IEEE TRANSACTIONS ON SONICS AND ULTRASONICS, VOL.SU-22, NO. 2, MARCH
60
1975
Industrial Applications of Ultrasound -A Review
I. Hish-Power Ultrasound
Abstract-The estimated worldwide sales of ultrasonic power
equipment for industrial uses total nearly $100 million a year. The
industry had its beginnings shortly after WorldWar II and grew
steadily over the next two and a half decades.
Lower cost of ultrasonic power made possible by advancesin
electromechanical power conversion materials and power semiconductors has greatly contributed to the practicality of ultrasonic
equipment. Yet the main reason behind the growth of power ultrasound is the ability to perform some unique jobs that save money
and have become indispensable in modern manufacturing.
Not all attempts to implement ultrasonic power devices have been
successful, butcommercial success is a function of technological
state of the art and the need for the process. Since both change
with time, surprises are likely. Who would have guessed the potential of ultrasonic plastic welding, letalone
that of ultrasonic
“sewing”? ’
While stressing the more established applications, this article
takes a broaderlookat
the uses of high frequency mechanical
vibratory energy, outlining the advantages and the limitations of
each process.
I. GENERAL
I
N CONTRASTto ultrasonic nondestructivetesting,
theobject of a macrosonicapplication is to expose
the workpiece to enough vibratory energy to bring about
some permanent physicalchange. This involves a flow
of mechanical power from the source to the workpiece,
which,dependingontheapplication,mayrangefrom
a few wattspersquareinch
to tens of thousands of
watts per square inch. Vibratory input, during the time
of exposure, is normally of thecontinuousRavetype.
Macrosonicphenomenaextend well intothemegahertz
range, butmost practicalworkisdone
at frequencies
of
between 20 and 60 kHz, somewhat above the range
human hearing.
A basic macrosonic systemconsists
of an electromechanicaltransducerandahighfrequencyelectric
power supply. The power supply converts the available
elect’riclinepower
intohighfrequency
electricpower
which is used to drive the electromechanical transducer.
The transducers are typically of a compound design, but
at theirheart use electrostrictiveor
magnetostrictive
elements which changephysicaldimensions
inresponse
to an electric or a magnetic field. Mostmoderntransducers use piezoelectric ceramicsof lead zirconate titanate
due to its
superior electromechanical conversionefficiency,
typically in the orderof 95% or better.
Manuscript received November 8, 1974.
The author is with Branson Ultrasonics Corporation, Subsidiary
of Smith Kline Corporation, Eagle Rd., Danbury, Conn. 06810.
Just what are the limits of practical ultrasonic power
today? If the application allows stacking of sonic power
sources, no particular limit to the maximum t,otal power
exists. The poweravailablefrom
a single half-wave
transducer, however, is limited bythe volume of the
electromechanicalconversionmaterial
that canbe accommodated and varies inversely uit’h the square of the
frequency. As transducer design dependson
the use,
exact power limits are not possible to pin down, but,4 kW
a t 20 kHz could serve as a rough reference.
Bydefinition, the mechanical power transferred from
the sonic source to the load is the product of sonic source
velocity at the loadinterface and the mechanical force
resisting the sourcevelocity [l]. The force is produced
by the medium on.which the sonic source is acting.
Transducer output velocity and frequency can be used
as primarysourceparameters.
The product of velocity
andfrequency
defines acceleration, andtheratio
of
velocity andfrequency defines t’he transduceroutput
displacement. See Table I.
As a point of interest,practicalultrasonicpower
sources are by nature velocity or displacement generating
devices, where due to high mechanical Q the motion is
sinusoidal, andthereareno
practicalways of directly
generating ultrasonic forces.
The most commonly used transducers are of extensional
type where the output face of the transducer is a circular
piston area vibrating sinusoidally in the direction of t’he
transducer axis. Thetransduceroutput
facecan
be
applied directly to the load, or coupled to intermediate
sonic resonators (Fig. 1). Extensionaltransducersimpart compressional waves to the load. Transducers can
also be designed to produceshear,torsional or flexural
vibration, or to focus vibrational intensity in fluid media.
Contrarytothepopularmyth,
ultrasonic treatment
isnormallynotdoneby
focusing soundwaveson
the
work through the air. In most cases a direct contact with
the vibratory tool is needed, or liquid is used as a vehicle.
