Method for precise removal of recast layer and over corrosion inhibition

Abstract

The application provides a recast layer precise removal and over-corrosion inhibition method, and belongs to the technical field of electric processing. The application firstly obtains the electric quantity Q0 required for breaking the passivation film per unit area of a workpiece to be processed containing a recast layer and the electric quantity Q1 required for removing the recast layer per unit area of the workpiece to be processed containing the recast layer without over-corrosion of the base body, then determines the electrolytic finishing machining parameters meeting the electric quantity condition through simulation, and finally performs electrolytic finishing machining on the workpiece to be processed containing the recast layer by using the determined electrolytic finishing machining parameters, so that the passivation film is quickly broken, the recast layer is precisely removed, and the over-corrosion phenomenon of the workpiece surface caused by as little electric quantity as possible is avoided, and the workpiece surface quality is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrical processing, and particularly relates to a method for precisely removing recast layer and inhibiting over-corrosion. BACKGROUND

[0002] Electrical discharge machining (EDM) is widely used in the machining of various conductive materials in manufacturing industry, and has high precision and high efficiency. During EDM, the electric arc melts the metal at high temperature, and the molten metal droplets re-solidify on the surface of the electrode. The solidified metal layer is called recast layer. The recast layer has different organization and properties from the original metal, and is more brittle than the original metal, and may have pores, cracks and other defects. In addition, the presence of the recast layer will reduce the fatigue strength and service life of the material. Therefore, removing the recast layer is an important measure to improve the machining quality of the workpiece surface.

[0003] Electrochemical machining (ECM) technology usually uses a conductive wire or a conductive rod as a cutting cathode tool, and the workpiece to be machined as an anode. The two are immersed in an electrolyte to undergo an electrochemical anodic dissolution reaction to remove the recast layer. However, the current ECM technology lacks precise control of the electric quantity during the removal process, and mainly relies on experience or experiments to determine the cathode feed rate and power voltage, which leads to incomplete dissolution of the passivation film, incomplete removal of the recast layer, or over-corrosion of the substrate due to electric quantity overflow, thereby affecting the removal quality. Therefore, it is necessary to propose a method for precisely removing the recast layer and inhibiting over-corrosion to improve the machining precision and surface quality of electrochemical finishing. SUMMARY

[0004] The purpose of the present application is to provide a method for precisely removing recast layer and inhibiting over-corrosion. The method provided by the present application can achieve rapid breakdown of the passivation film, precise removal of the recast layer, and as little as possible over-corrosion of the workpiece surface caused by electric quantity escape.

[0005] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0006] The present application provides a method for precisely removing recast layer and inhibiting over-corrosion, comprising the following steps:

[0007] (1) using a conductive metal as a cathode, using a workpiece with a heavy casting layer as an anode, and performing anodic dissolution in an electrolyte at a constant current density, observing the micro-morphology of the surface of the workpiece after different anodic dissolution times, determining the breakdown time of the passivation film on the surface of the workpiece with a heavy casting layer and the time at which the heavy casting layer on the surface of the workpiece with a heavy casting layer is completely removed and the substrate is not excessively corroded, and then calculating the electric quantity Q0 required for breaking through the passivation film per unit area of the workpiece with a heavy casting layer and the electric quantity Q1 required for removing the heavy casting layer per unit area of the workpiece with a heavy casting layer and the substrate not being excessively corroded according to the current density and the time; the area of the cathode is greater than the area of the heavy casting layer of the workpiece with a heavy casting layer;

[0008] (2) simulating the electrolytic finishing machining process of the workpiece with a heavy casting layer at different feed speeds and power voltages by using simulation software, and determining the electrolytic finishing machining parameters meeting the electric quantity condition; the electric quantity condition is that the electric quantity Q per unit area of the surface of the workpiece with a heavy casting layer and Q0 and Q1 obtained in the step (1) satisfy: 0≤Q-(Q0+Q1)≤100C / cm 2 ; in the simulation, the electrolyte for electrolytic finishing machining is the same as the electrolyte in the step (1);

[0009] (3) performing electrolytic finishing machining on the workpiece with a heavy casting layer by using the electrolytic finishing machining parameters determined in the step (2), and obtaining a workpiece with the heavy casting layer removed.

[0010] Preferably, the cathode for electrolytic finishing machining in the step (2) comprises a wire electrode, a rectangular electrode, a tube electrode or a profiled electrode.

[0011] Preferably, the diameter of the wire electrode is 0.5-1 mm.

[0012] Preferably, the electrolyte in the step (2) comprises a glycol-based electrolyte or a water-based electrolyte.

[0013] Preferably, the initial machining gap for electrolytic finishing machining in the step (2) is 0-100 μm.

