Method for precisely removing recast layer and inhibiting over-corrosion

Abstract

The invention provides a precise removal and over-corrosion inhibition method for a recast layer, and belongs to the technical field of electromachining. The method comprises the following steps: firstly, obtaining electric quantity Q0 required for puncturing a passivation film in unit area of a to-be-processed workpiece containing a recast layer and electric quantity Q1 required for removing the recast layer in unit area of the to-be-processed workpiece containing the recast layer and preventing a matrix from being excessively corroded, and then determining electrolytic finishing parameters meeting the electric quantity condition through simulation; and then the to-be-machined workpiece containing the recasting layer is subjected to electrolytic finishing according to the determined electrolytic finishing parameters, so that rapid breakdown of a passive film, accurate removal of the recasting layer and over-corrosion of the surface of the workpiece caused by electricity escape as little as possible are achieved, and the surface quality of the workpiece is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical machining, and in particular relates to a method for accurately removing a recast layer and inhibiting over-corrosion. Background Art

[0002] Electrospark machining is widely used in the processing of various conductive materials in the manufacturing industry with high precision and high efficiency. During electrospark machining, the arc melts the metal at high temperature, and the molten metal droplets re-condense on the electrode surface. The condensed metal layer is the recast layer. The recast layer has different structures and properties from the original metal. It 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 surface processing quality of the workpiece.

[0003] Electrolytic machining technology usually uses a conductive metal wire or a conductive metal rod as a cutting cathode tool, and the workpiece to be machined is used as an anode. The two are immersed in an electrolyte to produce an electrochemical anodic dissolution reaction to remove the recast layer. However, the current electrolytic machining technology lacks precise control of the amount of electricity in the removal process, and mainly relies on experience or experiments to determine the cathode feed speed and power supply voltage, resulting in incomplete dissolution of the passivation film, incomplete removal of the recast layer, or excessive corrosion of the substrate due to overflow of electricity, thereby affecting the removal quality. Therefore, it is necessary to propose a method for achieving precise removal of the recast layer and suppression of over-corrosion, so as to improve the machining accuracy and surface quality of electrolytic finishing. Summary of the invention

[0004] The purpose of the present invention is to provide a method for accurately removing the recast layer and inhibiting over-corrosion. The method provided by the present invention can achieve rapid breakdown of the passivation film, accurate removal of the recast layer, and minimize the amount of electricity released to cause over-corrosion on the workpiece surface.

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

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

[0007] (1) Using a conductive metal as a cathode and a workpiece to be processed containing a recast layer as an anode, anodic dissolution is performed in an electrolyte at a constant current density, and by observing the microscopic morphology of the workpiece surface after different times of anodic dissolution, the breakdown time of the passivation film on the surface of the workpiece to be processed containing the recast layer and the time when the recast layer on the surface of the workpiece to be processed containing the recast layer is completely removed without excessive corrosion of the substrate are determined, and then, based on the current density and time, the amount of electricity Q0 required to break through the passivation film per unit area of ​​the workpiece to be processed containing the recast layer and the amount of electricity Q1 required to remove the recast layer per unit area of ​​the workpiece to be processed containing the recast layer without excessive corrosion of the substrate are calculated; the area of ​​the cathode is larger than the area of ​​the recast layer of the workpiece to be processed containing the recast layer;

[0008] (2) The electrolytic finishing process of the workpiece to be processed containing the recast layer at different feed speeds and power supply voltages is simulated by using simulation software to determine the electrolytic finishing parameters that meet the electrical quantity condition; the electrical quantity condition is: the electrical quantity Q per unit area of ​​the surface of the workpiece to be processed containing the recast layer and Q0 and Q1 obtained in 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 step (1);

[0009] (3) Using the electrolytic finishing processing parameters determined in step (2) to perform electrolytic finishing processing on the workpiece to be processed containing the recast layer, to obtain a workpiece with the recast layer removed.

[0010] Preferably, the cathode of the electrolytic finishing process in step (2) comprises a wire electrode, a rectangular electrode, a tube electrode or a contoured electrode.

