JPH02250720A - Electric corrosive grinding of abrasive - Google Patents

Abstract

PURPOSE: To improve dielectric strength of a clearance between electrodes by applying rectified voltage having the amplitude and the ripple factor for securing formation of an insulating oxide film on the front surface of a grinding wheel to the electrodes, and using coolant having conductivity in the range of 2.10<-3> ohm<-1> cm<-1> to 2.10<-2> ohm<-1> cm<-1> . CONSTITUTION: Pulse voltage is applied to a grinding wheel 1 by a pulse voltage source 11 in the grinding range 2 for a work piece 6 by using the grinding wheel 1 and coolant bound by a metal. An electrode 4 for providing the additional electric action to the grinding wheel 1 is arranged outside the grinding range 2. In this case, rectified voltage having the amplitude and the ripple factor for forming an insulating oxide film on the front surface of the grinding wheel 1 is applied to the electrode 4 by a D.C. voltage source 10, and coolant has conductivity in the range of 2.10<-3> ohm<-1> cm<-1> to 2.10<-2> ohm<-1> cm<-1> .

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the field of grinding, and more particularly to a method of abrasive grinding.
electroerosion grindiB).

Most advantageously, the invention applies to hard magnetic alloys, stainless steels, and high-temperature steels, such as hard magnetic alloys, stainless steels, and high-temperature steels.
Difficult-to-w materials, aluminum and its alloys, copper and its alloys
It is used for surface, cylindrical and internal grinding of materials (hard or brittle or tough) and for sharpening cutting tools made of any grade of hard and high speed steel.

The invention may also be used to grind conventional structural steel or cast iron articles where there is a need to reduce the forces applied to the surface being ground and the heat generated in the surface being ground.

[Prior art]

The development of core industries is the development of secondary industries, which are characterized by less machinable properties but high use properties (e.g. heat-resistant ultra-hard materials, desirable electronic or electrical engineering properties, etc.). At the same time, with a continuous increase in the scope and area of materials (such as materials), the demands on the machining quality of such materials are constantly increasing, and the main of these demands are:
Defects such as chipping, microcracks (a+1 cr
No defects such as ocracks or burns, and low surface roughness.

Moreover, from technical and economical points of view, there are also general demands such as high production capacity and reasonable wear resistance of grinding tools.

Conventional abrasive grinding
) It is not possible in most cases to meet all these requirements using methods. Therefore, in order to grind such difficult-to-process materials, a method of diamond-electrochemical grinding (methoa of diamond), which combines the V & shredding process of the workpiece metal and the electrochemical removal process, is required.
nd-electro che+*1cal Hr
indiB) is often used. However, this method has a number of disadvantages that limit and prevent its application.

The main such disadvantages include: the necessity of making the most important parts of the machine from corrosion-resistant materials due to the use of an electrolyte solution as the working medium; the large dimensions of the diamond-electrochemical grinding machine; high cost and complex maintenance;
There is a high power consumption of the method, large operating currents (up to several thousand amperes).

Metallic-bond grinding wheel (s+metallic-bon)
A method of abrasive galvanic erosion grinding of difficult-to-process materials using a d wheel) and a coolant is known in the art (SU,
^, No.

841.889), in which a pulsed voltage is applied to the grinding wheel in the grinding area of the workpiece, and electrodes are placed outside this area to produce an additional electrical effect on the grinding wheel. . The use of non-corrosive cooling fluids as a working medium for carrying out this method makes it possible to use existing grinding machines and also to use conventional structural forest materials in newly developed machines. . Furthermore, compared to the diamond-electrochemical method, S
U, ^.

The method according to No. 841.889 has the following advantages: reduction of working current by several tens of minutes (less than 50 8), reduction of power consumption by 15
% to 20% reduction, with ancillary equipment (tanks, cleaning systems, power supplies) dimensions reduced by a factor of 2 to 4.

However, when implementing this prior art abrasive galvanic erosion grinding method, there is still considerable wear on the abrasive tool (5
g/g to 30-g/g), which results in high consumption of the grinding wheel and often requires its replacement. This machining process is also accompanied by relatively strong spark generation, light radiation and noise, and in many cases (e.g. in the case of high productivity rough grinding) the cutting properties of the abrasive tool are stabilized with the aid of electrical effects. I can't.

