an investigation into vibrationvibration--assisted grindingassisted grinding · 2009-04-16 · an...

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AN INVESTIGATION INTO AN INVESTIGATION INTO VIBRATIONVIBRATION--ASSISTED GRINDINGASSISTED GRINDING

VAIOS TSIAKOUMIS VAIOS TSIAKOUMIS

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General Engineering Research InstituteGeneral Engineering Research Institute(G.E.R.I.)(G.E.R.I.)AMTReLAMTReL

CONTENTSCONTENTSIntroductionIntroduction

Project AimProject Aim

ObjectivesObjectives

LiteratureLiterature

Vibration Vibration –– Assisted GrindingAssisted Grinding

MicroMicro--Vibration DevicesVibration Devices

Grinding ForcesGrinding Forces

Design Design –– Simulation ResultsSimulation Results

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ConclusionConclusion

Further workFurther work

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INTRODUCTIONINTRODUCTION

GrindingGrinding is an operation in which material is removed from the workpiece by a powered is an operation in which material is removed from the workpiece by a powered abrasive wheel. An abrasive material rubs against the metal part and removes tiny pieces abrasive wheel. An abrasive material rubs against the metal part and removes tiny pieces of material. In manufacturing high precision parts with tight tolerances are obtained by of material. In manufacturing high precision parts with tight tolerances are obtained by grinding.grinding.g gg g

Two of the most known types of grinding are:Two of the most known types of grinding are:

Surface GrindingSurface GrindingCylindrical Grinding Cylindrical Grinding

O.D, I.D O.D, I.D CenterlessCenterless

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Grinding wheelGrinding wheel is composed of an abrasive grits clustered together with special bound.is composed of an abrasive grits clustered together with special bound.

Types of Abrasives: Types of Abrasives: NaturalNatural: : Emery, Corundum, DiamondsEmery, Corundum, Diamonds

SyntheticSynthetic: : SiCSiC, Al, Al22OO3, 3, Cubic Boron Nitride (CBN), Cubic Boron Nitride (CBN), DiamondsDiamonds

in GENERAL in GENERAL Grinding is a popular method of material removal

Construction

Aviation Automotive

Optics Optical lenses, giant telescope mirrors

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GRINDING WHEELSGRINDING WHEELSWide range of wheels

Size and shape dependson the purposes.Intense cutting forces Intense cutting forces

Increase in Grinding PowerIncrease in Grinding Power

High temperature in the High temperature in the grinding zonegrinding zone

Damage to workpieceDamage to workpiece

Wheel loadingWheel loading

Wheel Wear Wheel Wear

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PROJECT AIMPROJECT AIM

TheThe aimaim ofof thisthis projectproject isis toto designdesign anan micromicro--vibratingvibratingdevicedevice thatthat allowsallows forfor thethe oscillationoscillation ofof thethe workpieceworkpiece ininactualactual grindinggrinding inin orderorder toto improveimprove thethe performanceperformance ofofthethe processprocess..

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OBJECTIVESOBJECTIVES

Basic study of vibration assisted machining; application of vibration in grindingBasic study of vibration assisted machining; application of vibration in grinding

hi l d i id ifi i f l f i f h i dl ihi l d i id ifi i f l f i f h i dl iMachine tool dynamics: identification of natural frequencies of the spindle unit.Machine tool dynamics: identification of natural frequencies of the spindle unit.

Research and design of vibrating jigs for surface grinding.Research and design of vibrating jigs for surface grinding.

Temperature measurement techniques for vibration assisted grinding.Temperature measurement techniques for vibration assisted grinding.

Vibration assisted surface grinding.Vibration assisted surface grinding.

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Process Process characterisationcharacterisation

WHY VIBRATION ASSISTED GRINDING?WHY VIBRATION ASSISTED GRINDING?

Reduction of cutting forces.Reduction of cutting forces.

Better coolant delivery over the entire contact zone.Better coolant delivery over the entire contact zone.Better coolant delivery over the entire contact zone.Better coolant delivery over the entire contact zone.

Better heat removal from the grinding zone.Better heat removal from the grinding zone.