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

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

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

[0014] The present invention provides a method for accurately removing a recast layer and inhibiting excessive corrosion, comprising the following steps: (1) using a conductive metal as a cathode and a workpiece to be processed containing a recast layer as an anode, performing anodic dissolution in an electrolyte at a constant current density, observing the microscopic morphology of the workpiece surface after anodic dissolution for different times, determining the breakdown time of the passivation film on the surface of the workpiece to be processed containing the recast layer and the time when the recast layer on the surface of the workpiece to be processed containing the recast layer is completely removed and the substrate is not excessively corroded, and then calculating the current density and time required to break through the passivation film per unit area of ​​the workpiece to be processed containing the recast layer. The amount Q0 and the amount of electricity Q1 required to remove the recast layer per unit area of ​​the workpiece to be processed containing the recast layer without excessive corrosion of the substrate; the area of ​​the cathode is larger than the area of ​​the recast layer of the workpiece to be processed containing the recast layer; (2) using simulation software to simulate the electrolytic finishing process of the workpiece to be processed containing the recast layer at different feed speeds and power supply voltages, and determine the electrolytic finishing processing parameters that meet the electricity condition; the electricity condition is: the unit area electricity Q of the surface of the workpiece to be processed containing the recast layer and Q0 and Q1 obtained in 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 step (1); (3) the workpiece to be processed containing the recast layer is subjected to electrolytic finishing using the electrolytic finishing processing parameters determined in step (2) to obtain a workpiece with the recast layer removed. The present invention first obtains the amount of electricity Q0 required to break through the passivation film per unit area of ​​the workpiece to be processed containing the recast layer and the amount of electricity Q1 required to remove the recast layer per unit area of ​​the workpiece to be processed containing the recast layer without excessive corrosion of the substrate, and then determines the electrolytic finishing processing parameters that meet the electricity conditions through simulation, and then performs electrolytic finishing processing on the workpiece to be processed containing the recast layer using the determined electrolytic finishing processing parameters, thereby achieving rapid breakdown of the passivation film, precise removal of the recast layer, and as little electricity as possible escaping to cause excessive corrosion on the workpiece surface, which is beneficial to improving the surface quality of the workpiece. The results of the embodiment show that after being processed using the method of the present invention, the recast layer on the surface of the workpiece to be processed is completely removed, and the processed surface is smooth. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of a simulation model established by the present invention for accurate removal of the recast layer and inhibition of over-corrosion;

[0016] Figure 2 A schematic diagram of a device used in the method for accurately removing the recast layer and inhibiting over-corrosion according to the present invention;

[0017] Figure 3 The SEM images of the initial surface of the workpiece to be processed containing the recast layer in step (1) of Example 1 (0s), and the SEM images of the surface of the workpiece after processing at different times (28s, 35s, 45s, 57s, 63s and 82s);

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

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

[0020] Figure 6 is a relationship diagram of the electric quantity at point P1 on the workpiece surface, the cathode feed speed and the power supply voltage in Example 1;

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

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

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

[0024] Fig.10 This is a surface metallographic image of the workpiece after being treated by the method of Example 1;

[0025] Fig.11 This is a surface SEM image of the workpiece after being treated by the method of Example 1;

[0026] Fig.12 is the surface roughness of the workpiece after being treated by the method of Example 1;

[0027] Fig.13 This is a surface metallographic image of the workpiece after being treated by the method of Comparative Example 1;

[0028] Fig.14 This is a surface SEM image of the workpiece after being treated by the method of Comparative Example 1;

[0029] Fig.15 is the surface roughness of the workpiece after being treated by the method of Comparative Example 1;

[0030] Fig.16 This is the surface metallographic image of the workpiece after being treated by the method of Comparative Example 2;

[0031] Fig.17 This is the surface SEM image of the workpiece after being treated by the method of Comparative Example 2;

[0032] Fig.18is the surface roughness of the workpiece after being treated by the method of Comparative Example 2;

[0033] Fig.19 The SEM images of the initial surface of the workpiece to be processed containing the 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);

