Electrode generating hydro-dynamic pressure in combination with grinding wheel

There is disclosed an electrode 10 generating hydro-dynamic pressure for electrolytic dressing grinding. The electrode has a plurality of narrow portions 11 having constant gaps from a processed surface 1a of a grinding wheel 1, and a plurality of concave portions 12 each disposed between the narrow portions and having a gap wider than the narrow portion. A section of flow path (gap) formed between the grinding wheel 1 and the electrode 10 becomes concave/convex along a moving direction of the grinding wheel 1. When the liquid repeatedly flows through the concave/convex gap, dynamic and static pressures generated in the gap largely fluctuate. By the fluctuation, the adhesion of metal deposits to the narrow portions 11 is reduced, and the concave portions 12 form pockets, so that the electrolytic liquid can be stably supplied and the inclusion of air can be reduced.

BACKGROUND OF THE INVENTION 
1. Technical Field of the Invention 
The present invention relates to an electrode generating hydro-dynamic 
pressure which generates a dynamic pressure in a gap with a grinding wheel 
by rotation of the grinding wheel for electrolytic dressing grinding. 
2. Description of the Related Art 
With the recent progress in scientific technique, requirements for 
superfine processing have been rapidly heightened. As mirror surface 
grinding means for satisfying the requirements, the present applicant et 
al. have developed and published an electrolytic in-process dressing 
grinding method (ELID grinding method) (Riken Symposium "Latest Technique 
Trend of Mirror surface Grinding" held on Mar. 5, 1991). 
In the ELID grinding method, as diagrammatically shown in FIG. 1, instead 
of an electrode in conventional electrolytic grinding, an 
electrically-conductive grinding wheel 1 is used, an electrode 2 is 
disposed opposite to the grinding wheel 1 with a gap therefrom, and an 
electrically-conductive liquid 3 is passed between the grinding wheel and 
the electrode to apply a voltage to between the grinding wheel 1 and the 
electrode 2. During electrolytic dressing of the grinding wheel, a 
workpiece is ground by the grinding wheel. Specifically, in the grinding 
method, the metal-bonded grinding wheel 1 is used as an anode, while the 
electrode 2 opposite to the surface of the grinding wheel with a gap 
therefrom is used as a cathode. By performing the electrolytic dressing of 
the grinding wheel simultaneously with grinding operation, the grinding 
performance can be maintained/stabilized. Additionally, in FIG. 1, numeral 
4 denotes a workpiece (material to be ground), 5 denotes an ELID power 
source, 6 denotes a power supplier, and 7 denotes a nozzle of the 
electrically-conductive liquid. 
In the ELID grinding method, even if abrasive grains are fine, the clogging 
of the grinding wheel does not occur through the electrolytic dressing of 
the abrasive grains. By making fine the abrasive grains, a remarkably 
superior processed surface like a mirror surface can be obtained by the 
grinding processing. Therefore, it is expected that the ELID grinding 
method be applied to various grinding processings as means which can 
maintain the ability of the grinding wheel in an operation ranging from a 
highly efficient grinding to a mirror surface grinding and which can form 
in a short time a highly precise surface unable to be formed in the prior 
art. 
In the ELID grinding described above, on the surface of the cathode 2 
opposed to the anode of the metal-bonded grinding wheel 1, a 
characteristic phenomenon is observed that metal components of a grinding 
wheel bonding material are deposited based on the principle of electric 
plating, contrary to the electrolytic erosion of the grinding wheel 
bonding material, i.e., anode reaction. In principle, since the deposits 
on the cathode surface have a composition close to that of a pure metal, 
electric conductivity is not lost. However, when the ELID grinding 
processing is performed for a long time, problems arise: (1) the gap 
between the cathode and the grinding wheel is filled with the deposits; 
(2) a sufficient amount of electrolytic liquid cannot be stably supplied; 
and further (3) air is drawn in the electrode gap to make unstable the 
electrolytic dressing of the grinding wheel. Therefore, ELID grinding 
effect cannot be maintained at the time of a continuous unmanned 
operation, and it has been recognized that the problems should be solved 
to realize complete automation. 
SUMMARY OF THE INVENTION 
The present invention have been developed to solve the problems. 
