Davim J. Paulo (editor). Machining. Fundamentals and Recent Advances
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Grinding Technology and New Grinding Wheels 261
Table 9.5. CBN abrasive grain selection chart based on camshaft and crankshaft grinding
applications
CBN grain
size
Surface roughness, R
a
(μm)
Maximum specific metal removal rate,
Q
’
w max
(mm
3
/mm.s)
B46
0.15–0.3
1
B54
0.25–0.4
3
B64
0.3–0.5
5
B76
0.35–0.55
10
B91
0.4–0.6
20
B107
0.5–0.7
30
B126
0.6–0.8
40
B151
0.7–0.9
50
B181
0.8–1
70
Table 9.6. Vitrified CBN grinding wheel specification chart and associated grinding wheel
speeds based on camshaft and crankshaft grinding applications
Workpiece
material
Grinding
wheel speed,
v
s
(m/s)
Vitrified CBN wheel
specification
Application details
Chilled cast
iron
120 B181R200VSS
B126P200VSS
B107N200VSS
High Q
’
w.
Medium Q
’
w.
Low Q
’
w.
Nodular cast
iron
80
B181P200VSS
B181K200VSS
B181L150VSS
B181L150VDB
Little or no wheel loading
Wheel loading significant
Low stiffness workpiece
Very low-stiffness workpiece
AISI 1050
steel
(hardened)
80 B126N150VSS
B126N150VTR
Standard specification wheel
For use on low-power ma-
chine tools
AISI 1050
steel (soft
condition)
120 B181K200VSS Standard specification wheel
High-speed
tool steel
60 B107N150VSS Standard specification wheel
Inconel (poor
grindability)
50
B181T100VTR
B181T125VTR
B181B200VSS
Form dressing is usually
required with all wheel speci-
fications.
262 M.J. Jackson
0
50
100
150
25 50 75 100 125 150
Grinding wheel speed (m/s)
Speed ratio (wheel speed/work speed)
Low s
p
eed ratio Standard s
p
eed ratio Hi
g
h s
p
eed rati
o
Figure 9.4. Work speed selection chart for camshaft and crankshaft grinding operations
Softer steels are typically not burn sensitive, but do tend to burr when ground.
Maximum wheel and work speeds are required in order to reduce equivalent chip
thickness. High-pressure wheel scrubbers are required in order to prevent the grind-
ing wheel from loading. The grinding wheel specification is based on an abrasive
content in the region of 50 vol.% and a bonding content of 20 vol.% using the standard
bonding system operating at 120 m/s. Tool steels are very hard and grinding wheels
should contain 23 vol.% standard bonding system and 37.5 vol.% CBN abrasive
working at speeds of 60 m/s. Inconel materials are extremely burn sensitive, are lim-
ited to wheel speeds of 50 m/s and have large surface roughness requirements, typi-
cally 1 μm Ra. These grinding wheels contain porous glass sphere bonding systems
with 29 vol.% bond, or 11 vol.% bond content using the standard bonding system.
Figure 9.5 shows a micrograph with standard porosity that is formed by pressing to a
known volume. Figure 9.6 shows a recent development known as induced porosity in
which CBN bond formulations are supplemented with hollow alumina pores that
create porosity at the contact zone between grinding wheel and workpiece. The level
of porosity created at the contact zone is dependent upon the material removal rate.
Figure 9.7 shows a micrograph detailing open and distributed porosity that is
similar to that created in porous conventional grinding wheels to grind aerospace
materials. Developments in bonding and bonding systems have recently been
described by Jackson and Mills [4] and Jackson [5,
6].
Grinding Technology and New Grinding Wheels 263
Figure 9.5. Micrograph of vitrified CBN grinding wheel with standard porosity
Figure 9.6. Micrograph of vitrified CBN grinding wheel with induced porosity
264 M.J. Jackson
Figure 9.7. Micrograph of vitrified CBN grinding wheel with open distributed porosity
High-efficiency grinding with internal grinding wheels is limited by the burst-
ing speed of the grinding wheel and the effects of coolant. The quill is an inher-
ently weak part of the system and must be carefully controlled when using CBN in
order to avoid the problems associated with changes in normal grinding forces.
Quills should have a large diameter and a short length, and should be made from
a stiff material such as Ferro-TiC, which has a relatively low density.