[0014] The application provides a method for precisely removing a heavy casting layer and inhibiting over-corrosion, comprising the following steps: (1) taking a conductive metal as a cathode, taking a workpiece with a heavy casting layer as an anode, and performing anodic dissolution in an electrolyte at a constant current density, observing the micro-morphology of the workpiece surface after different anodic dissolution times, determining the breakdown time of the passivation film on the surface of the workpiece with the heavy casting layer and the time at which the heavy casting layer on the surface of the workpiece with the heavy casting layer is completely removed and the substrate is not excessively corroded, and then calculating the electric quantity Q0 required for breaking through the passivation film per unit area of the workpiece with the heavy casting layer and the electric quantity Q1 required for removing the heavy casting layer per unit area of the workpiece with the heavy casting layer and the substrate not being excessively corroded according to the current density and the time; the area of the cathode is greater than the area of the heavy casting layer of the workpiece with the heavy casting layer; (2) simulating the electrolytic finishing process of the workpiece with the heavy casting layer at different feed speeds and power voltages by using a simulation software, and determining electrolytic finishing parameters meeting the electric quantity condition; the electric quantity condition is that the electric quantity Q per unit area of the surface of the workpiece with the heavy casting layer and the Q0 and Q1 obtained in the step (1) meet 0≤Q-(Q0+Q1)≤100 C / cm2; in the simulation, the electrolyte for electrolytic finishing is the same as the electrolyte in the step (1); and (3) performing electrolytic finishing on the workpiece with the heavy casting layer by using the electrolytic finishing parameters determined in the step (2), to obtain a workpiece with the heavy casting layer removed. 2 The application first obtains the electric quantity Q0 required for breaking through the passivation film per unit area of the workpiece with the heavy casting layer and the electric quantity Q1 required for removing the heavy casting layer per unit area of the workpiece with the heavy casting layer and the substrate not being excessively corroded, then determines electrolytic finishing parameters meeting the electric quantity condition by simulation, and finally performs electrolytic finishing on the workpiece with the heavy casting layer by using the determined electrolytic finishing parameters, so that the passivation film is quickly broken through, the heavy casting layer is precisely removed, and the phenomenon of over-corrosion of the workpiece surface caused by as little electric quantity as possible is avoided, which is beneficial to improving the surface quality of the workpiece. The results of the embodiments show that, after the workpiece is treated by using the method, the heavy casting layer on the surface of the workpiece is completely removed, and the processed surface is smooth. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A simulation model for precisely removing a heavy casting layer and inhibiting over-corrosion established by the application;

[0016] Figure 2 A device used in the method for precisely removing a heavy casting layer and inhibiting over-corrosion;

[0017] Figure 3 SEM images of the initial surface of the workpiece with the heavy casting layer in step (1) of Example 1 (0 s) and the surface of the workpiece after treatment at different times (28 s, 35 s, 45 s, 57 s, 63 s and 82 s).

[0018] Figure 4 The current density-time curve of the workpiece surface P1 point at different cathode feeding speeds when the power supply voltage is 30V obtained by simulation in step (2) of Example 1;

[0019] Figure 5 The current density-time curve of the workpiece surface P1 point at different power supply voltages when the cathode feeding speed is 50μm / s obtained by simulation in step (2) of Example 1;

[0020] Figure 6 The relationship between the electric quantity of the workpiece surface P1 point and the cathode feeding speed and the power supply voltage in Example 1;

[0021] Figure 7 The surface metallographic phase diagram of the workpiece containing recast layer to be processed in step (3) of Example 1;

[0022] Figure 8 The surface SEM diagram of the workpiece containing recast layer to be processed in step (3) of Example 1;

[0023] Figure 9 The surface roughness of the workpiece containing recast layer to be processed in step (3) of Example 1;

[0024] Figure 10 The surface metallographic phase diagram of the workpiece after being processed by the method of Example 1;

[0025] Figure 11 The surface SEM diagram of the workpiece after being processed by the method of Example 1;

[0026] Figure 12 The surface roughness of the workpiece after being processed by the method of Example 1;

[0027] Figure 13 The surface metallographic phase diagram of the workpiece after being processed by the method of Comparative Example 1;

[0028] Figure 14 The surface SEM diagram of the workpiece after being processed by the method of Comparative Example 1;

[0029] Figure 15 The surface roughness of the workpiece after being processed by the method of Comparative Example 1;

[0030] Figure 16 The surface metallographic phase diagram of the workpiece after being processed by the method of Comparative Example 2;

[0031] Figure 17 The surface SEM diagram of the workpiece after being processed by the method of Comparative Example 2;

[0032] Figure 18Surface roughness of the workpiece after the method of Comparative Example 2;

[0033] Figure 19 SEM images of the initial surface of the workpiece containing recast layer in step (1) of Example 2 (0s), and SEM images of the surface of the workpiece after treatment at different times (34s, 40s, 45s, 60s, 80s and 100s);

[0034] Figure 20 Current density-time curves of point P1 on the surface of the workpiece at different cathode feeding speeds under the power supply voltage of 15V obtained by simulation in step (2) of Example 2;

[0035] Figure 21 Current density-time curves of point P1 on the surface of the workpiece at different power supply voltages under the cathode feeding speed of 120μm / s obtained by simulation in step (2) of Example 2;

[0036] Figure 22 Relationship diagram of the electric quantity of point P1 on the surface of the workpiece with the cathode feeding speed and the power supply voltage in Example 2;

[0037] Figure 23 Metallographic image of the surface of the workpiece containing recast layer in step (3) of Example 2;

[0038] Figure 24 SEM image of the surface of the workpiece containing recast layer in step (3) of Example 2;

[0039] Figure 25 Surface roughness of the workpiece containing recast layer in step (3) of Example 2;

