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Acoustic Emission as a Tool of In Process Monitoring of Workpiece Roundness in

Cylindrical Grinding.

Siew Yan Goh

AMTREL,GERI

Contents

Project aim and objectiveG i di Grinding

Vibration Acoustic Emission Roundness Experimental work Result Result Future work

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Project aim and objectives:

Project Aim: To employ acoustic emission as a tool for in-process monitoring of workpiece roundness in plunge grinding.

Objective of the project:

Overview of grinding technology:

Investigation of acoustic emission signal in grinding process: detection method, signal capture, processing techniques and data extraction in

frequency domain.

Experimental work: Experimental work: Initial Batch- dressing condition, in-process and offline roundness measurement,

calibration process Experiment Refinement and batch grinding

Development of online control strategy. Develop a feedback system to control the roundness of workpiece in grinding.

GrindingGrinding is a material removal method that is used to improve the surface finish and

achieve high dimension accuracy of the workpiece. This process is commonly apply as the finishing process in manufacturing.

Problem in GrindingSurface Grinding Cylindrical Grinding Centreless Grinding

Grinding wheel: Wheel wear Lubricant/Coolant: Thermal damage Dressing Condition: Roughness Grinding Condition: Chatter, vibration

images sources: http://www.dkprecision.co.ukhttp://www.jet-thrust.comhttp://www.germanmach.com

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Vibration

Vibration is one of the problems in grinding that affect the productivity and the accuracy of workpiece.

Type of vibration in grinding:

(a) External excited Vibration / Forced VibrationSources : Machine tool fault, hydraulic system, Mass unbalance

(b) Self-excited Vibration/ Chatter VibrationSources: Regenerative effect of the workpiece surface and the grinding wheel.

Irregularities (uneven wheel wear) during the grinding process cause g ( ) g g g pthe variation in grinding force. This excites the machine-tool and cause the undulation of contact force hence affects workpiece surface quality.

Generally the frequency of the vibration could reach up to 20kHz.

Acoustic Emission

Acoustic emission (AE) is defined as the variation of elastic wave generated by the rearrangement of the internal structure of a material.

The main source of acoustic emission is the interact of each grain of grinding wheel with workpiece. An AE sensor located on the machine tool is able pick up the signal

t d i th i digenerated in the grinding zone.

AE signal is used to control of thermal damage, gap detection, wheel wear, dressing control.

Most of the control strategies in grinding is based on power measurement. However, it has been noticed that power signal lag in time behind acoustic emission. This provides a room for process improvement

Early detection of errors in any process is crucial, therefore the use of AE as control tool could be beneficial in grinding.

AE frequency range 104 to 106 Hz

Acoustic emission

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Roundness

Roundness is an important factor in cylindrical grinding as it defines the actual shape location of the ground workpiece between the minimum and maximum reference circles (theoretical).

Online roundness measurement is more effective as in-process control system. This reduce manufacturing time but the equipment is complex and expensive.

Off-line roundness measurement is reliable but requires stable room temperature and the equipment is also expensive (>50K).

Eccentricity Concentricity Runout Cylindricity Co-axiality

On-line roundness measurement

Off-line roundness measurement

Off-line roundness measurement

Vibration & workpiece roundness

1 3

2

Grinding wheels are carefully balanced manually before mounting on the machine.Modern machine tool have real time dynamic balancing that counter act any runout of the wheel.

Man al balance se 3 balance segments

Uneven wheel wear is one of the main sources of chattering in grinding. grinding wheel unbalance Wheel workpiece compliance Machine tool stiffness. As consequence, this generates waviness on the surface of ground workpiece.

1 3Manual balance use 3 balance segments.

workpieceGrinding wheelWorkpiece

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Grinding - Equipment Machine:

Jones and Shipman Cylindrical Grinder

Accelerometer is used to measure the vibration and is place at the same travel direction as the grinding wheel.

The machine equip with in-process gauging which allow to measure the diameter and roundness of ground workpiece.

On-line gauging SystemGrinding Wheel Tail Stock

Grinding - Equipment

1. Acoustic Emission Sensor:Frequency Range: 50 500kHz

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2. Acoustic Emission Sensor:Frequency Range: 1-50kHzFrequency Range: 50-500kHz

Sensitivity: 50gFunction: Wheel crash control

Dressing cycle controlUnit output: Voltage

Frequency Range: 1 50kHzSensitivity: 50gFunction: Gap eliminator Unit output: Voltage

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Roundness measurement Talyrond 210 provides: roundness analysisharmonic analysis

Measurement Equipment

harmonic analysis.

