Chap-25-1.ppt

Manufacturing Technology – II
ME 307
Chapter # 25

©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Chapter 25
GRINDING AND OTHER ABRASIVE
PROCESS

Abrasive Machining
 Material removal by the action of hard, abrasive
particles that are usually in the form of a
bonded wheel.
 Grinding is the most important abrasive
process.
 Other traditional abrasive processes include
 Honing,
 lapping,
 superfinishing,
 polishing, and
 buffing.
 Generally used as finishing operations.

Abrasive Machining
Abrasive processes are important commercially
and technologically for the following reasons:
 They can be used on all types of materials
ranging from soft metals to hardened steels
and hard nonmetallic materials such as
ceramics and silicon.
 can produce extremely fine surface finishes, to
0.025 mm (1 m-in).
 dimensions can be held to extremely close
tolerances.

What is Grinding
 Abrasive material removal process
 Grinding is achieved by a bonded grinding
wheel rotating at high speed
 Tool i.e. Grinding wheel is usually disk shaped
 Precisely balanced
 Similar to Milling but with almost infinite cutting
teeth (abrasive particles) rotating at very high
speed.

After Materials and Processes in Manufacturing, by E. Paul DeGarmo, J.T. Black,
and Ronald A. Kohser, Prentice Hall of India, 2001.

©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern
Manufacturing 4/e
Workpieces and Operations Used in
Grinding
Figure 26.2 The types of workpieces and operations typical of grinding: (a) cylindrical
surfaces, (b) conical surfaces. (c) fillets on a shaft, (d) helical profiles, (e) concave
shape, (f) cutting off or slotting with thin wheels, and (g) internal grinding.

Grinding vs Milling
• the abrasive grains in the wheel are much
smaller and more numerous than the teeth on a
milling cutter;
• cutting speeds in grinding are much higher than
in milling;
• the abrasive grits in a grinding wheel are
randomly oriented and possess on average a
very high negative rake angle; and
• a grinding wheel is self-sharpening—as the
wheel wears, the abrasive particles become
dull and either fracture to create fresh cutting
edges or are pulled out of the surface of the
wheel to expose new grains.

Grinding Wheel
 Abrasive Material
 Grain Size
 Bonding Material
 Wheel Grade
 Wheel Structure

Abrasive Material
 High Hardness
 Wear Resistance
 Toughness
 Friability
 It is the capacity of the abrasive material to
fracture when cutting edge become dull,
thereby exposing a new surface

Abrasive Material

Grain size
 Important parameter in determining surface
finish and material removal (MRR)
• Small Grain size more finish
• Large grain size better MRR
 Harder work materials require smaller grain
sizes
 softer materials require larger grit sizes.
 Grain size is determined by Screen Mesh
 Grain size varies from 8 to 250 with size 8
being very coarse.

Figure 28.3:
Typical screens for sifting abrasives into sizez. The larger the screen
number (of opening per linear inch), the smaller the grain size.
(Courtesy of Corborundum Cornpony.)

Figure 28.2:
Loose abrasive grains at high magnification, showing their irregular, sharp cutting
edges. (Courtesy of Norton Cornpony.)

Bond Material
 The bonding material holds the abrasive grains
and establishes shape and structural integrity
of the grinding wheel
 The bonding material should withstand
 grinding forces,
 high temperatures,
 shock loading and
 rigidly holding the abrasive grains.

Bond Material

Wheel Structure
 Relative Spacing of abrasive grains in the
wheel
 The total structure is made up of abrasive
grains, bond material and air
Pg+Pb+Pp=1.0
 Wheel may be open or dense
 Open structure is one in which Pp is large,
while in dense structure Pg is Large
 Dense structure is used for better surface finish

Wheel Structure
FIGURE 25.1
Typical structure of a grinding wheel.

Grinding Wheel Model
Figure 26.3 Schematic illustration of a physical model of a grinding wheel
showing its structure and wear and fracture patterns.