[0040] Figure 26 Metallographic image of the surface of the workpiece after the method of Example 2;

[0041] Figure 27 SEM image of the surface of the workpiece after the method of Example 2;

[0042] Figure 28 Surface roughness of the workpiece after the method of Example 2;

[0043] Figure 29 Metallographic image of the surface of the workpiece after the method of Comparative Example 3;

[0044] Figure 30 SEM image of the surface of the workpiece after the method of Comparative Example 3;

[0045] Figure 31 Surface roughness of the workpiece after the method of Comparative Example 3;

[0046] Figure 32 A metallographic image of the surface of the workpiece after the method of Comparative Example 4 was processed;

[0047] Figure 33 An SEM image of the surface of the workpiece after the method of Comparative Example 4 was processed;

[0048] Figure 34 The surface roughness of the workpiece after the method of Comparative Example 4 was processed. DETAILED DESCRIPTION

[0049] The present application provides a recast layer precise removal and over-corrosion inhibition method, comprising the following steps:

[0050] (1) using a conductive metal as a cathode and a workpiece containing a recast layer to be processed as an anode, anodic dissolution is carried out in an electrolyte at a constant current density, the surface micro-morphology of the workpiece after different anodic dissolution times is observed, the breakdown time of the passivation film on the surface of the workpiece containing the recast layer to be processed and the time at which the recast layer on the surface of the workpiece containing the recast layer to be processed is completely removed and the substrate is not excessively corroded are determined, then the electric quantity Q0 required to break down the unit area passivation film of the workpiece containing the recast layer to be processed and the electric quantity Q1 required to remove the unit area recast layer of the workpiece containing the recast layer to be processed and the substrate not to be excessively corroded are calculated according to the current density and the time; the area of the cathode is greater than the area of the recast layer of the workpiece containing the recast layer to be processed;

[0051] (2) the electrolytic finishing process of the workpiece containing the recast layer to be processed at different feed speeds and power voltages is simulated respectively by using simulation software, and the electrolytic finishing process parameters meeting the electric quantity condition are determined; the electric quantity condition is that the unit area electric quantity Q of the surface of the workpiece containing the recast layer to be processed and Q0 and Q1 obtained in the step (1) satisfy: 0≤Q-(Q0+Q1)≤100C / cm 2 ; during the simulation, the electrolyte for electrolytic finishing is the same as the electrolyte in the step (1);

[0052] (3) the workpiece containing the recast layer to be processed is subjected to electrolytic finishing by using the electrolytic finishing process parameters determined in the step (2), and a workpiece with the recast layer removed is obtained.

[0053] The present application uses conductive metal as cathode, uses the workpiece with heavy casting layer as anode, carries out anodic dissolution in electrolyte with constant current density, determines the breakdown time of passivation film on the surface of the workpiece with heavy casting layer and the time when the heavy casting layer on the surface of the workpiece with heavy casting layer is completely removed and the substrate is not excessively corroded by observing the micro-morphology of the surface of the workpiece with heavy casting layer after anodic dissolution for different time, and then calculates the electric quantity Q0 required for breaking through the passivation film per unit area of the workpiece with heavy casting layer and the electric quantity Q1 required for removing the heavy casting layer per unit area of the workpiece with heavy casting layer and the substrate not being excessively corroded according to the current density and time.

[0054] In the present application, the material of the conductive metal preferably includes tungsten, molybdenum or stainless steel.

[0055] In the present application, the area of the cathode is greater than the area of the heavy casting layer of the workpiece with heavy casting layer. The present application does not have special limitation on the specific area of the cathode and the heavy casting layer of the workpiece with heavy casting layer, and it is only required to ensure that the area of the cathode is greater than the area of the heavy casting layer of the workpiece with heavy casting layer.

[0056] The present application does not have special limitation on the material and size of the workpiece with heavy casting layer, and any workpiece with heavy casting layer known to those skilled in the art can be used. In the present application, the workpiece with heavy casting layer for testing electric quantity is the same as the workpiece to be processed when the method is actually applied. In the embodiment of the present application, the workpiece with heavy casting layer is FGH96 workpiece after electric spark machining.

[0057] In the present application, the electrolyte preferably includes glycol-based electrolyte or water-based electrolyte, and more preferably includes sodium chloride glycol solution and sodium nitrate aqueous solution.

[0058] In the present application, the concentration of the sodium chloride glycol solution is preferably 0.5-2 mol / L, and more preferably 1 mol / L; and the conductivity of the sodium chloride glycol solution is preferably 0.33 S / m.

[0059] In the present application, the mass concentration of the sodium nitrate aqueous solution is preferably 15-25%, and more preferably 20%; and the conductivity of the sodium nitrate aqueous solution is preferably 14.2 S / m.

[0060] In the present application, the current density is preferably 2-50 A·cm -2 The present application controls the current density in the above range, which is more conducive to accurately determining the breakdown time of passivation film on the surface of the workpiece with heavy casting layer and the time when the heavy casting layer on the surface of the workpiece with heavy casting layer is completely removed and the substrate is not excessively corroded.

[0061] In the embodiments of the present application, the different times can be specifically 28s, 35s, 45s, 57s, 63s and 82s in sequence, or can be specifically 34s, 40s, 45s, 60s, 80s and 100s in sequence.

