NGUYEN Tien Dong, Koji MATSUMARU, Masakazu TAKATSU and Kozo ISHIZAKI
Copyright AD-TECH; licensee AZoM.com Pty Ltd.
This is an AZo
Open Access Rewards System (AZo-OARS) article distributed under the terms of the
which permits unrestricted use provided the original work is properly cited but
is limited to non-commercial distribution and reproduction.
1833-122X) Volume 6 December 2010
Diamond Grinding Wheels with Hexagonal Structure
Grinding-wheel loading can be defined as ground material either adhere to abrasive grains or become embedded in voids on a
grinding-wheel surface. This phenomenon deteriorates grinding-wheels, and consequently the surface integrity of ground
materials, such as surface roughness of the ground materials due to excessive friction and heat. Newly developed cup-type
diamond-grinding-wheels with hexagonal pattern were used to grind a magnesium alloy AZ31B in the present work.
The hexagon edges of 1 or 2 mm width contain diamond grains and, the inside of hexagons contains porous green carborundum
without diamond grains. The direction of hexagonal edges can be located roughly either parallel or perpendicular to wheel-
rotating direction, i. e., wheel-circumferential direction or wheel-radial direction, respectively. Wheel loadings appear in
the hexagonal edges along circumferential direction on hexagonal wheel surfaces, but do not appear in those along radial
direction, while appear equally at any positions on conventional wheel surface. Previous researches considered that the
mechanism of the loading was based on rather microscopic phenomenon, i. e., caused by one grain or neighboring two abrasive
grains. In this paper, a new phenomenological mechanism of wheel loading is presented in which the mechanism of wheel
loading is totally different to those proposed by the previous researches. Hexagonal structure shows the advantage to reduce
wheel loading phenomenon in grinding light metals such as magnesium alloys.
Wheel Loading, Magnesium Alloys, Hexagonal Structure, Surface Roughness, Grinding
Recently, light metals, e. g., aluminum, magnesium and their alloys, offer the greatest potential for weight reduction of
all metallic materials, which have been used in automobile, aerospace, agricultural, chemical and construction industries as
well as electrical appliances. The main concern in machining these light materials is chip adhesion on cutting tool
surfaces. In grinding process, this phenomenon is called “(wheel) loading”, which can be defined as the state of a grinding
wheel when particles of a work-piece material either adhere to the grits or become embedded in the spaces between abrasive
grains on grinding wheels. The loaded grinding wheel becomes dull very fast, raising grinding forces and temperature thus
reducing its grinding ability. The wheel loading phenomenon is to be regarded as one of the most disturbing factors in
grinding process, and it is about 15% of decisive criterion for redressing of grinding wheels . Magnesium alloys have
been used for a broad range of industrial applications from aerospace to transportation and more due to their high specific
strength and the lowest density of all metallic structural materials. Magnesium alloy AZ31B (ASTM – American Society for
Testing & Materials) was selected to represent a light metals in the present work.
There have been many researches on various aspects of wheel loading in grinding various materials such as Ti alloys,
stainless steel or aluminum oxide by straight-type conventional grinding wheels. These researchers dealt with investigating
the loading phenomenon under different grinding parameters such as wheel speed, cutting depth, and work-piece feeding speed
[2-5]. They reported that any noticeable loading was not found for low cutting depth , or the loading tendency increased
with the greater removal rate, i. e., the greater cutting depth and/or the greater feeding speed . Srivastava et al.
contradictorily reported that feeding speed has no significant effect on wheel loading . Koshima et al. presented that
the loading of CBN wheels in up-cut grinding was less than that in down-cut grinding .
Other researches aimed to explain the mechanism of wheel loading by giving some aspects on chip formation processes.
Schmaltz and Konig reported that the mechanical interlocking of the chips with the wheel surface and the chemical affinity
between the work-piece and grits materials might be the possible causes of loading . Komanduri and Shaw suggested that the
loading over the wheel surface may be due to pressure welding of ground chips on abrasive grits . Yossifon and Rubenstein
also revealed the same phenomenon, but added a possibility that wheel loading is determined by the presence of protecting
oxide layer on the work-piece during grinding in air .