9.3.3 Grinding Machine Requirements for High-efficiency CBN Grinding
The advantages of high-speed CBN grinding can only be realised in an effective
manner if the machine tool is adapted to operate at high cutting speeds. In order to
attain very high cutting speeds, grinding wheel spindles and bearings are required to
operate at speeds on the order of 20,000 rev min
–1
.The grinding wheel/spindle/ mo-
tor system must run with extreme accuracy and minimum vibration in order to
minimise the level of dynamic process forces. Therefore, a high level of rigidity is
required for the entire machine tool. Balancing of high-speed grinding wheels is also
necessary at high operating speeds using dynamic balancing techniques. These tech-
niques are required so that workpiece quality and increased tool life is preserved.
Another important consideration is the level of drive power required when in-
creases in rotational speed become considerable. The required total output is com-
posed of the cutting power, P
c
, and the power loss, P
l
,
=+
total c l
PPP (9.1)
Grinding Technology and New Grinding Wheels 265
The cutting power is the product of the tangential grinding force and the cutting
speed,
=
ctc
PF'.v (9.2)
The power loss of the drive is comprised of the idle power of the spindle, P
L
,
and power losses caused by the coolant, P
KSS
, and by spray cleaning of the grind-
ing wheel, P
SSP
, thus,
=+ +
l L KSS SSP
PPP P (9.3)
The grinding power, P
c
, increases by a relatively small amount when the cut-
ting speed increases and all other grinding parameters remain constant. However,
this means that the substantial power requirement that applies at maximum cutting
speeds results from a strong increase in power due to rotation of the grinding
wheel, the supply of coolant and the cleaning of the wheel. The quantities and
pressures of coolant supplied to the grinding wheel and the wheel cleaning process
are the focus of attention by machine tool designers. The power losses associated
with the rotation of the grinding wheel are supplemented by losses associated with
coolant supply and wheel cleaning. The losses are dependent on machining pa-
rameters, implying that machine settings and coolant supply need to be optimised
for high-speed grinding. In addition to the advantage of effectively reducing the
power required for grinding, optimisation of the coolant supply also offers eco-
logical benefits as a result of reducing the quantities of coolant required. Various
methods of coolant supply are available such as the free-flow nozzle that is con-
ventionally used, the shoe nozzle that ensures reduced quantity lubrication and the
mixture nozzle that ensures minimum quantity lubrication. The common task is to
ensure that an adequate supply of coolant is presented at the grinding wheel–
workpiece interface. The systems differ substantially regarding their operation and
the amount of energy required supplying the coolant.
A shoe nozzle, or supply through the grinding wheel, enables coolant to be di-
rected into the workpiece–wheel contact zone. A substantial reduction in volumet-
ric flow can be achieved in this way. In comparison to the shoe nozzle, supply
through the grinding wheel requires more complex design and production proc-
esses for the grinding wheel and fixtures. An advantage of this supply system is
that it is independent of a particular grinding process. Both systems involve a
drastic reduction in supply pressures as the grinding wheel effects acceleration of
the coolant. A more effective reduction in the quantity of the coolant results in
minimal quantity coolant supply, amounting to several millilitres of coolant per
hour. As the cooling effect is reduced, dosing nozzles are used exclusively to lu-
bricate the contact zone.
9.3.4 Dressing High-efficiency CBN Grinding Wheels
Dressing is the most important factor when achieving success with CBN grinding
wheels. CBN abrasive grains have distinct cleavage characteristics that directly
affect the performance of dressing tools. A dress depth of cut of 1 μm produces a
microfractured grain, whilst a depth of cut of 2–3 μm produces a macrofractured
266 M.J. Jackson
grain. The latter effect produces a rough workpiece surface and shorter CBN tool
life. The active surface roughness of the grinding wheel generally increases as
grinding proceeds, which means that the vitrified CBN grinding wheel must be
dressed in such a way that microfracture of the CBN grains is achieved. This
means that touch sensors are needed in order to find the relative position of grind-
ing wheel and dressing wheel because thermal movements in the machine tool far
exceed the in-feed movements of the dressing wheel. The design of the dressing
wheel for vitrified CBN is based on traversing a single row of diamonds so that
the overlap factor can be accurately controlled. The spindles used for transmitting
power to such wheels are usually electric spindles because they provide high
torque and do not generate heat during operation. Therefore, they assist in the
accurate determination of the relative position of dressing wheel and grinding
wheel.
