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CIRP JANUARY MEETINGS 2011, PARIS

MULTI-SENSORY APPROACH FOR CONDITION MONITORING OF ABRASIVE WATERJET CUTTING HEADABRASIVE WATERJET CUTTING HEAD

N. RAMESH BABU AND J. JOHN ROZARIO JEGARAJ

MANUFACTURING ENGINEERING SECTIONDEPARTMENT OF MECHANICAL ENGINEERING INDIAN INSTITUTE OF TECHNOLOGY MADRASINDIAN INSTITUTE OF TECHNOLOGY MADRAS

CHENNAI – 600 036

ACKNOWLEDGEMENTS

• Thanks to Volkswagen Stiftung for financial support to this Collaborative Research Project on “Adaptive Control of Abrasive Water Jet Cutting Process with S ft C ti A h ”Soft Computing Approaches”

Th k t P f D I H t t L i W t J t• Thanks to Prof. Dr. –Ing. Hartmut Louis, Water Jet Laboratory, University of Hannover, Hannover, GermanyGermany

• Thanks to Prof Dr – Ing Bach and Prof Dr – Ing• Thanks to Prof. Dr. – Ing. Bach and Prof. Dr. – Ing. Haferkamp, University of Hannover

OUTLINE OF PRESENTATION

Introduction Motivation and Importance of the Work Objectives Objectives Methodology for Monitoring of Cutting Head St t i f it i th diti f tti Strategies for monitoring the condition of cutting

head Conclusions

INTRODUCTION

AWIJ AWSJ

Source: Waterjet laboratory University of HannoverSource: Waterjet laboratory, University of Hannover

TYPES OF ABRASIVE WATERJETS

FOCUS ON AWIJ CUTTING SYSTEM

HP Water

Abrasive

!

Abrasive Waterjet Cutting System Cutting Head Mixing Head

PROCESS PARAMETERS IN AWJ CUTTING

1. Hydraulic1. Waterjet Orifice2. Waterjet Pressure

2. AbrasiveG S1. Abrasive Grit Size

2. Abrasive Material3. Abrasive Flow rate

3. Focusing Nozzle1. Bore Diameter2. Tube Length Performance3. Material

4. Cutting Parameters1 T S d

Performance1. Depth of cut2. Kerf Width3 Surface Roughness1. Traverse Speed

2. Standoff Distance3. Angle of Attack

3. Surface Roughness4. Material Removal

Rate5. Cutting Efficiency

February 3, 2011 65. Work / Target Material

CUT SURFACE TOPOGRAPHYKERF GEOMETRY

INTRODUCTION …contd.CUT SURFACE TOPOGRAPHYKERF GEOMETRY

1

Jet TraverseSmooth zone

2Transition zone

Rough zone

3

1 Smooth zone1. Smooth zone2. Transition Zone3. Striation zone

PERFORMANCE OPTIMIZATION

Criteria employed for optimum performance

Minimise the cost per unit volume of material removed p

High rate of cutting

Achieve consistent quality

Based on the applications, abrasive waterjet cut can be characterised into

Separation Cut - energy efficient, rough surface finish

Application : Rough cutting

Quality Cut - High energy requirement, Good surface finish and kerf quality

Application : Precision cuttingApplication : Precision cutting

Blind Cut - Cutting depends on input energy of AWJ

Application : Pocket millingApplication : Pocket milling

REVIEW OF WORK ON PARAMETRIC STUDIESEFFECT OF PROCESS PARAMETERS

DYNAMIC VARIABLES QUASI STATIC VARIABLES STATIC VARIAB ESDYNAMIC VARIABLES• Waterjet Pressure

• Abrasive Flow Rate

QUASI – STATIC VARIABLES• Orifice diameter

• Focusing nozzle diameter

STATIC VARIABLES• Focusing Nozzle Length• Abrasives size and

quality• Traverse Rate diameter

- Hashish (1989)

quality

Controllable Uncontrollable( )

February 3, 2011 9(Momber and Kovacevic 1998)

Parametric Studies

EFFECT OF PROCESS PARAMETERS

OrificeEnergy of jet

Structure of jet

Geometry of

affectPerformance

Focusing nozzleStructure of jet

February 3, 2011 10

(Nanduri et al. 1999)(Momber and Kovacevic 1998) (Nanduri et al. 1999)

IMPORTANCE OF THE WORK

Monitoring of nozzle wear is a key aspect in producing high quality parts on a fully automated abrasive waterjet cutting system

- Kovacevic et al. (1989)

The coherence length of the waterjet depends on the health of theorifice. A long coherence length provides efficient and stable machining conditions.