Oscillation allows the grains to cut with more than one edge.Oscillation allows the grains to cut with more than one edge.

Shelf-SharpeningProcess of the Wheel

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Oscillation reduces the load per grain therefore, reduces the wheel wear.Oscillation reduces the load per grain therefore, reduces the wheel wear.

Better surface finish due to lapping / polishing effectBetter surface finish due to lapping / polishing effect

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LITERATURELITERATURELimited material is available on vibration assisted grinding. Limited material is available on vibration assisted grinding.

The reason being that vibration is thought to be harmful to grinding process.The reason being that vibration is thought to be harmful to grinding process.Indeed uncontrolled vibration creates chatter and lead to surface deterioration.Indeed uncontrolled vibration creates chatter and lead to surface deterioration.

ZhZh t l (2004) h d th f l f ib ti i t d i dit l (2004) h d th f l f ib ti i t d i diZhongZhong et al (2004), showed the usefulness of vibration assisted grinding. et al (2004), showed the usefulness of vibration assisted grinding. Below is his complex design used to generate microBelow is his complex design used to generate micro--vibration in surface grinding of vibration in surface grinding of silicon wafer.silicon wafer.--initial results showed improved surface and reduced normal force. initial results showed improved surface and reduced normal force.

99Zhong et al (2004)

LITERATURELITERATUREGrinding parameters in Zhang experiments in siliconGrinding parameters in Zhang experiments in siliconWheel speed:Wheel speed: 33 m/s33 m/sWorkspeedWorkspeed:: 16 mm/s16 mm/s Results showed:Results showed:

Depth of cut:Depth of cut: 5, 10, 30 5, 10, 30 µµmmVibration frequency 200 HzVibration frequency 200 HzAmplitude :Amplitude : 10 10 µµmm

••Reduction in normal forceReduction in normal force••Improve surface roughnessImprove surface roughness•• Low surface temperatureLow surface temperature••Little reduction in tangential forceLittle reduction in tangential force

1010Surface roughness in VA grindingCutting Force in VA grinding (Zhang et al 2006)

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VIBRATIONS DEVICESVIBRATIONS DEVICES

MaterialsMaterials::PiezoPiezo--ceramic (Lead ceramic (Lead zirconatezirconate titanatetitanate))(( ))

TerfenolTerfenol--d (alloy of Terbium, Dysprosium, and Iron) d (alloy of Terbium, Dysprosium, and Iron)

Devices:Devices:

Produces very high magnetostriction.

Very High Force and Displacement.

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Devices:Devices:ElectroElectro--dynamic Shakersdynamic Shakers

Piezoelectric ActuatorsPiezoelectric Actuators

Ultrasonic Vibration DevicesUltrasonic Vibration Devices

ELECTRODYNAMIC SHAKERSELECTRODYNAMIC SHAKERS

ElectrodynamicElectrodynamic shakers shakers have a permanent magnet and create vibration by moving a coil have a permanent magnet and create vibration by moving a coil when alternating electric power is applied. when alternating electric power is applied.

Shakers are used in diverse activities such as product evaluation, stress screening, squeakShakers are used in diverse activities such as product evaluation, stress screening, squeak--dd l i d d l l il i d d l l iandand--rattle testing and modal analysis. rattle testing and modal analysis.

Three Functional Limits:Three Functional Limits:

DisplacementDisplacement

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AccelerationAcceleration

VelocityVelocity

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PIEZOELECTRIC ACTUATORSPIEZOELECTRIC ACTUATORS

Piezoelectric actuators Piezoelectric actuators are devices that produce oscillations by the expansion and are devices that produce oscillations by the expansion and contraction of piezo elements depending on the applied voltagecontraction of piezo elements depending on the applied voltage. . They are driven by They are driven by the output voltage of a power amplifier that amplifies a small sinusoidal input the output voltage of a power amplifier that amplifies a small sinusoidal input signal from a function generatorsignal from a function generatorsignal from a function generator.signal from a function generator.

