CN110919115A

CN110919115A - Phosphoric acid-ethanol mixed electrolyte for micro-electrolysis linear cutting and polishing and method thereof

Info

Publication number: CN110919115A
Application number: CN201911281757.1A
Authority: CN
Inventors: 曾永彬; 李守业; 杨涛; 杭雨森
Original assignee: Nanjing University of Aeronautics and Astronautics
Current assignee: Nanjing University of Aeronautics and Astronautics
Priority date: 2019-12-13
Filing date: 2019-12-13
Publication date: 2020-03-27
Anticipated expiration: 2039-12-13
Also published as: CN110919115B

Abstract

The invention relates to a phosphoric acid-ethanol mixed electrolyte for micro-electrolysis linear cutting and polishing and a method thereof, belonging to the technical field of electrochemical machining. The main characteristics are as follows: the method comprises the steps of using an ethanol phosphate solution as electrolyte to carry out electrolytic machining on a metal material, using a wire electrode to simultaneously carry out micro-slit cutting and joint-cutting side wall polishing, combining the electrolytic wire cutting with the electric polishing, finishing the machining and surface treatment of a microstructure in one step, and greatly improving the surface quality and the machining efficiency of a product. The ethanol with low density enables bubbles and other electrolysis products in the machining gap to be discharged with low resistance, and the rapid discharge of the electrolysis products and the timely update of the electrolyte enable the electric field distribution in the machining gap to be more uniform and the surface of the microstructure to be smoother.

Description

Phosphoric acid-ethanol mixed electrolyte for micro-electrolysis linear cutting and polishing and method thereof

Technical Field

The invention relates to a synchronous processing method for cutting and polishing a micro electrolytic wire in a phosphoric acid ethanol solution, belonging to the technical field of electrochemical processing.

Background

The micro-electro-mechanical system has very small size, and the internal structure and parts of the micro-electro-mechanical system are usually in the micron level or even the nanometer level. The microstructure has high precision requirement and good mechanical property of the material for processing the microstructure, so the processing difficulty is very high, the traditional mechanical processing is difficult to realize, and a special processing method is generally adopted for processing. The special processing method is suitable for processing various special materials with high hardness, strong corrosion resistance and high melting point. Common special machining methods include laser machining, micro electric discharge machining, micro electrolytic machining, ion beam machining and the like. Among them, the electrolytic machining method has advantages that other machining methods do not have. During the electrolytic machining, the tool is not in contact with the workpiece, the workpiece is not deformed, a heat affected zone in the electric discharge machining is not generated, and the like. Therefore, the micro electrolysis method is suitable for workpieces with high processing precision requirements and tiny sizes.

The micro electrolytic wire cutting process adopts tungsten wires or molybdenum wires with the diameter of tens of microns or even several microns as the cathode, has short electrode manufacturing time, low cost and small kerf width, and can obtain higher processing precision. During fine electrolytic wire cutting, hydrogen is generated at the cathode due to reduction reaction, and soluble or insoluble electrolysis products are generated at the anode due to oxidation reaction. However, since the machining gap is small, electrolytic products cannot be discharged out of the gap in time by only gravity or diffusion, so that short circuits are easily generated, and the uneven electric field distribution or short circuits also cause poor surface quality of the kerf sidewalls.

The discharge efficiency of the electrolytic product has a great influence on the surface quality of the product. Researchers have conducted extensive research and proposed some optimization solutions to the problem of electrolytic product discharge. Such as: the axial reciprocating motion of the wire electrode is matched with the micro-amplitude vibration, unidirectional wire conveying or reciprocating wire conveying of the anode workpiece to drag bubbles and electrolytic products, so that the discharge of the processed products and the update of electrolyte are accelerated, however, the surface of the wire electrode is smooth, and the dragging effect is not obvious; the method adopts a hydrophilic electrode, such as a micro electrode with a rough surface or a microstructure, to perform electrolytic wire cutting, so that the dragging effect of an electrode wire on a product can be enhanced, but the preparation method of the wire electrode is more complicated, and due to the material reduction preparation, the tension of the electrode is reduced, the tensioning effect is poor, and the processing effect is also influenced; axial flushing is carried out, electrolytic products in the machining gap are taken away by high-speed liquid flow, electrolyte in the machining gap is updated quickly, machining stability and machining efficiency are improved, but liquid flow pressure can be attenuated in the gap, and thin electrode wires are poor in stability and are not suitable for the method; the spiral electrode electrolytic wire cutting utilizes the high-speed rotating spiral electrode to form high-speed liquid flow in the axial direction, takes away electrolytic products and updates electrolyte, the electric field in a machining gap is uniform, the machining efficiency, the machining stability and the surface quality are greatly improved, but the electrode size is often large, and the electrode is not suitable for the case that the requirement on the machining precision of a workpiece is very high.

