Ultrasonic Assisted Drilling - McMaster...

FAIM 2004, July 12-14, Toronto, Canada

Ultrasonic Assisted DrillingSimon S.F. Chang*Gary M. Bone‡

* Machining Systems Laboratory.‡ Robotics and Manufacturing Automation Laboratory.McMaster Manufacturing Research Institute (MMRI),McMaster University, Hamilton, Ontario, Canada

The 14th International Conference onFlexible Automation and Intelligent Manufacturing (FAIM2004)

MMRI, McMaster University, Hamilton, Ontario, Canada


Motivation

! Drilling ductile materials forms largeburrs

! Burrs affect quality of parts andassembly

! Deburring is expensive! Ultrasonic assisted drilling alter the

machining process to reduce burr size



Topics of Discussion

! Burr Formation! Ultrasonic Assisted Drilling! Actuated Workpiece Holder Design! Drive Circuit Design! Experimental Investigation! Conclusion



Burr Formation

! Undesirable projection of work material! Result from plastic deformation! Poisson Burr, Entrance Burr, Rollover

Burr, Tear Burr, Cutoff Burr! Drilling forms combination of Rollover

Burr and Tear Burr at the exit surface



Burr Formation

! Exit burr size is defined by the heightand the width

h

w

Workpiece

Drill

ExitBurr



Ultrasonic Assisted Drilling

! Adding high frequency and lowamplitude vibration in the direction ofdrill feed

! High Frequency – 1 - 200kHz! Low Amplitude – 1 - 13µm



Actuated Workpiece Holderdesign

! Piezoelectric stack actuator! Pre-loading mechanism! Aluminum fixture! Stainless steel shell! Base plate




Diaphragm

StainlessSteel Shell

Aluminum Fixture

BoltsDrill

Workpiece

Base PlateActuator




! Desired actuator performance:! Freq. Range 0-20kHz! Disp. Range 0-10µm

! Required force delivery! X (t )= Au sin(2π fut)! V (t )= 2π fuAu cos(2π fut)! a (t )= - 4π2 fu2Au sin(2π fut)! Fw(t )= - 4π2 fu2Au mw sin(2π fut)! Fmax = 4π2 fu2Au mw = 8 kN

Fw

mwX(t)




! Chosen actuator! Sensor Tech. Ltd. BM532 series 33 layers

stack actuator! Freq. Range 0-20kHz! Disp. Range 0-4µm! Force Delivery 5kN! Applied Voltage (Va) 200V! Capacitance (C) 290nF



Drive Circuit Design

! Operating frequency 20kHz! Required 200V pk-pk drive voltage! Required drive current can be computed

by considering the electric model of theactuator




! Electric model of the actuator

! Required charging current can becomputed using the relation:

ca i

dtdVC =

i icir

Va

InternalCapacitance (C)

InternalResistance




! Required charging current = 2.3AActuator's Voltage vs Time

0

50

100

150

200

250

0 0.000025 0.00005 0.000075 0.0001

Time (s)

App

lied

Volta

ge (V

)

Desired Applied Voltage Approximated Applied Voltage



+

-

Drive Circuit Design! Polarity Switching Circuit

Transformer

MOSFET Halfbridgedriver

Signalgenerator

Actuator



+

-

+

-


Transformer


Signalgenerator

Actuator



-+

+

-


Transformer


Signalgenerator

Actuator



Experimental Investigation! Experimental Setup

! CNC milling machine! 5 specimen for each test! New finished High Speed Steel

twist drill! Burr height measured under

scaled microscope! Burr width measured by vernier

caliper



Experimental Investigation

BurrUltrasonic Assisted

20kHz 4µm

Burr

Conventional

3.175mm drill 6000RPM 1.905mm/s feed

1mm 1mm

! Example of samples



Experimental Investigation! Vibration Frequency! Peak to Peak Vibration! Spindle Speed! Other Findings! Tool Wear



