CN108890052B

CN108890052B - Gas injection auxiliary insulation type electrolytic cutting machining method

Info

Publication number: CN108890052B
Application number: CN201810693234.7A
Authority: CN
Inventors: 曾永彬; 杨涛; 朱荻
Original assignee: Nanjing University of Aeronautics and Astronautics
Current assignee: Nanjing University of Aeronautics and Astronautics
Priority date: 2018-06-29
Filing date: 2018-06-29
Publication date: 2020-04-07
Anticipated expiration: 2038-06-29
Also published as: CN108890052A

Abstract

The invention relates to a gas injection-assisted insulating electrolytic cutting processing method, which belongs to the technical field of electrochemical processing. It is characterized in that: a fine hollow metal tube with one end closed is selected as the tool cathode during electrolytic cutting, and a number of tiny holes are opened on the non-working surface of the electrode of the fine tube. During electrolytic cutting, the inert gas enters from one end of the micro-tube electrode, overflows from the tiny holes on the non-working surface and forms micro-bubbles in the electrolyte. The current density between the non-working surface of the micro-tube electrode and the machined surface of the workpiece is weakened, the stray corrosion to the machined surface of the workpiece is reduced, and the electrolytic cutting precision is improved.

Description

Gas injection auxiliary insulation type electrolytic cutting machining method

Technical Field

The invention relates to a gas injection auxiliary insulation type electrolytic cutting machining method, and belongs to the technical field of electrochemical machining.

Background

The electrochemical machining technology is a manufacturing method for removing metal materials based on the electrochemical anode dissolution principle, and in the machining process, a tool electrode is used as a cathode and connected with a power supply cathode to perform hydrogen evolution reduction reaction; the metal workpiece is used as an anode and is connected with the anode of a power supply to generate oxidation reaction, and the workpiece is dissolved and removed in the form of ions. With the tool cathode being fed continuously, the workpiece surface eventually forms features that are the inverse of the tool cathode shape. The electrochemical machining has the advantages of no loss of a tool cathode, negligible hardness of workpiece materials, good quality of a machined surface, high machining efficiency and the like, and is commonly used for machining materials which are complex in shape and difficult to cut, such as aeroengine impellers, blades, micro-filtration screens, molds and the like, in the fields of aerospace, precision instruments, biomedical treatment and the like.

But electrolytic machining also has a big defect: stray corrosion. During electrolytic machining, electrolyte is filled between the tool electrode and the workpiece, so that anodic dissolution can occur, but material dissolution and removal can also occur at some machined parts or parts which do not need to be machined, and stray corrosion is caused. Stray corrosion can damage the machined surface, reducing machining accuracy and surface quality. To completely eliminate the stray corrosion, it is not practical at present, and the stray corrosion can be reduced as much as possible. Researchers have proposed methods to reduce stray corrosion, such as: the passive electrolyte is adopted, the dissolution speed and the current efficiency of the electrolyte are in a nonlinear relation (for most metal materials), the current efficiency is high at high current density, and the current efficiency is low at low current density, so that the material removal speed of a non-processing surface is reduced, the stray corrosion is reduced, and the processing precision is improved; by adopting a gas-mixed electrolytic processing method, a large amount of compressed gas is mixed before the electrolyte enters a processing area, so that the electrolyte becomes a gas-liquid mixed two-phase flow (bubble flow), the pressure of the electrolyte in the flowing direction in a side clearance area is rapidly reduced, and the volume of bubbles is rapidly increased, so that the conductivity of the local electrolyte is remarkably reduced, and the aim of reducing the dissolving speed is fulfilled; a non-working surface insulated electrode is adopted, and in electrolytic machining, a layer of insulating layer is uniformly coated on the non-working surface of the electrode, so that the electric field distribution of a non-working surface area is changed, the current density is reduced, and the stray corrosion is reduced; the auxiliary anode is adopted to change the electric field distribution of the side gap area and reduce the current density on the side wall, thereby reducing the stray corrosion.

The methods are mainly used in the processes of electrolytic machining of holes, cavities and nesting and are not applicable to the electrolytic cutting process. Because the electrolytic wire cutting processing technology is an electrolytic processing method for cutting a metal material by using a metal wire electrode as a tool cathode, the processing of a workpiece is realized by controlling the relative motion track between the metal wire electrode and the workpiece. During electrolytic cutting, the workpiece is corroded and removed along the feeding direction of the wire electrode, the front surface of the wire electrode is a working surface, but electric field distribution still exists between the workpiece and the surfaces of the two sides and the rear part of the wire electrode, the cut part is still subjected to dissolution corrosion, and the electrolytic cutting precision is reduced. The adoption of the passivation electrolyte can reduce stray corrosion to a certain extent, but the processing efficiency is low, and particularly when alloy materials are cut, a passivation film is easily formed to hinder an electrolytic reaction; the method is ideal theoretically by adopting non-working surface insulated electrode electrolytic cutting, but is difficult to implement, because the diameter of a wire electrode during electrolytic cutting is in a micro scale, the thickness of the insulated layer must be very thin, tens of micrometers or even micrometers, a certain bonding strength needs to be formed between the insulated layer and the wire electrode, the insulated layer is prevented from falling off under the impact action of electrolyte, in addition, most of the electrolyte is corrosive solution, and the insulated layer is required to have certain corrosion resistance.