Specifically, an object of the present invention is to provide an 
electrolytic dressing grinding electrode in which (1) the generation of 
deposits deposited on a cathode surface can be reduced, (2) a sufficient 
amount of electrolytic liquid can be stably supplied, and (3) inclusion of 
air into an electrode gap can be reduced, so that an unmanned operation 
for ELID grinding can be stably performed for a long time. 
To attain this and other objects, the present invention provides an 
electrode generating hydro-dynamic pressure for electrolytic dressing 
grinding which is disposed opposite to a surface to be processed of an 
electrically-conductive grinding wheel with a gap therefrom. An 
electrically-conductive liquid is passed between the electrode and the 
processed surface to apply a voltage therebetween, and a workpiece is 
ground while electrolytic dressing of the grinding wheel is performed. The 
electrode has a plurality of narrow portions arranged at intervals in a 
moving direction of the grinding wheel and having constant gaps from the 
processed surface of the grinding wheel, and a plurality of concave 
portions each disposed between the narrow portions and having a gap wider 
than the narrow portion. 
In the structure of the present invention, the electrode disposed opposite 
to the processed surface of the electrically-conductive grinding wheel 
with a gap therefrom has a plurality of narrow portions having constant 
gaps from the processed surface of the grinding wheel and a plurality of 
concave portions disposed between the narrow portions and having gaps 
wider than the narrow portions. Therefore, the section of a flow path of 
the electrically-conductive liquid formed between the grinding wheel and 
the electrode becomes wider where the concave portions exist, and narrower 
where no concave portions exist, so that the gap becomes concave/convex 
along the moving direction of the grinding wheel. 
Therefore, the grinding wheel rotates along the concave/convex electrode 
surface, and the electrically-conductive liquid (electrolytic liquid, 
fluid) with which the gap is filled is circulated as the grinding wheel 
rotates. When the liquid repeatedly flows through the concave/convex gap, 
a dynamic pressure generated therebetween largely fluctuates. 
Specifically, the gap between the grinding wheel and the electrode has an 
outer peripheral portion open to atmospheric air. Therefore, according to 
so-called Bernoulli's theorem, the dynamic pressure is increased while a 
static pressure is reduced in the narrow portion in which the gap is small 
and the flow rate is high (close to the rate of the grinding wheel). 
Contrarily, the dynamic pressure is reduced while the static pressure is 
increased in the concave portion in which the gap is large and the flow 
rate is low. Therefore, a pressure pushed from the electrode side is 
exerted on the narrow portion, while a pressure drawn toward the electrode 
side is exerted to the concave portion. 
As a result, the flow rate, the dynamic pressure and the static pressure 
largely fluctuate along the moving direction of the grinding wheel in the 
flow path of the electrically-conductive liquid, i.e., the concave/convex 
gap, and the adhesion of metal deposits which move to the cathode surface 
can be reduced by the fluctuation. Specifically, since the flow rate is 
high and the static pressure is large in the narrow portion in which the 
electrode closely abuts on the grinding wheel, most of the metal 
components of the grinding wheel bonding material are forced to flow to 
the concave portion without reaching the electrode. Therefore, the 
adhesion of the metal deposits to the narrow portions important for ELID 
grinding processing is reduced. Additionally, since the gap of the concave 
portion is set sufficiently larger as compared with the narrow portion, 
the adhesion of the metal deposits to the concave portion produces no 
adverse influence. 
The concave portion formed in the electrode forms a source for generating a 
pressure fluctuation. Moreover, since the concave portion forms a pocket 
to hold electrolytic liquid (electrically-conductive liquid) containing no 
air, the electrolytic liquid can be stably supplied to the narrow portion 
with a narrow gap adjacent to the concave portion from the concave 
portion. Additionally, by stably supplying the electrolytic liquid, the 
air drawn into the electrode gap can be reduced. Therefore, ELID grinding 
can be performed in an unmanned operation stably for a long time. 
According to a preferable embodiment of the present invention, the concave 
portions are formed in such a manner that the gap changes along the moving 
direction of the grinding wheel. In the structure, the pressure 
fluctuation along the grinding wheel can be appropriately adjusted. 