Advantages FeaturesAdvantages Features

They perform subThey perform sub--nanometer moves at high frequencies.nanometer moves at high frequencies.No rotating or sliding parts to cause friction.No rotating or sliding parts to cause friction.They can move high loads up to several tonsThey can move high loads up to several tons

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They can move high loads up to several tons.They can move high loads up to several tons.Do not require maintenance because of noDo not require maintenance because of no--moving parts. moving parts.

Principle of Piezo-actuator

GRINDING FORCESGRINDING FORCESIn precision grinding operations, the magnitude of cutting forces is important since it affects the In precision grinding operations, the magnitude of cutting forces is important since it affects the

workpiece quality. workpiece quality. The magnitude of cutting forces can be affected by different factors such The magnitude of cutting forces can be affected by different factors such as the material properties, the tool geometry, the table speed, depth of cut and grinding as the material properties, the tool geometry, the table speed, depth of cut and grinding fluids.fluids.

The grinding force (The grinding force (FF) is made of the tangential and the normal components.) is made of the tangential and the normal components.Normal Force (Normal Force (FFnn) ) Has an influence on the surface deformation.Has an influence on the surface deformation.Tangential Force (Tangential Force (FFtt) ) Affects the power consumption and service life of the wheel.Affects the power consumption and service life of the wheel.

The ratio The ratio FFtt / F/ Fn n determine the interfacial frictiondetermine the interfacial friction

Vs

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Fn

FtWP

Vs

Vw

F

VwVw: Workpiece Velocity: Workpiece Velocity

Vs: Wheel VelocityVs: Wheel Velocity

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In order to investigate the response of the system in the presence of vibration several In order to investigate the response of the system in the presence of vibration several models have been developed: models have been developed: Solid model with flexible hinges.Solid model with flexible hinges.Table with Cylindrical springsTable with Cylindrical springs

DESIGNDESIGN

Table with Cylindrical springs.Table with Cylindrical springs.Table with four flat springs.Table with four flat springs.

The dimensions were chosen in a manner that the device could be accommodated within The dimensions were chosen in a manner that the device could be accommodated within the space available between the wheel and the worktable of the grinding machine. the space available between the wheel and the worktable of the grinding machine.

Basic AssumptionsBasic Assumptions

Only the flexible hinges and the springs are subjected to elastic deformation.Only the flexible hinges and the springs are subjected to elastic deformation.Other parts of the devices are considered as rigid bodies.Other parts of the devices are considered as rigid bodies.

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There is no displacement in vertical axis. There is no displacement in vertical axis. The system is allowed to translate laterally only in the horizontal axis under the The system is allowed to translate laterally only in the horizontal axis under the excitation force. excitation force. The bottom plate is fixed to the grinding table. The bottom plate is fixed to the grinding table. The flat springs are weightless.The flat springs are weightless.Damping in the system is considered as internal friction and is neglected.Damping in the system is considered as internal friction and is neglected.

These assumptions reduce the model to a single degree of freedom systemThese assumptions reduce the model to a single degree of freedom system

SPECIFICATIONS OF VIBRATION SPECIFICATIONS OF VIBRATION DEVICESDEVICES

Electrodynamic ShakerElectrodynamic Shaker

Sine force Peak: 17.8 NSine force Peak: 17.8 NSystem Displacement: 5mmSystem Displacement: 5mm

Dimensions

Diameter: 78mmy py pArmature Resonance Frequency: 13kHzArmature Resonance Frequency: 13kHzMass: 3.17 KgMass: 3.17 Kg

Piezoelectric ActuatorPiezoelectric Actuator

Maximum Displacement: 120 Maximum Displacement: 120 µµmmMaximum Pushing Force: 2000 NMaximum Pushing Force: 2000 N

Length: 121 mm

Diameter: 18mm

Length: 139 mmMaximum Pushing Force: 2000 NMaximum Pushing Force: 2000 NPulling Forces: 500 NPulling Forces: 500 NMass: 0.37 KgMass: 0.37 Kg

Two values were used for the max force in the simulation: Two values were used for the max force in the simulation: 17.8 N and 150 N were applied respectively17.8 N and 150 N were applied respectively

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TheThe modelmodel withwith flexibleflexible hingeshinges isis mademade ofof aa singlesingle metalmetal piecepiece whichwhich isis milledmilled toto thetherequiredrequired shapeshape..