The previous researchers clearly indicated that the mechanism of wheel loading was the adhesion between abrasive grains
and the work-piece material during grinding process. They proposed a mechanism of wheel loading by one abrasive grain or two
neighboring abrasive grains. In other words, the loading phenomenon is rather microscopic phenomenon at most 100 μm, i.
e., the dimension of the distance between abrasive grains. In this work, newly developed cup-type diamond grinding wheels
were used to grind a magnesium alloys. The effects of hexagonal structure on ground surface and the integrity of grinding
wheel were evaluated. This paper presents a new mechanism of wheel loading, and proposes a new method to enhance the
performance of grinding light metals such as magnesium alloys.
Diamond Grinding Wheels with Hexagonal Structure
Diamond grinding wheels are newly developed with hexagonal pattern, which contain abrasive diamond grains on hexagon edges
and green carborundum porous material without diamond grains in inside of the hexagons . These wheels are characterized by
hexagonal geometrical factors: size of hexagons, x, and width of hexagon edges containing diamond grains, w as shown in Fig.
1 (a). The direction of hexagonal edges can be located roughly either parallel or perpendicular to wheel-rotating direction
in Fig. 1 (b). Grinding stone ratio, R is defined as the ratio between the hexagonal edge area containing abrasive grains
and the total area of the wheel surface. Four newly developed diamond grinding wheels with different R (13%, 19%, 25% and
36%) and a conventional wheel (R 100%) (diamond grain size: #200, grain concentration 0.48, vitrified bond 20 mass %,
porosity 32%, NanoTEM Co. Ltd., Nagaoka, Japan) were used as shown in Table 1.
Figure 1. Hexagonal diamond grinding wheel schematically shown by (a), and photographically shown by
(b). Hexagonal structural is characterized by hexagonal geometrical factors: hexagon size, x, and an edge width, w. Diamond
abrasive grains are placed only within the edge width, which is order of mm.
Table 1. Grinding stone ratios, R for hexagonal wheels and a conventional wheel.
|Hexagonal wheels, R
|Conventional wheel, R 100%
A regulated-force-feeding (RFF) grinding system, which was developed by Kim et al., was employed in the present work [10,
11]. The table feeding force was kept constant at 3.8 N during process. Samples were magnesium alloys AZ31B (Al 3%, Zn 1%,
Mn 0.45%) (Kamado Laboratory, Nagaoka University of Technology, Nagaoka, Japan) with dimensions of 50 x 40 x 1.5 mm, and was
placed on vacuum vise. Grinding wheel rotation speeds, n were 500, 1500 and 3000 rpm, cutting depth was 10 μm per pass,
and total cutting depth was 200 μm. The wheels were re-dressed before each grinding experiment. The coolant water was
sprayed into the contact zone between grinding wheel and sample during truing, dressing, and grinding process with 0.5 l/min
flow rate. Grinding conditions are listed in Table 2.
Wheel loading did not occur for n at 500 and 1500 rpm, but for n 3000 rpm, and appeared equally at any positions on
conventional wheel surfaces as shown in Fig. 2(a), while appeared only in the hexagonal edges along circumferential, i. e.,
parallel to the wheel-rotating direction on the hexagonal wheel surfaces, but not in the edges along radial direction as
shown in Figs. 2 (b) (c) (d) and (e).
Figure 2. Grinding wheel surface after grinding experiments. White areas correspond to loaded
magnesium alloy. (a) conventional wheel with R = 100%. (b), (c), (d) and (e) are for hexagonal grinding wheels with R =
13%, 19%, 25%, and 36%, respectively.
Table 2. Specifications of grinding wheels, grinding conditions and sample.
||Rotation speed, n/ rpm 500, 1500, 3000
|- Outer, DO 250 mm
||Cutting depth, 10 μm
||Dimensions 50 x 40 mm
|- Inner, DI 80 mm
||Total cutting depth 200 μm
||Thickness 1.5 mm
|Grain size (#200), d 74 μm
||Constant table feeding force 3.8 N
|Bonding material Vitrified
||Coolant water, 0.5 lmin-1
Previous researchers considered that all wheel loading phenomena were started with chip adherence on the rake face of the
same cutting grain and continued to grow. In a recent paper, Gift el al. suggested a mechanism of wheel loading in six
stages, and proposed a mechanism of wheel loading by neighboring abrasive grains . In other words, the loading
phenomenon is rather microscopic phenomenon, i. e., the dimension of the neighboring distance between abrasive grains. There
may be a small difference in the loading mechanisms proposed till now. But all of them consisted on the loading initiates by
only one abrasive grain or at most two neighboring grits, and focused rather microscopic adhesion, between abrasive grains
and work-piece materials.
