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Investigation of ElectroDischarge Mechanical Dressing (EDMD) of Diamond
Abrasive Wheels with Conductive Bonds Using Brush Electrodes
Article in Proceedings of the Institution of Mechanical Engineers Part B Journal of Engineering Manufacture · June 2006
DOI: 10.1243/095440505X32922
3 authors, including:
B. Nowicki
Sławomir Spadło
Warsaw University of Technology
Politechnika Świętokrzyska
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Investigation of electro-discharge mechanical dressing
(EDMD) of diamond abrasive wheels with conductive
bonds using brush electrodes
B Nowicki1, R Pierzynowski1*, and S Spadło2
Faculty of Production Engineering, Warsaw University of Technology, Warsaw, Poland
Faculty of Mechanical Engineering, University of Technology in Kielce, Poland
The manuscript was received on 2 February 2005 and was accepted after revision for publication on
22 September 2005.
DOI: 10.1243/095440505X32922
Abstract: The authors have presented a new method of electro-discharge mechanical dressing
of ultra-hard abrasive tools with metal bonds in which brush electrodes were used. This kind of
machining is denoted as EDMD (electro-discharge mechanical dressing) and combines
features of electro-discharge machining with mechanical treatment so that thin layers of the
bond are removed. Moreover, the brush electrode offers the additional possibility of
introducing the advantageous (having the anchorage of the abrasive grains in mind) state of
compressive stress and strain hardening of the outer layer of the bond.
Keywords: electro-discharge machining, surface layer, dressing, diamond abrasive wheels
The progress observed in the field of materials engineering and the improved quality of the mechanical
treatment (hardness, material strength, wear resistance) of the construction materials is accompanied
by an increase in the abrasive machining share in
manufacturing processes and by an increase in
demand for modern abrasive tools. The abovementioned considerations necessitate notable
progress in the development of modern abrasive
tools including metal-bonded grinding wheels and
it has recently taken place. The diamond tools, taking the forms of wheels, honing stones, abrasive
strips, etc., with metal bonds, are used more and
more widely in industries such as mechanical engineering, glasswork, optical, stonework, geological
drilling, dental services, and many others and their
share in abrasive machining approaches 20 per cent.
The principal drawback of dressing the ultra-hard
materials results from the abrasive hardness and
high strength of the metal bond. A few methods
are used in profiling and sharpening diamond
*Corresponding author: Faculty of Production Engineering,
Warsaw University of Technology, Al. Niepodleglosci 222, r. 162,
Warsaw, 00-663, Poland. email: rpierzyn@meil.pw.edu.pl
JEM294 IMechE 2006
wheels with metal bond apart from dressing:
electro-discharge machining (EDM), electrochemical machining (ECM), abrasive machining of
honing sticks, abrasive jet, and so on [1, 2]. The
operation of such grinding wheels includes wear of
the abrasive grains, which results in lowering the
height of protrusions over the bond surface, dulling
the corners and cutting edges, gumming the wheel
active surface with the erosion products, and
changes in the wheel macrogeometry. In the wake
of these processes, grinding wheels become deprived
of their operational features (mainly their cutting
properties) [3, 4]. Sharpening of the diamond wheels
should imply minimum wheel loss because of their
high manufacturing costs [5, 6]. The standard
methods of sharpening used so far are connected
with the technical problems and are in numerous
cases impractical or inefficient.
This requirement is met in the case of a new
method for electro-erosion wheel sharpening, as
suggested by the authors, where rotary brush electrodes have been employed. This method has been
denoted as EDMD (electro-discharge mechanical
dressing). It combines features of electro-erosion
and mechanical machining without disadvantageous thermal interactions. EDMD enables thin
bond layers to be removed and contributes to the
Proc. IMechE Vol. 220 Part B: J. Engineering Manufacture
B Nowicki, R Pierzynowski, and S Spadło
introduction of a favourable state of stress, advantageous for locking the abrasive grains in the wheel
bond and for strain hardening of the outer layer of
the bond. EDMD is an effective method of sharpening the abrasive tools of the following kinds: abrasive
wheels, hones, multilayer abrasive tapes containing
metal bonds, etc.