Furthermore, the concave portion may be provided with a gradually changing 
portion in which the gap gradually changes along the moving direction of 
the grinding wheel and a rapidly changing portion in which the gap rapidly 
changes. In the structure, the pressure fluctuation can be set large in 
the rapidly changing portion, and small in the gradually changing portion. 
According to another preferred embodiment, the concave portions comprises a 
plurality of holes formed along the moving direction of the grinding 
wheel. The holes may have circular, rectangular, triangular and other 
optional configurations, and have optional size or distribution. Thereby, 
the pressure fluctuation along the grinding wheel can be adjusted in a 
wide range. 
Other objects and advantageous characteristics of the present invention 
will become apparent from the following description with reference to the 
accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Hereinafter, preferred embodiments of the present invention will be 
described with reference to the drawings. Additionally, in the figures, 
common portions are denoted by the same reference characters, and 
duplicated description is omitted. 
FIG. 2A is a side view of an electrode generating hydro-dynamic pressure of 
the present invention, and FIG. 2B is an enlarged view of a portion B. 
Additionally, the electrode can be applied to the ELID grinding device 
shown in FIG. 1. 
Specifically, such as electrode 2 shown in FIG. 1, an electrode generating 
hydro-dynamic pressure 10 of the present invention is an electrolytic 
dressing grinding electrode which is disposed opposite to a processed 
surface of the electrically-conductive grinding wheel 1 with a gap 
therefrom. While the electrically-conductive liquid 3 is passed between 
the electrode 10 and the processed surface, a voltage is applied by the 
ELID power source 5. While electrolytic dressing of the grinding wheel 1 
is performed, the workpiece 4 is ground. 
In FIG. 2A, the electrode 10 has a plurality of narrow portions 11 and a 
plurality of concave portions 12 each disposed between adjoining narrow 
portions on its surface opposite to the grinding wheel 1. The narrow 
portions 11 are arranged at intervals in the moving direction of the 
grinding wheel 1, and have constant gaps from a processed surface 1a of 
the grinding wheel 1. Additionally, the concave portion 12 has a gap from 
the processed surface 1a wider than the narrow portion 11. Specifically, 
in FIG. 2A, numeral 11 represents a portion other than the concave portion 
12 on the surface of the electrode 10 opposite to the grinding wheel 1. 
The portion has a constant gap from the grinding wheel, and forms a 
narrowest portion between the electrode 10 and the grinding wheel 1. 
In the structure described above, dirt on the electrode generated at the 
time of ELID grinding can be avoided, and water flow can simultaneously be 
secured. Specifically, according to the structure of the present 
invention, the electrode 10 disposed opposite to the processed surface 1a 
of the electrically-conductive grinding wheel 1 with a gap therebetween 
has a plurality of narrow portions 11 having a constant gap from the 
processed surface of the grinding wheel and a plurality of concave 
portions arranged between the narrow portions 11 and having a wider gap 
than the narrow portions 11. Therefore, the section of a flow path of the 
electrically-conductive liquid 3 formed between the grinding wheel 1 and 
the electrode 10 becomes wider where the concave portions 12 exist, and 
narrower where no concave portions 12 (narrow portions 11) exist, so that 
the gap becomes concave/convex along the moving direction of the grinding 
wheel 1. 
Therefore, the grinding wheel 1 rotates along the concave/convex surface 
(inner surface in the example) of the electrode 10, and the 
electrically-conductive liquid 3 (electrolytic liquid, fluid) with which 
the gap is filled is circulated as the grinding wheel 1 rotates. When the 
liquid repeatedly flows through the concave/convex gap, a dynamic pressure 
generated therebetween largely fluctuates. Specifically, the gap between 
the grinding wheel 1 and the electrode 10 has an outer peripheral portion 
open to atmospheric air. Therefore, according to so-called Bernoulli's 
theorem, the dynamic pressure is increased while a static pressure is 
reduced in the narrow portion 11 in which the gap is small and the flow 
rate is high (close to the rate of the grinding wheel). Contrarily, the 
dynamic pressure is reduced while the static pressure is increased in the 
concave portion 12 in which the gap is large and the flow rate is low. 
Therefore, a pressure pushed from the side of electrode 10 is exerted on 
the narrow portion 11, while a pressure drawn toward the electrode side is 
exerted to the concave portion 12. 