Neither is therea commonmechanismresponsiblefor
all sonic effects: ultrasonic metal welding is unrelated to
ultrasonic aerosol production, and plastic welding is
unrelated to ultrasonic cleaning.
Yet there are some peculiarities about the basic ultrasonic parameters, as shown in the following example.
A 20 kHztransduceroperating
a t apeakoutput
velocity of 26 ft./sec. will havepeak-to-peak displacementamplitude of 0.005 inches andpeak acceleration
of 10 X l@g. To load t8he transducer to 1 kW the load
61
SHOE: INDUSTRIAL APPLICATIONS OF ULTRASOUND
TABLE I
EFFECT
OF FREQUENCY
ON TRANSDUCER
PARAMETERS
PARAMETER
FREQUENCY
FREQUENCY x 2
Length
L
L/2
Width
W
w/2
Weight
K
W8
Sonics and Liquids and Sonics and Solids give an overview of macrosonicapplications and highlightsome of
the more intriguing developments.
11. FIVE MAJOR APPLICATIONS
A . Cleaning
Ultrasoniccleaning
is the oldest industrial applicaPower density
P
P
tion
of
power
ultrasound.
Present-day uses span a wide
D
D/Z
Displacement
variety
of
industries
ranging
from
castings to semiAcceleration
A
ZA
conductors.
Ultrasonic
cleaning
is
often
combined with
V
V
Output velocity
other pre- and post-cleaningoperationssuch
as presoaking or vapor rinsing and makes
use of a variety of
detergentsand
cleaningsolutions.Descaling
and degreasing are also done.
Themainadvantage
of ultrasoniccleaning
lies in
“brushlessscrubbing”due
to cavitation, which ina
well-designed cleaner is evenly distributed throughout the
volume of the liquid and is capable of reaching normally
inaccessible places.Ballbearings,
carburetorparts,and
vessels with complex internal cavities can be effectively
cleaned.
works best,
on
relatively
hard
Ultrasonic
cleaning
materialssuchas
metals, glass,, ceramics, and plastics,
which reflect rather than absorb sound. Cleaning equipment normally operates in the range
of 20-50 kHz.
The phenomenon responsible for ultrasonic cleaning is
cavitation.Highfrequencyalternating
pressure in a
liquidforms microscopic voids whichgrow t o a certain
size, then collapse, causing very
high
instantaneous
temperatures
and
pressures.
This
implosion
of cavitaFig. 1. Sonicandultrasonicpowertransducers:
S kW, 10 kHz;
1 kW, 20 kHz; and 40W, 40 kHz. Transducers are of piezoelectric tionalbubbles
does therough work of loosening dirt
type.
and grease stuck to the workpiece. Oscillation of stable
cavitational bubbles. andtheresult’antmicrostreaming
must exert onthetransducerapeak
force of 57 lbs. also contribute to cleaning [ S ] .
(excluding any reactive loading).Theworkperformed
Cavitationcanbeproducedbyothermethodsthan
by this transducer in one second is equivalent t o lifting ultrasonics and is commonwith
underwater propeller
a 740 lb. load to a height of one foot. What is so unusual blades and steam turbines. Ultrasonically induced cavitaabout these values?
tion, however, can be produced as a far field effect,, away
is characterized by very high from the source, andwithoutany
First,powerultrasound
gross movement of
repetition
rates,
small
displacements,
moderate point the liquid. Far field effect. is achieved by resonating the
velocities, and very high accelerations. Second, large amounts total volume of the liquid in the cleaner. ,4t frequencies
of work can be done without application of high forces and of interest, the layers of maximum cavitational intensity
large displacements. The
transducer
in
the
example,
repeat every 0.5 to 1.5 inches producing fairly uniform
incidentally, would weigh about 2 lbs.
cleaning throughoutthe volume. For moreuniformity
Another useful characteristic is the ability to propagat e the parts may be moved duringexposure.
Power density of ultrasonic cleaners is relatively
through solids, liquids, and gasses and form a resonant
low,
pattern. This allows work to be done at areas away from usually below 10 watts per square inch of driving area.
results in a loss of
the source and makes it possible to treat a large volume An attempt to “overdrive” t8he tank
the far field effect and causes pronounced cavitation and
of material.