- Hashish (1993)

Focusing tube is the most critical component for the technical andeconomic performance of AWJeconomic performance of AWJ

- Hashish (1994)

AWJ nozzle wear causes incomplete mixing of the abrasive particles with high p g p gvelocity waterjet results in deterioration in cutting ability, poor surface Quality and affects the precision of machining.

Hence suitable methods to be devised to ensure uniform product quality at

desired levels, by replacing or compensating for the worn nozzle at the right time

- Kovacevic, Hashish, Ramulu, Kim, Geskin (1997)

RECOMMENDED SPECIFICATIONSF AWJ i h di h f 2 2 li / i h For AWJ system with discharge rate of 2.2 litres / min, the recommended specifications of orifice and focusing nozzle are Orifice – 0.25 mm

Focusing nozzle - 0.76 mm (Orifice to focusing nozzle ratio – 1:3)

1 .6Not widely used

1

1 .2

1 .4

ize

(mm

)

y

Not investigated

Acceptable

0 .6

0 .8

1

g no

zzle

s Not investigated

0 .2

0 .4

0 .6

Focu

sin

00 .15 0 .2 0 .25 0 .3 0 .35 0 .4

Orifice s ize (m m )

February 3, 2011 12

Orifice s ize (m m )

ISSUES

ORIFICE AND FOCUSING NOZZLE

Process output Process monitoring

DECISION STRATEGY

OBJECTIVES

To investigate the influence of orifice and focusing nozzle size on tti f ffi i d lit f tti ith b icutting performance, efficiency and quality of cutting with abrasive

waterjets

To develop an integrated monitoring system for focusing nozzle wear g g y gand orifice wear in AWJ Cutting

Orifice wearOrifice wear

0 25 0 3 0 40.25 0.3 0.4

0.76 1.02 1.2 1.6

Focusing Tube Wear

Waterjet PressureWaterjet Pressure

Abrasive Flow Rate

100 MPa 175 MPa 250 MPa

Abrasive Flow Rate

0.07 kg/min

0.11 kg/min

0.22 kg/min

EXPERIMENTAL STUDIES – Design of Experiments

ORIFICE

• 0.25 mm

FOCUSING TUBE

• 0.76 mm

PRESSURE

• 100 MPa

ABRASIVE FLOW RATE

• 0 027 kg/min

TRAVERSE RATE

• 30 mm/min• 0.30 mm

• 0.35 mm

• 1.20 mm

• 1.60 mm

• 175 MPa

• 250 MPa

• 0.027 kg/min

• 0.149 kg/min

• 0.272 kg/min

30 mm/min

• 60 mm/min

• 90 mm/min

DOE

using L27 OAMaterial

Aluminum 6063 – T6 alloy

Effect of Pressure

Effect of Abrasive Flow RateInteraction of orifice size Effect of Abrasive Flow Rate

Effect of Traverse rate

Effect of Orifice size

Interaction of orifice size and focusing tube size

Interaction of abrasive flow

Depth of cut, Top Kerf width, Surface Roughness (upper)

Effect of Focusing tube sizerate and focusing tube size

PRELIMINARY STUDIES

EXPERIMENTATION - Design of Experiments (L27 OA)

35

MEAN RESPONSE CURVE - Depth of Cut

PRELIMINARY STUDIES

25

30

35

mm

)

do1

do2df3

df2

df1

15

20

h of

cut

(m do3 df2

df1

df1

0

5

10

Dep

t

df3

0

P1 P2 P3 m1

m2

m3 v1 v2 v3 do1

do2

do3

df1

df 2 df3 m1

m2

m3

m1

m2

m3

do1

do2

do3

Process parameters

b i fl t (0 03 0 15 0 27 k / i ) d ifi i (0 25 0 3 0 35 ) m – abrasive flow rate (0.03, 0.15, 0.27 kg/min) ; do – orifice size (0.25, 0.3, 0.35 mm);

df – Focusing nozzle size (0.76, 1.2, 1.6 mm) ; P – Waterjet pressure (100, 175 , 250 MPa);

v – Traverse rate (30, 60, 90 mm/min)