[0062] In the present application, the micro-morphology of the workpiece surface after the anode dissolution for different times is preferably observed by a scanning electron microscope, a scanning electron microscope image is obtained, and then the passivation film breakdown time of the workpiece surface containing the heavy recast layer and the time at which the heavy recast layer on the workpiece surface containing the heavy recast layer is completely removed and the base body is not excessively corroded are determined according to the scanning electron microscope image. The workpiece surface containing the heavy recast layer is crater-like, the workpiece surface on which the heavy recast layer is completely removed and the base body is not excessively corroded is smooth and flat without features, and the workpiece surface that is excessively corroded is a base body structure with obvious grain boundaries and grains. The micro-morphology obtained from the scanning electron microscope image is used as the basis for determining the time required for the heavy recast layer to be completely removed.

[0063] In the present application, the integral calculation formula of the current density with respect to the time required for the heavy recast layer to be completely removed is to obtain the electric quantity Q0 required for breaking down the unit area passivation film of the workpiece containing the heavy recast layer and the electric quantity Q1 required for removing the unit area heavy recast layer of the workpiece containing the heavy recast layer and the base body not being excessively corroded.

[0064] After obtaining the electric quantity Q0 required for breaking down the unit area passivation film of the workpiece containing the heavy recast layer and the electric quantity Q1 required for removing the unit area heavy recast layer of the workpiece containing the heavy recast layer and the base body not being excessively corroded, the present application simulates the electrolytic finishing machining process of the workpiece containing the heavy recast layer at different feed speeds and power voltages by using simulation software to determine the electrolytic finishing machining parameters that meet the electric quantity condition.

[0065] In the present application, the electric quantity required for breaking down the unit area passivation film of the workpiece containing the heavy recast layer is Q0, the electric quantity required for removing the unit area heavy recast layer of the workpiece containing the heavy recast layer and the base body not being excessively corroded is Q1, and the overcut electric quantity of the unit area of the workpiece base body material is Q2. With the cathode feed movement, the unit area electric quantity Q of the workpiece surface can be in the following states: Q < Q0, the passivation film is not completely broken and dissolved. Q0≤Q<Q0+Q1, the passivation film is broken and dissolved, but the heavy recast layer is not completely removed. Q≥Q0+Q1, the heavy recast layer is completely removed, but the processing surface is overcut, the overcut electric quantity Q2 is Q-Q0-Q1. Q=Q0+Q1, the heavy recast layer is completely removed and the workpiece base body surface will not be overcut.

[0066] In the present application, the electric quantity condition is that the unit area electric quantity Q of the workpiece surface containing the heavy recast layer and Q0 and Q1 obtained in the above technical solution satisfy: 0≤Q-(Q0+Q1)≤100C / cm 2 .

[0067] The simulation is preferably performed by COMSOL Multiphysics simulation software.

[0068] As an embodiment of the present application, the parameters of the electrolytic finishing process in the simulation can be as follows:

[0069] The initial machining gap of the electrolytic finishing process is 0-100 μm;

[0070] The feed depth of the electrolytic finishing process is 15-25 μm;

[0071] The electrolyte of the electrolytic finishing process is the same as the electrolyte described above;

[0072] The cathode feed speed of the electrolytic finishing process can be 25-150 μm / s; the feed direction of the cathode is parallel to the recast layer surface of the workpiece to be machined containing the recast layer;

[0073] The power supply voltage of the electrolytic finishing process can be 10-50 V.

[0074] In the present application, the cathode of the electrolytic finishing process preferably includes a wire electrode, a rectangular electrode, a tube electrode or a profiled electrode.

[0075] In the present application, the diameter of the wire electrode is preferably 0.5-1 mm.

[0076] The present application preferably controls the recast layer precise removal scheme by formulating the cathode feed speed and the power supply voltage in combination, simulates the electric field and calculates the electric quantity according to the electric quantity formula calculates the workpiece surface machining electric quantity in different electric parameter combinations in the recast layer removal process of the electrolytic finishing process, wherein i(t) is the function of the current density with respect to time, and determines the electrolytic finishing process parameters satisfying the electric quantity condition.

[0077] The simulation model for recast layer precise removal and over-corrosion inhibition established in the present application is shown in Figure 1 , wherein Γ1 is the cathode surface, Γ2 is the workpiece surface, Δ is the initial machining gap, and e is the feed depth. In order to simplify the model, the influences of ion concentration, heat, product and bubbles and the profile evolution of the workpiece are ignored. The electric quantity (Q) of the P1 point on the workpiece surface is taken as the criterion for complete removal of the recast layer, so as to optimize the machining parameters and ensure efficient removal of the recast layer under electric quantity control. In the present application, the P1 point is preferably any point on the workpiece surface, and more preferably the center point on the workpiece surface.

[0078] In the present application, the simulation boundary parameters are preferably: the voltage of the cathode surface (Γ1) the cathode feed speed (V f) = 25, 50, 60, 90, 100, 120, 125 or 150 µm / s; voltage of the anode surface (Γ2) 15, 20, 25, 30, 40 or 50 V; electrolyte (Γ3, Γ4, Γ5, Γ6): wherein n is the direction of the potential gradient, and i is the current density.