Figure 28.6:
The cavities or voids between the grains must be large enough to hold
all the chips during the cut.

Wheel Grade
 It indicates the grinding wheel’s bond strength
in retaining the abrasive grits during cutting.
 largely dependent on the amount of bonding
material present in the wheel structure.
 ranges between soft and hard.
– Soft
• lose grains readily.
• generally used for applications requiring
– low material removal rates and
– grinding of hard work materials.
– Hard
• retain their abrasive grains.
• Typically used to achieve
– high stock removal rates and
– for grinding of relative soft work materials.

Grinding Wheel Specification

FIGURE 25.2
Some of the standard grinding wheel shapes: (a) straight, (b) recessed two sides, (c)
metal wheel frame with abrasive bonded to outside circumference, (d) abrasive cutoff
wheel.

FIGURE 25.2
Some of the standard grinding wheel shapes: (e) cylinder wheel, (f) straight cup wheel,
and (g) ﬂaring cup wheel.

Bonded Abrasives Used in Abrasive-Machining Processes
Figure 25.1 A variety of bonded abrasives used in abrasive-
machining processes. Source: Courtesy of Norton Company.

Figure 28.25: Examples of mountedabrassive wheels & Points. (Courtesy
of Norton Company)n

Manufacturing 4/e
Grinding Wheels
Figure 26.4 Common
types of grinding wheels
made with conventional
abrasives. Note that
each wheel has a specific
grinding face; grinding on
other surfaces is
improper and unsafe.

ANALYSIS OF THE GRINDING
PROCESS
 The cutting conditions in grinding:
very high speeds and
very small cut size, (compared to milling)
 The peripheral speed is determined by:
v = πDN
where v = surface speed of wheel, m/min (ft/min);
N = spindle speed, rev/min; and D = wheel
diameter, m (ft).

PROCESS
FIGURE 25.3
(a) The geometry of surface grinding, showing the cutting conditions; (b) assumed
longitudinal shape and (c) cross section of a single chip.

PROCESS
Infeed
 Depth of cut d,
 It is the penetration of the wheel below the
original work surface.
Crossfeed
 the lateral feed of grinding wheel across the
surface of the work on each pass.
 it determines the width of the grinding path w.
 The width w, multiplied by depth d determines the
cross-sectional area of the cut.
 the work moves past the wheel at a speed vw, so
the material removal rate is
RMR = vw wd

 we are interested in how the cutting conditions
combine with the grinding wheel parameters to
affect
• surface finish,
• forces and energy,
• temperature of the work surface, and
• wheel wear.
PROCESS

Grinding Wheel Surface
Figure 26.9 The surface of a grinding wheel (A46-J8V) showing abrasive grains,
wheel porosity, wear flats on grains, and metal chips from the workpiece adhering to
the grains. Note the random distribution and shape of the abrasive grains.
Magnification: 50x. Source: S. Kalpakjian.

Manufacturing 4/e
Abrasive Grain Plowing Workpiece Surface
Figure 26.11 Chip formation and plowing of the workpiece surface by an abrasive grain.

 Grinding achieves a surface finish that is superior to
that of conventional machining.
 It is affected by the size of the individual chips
formed during grinding.
 One obvious factor in determining chip size is grit
size
– smaller grit sizes yield better finishes.
it can be shown that the average length of a chip
is given by:
where lc is the length of the chip, mm; D = wheel
diameter, mm; and d = depth of cut, or infeed, mm.
This assumes the chip is formed by a grit that acts
throughout the entire sweep arc.
Surface Finish

 The assumed cross-sectional shape is
triangular
 width w' being greater than the thickness t by a
factor called the grain aspect ratio rg, defined
by
 Typical values of grain aspect ratio are
between 10 and 20.
Surface Finish