February 3, 2011 17

PRELIMINARY STUDIES


MEAN RESPONSE CURVE - Kerf Width at Top region

PRELIMINARY STUDIES

1 41.61.8

2

(mm

)

do1

df3df3

df2

0 60.8

11.21.4

erf W

idth

do1do2do3

df2

df1

df2

df1

00.20.40.6

Top

Ke

P1 P3 m1

m3 v1 v3 do1

do3

df1

df3 m1

m3

m1

m3

do1

do3

Process parameters

m – abrasive flow rate (0 03 0 15 0 27 kg/min) ; do – orifice size (0 25 0 3 0 35 mm); m abrasive flow rate (0.03, 0.15, 0.27 kg/min) ; do orifice size (0.25, 0.3, 0.35 mm);



February 3, 2011 18

PRELIMINARY STUDIES


MEAN RESPONSE CURVE - Surface Roughness at upper region

PRELIMINARY STUDIES

8

9

ough

ness

df2df2

d 3

5

6

7

Surf

ace

Ro

(µm

)

df1

df1

df3

do3

do1

do2

3

4

5

Ave

rage

S df3do2

P1 P3 m1

m3 v1 v3 do1

do3

df1

df3

m1

m3

m1

m3

do1

do3

Process parameters

m – abrasive flow rate (0 03 0 15 0 27 kg/min) ; do – orifice size (0 25 0 3 0 35 mm); m abrasive flow rate (0.03, 0.15, 0.27 kg/min) ; do orifice size (0.25, 0.3, 0.35 mm);



February 3, 2011 19

PRELIMINARY STUDIES


CONTRIBUTION OF VARIOUS PROCESS PARAMETERS ON PERFORMANCE

PRELIMINARY STUDIES

Others2%

Pressure15%

Traverse rate22%

Orif ice size5%

Focusing Abrasive f low rate

7%

Traverse

Others36%

Abrasive

Focusing nozzle size

1%

others 20%


98%

rate18%

Orif ice size3%


Abrasive f low rate

33%

20%

Pressure19%(a) (b) (c) 3%nozzle size

21%19%(a) (b) (c)

kerf width at top region

Surface roughness (Ra) at upper region

Depth of cut

February 3, 2011 20

ORIFICE DAMAGE MODES OF WEAR IN FOCUSING NOZZLEMONITORING OF CUTTING HEAD

Modes of wear

1. Impact erosionbeginning atthe entry zone

SMOOTH BORE

the entry zone

2. Sliding erosion inthe downstream areaWATER

ORIFICEJET

SPREADING

RANDOM IMPACT

RANDOM PARTICLE ENTRY

DAMAGED BORESHALLOW IMPACT ANGLES OR ABRASION

ZONE

ANGLES OR ABRASIONMIXING TUBE

ORIFICE DAMAGE

MONITORING OF CUTTING HEAD …contd.

Orifice size : 0.25 mm; 0.30 mm;

0.35 mm; 0.40 mm

Orifice (a) New Orifice

(b) Used Orifice(b) Used Orifice

VISUALIZATION


VISUALIZATION

Comparison of the image of the jet emerging out of new orifice and worn out orifice

Orifice 0.25 mm (new)Orifice 0.40 mm (new)

IMPRINT TAKEN ON COPPER PLATE

Orifice 0.25 mm (old) Orifice 0.40 mm (old)


VISUALIZATION

I f th j t i t f f i lImage of the jet emerging out of focusing nozzle

Pressure - 50 MPa

Focusing Nozzle size - 0.76, 1.02, 1.2, 1.6 mm

LITERATURE – Monitoring studies


Orifice Conditiong

Direct Methods Indirect Methods

Optical Tracking Visual Examination Acoustic based approach Vacuum based approach

Visual Examination

Focusing Nozzle Wear

Direct Methods Indirect Methods

W i ht L Optical Tracking Noise monitoring Weight Loss Wear Profiling X Ray examination

Optical Tracking

Ultrasonic gauging

Vibration monitoring

Noise monitoring

Using Wear Sensor probe

Vacuum Measurement Vibration monitoring Vacuum Measurement in the mixing chamber


Sl. No

Authors and year of Publication

Target parameters

Method of monitoring Remarks(if any)