[0034] Fig. 20 The curve of the change of the current density at point P1 on the workpiece surface with time at different cathode feed speeds obtained by simulation in step (2) of Example 2 is 15V;

[0035] Fig.21 The curve of the change of the current density at point P1 on the workpiece surface with time under different power supply voltages obtained by simulation in step (2) of Example 2 when the cathode feed speed is 120 μm / s;

[0036] Fig. 22 is a relationship diagram of the electric quantity at point P1 on the workpiece surface, the cathode feed speed and the power supply voltage in Example 2;

[0037] Fig.23 The surface metallographic image of the workpiece to be processed containing the recast layer in step (3) of Example 2;

[0038] Fig.24 The surface SEM image of the workpiece to be processed containing the recast layer in step (3) of Example 2;

[0039] Fig.25 is the surface roughness of the workpiece to be processed containing the recast layer in step (3) of Example 2;

[0040] Fig.26 This is a surface metallographic image of the workpiece after being treated by the method of Example 2;

[0041] Fig. 27 This is a surface SEM image of the workpiece after being treated by the method of Example 2;

[0042] Fig.28 is the surface roughness of the workpiece after being treated by the method of Example 2;

[0043] Fig.29 This is the surface metallographic image of the workpiece after being treated by the method of Comparative Example 3;

[0044] Fig.30 This is a surface SEM image of the workpiece after being treated by the method of Comparative Example 3;

[0045] Fig.31 is the surface roughness of the workpiece after being treated by the method of Comparative Example 3;

[0046] Fig.32 This is a surface metallographic image of the workpiece after being treated by the method of Comparative Example 4;

[0047] Fig.33 This is a surface SEM image of the workpiece after being treated by the method of Comparative Example 4;

[0048] Fig.34 It is the surface roughness of the workpiece after being treated by the method of comparative example 4. DETAILED DESCRIPTION

[0049] The present invention provides a method for accurately removing a recast layer and inhibiting over-corrosion, comprising the following steps:

[0050] (1) Using a conductive metal as a cathode and a workpiece to be processed containing a recast layer as an anode, anodic dissolution is performed in an electrolyte at a constant current density, and by observing the microscopic morphology of the workpiece surface after different times of anodic dissolution, the breakdown time of the passivation film on the surface of the workpiece to be processed containing the recast layer and the time when the recast layer on the surface of the workpiece to be processed containing the recast layer is completely removed without excessive corrosion of the substrate are determined, and then, based on the current density and time, the amount of electricity Q0 required to break through the passivation film per unit area of ​​the workpiece to be processed containing the recast layer and the amount of electricity Q1 required to remove the recast layer per unit area of ​​the workpiece to be processed containing the recast layer without excessive corrosion of the substrate are calculated; the area of ​​the cathode is larger than the area of ​​the recast layer of the workpiece to be processed containing the recast layer;

[0051] (2) The electrolytic finishing process of the workpiece to be processed containing the recast layer at different feed speeds and power supply voltages is simulated by using simulation software to determine the electrolytic finishing parameters that meet the electrical quantity condition; the electrical quantity condition is: the electrical quantity Q per unit area of ​​the surface of the workpiece to be processed containing the recast layer and Q0 and Q1 obtained in 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 step (1);

[0052] (3) Using the electrolytic finishing processing parameters determined in step (2) to perform electrolytic finishing processing on the workpiece to be processed containing the recast layer, to obtain a workpiece with the recast layer removed.

[0053] The present invention uses a conductive metal as a cathode and a workpiece to be processed containing a recast layer as an anode, performs anodic dissolution in an electrolyte at a constant current density, and observes the microscopic morphology of the workpiece surface after different anodic dissolution times to determine the breakdown time of the passivation film on the surface of the workpiece to be processed containing the recast layer and the time when the recast layer on the surface of the workpiece to be processed containing the recast layer is completely removed without excessive corrosion of the substrate. Then, based on the current density and time, the electric quantity Q0 required to break through the passivation film per unit area of ​​the workpiece to be processed containing the recast layer and the electric quantity Q1 required to remove the recast layer per unit area of ​​the workpiece to be processed containing the recast layer without excessive corrosion of the substrate are calculated.