How to efficiently process microstructures with high precision and high surface quality remains a challenging challenge.

Disclosure of Invention

Aiming at the problems of poor surface quality and low processing efficiency of the microstructure, the invention provides a micro-electrolysis linear cutting and polishing synchronous processing method in a phosphoric acid solution, and aims to process the microstructure with high surface quality in one step.

A phosphoric acid-ethanol solution mixed solution of electrolyte used in micro-electrolysis wire cutting and polishing is characterized in that: the solute in the mixed solution is phosphoric acid and ethanol, and the solvent is water; the content of each component in the mixed solution is calculated according to the mass fraction, the content of phosphoric acid is 10-30%, the content of deionized water is 10-20%, and the balance is ethanol.

The micro-electrolysis linear cutting and polishing method taking the phosphoric acid ethanol mixed solution as electrolyte is characterized by comprising the following steps: measuring the polarization curve of metal in phosphoric acid-ethanol mixed solution, and dividing the polarization curve into an activation region, a passivation region and a super-passivation region according to the change of current density; the voltage of a pulse power supply is arranged in a super-passivation region of a polarization curve, and the potential is gradually reduced from near to far along with the distance from an electrode; switching on a pulse power supply, and simultaneously completing cutting and polishing of the metal microstructure in the phosphoric acid-ethanol mixed solution through numerical control movement of the wire electrode relative to the workpiece; when the wire electrode and the workpiece move relatively, the side wall of the cutting seam is divided into a cutting area, a polishing area and a polished area in sequence; wherein, the area of the front surface of the wire electrode opposite to the workpiece is called a cutting area, the electric potential of the cutting area is in a super-passivation area, the current density is high, the material is quickly dissolved, and a micro-seam is cut; the area of the side face of the wire electrode, which is opposite to the workpiece, is called a polishing area, the material of the polishing area is far away from a cathode, the potential is in a passivation area, according to the principle of electropolishing, when the area is in the voltage range, a layer of adhesive film layer can be formed on the surface of the material, the adhesive film layer covers the surface of the material, and at the bulge of the surface of the material, the adhesive film layer is thin, the resistance is small, the corrosion speed of the material is high, so that the bulge is removed more quickly, and the surface is leveled. The potential of the polished area farther away from the line electrode is lower than that of the passivated area, and the dissolution is stopped; with the continuous feeding of the wire electrode, each position of the material in the feeding direction of the wire electrode sequentially becomes a cutting area and a polishing area, so that cutting and polishing are achieved, and synchronous machining of cutting and polishing is achieved.

The pulse parameters of the pulse power supply are characterized in that: the parameters of the pulse power supply are set to be pulse voltage of 8V-10V, pulse period of 2 mus-3 mus and duty ratio of 4% -6%.

Since insoluble electrolysis products are not generated in a strong acid solution such as hydrochloric acid, and the electrolytic processing is often performed with high processing efficiency, such an acid solution is used. However, the stray corrosion of the side wall of the micro-gap is serious after the micro-gap is processed by using hydrochloric acid, the surface roughness of the processed micro-structure is high, the surface of the micro-structure needs to be leveled by an electric polishing method in polishing solution (phosphoric acid and the like), and the total processing efficiency is low. Therefore, the phosphoric acid is adopted to directly process the material, so that the polishing step can be omitted, and the processing efficiency is improved. Phosphoric acid viscosity increases with increasing concentration; the viscosity of the concentrated phosphoric acid is high, and bubbles and electrolysis products in a processing gap are difficult to discharge quickly, so the concentration of the phosphoric acid is not higher than 30%; the viscosity of the electrolyte can be reduced by adding ethanol with lower density than water into phosphoric acid, the higher the ethanol content is, the lower the density of the electrolyte is, and the more easily bubbles and electrolysis products are quickly discharged out of a processing area, so that the electric field distribution of the processing area is more uniform, and the processing precision and the surface quality of a microstructure are higher. However, if the ethanol content is too high and the water content is too low, the amount of ionized phosphoric acid molecules in the solution is small, the conductivity of the solution is too low, and the material removal rate is too low, so that a certain proportion of water in the electrolyte needs to be ensured to ensure the processing capacity of the electrolyte.

