in that: According to the heat transfer effect and heat conduction theory, in order to meet the low-loss requirements of flexible electrodes, the following low-loss conditions must be met: Among them, t i is the discharge time, is the discharge current amplitude, θ m Electrode material melting point, λ electrode material thermal conductivity, C electrode material specific heat capacity, ρ electrode material density.

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