[0079] The present application does not have special limitations on other operations simulated by COMSOL Multiphysics simulation software, and any technical solution known to those skilled in the art can be used.

[0080] After determining the electrolytic finishing machining parameters meeting the electric quantity condition through simulation, the present application uses the determined electrolytic finishing machining parameters to perform electrolytic finishing machining on the workpiece containing a heavy casting layer, so as to obtain a workpiece with the heavy casting layer removed.

[0081] In the present application, the material of the cathode, the anode and the electrolyte during electrolytic finishing machining are the same as those in the process of determining Q0 and Q1, which will not be described here.

[0082] In the present application, the cathode during electrolytic finishing machining preferably includes a wire electrode, a rectangular electrode, a tube electrode or a profiled electrode.

[0083] In the present application, the diameter of the wire electrode is preferably 0.5-1 mm.

[0084] The present application first obtains the electric quantity Q0 required for breaking through the passivation film per unit area of the workpiece containing a heavy casting layer and the electric quantity Q1 required for removing the heavy casting layer per unit area of the workpiece containing a heavy casting layer without excessive corrosion of the base body, then determines the electrolytic finishing machining parameters meeting the electric quantity condition through simulation, and finally performs electrolytic finishing machining on the workpiece containing a heavy casting layer by using the determined electrolytic finishing machining parameters, so as to realize rapid breaking through of the passivation film, accurate removal of the heavy casting layer and as little as possible over-corrosion of the workpiece surface caused by electric quantity escape, which is conducive to improving the surface quality of the workpiece.

[0085] The device schematic diagram used in the method for accurate removal of the heavy casting layer and inhibition of over-corrosion according to the present application is preferably as shown in Figure 2As shown in the figure, wherein 1 is the X axis, 2 is the electrolyte tank, 3 is the electrolyte, 4 is the liquid inlet pipe, 5 is the Z axis, 6 is the power supply, 7 is the wire electrode clamp, 8 is the wire electrode (cathode), 9 is the workpiece clamp, 10 is the workpiece to be processed containing heavy casting layer, and 11 is the Y axis. In use, the electrolyte 3 enters the electrolyte tank 2 through the liquid inlet pipe 4, the wire electrode clamp 7 is used to fix the wire electrode 8, the workpiece clamp 9 is used to fix the workpiece to be processed containing heavy casting layer 10, the workpiece to be processed containing heavy casting layer 10 and the wire electrode 8 are both immersed in the electrolyte 3, one end of the workpiece to be processed containing heavy casting layer 10 is connected with the positive electrode of the power supply 6, one end of the wire electrode 8 is connected with the negative electrode of the power supply 6, and the wire electrode 8 is vertically arranged.

[0086] The size and material of the electrolyte tank 2, the liquid inlet pipe 4, the wire electrode clamp 7 and the workpiece clamp 9 are not specially limited in the present application, and materials well known to those skilled in the art can be used, and the size can be selected according to actual needs.

[0087] The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0088] Embodiment 1

[0089] A method for precisely removing heavy casting layer and inhibiting over-corrosion: (1) taking 304 stainless steel as cathode and taking the workpiece to be processed containing heavy casting layer (FGH96 workpiece after electric spark machining, the thickness of the heavy casting layer is 10 μm) as anode, anodic dissolution is carried out in electrolyte (1 mol / L sodium chloride ethylene glycol solution), the current density is 15 A·cm -2 , the microstructure of the workpiece surface after anodic dissolution for different time is observed by scanning electron microscope, the scanning electron microscope (SEM) images of the workpiece surface after treatment for different time (28 s, 35 s, 45 s, 57 s, 63 s and 82 s) are obtained, the passivation film breakdown time of the workpiece to be processed containing heavy casting layer and the time when the heavy casting layer of the workpiece to be processed containing heavy casting layer is completely removed and the substrate is not excessively corroded are determined through the SEM images of the workpiece surface after treatment for different time, the electric quantity Q0 required for breaking down the passivation film per unit area of the workpiece to be processed containing heavy casting layer and the electric quantity Q1 required for removing the heavy casting layer per unit area of the workpiece to be processed containing heavy casting layer and the substrate not being excessively corroded are calculated according to the current density and the time, and then Q0+Q1 is calculated to be 125 C / cm 2 ;

[0090] (2) through COMSOL Multiphysics simulation software simulation, the different cathode feed rate and power supply voltage, the surface of the workpiece to be processed containing heavy layer of P1 point of the unit area of the electric quantity, so that the surface of the workpiece to be processed containing heavy layer of P1 point of the unit area of the electric quantity close to Q0+Q1(125C / cm 2 ), simulation when the cathode is a diameter of 0.5mm wire electrode, electrolyte is a concentration of 1mol / L sodium chloride glycol solution, the conductivity is 0.33S / m constant, the initial machining gap is 50μm, the feed depth is 20μm, the simulation boundary parameters are: the voltage of the cathode surface(Γ1) Cathode feed rate(V f ) = 25, 50, 100 or 125μm / s; the voltage of the anode surface(Γ2) 30, 40 or 50V; electrolyte(Γ3, Γ4, Γ5, Γ6): When the cathode feed rate is 50μm / s, the power supply voltage is 30V, the surface of the workpiece to be processed containing heavy layer of P1 point of the unit area of the electric quantity(Q) is 125C / cm 2 ;

[0091] (3) with a diameter of 0.5mm tungsten wire as the cathode, the workpiece to be processed containing heavy layer(FGH96 workpiece after EDM, the heavy layer thickness is 10μm) as the anode, in the electrolyte(concentration of 1mol / L sodium chloride glycol solution) anodic dissolution, the initial machining gap is 50μm, the feed depth is 20μm, the cathode feed rate is 50μm / s, the power supply voltage is 30V, the unit area of the workpiece surface containing heavy layer of electric quantity(Q) is 125C / cm 2 , get the workpiece without heavy layer.