Analysis of the methods used so far for the ultra-hard
abrasive wheels indicates their diversified usefulness. Conventional methods of wheel dressing,
which used to be simple and popular, cannot be
used for the effective shaping of the ultra-hard
active wheel surfaces. Their disadvantages consist
in superfluous wear of the expensive wheels and
many problems with automation of the sharpening
process [5].
Methods of abrasive microdressing that can be
used for removing the abrasive layers of several mm
in thickness are difficult for practical realization
and can be employed in a limited range for sharpening wheels intended for particularly fine grinding [7].
Methods of abrasive jet sharpening do not ensure
uniformity of the operating conditions within the
jet range and are difficult to employ on the grinders
because they are hazardous for the environment
and for the machine tool durability.
Electro-discharge sharpening employing typical
conditions of the process run can introduce
thermal-induced damage of the abrasive grains and
it results in an unfavourable state of stress in the
surface layer. The practical implementation of this
method necessitates the use of expensive instruments such as generators, control systems for the
working electrode feeding movement, systems for
the dielectric supply etc. Because of the above,
such methods are rarely used [8].
Electrochemical dressing employing direct current
is actually considered as the most prospective
method for shaping the ultra-hard active wheel
surfaces [1]. Trials concerning the ECM including
typical conditions are much limited. The basic disadvantages consist of difficulties in shaping the
wheel active surface and restoring its cutting properties which have been lost during grinding. A lot of
research has been devoted to this issue [1, 7, 8].
Disadvantages of the above-mentioned methods
justify the purposefulness of continuing research in
the field of the unconventional methods of sharpening while paying special attention to the combined
erosion and mechanical methods being analysed
by the authors.
Proc. IMechE Vol. 220 Part B: J. Engineering Manufacture
Analysis of the erosion–mechanical machining with
a rotary brush electrode application [9, 10] and preliminary research show that it is possible to sharpen
the abrasive tools with the EDMD method. The
method is featured by discharges at a low energy
level and by mechanical interaction of the elastic
elements where the rotary brush is an electrode,
resulting in material removal from the active wheel
surface. Then, the abrasive grains are exposed
because of the bond material removal due to electric
erosion (which is responsible for the sharpening
effect in the first place); however, mechanical hardening of the bond superficial layers also takes place
due to the dynamic interaction of the brush elements with the metal bond. Thus, in the method presented, the controllable compressing stress can be
introduced into the surface layer of the metal bond
(it can be controlled by the appropriate selection of
the process parameters). The authors’ own experimental research proved that machining with the
pulse generator in the ‘off ’ position results in inducing compressive stress in the surface layer of the
grinding wheel subjected to the machining process
[9]. The advantage of the presented method is that
the spark voltage employed in this EDM variety is
considerably smaller than in the case of standard
EDM (the power supply voltage in the beginning is
considered to amount to 3–5 V and is just 1/50 of
the voltage that is necessary to initiate discharges
in a typical EDM case). The low-voltage discharges
are initiated by the sudden rupture of contact
between the bond and the brush filaments (due to
the brush rotary motion or vibrations of the brush
wires). Generation of the electric discharges is
possible only in the area of contact between the
brush and the conductive bond. Selection of the
proper machining parameters (voltage, wire diameter, wire material, etc.) makes it possible to
remove thin layers of bond in a controllable way,
without any thermal damage to the diamond grains.
The diagram in Fig. 1 shows the erosion–
mechanical dressing process used in the case of
abrasive tools. In the EDMD process, the work electrode is in the form of a rotary brush (2). The
machining processes are carried out in the presence
of a working fluid which is supplied by a nozzle (3).