REVIEW OF LITERATURE – Monitoring studies

No. year of Publication parameters (if any)1. Nanduri et al. (1996) Focusing

nozzle wearWear profiling –Pinning and casting

Offline

2 Kovacevic et al Focusing Optical jet tracking Online2. Kovacevic et al. (1990)

Focusing nozzle wear

Optical jet trackingUltrasonic gaugingVibration monitoringNoise monitoring

Online

3. Kovacevic et al.(1991) Focusing nozzle wear Wear probe sensor Online

4. Zeng et al ( 1994). Focusing nozzle wear, Orifice wear

Vacuum pressure monitoring

Online

5. Hashish et al.(1993)

Orifice wear Acoustic based approachVacuum based approach

Online

6. Knaupp (1993) Orifice wear Optical inspection of jet Online

7. Kovacevic (1992) Depth ofpenetration

Normal Reaction Forcesensing

Online

HIGH PRESSURE SENSOR

MULTI SENSORY APPROACH


ENTRAIMENT VACUUM SENSOR

THICKNESSTHICKNESS MEASUREMENT

TEMPERATURE MEASUREMENT

IMAGE PROCESSING

FORCEFORCE DYNAMOMETER

EXPERIMENTATION PLANMONITORING OF CUTTING HEAD …contd.

EXPERIMENTATION

ORIFICE FOCUSINGNOZZLE

Wear Variation in size WearVariation in size

AB BA

Monitoring StudiesMonitoring Studies

Monitoring Studies

3 0 0 0

d : 0 .2 5 m m d : 0 .3 0 m m d : 0 .3 5 m m d : 0 .4 0 m m

MONITORING OF CUTTING HEAD - HIGH PRESSURE SENSOR

2 0 0 0

2 5 0 0

sing

sen

sor

1 0 0 0

1 5 0 0

ed p

ress

ure

us

(bar

)

RESULTS

CONDITION - A

0

5 0 0

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0

Mea

sure

H y d r a u lic P u m p s e t p r e s s u r e ( b a r )

6

P:100 MPa P:150 MPa

P:200 MPa P : 250 MPa

4

5

put (

Volts

)

1

2

3

Sens

or O

utpu

00.25 0.3 0.35 0.4

Orifice size (mm)

S

RESULTS


d : 0.25 mm; P : 100 MPa6

d : 0.25 mm; P :250 MPa6

CONDITION - A

3

4

5

outp

ut (v

olts

)

3

4

5

outp

ut (v

olts

)

0

1

2

0 2 4 6 8 10

Sens

or o

0

1

2

0 2 4 6 8 10

Sens

or o

0 2 4 6 8 10Time (sec)

0 2 4 6 8 10Time (sec)

d : 0.30 mm ; P :100 MPa d : 0.30 mm; P : 250 MPa

3

4

5

6

put (

volts

)

3

4

5

6pu

t (Vo

lts)

0

1

2

3

0 2 4 6 8 10

Sens

or o

ut

0

1

2

3

0 2 4 6 8 10

Sens

or o

ut

Time (sec) Time (sec)

RESULTS


d : 0.35 mm; P : 100 MPa6

d : 0.35 mm; P : 250 MPa

5

6

CONDITION - A

3

4

5

outp

ut (v

olts

)

3

4

5

r out

put (

volts

)

0

1

2

Sens

or o

0

1

2

0 2 4 6 8 10

Sens

or

0 2 4 6 8 10Time (sec)

0 2 4 6 8 10Time (sec)

d : 0.40 mm; P : 100 MPa6

d : 0.4 mm; P : 250 MPa6

3

4

5

tput

(vol

ts)

3

4

5tp

ut (v

olts

)

0

1

2

3

Sens

or o

ut

0

1

2

Sens

or o

ut

00 2 4 6 8 10

Time (sec)

00 2 4 6 8 10

Time (sec)

RESULTSCONDITION A


Orifice 0.25 mm; P 100 MPa Orifice 0.25 mm; P 250 MPaCONDITION - A

Orifice 0.30 mm; P 100 MPa Orifice 0.30 mm; P 250 MPa

RESULTSCONDITION - A



CONDITION - A



RESULTS

CONDITION - A

0.16

d :0.25 mm d: 0.30 mm d : 0.35 mm d : 0.40 mm

0.08

0.12

valu

e (v

olts

)

0

0.04

100 150 200 250

RM

S v

100 150 200 250

Waterjet set pressure (MPa)

MONITORING SUCTION PRESSURE

MONITORING OF CUTTING HEAD

INSIDE MIXING CHAMBERIn abrasive water injection jets

orifice mixing chamber and focusing orifice, mixing chamber and focusing tube is similar to a jet pump

The suction pressure is proportional to

the quantity of liquid flow through the orifice.

the diameter of focusing tube

Pressure fluctuations

Turbulence

S f Size of suction duct etc.