[0092] The SEM images of the initial surface of the workpiece to be processed containing heavy layer in step(1) of example 1(0s), the SEM images of the workpiece surface after processing at different times(28s, 35s, 45s, 57s, 63s and 82s) are shown in Figure 3 From Figure 3 , when the electric quantity reaches 125C / cm 2 , the heavy layer is completely removed, and at this time the matrix is not over corroded.

[0093] The power supply voltage is 30V, the current density of the workpiece surface P1 point at different cathode feed rates changes with time through simulation in step(2) of example 1, as shown in Figure 4 ; the cathode feed rate is 50μm / s(3mm / min), the current density of the workpiece surface P1 point at different power supply voltages changes with time through simulation, as shown in Figure 5 .Figure 4 and Figure 5 The area of the shadow part in 2 From Figure 4 , it can be seen that the surface charge of the workpiece gradually increases as the feed speed decreases or the voltage increases. When the feed speed of the wire electrode exceeds 50 μm / s while the power supply voltage remains unchanged, the surface current density of the workpiece quickly reaches a peak value, and the surface charge quickly exceeds 125 C / cm 2 , causing the passivation film and the recast layer to be broken down at the same time, but the over-corrosion phenomenon caused by the overflow of the surface charge is likely to occur. In contrast, if the feed speed is lower than 50 μm / s, it takes a long time to reach 125 C / cm 2 of the surface charge, and the breakdown process of the passivation film and the recast layer is relatively slow; from Figure 5 , it can be seen that, at a fixed feed speed, when the power supply voltage exceeds 30 V, the peak value of the current density increases, and the surface charge of the workpiece quickly exceeds 125 C / cm 2 , causing the passivation film and the recast layer to be dissolved quickly, but the over-corrosion phenomenon caused by the overflow of the surface charge is likely to occur; when the voltage is lower than 30 V, the peak value of the current density is low, and the surface charge is slow to reach or insufficient to reach 125 C / cm 2 , causing the dissolution speed to slow down. Based on the above analysis, the combination of the wire electrode feed speed of 50 μm / s and the power supply voltage of 30 V is selected, so that the surface charge of the workpiece is close to 125 C / cm 2 , the passivation film is quickly broken down, the recast layer is accurately removed, and the over-corrosion phenomenon caused by the overflow of the surface charge is minimized.

[0094] The relationship between the surface charge of the workpiece at point P1 and the cathode feed speed and the power supply voltage is shown in Figure 6 . From Figure 6 , it can be seen that the surface charge of the workpiece gradually increases as the feed speed decreases or the voltage increases. To achieve a target surface charge close to 125 C / cm 2 , the parameter combination of the cathode feed speed of 50 μm / s and the power supply voltage of 30 V is selected, so that the recast layer is accurately removed while the over-corrosion phenomenon is effectively inhibited.

[0095] Comparative Example 1

[0096] The power supply voltage in step (3) of Example 1 is replaced by 20 V, at which time the surface charge of the workpiece is 45 C / cm 2 , and the other parameters are the same as those of Example 1.

[0097] Comparative Example 2

[0098] The power supply voltage in step (3) of Example 1 is replaced by 40 V, at which time the surface charge of the workpiece is 225 C / cm 2 , and the other parameters are the same as those of Example 1.

[0099] The surface metallograph of the workpiece to be processed containing recast layer in step (3) of Example 1 is shown in Figure 7 , the SEM image is shown in Figure 8 , and the roughness of the workpiece surface is shown in Figure 9 .

[0100] The surface metallograph of the workpiece after being processed by the method of Example 1 is shown in Figure 10 , the SEM image is shown in Figure 11 , and the roughness of the workpiece surface is shown in Figure 12 .

[0101] The surface metallograph of the workpiece after being processed by the method of Comparative Example 1 is shown in Figure 13 , the SEM image is shown in Figure 14 , and the roughness of the workpiece surface is shown in Figure 15 .

[0102] The surface metallograph of the workpiece after being processed by the method of Comparative Example 2 is shown in Figure 16 , the SEM image is shown in Figure 17 , and the roughness of the workpiece surface is shown in Figure 18 .

[0103] It can be seen from Figures 7-18 that when the removed electric quantity is less than 125 C / cm 2 , there is still residual recast layer attached to the processed surface, and the surface roughness is 0.524 μm; when the electric quantity is far more than 125 C / cm 2 , the base material is excessively corroded, the surface quality is reduced, and the surface roughness is 0.334 μm; and when the electric quantity is close to 125 C / cm 2 , the surface roughness Ra value is the smallest, which is 0.325 μm.