The mutual location of the tool and the workpiece
is such that the individual wires of the brush are
deflected by the D value during the brush motion
along the machining surface and the pressure value
is high enough to initiate a spark discharge. After
the discharge has been initiated and the plasma
channel has been formed, a sudden local temperature increase of the microroughness peaks is noticed
and melting, evaporating, and bond material
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Investigation of EDMD of diamond abrasive wheels
Fig. 1 Schematic diagram of the erosion–mechanical dressing process (EDMD) principle
removal take place. The main factors contributing to
the EDMD process are: electro-erosion, mechanical,
and thermomechanical interactions.
Initial experiments [9, 10] made it possible to determine the most important parameters that influence
the machining process. In order to determine the
ranges of machining parameters, a series of singlefactor experiments have been performed where the
following variables have been taken into account:
machining voltage (U), brush electrode deflection
(D), wire diameter (d), peripheral speed of the electrode (v0), and feed rate (vf). The wires made of
constructional steel of standard quality St5, tungsten, and stainless steel 1H18N9 were used in the
experiment. In the preliminary investigations a water
solution of sodium silicate of low concentration, air,
water, and a typical coolant for the grinding process
were used as working media.
Research has shown that using air as the natural
environment initiates the graphitization effect for
much lower machining voltages than technological
water and water–oil emulsion. The results of investigations of the efficiency of diamond wheel sharpening in the above-mentioned media were shown in
Fig. 2. Water–oil emulsion has been selected for
further experiments as the natural medium for the
grinding process. It ensures good results of diamond
wheel sharpening and because it is a regular grinding medium there is no need to use extra hydraulic
systems for the liquids that are employed in wheel
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Machining with wire electrodes at low voltages is
sensitive to selection of proper force applied by the
brush to the machined surface. Optimum forces Fn
range between 1 and 3 N. For the force values above
3 N short-circuits are prevalent and for forces lower
than 1 N the interactions are too weak to initiate
sparks. The diagrams of voltages for various loads
were presented in Fig. 3.
Analysis of the experimental results made it possible to determine the variance ranges of the following
machining parameters: deflection D ¼ 0.1–1 mm,
wire diameter d ¼ 0.1–0.7 mm, peripheral speed of
the wheel v0 ¼ 3.76 m/s, feed rate vf ¼ 4.7 mm/min,
and voltage U ¼ 3–12 V. The advantageous localization of the discharges and their low energy do not
have an adverse effect on the diamond grains (graphitization, cracking, and crush dressing) and they
do not cause tensile stresses or microcracks in the
bond surface layers, or even high roughness of the
active wheel surface that diminishes the cutting
properties of the wheels. It has been confirmed in
the hitherto performed investigations that the spark
discharges of low-energy level do not contribute to
the diamond grain destruction and that they effectively remove the small chips gummed up to the
active wheel surface.
The usage of brush electrodes in the process of
sharpening metal-bonded grinding wheels is connected with the additional abrasive grain support.
It is because of overshadowing of the areas placed
directly behind the abrasive grains that are attacked
simultaneously by the unilateral interaction of the
brush wires and erosion (Fig. 4). As a result of the
favourably shaped stereo metric active wheel surface
features, the force of locking the grains in the bond is
Proc. IMechE Vol. 220 Part B: J. Engineering Manufacture
B Nowicki, R Pierzynowski, and S Spadło
Medium mass decrement
∆m [mg]
Fig. 2 Relationship between the efficiency of diamond, metal-bonded hone sharpening, and the employed medium type
Fig. 3 Typical voltage diagrams for various forces
applied by the brush: (a) Fn ¼ 4 N – excessive,
(b) Fn ¼ 1 N – insufficient, (c) Fn ¼ 2 N – proper
larger than for any other methods. The strain hardening phenomenon of the surface bond layers is an
important factor, contributing to the increase in the
locking force mentioned above. It results from the
dynamic interaction between the working electrode
wires and the wheel bond material. A further
improvement in the grain locking will be possible
if the following two processes are consecutively
applied: erosion–mechanical machining and
mechanical interaction of the brush without the
electric power supply.