[0054] In the present invention, the conductive metal is preferably made of tungsten, molybdenum or stainless steel.

[0055] In the present invention, the area of ​​the cathode is larger than the area of ​​the recast layer of the workpiece to be processed containing the recast layer. The present invention has no special restrictions on the specific area sizes of the cathode and the recast layer of the workpiece to be processed containing the recast layer, and it is sufficient to ensure that the area of ​​the cathode is larger than the area of ​​the recast layer of the workpiece to be processed containing the recast layer.

[0056] The present invention has no special restrictions on the material and size of the workpiece to be processed containing the recast layer, and a workpiece to be processed containing the recast layer known to those skilled in the art can be used. In the present invention, the workpiece to be processed containing the recast layer during the test of the electrical quantity is the same as the workpiece to be processed when the method is actually applied. In an embodiment of the present invention, the workpiece to be processed containing the recast layer is an FGH96 workpiece after electrospark machining.

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

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

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

[0060] In the present invention, the current density is preferably 2 to 50 A·cm -2 The present invention controls the current density within the above range, which is more conducive to accurately determining 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 is completely removed and the substrate is not excessively corroded.

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

[0062] The present invention preferably uses a scanning electron microscope to observe the microscopic morphology of the workpiece surface after different times of anodic dissolution, obtain a scanning electron microscope image, and then determine the breakdown time of the passivation film on the surface of the workpiece to be processed containing the recast layer and the time when the recast layer on the surface of the workpiece to be processed containing the recast layer is completely removed and the substrate is not over-corroded according to the scanning electron microscope image. Among them, the surface of the workpiece to be processed with the recast layer has a crater-like morphology, the surface of the workpiece with the recast layer completely removed and the substrate not over-corroded has a smooth and flat featureless morphology, and the surface of the over-corroded workpiece has a matrix structure morphology with obvious grain boundaries and grains. The microscopic morphology obtained from the scanning electron microscope image is used as the determination basis for the time required to completely remove the recast layer.

[0063] The present invention preferably obtains the electric quantity Q0 required to break down the passivation film per unit area of the workpiece to be processed containing the recast layer and the electric quantity Q1 required to remove the recast layer per unit area of the workpiece to be processed containing the recast layer and the substrate not being over-corroded through the integral calculation formula of the time required to completely remove the recast layer. The present invention obtains the electric quantity Q0 required to break down the passivation film per unit area of the workpiece to be processed containing the recast layer and the electric quantity Q1 required to remove the recast layer per unit area of the workpiece to be processed containing the recast layer and the substrate not being over-corroded.

[0064] After obtaining the electric quantity Q0 required to break down the passivation film per unit area of the workpiece to be processed containing the recast layer and the electric quantity Q1 required to remove the recast layer per unit area of the workpiece to be processed containing the recast layer and the substrate not being over-corroded, the present invention uses simulation software to simulate the electrolytic finishing process of the workpiece to be processed containing the recast layer under different feed rates and power supply voltages respectively, and determines the electrolytic finishing process parameters that meet the electric quantity conditions.

[0065] In the present invention, the electric quantity required to break down the passivation film per unit area of the workpiece to be processed containing the recast layer is Q0, the electric quantity required to remove the recast layer per unit area of the workpiece to be processed containing the recast layer and the substrate not being over-corroded is Q1, and the over-cut electric quantity per unit area of the workpiece substrate material is Q2. With the movement of the cathode feed, the electric quantity Q per unit area on the surface of the workpiece to be processed 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 recast layer is not completely removed. Q ≥ Q0 + Q1, the recast layer is completely removed, but over-cut occurs on the processed surface, and the over-cut electric quantity Q2 is Q - Q0 - Q1. Q = Q0 + Q1, the recast layer is completely removed and over-cut does not occur on the surface of the workpiece substrate.

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

[0067] The present invention is preferably simulated by COMSOL Multiphysics simulation software.

