grinding.pdf finishing operation machining

ME 338: Manufacturing Processes II
Instructor: Ramesh Singh; Notes: Profs.
Singh/Melkote/Colton
Grinding and Finishing
Illegitimi non carborundum
ver. 1
1

Overview
• Processes
• Analysis
2

3

Horizontal Grinding
4

5

6
Horizontal grinding Vertical grinding

7
Centered grinding
Centerless grinding

Creep Feed Grinding
8
• Full depth and stock is removed with
one or two passes at low work speed
• Very high forces are generated
• High rigidity and power
Advantages
• Increased accuracy
• Efficiency
• Improved surface finish
• Burr reduction
• Reduced stress and fatigue

9

10

11

12

Grinding Wheels
13

Grinding Wheels
14

Grinding Wheel Information
15

16
Correctly Mounted Wheel

Grinding Wheel Surface
17

Grind Wheel Dressing
18

Grinding Wheel Dressing
19

Grinding Chips
20

Chip formation geometry
21
D
v
V
d
t
q
l
w
t
l

Chip geometry
• As with rolling contact length, the chip length,
l
– D = wheel diameter, d = depth of cut
• Material removal rate, MRR
– v = workpiece velocity, d = depth of cut, b = width
of cut
23
d
D
l 

b
d
v
MRR 



Material removal rate
• The chips have a triangular cross-section,
and ratio (r) of chip thickness (t) to chip width
(w)
• So, the average volume per chip
24
20
10 to
t
w
r 

wtl
l
t
w
Volchip
4
1
2
1
2
1




w
t
l

Chips
• The number of chips removed per unit time
(n), where c = number of cutting edges
(grains) per unit area (typ. 0.1 to 10 per mm2,
and V = peripheral wheel velocity
25
c
b
V
n 



Combining
26
t
r
w 
 d
D
l 

chip
Vol
n
b
d
v
MRR 




wtl
Vbc
b
d
v
4
1




d
D
t
t
r
b
c
V
b
d
v 









4
1

Chip thickness
27
d
D
r
c
V
d
v
t





4
2
or
D
d
r
c
V
v
t



4

Specific grinding energy, u
• Consist of chip formation, plowing, and sliding
28
sliding
plowing
chip u
u
u
u 



Total grinding force
• Get force from power
29
MRR
u
Power 

b
d
v
u
V
Fgrinding 




V
b
d
v
u
Fgrinding





• From empirical results, as t decreases, the
friction component of u increases
30
t
u
1

t
K
u
1
1 

or
substituting
V
b
d
v
t
K
Fgrinding





1
1

31
ME 6222: Manufacturing Processes and
Systems Prof. J.S. Colton © GIT 2006
Substituting for t
V
b
d
v
D
d
r
c
V
v
K
Fgrinding








4
1
1
rearranging
d
D
V
v
r
c
d
b
K
Fgrinding 







4
1

Force on a grain
• The force per grain can be calculated
32
Area
u
Fgrain 

wt
u
Fgrain
2
1


rt
w
and
t
K
u
1
1 

t
t
r
t
K
Fgrain 





2
1
1
1

Force on a grain
33
ME 6222: Manufacturing Processes and
Systems Prof. J.S. Colton © GIT 2006
substituting for t, and rearranging
D
d
r
c
V
v
r
K
Fgrain





4
2
1
D
d
c
V
r
v
K
Fgrain



 1

Grinding temperature
• Temperature rise goes with energy delivered
per unit area
34
area
input
Energy
K
T 

 2
d
t
K
K
l
b
d
l
b
u
K
T 










1
1
2
2
D
d
Vcr
v
d
K
K
T
4
1
2
1 





Grinding temperature
• Rearranging
∆𝑇 = 𝐾1𝐾2𝑑
3
4
𝑉 𝑐 𝑟
4 𝑣
𝐷
• Temperatures can be up to 1600oC, but for a
short time.
35

Grinding – Ex. 1-1
• You are grinding a steel, which has a specific
grinding energy (u) of 35 W-s/mm3.
• The grinding wheel rotates at 3600 rpm, has a
diameter (D) of 150 mm, thickness (b) of 25 mm, and
(c) 5 grains per mm2. The motor has a power of 2
kW.
• The work piece moves (v) at 1.5 m/min. The chip
thickness ratio (r) is 10.
• Determine the grinding force and force per grain.
• Determine the temperature (K2 is 0.2oK-mm/N).
Room temperature is 20oC.
36

• First we need to calculate the depth of cut.
We can do this from the power.
37
b
d
v
u
MRR
u
Power 





sec
60
min
10
25
min
5
.
1
35
2000 2
2
6
3







m
mm
mm
d
m
mm
s
W
W
m
d 6
10
4
.
91 



• Now for the total grinding force
38
V
b
d
v
u
Fgrinding




mm
m
rev
mm
rev
mm
mm
mm
mm
s
W
Fgrinding
1000
150
min
3600
25
10
4
.
91
min
1500
35
3
3