The main cause of such disadvantages lies in the conductance (albeit insignificant) of the working medium used, which leads to a reduction in the dielectric strength of the gap between the electrodes; This results in energy loss to the medium and insufficient localization of the discharge at the electrode surface.

To compensate for these losses, it is necessary to increase the pulse voltage amplitude and the power of the power supply, which results in increased noise and light radiation and wear on the grinding wheel. The use of organic liquids (kerosene, oil, etc.) commonly used in galvanic corrosion machines as a working medium means that, in the case of grinding machines, the liquid is atomized by a grinding wheel rotating at a speed of 15 to 30 m/s. Not permissible due to ignition risk.

[Problem that the invention seeks to solve]

The present invention uses a metal-bonded grinding wheel and a coolant, and the mode of electrical action on the grinding wheel and the parameters of the working medium are selected to ensure the formation of a stable oxide film on the surface of the grinding wheel. An object of the present invention is to provide an abrasive electrolytic corrosion grinding method using a metal-bonded grinding wheel and a coolant.

The oxide film increases the dielectric strength of the gap between the electrodes, thereby reducing energy loss, RI wear of the grinding wheel, and the level of light and sound radiation.

[Means for solving problems]

This purpose uses a metal-bonded grinding wheel and a coolant adapted to generate an additional electrical effect on the grinding wheel while a pulsed voltage is applied to the grinding wheel in the grinding area of the workpiece. In an abrasive galvanic grinding method in which a fixed electrode is placed outside the grinding area, according to the invention, a rectified voltage having an amplitude and a pulsation rate that ensures the formation of an insulating oxide film on the surface of the grinding wheel is applied to the electrode. The coolant is applied to
This is achieved by having a conductivity of 0-''ohm-1 cm-'.

The method according to the invention ensures a reduction in the wear of the grinding wheel, a high production capacity for machining any material parts that are difficult to machine, a stability of the cutting properties of the grinding wheel throughout the entire service life of the grinding wheel and in the grinding process. A reduction in the level of noise and light radiation is obtained.

In order to obtain such an effect, it is necessary to ensure the formation of a stable oxide film having insulating properties on the working surface of the grinding wheel. This formation is accomplished by applying a positive voltage to the grinding wheel from a DC power source. In a poorly conductive medium, expressed as a coolant, the metal bond of the grinding wheel, containing copper or aluminum, is anodic-fused and then acted upon by an electric current flowing between the grinding wheel and the electrodes. The amplitude and pulse conductivity of the rectified current, followed by a passivation process, i.e. an oxidation process leading to the formation of an insulating film, prevents discharges in the gap between the electrodes, which would lead to the destruction of the oxide film, while ensuring sufficient formation of this film. Properly selected to ensure speed. This is also achieved by limiting the electrical conductivity of the working medium to a certain extent. 2・
If the conductivity is less than 1010-3oh1cm-', the generated current is insufficient to form an oxide film, and 2.10-3oh1cm-' or less
At conductivities above ``ohm-1 cm-'' there is a danger of corrosion of the equipment, while on the other hand there is a risk of repassivation.
There is a risk of partial dissolution of the oxide film due to ssivation).

The increase in the overall dielectric strength of the gap between the electrodes by providing the oxide film ensures a more sufficient use of the discharge energy for an effective process of galvanic finishing of the grinding wheel. This allows the pulse voltage amplitude to be reduced compared to the amplitude used in prior art abrasive galvanic grinding methods, which reduces the energy consumed during the process, the wear of the grinding wheel, and the noise and light emissions. resulting in a decrease in the level of

The fact is that in the method according to the invention, the exposure of fresh abrasive grains instead of dull abrasive grains is caused simultaneously by electrochemical dissolution and galvanic fracturing of the bonding family, so that the cutting of the grinding wheel The high stability of the characteristics lasts for the whole practical period (s
service period). Moreover, the oxide film formed on the grinding wheel reduces friction in the grinding area, which also contributes to an additional reduction in the energy consumed in machining and to an increase in its efficiency.

Due to the galvanic corrosion effect exerted on the grinding wheel, the oxide film is removed from the most protruding part of the relief in the first revolution, thus speeding up the correction process of the outer surface shape of the grinding wheel.

The oxidation treatment on the surface of the grinding wheel is 2・10-cooh+s-'a
It is carried out in an aqueous coolant with a conductivity of s+-' to 2.10-''ohm-1 cm-'.
discharge commutation conditions (eei+1cal current))
on) and because it worsens the mechanical unit (ma
It is not a good idea because it corrodes the chine units).