 C = The number of active grits (cutting teeth)
per square inch on the outside periphery of the
grinding wheel.
 smaller grain sizes give larger C values.
 A denser structure means more grits per area.
 the number of chips formed per time is
nc = v w C
where v = wheel speed, mm/min; w = crossfeed,
mm; and C = grits per area on the grinding
wheel surface, grits/mm2.
• surface finish improve by increase in number of
chips formed per unit time on the work surface
for a given width w.
– Therefore, increasing v and/or C will
Surface Finish

 The specific energy can be determined as:
where U = specific energy, J/mm3; Fc = cutting
force, N; v = wheel speed, m/min; vw = work
speed, mm/min; w = width of cut, mm; and d =
depth of cut, mm.
Forces and Energy

Manufacturing 4/e
Approximate Specific-Energy Requirements
for Surface Grinding

In grinding, the specific energy is much greater
than in conventional machining. because:
• Size effect. The chip thickness in grinding is
comparatively much smaller.
– Therefore the energy required to remove unit
volume of material is significantly higher than in
conventional machining—roughly 10 times higher.
• The individual grains possess extremely
negative rake angles. (average about –30o,
some values as low as –60o).
– These result in low values of shear plane angle
and high shear strains, both of which mean higher
energy levels in grinding.
Forces and Energy

• not all of the individual grits are engaged in
actual cutting.
– Because of the random positions and orientations
of the grains, some grains do not project far
enough into the work surface to accomplish
cutting.
Forces and Energy

Three types of grain actions:
• cutting, in which the grit projects far enough
into the work surface to form a chip and
remove material;
• plowing, in which the grit projects into the work,
but not far enough to cause cutting; instead,
the work surface is deformed.
– energy is consumed without any material removal;
– rubbing, in which the grit contacts the surface
during its sweep, but only rubbing friction occurs,
• consume energy without removing any material.
Grain Actions

FIGURE 25.4: Three types of grain action in grinding: (a)
cutting, (b) plowing, and (c) rubbing.
The size effect, negative rake angles, and ineffective grain
actions combine to make the grinding process inefficient in terms
of energy consumption per volume of material removed.

Figure 28.7:
The grits interact with the surface
in three ways: cutting, plowing,
and rubbing.

 Using the specific energy relationship, and
 assuming that the cutting force acting on a
single grain in the grinding wheel is
proportional to rgt,
where
F'c = the cutting force on an individual grain,
K1 = constant of proportionality
Forces and Energy

 Because of
• size effect,
• high negative rake angles, and
• plowing and rubbing
the grinding process is characterized by high
temperatures.
 In conventional machining most of the heat
generated is carried off in the chip
 In grinding much of the energy remains in the
ground surface, resulting in high work surface
temperatures.
Temperatures at the Work Surface

1. The high temperatures may result in surface burns and
cracks.
 The burn marks appear as discoloration.
 burns are sign of metallurgical damage immediately
beneath the surface.
 The surface cracks are perpendicular to the wheel
speed direction.
 They indicate an extreme case of thermal damage to
the work surface.
1. The high temperatures may result in softening of the
work surface.
2. Thermal effects can cause residual stresses in the work
surface, possibly decreasing the fatigue strength of the
part.
Temperatures at the Work Surface

• Experimental observations ---- surface
temperature is dependent on
• energy per surface area ground (U).
where K2 = a constant of proportionality
Factors Influencing Work Surface
Temperatures

• high work temperatures can be mitigated by
 decreasing depth of cut d,
 decreasing wheel speed v, and
 decreasing number of active grits per square
inch C, or
 by increasing work speed vw.
• In addition,
 dull grinding wheels and
 wheels that have a hard grade and dense
structure
tend to cause thermal problems.
• using a cutting fluid can also reduce grinding
temperatures.
Factors Influencing Work Surface
Temperatures

1. Grain fracture,
2. attritious wear, and
3. bond fracture.
• Grain fracture occurs when a portion of the
grain breaks off, but the rest of the grain
remains bonded in the wheel.
• The edges of the fractured area become new
cutting edges.
• This tendency of the grain to fracture is called
friability.
• High friability means ---- the grains fracture
more readily.
Wheel Wear