The latter treatment is used for diminishing the
tensile stress level or generating the compression
stress in the surface layer, and consecutively for the
improved locking of the abrasive grains. The desired
level of the stress and strain hardening can be
obtained by appropriate selection of the mechanical
process. The applied experimental investigations
have been performed as a two-stage procedure:
(a) investigation of how the EDMD conditions
influence the results, i.e. efficiency of
Proc. IMechE Vol. 220 Part B: J. Engineering Manufacture
sharpening and state of the cutting grains and
wheel active surface;
(b) investigation of the changes of the wheel active
surface state and results of grinding using
wheels that were sharpened by the presented
method, compared with the results obtained
using the same wheels, which were sharpened
by a conventional method.
Examination of the influence of sharpening a diamond wheel with a metal bond on the wheel active
surface state using the EDMD method has been
performed with the metal-bonded hones of size
L · B · H ¼ 10 · 5 · 8 mm and grain size a ¼ 400 mm.
The layout of the experimental set-up for investigating the wheel sharpening process is presented in
Fig. 1. The hones were fixed in a vice and were
connected to the positive pole of a d.c. generator,
with a rotary brush as the working electrode connected to the negative pole of the generator and
slightly pressed against the hone surface. The
brushes of diameter D ¼ 80 mm and wires of conventional carbon steel and diameter d ¼ 0.2 mm were
used. Preliminary investigations of the EDMD process, which were carried out for the following media,
industrial water, water–oil emulsion, and the air,
have shown that water–oil emulsion should be
further investigated as a natural media for the
EDMD processes using grinders.
The most important investigations were carried
out according to an experimental design principle,
with the following independent variables:
(a) brush rotational speed;
(b) force exerted by brush wires on the surface;
(c) interelectrode voltage.
Photographs of typical hone active surfaces after
being sharpened by the EDMD method are shown
in Figs 5(a) and (b). The hones which were sharpened at U ¼ 9 V are featured by distinctly exposed
grains with sharp corners and edges which are present well above the bond level.
JEM294 IMechE 2006
Investigation of EDMD of diamond abrasive wheels
Fig. 4 SEM photograph of an individual grain on the hone surface: (a) sharpened by the EDMD (with visible effect of the
grain support), (b) worn grain (·100)
Fig. 5 Image of surfaces of hones sharpened at working voltages: (a) U ¼ 9 V, (b) U ¼ 12 V (visible traces of graphitization
have been marked)
(a) abrasive grains after machining at voltages U
lower than 9 V (a ¼ 400 mm) do not display any
signs of graphitization and are featured with
sharp and not damaged corners and edges;
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Mass decrement [mg]
The surface of the hone sharpened at U ¼ 12 V is
presented in Fig. 5(b). The dark diamond grains
with rounded corners and edges are visible on the
surface and result from graphitization induced by
the interaction of spark channels transporting high
energy. The relationship between machining conditions and hone mass decrement has been shown in
Fig. 6. This relationship is useful when calculating
the time necessary for grinding wheel sharpening
with the predetermined thickness of the removed
wheel layer.
The analysis of the investigation results has
shown that:
speed n [rpm.]
Voltage U
Fig. 6 Efficiency of diamond hone sharpening versus
machining parameters (water–oil emulsion as
medium, d.c. generator)
Proc. IMechE Vol. 220 Part B: J. Engineering Manufacture
B Nowicki, R Pierzynowski, and S Spadło
(b) behind the grains there is the so-called shaded
zone, a strip (elevation) of the bond material
that can operate as an additional grain support
during the grinding process;
(c) after a prolonged machining process without
the transverse movement of the hone relative
to the brush electrode, microgrooves may
appear on its surface as a result of multiple
interaction from the wires in the same place of
the hone;
(d) application of voltages U greater than 10 V (a ¼
400 mm) may result in partial or total
graphitization of the diamond grains;
The performed investigations have shown that for a
wide range of voltages, wire diameters of the brush,
and kinematics parameters of the EDMA process, a
satisfactory condition of the wheel active surface
can result.