If the conductivity is less than 2·10 ohm-3 ohm-', the rate of oxide film formation is insufficient to achieve the inherent effects of the present invention.

The amplitude of the rectified voltage is preferably set within the limits of 5 to 35 V. This makes it possible in all cases to provide the desired oxide formation rate, depending on the morphology of the material to be ground, the required productivity and the nature of the surface. The lower voltage (5 to 15 V) is preferably used for grinding materials that are easily passivated (aluminum, steel, tungsten, etc.) and for grinding tolerances to be removed from the workpiece at relatively low productivity. Used in few cases.

If the voltage is less than 5 V, the oxide II destroyed in the grinding area will not be restored quickly, so the film formation rate will be insufficient even in the above case. Using rectified voltage amplitude values above 35 V initiates repassivation, or electrochemical dissolution of the oxide film.

Furthermore, the energy consumption of machining increases excessively, and electrical discharges occur that destroy the continuity of the antinode. As a result, using a rectified voltage amplitude value higher or lower than the range specified in the present invention will disturb the oxide film formation process on the grinding wheel surface, which will lead to an increase in the thickness of the grinding wheel and the cutting characteristics of the grinding wheel. resulting in deterioration.

The pulsation rate of the rectified voltage is preferably set to 10 to 15%. This allows, on the one hand, a sufficient rate of oxide film formation at a given voltage amplitude value and, on the other hand, a relatively simple power supply without an additional complex smoothing system that provides a reduction of pulsating waves in the method according to the invention. Any source can be used.

Deviations from the above-mentioned rectified voltage values and working medium parameters can lead to increased wear of the grinding wheel (due to sparks or insufficient oxide formation rate) or to a gradual decrease in its cutting properties, and therefore to a deterioration of the machining process. This results in poor quality and decreased productivity. Preferably, the electrodes are supplied with a rectified voltage having an amplitude of about 32 V and a pulsation rate of about 12%;
It is preferable to use a coolant having a conductivity of 10-oh+*-1 cm-'.

These conditions determine the materials to be processed, the form of the workpiece, and the production operations.
) yields good results in terms of grinding efficiency, product quality and reduced tool wear over a wide range of applications, and at the same time
Various grades of grinding wheels can be used.

〔Example〕

The abrasive electro-corrosion grinding method according to the present invention is based on research conducted by the inventors, and the results of the research were confirmed under production conditions. If an insulating oxide film is previously formed on the surface of the grinding wheel 1, the grinding wheel 1 may be subjected to electrolytic corrosion cleaning (eleatoeros) to remove cutting products (granules).
It has been demonstrated that the ion cleaning process and the exposure of new abrasive grains proceed more effectively. By equipping the grinding wheel 1 with such a membrane, the amplitude of the pulse voltage can be reduced to 20-35 V, the value of the working pulse current can be lowered to 2-4 A, and the wear of the grinding wheel can be reduced by 1
~5-g/g, reducing the metal removal rate from the workpiece to 1
．． It can increase the level of noise and light radiation due to electrical discharge in the grinding area by 2 to 4 times (fac-tor
) reduction, i.e., can be reduced to -2 to 4 minutes.

In order to form an oxide film disposed in the grinding zone 2, an electrochemical (anodic) oxidation zone 3 of the metal bond of the grinding wheel 1 is provided, in which a DC voltage is applied to the grinding wheel 1 and the electrodes 4. A cooling liquid consisting of a poorly conductive aqueous solution of an inorganic substance (for example sodium nitrite) or an organic substance (for example triethanolamine) is supplied to the gap 5 between the electrodes. Under the action of the electrochemical processes occurring in the gap 5 between the electrodes, anodic dissolution of the binder begins, resulting in partial exposure of the working abrasive grain. Since the binder is made of either copper or aluminum, i.e. a metal that is easily oxidized, the dissolution process of the binder will gradually end and the working surface of the grinding wheel 1 will be covered with an oxide film, resulting in a sudden decrease in the zero working current value. (Several tens of amperes to zero amperes) indicates that the anodic dissolution process and film formation process have been completed.

The electrical discharge that occurs in the grinding area as a result of the application of a pulsed voltage to the grinding wheel 1 and the workpiece 6 causes the electrolytic fracture of the bond (
electroerosion crushing)
, causing exposure of the cutting abrasive grains and removal of stuck grains from the surface of the grinding wheel 1.