[0104] Example 2

[0105] (1) 304 stainless steel is used as the cathode, the workpiece to be processed containing recast layer (FGH96 workpiece after electric spark machining, the thickness of the recast layer is 20 μm) is used as the anode, anodic dissolution is carried out in an electrolyte (20% sodium nitrate aqueous solution in mass concentration), and the current density is 15 A·cm -2The microscopic morphology of the workpiece surface after anodic dissolution for different times was observed by scanning electron microscopy, and scanning electron microscope (SEM) images of the workpiece surface after treatment at different times (34s, 40s, 45s, 60s, 80s and 100s) were obtained. The SEM images of the workpiece surface after treatment at different times were used to determine the breakdown time of the passivation film on the surface of the workpiece containing the recast layer and the time when the recast layer on the surface of the workpiece containing the recast layer was completely removed without excessive corrosion of the substrate. According to the current density and time, the power Q0 required to break through the passivation film per unit area of ​​the workpiece containing the recast layer and the power Q1 required to remove the recast layer per unit area of ​​the workpiece containing the recast layer without excessive corrosion of the substrate were calculated. Then, Q0+Q1 was calculated to be 500C / cm 2 ;

[0106] (2) The COMSOL Multiphysics simulation software was used to simulate the charge per unit area of ​​the workpiece surface P1 containing the recast layer at different cathode feed speeds and power supply voltages, so that the charge per unit area of ​​the workpiece surface P1 containing the recast layer is close to Q0+Q1(500C / cm 2 ), the cathode is a wire electrode with a diameter of 0.5 mm, the electrolyte is a sodium nitrate aqueous solution with a mass concentration of 20%, the conductivity is a constant of 14.2 S / m, the initial machining gap is 50 μm, the feed depth is 20 μm, and the simulation boundary parameters are: the voltage on the cathode surface (Γ1) Cathode feed speed (V f )=60、90、120 or 150μm / s;the voltage of the anode surface (Γ2) 15, 20 or 25V; electrolyte (Γ3, Γ4, Γ5, Γ6): When the cathode feed speed is 120 μm / s and the power supply voltage is 15 V, the charge per unit area (Q) at point P1 on the workpiece surface containing the recast layer is 580 C / cm 2 , close to 500C / cm 2 ;

[0107] (3) A tungsten wire with a diameter of 0.5 mm was used as the cathode and the workpiece to be machined (FGH96 workpiece after electrospark machining, with a recast layer thickness of 20 μm) with a recast layer thickness of 20 μm was used as the anode. Anodic dissolution was performed in an electrolyte (a sodium nitrate aqueous solution with a mass concentration of 20%). The initial machining gap was 50 μm, the feed depth was 20 μm, the cathode feed speed was 120 μm / s, the power supply voltage was 15 V, and the unit area charge (Q) of the workpiece surface with the recast layer to be machined was 580 C / cm 2 , and the workpiece with the recast layer removed is obtained.

[0108] The SEM images of the initial surface of the workpiece to be processed containing recast layer in step (1) of Example 2 (0s), and the SEM images of the surface of the workpiece after processing at different times (34s, 40s, 45s, 60s, 80s and 100s) are shown in Figure 19 , Figure 19 I-VII in Figure 19 represent the SEM images of the surface of the workpiece after 0s, 34s, 40s, 45s, 60s, 80s and 100s, respectively. From , it can be seen that when the electric quantity reaches 500C / cm 2 , the recast layer is completely removed, and at this time the substrate is not excessively corroded.

[0109] Figure 20 The current density-time curve of the workpiece surface P1 point at different cathode feeding speeds when the power supply voltage is 15V obtained by simulation is shown in Figure 21 ; and the current density-time curve of the workpiece surface P1 point at different power supply voltages when the cathode feeding speed is 120μm / s obtained by simulation is shown in Figure 20 . Figure 21 The area of the shaded part in 2 is 500C / cm 2 . From Figure 20 , it can be seen that as the feeding speed decreases or the voltage increases, the electric quantity of the workpiece surface gradually increases. When the power supply voltage remains unchanged and the wire electrode feeding speed exceeds 120μm / s, the current density of the workpiece surface quickly reaches the peak value, and the electric quantity quickly exceeds 500C / cm 2 , resulting in the simultaneous breakdown of the passivation film and the recast layer, but it is easy to cause over-corrosion due to electric quantity overflow. Conversely, if the feeding speed is lower than 120μm / s, it takes a long time to reach 500C / cm 2 , and the breakdown process of the passivation film and the recast layer is relatively slow; from Figure 21 , it can be seen that at a fixed feeding speed, when the power supply voltage exceeds 15V, the peak value of the current density increases, and the electric quantity of the workpiece surface quickly exceeds 500C / cm 2 , so that the passivation film and the recast layer are quickly dissolved, but it may also lead to over-corrosion of the surface due to electric quantity overflow; when the voltage is lower than 15V, the peak value of the current density is lower, and the surface electric quantity slowly reaches or is insufficient to reach 500C / cm 2 , resulting in a slow dissolution rate. Based on the above analysis, the combination of the wire electrode feeding speed of 120μm / s and the power supply voltage of 15V is selected, so that the electric quantity of the workpiece surface is close to 500C / cm 2 , the passivation film is quickly broken down, the recast layer is accurately removed, and the over-corrosion phenomenon caused by electric quantity overflow is minimized.