Most uses of macrosound depend on compound vibrawear at the driving surface.
tion-induced phenomena occurring in matter. These are
The choice of cleanerfrequencyisnormallydet’er1) cavitation and microstreaming in liquids [ 2 ] , [3]
mined
by
the
application. Since cavitational
shock
2 ) surfaceinstability
occurring at liquid-liquid and intensity is higher at, lower frequencies, a 2.5 kHz cleaner
liquid-gas interfaces [4],
will havemorebrute
cleaningability thana 40 kHz
3) heating and fatiguing in solids..
cleaner.However
lower frequencies havebeenfound
Major uses of macrosound are discussed next in order
damaging to somedelicate parts,and for cleaning of
of commercial significance. Since hardfactsarenot
semiconductors, for instance, 40 kHz may be preferable.
available, the ranking is by necessity subjective. Sections 40 kHz cleaning is also quieter.
Output surface
S
W 4
Power
P
P/4
62
IEEE TRANSACTIONS ON SOMCS AND ULTRASONICS, MARCH 1975
choice of optimum cleaning paramet.erscanbe
and further advances in this area are
likely.
tricky
B . Plastic Welding
Fig. 2. Monorail automated ultrasonic cleaning system for cleaning, rinsing, and drying automotive ring andpinion gears.
Fig. 3.
with power Buppliea mounted in
the base.
Smallultrasoniccleaners
Standard industrial cleaners typically range inpower
fromone hundredtoacouple
of thousandwattswith
corresponding tank capacities of 1-44 gallons.Multikilowatt special syst,ems with
tank capacities of several
2 ) . In recent
hundred gallons arenotuncommon(Fig.
years, low power, low cost(below $100) cleaners have
becomeavailable,which
hasmade ultrasoniccleaning
accessible to m a l l shops and laboratories (Fig. 3).
Modernultrasoniccleanersemploysolid-state
electronic power supplies with automatic tuning and do not
require operatorattention. A commonproblem to all
ultrasoniccleaners is gradualdeterioration of the tank
due to cavitational erosion. This depends largely on the
application, and well-designed systems can give years of
satisfactory service.
It is hard to envision any dramatic breakthroughs in
ultrasonic
cleaning.
Tank
materials
and
design can
probably be further improved to extend life and enhance
for
cleaning. Since cavitationalbehavior
is
different
different,solvents, and alsochangeswithtemperature,
Probablywithout
knowing it, most, people in the
United States come in daily contact with ultmsonically
m-elded plastic parts. The processwasdeveloped in tho
was quickly accepted in asscmbly of
last ten years and
toys, appliances, and indust,rial thermoplastic parts. The
big break came with discovery of far field welding, which
made welding of rigid thermoplastics possible and extendedthetechniquebeyond
welding of plastic films
practiced earlier.
Ultrasonic welding hasan idealcombination of ingredients sought in modern manufacturing. The
process
is fastand
clean,requiresnoconsumables,
does not
need a skilled operator, and lends itself readily t,o automation. It is used extensively in the automotive industry
for assembly of taillights, dashboards, heater duct,s, and
other components where plastics have replaced thc traditional use of glass and metal.
How does the process work? Essentially, highfrc?qut*ncy
vibrationproducesheat
whichmelts
the plastic. Yct
ultrasonically induced heat can be generated sclr:c:tivc~ly,
precisely at the interface of the parts being joined without indiscriminate heating of the surrounding material.
Less weld energy is used, resulting in less dist,ortion and
material degradat’ion. Sinco tha heat is gctneratcd within
the plastic and not conducted from the t,oo1, welding can
be a.ccomplished in completely inaccessible placps.
Mostthermoplasticshavecharacteristicssuitablefor
ultrasonic welding [S]. This includes theabilityto
transmit and to absorb vibration, as ~vell as low thermal
conductivity to facilitatelocal build-upof heat,.
Heatingin plasticis a function of ultrasonicstress
and varies roughly as the square of stress amplitmud(;.To
maximize the stress in the weld region, the cwntact’ area
between the parts being joined is rcduced. Static: clamping force is used t o keep the parts together during wclding. A “holdtime” of a fraction of a second is added
after ultrasonic exposure to allow the plastic t80solidify
before unclamping. Typical welds arc don(. in less than a
second.