Therefore, how to reduce the stray corrosion and improve the electrolytic cutting precision is still an important problem of the electrolytic cutting technology.

Disclosure of Invention

Aiming at the problem of stray corrosion in the electrolytic wire cutting process, the invention provides a gas injection auxiliary insulation type electrolytic cutting processing method which can reduce the stray corrosion in the electrolytic cutting process and improve the electrolytic cutting precision.

A gas injection auxiliary insulation type electrolytic cutting cathode is characterized in that: the processing cathode is a micro-tube electrode, and one end of the processing cathode is closed; according to the technical characteristics of electrolytic wire cutting, along the feeding direction of the tube electrode, the front half part of the side surface of the tube electrode is defined as an electrolytic cutting working surface, and the rear half part of the side surface of the tube electrode is defined as a non-working surface; the non-working surface of the microtube electrode is provided with a plurality of micro holes.

The processing method of the gas injection auxiliary insulation type electrolytic cutting cathode is characterized in that: during electrolytic cutting, one end of the microtube electrode is connected with an inert gas source, the injection pressure of the inert gas is greater than the internal hydraulic pressure of the electrolyte, the inert gas enters from one end of the microtube electrode, overflows from the micro-holes on the non-working surface and forms micro-bubbles in the electrolyte; the inert gas can not participate in the electrochemical reaction in the machining process, the micro-bubble intervention plays a certain insulating role on the non-working surface of the micro-tube electrode, the current density between the non-working surface of the micro-tube electrode and the machined surface of the workpiece is weakened, the stray corrosion to the machined surface of the workpiece is reduced, and the electrolytic cutting precision is improved.

The invention has the beneficial effects that: 1. the micro-tube electrode is used as a cathode in electrolytic cutting, inert gas enters from one end of the micro-tube electrode, overflows from micro holes on a non-working surface and forms micro bubbles in electrolyte, and the micro bubbles intervene to carry out insulation protection on the non-working surface of the micro-tube electrode, so that the current density between the non-working surface of the micro-tube electrode and a machined surface of a workpiece is weakened, stray corrosion to the machined surface of the workpiece is reduced, and the electrolytic cutting machining precision is improved; meanwhile, a large amount of micro bubbles rise rapidly under the buoyancy effect of the electrolyte, play a certain disturbing role in the electrolyte in the machining gap, promote the flow of the electrolyte, accelerate the discharge of electrolysis products in the cutting seam and the update of the electrolyte, and improve the electrolysis cutting efficiency. 2. The pressure of the injected gas is greater than the internal hydraulic pressure of the electrolyte, so that the gas can be injected into the electrolyte through the micro-holes, a micro-bubble insulating layer is formed between the tube electrode and the electrolyte, and the injected inert gas does not participate in the electrochemical reaction in the processing process.

The gas injection auxiliary insulation type electrolytic cutting machining method is characterized by comprising the following steps: the inert gas source is a helium gas source. Helium gas is selected to be less dense and chemically inert because helium gas is much less dense than air (air density 1.29kg/m3, helium density 0.19 kg/m 3), helium bubbles float more easily in the electrolyte, and helium gas is chemically inert and does not participate in the electrochemical reaction during processing.

The gas injection auxiliary insulation type electrolytic cutting cathode is characterized in that: the micro holes are uniformly distributed on the non-working surface. The inert gas forms micro bubbles on the non-working surface after passing through the micro holes, so as to insulate the non-working.

The gas injection auxiliary insulation type electrolytic cutting cathode is characterized in that: the micro-tube electrode has an outer diameter of 50-300um and an inner diameter of 30-200um, which not only ensures the circulation of inert gas in the micro-tube electrode, but also ensures the strength and rigidity of the micro-tube electrode, prevents the micro-tube electrode from deformation such as bending and twisting in electrolytic cutting, and simultaneously obtains an electrolytic cutting seam with small seam width.