• Attritious wear involves dulling of the individual
grains, resulting in flat spots and rounded
edges.
• analogous to tool wear in a conventional
cutting tool.
• caused by
 friction and diffusion,
 chemical reactions between the abrasive and
the work material.
Wheel Wear

• Bond fracture occurs when the individual
grains are pulled out of the bonding material.
• along other factors it depends on wheel grade.
• occurs because of dull grains caused by
attritious wear,
• The resulting cutting force is excessive.
• Sharp grains cut more efficiently with lower
cutting forces;
 hence, they remain attached in the bond
structure.
Wheel Wear

Wheel Wear
FIGURE 25.5: Typical wear curve of a grinding wheel. Wear is
conveniently plotted as a function of volume of material removed,
rather than as a function of time. (Based on [16].)

The three mechanisms combine to cause the
grinding wheel to wear.
1. grain fracture: the grains are initially sharp,
and wear is accelerated because of grain
fracture.
2. attritious wear: the wear rate is fairly constant,
resulting in a linear relationship between
wheel wear and volume of metal removed.
Mainly characterized by attritious wear, with
some grain and bond fracture.
Wheel Wear

3. the grains become dull, and the amount of
plowing and rubbing increases relative to
cutting.
In addition, some of the chips become clogged in
the pores (called wheel loading), which impairs
the cutting action and leads to higher heat and
temperatures.
grinding efficiency decreases, and the volume of
wheel removed increases relative to the volume of
metal removed.
Wheel Wear

Grinding ratio: a term used to indicate the slope
of the wheel wear curve.
where GR = the grinding ratio, Vw = the volume of
work material removed, and Vg = the
corresponding volume of the grinding wheel
that is worn in the process.
Typical values of GR range between 95 and
125,
about five orders of magnitude less than the
analogous ratio in conventional machining.
Wheel Wear

Grinding ratio:
It generally increases by increasing wheel
speed v.
higher wheel speeds also improve surface
finish.
However, when speeds become too high,
attritious wear and surface temperatures
increase.
As a result, the GR is reduced and the surface
finish is impaired.
Wheel Wear

Wheel Wear
FIGURE 25.6: Grinding ratio and surface ﬁnish as a function
of wheel speed. (Based on data in Krabacher [14].)

Dressing: When the wheel is in the third region, it
must be resharpened by a procedure called
dressing. which consists of:
1. breaking off the dulled grits on the outside
periphery of the grinding wheel in order to expose
fresh sharp grains and
2. removing chips that have become clogged in the
wheel.
• It is accomplished by
– a rotating disk,
– an abrasive stick, or
– another grinding wheel operating at higher speed.
Wheel Wear

Turning:
• Although dressing sharpens the wheel, it does
not guarantee the shape of the wheel.
• Truing is an alternative procedure that
1. sharpens the wheel,
2. restores its cylindrical shape and
3. ensures that it is straight across its outside
perimeter.
• The procedure uses a diamond-pointed tool
(or other truing tools) fed slowly and precisely
across the wheel as it rotates.
• A very light depth is taken (0.025 mm or less).
Wheel Wear

Manufacturing 4/e
Grinding-
Wheel
Dressing
Figure 26.12 (a) Forms of grinding-wheel dressing. (b) Shaping the grinding face of a
wheel by dressing it with computer control. Note that the diamond dressing tool is normal
to the surface at point of contact with the wheel. Source: Courtesy of Okuma Machinery
Works Ltd.