[0068] As an embodiment of the present invention, during the simulation, the parameters of the electrolytic finishing process may be as follows:

[0069] The initial machining gap of electrolytic finishing is 0 to 100 μm;

[0070] The feed depth of electrolytic finishing is 15 to 25 μm;

[0071] The electrolyte for electrolytic finishing 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 cathode feed direction is parallel to the recast layer surface of the workpiece to be processed containing the recast layer;

[0073] The power supply voltage for electrolytic finishing can be 10 to 50V.

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

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

[0076] The present invention preferably formulates a precise removal scheme of the recast layer by jointly controlling the cathode feed speed and the power supply voltage, and performs electric field simulation and according to the electric quantity calculation formula The amount of workpiece surface machining power for different electrical parameter combinations during electrolytic finishing to remove the recast layer is calculated, where i(t) is a function of current density with respect to time, and the electrolytic finishing parameters that meet the power conditions are determined.

[0077] The schematic diagram of the simulation model established by the present invention for accurate removal of the recast layer and inhibition of over-corrosion is as follows: Figure 1 As shown, Γ1 is the cathode surface, Γ2 is the workpiece surface, Δ is the initial machining gap, e is the feed depth, and in order to simplify the model, the influence of ion concentration, heat, products and bubbles, and the contour evolution of the workpiece are ignored. The charge (Q) at point P1 on the workpiece surface is used as the criterion for complete removal of the recast layer, thereby optimizing the machining parameters to ensure efficient removal of the recast layer under charge control. In the present invention, the point P1 is preferably any point on the workpiece surface, and more preferably the center point of the workpiece surface.

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

[0079] The present invention has no special limitation on other operations simulated by the COMSOL Multiphysics simulation software, and technical solutions well known to those skilled in the art may be adopted.

[0080] After determining the electrolytic finishing processing parameters that meet the power condition through simulation, the present invention uses the determined electrolytic finishing processing parameters to perform electrolytic finishing processing on the workpiece to be processed containing the recast layer to obtain the workpiece with the recast layer removed.

[0081] In the present invention, the material of the cathode, the anode, and the electrolyte during the electrolytic finishing process are the same as those of the cathode, the anode, and the electrolyte in the above-mentioned process of determining Q0 and Q1, and will not be described in detail here.

[0082] In the present invention, the cathode during the electrolytic finishing process preferably includes a wire electrode, a rectangular electrode, a tube electrode or a contour electrode.

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

[0084] The present invention first obtains the electric quantity Q0 required to break through the passivation film per unit area of ​​the workpiece to be processed containing the recast layer and the electric quantity Q1 required to remove the recast layer per unit area of ​​the workpiece to be processed containing the recast layer without excessive corrosion of the substrate, and then determines the electrolytic finishing processing parameters that meet the electric quantity conditions through simulation, and then performs electrolytic finishing processing on the workpiece to be processed containing the recast layer according to the determined electrolytic finishing processing parameters, thereby achieving rapid breakdown of the passivation film, precise removal of the recast layer and as little electric quantity as possible escaping to cause excessive corrosion on the workpiece surface, which is beneficial to improving the surface quality of the workpiece.

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

[0086] The present invention has no special limitation on the size and material of the electrolyte tank 2, the liquid inlet pipe 4, the wire electrode fixture 7, and the workpiece fixture 9. The 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 invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0088] Example 1

[0089] A method for accurately removing the recast layer and inhibiting over-corrosion: (1) Using 304 stainless steel as the cathode and a workpiece to be processed containing a recast layer (FGH96 workpiece after electrospark machining, with a recast layer thickness of 10 μm) as the anode, anodic dissolution is performed in an electrolyte (sodium chloride ethylene glycol solution with a concentration of 1 mol / L) at a current density of 15 A·cm -2 The microscopic morphology of the workpiece surface after anodic dissolution for different times was observed by scanning electron microscope, and scanning electron microscope (SEM) images of the workpiece surface after treatment at different times (28s, 35s, 45s, 57s, 63s and 82s) were obtained. The SEM images of the workpiece surface after treatment at different times were used to determine the breakdown time of the passive 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 and the substrate was not excessively corroded. According to the current density and time, the amount of electricity Q0 required to break through the passive film per unit area of ​​the workpiece containing the recast layer and the amount of electricity Q1 required to remove the recast layer per unit area of ​​the workpiece containing the recast layer and the substrate was not excessively corroded were calculated, and then Q0+Q1 was calculated to be 125C / cm 2 ;

