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12/18/2008
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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
SYSTEM with FLEXIBLE HINGESSYSTEM with 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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SYSTEM with FLEXIBLE HINGESSYSTEM with FLEXIBLE HINGES
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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SYSTEM with FLEXIBLE HINGESSYSTEM with FLEXIBLE HINGES
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
SYSTEM with CYLINDRICAL SPRINGSSYSTEM with CYLINDRICAL SPRINGS
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
SYSTEM with CYLINDRICAL SPRINGSSYSTEM with CYLINDRICAL SPRINGS
X
Y
Displacement (X) Axis Von-Mises Stress
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FREQUENCYFREQUENCY--AMPLITUDE CHARACTERISTICSAMPLITUDE CHARACTERISTICS
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Natural Frequency of the model: ωn = 1840 Hz
Advantages:
High stiffness-avoid
Disadvantages:
Difficult to manufacture
SYSTEM with CYLINDRICAL SPRINGSSYSTEM with CYLINDRICAL SPRINGS
g s ess vo dbuckling phenomena
Lower values of stresses
Low possibility of failure
Adaptable to different grinding conditions
Difficult to manufacture
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
SYSTEM with FLAT SPRINGSSYSTEM with FLAT SPRINGS
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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SYSTEM with FLAT SPRINGSSYSTEM with FLAT SPRINGS
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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Natural Frequency of the model: ωn = 630 Hz
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SYSTEM with FLAT SPRINGSSYSTEM with FLAT SPRINGS
Advantages:
Easy to manufacture
Disadvantages:
High values of stressessy o u c u e
Easy to reconfigure
Adaptable to different grinding conditions
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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SYSTEM with FLAT SPRINGSSYSTEM with FLAT SPRINGS
Advantages of Flat Spring System
Simple designSimple design
Easy to manufacture.
Easy to reconfigure.
Adaptable to different grinding conditions
Allow for various stiffness
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System Configuration
SYSTEM with FLAT SPRINGSSYSTEM with FLAT SPRINGS
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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