Drawings

FIG. 1 is a schematic diagram of a gas injection-assisted insulated electrolytic cutting process;

FIG. 2 is a view showing the entire construction of a gas injection auxiliary insulation type electrolytic cutting apparatus;

FIG. 3 is a schematic view of electrolytic cutting with gas injection assisted insulation;

FIG. 4 is a microtube electrode with micro-holes on a non-working surface;

FIG. 5 is a simulation model of the electric field distribution of the machining gap during electrolytic cutting;

FIG. 6 is a graph showing a current density distribution in a machining gap in the case of conventional electrolytic cutting;

FIG. 7 is a diagram showing a current density distribution in a machining gap during gas injection-assisted insulation type electrolytic cutting

The reference numbers are respectively as follows: 1. the device comprises a machine tool, 2, a motion control card, 3, an industrial personal computer, 4, a pulse power supply, 5, a micro-tube electrode clamping system, 6, a micro-tube electrode, 7, a workpiece, 8, a workpiece clamp, 9, a machine tool base body, 10, a micro air pump, 11, a helium source, 12, an electrolytic cell, 13, an electrolyte, 14, an air guide pipe, 15, a bracket, 16, a positioning hole, 17, a rotary joint, 18, a hollow spindle, 19, a hollow spindle motor, 20, an upper bracket, 21, a switching nozzle, 22, a lower bracket, 23, a guider, 24, a micro hole, 25 and micro bubbles.

Detailed Description

According to the figure 2, the gas injection auxiliary insulation type electrolytic cutting cathode and the processing method thereof provided by the invention mainly comprise a machine tool 1, a motion control card 2, an industrial personal computer 3, a pulse power supply 4, a micro-tube electrode clamping system 5, a micro-tube electrode 6, a workpiece 7, a micro air pump 10 and electrolyte 13.

As shown in FIG. 3, the microtube electrode clamping system 5 mainly comprises a bracket 15, a rotary joint 17, a hollow shaft motor 19, a switching nozzle 21, a guider 23 and a microtube electrode 6; the bracket 15 comprises an upper bracket 20 and a lower bracket 22, and the upper part of the bracket 15 is provided with a positioning hole 16; a hollow shaft motor 19 is arranged in an upper bracket 20, a rotary joint 17 is arranged at the upper end of a hollow main shaft 18 of the hollow shaft motor 19, a switching nozzle 21 is arranged at the lower end of the hollow main shaft 18 of the hollow shaft motor 19, the hollow shaft motor 19 is mainly used for guiding gas, installing a micro-tube electrode 6 and driving the micro-tube electrode 6 to rotate so as to change the overflow direction of micro-bubbles 25, and the working surface of the micro-tube electrode 6 is ensured to move along the feeding direction all the time by combining the relative movement of the micro-tube electrode 6 and a workpiece 7, so that the workpiece 7 is cut in a turning way; the guider 23 is arranged in the lower bracket 22 and is mainly used for restraining the micro-tube electrode 6, preventing the lower end of the micro-tube electrode 6 from deviating and ensuring that the whole micro-tube electrode 6 is in a linear state; the upper part of the micro-tube electrode 6 is arranged in the adapter nozzle 21, the lower part is a closed end and is arranged in the guider 23; the hollow spindle 18 of the hollow shaft motor 19, the adapter nozzle 21, the microtube electrode 6, and the guide 23 are coaxial.

The micro bubbles 25 are helium bubbles, helium is injected from the upper end of the micro-tube electrode 6 through the micro air pump 10, the air duct 14, the rotary joint 17, the hollow main shaft 18 and the adapter nozzle 21 and overflows from micro holes 24 on the micro-tube electrode 6, and the injection pressure is higher than the hydraulic pressure in the electrolyte 13, so that gas can be injected into the electrolyte 13 through the micro holes 24, and a micro bubble 25 insulating layer is formed in the tube electrode and the electrolyte.

As shown in FIG. 4, the microtube electrode 6 is a hollow metal microtube with a closed end, an outer diameter of 50-300um and an inner diameter of 30-200um, and a certain number of micropores 24 are opened on the non-working surface of the microtube electrode 6.

The operation process of the gas injection auxiliary insulation type electrolytic cutting cathode and the processing method of the invention is as follows:

step 1, referring to fig. 3, installing the upper end of a micro-fine tube electrode 6 in a switching nozzle 21, placing the lower end of the micro-fine tube electrode as a closed end in a guider 23, and installing a micro-fine tube electrode clamping system 5 on a Z axis of a machine tool 1 through a positioning hole 16;

step 2, referring to fig. 2, installing an electrolytic bath 12 on a machine tool base body 9, installing a workpiece clamp 8 in the electrolytic bath 12, and installing a workpiece 7 in the workpiece clamp 8; injecting a proper amount of electrolyte 13 to immerse the workpiece 7 therein;

step 3, referring to fig. 3, starting the micro air pump 10, injecting helium from the upper end of the microtube electrode 6 through the air duct 14, the rotary joint 17, the hollow main shaft 18 and the adapter nozzle 21 by the micro air pump 10, overflowing from the micro holes 24 on the microtube electrode 6, and forming micro bubbles 25 in the electrolyte 13;