The investigations of the results of machining with
the grinding wheels have been carried out on a type
SPC-20 plane grinder. The experiments included
the following measurements:
(a) cutting forces (Fy and Fc) using a strain gauge
(b) volume of material (tungsten carbide) removed
in the grinding process;
(c) linear removal rate (for standard times of 5 and
10 s) for a special sample made of tungsten
carbide, pressed against the wheel surface with
constant force;
(d) roughness of the ground element and a special
sample of tungsten carbide;
(e) wheel active surface roughness as measured on
the replication surface;
(f) visual inspection of the wheel surface condition
as based on the microscopic images.
The wheel active surface has been examined by
special replication surfaces which mirrored the
active surface of the grinding wheel. Then, the active
wheel surface was measured with a Talysurf-10
profilometer equipped with a computer system for
analysis of the surface geometric structure. The
wheel decrement (wear) has been determined using
an artificial basic method. The wheel surface was
marked with scratches of special geometry before
the machining and after each experiment a replication of this scratch was made and then its depth
was measured using a profilometer.
The experiments included wheels sharpened by
EDMD with appropriate parameter levels applied.
Moreover, for comparison purposes these wheels
were sharpened using a block of the abrasive material; this method is the most widely used in industrial
practice. The voltage applied when sharpening by
the EDMA method has been selected within the
Proc. IMechE Vol. 220 Part B: J. Engineering Manufacture
range where graphitization does not occur, namely
U 6 9 V, and sharpening time was selected based
on the results of the previous hone sharpening so
that the cutting grain edges are exposed up to a
given level above the bond and it is usually equal to
30–50 per cent of the average grain size a.
All measurements have been carried out for
strictly defined periods of the cutting wheel operation time t ¼ 1, 2, 4, 8, 16, 32, 48, and 64 min.
Figure 7 shows diagrams of the tangential force for
grinding of tungsten carbide with the diamond
grinding wheel, grain size a ¼ 100 mm, metalbonded, sharpened conventionally, and by EDMD
applying various parameters. Analysis of the diagrams shows that only for very short machining
times there are differences between the tangent
component of the cutting force measured for conventional and EDMD sharpening. The Fc force in
the latter case is up to 40 per cent larger when the
grinding time t ¼ 1–2 min. There are no significant
differences between the relevant forces for t > 4 min.
The relationship between productivity and
machining time is similar (Fig. 8). Differences that
count appeared only in the case of conventionally
sharpened wheels when machining times were lower
than t ¼ 4 min (right after the wheel sharpening). For
a longer machining time the differences are insignificant and the highest efficiency was obtained for
the wheel sharpened by EDMD and for the highest
parameters of sharpening.
Figure 9 shows typical roughness profilograms for
the tungsten carbide ground in the experiments.
Analysis of the profilograms shows that the roughness height for surfaces sharpened by the EDMD
method is a little lower than in the case of machining
with wheels sharpened by the conventional method.
Fc force [N]
E 3V 17 min
E 3V 30 min
E 4V 5 min
machine time [min]
Fig. 7 Tangential grinding force versus time for a grinding wheel sharpened by EDMD (with various
machining parameters applied:E3V17min denotes
the EDMD method, U ¼ 3 V, t ¼ 17 min; E3V30min
denotes the EDMD method, U ¼ 3 V, t ¼ 30 min;
E4V5min denotes the EDMD method, U ¼ 4 V,
t ¼ 5 min) and by the abrasive method which
denotes ceramic
JEM294 IMechE 2006
Height decrement [mm]
Investigation of EDMD of diamond abrasive wheels
E 3V 17 min
E 3V 30 min
E 4V 5 min
machine time [min]
Fig. 8 Grinding efficiency for sintered carbide sample ground versus time for a grinding wheel sharpened by EDMD (various machining parameters were used:E3V17min denotes the EDMD method, U ¼ 3 V, t ¼ 17 min) and by the abrasive method, which denotes ceramic
Fig. 9 Surface profilograms for sintered carbide sample ground by the wheel sharpened by EDMD (various machining
parameters were used) and by the abrasive method. Conventional method: (a) t ¼ 2 min (Ra ¼ 0.54 mm,
Rt ¼ 4.7 mm); (b) t ¼ 48 min (Ra ¼ 0.51 mm, Rt ¼ 4.0 mm); EDMD method: (c) t ¼ 2 min (Ra ¼ 0.43 mm, Rt ¼ 4.2 mm);
(d) t ¼ 46 min (Ra ¼ 0.47 mm, Rt ¼ 3.8 mm)
For both methods, the roughness of ground surfaces
decreases slowly with passing time.