APPLICATION CONSIDERATIONS IN
GRINDING

Grinding Fluids:
 The functions performed by grinding fluids are
similar to those performed by cutting fluids.
– Reducing friction and
– removing heat from the process.
– washing away chips and
– reducing temperature of the work surface.
 Types of grinding fluids by chemistry include
– grinding oils and
– emulsified oils.
GRINDING
GRINDING

Manufacturing 4/e
General Recommendations for Grinding
Fluids

 Grinding is traditionally used to finish parts whose
geometries have already been created by other
operations.
 In addition applications include more high speed,
high material removal operations.
The Grinding operations and machines includes the
following types:
1. surface grinding,
2. cylindrical grinding,
3. centerless grinding,
4. creep feed grinding, and
5. other grinding operations.
GRINDING OPERATIONS AND
GRINDING MACHINES

 Normally used to grind plain flat surfaces.
 It is performed using either
– peripheral grinding or
– face grinding.
SURFACE GRINDING

FIGURE 25.7 Four types of surface grinding: (a) horizontal spindle with
reciprocating worktable, (b) horizontal spindle with rotating worktable, (c)
vertical spindle with reciprocating worktable, and (d) vertical spindle with
rotating worktable.

Manufacturing 4/e
Various Surface-Grinding Operations
Figure 26.13 Schematic illustrations of various surface-grinding operations. (a) Traverse
grinding with a horizontal-spindle surface grinder. (b) Plunge grinding with a horizontal-
spindle surface grinder. (c) A vertical-spindle rotary-table grinder (also known as the
Blanchard type.)

FIGURE 25.8
Surface grinder with horizontal spindle and reciprocating worktable.

 used for rotational parts.
 divided into two basic types
(a) external cylindrical grinding and
(b) internal cylindrical grinding.
CYLINDRICAL GRINDING
FIGURE 25.9 Two types
of cylindrical grinding: (a)
external, and (b) internal.

 performed much like a turning operation.
 These grinding machines closely resemble a lathe.
 The workpiece is rotated at a surface speed of 18
to 30 m/min, and the grinding wheel, at 1200 to
2000 m/min.
 Two types of feed motion possible,
– traverse feed and
– plunge-cut.
 The infeed is set within a range typically from
0.0075 to 0.075 mm.
 used to finish parts, machined to approximate size
and heat treated to desired hardness. e.g. axles,
crank-shafts, spindles, bearings and bushings, and
rolls for rolling mills.
External cylindrical grinding
(center-type grinding)

External cylindrical grinding
(center-type grinding)
FIGURE 25.10
Two types of feed motion in external cylindrical grinding: (a)
traverse feed, and (b) plunge-cut.

Manufacturing 4/e
Cylindrical-Grinding Operations
Figure 26.16 Examples of various cylindrical-grinding operations. (a) Traverse grinding,
(b) plunge grinding, and (c) profile grinding. Source: Courtesy of Okuma Machinery
Works Ltd.

Manufacturing 4/e
Plunge Grinding on Cylindrical Grinder
Figure 26.17 Plunge grinding of a workpiece on a cylindrical
grinder with the wheel dressed to a stepped shape.

Manufacturing 4/e
Grinding a Noncylindrical Part on Cylindrical Grinder
Figure 26.18 Schematic illustration of grinding a noncylindrical part on a
cylindrical grinder with computer controls to produce the shape. The part
rotation and the distance x between centers is varied and synchronized to
grind the particular workpiece shape.

 operates somewhat like a boring operation.
 The work-piece is rotated at surface speeds of 20
to 60 m/min. Wheel surface speeds similar to
external cylindrical grinding.
 The wheel is fed in either
– traverse feed, or
– plunge feed.
 the wheel diameter must be smaller than the bore
hole, which necessitate very high rotational speeds
in order to achieve the desired surface speed.
 used to finish the hardened inside surfaces of
bearing races and bushing surfaces.
Internal cylindrical grinding

Manufacturing 4/e
Internal Grinding Operations
Figure 26.21 Schematic illustrations of internal grinding operations:
(a) traverse grinding, (b) plunge grinding, and (c) profile grinding.

 It is an alternative process for grinding external and
internal cylindrical surfaces.
 As its name suggests, the workpiece is not held
between centers.
 This results in a reduction in work handling time;
hence used for high-production work.
 The workparts are supported by a rest blade and
fed through between the two wheels.
 The grinding wheel rotate at surface speeds of
1200 to 1800 m/min.
 The regulating wheel rotates at much lower speeds
and is inclined at a slight angle I to control
throughfeed.
Centerless Grinding

Centerless Grinding
FIGURE 25.11
External centerless grinding.