Compared to cleaning,
ultrasonic
plastic
wdding
requires much higher power densities, typically hundrcds
of watts per square inch at’ the weld, and at t8he contact
of the toolwith the workpiecc. To deliversuch power
densities plastic welding horns operate at amplit,udcs of
0.001 to 0.005 inches (over ten times higher than cleaning), and due t o high energy storage exhibit very sha,rp
mechanicalresonances.Additionally,dependingon
the
application,theymustaccomrnodatc
a wide variety of
loads, andduringthe welding mechanicalloadingmay
vary. To satisfy these requirementjs a new breed of rquipmenthadtobedeveloped,
raisingultrasonicpower
technology to a new level.
Modern
ultrasonic
plastic
welders operate prodominantlyaround 20 kHz at power outputss below 1000
63
SHOH: INDUSTRIAL APPLICATIONS OF ULTRASOUND
Fig. 6.
Ultrasonic man welder for assembly of large plastic panels,
such as used in plastic furniture.
Fig. 4. 700 W, 20 kHz ultrasonic pl&ic welder.
Fig. 5. Two ormore horns areoften usedforweldinglargerparts.
Horns are slotted to produce uniform vibration.
watts, lock automatically on the hornresonance,
and
holdvibrationalamplitudeconstantforvarying
mechanical loads. Another useful innovation has been the use
of mechanical amplitude transformers to facilitate matchis
ing of equipment t’o the load.Ultrasonicexposure
controlled by accurate electronic timers (Fig. 4).
The mostvisibleprogressover
the yearshasbeen
made in thesize of plastic parts t’han can be
ultrasonically
welded, primarily helped byhigher
power equipment
andadvancesin
ultrasonic horndevelopment(Figs.
5
Fig. 7. Spot welding ribsontoplastic
boat.
and 6 ) . Improvementsinjoint
design havecxtendcd
ultrasonic welding to more difficult plastics and shapes.
Ramifications of ultrasonic welding processinclude
ultrasonic staking, spot welding, and inscrting of metal
parts into plastic [7] (Fig. 7 ) .
An areadeservingspecialconsiderationisultrasonic
welding of woven and nonwoven fibers [S], [S]. Thermoplastic textiles with up to 35% natural fiber content can
be ultrasonically “sewn”. Thc advantages include absence
of thread and its color-matching problems, simultaneous
64
IEEE TRANSACTIONS ON SONICS AND ULTRSSONICS, MARCH
1975
Fig. 10. 1200 W, 20 kHz ultrasonicmetalwelder.Lapweldsare
produced by ultrasonic shear at the interface.
v.
Fi
8 Ultrsllonic“sewingmachine”
for joiningthermoplastic
abrlcs withoutneedle or thread. U p t o35% natural fibre content
is acceptable.
Fig. 9.
Stitch patterns possible with ultrasonic sewing.
execution of several stitches, and numerous variations of
simultaneous cut and seal operations (Figs. 8 and 9).
Further developments in ultrasonic plastic welding are
likely to be in the area of horn improvement to expand
the size andwear. Shift to lower frequenciesis a possibilitysince
many welding operat’ions areautomated
and the noise can be conveniently shielded.
C . Metal W e l d i n g
Commercialcquipment for ultrasonic metal welding
was introduced in t,he late 1950’s. Originally the process
found
acceptance
in
the semiconductorindustry
for
welding of miniature conductors,known asmicrobonding [lo]. lieccnt advances in equipment design and the
need for better ways of joining high conductivity metals
haverevivedtheinterestin
ultrasonic metal welding
on furtherimprovement
of tho process.
andspurred
Standard cquipment is available to weld parts up to 1/8”
thickand larger,dependingon
thematerialandpart
configuration (Fig. 10).
Fig. 11. Automotive starter motor armature with armature
windings ultrasonically welded t o commutator segments; both metals
are copper (Courtesy of Ford Motor Co.).
The uniqueness of ultrasonic metal welding resides in
the fact t,hat theprocess is relat,ively “cold”. While some
heating occurs, the welding dependsmoreoncleaning
than on material melting. Ultrasonic shear causes mutual
abrasion of the surfacesbeingjoined,breaking
up and
dispersing oxides and other contamination. The exposed,
plast’icized, metal surfaces arebroughttogetherunder
pressure and solid-statebonding
takes place [lo]. In
this respect ultrasonic welding resembles spin welding, or
pressure welding, with the noted difference that there is
no gross movement of parts or largedisplacement of
material.