Roundness measurement Harmonic Analysis

A harmonic can define as a uniform waveform (Sine wave).

Harmonic Analysis

Harmonic Analysis

3rd Harmonic 6th Harmonic 50th HarmonicCombination of

3rd,6th and 50th harmonic

Fast Fourier Transform (FFT)-Break down the profile into

its constituent waveform

Undulation per revolution (upr)

ampl

itude

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Data acquisition set up

NI-cDAQ-9172

BNC connectorSpecial Cable B type

Raw AE Signal

AE SensorFrequency 1..500 kHz BNC connector

for Data Acquisition

BNC connector for Data

Acquisition

Special Cable A type (4 pole +

B type (7 pole + BNC)

AE

IBM Compatible

Data Acquisition LabView

TOUCH DETECTOR CARD

Connector T2 (4 Pole)Connector T3 (4 Pole)

(4 pole + BNC)

AE Ultrasonic SensorFrequency 0.5..25 kHz

Data Acquisition- LabViewSignal Processing

Data Acquisition System : National Instrument Software : Data Acquisition (LabView)

Signal Processing (Matlab And LabView)

Experimental Materials

The materials for a range of experimentation

Ground to initial size

measured

grouped by size

In total 6 batches of 40 workpieces in each will be used in the grinding tests

Red and white batchBlue and Green batch Laser micrometer

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Results

Recorded signal from the sensors

4

6

8

10

12data1data2data3data4

0 5 10 15 20 25 30 35 40 45-2

0

2

Results

Results with running average

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.01

X: 37.8Y: 0.009169

X: 75.6Y: 0.005435

X: 113.4Y: 0.003365

abso

lute

mag

nitu

de

X 160 7

0 20 40 60 80 100 120 140 160 180 2000

0.001

0.002

Frequency,Hz

X: 160.7Y: 0.001808

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Results

Results with filter

0 1

0.15

0.2

0.25

0.3

0.35

X: 157.4Y: 0.1514

X: 104.4Y: 0.2481

X: 22.89Y: 0.2822

X: 98.71Y: 0.2762

X: 48.64Y: 0.3307

bsol

ute

mag

nitu

de X: 74.39Y: 0.1768

20 40 60 80 100 120 140 160 180 200

0

0.05

0.1

Frequency,Hz

ab

Results

Results with no filter

0.3

0.4

0.5

0.6

0.7

0.8

0.9

X: 4.739Y: 0.8623

X: 13.54Y: 0.639

X: 69.74X: 20.31Y: 0 2209 X 34 53

100

150

200

250

X: 1419Y: 113.6

abso

lute

mag

nitu

de

20 40 60 80 100 120

0

0.1

0.2Y: 0.2065X: 56.2

Y: 0.143

Y: 0.2209 X: 34.53Y: 0.1742

0 500 1000 1500 2000 2500 3000 3500

50

X: 1740Y: 55.44

X: 595.1Y: 10.31

Frequency,Hz

a

X: 1099Y: 19.94

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Attempt to analyse the power signal

In-process signal analysis

Strategy

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ConclusionsInitialliteraturereviewhasbeencovered.

Studyofmachinetoolandequipmentoperationcompleted.

StudyofDataacquisitionandprocessfeatureextractioncompleted

Aninitialsoftwaredevelopmenthasbeenundertakenandallowbasicfeatureextraction.

Testworkpiecehavebeenpreparedmeasuredandgroupedbybatchforfullexperiment.

Initialbatchgrindingrevealedthatdataacquisitionsystemneedsrefinementduetosignalovershootandavoltagedividerhasbeendesignedtosolvethisproblem.

the obtained results has shown that is possible to extract workpiece roundness profiletheobtainedresultshasshownthatispossibletoextractworkpieceroundnessprofilefromAEsignal.

Future work

Finetuningofthedevelopedcodeforprocessfeatureextraction.

FurtherdevelopmentofrealtimesignalprocesswiththeintegrationofLabview.

Fulldeploymentofexperimentation:p y pbatchgrindingroundnessmeasurementsignalprocessingwheelwearanddressing

Calibrationofsoftwareagainstmeasurementequipment.

DevelopmentandintegrationofcontrolstrategycycletimesegmentationinmanualmodecycletimesegmentationinautomaticmodeContinuouschangeofwheelworkpiecespeedratio.

IntegrationofcontrolstrategyintoPC/CNCautomaticfeedcyclemode.

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Thank You