Centerless Grinding
Figure 28.22: Centerless grinding showing the relationship among the grinding wheel, the regulating
wheel, and the workpiece in centerless method. (Courtesy of Carborundum Company.)

Manufacturing 4/e
Centerless Grinding
Operations
Figure 26.22 Schematic
illustration of centerless
grinding operations: (a)
through-feed grinding, (b)
plunge grinding, (c) internal
grinding, and (d) a
computer numerical-control
cylindrical-grinding
machine. Source:
Courtesy of Cincinnati
Milacron, Inc.

 The following equation can be used to predict
throughfeed rate:
fr = π Dr Nr sin I
where fr = throughfeed rate, mm/min; Dr =
diameter of the regulating wheel, mm; Nr
= rotational speed of the regulating
wheel, rev/min; and I = inclination angle
of the regulating wheel.
Centerless Grinding

 In place of the rest blade, two support rolls are
used.
 The regulating wheel is tilted at a small inclination
angle to control the feed.
 Because of the need to support the grinding wheel,
throughfeed is not possible.
 Therefore it cannot achieve the high-production
rates as in the external process.
 capable of providing very close concentricity
between internal and external diameters on a
tubular part such as a roller bearing race.
Internal Centerless Grinding

Internal Centerless Grinding
FIGURE 25.12
Internal centerless grinding.

 It is performed at very high depths of cut and very
low feed rates; hence, the name creep feed.
 Depths of cut are 1000 to 10,000 times greater than
conventional surface grinding.
 the feed rates are reduced by about the same
proportion.
 However, material removal rate and productivity are
increased because the wheel is continuously
cutting.
 Typical advantages include:
1. high material removal rates,
2. Improved accuracy for formed surfaces, and
3. reduced temperatures at the work surface.
Creep Feed Grinding

Creep Feed Grinding
FIGURE 25.13
Comparison of (a) conventional surface grinding and (b) creep feed
grinding.

 It can be applied in both surface grinding and
external cylindrical grinding.
 Surface grinding applications include grinding of
slots and profiles.
 Especially suited to cases in which depth-to-width
ratios are relatively large.
 The cylindrical applications include threads, formed
gear shapes, and other cylindrical components.
 The term deep grinding is used in Europe.
Creep Feed Grinding

 Special features for creep feed grinding:
high static and dynamic stability,
highly accurate slides,
2-3 times the spindle power of conventional
grinding machines,
consistent table speeds for low feeds,
high-pressure grinding fluid delivery systems, and
dressing systems capable of dressing the grinding
wheels during the process.
Creep Feed Grinding Machines

Manufacturing 4/e
Creep-Feed Grinding
Figure 26.23 (a) Schematic illustration of the creep-feed grinding process. Note
the large wheel depth-of-cut, d. (b) A shaped groove produced on a flat surface
by creep-grinding in one pass. Groove depth is typically on the order of a few mm.
(c) An example of creep-feed grinding with a shaped wheel. This operation also
can be performed by some of the processes described in Chapter 27. Source:
Courtesy of Blohm, Inc.

 Special grinding machines of various designs to sharpen
and recondition cutting tools.
 They have devices for positioning and orienting the tools
to grind the desired surfaces at specified angles and
radii.
 Some are general purpose while others cut the unique
geometries of specific tool types.
 General-purpose grinders use special attachments and
adjustments to accommodate a variety of tool
geometries.
 Single-purpose tool grinders include
– gear cutter sharpeners,
– milling cutter grinders of various types,
– broach sharpeners, and
– drill point grinders.
Tool Grinding

Figure 28.24: Three typical setups for grinding single and multiple-edge tools
on a universal tool & cutter grinder. (a) single point tool is held in a device that
permits all possible angles to be ground. (b) Edgers of a large hand reamer
are being ground. (c) Milling cutter is sharpened with cupped grinding wheel.