Monitoring of suction pressure inside chamber is useful to study

Orifice condition

Focusing tube conditionAWJC set up with vacuum sensor

Abrasive flow condition etc.

Vacuum sensor

SIMULATION STUDIES – MONITORING SUCTION PRESSURE INSIDE MIXING CHAMBER

MONITORING OF CUTTING HEAD - VACUUM SENSOR

0.25 0.3 0.35Orifice

CHAMBER0.4

0.76 1.02 1.2 1.6 0.76 1.02 1.2 1.6 0.76 1.02 1.2 1.6

Focusing tube Focusing tube Focusing tube

0.76 1.02 1.2 1.6

Focusing tube

Pressure25 – 300 MPa




SUCTION PRESSURE INSIDE MIXING CHAMBER

Condition abrasive feed line - blocked

VACUUM MONITORING SETUP


Hopper

Vacuum sensorHP WATER

Vibratory Feeder

Orifice

Abrasive shut off valve

Vacuum Sensor

Mixing CChamber

Focusing Nozzle

Focusing tube

Catcher Tank

MIXING CHAMBER - EJECTOR


Variation of suction pressure inside mixing chamber (orifice - 0 25mm)

RESULTS CONDITION - A

chamber (orifice - 0.25mm)

600700

FN - 0.76 FN - 1.02mm FN - 1.2mm FN - 1.6mm

300

400500600

olut

e su

ctio

n su

re (m

illib

ar)

0100200

0 50 100 150 200 250 300 350

Abs

opr

ess

Abrasive flow rate : NilCondition : blocked abrasive feed line

Waterjet Pressure (MPa)



Variation of Suction inside mixing chamber

RESULTS CONDITION - A

250

300

insi

de

illib

ar) d : 0.76 mm d : 1.02 mm d : 1.2 mm d : 1.6 mm

0.25 mm 0.30 mm 0.35 mm 0.4 mm

100

150

200

te p

ress

ure

cham

ber (

m

0

50

50 100 150 200 250 50 100 150 200 250 50 100 150 200 250 50 100 150 200 250

Abs

olut

mix

ing

c

Waterjet set pressure (MPa)

Abrasive flow rate : NilCondition : abrasive feed line - blocked




2

2.5

tput

(Vol

ts)

2

2.5

tput

(Vol

ts)

0.5

1

1.5

acuu

m s

enso

r out

0.5

1

1.5

acuu

m s

enso

r out

Orifice : 0.25 mm Orifice : 0.25 mm

00 5 10 15 20

Time (sec)

Va 00 5 10 15 20

Time (sec)

Va

Focusing Nozzle : 0.76 mmWaterjet Pressure : 50 MPa

Focusing Nozzle : 1.02 mmWaterjet Pressure : 50 MPa

2.5

olts

) 2.5

olts

)1

1.5

2

sens

or o

utpu

t (vo

1

1.5

2

sens

or o

utpu

t (vo

0

0.5

0 5 10 15 20

Time (sec)

Vacu

um

0

0.5

0 5 10 15 20

Time (sec)

Vacu

um

Orifice : 0.25 mmFocusing Nozzle : 1.20 mmWaterjet Pressure : 50 MPa


2 5 2 5



1.5

2

2.5or

out

put (

Volts

)

1.5

2

2.5

or o

utpu

t (vo

lts)

0

0.5

1

0 10 1 20

Vacu

um s

enso

0

0.5

1

0 10 1 20

Vacu

um s

enso

0 5 10 15 20

Time (sec)

Orifice : 0.40 mmFocusing Nozzle : 0 76 mm

0 5 10 15 20

Time (sec)