Ultrasonic metal welds are thus characterized by low
heat and relatively low distortion. Welding temperatures
are typically below the meltingtemperatures
of the
metals, whichhelps to avoid embrittlement and formation of highresistance intermetalliccompounds in dissimiiar metal welds.
Since electricalconductivity plays1x0 rolc in theprocess,
with
applications that are difficult, or impossible,
65
SHOE: INDUSTRIAL APPLICATIONS OF ULTRASOUND
Fig. 13. Large'ultrasonic tank for immersion soldering.
Fig. 12. Low heat of ultrasonic metal welding allows sealing liquidfilled copper tubing. Typically no pre-cleaning is needed on high
conductivity mehls.
resistance welding can
be
done
ultrasonically.
This
includes melding of high conductivitymetals,suchas
electric grade aluminum and copper (Fig. l l ) , also combinations of metals of differentresistivitieslikecopper
and steel.
Welding of parts widely differing inheatcapacity,
such as foil to thicksections, is difficult withheat-dependent methods but can be done with ultrasound. Other
uses include sealing of liquid-filled containers(Fig. 12)
and packaging of heat-damageable contentsand
explosives.
Ultrasonic metal welding as an industrial process has
the desirable characterist,ics of ultrasonic plastic welding
but also has more competition from other metal-joining
methods. Besides microbonding, its applications are
mainlyin electric and electronicindustries in assembly
of electric motors,transformers,
switches, and relays.
Current trend t o replace copper by aluminum is helped
by ultrasonic welding since there are not many reliable
alternatives for joining aluminum conductors.
Since metal welding requiresshearultrasonicmotion
parallel to the plane of the weld, far field welding is not
practical. The method is essentially suitable for producing
spot, welds and line welds. Continuous seaming of metal
foil and sheet is also possible.
Ultrasonic power densit'ies atthecontact
with the
welding tip are very high, in the order of 10,000 watts
per square inch. This causes tip wear and atpresent makes
ultrasonic welding impractical for hard metals. hnother
limitation is compatibility of materials which dueto
requirementformutualabrading
ab2it.y mustnotbe
too far apart inhardness.
The equipmentforultrasonicmetal
welding ranges
40
from low power microbonders
operating
between
and 60 kHzto
machines of severalkilowatt
output
capacity operating between 10 and 20 kHz, for welding
of larger parts.It, should benotedthat,
onhigh con-
Fig. 14. Ultrasonicallysolderedaluminum
was used.
radiator ducts. No flux
duct'ivitymaterialsultrasonic
welding canbe over 20
timesmore
efficient compared to resistance welding.
Thus a 5 k W ultrasonic welder may be equivalent to a
100 kVA resistance welder. Automatic tuning and constant amplitude control are a must on larger ultrasonic
welders.
Furtheracceptance of ultrasonicmetal welding d l
largelydepend
on effective solutions t o properjoint
design and dissemination of this knowledge to potential
users. Totake
full
advant,age
of ultrasonic welding
thepartsmustbe
designed for the process. Improvementsin
welding tip materialsand
design are also
probable.
D. Soldering
Ultrasonicsolderingcan
tin without fluxes and improves wettability under most conditions. The process is
fundament'ally similar t'o ultrasonic cleaning and has been
triedwith
various degrees of success since the early
1930's. Growing need for fluxless soldering of aluminum
and a general striving for
quality have given ultrasonic
soldering a new significance.
Applications of ultrasonic soldering [1l] include electric
and electronic components where nickel, Kovar, and other
hard-to-tin metals are often used. Tinning of transformer
leads, both copper and aluminum, is also effect'ive.
66
Continuoussoldering of printedcircuits C121 and continuous wire tinning is another area
of interest. Recent
activity in aluminum heat exchangers with the inherent
problem of trapped flux has created an opportunity for
ultrasonics in the air conditioning industry and inspired
development of large ultrasonic soldering tanks (Figs. 13
and 14).
Overall processing times with ultrasonic soldering can
be improved
because
pre-cleaning and post-cleaning
operations are usually eliminated. Also, the actual soldering is faster. Tinning is more uniform.
The principle of operation is simultaneous cleaning and
tinning.
Cavitation
in
molten
solder erodes surface
oxides and exposes clean metal to solder. Design of ultrasonic solderingequipment, however, ismoreinvolved
dueto highoperatingtemperat'ures.Presentultrasonic
soldering tanks operate a t temperatures up to850°F.