The present research shows the phenomena are based on rather macroscopic effects, and on cooperative work of many grits.
These results reveal that the mechanism of wheel loading is not microscopic phenomenon, i.e., loading can be initiated by
only one grit or at most two neighboring grits as proposed previously, but rather a phenomenon which is caused by
macroscopic, i. e., order of hexagon length or 10 mm length. The phenomena can be explained by cooperative work of many
grits. The lengths of hexagonal edges are order of 10 mm.
The average neighbor distance between diamond grains on the wheel surface is about 70 μm. The edge width of hexagons
is 1 mm or 2 mm. Therefore there are about 14 or 30 grains in the hexagon edges in the transverse direction on the grinding
surface. But there were no loadings in the edges along the radial direction of the wheels. The loadings can be found only
in the edges located along the circumferential direction of the wheels. The longitudinal length of the edges is in the order
of 10 mm as seen in Figs. 2 (b) (c) (d) and (e). Along this direction of edges, there about 300 grits. If the mechanisms
proposed previously would be right, there must be loadings on all edges of hexagons, because there are more than enough
diamond grains in all edges. The loading is not caused by one or two grits, but caused by many grits.
The loading mechanism proposed here is as the following. To initiate loading hot ground chips must grow a critical size
to touch hot abrasive grains. The ground chips may be molten metal or solid metal at temperature close to melting point to
form critical size of droplets to initiate loading. Hot ground chips move and join together to form large droplets of hot
metal, and hit hot diamond grains to adhere them. About 100 ground chips need to form rather large molten metal droplets to
start loading for the present grinding conditions. This is the critical size of droplets for loading. Ground chips along
circumferential edges of length of about 10 mm may face 300 grits and about the same number of ground hot chips at the end of
hexagonal edge along the circumferential movement. Therefore the loadings start at the end of the hexagonal edge along the
circumferential motion. This may be the reason why we can find the formation of loadings at the downstream side of hexagonal
circumferential edges to form a shape close to letter “Y”, as seen in Figs. 2 (b) and (c) for hexagon edge width of 1 mm.
For thicker hexagonal edges of 2 mm width, this initial point of loading may occur at any positions in the edges as seen in
Figs. 2 (d) and (e) since there are more chances for chips to join in any positions of hexagon edges along circumferential
In hexagonal grinding wheels, there is difference in height of hexagonal edges and inner green carborundum parts after
dressing. The difference is about 30 to 40 μm. Hot chips ground by the radial edges pass and join to form a small
droplet through moving 14 to 30 grits, and fall into practically empty space between lower green carborundum and work-piece.
They are too small to start loading. While moving this green carborundum space, chips will be cooled down. The cold chips
or droplets formed by a few chips hit hot diamond grains which are located in the next hexagonal edge along radial direction,
can not join to form larger droplets because of low temperature, and do not react with the diamond grains because of low
temperature and too small droplet size. This is the reason why loadings can not be found hexagon edges along radial
Therefore, wheel loading can be found at any positions in conventional wheels. For slow grinding speed of n = 500 and 1500
rpm, cooling speed was fast enough to prevent to form critical size of droplets for all grinding wheels. If the grinding
conditions would be severe, loadings could be found in more possible locations. In this case a few large ground chips must
be enough to form a critical size droplet. The ideal design of grinding wheel to prevent loading consist only radial
direction of abrasive grains with long interval volume of non abrasive grains.
In this work, a magnesium alloy is ground by a conventional and newly developed hexagonal diamond grinding wheels.