 Traditionally used to grind holes in hardened steel parts
to high accuracies.
 Applications include
– pressworking dies and tools.
– broader range of applications in which high accuracy
and good finish are required on hardened
components.
 Numerical control is available on modern jig grinding
machines.
Jig Grinding

 Grinding machines with large abrasive disks mounted on
either end of a horizontal spindle.
 The work is held (usually manually) against the flat
surface of the wheel.
 Some machines have double opposing spindles.
– By setting the disks at the desired separation, the
workpart can be fed automatically between the two
disks and ground simultaneously on opposite sides.
 Advantages are
– good flatness and
– parallelism
at high production rates.
Disk Grinding

Disk Grinding
FIGURE 25.14
Typical conﬁguration of a disk grinder.

 It is similar in configuration to a disk grinder.
– The difference is that the grinding is done on the
outside periphery of the wheel rather than on the side
flat surface.
 The grinding wheels are therefore different in design.
 It is generally a manual operation, used for rough
grinding operations such as
– removing the flash from castings and forgings, and
– smoothing weld joints.
Snag Grinding

 It uses abrasive particles bonded to a flexible
(cloth) belt.
 A platen located behind the belt provides it
support required when the work is pressed
against it. This support is by a
– roll or
– a flat platen (for work having a flat surface).
– a soft platen if it is desirable for the abrasive
belt to conform to the general contour of the
part.
 Belt speed depends on the material being
ground; typical range 750 to 1700 m/min.
Abrasive Belt Grinding

 traditional applications in light grinding.
 Belt sanding: light grinding applications to
remove burrs and high spots, and produce an
improved finish quickly by hand.
 Owing to improvements in abrasives and
bonding materials, being used increasingly for
heavy stock removal rates,

FIGURE 25.15 Abrasive belt grinding.

Manufacturing 4/e
Belt Grinding of Turbine Nozzle Vanes
Figure 26.26 – Belt grinding of turbine nozzle vanes.

Other abrasive processes include
 honing,
 lapping,
 superfinishing,
 polishing, and buffing.
RELATED ABRASIVE PROCESSES

 It is an abrasive process performed by a set of
bonded abrasive sticks.
 Applications include finishing the bores of
– internal combustion engines (common).
– bearings,
– hydraulic cylinders, and
– gun barrels.
 Surface finishes of around 0.12 µm or slightly
better are typical.
 In addition, it produces a cross-hatched surface
that tends to retain lubrication, thus contributing
to its function and service life.
HONING

HONING
FIGURE 25.16
The honing process: (a) the honing tool used for internal bore surface, and (b)
cross-hatched surface pattern created by the action of the honing tool.

 The tool consists of a set of bonded abrasive
sticks.
 The number of sticks depends on hole size.
– Two to four sticks used for small holes (e.g.,
gun barrels), and
– a dozen or more used for larger diameter
holes.
 The motion of the tool is a combination of
rotation and linear reciprocation, regulated in
such a way that a given point on the abrasive
stick does not trace the same path repeatedly.
 This complex motion accounts for the cross-
hatched pattern on the bore surface.
HONING

HONING

 Honing speeds are 15 to 150 m/min.
 During the process, the sticks are pressed
outward against the hole surface to produce
the desired abrasive cutting action.
 Hone pressures of 1 to 3 MPa are typical.
 The honing tool is supported in the hole by two
universal joints,
– causing the tool to follow the previously
defined hole axis.
– It enlarges and finishes the hole but cannot
change its location.
HONING

 Grit sizes range between 30 and 600.
 The amount of material removed during a
honing operation may be as much as 0.5 mm,
but is usually much less than this. A
 cutting fluid must be used in honing to
– cool and lubricate the tool and
– to help remove the chips.
HONING

Manufacturing 4/e
Honing Tool
Figure 26.27 Schematic illustration of a honing tool used
to improve the surface finish of bored or ground holes.