The polarization curve is a curve showing the change of current density with voltage when the material is dissolved in the solution, and reflects the dissolution condition of the material. It was found that the surface of a metallic material can be polished when the metallic material is energized with a voltage in the passivation region of the polarization curve in phosphoric acid. Under the voltage of a passivation area, the current density is relatively small, according to the mucosa theory in electropolishing, the surface of the material is covered with a layer of mucosa, and at the convex part of the surface of the material, the mucosa layer is thin, the resistance is small, and the corrosion speed of the material is high; and because the distance is short, the electric field intensity is large, more negative ions are accumulated to the convex part, the speed is higher, so that the convex part has more chances to be corroded, and the surface is leveled, which is the polishing principle of phosphoric acid. In addition, according to the polarization curve, when the voltage is in the super-passivation region, the current density on the surface of the material is high, the material can be quickly removed, and the method is suitable for cutting workpieces. The phosphoric acid solution can quickly remove materials and polish the surfaces of the materials due to the electrochemical characteristics of the phosphoric acid solution, and when the phosphoric acid solution is applied to micro electrochemical machining, the cutting and polishing can be synchronously carried out, so that the surface quality and the machining efficiency are improved.

The initial potential of the super-passivation region of the metal material in the phosphoric acid-ethanol mixed solution is generally 1V-2V. The machining voltage is set to be higher in the super-passivation region, so that the potential of the machining region can be ensured to be gradually reduced to be lower than the passivation potential from the super-passivation potential along with the increase of the distance from the wire electrode, different machining effects of phosphoric acid under different potentials can be realized, the higher the voltage is, the higher the current density is, the higher the material removal rate is, and the machining efficiency is ensured. The pulse period is large, the duty ratio is small, the number of pulses in unit time is small, the energy of a single pulse is small, the material removal amount is small, and higher processing precision is favorably obtained; too large a pulse period or too small a duty cycle may result in too low a pulse energy to ensure processing efficiency. The pulse period and duty cycle should be controlled within a certain range.

Drawings

FIG. 1 is a schematic view of a microelectrolysis process of an ethanolic phosphate solution;

FIG. 2 is a schematic view of a cutting and polishing synchronous machining;

FIG. 3 is a schematic illustration of the polarization curve of a metal in phosphoric acid;

FIG. 4 is a polishing principle of a phosphoric acid solution;

the reference numbers are respectively as follows: 1. the method comprises the steps of wire electrode, 2, workpiece, 3, phosphoric acid-ethanol mixed solution, 4, pulse power supply, 5, air bubbles, 6, cutting area, 7, polishing area, 8, polished area, 9, adhesive film layer, 10, activation area, 11, passivation area, 12, super-passivation area, 13, negative ions, 14, material surface protrusion, 15 and material surface depression.

Detailed Description

The phosphoric acid-ethanol solution mixed solution used for the electrolyte in the micro-electrolysis linear cutting and polishing is characterized by comprising the following components in parts by weight: the solute in the mixed solution is phosphoric acid and ethanol, and the solvent is water; the content of each component in the mixed solution is calculated according to the mass fraction, the content of phosphoric acid is 10-30%, the content of deionized water is 10-20%, and the balance is ethanol.