step 4, referring to fig. 3, connecting the workpiece 7 with the positive electrode of the pulse power supply 4, connecting the microtube electrode 6 with the negative electrode of the pulse power supply 4, starting the pulse power supply 4, and setting appropriate electrical parameters;

step 5, referring to fig. 2, an industrial personal computer 3 controls the machine tool 1 to move through a motion control card 2, so that relative motion between a micro-tube electrode 6 and a workpiece 7 is realized, the workpiece 7 is corroded and cut, in the electrolytic cutting process, a hollow shaft motor 19 drives the micro-tube electrode 6 to rotate, the overflow direction of micro-bubbles 25 is changed, the working surface of the micro-tube electrode 6 is guaranteed to move along the feeding direction all the time, and steering cutting of the workpiece 7 is realized;

and 6, after the machining is finished, closing the pulse power supply 4 and the micro air pump 10, and separating and cleaning the workpiece 7.

In order to verify the insulation effect of the micro-bubbles 25 on the non-working surface of the microtube electrode 6 and the feasibility of the method for reducing the stray corrosion in the electrolytic cutting, COMSOL5.2a simulation software is used for simulating the current density in the machining gap, a simulation model is established by referring to FIG. 4, and the simulation conditions are as follows: the microtube electrode 6 had an outer diameter of 0.15mm, a slit width of 0.2mm, an electric conductivity of the electrolyte 13 of 1.83S/m, and a processing voltage of 10V.

FIG. 5 is a graph showing a current density distribution in a machining gap in the conventional electrolytic cutting, from which it can be seen that the current density at the point A1 is 0.636A/mm²The current density of B1 was 0.607A/mm²The current densities at the positions A1 and B1 are very different, which indicates that when the micro-tube electrode 6 cuts the workpiece 7 along the feeding direction, the machined parts at both sides are still etched and cut, and the etching rates are similar.

FIG. 6 is a graph showing a current density distribution in a machining gap during gas injection-assisted insulated electrolytic cutting, from which it can be seen that the current density at the point A2 is 0.636A/mm²B2 Current Density of 0.315A/mm²The current densities at the points a2 and B2 are nearly twice different, and the micro-tube electrode 6 cuts the workpiece 7 in the feeding direction, but the cut-off rates are greatly different from each other. The micro holes 24 of the micro-tube electrode 6 are optimized, and proper processing parameters are selected, so that the effect is better.

As can be seen by carrying out simulation comparison on the current density in the machining gap, the gas injection auxiliary type electrolytic cutting cathode and the machining method provided by the invention can reduce stray corrosion in electrolytic cutting and improve the machining precision of electrolytic cutting.

Claims

1. The gas injection auxiliary insulation type electrolytic cutting processing method is characterized by comprising the following steps:

the gas injection auxiliary insulation type electrolytic cutting cathode structure is as follows: the processing cathode is a micro-tube electrode (6), and one end of the processing cathode is closed; according to the technical characteristics of electrolytic wire cutting, along the feeding direction of the tube electrode, the front half part of the side surface of the tube electrode is defined as an electrolytic cutting working surface, and the rear half part of the side surface of the tube electrode is defined as a non-working surface; a plurality of micro holes (24) are arranged on the non-working surface of the micro-tube electrode (6);

the processing method comprises the following steps: during electrolytic cutting, one end of the microtube electrode (6) is connected with an inert gas source, the injection pressure of the inert gas is greater than the internal hydraulic pressure of the electrolyte (13), the inert gas enters from one end of the microtube electrode (6), overflows from the micropores (24) on the non-working surface and forms microbubbles (25) in the electrolyte (13);

the inert gas can not participate in the electrochemical reaction in the machining process, the micro-bubbles (25) play a certain insulating role on the non-working surface of the micro-tube electrode (6), the current density between the non-working surface of the micro-tube electrode (6) and the machined surface of the workpiece (7) is weakened, the stray corrosion to the machined surface of the workpiece (7) is reduced, and the electrolytic cutting precision is improved.

2. The gas injection auxiliary insulation type electrolytic cutting machining method according to claim 1, characterized in that:

the inert gas source is a helium gas source.

3. The gas injection auxiliary insulation type electrolytic cutting machining method according to claim 1, characterized in that:

the micro-tube electrode (6) of the gas injection auxiliary insulation type electrolytic cutting cathode has the outer diameter of 50-300um and the inner diameter of 30-200 um.

4. The gas injection auxiliary insulation type electrolytic cutting machining method according to claim 1, characterized in that:

the tiny holes (24) of the gas injection auxiliary insulation type electrolysis cutting cathode are uniformly distributed on the non-working surface.