[0090] (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(125C / cm 2 ), the cathode is a wire electrode with a diameter of 0.5 mm, the electrolyte is a sodium chloride ethylene glycol solution with a concentration of 1 mol / L, the conductivity is a constant of 0.33 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 ) = 25, 50, 100 or 125 μm / s; the voltage on the anode surface (Γ2) 30, 40 or 50V; electrolyte (Γ3, Γ4, Γ5, Γ6): When the cathode feed speed is 50 μm / s and the power supply voltage is 30 V, the unit area charge (Q) of the workpiece surface P1 containing the recast layer is 125 C / cm 2 ;

[0091] (3) A tungsten wire with a diameter of 0.5 mm was used as the cathode and the workpiece to be processed with a recast layer (FGH96 workpiece after EDM, with a recast layer thickness of 10 μm) was used as the anode. Anodic dissolution was performed in an electrolyte (1 mol / L sodium chloride ethylene glycol solution). The initial processing gap was 50 μm, the feed depth was 20 μm, the cathode feed speed was 50 μm / s, the power supply voltage was 30 V, and the unit area charge (Q) of the surface of the workpiece to be processed with a recast layer was 125 C / cm 2 , and obtain the workpiece with the recast layer removed.

[0092] The SEM images of the initial surface of the workpiece to be processed containing the recast layer in step (1) of Example 1 (0s) and the SEM images of the surface of the workpiece after processing at different times (28s, 35s, 45s, 57s, 63s and 82s) are as follows: Figure 3 As shown. Figure 3 Yes, when the charge reaches 125C / cm 2 The recast layer is completely removed and the substrate is not excessively corroded.

[0093] The power supply voltage obtained by simulation in step (2) of Example 1 is 30V. The current density at point P1 on the workpiece surface changes with time at different cathode feed speeds is shown in the figure below: Figure 4 As shown in the figure, the cathode feed speed obtained by simulation is 50 μm / s (3 mm / min), and the current density at point P1 on the workpiece surface under different power supply voltages varies with time. Figure 5 shown. Figure 4 and Figure 5 The shaded area is 125C / cm 2 .from Figure 4 It can be seen that as the feed speed decreases or the voltage increases, the charge on the workpiece surface gradually increases. When the power supply voltage remains unchanged and the wire electrode feed speed exceeds 50μm / s, the current density on the workpiece surface quickly reaches the peak value and the charge quickly exceeds 125C / cm 2 , resulting in the breakdown of the passivation film and the recast layer at the same time, but it is easy to cause the overflow of electricity and lead to over-corrosion. On the contrary, if the feed speed is lower than 50μm / s and reaches 125C / cm 2 The power consumption is long, and the breakdown process of the passivation film and the recast layer is slow; Figure 5 It can be seen that at a fixed feed speed, when the power supply voltage exceeds 30V, the current density peak increases and the charge on the workpiece surface quickly exceeds 125C / cm 2 , which causes the passivation film and the recast layer to dissolve rapidly, but may also cause the surface to corrode due to overflow of electricity; when the voltage is lower than 30V, the current density peak is lower, and the surface electricity slowly reaches or is insufficient to reach 125C / cm 2 Based on the above analysis, the combination of wire electrode feed speed of 50μm / s and power supply voltage of 30V can make the surface charge of the workpiece close to 125C / cm 2 , achieving rapid breakdown of the passivation film, precise removal of the recast layer, and minimizing over-corrosion caused by power overflow.