Both far field and near field soldering are done, ranging
in power densities from a few watts t o several hundred
watts per square inch. Resistance t o cavitat,ional erosion
is an important consideration in the design of equipment
and is compounded by the requirement for metallurgical
compat,ibility.
Future developments are likely t o bring more efficient
ways of couplingultrasonicenergy to the workpiece as
well as
improvements
in
ultrasonic
tank
materials.
Operatingtemperaturelimits
will probably be raised,
which may make volume treatment of high temperature
metals practical.
IEEE TRANSACTIONS ON SONICS -4ND ULTRASONICS, MARCH
Fig. 15. Ultrasonic
rotary
machine
threading. Axial ultrasonic
vibration
motion of the drill.
1975
for drilling,
milling,
and
is added t o rotational
small-diameter,deep,intersecting
holes i n quartzfor
lasers,
machining
nuclear
react,or
matcrinls,
plasma
E. Machining
sprayedcoatings
and ferrite con1putc.r parts. Drilling,
of
possible. Tho toolsaro
To date, ultrasonic machining has proved most effec- milling, andthreadingarc
various shapes and sizes, from 0.02 to 1.5 inches in diamtive on hard,
brittle
materials,
like
alumina,
other
ceramics, and glass. Two methods are currently in
use. eter. 20 kHz frequency is used (Figs. 16 and 17).
Drilling of boron-epoxy composites laminatcdwith
The older method, knownas ultrasonic impact grinding,
steel and t>itaniumsheetrepresents an int,erestingcase
makesuse
of abrasiveslurry(usuallyboroncarbide,
silicon carbide, or aluminum oxide) fed between the non- and has beenresearched to someextent [15]. Convcntional tools that cut, boron fibres do not work on metal,
rotatingvibrating tool andthe workpiece. Oddthreedimensional shapes can be reproduced, wherethe resulting and vice versa. Ultrasonic drilling promises a compromise.
Ultrasonic rotary machining is a useful and, insome
impression is negative
a
of the t,ool. Simultaneous
machining of clusters of holes is also possible. The method cases, indispensable process of somewhat 1imit)ed comis inherently slow and therefore has limited possibilities mercial potential due to the exotic nature of its applications.
in the industry.
In the more recent development, known as ultrasonic
111. SONICS AND LIQUIIIS:
is superrotary machining,axialult'rasonicvibration
OTHER APPLICATIONS
imposedupon the rotary motion of the drill. Diamond
An extensive list o f applications is given in Tablc 11.
impregnated or plated core drills, water-cooled through
It is intcrosting to not'c that tl1c majority o f macrosonic
the center, are used. The tools operate typically around
wit,ll fen- cixcept,ions
5 000 rpm,andtheoperationis
essentially high speed applicationsinvolveliquids,and
depend either on cavitation,
or, like aerosol production,
abrasion (Fig. 15).
on surfacc instability. It is also intercsting that to date
Ultrasonic rotary machining
subst'antially
increases
cutting rates, extends tool life, and due to the lower tool no other liquid-related sonic appliration has had anypressures used allows better dimensionalcontrol
and thing vaguely resembling the commcwial succcss of ultrareduccs chipping. A simple explanation of the process is sonic cleaning.
continuous cleaning of the tool by cavitation of the
coolant,furtheraidedbyultrasonic
acceleration of the A . Extractim
?\lost popular here is thc us(: o f high intensity cavitatool. The tool loads less and cuts more efficiently.
and low
Uses for ultrasonic rotary machining [13], C141 include tion for biological cell disruptioninresearch
machining of precision ceramic
components,
drilling
volume processing.
07
SHOH: INDUSTRIAL APPLICATIONS OF ULTRASOUND
Fig. 16. Glass, aluminum oxide, and
ferrite
parts
drilled
and
machined with ultrasound. Rotary method waa used.
Fig. 17. Diamond
impregnated
and
plated tools used in rotary
ultrasonic machining, Most areliquidcooledthrough
the center.
TABLE I1
MACROSONIC
APPLICATIONS-LIQUIDS
APPLICATIONS
PROCESS
RANKING
ALSJANTAGES
CLEANING
Cleaning, degreasing, descaling
industrial parts. Cleaning
hospital equipment.
Saves time and manual labor.
Cleans hard-to-reach areas.