As a result, the flow rate, the dynamic pressure and the static pressure 
largely fluctuate along the moving direction of the grinding wheel 1 in 
the flow path of the electrically-conductive liquid 3, i.e., the 
concave/convex gap, and the fluctuation can reduce the adhesion of metal 
deposits which move to the cathode surface. Specifically, since the flow 
rate is high and the static pressure is large in the narrow portion 11 in 
which the electrode 10 closely abuts on the grinding wheel 1, most of the 
metal components of the grinding wheel bonding material are forced to flow 
to the concave portion 12 without reaching the electrode. Therefore, the 
adhesion of the metal deposits to the narrow portions 11 important for 
ELID grinding processing is reduced. Additionally, when the gap of the 
concave portion 12 is set sufficiently larger as compared with the narrow 
portion 11, the adhesion of the metal deposits to the concave portion 
produces no adverse influence. 
The concave portion 12 formed in the electrode 10 forms a source for 
generating a pressure fluctuation. Moreover, since the concave portion 
forms a pocket to hold electrolytic liquid (electrically-conductive 
liquid) containing no air, the electrolytic liquid can be stably supplied 
to the narrow portion 11 with a narrow gap adjacent to the concave portion 
12 from the concave portion 12. Additionally, by stably supplying the 
electrolytic liquid, the air drawn into the electrode gap can be reduced. 
Therefore, ELID grinding can be performed in an unmanned operation stably 
for a long time. 
Moreover, as shown in FIG. 2B, in the embodiment, the concave portions 12 
are formed in such a manner that the gap changes along the moving 
direction of the grinding wheel 1. Specifically, the concave portion may 
be provided with a gradually changing portion 12b in which the gap 
gradually changes along the moving direction of the grinding wheel 1 and a 
rapidly changing portion 12a in which the gap rapidly changes. 
Additionally, in the embodiment, the gradually changing portion 12b is 
formed on the upstream side, while the rapidly changing portion 12a is 
formed on the downstream side relative to the rotary direction of the 
grinding wheel 1, but the arrangement of the rapidly changing portion 12a 
and the gradually changing portion 12b may be reversed. In the structure, 
the pressure fluctuation is set large in the rapidly changing portion 12a, 
and small in the gradually changing portion 12b, so that the pressure 
fluctuation along the grinding wheel 1 can be appropriately adjusted. 
FIG. 2C is an enlarged view similar to FIG. 2B, showing another embodiment 
of the present invention. As shown in FIG. 2C, the concave portions 12 may 
comprise a plurality of holes 12c formed along the moving direction of the 
grinding wheel 1. The holes 12c may have, for example, circular, 
rectangular, triangular and other optional configurations. The holes may 
be extended in the width direction of the grinding wheel 1, or maybe 
distributed independently. Specifically, the holes 12c may have optional 
size or distribution. Thereby, the pressure fluctuation along the grinding 
wheel 1 can be adjusted in a wide range. 
As aforementioned, in the ELID grinding device of the present invention, a 
special surface structure is formed in which a dynamic pressure is 
generated on the cathode surface by its relative movement to the 
metal-bonded grinding wheel and a plurality of electrolytic liquid pockets 
are produced. Thereby, cathode products in ELID grinding are reduced. 
EXAMPLES 
Examples of the present invention will next be described. 
The electrode 10 generating hydro-dynamic pressure shown in FIG. 2A was 
prepared by way of trial and applied to electrolytic dressing grinding. 
The surface of the experimental electrode is provided with a multiplicity 
of stepped concave portions 12 each having the rapidly changing portion 
12a and the gradually changing portion 12b, and a dynamic pressure can be 
generated in the electrolytic liquid 3 by rotation of the grinding wheel. 
Additionally, the experimental electrode is designed in accordance with a 
grinding wheel diameter of 150 mm, the opposed area has a size of about 
1/4 of a grinding wheel peripheral length, and each groove has a maximum 
depth of about 1 mm. 
A device and system for use in an experiment are as follows: 
(1) Grinding Device 
A reciprocating type surface grinding machine was used, and ELID electrode, 
a power supplier were mounted on the machine for use in the experiment. 