Orifice : 0.40 mmF i N l 1 02Focusing Nozzle : 0.76 mm

Waterjet Pressure : 50 MPaFocusing Nozzle : 1.02 mmWaterjet Pressure : 50 MPa

2.5

volts

) 2.5

olts

)

1

1.5

2

m s

enso

r out

put (

v

1

1.5

2

sens

or o

utpu

t (vo

0

0.5

0 5 10 15 20

Time (sec)

Vacu

um

0

0.5

0 5 10 15 20

Time (sec)

Vacu

um s


( )



COMPARISON OF SUCTION PRESSURE INSIDE MIXING CHAMBER OBTAINED WITH NEW AND USED ORIFICE

1200

de

ar)

New orifice Used orifice0.25mm 0.30 mm 0.4 mm

600

800

1000

ress

ure

insi

mbe

r (m

illib

a

200

400

Abs

olut

e pr

mix

ing

cham

00.76 1.02 1.2 1.6 0.76 1.02 1.2 1.6 0.76 1.02 1.2 1.6

Focusing Nozzle Diameter (mm)

A m

Orifice : 0 25 mm; 0 30 mm; 0 40 mmOrifice : 0.25 mm; 0.30 mm; 0.40 mmFocusing Nozzle : 0.76 mm; 1.02 mm; 1.2 mm; 1.6 mmWaterjet Pressure : 50 MPa


ABSOLUTE PRESSURE INSIDE MIXING CHAMBER UNDER VARIOUS CONDITIONS OF ABRASIVE WATERJET

2500be

r in

1500

2000

ixin

g ch

amb

Blocked focusing tube / orificedamage

1000

1500

ure

insi

de m

mba

r Abrasive free flow condition

Blocked abrasive feed line

Patm

500

olut

e pr

essu

0Abs

o

SIMULATION STUDIES – Variation in suction pressure with abrasive flow rateO ifi i


Orifice size

0.25 mm

Focusing tube

0.76 mm

Pressure

100 MPa100 MPa

Abrasive Flow Rate

0.027 kg/min - 0.415 kg/min.



SUCTION PRESSURE INSIDE MIXING CHAMBER FOR CHANGE IN ABRASIVE FLOW RATE

980

1000

nsid

e m

bar

940

960

pre

ssur

e in

cham

ber,

in

900

920

Abs

olut

em

ixin

g c

0 0.1 0.2 0.3 0.4 0.5Abrasive flow rate, in kg/min

CONDITION :Orifice – 0.25 mm Focusing Tube – 0.76 mmWaterjet Pressure – 150 MPa

MONITORING OF CUTTING HEADMonitoring of force exerted by jetMonitoring of force exerted by jet

IMPACT FORCE

Impact force exerted by the jet is proportional to theImpact force exerted by the jet is proportional to the velocity of the jet, density of the slurry and volume flow rate.

Parameters Operating Rangep g g

Orifice (mm) 0.25, 0.30, 0.35, 0.4

Focusing Nozzle (mm)

0.76, 1.02, 1.2, 1.6(mm)

Pressure (MPa) 100, 175, 250

Instrument used KISTLER 3 component force dynamometerdynamometer

Experiment conditions

FORCE SENSOR

Make : M/s KISTLER, 9257BRange : 5 to 5 kN (F F F )

Condition 1 : Orifice without considering

focusing nozzle

Condition 2 : Orifice considering focusing nozzle

February 3, 2011 46

Range : -5 to 5 kN (Fx, Fy, Fz)Range setting: 0 – 100 N (Fz)

MONITORING OF CUTTING HEADMonitoring of force exerted by jet

Force exerted by pure waterjet emerging from orificeP : 1 0 0 MPa P : 1 7 5 MPa P : 2 5 0 MPa

Monitoring of force exerted by jetStatic Analysis

2 02 5

3 03 5

orce

(N)

05

1 01 5

Impa

ct fo

2P : 100 MPa P : 250 MPa

5P : 100 MPa P : 250 MPa

O ifi 0 25 O ifi 0 40

0 .25 0 .3 0 .3 5 0 .4O r if ic e s iz e (m m )

Signal obtained from the sensor

1

1.5

sor s

igna

l (V)

3

4

sor s

igna

l (V)Orifice : 0.25 mm Orifice : 0.40 mm

0

0.5

Forc

e se

ns

0

1

2Fo

rce

sens

February 3, 2011 47

00 2 4 6 8 10

Time (seconds)