The micro-electrolysis wire cutting and polishing method using the phosphoric acid-ethanol solution mixed solution as electrolyte is characterized by comprising the following steps: the polarization curve of the metal in the phosphoric acid-ethanol mixed solution, namely the current density-voltage relation curve, is measured. The voltage of a pulse power supply 4 is arranged in a super-passivation region 12 of a polarization curve, the potential is sequentially reduced from near to far away from an electrode, and the side wall of the cutting seam is sequentially divided into a cutting region 6, a polishing region 7, a passivation region 11 and a polished region 8, wherein the potential is lower than that of the passivation region 11. Switching on a pulse power supply 4, and simultaneously completing cutting and polishing of the metal microstructure in the phosphoric acid-ethanol mixed solution 3 through numerical control movement of the wire electrode 1 relative to the workpiece 2; when the wire electrode 1 and the workpiece 2 move relatively, the area, opposite to the workpiece 2, of the front surface of the wire electrode 1 is called a cutting area 6, the cutting area 6 is in an ultra-passivation potential, the current density is high, the material is rapidly dissolved, and micro-cracks are cut; the area of the side of the wire electrode 1 opposite the workpiece 2 is called the polishing zone 7, and the material of the polishing zone 7 is further away from the cathode and is at a passivating potential. The material of the polished zone 8 further from the line electrode 1 stops dissolving due to the lower potential; with the continuous feeding of the wire electrode 1, each position of the material in the feeding direction of the wire electrode 1 sequentially becomes a cutting area 6, a polishing area 7 and a polished area 8, and the dissolution is stopped after the cutting and polishing are sequentially performed, so that the synchronous processing of the cutting and polishing is realized.

The pulse power supply pulse parameters are characterized in that: the parameters of the pulse power supply are set to be pulse voltage 8V-10V, pulse period 2 mus-3 mus and duty ratio 4% -6%.

Due to the high viscosity of phosphoric acid, the bubbles 5 and electrolysis products in the machining gap are difficult to be rapidly discharged. The ethanol with the density lower than that of water is added into the phosphoric acid, so that the bubbles 5 and the electrolysis products are more easily and quickly discharged out of the processing area, the electric field distribution of the processing area is uniform, and the processing precision and the surface quality of the microstructure are improved. Phosphoric acid viscosity increases with increasing concentration; the viscosity of the concentrated phosphoric acid is high, and bubbles and electrolysis products in a processing gap are difficult to discharge quickly, so the concentration of the phosphoric acid is not higher than 30%; the higher the ethanol content, the lower the electrolyte density, and the more easily bubbles and electrolysis products are rapidly discharged out of the machining region, so that the more uniformly the electric field distribution in the machining region, the higher the machining precision and surface quality of the microstructure. However, if the ethanol content is too high and the water content is too low, the amount of ionized phosphoric acid molecules in the solution is small, the conductivity of the solution is too low, and the material removal rate is too low, so that a certain proportion of water in the electrolyte needs to be ensured to ensure the processing capacity of the electrolyte.

The polarization curve is a curve showing the change of current density with voltage when the material is dissolved in the solution, and reflects the dissolution condition of the material. As shown in fig. 3, the polarization curve of metal in phosphoric acid is divided into three parts, namely an active region 10, a passive region 11 and a super-passive region 12 by using a dotted line as a boundary, as shown in fig. 3. It has been found that when a metallic material is energized in phosphoric acid with a voltage in the passivation region 11, the surface thereof can be polished. Under the voltage of the passivation region 11, the current density is relatively small, according to the mucosa theory in electropolishing, a layer of adhesive film layer 9 is formed on the surface of the material, as shown in fig. 4, at the convex part 14 of the surface of the material, the adhesive film layer 9 is thin, the resistance is small, and the corrosion speed of the material is high; and because the distance is short, the electric field intensity is large, the negative ions 13 are accumulated to the convex part more and the speed is faster, so the convex part 14 has more chances to be corroded, and the surface is leveled, which is the polishing principle of phosphoric acid. When the voltage is in the ultra-passivation region 12, the current density on the surface of the material is high, and the material can be quickly removed, so that the material is suitable for cutting a workpiece. The phosphoric acid solution can not only remove the material rapidly, but also polish the surface of the material due to the electrochemical characteristics of the phosphoric acid solution.