When the grinding wheel 1 arrives at the grinding zone 2 with an oxide film formed on its working surface, electrolytic removal of said binder (
electroerosive res+oval)
conditions are created for the most complete utilization of the discharge energy. Thereby, the discharge energy can be reduced compared to the discharge energy used in such electroerosion grinding without an oxide film, and as a result, the wear of the grinding wheel 1, the energy consumed in machining, and the grinding area 2 are reduced. can reduce noise and sparks in Depending on the type of material to be ground, the properties of the grinding wheel and the requirements for machining quality and productivity, the value of the pulse voltage (either pulse frequency or pulse width or both simultaneously) can be determined by two main methods: The requirements are varied on the basis that the cutting capacity of the knee grinding wheel is as high as possible and does not change prematurely, and that the wear of the grinding wheel is as small as possible.

However, while the discharge fractures the binder, it also destroys the oxide film. The recovery of the oxide film has to take place in a fairly short period of time (several milliseconds) during which each part of the grinding wheel remains in the anodized area, as the electrodes and the applied voltage to the grinding wheel have to do. A high rate of formation of an oxide film on the surface of the grinding wheel is obtained if special conditions are met, which are primarily related to the parameters of the direct voltage and the properties of the working fluid.

The composition and parameters of the coolant promote rapid oxide formation, oxide continuity, and dielectric strength.

It has been found that water-based coolants containing anti-corrosion and anti-friction agents in the form of inorganic sodium salts, triethanolamine, etc. meet these requirements to the highest degree. The above-mentioned cooling liquid is 2.10-3 ohm-'am-' to 2
- Appearance of corrosion of mechanical constituent units that must have electrical conductivity in the range of 10-"ohm-1 cm-' and deterioration of commutation conditions for electrical discharge in the grinding area due to increased leakage current (electrolytic current), etc. For reasons higher conductivity of the medium is not advisable.

The research identified in the present invention also shows that media with conductivities below 2.10-3 ohm+-'es-' are not practical due to the insufficient rate of oxide film formation within the media. It has been shown that any available aqueous coolant can be used within the conductivity range.

The amplitude of the rectified voltage is set in the range of 5 to 35V. Voltages above 35V cause repassivation, i.e. dissolution of the oxide film, increasing the power consumption of the process, and furthermore, the discharge causes galvanic fragmentation of the oxide film; at voltages below 5V, the oxide film is crushed by the grinding wheel. Formed only in separate parts of the working surface of the car, this impairs all machining properties.

The DC voltage amplitude should be selected experimentally for each material being machined, the production process and the type of grinding wheel;
Also, depending on the requirements placed on the article, there is an individual optimum value of this parameter which provides a minimum amount of grinding wheel wear as well as a stable cutting capacity of the grinding wheel over time.

Even with equal amplitudes, the average voltages (and therefore average currents) are different, so the selection of voltage amplitude values is still not sufficient, and also for rapid formation of the oxide film. Ripples not exceeding 10-15%
It has been found that by using this method, the oxide film can be completely restored while the grinding wheel remains in the oxidized region.

For a rectified voltage amplitude equal to 32 V, a pulsation rate equal to 12% and a medium conductivity equal to 5.1010-3 oh'ca-', the grinding method of the invention is the most versatile, i.e. for different types. grinding wheels make it possible to have considerably high technical and economical indices when machining a wide range of materials and workpieces in different production operations.

For a better understanding, the invention will be explained in more detail with reference to an embodiment shown in a schematic diagram.

Fixed to the grinding wheel head 7 is an electrode 4 which is electrically isolated from the machine frame 8 and is connected to a system 9 which feeds the electrode 4 towards the grinding wheel 1. The negative terminal of the DC voltage source 10 is connected to the electrode 4, and the positive terminal is connected to a metal-bonded diamond grinding wheel (
steel eillilic-bond diamond whe
el). A pulse voltage source 11 is connected to the workpiece 6 via its negative terminal and to the grinding wheel 1 via its positive terminal. A plate made of any conductive material such as steel or brass can be used as the electrode 4. In the examples described below, a cylindrical diamond grinding wheel with a diameter of 250mm and a height of 20mm, having a grain size of 125μ to 160μ and a metal bond made of copper, is used as a tool, and a coolant is used. As conductivity 2.7・10
- Sodium nitrite with ohm-1 cm-' (
The surface to be ground has an area of 24 am” and contains 92% tungsten carbide and 8% cobalt.
It is a workpiece made of hard alloy plate and steel mixed with 1:1 area ratio of drawing plate. The electric depth used was a pulse repetition frequency of 50 Hz and a rated current of 1.
1 kM pulse generator with 5 A and a rated current of 2
It is a 5 A, 1 kW three-phase full wave rectifier.