[0094] The relationship between the charge at point P1 on the workpiece surface and the cathode feed speed and power supply voltage is shown in the figure below: Figure 6 As shown. Figure 6 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 is set by selecting a cathode feed speed of 50 μm / s and a power supply voltage of 30 V, which can effectively suppress over-corrosion while accurately removing the recast layer.

[0095] Comparative Example 1

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

[0097] Comparative Example 2

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

[0099] The surface metallographic image of the workpiece to be processed containing the recast layer in step (3) of Example 1 is as follows: Figure 7 As shown in the SEM images Figure 8 As shown in Fig. 9 shown.

[0100] The surface metallographic image of the workpiece after being treated by the method of Example 1 is as follows: Fig.10 As shown in the SEM images Fig.11 As shown in Fig.12 shown.

[0101] The surface metallographic image of the workpiece after being treated by the method of comparative example 1 is as follows: Fig.13 As shown in the SEM images Fig.14 As shown in Fig.15 shown.

[0102] The surface metallographic image of the workpiece after being treated by the method of comparative example 2 is as follows: Fig.16 As shown in the SEM images Fig.17 As shown in Fig.18 shown.

[0103] from Figures 7 to 18 It can be seen that when the removal charge is less than 125C / cm 2 When the recast layer is still attached to the machined surface, the surface roughness is 0.524μm; the charge is far more than 125C / cm 2 When the substrate material is over-corroded, the surface quality is reduced, and the surface roughness is 0.334μm; the charge is close to 125C / cm 2 The minimum surface roughness Ra value is 0.325μm.

[0104] Example 2

[0105] (1) Using 304 stainless steel as the cathode and the workpiece to be processed (FGH96 workpiece after electrospark machining, the thickness of the recast layer is 20 μm) as the anode, anodic dissolution was carried out in an electrolyte (a sodium nitrate aqueous solution with a mass concentration of 20%) at a current density of 15 A cm -2The microscopic morphology of the workpiece surface after anodic dissolution for different times was observed by scanning electron microscope, 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 breakdown time of the passive 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 were determined by SEM images of the workpiece surface after treatment at different times. According to the current density and time, the power Q0 required to break through the passive 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, and 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 150 μm / s; the voltage on 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 unit area charge (Q) of the workpiece surface P1 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 processed containing a recast layer (FGH96 workpiece after electrospark machining, 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 surface of the workpiece to be processed containing a recast layer was 580 C / cm 2 , and obtain the workpiece with the recast layer removed.

[0108] The SEM images of the initial surface of the workpiece to be processed containing the 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 as follows: Fig.19 As shown, Fig.19 I to VII in the figure represent the SEM images of the workpiece surface after 0s, 34s, 40s, 45s, 60s, 80s and 100s respectively. Fig.19 Yes, when the charge reaches 500C / cm 2 The recast layer is completely removed and the substrate is not excessively corroded.

[0109] The power supply voltage obtained by simulation in step (2) of Example 2 is 15V. The curves of the current density at point P1 on the workpiece surface changing with time at different cathode feed speeds are as follows: Fig. 20 As shown in the figure, the cathode feed speed obtained by simulation is 120 μm / s, and the current density at point P1 on the workpiece surface changes with time under different power supply voltages is shown in the figure. Fig.21 shown. Fig. 20 and Fig.21 The shaded area is 500C / cm 2 .from Fig. 20 It can be seen that as the feed speed decreases or the voltage increases, the charge on the workpiece surface gradually increases. When the power supply voltage remains unchanged and the wire electrode feed speed exceeds 120μm / s, the current density on the workpiece surface quickly reaches the peak value and the charge quickly exceeds 500C / cm 2 , resulting in the breakdown of the passivation film and the recast layer at the same time, but it is easy to cause the overflow of electricity and lead to over-corrosion. On the contrary, if the feed speed is lower than 120μm / s and reaches 500C / cm 2 The power consumption is long, and the breakdown process of the passivation film and the recast layer is slow; Fig.21 It can be seen that at a fixed feed speed, when the power supply voltage exceeds 15V, the current density peak increases and the charge on the workpiece surface quickly exceeds 500C / cm 2 , which causes the passivation film and the recast layer to dissolve rapidly, but may also cause the surface to corrode due to overflow of electricity; when the voltage is lower than 15V, the current density peak is lower, and the surface electricity slowly reaches or is insufficient to reach 500C / cm 2 Based on the above analysis, the combination of wire electrode feed speed of 120 μm / s and power supply voltage of 15 V can make the surface charge of the workpiece close to 500 C / cm 2 , achieving rapid breakdown of the passivation film, precise removal of the recast layer, and minimizing over-corrosion caused by power overflow.