SYSTEM with FLEXIBLE HINGESSYSTEM with FLEXIBLE HINGES

The force is applied horizontally to the top plate.The force is applied horizontally to the top plate.

Applied Force

Workpiece

Direction of oscillation

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Base

pp

Flexible Hinges


A finite element analysis allowed obtainingA finite element analysis allowed obtaining: (F = 17.8 N): (F = 17.8 N)•• High stress concentration areas High stress concentration areas •• Maximum displacement in (Y) axis due to normal grinding Maximum displacement in (Y) axis due to normal grinding •• Maximum displacement in (X) axis caused by the applied excitation force and the tangential forceMaximum displacement in (X) axis caused by the applied excitation force and the tangential force

Displacement (Y) AxisDisplacement (X) AxisX

Y

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As assumed, the normal displacement is negligible ~0.03µm

Displacement (X) ~ 0.5µm

Static Deflection

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F = 150 N, F = 150 N, ω = 300ω = 300HzHz

X Displacement (X) AxisX

Y

Von-Mises Stress

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FREQUENCYFREQUENCY--AMPLITUDE CHARACTERISTICSAMPLITUDE CHARACTERISTICS

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Natural Frequency of the model: ωn = 813 Hz

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Advantages:

Solid model, not many

Disadvantages:

Difficult to manufactureSo d ode , o ymoving parts

High stiffness-avoid buckling phenomena

Lower values of stresses

Low possibility of failure

Difficult to manufacture

Difficult to reconfigure

Does not allow various stiffness

Not adaptable to different grinding conditions

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SYSTEM with CYLINDRICAL SPRINGSSYSTEM with CYLINDRICAL SPRINGS

The device is made of two plates supported by four Cylindrical springs .The device is made of two plates supported by four Cylindrical springs .The top plate carries the workpieceThe top plate carries the workpieceThe force is applied horizontally to the top plateThe force is applied horizontally to the top plateThe force is applied horizontally to the top plate.The force is applied horizontally to the top plate.

Applied Force Top Plate

WorkpieceDirection of oscillation

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Bottom Plate

Cylindrical Spring

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A finite element analysis allowed obtaining: A finite element analysis allowed obtaining: (F = 17.8 N)(F = 17.8 N)•• high stress concentration areas high stress concentration areas •• maximum displacement in (Y) axis due to normal grinding maximum displacement in (Y) axis due to normal grinding •• maximum displacement in (X) axis caused the applied excitation force maximum displacement in (X) axis caused the applied excitation force


Displacement (X) Axis Displacement (Y) AxisX

Y

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As assumed, the normal displacement is negligible ~0.2um

Displacement (X) ~ 0.57um

Static Deflection

F = 150 N, F = 150 N, ω = 300ω = 300HzHz


X

Y

Displacement (X) Axis Von-Mises Stress

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FREQUENCYFREQUENCY--AMPLITUDE CHARACTERISTICSAMPLITUDE CHARACTERISTICS

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Advantages:

High stiffness-avoid

Disadvantages:



g s ess vo dbuckling phenomena

Lower values of stresses

Low possibility of failure

Adaptable to different grinding conditions


More material needed

Reconfiguration need more work

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Allow various stiffness

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SYSTEM with FLAT SPRINGSSYSTEM with FLAT SPRINGS

The device is made of two plates supported by four flat springs .The device is made of two plates supported by four flat springs .The top plate carries the workpieceThe top plate carries the workpieceThe force is applied horizontally to the top plateThe force is applied horizontally to the top plateThe force is applied horizontally to the top plate.The force is applied horizontally to the top plate.