Grinding conditions (1) Mechanical conditions - Number of table double 5 strokes per minute 7
2 - Value of vertical feed per two strokes, wheel - / two strokes 0.02 (2) Electrical conditions - Amplitude of pulse voltage, V 25 - Amplitude of DC current voltage, V 23 Name to realize this method Next, open the working knee working fluid supply and start and rotate the grinding wheel; place one electrode in contact with the grinding wheel and place an equidistant wheel surface mark on the grinding wheel.
remar & ), separate the ti from the grinding wheel, and set the required interelectrode gap. - Switch on the rectified voltage power supply and form an oxide film on the entire surface of the grinding wheel; - Turn on the pulse voltage power supply and execute the grinding process of the workpiece.

Under the above conditions, in the grinding process of workpieces made of hard alloys and steel, the amount of corrosion current is 2.3 A, the amount of direct current is 11 A, and the production capacity is 800 - plow 3/g.
in, the amount of wear on the grinding wheel is 1.5 mg/g,
The power consumption of the spindle drive is 0.62 k−,
The energy consumed in the process was 49 J/-
The spindle drive power value, which indirectly characterizes the cutting characteristics of the grinding wheel, did not change during the 300 minutes of operation.

When the same workpiece was ground by the prior art diamond electroerosion grinding method, the current was 28 A, the productivity was 620 myh37 sin, the grinding wheel wear was 4.8 mg/g, and the process The amount of electricity consumed was 86J/+*m'. Spindle drive power from 0.63 kM to 0.78 k during 70 minutes operation
increased to ill. After 120 minutes of continuous operation, the grinding process was stopped and the grinding wheel was surface-finished.

〔Effect of the invention〕

Thus, by using the method according to the invention, the grinding process of difficult-to-machine materials can be enhanced, the consumption of expensive diamond tools and cubic boron nitride tools can be reduced, and the power consumption of machining can be reduced. can be lowered,
It also makes it possible to improve the sanitary and health conditions of work.

The method according to the invention can be applied in metalworking plants where parts made of hard, brittle or tough materials are ground.

[Brief explanation of drawings]

The figure is a schematic diagram of a machine for implementing the abrasive electrocorrosion grinding method according to the present invention. As for the reference numbers, 1 is the grinding wheel, 2 is the grinding area, 3 is the electrochemical oxidation treatment area, 4 is the electrode, 5 is the gap between the electrodes, 6 is the workpiece, 7 is the grinding wheel head, 8 is the machine frame, 9 an electrode feeding system, 10 a DC voltage source, and 1
1 is a pulse voltage source.

Claims (4)

[Claims] (1) With a metal-coupled grinding wheel and a coolant, a pulsed voltage is applied to the grinding wheel within the grinding zone of the workpiece, while electrodes for exerting an additional electrical effect on the grinding wheel are in the grinding zone. In the method of galvanic erosion grinding of an abrasive material, the electrodes are applied with a rectified voltage having an amplitude and a pulsation rate that results in the formation of an insulating oxide film on the surface of the grinding wheel, and the cooling liquid is ^-^3ohm^-^1cm^
-^1 to 2.10^-^2ohm^-^1cm^-
A method for electro-corrosion grinding of an abrasive material characterized by having an electrical conductivity of ^1. (2) The method for electrolytic corrosion grinding of an abrasive material according to claim 1, wherein the amplitude of the rectified voltage is set within a range of 5V to 35V. (3) The abrasive electrolytic corrosion grinding method according to claim 1, wherein the pulsation rate of the rectified voltage is set to be between 10% and 15%. (4) The rectified voltage applied to the electrode (4) has an amplitude of about 32V and a pulsation rate of about 12%, and the coolant used is about 5.10^-^3ohm^-^1cm^- 2. The method of electrolytic corrosion grinding of an abrasive material according to claim 1, wherein the abrasive material has an electrical conductivity of ^1.