00 2 4 6 8 10

Time (seconds)


Force exerted by pure waterjet emerging from orifice

Monitoring of force exerted by jet

Dynamic Analysis

P : 250 MPa DISCUSSION

Force sensor : 1. The impact force increases

with an increase in size of orifice in case of impact produced by direct jet fromproduced by direct jet from the orifice

2. The PSD spectrum shows a sudden increase in PSD

P : 100 MPa P : 175 MPa P : 250 MPasudden increase in PSD value with increase in orifice size greater than 0.35 mm

1

1.5

2

Am

plitu

de

mpl

itude

(V2 )

0

0.5

1

PSD

Pea

k A

PS

D P

eak

A

February 3, 2011 48

00.25 0.3 0.35 0.4

Orifice size (mm)


df: 0.76 mm df: 1.02 mm df: 1.2 mm df: 1.6 mm

Force exerted by pure waterjet emerging from focusing nozzle

Monitoring of force exerted by jetStatic Analysis

DISCUSSION

20

25

30

rce

(N) 100 MPa 175 MPa 250 MPa Force sensor :

1. With focusing nozzle, the i t f d ith

0

5

10

15

Impa

ct fo

r impact force decreases with reduction in the orifice to focusing nozzle ratio. This reduction is due to large

df : 0.76 mm df : 1.02 mm df : 1.2 mm df : 1.6 mm

0

0.25 0.3 0.35 0.4 0.25 0.3 0.35 0.4 0.25 0.3 0.35 0.4Orifice size (mm)

reduction is due to large friction offered by the walls of the focusing nozzle.

2. The loss of impact force

15

20

25

ct fo

rce

(N)

100 MPa 175 MPa 250 MPa

2. The loss of impact force found increased beyond orifice of 0.3 mm

0

5

10

Loss

in Im

pac

February 3, 2011 49

00.25 0.3 0.35 0.4 0.25 0.3 0.35 0.4 0.25 0.3 0.35 0.4

Orifice size (mm)

L


DISCUSSIONOrifice : 0.25 mm Orifice : 0.40 mm

Monitoring of force exerted by jetDynamic Analysis

Force sensor : 1. The PSD spectrum shows the

peak amplitude that p pincreased drastically with orifice wear beyond 0.35 mm

4

5

2Hz

df : 0.76 mm df : 1.02 mm df : 1.2 mm df : 1.6 mm

(V2 )

Frequency : 2 Hz2

3

4

Am

plitu

de a

t 2ea

k A

mpl

itude

0

1

0.25 0.3 0.35 0.4Orifice size (mm)

PSD

AP

SD

Pe

February 3, 2011 50

Orifice size (mm)

MONITORING OF CUTTING HEADMULTI SENSORY APPROACH

HOPPER

Vacuum Sensor

CRO

MULTI – SENSORY APPROACH

VACUUM SENSOR

HP WATERVIBRATORY FEEDER

High Pressure Sensor

AD

CRO

SC

HIGH PRESSURE SENSOR

SHUT OFF VALVE

ROTOMETERAD

CRO

SC

Force Sensor

A

CRO

FORCE SENSOR

AD

SC

Experimental set up showing multi sensors attached to the cutting head

February 3, 2011 51

MONITORING OF CUTTING HEADSUMMARY

ProblemIndications

High Pressure sensor Low Pressure sensor

Blockage in orifice RMS value : Equals to the set pressure

RMS value : Equal to atmospheric pressure when abrasive line is open

Orifice damaged RMS value : Drops beyond RMS value : Higher positive pressure et ives)

11% with respect to set pressure (at 100 MPa)

PSD Value : Very high peak f i l t l

above atmospheric pressure (>1000mbar) (or)RMS value : Very low absolute pressure below 70 millibar at waterjet pressure of u

re w

ate

rje

ho

ut

ab

rasi

power of signal at low frequency

below 70 millibar at waterjet pressure of 50 MPa (Condition : abrasive feed line closed)

Blockage in focusing nozzle

No significant change RMS value : Positive pressure above atmospheric pressure

Pu

(wit

h

nozzle atmospheric pressure

Focusing nozzle worn out

No significant change RMS value : Low absolute pressurePSD value: Very high peak power of signal at low frequency