The machining voltage is set to be the voltage of the super-passivation region 12, so that the potential of the machining region can be ensured to be gradually reduced to be lower than the passivation potential from the super-passivation potential along with the increase of the distance from the wire electrode 1, and different machining effects of phosphoric acid under different potentials can be realized. The higher the voltage, the higher the current density, and the higher the material removal rate, and to ensure the processing efficiency, the higher the voltage in the ultra-passivation region 12 can be selected. The pulse period is large, the duty ratio is small, the number of pulses in unit time is small, the energy of a single pulse is small, the material removal amount is small, and higher processing precision is favorably obtained; too large a pulse period or too small a duty cycle may result in too low a pulse energy to ensure processing efficiency. The pulse period and duty cycle should be controlled within a certain range.

The operation of the method for performing the synchronous processing of micro-electro-mechanical cutting and polishing in phosphoric acid ethanol solution according to the present invention will be described with reference to FIGS. 1 and 3.

Step 1, preparing a phosphoric acid-ethanol mixed solution by using phosphoric acid, ethanol and deionized water;

step 2, measuring a polarization curve of the material to be processed in the phosphoric acid-ethanol mixed solution 3;

step 3, pouring the phosphoric acid-ethanol mixed solution 3 into an electrolytic bath, and immersing the wire electrode 1 and the workpiece 2;

step 4, connecting a pulse power supply 4 with the anode workpiece 2 and the cathode wiring electrode 1, setting the voltage of the pulse power supply 4 as the voltage in the polarization curve super-passivation region 12, switching on the pulse power supply 4, and machining the micro-seam with smooth side wall through the numerical control movement of the wire electrode 1;

and 5, separating and cleaning the workpiece 2 after the machining is finished.

Claims

1. A phosphoric acid-ethanol mixed electrolyte for micro-electrolysis wire cutting and polishing is characterized in that:

the solute in the mixed solution is phosphoric acid and ethanol, and the solvent is water;

the content of each component in the mixed solution is calculated according to the mass fraction, the content of phosphoric acid is 10-30%, the content of deionized water is 10-20%, and the balance is ethanol.

2. The fine electrolytic wire cutting polishing method using the phosphoric acid-ethanol mixed electrolyte for fine electrolytic wire cutting polishing as set forth in claim 1, characterized by comprising the following processes:

measuring the polarization curve of metal in the phosphoric acid-ethanol mixed solution (3), and dividing the polarization curve into an activation region (10), a passivation region (11) and a super-passivation region (12) according to the change of the current density;

the voltage of a pulse power supply (4) is arranged in a super-passivation region (12) of a polarization curve, and the potential is gradually reduced from near to far away from the electrode;

switching on a pulse power supply (4), and simultaneously completing cutting and polishing of a metal microstructure in a phosphoric acid-ethanol mixed solution (3) through numerical control movement of a wire electrode (1) relative to a workpiece (2);

when the wire electrode (1) and the workpiece (2) move relatively, the side wall of the cutting seam is divided into a cutting area (6), a polishing area (7) and a polished area (8) in sequence;

the region of the front surface of the wire electrode (1) opposite to the workpiece (2) is called a cutting region (6), the potential of the cutting region 6 is in a super-passivation region (12), the current density is high, the material is rapidly dissolved, and a micro-slit is cut;

the area of the side face of the wire electrode (1) opposite to the workpiece (2) is called a polishing area (7), the material of the polishing area (7) is far away from a cathode, the potential is in a passivation area (11), according to the principle of electropolishing, when the area is in the voltage range, a layer of adhesive film layer (9) can be formed on the surface of the material, the adhesive film layer covers the surface of the material, and at the bulge of the surface of the material, the adhesive film layer (9) is thin, the resistance is small, the corrosion speed of the material is high, so that the bulge is removed more quickly, and the surface is leveled;

the potential of a polished area (8) which is farther away from the line electrode (1) is lower than that of a passivation area (11) and the dissolution is stopped;

with the continuous feeding of the wire electrode (1), each position of the material in the feeding direction of the wire electrode (1) sequentially becomes a cutting area (6) and a polishing area (7) to be cut and polished, and the synchronous processing of cutting and polishing is realized.

3. The micro electrolytic wire cutting polishing method according to claim 2, characterized in that:

the parameters of the pulse power supply are set to be pulse voltage of 8V-10V, pulse period of 2 mus-3 mus and duty ratio of 4% -6%.