[0110] The relationship diagram of the electric quantity of the workpiece surface P1 point and the cathode feeding speed and the power supply voltage is shown inFigure 22 As shown. Figure 22 It can be seen that as the feed speed decreases or the voltage increases, the charge on the workpiece surface gradually increases. 2 The target power was set at 120 μm / s cathode feed speed and 15 V power supply voltage, which could effectively suppress over-corrosion while accurately removing the recast layer.

[0111] Comparative Example 3

[0112] The cathode feed speed in step (3) of Example 2 was replaced with 10 μm / s, and the surface charge of the workpiece was 340 C / cm 2 , other parameters are the same as those in Example 1.

[0113] Comparative Example 4

[0114] The power supply voltage in step (3) of Example 2 is replaced with 20V. At this time, the surface charge of the workpiece is 1100C / cm 2 , other parameters are the same as those in Example 2.

[0115] The surface metallographic image of the workpiece to be processed containing the recast layer in step (3) of Example 2 is as follows: Figure 23 As shown in the SEM images Figure 24 As shown in the figure, the roughness of the workpiece surface is Figure 25 shown.

[0116] The surface metallographic image of the workpiece after being treated by the method of Example 2 is as follows: Figure 26 As shown in the SEM images Figure 27 As shown in the figure, the roughness of the workpiece surface is Figure 28 shown.

[0117] The surface metallographic image of the workpiece after being treated by the method of comparative example 3 is as follows: Figure 29 As shown in the SEM images Figure 30 As shown in the figure, the roughness of the workpiece surface is Figure 31 shown.

[0118] The surface metallographic image of the workpiece after being treated by the method of comparative example 4 is as follows: Figure 32 As shown in the SEM images Figure 33 As shown in the figure, the roughness of the workpiece surface is Figure 34 shown.

[0119] from Figures 23-34 It can be seen that when the removal charge is less than 500C / cm 2 When the recast layer is still attached to the machined surface, the surface roughness is 2.342μm; the charge is far more than 500C / cm 2When the electric quantity is 500C / cm, the base material is excessively corroded, the surface quality is reduced, and the surface roughness is 1.575 mu m 2 When the electric quantity is 500C / cm, the base material is excessively corroded, the surface quality is reduced, and the surface roughness is 1.575 mu m

[0120] In conclusion, by accurately controlling the electric quantity, the cathode feeding speed and the power supply voltage, the workpiece surface electric quantity is close to Q0+Q1, through the electric quantity control, not only the breakdown speed of the passivation film is accelerated, the accurate removal of the recast layer is realized, but also the over-corrosion phenomenon caused by the electric quantity overflow is maximally inhibited, and the quality of the processed surface is significantly improved.

[0121] The above only describes the preferred embodiments of the present application, and it should be noted that, for those skilled in the art, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

Claims

1. A method for precisely removing recast layer and inhibiting over-corrosion, comprising the following steps: (1) taking a conductive metal as a cathode and a workpiece containing a recast layer as an anode, and performing anodic dissolution in an electrolyte at a constant current density, observing the micro-morphology of the workpiece surface after different anodic dissolution times, determining the breakdown time of the passivation film on the surface of the workpiece containing a recast layer and the time at which the recast layer on the surface of the workpiece containing a recast layer is completely removed and the substrate is not excessively corroded, and then calculating the electric quantity Q0 required for breaking down the passivation film per unit area of the workpiece containing a recast layer and the electric quantity Q1 required for removing the recast layer per unit area of the workpiece containing a recast layer and the substrate not being excessively corroded according to the current density and time; the area of the cathode is greater than the area of the recast layer of the workpiece containing a recast layer; (2) using simulation software to simulate the electrolytic finishing process of the workpiece with heavy casting layer at different feed rates and power voltages, and determine the electrolytic finishing parameters that meet the electricity conditions; the electricity conditions are that the unit area electricity Q of the surface of the workpiece with heavy casting layer and Q0 and Q1 obtained in step (1) satisfy: 0≤Q-(Q0+Q1)≤100C / cm 2 ; in the simulation, the electrolyte for electrolytic finishing is the same as that in step (1); (3) performing electrolytic finishing machining on the workpiece containing a recast layer using the electrolytic finishing machining parameters determined in the step (2) to obtain a workpiece with the recast layer removed.

2. The method of claim 1, wherein the method further comprises: The cathode for electrolytic finishing machining in the step (2) comprises a wire electrode, a rectangular electrode, a tube electrode or a profiled electrode.

3. The method of claim 2, wherein the re-coat layer is removed precisely and over-etching is inhibited. The diameter of the wire electrode is 0.5-1 mm.

4. The method of claim 1, wherein the re-coat layer is removed precisely and over-etching is inhibited. The electrolyte in the step (2) comprises a glycol-based electrolyte or a water-based electrolyte.

5. The method of claim 1, wherein the re-coat layer is removed precisely and over-etching is inhibited. The initial machining gap for electrolytic finishing machining in the step (2) is 0-100 μm.

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