Blockage in abrasive No significant change RMS Value : Absolute pressure below Blockage in abrasive feed line

No significant change RMS Value : Absolute pressure below 500 millibar

No abrasive in hopper No significant change RMS Value : Absolute pressure equal to atmospheric pressure

bra

sive

W

ate

rjet

February 3, 2011 52

Abrasive free flow No significant change RMS Value : Absolute pressure closer to atmospheric pressure in the range of 900 millibar to 1000 millibar

Ab

W

MONITORING OF CUTTING HEADSUMMARY

ProblemIndications

Flow sensor(Air Entrainment)

Flow sensor(Main stream water)

Force sensor(Air Entrainment) (Main stream water)

Blockage in orifice

No entrainment No flow of water Zero impact force

Orifice damaged No entrainment due to Increased flow RMS value : Low impact forceet ives)

positive pressure inside mixing chamber (or)Larger entrainment of air (> 300x10-6 m3/s at 100 MPa)

nearer to the maximum discharge capacity of pump

PSD Value: High peak power of signal at low frequency

ure

wate

rje

ho

ut

ab

rasi

pu p

Blockage in focusing nozzle

No entrainment and entry of water into abrasive feed line

No significant change

RMS value : Zero impact force

Focusing nozzle worn out

Larger entrainment of air ( > 300x10 6 m3/s at 100 MPa)



Pu

(wit

h

worn out ( > 300x10-6 m3/s at 100 MPa) change

Blockage in abrasive feed line

No entrainment No significant change

RMS value : Impact force equal to that of pure waterjet ( 5 – 10 N at 100 MPa)

No abrasive in hopper

Entrainment of air (< 300x10-6 m3/s at 100 MPa)


RMS value : Impact force equal to that of pure waterjet( 5 – 10 N at 100 MPa)

Abrasive free Normal entrainment of air No significant RMS value : Significant impact bra

sive

W

ate

rjet

February 3, 2011 53

Abrasive free flow

Normal entrainment of air (< 300x10-6 m3/s at 100 MPa)


RMS value : Significant impact force ( 5 – 10 N at 100 MPa)A

bW

DECISION SUPPORT SYSTEM

DECISION SUPPORT SYSTEM

Condition monitoring strategy

Process performance prediction strategy

Process control parameter selection strategy

Strategy to assess the condition of cutting head

Strategy to determine the size of orifice and focusing

nozzlenozzle

February 3, 2011 54

DECISION SUPPORT SYSTEMCondition monitoring Strategy

Patm - atmospheric pressure

g gy

Strategy to assess the condition of cutting head

(1 bar)P2 - absolute pressure inside

mixing chamberStart the Abrasive Waterjet Machine

Set the waterjet pressure to 100 MPa

Open the abrasive feed line

Read data

P2 from low pressure sensor

If P P If P 0 5 b If 0 9 P P bIf P abs >> P atm If P abs < 0.5 bar If P abs = P atm

Reason :1. Blockage in

Reason :1. Blockage in

Reason :1. No abrasive in

If 0.9 < P 2 < P atm bar

Reason :1. Abrasive free flow

Check the systemCheck the system

gfocusing tube

2. Orifice damage

gabrasive feed line hopper

2. Blockage in orifice

1. Abrasive free flow

February 3, 2011 55If pure waterjet experiment

YESB

NO

DECISION SUPPORT SYSTEMCondition monitoring Strategy

HIGH PRESSURE LOW PRESSURE FLOW SENSOR FLOW SENSOR

g gy

Strategy to determine the size of orifice and focusing nozzle

HIGH PRESSURESENSOR

LOW PRESSURESENSOR

FLOW SENSOR(Main stream)

FLOW SENSOR(Entrainment)

SIGNAL CONDITIONING & INTERFACING

IFU OF

U

DEF

DEFI

NPU

UZZIFI

Rule base for determining


Focusing nozzle (For do =0.25- 0.275)

UTP

UZZIFI

FUZZI

FUZZI

B C

UT

USER / AUTOMATIC

ICATI

Orifice


Focusing nozzle (For do =0.275- 0.33)

UT

do & df

ICATI

FICAT

FICAT

ON

FUZZY INFERENCE

ON

ION

IONMODULE 2

Determination of size

February 3, 2011 56KNOWLEDGE BASE

FUZZY SYSTEM

of orifice and focusing nozzle

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