Hexagonal wheels contain abrasive diamond grains on hexagon edges, and the inside potion of hexagons is filled up by porous
green carborundum without diamond grains. Depending on the direction of hexagon edges on the wheel surfaces, these edges can
be roughly located either parallel or perpendicular to the wheel-rotating direction during grinding process. The following
can be concluded:
1. The wheel loading mechanism is not related to local positioning of one or two abrasive grains, but related macroscopic
positions of several active grains. In other word, the characteristic distance of loading is not order of μm, but in
order of mm distance.
2. The mechanism of loading phenomenon appears equally at any positions on conventional wheel surface. However, the
hexagonal wheels show that loading occurs on the hexagonal edges parallel to the wheel-rotating direction than the edges
perpendicular to it.
3. It is possible to reduce and prevent loading phenomenon in grinding light metals such as magnesium alloys by designing
a grinding wheel with proper abrasive grain configuration.
The authors wish to express their gratitude to the Japanese government for partially supporting this work through the
21st Century Center of Excellency (COE) Program and City Area Nagaoka of Promotion of Science and Technology in
Regional Areas of the Ministry of Education, Culture, Sports, Sciences and Technology.
1. W. Konig and H. Lauer Schmaltz, “Loading of the Grinding Wheel Phenomenon and Measurement”, Annals of the
CIRP (College International pour la Recherche en Productique), 27  (1978) 217-220.
2. P. Nagaraj and A. K. Chattopadhyay, “On Some Aspects of Wheel Loading”, Wear, 135 (1989) 41-52.
3. P. G. Werner and H. L. Schmaltz, “Advanced Application of Coolants and Prevention of Wheel Loading in Grinding”,
Welding Journal, 18-19 (1980) 225-232.
4. K. Srivastava, K. S. Ram and G. K. Lal, “A Simple Analysis for Evaluating Grinding Wheel Loading”, Int. J. Mach. Tools
Manufact, 28  (1988) 181-190.
5. K. Koshima, H. Onikura and K. Sakuma, “Loading Phenomenon of CBN Wheel in Grinding of Stainless Steel”, Journal of the
Japan Society of Precision Engineering (JSPE), 58  (1992) 1209-1214.
6. H. Lauer Schmaltz and W. Konig, “Phenomenon of Wheel Loading Mechanisms in Grinding”, Annals of the CIRP (College
International pour la Recherche en Productique), 29  (1980) 201-207.
7. Komanduri and C. Shaw, “The Mechanism of Metal Build-up on Aluminum Oxide Abrasive”, Annals of the CIRP (College
International pour la Recherche en Productique), 25  (1976) 191-196.
8. S. Yossifon and C. Rubenstein, “The Grinding of Workpieces Exhibiting High Adhesion, Part 1-Mechanism”, Transactions
of the ASME Journal of Engineering for Industry, 103 (1981) 144-155.
9. K. Ishizaki and A. Takada, Patent No-156724, 15th June 1999, Japan.
10. H. Kim, K. Matsumaru, A. Takata and K. Ishizaki, “Grinding Behavior of Silicon Wafer and Sintered
Al2O3 by Constant Force Feeding Grinding System”, Adv. in Tech. of Mat. and Mat. Proc. J. (ATM), 5 
11. H. Kim, K. Matsumaru, A. Takata and K. Ishizaki, “Reduction of Ceramic Machining Defects by Regulated Force Feeding
Grinding System”, Adv. in Tech. of Mat. and Mat. Proc. J. (ATM), 6  (2004) 290-297.
12. F. C. Gift and Jr. W. Misiolek, “Mechanics of Loading for Electroplated Cubic Boron Nitride (CBN) Wheels during
Grinding of a Nickel-Based Superalloy in Water-Based Lubricating Fluids”, Journal of Tribology, 126 (2004) 795-801.
Tien Dong Nguyen, Koji Matsumaru and Kozo Ishizaki
Department of Mechanical Engineering
Nagaoka University of Technology
Nagaoka, Niigata 940-2188, Japan
Nano-TEM Co., Ltd.
Shimogejo 1-485, Nagaoka, Niigata 940-0012, Japan
This paper was also published in print form in "Advances in Technology
of Materials and Materials Processing", 11 (2009) 37-42.