(2) Grinding Wheel 
A cast-iron metal bond diamond grinding wheel (dia. 150 mm.times.width 10 
mm, straight type) was used. For grain sizes, #325 was used for rough 
grinding, while #4000 was used for finish grinding. In either grinding 
concentration degree was 100. 
(3) ELID Power Source 
For ELID grinding an exclusive high-frequency pulse (DC-direct current) 
power source was used. 
(4) Others 
For the electrolytic liquid, standard water-soluble electrolytic liquid was 
diluted 50 times by distilled water and used. 
(Experiment Method) 
After truing of each grinding wheel by a rotary truer using a #80 GC 
grinding wheel, rough grinding of a tungsten carbide was first performed 
with #325. Subsequently, a #4000 grinding wheel was used to examine 
electrolytic dressing characteristics of the electrode generating 
hydro-dynamic pressure, and ELID mirror surface grinding effect of the 
tungsten carbide were confirmed. Processing results were evaluated mainly 
by surface roughness (roughness measuring apparatus). 
(Experiment Results) 
(1) Electrical Behavior of Initial Electrolytic Dressing 
First, checking results of the electrical behavior of the initial 
electrolytic dressing by the electrode generating hydro-dynamic pressure 
are shown in FIG. 3. As compared with the usual electrode operation, a 
current value tends to be slightly large, while a voltage value tends to 
be reduced. 
(2) Insulating Layer by Electrolytic Dressing 
FIG. 4 shows checking results of the thickness of a insulating layer formed 
on the grinding wheel surface subjected to the initial electrolytic 
dressing by the electrode generating hydro-dynamic pressure. As a result, 
the thickness of the layer was smaller than that of a usual electrode, and 
became nearly 1/2 when 90V was applied. Since the average gap becomes 
larger than usual, the layer supposedly becomes thinner. 
(3) ELID Mirror Surface Grinding Effect 
Furthermore, the roughly ground tungsten carbide was subjected to ELID 
grinding using the #4000 grinding wheel to which the initial dressing was 
applied by the electrode generating hydro-dynamic pressure. Results are 
shown in FIG. 5. As seen from FIG. 5, although a maximum 1 mm gap exists, 
a mirror surface state of a quality equal to or higher than the quality 
obtained through ELID mirror surface grinding by the usual electrode can 
be realized. 
(4) Comparison of Cathode Products 
In the usual electrode, depending on the material to be processed, metal 
deposits on the electrode are accumulated 100 to 150 microns or more in 
about eight hours. In this case, usually the first set electrode gap of 
100 microns is almost filled. 
On the other hand, when the electrode surface is provided with stepped 
concave/convex portions as in the present invention, there is a slight 
dispersion in data measurement, but the amount of metal deposits is 
suppressed to about 20 to 30 microns. However, a sufficient thickness of 
electrolytic insulating layer was formed on the grinding wheel surface, a 
sufficient ELID mirror surface grinding effect was confirmed, and 
remarkably effective results were obtained. 
Specifically, as a result of examination of the electrode generating 
hydro-dynamic pressure surface after ELID mirror surface grinding was 
performed, it was seen that the amount of metal deposits was remarkably 
reduced as compared with the conventional electrode. Moreover, the effect 
of pockets on the electrode surface was used to realize ELID mirror 
surface grinding, and the effect of ELID mirror surface grinding by the 
electrode generating hydro-dynamic pressure could be confirmed. 
Additionally, the electrode generating hydro-dynamic pressure of the 
present invention is not limited to the electrolytic dressing grinding 
electrode shown in FIG. 1, and can be applied to any electrode for 
electrolytic dressing grinding. 
As aforementioned, the electrode generating hydro-dynamic pressure of the 
present invention can (1) reduce the generation of deposits deposited on 
the cathode surface, (2) stably supply a sufficient amount of electrolytic 
liquid, and (3) reduce the inclusion of air into the electrode gap. 
Thereby, ELID grinding can advantageously be performed in an unmanned 
operation stably for a long time, and other superior effects can be 
provided. 
Additionally, although the present invention has been described by some 
preferred embodiments, it will be understood that the scope of rights 
included in the present invention is not limited to the embodiments. On 
the contrary, the scope of rights of the present invention includes all of 
improvements, modifications, and equivalents included in the scope of the 
appended claims.