Applied Force Top Plate

WorkpieceDirection of oscillation

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Bottom Plate

Flat Spring

A finite element analysis allowed obtaining: A finite element analysis allowed obtaining: (F = 17.8 N)(F = 17.8 N)•• high stress concentration areas high stress concentration areas •• maximum displacement in (Y) axis due to normal grinding maximum displacement in (Y) axis due to normal grinding •• maximum displacement in (X) axis caused the applied excitation force maximum displacement in (X) axis caused the applied excitation force


Displacement (X) Axis Displacement (Y) AxisX

Y

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As assumed, the normal displacement is negligible ~0.24um

Displacement (X) ~ 2.3um

Static Deflection

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F = 150 N, F = 150 N, ω = 300ω = 300HzHz

X

Y

Displacement (X) Axis Von-Mises Stress

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ANSYS FREQUENCYANSYS FREQUENCY--AMPLITUDE AMPLITUDE CHARACTERISTICSCHARACTERISTICS

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Advantages:

Easy to manufacture

Disadvantages:

High values of stressessy o u c u e

Easy to reconfigure


Allow various stiffness

High values of stresses

Buckling risk

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OBSERVATIONS on the DESIGN OBSERVATIONS on the DESIGN

All three models have their advantages and disadvantages. Stress analysis provedthat there is no displacement in vertical axis and the systems are allowed tot l t l t ll l th h i t l i H th t ith th fl ttranslate laterally only on the horizontal axis. However, the system with the flatsprings appears to be the most appropriate for this specific application as it easyto manufacture, easy reconfigurable . However it has the potential of buckling.The simulation reveals all three models have the ability to withstand the forcegenerated in the grinding conditions.

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Advantages of Flat Spring System

Simple designSimple design

Easy to manufacture.

Easy to reconfigure.


Allow for various stiffness

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System Configuration


With the assumption adopted in this study, the device can be modelled as a system with one degree of freedom, the equation of motion of which is :

M = massK = stiffnessx = displacementF(t) = driving force

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Equivalent Model Amplitude Frequency response

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EQUIPMENTEQUIPMENT

Shaker configuration Piezo-actuator configuration

Function Amplifier

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Amplifier

ShakerAccelerometer

Function Generator

AmplifierPiezoelectric Actuator

Vibrating workpiece holder

Data Acquisition system

EQUIPMENT in Closed loop ConfigurationEQUIPMENT in Closed loop Configuration

The final target is to control the system in closed loop:The control parameter is the amplitude of the oscillations.The acceleration will be recorded during the grinding process.The displacement will be calculatedIf diff b h d i d d h d h h lifi i ill b dj dIf any difference between the desired and the measured then the amplification will be adjustedto keep target amplitude.A displacement sensor could be also used for this purpose.This process will repeated in a closed loop to provide a better performance of the system

Acceleration

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Displacement

Velocity

Acceleration

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CONCLUSIONCONCLUSION

Modelling of devices for vibration assisted grinding is almost completed.Modelling of devices for vibration assisted grinding is almost completed.

Models were developed in SolidWorks/COSMOS and ANSYS environments.Models were developed in SolidWorks/COSMOS and ANSYS environments.

FE analysis has been undertaken and the results fully supported the assumptions FE analysis has been undertaken and the results fully supported the assumptions made.made.

The FE results revealed critical points where the system might fail and this allowed The FE results revealed critical points where the system might fail and this allowed for the selection of the optimal system.for the selection of the optimal system.

The system with flat springs was selected for further development and an amplitudeThe system with flat springs was selected for further development and an amplitude

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The system with flat springs was selected for further development and an amplitude The system with flat springs was selected for further development and an amplitude frequency characteristics of the system has been obtained for different springs. frequency characteristics of the system has been obtained for different springs.

Data acquisition software completedData acquisition software completed

The selected system is already manufactured.The selected system is already manufactured.

FUTURE WORKFUTURE WORK

Undertake initial grinding test with the following measurableUndertake initial grinding test with the following measurableGrinding powerGrinding powerGrinding forcesGrinding forcesGrinding contact temperaturesGrinding contact temperaturesFinished surface roughnessFinished surface roughness

Full scale experimental study of Vibration Assisted GrindingFull scale experimental study of Vibration Assisted Grinding

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an investigation into vibrationvibration--assisted grindingassisted grinding · 2009-04-16 · an...

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