9.3.5 Selection of Dressing Parameters for High-efficiency CBN Grinding
Selecting the optimum dressing condition may appear to be complex owing to the
combination of abrasive grain sizes, grinding wheel–dressing wheel speed ratio,
dressing depth of cut, diamond dressing wheel design, dresser motor power, dress-
ing wheel stiffness and other factors. It is not surprising to learn that a compromise
may be required. For external grinding, the relative stiffness of external grinding
machines absorbs normal forces without significant changes in the quality of the
ground component. This means that the following recommendations can be made:
dressing wheel/grinding wheel velocity ratio between +0.2 to +0.5; dressing depth
of cut per pass 0.5–3 μm; total dressing depth 3–10 μm; traverse rate calculated by
multiplying the dressing wheel r.p.m. by the grain size of CBN and multiplying by
0.3–1, depending on the initial condition of the dressing wheel. It is also right to
specify the dressing wheel to be a single row, or a double row, of diamonds. For
internal grinding, the grinding system is not so stiff, which means that any change
in grinding power will result in significant changes in normal grinding forces and
quill deflection. In order to minimize the changes in power, the following dressing
parameters are recommended: dressing wheel/grinding wheel velocity ratio +0.8;
dressing depth of cut per pass 1–3 μm; total dressing depth 1–3 μm; traverse rate
calculated by multiplying the dressing wheel r.p.m. by the grain size of CBN
(which means that each CBN grain is dressed once). It is also right to specify the
dressing wheel to be a single row of diamonds set on a disc.
9.3.6 Selection of Cooling Lubrication for High-efficiency CBN Grinding
Wheels
The selection of the appropriate cooling lubrication for vitrified CBN are consid-
ered to be environmentally unfriendly. Although neat oil is the best solution, most
applications use soluble oil with sulphur- and chlorine-based extreme pressure
additives. Synthetic cooling lubricants have been used but lead to loading of the
wheel and excessive wear of the vitrified bond. Using air scrapers and jets of cool-
ing lubricants normal to the grinding wheel surface enhances grinding wheel life.
Grinding Technology and New Grinding Wheels 267
Pressurized shoe nozzles have also been used to break the flow of air around the
grinding wheel. In order to grind soft steel materials, or materials that load the
grinding wheel, high-pressure low-volume scrubbers are used to clean the grinding
wheel. It is clear that the experience of application engineers is of vital importance
when developing a vitrified CBN grinding solution to manufacturing process
problems.
9.4 Internet Resources
Grinding wheel suppliers:
www.citcodiamond.com – suppliers of CBN and diamond grinding and
dressing tools
www.tyrolit.com – suppliers of CBN and diamond grinding and dressing
tools
www.noritake.com – suppliers of CBN and diamond grinding and dressing
tools
www.sgabrasives.com – suppliers of CBN and diamond grinding and dress-
ing tools
www.nortonabrasive.com – suppliers of CBN and diamond grinding and
dressing tools
www.wendtgroup.com – suppliers of CBN and diamond grinding and dress-
ing tools
www.rappold-winterthur.com/usa – suppliers of CBN and diamond grinding
and dressing tools
Dressing wheel suppliers:
www.citcodiamond.com – suppliers of CBN and diamond grinding and
dressing tools
www.tyrolit.com – suppliers of CBN and diamond grinding and dressing
tools
www.noritake.com – suppliers of CBN and diamond grinding and dressing
tools
www.sgabrasives.com – suppliers of CBN and diamond grinding and dress-
ing tools
www.nortonabrasive.com – suppliers of CBN and diamond grinding and
dressing tools
www.wendtgroup.com – suppliers of CBN and diamond grinding and dress-
ing tools
www.rappold-winterthur.com/usa – suppliers of CBN and diamond grinding
and dressing tools
Grinding machine tool suppliers:
www.landis-lund.co.uk – suppliers of camshaft and crankshaft grinding ma-
chine tools
268 M.J. Jackson
www.toyoda-kouki.co.jp – suppliers of camshaft and crankshaft grinding
machine tools
www.toyodausa.com – suppliers of camshaft and crankshaft grinding ma-
chine tools
www.weldonmachinetool.com – suppliers of cylindrical grinders and other
special purpose grinding machine tools
www.landisgardner.com – suppliers of cylindrical grinders and other special
purpose grinding machine tools
www.unova.com – suppliers of cylindrical grinders and other special pur-
pose grinding machine tools
www.voumard.ch – suppliers of internal grinding machine tools
www.bryantgrinder.com – suppliers of internal grinding machine tools
For a complete list of grinding machine suppliers contact:
www.techspec.com/emdtt/grinding/manufacturers – index of grinding ma-
chine tool suppliers and machine tool specifications.