Vibration Frequency! Burr height and width

decreased after the frequencyreaches a threshold

! Trends suggested higherfrequency results in smallerburr

! Wavy chips were found at lowfrequency tests



Vibration Frequency

Burr Height vs Vibration Frequency (Test # 1, 2, 5, 6)(3.18mm Drill 4000RPM 1.90mm/s feed 4microns vibration)

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25

Frequency (kHz)

Burr

Hei

ght (

mm

Burr Width vs Vibration Frequency (Test # 1, 2, 5, 6)(3.18mm Drill 4000RPM 1.90mm/s feed 4microns vibration)

0.05

0.09

0.13

0.17

0.21

0.25

0 5 10 15 20 25

Frequency (kHz)

Bur

r Wid

th (m

m)

ConventionalConventional



Vibration Frequency! Wavy chip



Vibration Frequency! Continuous cutting occurs at

lower frequencies, forminglong wavy chips

! Ultrasonic impact actionoccurs at higher frequencies,segmenting the chips, formingfine chips



Peak to Peak VibrationMagnitude

! Burr height decreased butburr width increased afterthe magnitude reaches athreshold



Burr Height vs Vibration Amplitude (Test # 1, 2, 3, 4)(3.18mm Drill 4000RPM 1.90mm/s feed 20kHz frequency)

0.1

0.3

0.5

0.7

0.9

0 1 2 3 4 5

Amplitude (microns)

Bur

r Hei

ght (

mm

)

Peak to Peak VibrationMagnitude

Conventional

Burr Width vs Vibration Amplitude (Test # 1, 2, 3, 4)(3.18mm Drill 4000RPM 1.90mm/s feed 20kHz frequency)

0

0.05

0.1

0.15

0.2

0.25

0 1 2 3 4 5

Amplitude (microns)

Bur

r Wid

th (m

m)

Conventional



Peak-to-peak VibrationMagnitude

! Continuous cutting occurs atlower magnitudes, forminglong wavy chip

! Ultrasonic impact actiondominates at highermagnitudes! Rollover begins earlier! Forms short but wide burrs



Spindle Speed! Both burr height and width

reaches a minimum at6000rpm, and significantlysmaller than conventionaldrilling at 6000 and 8000rpm.

! Trends suggested a certainvibration condition cansignificantly reduce burr size



Burr Height vs Spindle Speed (Test # 1, 2, 13, 14, 15, 16)(3.175mm Drill 1.905mm/s feed vibration condition: 20kHz 4microns)

0

0.2

0.4

0.6

0.8

1

3000 4000 5000 6000 7000 8000 9000

Spindle Speed (RPM)

Bur

r Hei

ght (

mm

)

Spindle Speed

Conventional

Ultrasonic Assisted

Burr Width vs Spindle Speed (Test # 1, 2, 13, 14, 15, 16)(3.175mm Drill 1.905mm/s feed vibration condition: 20kHz 4microns)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

3000 4000 5000 6000 7000 8000 9000

Spindle Speed (RPM)

Bur

r Wid

th (m

m)

Ultrasonic Assisted

Conventional



Effect of Spindle Speed! Higher spindle speed with

same feed results inthinner chips that arebroken more easily by theultrasonic impact action,producing smaller burr



Other Findings! Ultrasonic assisted drilling

performs best in normalcutting feed, but degradesrapidly in high cutting feed

! Drill size has insignificanteffect on the efficiency ofultrasonic assisted drilling



Effect of Ultrasonic Assistancein Tool Wear

! Chipping observed on drills used inultrasonic assisted drillingexperiment

8000RPM, 3.81mm/s feed (left: UA; right: conventional)

1mm 1mm



Conclusion

! Ultrasonic assisted drilling in general:! Reduces burr height and width if the

vibration conditions for each particularcutting condition were chosen correctly

! Introduces challenges in the context of toolstrength and tool life

Ultrasonic Assisted Drilling - McMaster...

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