 An abrasive process used to produce surface
finishes of extreme accuracy and smoothness.
 used in the production of
– optical lenses,
– metallic bearing surfaces,
– gages, and
– parts requiring very good finishes.
 Applications
– Metal parts that are subject to fatigue
loading or
– surfaces that must be used to establish a
seal with a mating part.
LAPPING

LAPPING
FIGURE 25.17
The lapping process in lens-making.

 Instead of a bonded abrasive tool, a fluid
suspension (lapping compound) of very small
abrasive particles is used between the
workpiece and the lapping tool.
 The lapping compound has the general
appearance of a chalky paste.
 The fluids used to make the compound include
oils and kerosene.
 Common abrasives are
– aluminum oxide and
– silicon carbide
 typical grit sizes between 300 and 600.
LAPPING

 The lapping tool is called a lap,
 it has the reverse of the desired shape of the
workpart.
 The lap is pressed against the work and moved
back and forth over the surface
– in a figure-eight or
– other motion pattern,
subjecting all portions of the surface to the
same action.
 sometimes performed by hand,
 lapping machines accomplish the process with
greater consistency and efficiency.
LAPPING

 Materials used to make the lap range from
– steel and cast iron
– copper and
– Lead
– Wood
 It is hypothesized that two alternative cutting
mechanisms are at work in lapping.
1.the abrasive particles roll and slide between
the lap and the work, with very small cuts
occurring in both surfaces.
2.the abrasives become embedded in the lap
surface and the cutting action is very similar
to grinding.
LAPPING

 For laps made of soft materials, the embedded
grit mechanism is emphasized; and
 for hard laps, the rolling and sliding mechanism
dominates.
LAPPING

Manufacturing 4/e
Production Lapping
Figure 26.29 (a) Schematic illustration of the lapping process. (b) Production
lapping on flat surfaces. (c) Production lapping on cylindrical surfaces.

 It is an abrasive process similar to honing.
– Both processes use a bonded abrasive stick
moved with a reciprocating motion.
 The two differs in:
1.the strokes are shorter, 5 mm;
2.higher frequencies, up to 1500 strokes per
minute;
3.lower pressures are applied between the
tool and the surface, below 0.28 Mpa
4.workpiece speeds are lower, 15 m/min or
less; and
5.grit sizes are generally smaller.
SUPERFINISHING

SUPERFINISHING
FIGURE 25.18
Superﬁnishing on an external cylindrical surface.

 The relative motion of the abrasive stick is
varied so that individual grains do not retrace
the same path.
 Cutting fluid is used to
• cool the work surface
• wash away chips
• separate the abrasive stick from the work
surface after a certain level of smoothness
is achieved.
 The result is mirror-like finishes (surface
roughness around 0.025 mm).
 used to finish flat and external cylindrical
surfaces.
SUPERFINISHING

Manufacturing 4/e
Superfinishing Process
Figure 26.28 Schematic illustration of the superfinishing process for a cylindrical
part. (a) Cylindrical microhoning. (b) Centerless microhoning.

 Used to remove scratches and burrs and to
smooth rough surfaces
 abrasive grains are glued to the outside
periphery of the wheel
 Rotate at high speed—around 2300 m/min.
 The wheels are flexible and made of
• canvas,
• leather,
• felt, and even
• paper;
POLISHING

 After the abrasives have been worn down and
used up, the wheel is replenished with new
grits.
 Grit sizes
• 20 to 80 for rough polishing,
• 90 to 120 for finish polishing, and
• above 120 for fine finishing.
 Polishing operations are often accomplished
manually.
POLISHING

 Similar to polishing in appearance, but different
in function.
 used to provide attractive surfaces with high
luster.
 wheels materials similar to those used for
polishing wheels.
• but buffing wheels are generally softer.
 The abrasives are very fine and are contained
in a buffing compound.
 usually done manually, (automatic machines
also available)
 Speeds are generally 2400 to 5200 m/min
BUFFING

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