Case studies:
www.abrasives.net/en/solutions/casestudies.html – case studies containing a
variety of grinding applications using conventional and superabrasive mate-
rials
www.winter-diamantwerkz-saint-gobain.de – case studies of CBN grinding
wheel and diamond dressing wheel applications
www.weldonmachinetool.com/appFR.htm – grinding case studies
Cooling lubricant suppliers:
www.castrol.com – suppliers of grinding oils/fluids and lubrication applica-
tion specialists
www.hays-siferd.com – suppliers of grinding oils/fluids and lubrication ap-
plication specialists (formerly Master Chemicals)
www.quakerchem.com – suppliers of grinding oils/fluids and lubrication
application specialists
www.mobil.com – suppliers of grinding oils/fluids and lubrication applica-
tion specialists
www.exxonmobil.com – suppliers of grinding oils/fluids and lubrication ap-
plication specialists
www.nocco.com – suppliers of grinding oils/fluids and lubrication applica-
tion specialists
www.marandproducts.com – suppliers of grinding oils/fluids and lubrication
application specialists
www.metalworkinglubricants.com – suppliers of grinding oils/fluids and lu-
brication application specialists
Grinding Technology and New Grinding Wheels 269
References
[1] Jackson MJ, Mills B (2000) Materials selection applied to vitrified alumina and
c.B.N. grinding wheels. J Mater Process Technol 108: 114–124.
[2] Grinding Data Book (2000) Unicorn International, Stafford, United Kingdom.
[3] Jackson MJ, Davis CJ, Hitchiner MP, Mills B (2001) High-speed grinding with
c.B.N. grinding wheels – applications and future developments. J Mater Process
Technol 110: 78–88.
[4] Jackson MJ, Mills B (2004) Microscale wear of vitrified abrasive materials. J Mater
Sci 39: 2131–2143.
[5] Jackson MJ (2004) Fracture dominated wear of sharp abrasive grains and grinding
wheels. Proc Inst Mech Eng (London): Part J – J Eng Tribol 218: 225–235.
[6] Jackson MJ (2006) Tribological design of grinding wheels using X-ray diffraction
techniques. Proc Inst Mech Eng (London): Part J – J Eng Tribol 220 (1): 1–17.
10
Micro and Nanomachining
M.J. Jackson
Center for Advanced Manufacturing, College of Technology, Purdue University,
401 North Grant Street, West Lafayette, Indiana, IN 47907, USA.
E-mail: jacksomj@purdue.edu
Recent advances in miniaturization have led to the development of microscale
components, usually in silicon. However, components made from engineering
materials require shaping processes other than those established for processing
silicon. Therefore, traditional machining processes require further development in
order to machine components that are fit for purpose at the micro and nanoscales.
This chapter provides a timely review of the current developments and recent
advances in the area of micro and nanomachining.
10.1 Introduction
There is a substantial increase in the specific energy required with a decrease in
chip size during machining. It is believed that this is due to the fact that all metals
contain defects such as grain boundaries, missing and impurity atoms etc., and
when the size of the material removed decreases the probability of encountering
a stress-reducing defect decreases. Since the shear stress and strain in metal cut-
ting is unusually high, discontinuous microcracks usually form on the primary
shear plane. If the material is very brittle, or the compressive stress on the shear
plane is relatively low, microcracks will grow into larger cracks, giving rise to
discontinuous chip formation. When discontinuous microcracks form on the shear
plane they will weld and reform as strain proceeds, thus joining the transport of
dislocations in accounting for the total slip of the shear plane. In the presence of
a contaminant, such as carbon tetrachloride vapour at a low cutting speed, the re-
welding of microcracks will decrease, resulting in a decrease in the cutting force
required for chip formation. A number of special experiments that support the
transport of microcracks across the shear plane, and the important role compres-
sive stress plays on the shear plane are explained. An alternative explanation for