Experimental investigations of diamond metalbonded grinding wheels sharpened by the EDMD
method have shown the following.
1. Localization of discharges and application of the
brush electrodes and d.c. generator which
enables the generation of low-voltage electric
discharges of low-energy level do not cause
graphitization of the diamond grains.
2. Application of the mechanical interaction of the
brush elements in the final stage of dressing
JEM294 IMechE 2006
results in reinforcing the surface layer of the
bond and contributes to generation of compression stresses that are advantageous with
regard to locking the grains in the bond material.
3. The open-circuit nature of the discharges
causes the electric erosion processes to be
localized in the areas of contact between the
working electrode elements and the conductive
bond material.
4. Application of the flexible electrodes in the form
of rotary brushes enables both preparation of the
active abrasive tool surface and restoration of its
cutting ability.
5. The cutting capabilities of the diamond wheels
sharpened by EDMD are close to the capabilities
of conventionally sharpened wheels.
Proc. IMechE Vol. 220 Part B: J. Engineering Manufacture
B Nowicki, R Pierzynowski, and S Spadło
6. The EDMD process enables sharpening time
reduction by a few times when compared with
the conventional method.
7. Essential differences of the above features
appear only for short machining times, t ¼ 1–4
min, and for these time intervals conventionally
sharpened wheels display more favourable
properties than their EDMD counterparts.
These differences do not mean any significant
influence on the grinding wheel properties
when considering its whole life range after
dressing (60–90 min).
8. The EDMD process can be used for removing
very thin bond layers which economizes usage
of expensive diamond and cubic boron nitride
9. Sharpening of diamond metal-bonded grinding
wheels by the EDMD can be used effectively
directly on the grinders with the presence of
water–oil emulsion, which is widely used as a
grinding coolant.
10. The equipment needed for the EDMD process is
simple and can be installed on any grinder.
Szkoła Obróbki Ściernej on Podstawy i Technika
Obróbki Ściernej, Koszalin, 1993, pp. 129–144.
Schopf, M. Dressing of metal-bonded grinding wheels
by ECDM. Ind. Diamond Rev., 2002, 64(2), 82–85.
Schöpf, M. Truing and dressing of high precision
grinding tools with unconventional machining. In
Proceedings of 2-dn Euspen Information Conference,
Turin, Italy, 2001, pp. 816–819.
Bachtiarov, S. A. Rabotaspasobnost almaznych krugov
posle kontaktno-erozionnoj prawvki. Stanki i Instrument, 1989, 18–20.
Nowicki, B. and Spadło, S. Smoothing the surface by
brush electro-discharge mechanical machining –
BEDMM. Central European Exchange Program for University Studies Project PL-1 CEEPUS, Project Report,
1998, pp. 129–137.
Nowicki, B., Pierzynowski, R., and Spadło, S. The
forming of surface roughness by anodic-mechanical
machining with a discrete electrode. In CIM’99,
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Proc. IMechE Vol. 220 Part B: J. Engineering Manufacture
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Ra, Rt
grain size
diameter of the wire
diameter of the brush electrode
impulse energy
electrochemical machining
electro-discharge machining
electro-discharge mechanical dressing
roughness parameters
machining time
feed rate
rotational speed of the brush electrode
value of the deflection of the tool
impulse time duration
JEM294 IMechE 2006