[0110] The relationship between the charge at point P1 on the workpiece surface and the cathode feed speed and power supply voltage is shown in the figure below: Fig. 22 As shown. Fig. 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 is set at 120 μm / s cathode feed speed and 15 V power supply voltage, which can 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 20 V. At this time, the surface charge of the workpiece is 1100 C / 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: Fig.23 As shown in the SEM images Fig.24 As shown in Fig.25 shown.

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

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

[0118] The surface metallographic image of the workpiece after being treated by the method of comparative example 4 is as follows: Fig.32 As shown in the SEM images Fig.33 As shown in Fig.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 substrate material is over-corroded, the surface quality is reduced, and the surface roughness is 1.575μm; the charge is close to 500C / cm 2 When the surface roughness Ra value is as low as 1.363μm.

[0120] In summary, the present invention controls the cathode feed speed and the power supply voltage by precisely controlling the electric charge so that the surface charge of the workpiece is close to Q0+Q1. Through this electric charge control, not only the breakdown speed of the passivation film is accelerated, and the accurate removal of the recast layer is achieved, but also the over-corrosion caused by electric charge overflow is suppressed to the maximum extent, thereby significantly improving the quality of the processed surface.

[0121] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for accurately removing a recast layer and inhibiting over-corrosion, comprising the following steps: (1) Using a conductive metal as a cathode and a workpiece to be processed containing a recast layer as an anode, anodic dissolution is performed in an electrolyte at a constant current density, and by observing the microscopic morphology of the workpiece surface after different times of anodic dissolution, the breakdown time of the passivation film on the surface of the workpiece to be processed containing the recast layer and the time when the recast layer on the surface of the workpiece to be processed containing the recast layer is completely removed without excessive corrosion of the substrate are determined, and then, based on the current density and time, the amount of electricity Q0 required to break through the passivation film per unit area of ​​the workpiece to be processed containing the recast layer and the amount of electricity Q1 required to remove the recast layer per unit area of ​​the workpiece to be processed containing the recast layer without excessive corrosion of the substrate are calculated; the area of ​​the cathode is larger than the area of ​​the recast layer of the workpiece to be processed containing the recast layer; (2) The electrolytic finishing process of the workpiece to be processed containing the recast layer at different feed speeds and power supply voltages is simulated by using simulation software to determine the electrolytic finishing parameters that meet the electrical quantity condition; the electrical quantity condition is: the electrical quantity Q per unit area of ​​the surface of the workpiece to be processed containing the recast layer and Q0 and Q1 obtained in 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 step (1); (3) Using the electrolytic finishing processing parameters determined in step (2) to perform electrolytic finishing processing on the workpiece to be processed containing the recast layer, to obtain a workpiece with the recast layer removed.

2. The method for accurate removal of the recast layer and over-corrosion inhibition according to claim 1, characterized in that: The cathode of the electrolytic finishing process in step (2) includes a wire electrode, a rectangular electrode, a tube electrode or a contoured electrode.

3. The method for accurate removal of the recast layer and over-corrosion inhibition according to claim 2, characterized in that: The diameter of the wire electrode is 0.5-1 mm.

4. The method for accurate removal of the recast layer and over-corrosion inhibition according to claim 1, characterized in that: The electrolyte in step (2) includes an ethylene glycol-based electrolyte or a water-based electrolyte.

5. The method for accurate removal of the recast layer and over-corrosion inhibition according to claim 1, characterized in that: The initial machining gap of the electrolytic finishing process in step (2) is 0 to 100 μm.

Images