Micro Hole Drilling Using Ultrasonic Grinding

8/10/2019 Micro Hole Drilling Using Ultrasonic Grinding

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Micro Hole Drilling UsingUltrasonic GrindingVishnu Prasad K

No:17

S2, M Tech, Production Engineering

Mechanical Department


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Overview Introduction

Micro holes and Existing Techniques of production

Drilling by Grinding

Grinding Tool and Fabrication

Experimental Setup and Machine Specification

Experiment and Results: 30m

Experiment and Results: 20m

A.WITHOUT HELICAL FEEDING

B.WITH HELICAL FEEDING

Influence of Helical Feeding

Inference and 10m Hole drilling

Conclusion and References

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Introduction

Micro-hole

Holes with dimensions

most convenientlydescribed in micrometers

Used in:

Micro-nozzles

Micro-electro-mechanicalsystems (MEMS) -Accelerometer

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Existing Techniqueson Hard and Brittle Materials

Laser Processing

Low Dimensional Accuracy

High Surface Roughness

Chemical Etching

High Running Cost

Produces Toxic Chemicals

Ultrasonic Machining

Low Material Removal Rate

High Tool Wear Ratio

Thus a New Method is required for the Fabrication of micro-holeson Hard and Brittle Materials4


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Widely Used for Hard BrittleMaterials

Finishing-Plane and CurvedSurfaces, Also Drilling

Limited to sub-millimeterDimensions

Difficulty in Tool Making formicro dimensions

Tool Breakage Due toGrinding Forces

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High Dimensional Accuracy

Tool Used

Cemented TungstenCarbide

Fabricated by EDM

Ultrasonic Vibration

Reduce Grinding Force

Results in Drillingcapability down to 10m

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Grinding Tool

Referred as Micro-pins

Tool Made of Cemented

Tungsten Carbide

High Strength and HighFracture Toughness

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Tool Fabrication

Generally Micro Tools are Produced byElectroplating Abrasive-grains to Shank

Highly Costly-Shank making and ElectroplatingRequired

Difficult to Electroplate with Ultrafine Grains forMicro Tools with Constant Pitch and ProtrusionHeight of Grains

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Tool Fabrication

Tool Shank Machined byElectron Discharge MachiningCalled Wire-Electro DischargeGrinding (WEDG)

Wire Tool Electrode is Used forMachining

Wire is Guided so as to reduceVibrations

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Tool Fabrication

10Maximum Discharge Energy per Pulse is (1/2) CE^2


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Tool Fabrication

Cemented Tungsten Carbide PinPlaced in a mandrel and Clamped

Mandrel Placed on the V shapedBearing

Drive Provided through Belt drivefrom motor

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Tool and Work Setup

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Machine Spec

Machine Designed for Micro-Ultrasonic Machining

ASWU-1, Creative Tech Corp

Three axis Step Feed @ 0.05m

Work piece held on an Ultrasonic Transducer for Vertical

Oscillation mounted on a transducer holder

Electronic Balance-EB430H Shimadzu Corp-10 mgf leastincrement, 10 ms time resolution13


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Machine Spec

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Ultrasonic Grinding

Either Helical Feed or Axial Feed

Helical Feed Provided to AvoidGround Chip Clogging

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Experiment & Results: 30m

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Axial Feed Speed 0.27m (With or Without Helical feed)

Tool axial feed Length 30m

Tool Diameter: 25m with Planetary motion radius 2.5m- Helical Feed

30m- Non helical Feed


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Hole Drilled by Helical Feed was detected with a taper-Dueto horizontal deflection of tool from the inner surface of

hole by Grinding Force

Hole Without Helical Feed do not have taper

Probable that Ground Chip Clogging hardly occurredwithout Helical feed owing to Low aspect Ratio

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5 consecutive Holes Drilled-Axial Feed Speed 0.25m/sWithout Helical feed


Tool Dimensions:

Diameter: 20m

Length: 33m

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Experiment & Results: 20mA.WITHOUT HELICAL FEEDING:



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Grinding Thrust Force increased from 0N-First Hole to 0.2N

for fifth hole-Attributed to Tool Wear

Edges of the Fifth Hole cracked owing to huge grindingForce

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Experiment & Results: 20mB.WITH HELICAL FEEDING:

3 consecutive Holes Drilled-Axial Feed Speed 0.25m/sWithout Helical feed


Tool Dimensions:

Diameter: 15m Length: 32m

Planetary Motion Radius: 2.5m23


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Tool Broke when Drilling Third Hole

Accredited to High Aspect Ratio of the Tool by decreasein the Diameter

Extra Horizontal Force on the Tool due to Helical feeding




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First Hole produced has Taper similar to that of 30mHoles produced by Helical Feed

Dark Circle(12m) shows the Tool Position at end ofDrilling-Rounded Off by Wear

Tool Broke when Drilling Third Hole

Accredited to High Aspect Ratio of the Tool by decreasein the Diameter

Extra Horizontal Force on the Tool due to Helical feeding



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Evolution of Grinding forcewithout Helical Feeding

Evolution of Grinding forcewith Helical feeding

27 A Topic of Future Scope


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Inference from Experiments

Drilling by Helical Feeding do not Support high AspectRatio Tools

Also Helical Feeding causes Taper on the Hole drilled

Thrust force reduction is observed only at 20m Holes

which require further study to conform the influentialFactors

Hence a High Aspect Ratio Tool without Helical feeding wasemployed for Drilling 10m Holes

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Axial Feed Speed: 0.27m/s

Tool Axial Feed Length:30m

No Cracks were found at the edges except for few smallChippings

Hence a Micro hole of 10m Diameter was drilled for thefirst time

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E i t & R lt 10


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Conclusion

In drilling 30-m-diameter holes with helical feeding, thedrilled holes had a taper and the grinding-force-reducingeffect was not observed.

The grinding-force-reducing effect of helical feeding was

observed in the drilling of 20-m-diameter holes. However,it did not help prevent tool breakage, and the drilled holeswere tapered. These results suggest that helical feeding isunnecessary.

Tools with a lower aspect ratio can be used without helicalfeeding, leading to the improvement in tool breakageresistance that enables the use of smaller-diameter tools.As a result, the drilling of a micro hole 10 m in diameterwas successfully achieved. This is the smallest-diameterhole drilled by grinding, to the best of knowledge.31


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References

Kai Egashira, Ryokei Kumagai, Ryohei Okina, KeishiYamaguchi, Minoru Ota. Drilling of micro holes down to10m in diameter using ultrasonic grinding. PrecisionEngineering 2014

Egashira K, Mizutani K. Ultrasonic vibration drilling ofmicroholes in glass, CIRP Annals, 2002;51(1):339342

Masuzawa T, Fujino M, Kobayashi K. Wire electro-discharge grinding for micro-machining, CIRP Annals,1985;34(1):431434

Egashira K, Mizutani K. Micro-drilling of monocrystallinesilicon using a cutting tool, Precision Engineering,2002;26(3):263268

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THANK YOU

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Micro Hole Drilling Using Ultrasonic Grinding