N
Fgrinding 7
.
70


• Next, the force per grain
39
wt
u
Fgrain
2
1

 rt
w
t
t
r
u
Fgrain 



2
1
and
we need t
mm
mm
mm
grains
mm
mm
D
d
r
c
V
v
t
150
10
4
.
91
10
5
min
150
3600
min
1500
4
4 3
2











mm
t 3
10
32
.
1 



• Substituting
40
 2
3
10
32
.
1
10
2
1
35
2
1 








 t
t
r
u
Fgrain
mm
J
Fgrain /
10
05
.
3 4




• For the temperature, we need K1 and K2. K2 is
given, so we need to calculate K1.
41
t
r
K
t
t
r
t
K
t
t
r
u
Fgrain 














2
1
2
1
1
2
1
1
1
m
K
N 6
1
1
10
32
.
1
10
2
1
10
05
.
3 







m
N
K 3
1 10
2
.
46 


• substituting
42
K
m
m
m
N
N
m
K
T 








 

640
10
4
.
91
10
32
.
1
1
2
.
46
2
.
0 6
6
C
T
T
T initial 





 660
640
20
d
t
K
K
T 




1
1
2

Honing and Superfinishing
Honing tool used to improve
the surface finish of bored or
ground holes.
Schematic
illustrations of the
superfinishing
process for a
cylindrical part.
(a) Cylindrical
mircohoning, (b)
Centerless
microhoning.

Lapping
(a) Schematic illustration of the lapping process. (b)
Production lapping on flat surfaces. (c) Production lapping
on cylindrical surfaces.

Polishing Using Magnetic
Fields
Schematic illustration of polishing of balls and rollers
using magnetic fields. (a) Magnetic float polishing of
ceramic balls. (b) Magnetic-field-assisted polishing of
rollers. Source: R. Komanduri, M. Doc, and M. Fox.

Abrasive-Flow Machining
Schematic illustration of
abrasive flow machining to
deburr a turbine impeller.
The arrows indicate
movement of the abrasive
media. Note the special
fixture, which is usually
different for each part
design. Source: Extrude
Hone Corp.

Robotic Deburring
A deburring operation on a robot-held die-cast
part for an outboard motor housing, using a
grinding wheel. Abrasive belts or flexible
abrasive radial-wheel brushes can also be used
for such operations. Source: Courtesy of
Acme Manufacturing Company and
Manufacturing Engineering Magazine,
Society of Manufacturing Engineers.

Conformal Hydrodynamic Nanopolishing:
Case-study
Applications
• Optics
• Defence & Nuclear
• Electronics
• Industrial
Existing Methods
• Diamond Turning
• Precision Grinding
• Lapping
• Ion Beam Polishing
• Spot Hydrodynamic Polishing
Challenges
• Most processes can polish only flat
surfaces; concave/profiled surfaces
are difficult to superfinish
• Concave surface on hard brittle
materials, such as single crystal
sapphire can not be finished via form
grinding due to process-induced
cracks
• Diamond turning center can be used
for non ferrous materials but it is a
super-precision machine-tool (The
equipment cost is ~ 20 crores besides
the expensive operational cost)
1

Conformal Hydrodynamic
Nanopolishing Process and Machine
Process Description
• Improvement over existing
spot hydrodynamic polishing
methods
• Superfinish hard and brittle
concave surfaces, specially,
sapphire and hardened steels
• Mitigates existing surface
microcracks
• Polishing action due to
elastohydrodynamic film in
the slurry submerged
rotating conformal contact
(silicone ball in the cavity
being polished) 1st
Generation
2nd Generation Conformal Hydrodynamic Nanopolishing Machin
Delivered to Precison Engineering Division BARC
(designed and fabricated in the Machine Tools Lab
at IIT Bombay)
2

Novelty and Technology Breakthrough
• Existing hydrodynamic polishing employs spot polishing unable to
polish small cavities (< 6mm in dia)
– More than 3 degrees of freedom required to polish the entire cavity
effectively
– Small actuation system and polishing tool is required
• Conformal contact has a rotating soft tool which conforms to the shape
of the cavity
• Axis of this tool is inclined at 45˚ and the workpiece is rotated inside a
slurry filled tank which ensures non-zero relative motion between tool
and workpiece at every location in the cavity
• The entire cavity can be polished at once which will be much cheaper
and faster than programming the tool path
• Alternative to expensive Diamond Turning
• Can finish wide range of materials ceramics (sapphire, glass) and
hardened steels
3

Technology Outcomes
• Superfinished surfaces in
steels (< 3nm 3D surface
roughness)
• Crack-free surface of < 100
nm 3D surface roughness in
single crystal sapphire
cavity
• Process knowhow and
machine transferred to
Precision Engineering
Division, BARC for strategic
applications in a nuclear
device
• The superfinished obtained
at a fraction of cost of
Diamond turning
• It can also be used by gem
polishers which could
reduce the health hazard by
reducing the dust inhalation
and automation is possible
Nanometric finish on hardened steel
Crack-free superfinished surface on single
crystal sapphire cavity
4

Economics of Grinding and Finishing
Operations
Increase in the cost of
machining and finishing a
part as a function of the
surface finish required.
This is the main reason
that the surface finish
specified on parts should
not be any finer than
necessary for the part to
function properly.

Summary
• Overview of processes
• Analysis of process
• Example problem
54

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