Pneumatic Non-Contact Roughness Assessment

Pneumatic Non-Contact Roughness
Assessment of Moving Surfaces
D. Grandy, P. Koshy
McMaster University, Canada

F. Klocke
RWTH Aachen, Germany

www.taylor-hobson.com

www.taylor-hobson.com

Development towards in-process roughness estimation
Issues with machining debris and cutting fluid
Development of a pneumatic sensor

2/23
Pneumatic Non-contact Roughness Assessment of Moving Surfaces
D. Grandy, P. Koshy, F. Klocke

59th CIRP General Assembly
Boston, August 26, 2009

Principle of pneumatic gauging
ps air
control orifice

pb

pressure transducer
P

xi

ps
work

Back pressure pb depends on xi
Primarily quasi-static applications

pb

xi

3/23


Surface porosity detection in machined castings
air

piezoelectric
pressure transducer
Menzies & Koshy (2009)

work

transducer

workpiece

cutting tool

5 mm

nozzle

Sensor integrated
into the cutting tool
holder for in-process
application, in the
presence of a flood
coolant
4/23



Reliability of pneumatic
gauging deteriorates as
the peak-to-valley height
of the surface exceeds
about 3 µm
Related previous work

US patent 2,417,988 (1947)

Nicolau (1937)
Hamouda (1979)
Tanner (1982)
Wang & Hsu (1987)
Woolley (1992)

Nozzle is in contact with
workpiece, and is hence
not suitable for in-process
application

US patent 7,325,445 (2004)

5/23


The present work pertains
to non-contact roughness
assessment of moving
surfaces
Roughness is related to the
frequency content of the
back pressure signal

air
frequency
decomposition
P

pb
xi

work

6/23


Working principle
nozzle

7/23


Experiments on plane surfaces

piezo pressure
transducer
nozzle diameter (dn)

nozzle

1.5 mm

control orifice diameter (dc) 0.84 mm
supply pressure (ps)

138 kPa

stand-off distance (xi)

50 µm

nozzle feed rate

0.4 m/min

8/23


Comparison of stylus and pneumatic signals from
milled and turned surfaces of roughness 3.2 µm Ra
Height (µm)

15

milled surface

turned surface

10
5
0

stylus

-5

Voltage (V)

-10
1.0
0.5
0.0

pneumatic

-0.5
-1.0
0

2

4

6

8

Distance (mm)

10 0

2

4

6

8

10

Distance (mm)

9/23


Amplitude (V)

Amplitude (µm)

Frequency domain comparison of stylus and
pneumatic signals
6

milled surface

turned surface

4

stylus
2
0
0.45
0.30

pneumatic
0.15
0.00
0

1

2

3

4

5

Frequency (mm-1)

6 0

1

2

3

4

5

6

Frequency (mm-1)
10/23



Frequency spectra corresponding to milled surfaces
of various roughness values

5 plots shown for each roughness

??
11/23


Correlation of pneumatic indices to roughness
measured using a stylus instrument
Area under the frequency plot
Amplitude of dominant frequency
1.5
Amplitude (V)

Area (V/mm)

0.45
0.30
0.15
0.00

1.0

0.5
0.0

0

3

6

9

12 15

Roughness Ra (µm)

0

3

6

9

12 15

Roughness Ra (µm)

12/23


Normalized amplitude

Effect of supply pressure
9
6
3
0

0

100

200

300

400

Supply pressure (kPa)
ps
dc

air

pb

P

xi

dn
work
13/23


Effect of control orifice diameter dc
Normalized amplitude

3
dc = 0.50 mm

2

experimental

dc = 0.84 mm

1
0
3

dc = 0.50 mm

2

dc = 0.84 mm

1

analytical

0

ps

0

50

100

150

200

250

300

Stand-off distance (µm)

dc

air

pb

xi

dn
work
14/23


Experiments on rotating cylindrical surfaces
~25 mm

30 m/min

nozzle feed rate

0.2 mm/rev

stand-off distance (xi)

50 µm

supply pressure (ps)

138 kPa

nozzle diameter (dn)
turned surface

workpiece diameter

surface speed

nozzle

1.5 mm

control orifice diameter (dc)

0.84 mm

hardness

workpiece

nozzle

quenchant

15/23


Effect of increasing roughness
increasing roughness
quenched end
of Jominy specimen

Amplitude (V)

0.4

1.2 µm Ra

3.8 µm Ra

1 mm

0.3

1 mm

0.2
0.1
0.0
0

8

16 24 32 40 48
Frequency (Hz)

0

8

16 24 32 40 48
Frequency (Hz)
16/23



Effect of relative speed between nozzle and work
Sensor response
can be improved by
minimizing the
volume of the
variable pressure
chamber

60 m/min

0.10
100 m/min

200 m/min

0.05

Amplitude (V)

0.15

0.00

0

20

40

60

80

Frequency (Hz)
17/23


Effect of application of cutting fluid

without cutting fluid

0.3

with cutting fluid

0.2

0.1

Amplitude (V)

0.4

0.0

0

8

16

24

32

40

48

Frequency (Hz)

Flood coolant application
has minimal influence on
sensor performance

18/23


20
15
10
5
0

0.1 µm Ra ground

Amplitude (mV)

0

6
4
2
0

Amplitude (mV)

Amplitude (mV)

Recent work on extension to fine surfaces

15

5

10
15
20
-1)
Frequency (mm

12

25

30

9

6

0.1 µm Ra lapped

20
15
10
5
0
0

5

pressure

25

30

4

6

2

3
0

0

23

0 24 3

6

25 9

12

26
15

18

27
21

20
24

27

21
30

1.5

Amplitude (mV)

10
15
20
Frequency (mm-1)

vibration

1.2

0.9
0.6

0.3
0.0
0

3

6

9

12

15

18

21

Frequency (1/mm)

24

27

22

23

24

Back pressure
signals are
noisy, and are
affected by
vibration 

30
19/23

Principal Components Analysis
Observations

Variables
X1

X2

X3

…

…

G1
G2

X2

L1
L2

…

t2

P
S

X3

t1

X1
20/23



Application of principal components analysis

Workset
Predictionset

95% limit

20
lapped

tPS[2]
t2

10
0
-10

ground

-20

Filled symbols refer
to test data not
considered when
building the model

-40

-30

-20

-10

0

10

20

30

40

t1
tPS[1]
SIMCA-P 11.5 - 5/29/2009 9:40:58 AM

21/23


Conclusions
Proof-of-concept of pneumatic non-contact roughness
assessment of moving surfaces has been established
In its present state of development, the system is best
suited for in-situ process monitoring based on
appropriate calibration
The system exhibits potential for in-process application
in the presence of machining debris and cutting fluid
that generally obscure the measurement process when
using optical instruments
Future work will focus on the physics of jets impinging
on laterally moving surfaces, taking roughness into
consideration
22/23


Thank you
for
your attention!

Natural Sciences & Engineering
Research Council of Canada

For more details please see: D. Grandy, P. Koshy, F. Klocke, Pneumatic non-contact
roughness assessment of moving surfaces, CIRP Annals 58 (2009) 515-518.

23/23

Pneumatic Non-Contact Roughness Assessment

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