A
SOLDERING
Fluxless aluminum soldering.
Soldering and tinning electric
and electronic components.
Eliminates flux, pre- and postcleaning. reduces rejects.
B
EXTRACTION
Blological cell breakage for
research. Antigen extraction.
Simple to use. Reduces damage
to contents.
B
Extracting perfume, juices,
chemicals from flowers, fruits,
plants.
Speeds up extraction. Increases
yields. Allows lower temperatures.
Emulsifying cosmetic toilet
preparations, essential and
mineral oils. Waste treatment.
Emulsifies without pre-mixing.
Reduces or eliminates surfactants.
Dye pigment and
dye dispersion.
Insecticide preparation.
Fine, uniform dispersion. No
flocculation.
Medical inhalatlon, nebulizing.
Small particles, controlled
slze.
No gas used.
Small particles, controlled
size.
More efficient burning.
HOMOGENIZING
ATOMIZATION
Fuel atomization, Metal powder
production.
B
B
C
DRYING
Drying heat sensitive powders,
food stuff, pharmaceuticals,
defoaming.
Lower temperatures. Prevents
damage to perishables.
C
DEGASSING
Beer and carbonated drink
"fobbing".Photographic
solutlon agltatlon.
Better control, safe for glass
containers.
C
Degassing
glass.
Reduces
molten
metals
and
CHEMICAL PROCESS Electroplatlng.
ENHANCEMENT
Increases platlng rates. Denser,
more uniform deposit.
Aging alcoholic beverages.
PZIROUS MEDIA
porosity.
FLOW Filtering; Impregnation
ENHANCEMENT
C
Speeds up process.
Increases flow rates.
Better penetration.
C
EROSION
Cavitation eroslon testlng.
Deburring, stripplng.
Convenient to use.
Saves labor.
C
CRYSTALLIZATION
Metal treatment durrngcasting
and weldlng.
Refines grain, reduces stresses.
X
TtD2FUG.L TPANSPORT
Uistlllation
processes.
DEPOLYMERIZATION
Extruding plastics. Plastic
flbre manufacturing.
A
B
-
and
other
chemical Speeds up heat exchange.
Lowers viscoslty.
Established large-scale process
Established small-scale process
C
X
-
Some industrial use
Experimental
X
X
68
IEEE TRANSACTIOKS ON SONICS AND ULTRASONICS, MARCH
1975
of residualstresseshave
also
Near field cavit'ation breaks downcell walls and releases Degassing andremoval
cell contents into the surrounding liquid. The method
is been reported.
In spite of a large volume of reference material on this
used to extract active antigens for making vaccines and
subject [19], there is no evidence of commercial impleas a general tool for studying cell structure. Lltrasonic
some installationsineastern
extraction is simple and, if cooling is used, causes minimal mentation.Theremaybe
Europe [5 3.
degradation of contents.
The obvious difficulties here are the severe environment
The equipment is normally in the range of 100 to 500
for the ultrasonicequipmentandtherequirement
for
watts,operatingaround 20 kHz.Highamplitudehorns
are used, producing power densities in the order of 500 treating a large volume. These, again, may be helped by
watts per square inch. Batch and continuous
processing current research in ultrasonic soldering.
are done.
Other extractionuses include extractionof perfume from C . Emulsification
The main advantage of ultrasonic emulsification is in
flowers, essential oils from hops, juices from fruits, and
the ability bo mix some immiscible liquids wit'hout addichemicalsfrom
plants [S],
[16].
Thepotentialhere
tives (surfactants). Recent publicity has called attention
seems great,but'application
progress, atleastinthe
United States, has been slow. A review of high intensitm y to the emulsification of water in heating oil for bet'ter
liquid processing is neededin view of the powerful 10 kHz fuel economy and less pollution [20]. Fuel saving seems
uncertain, but there may
besome substance to cleaner
equipment and other equipment improvernents available
burning, and it is an interesting development to watch.
today.
B . Atomization
D. Heat Transfer [all
Ultrasonicatomizerscanproducesmalldroplets
of
predictable size. Foragivenliquid,droplet
size isa
function of atomizerfrequencyandgetssmalleras
the
frequency is increased [4].
1. Ultrasonicnebulizers
for medicalinhalationhave
shown best commercial progress. Medical nebulizers
operate bet,ween 1 and 3 megahertz and produce droplets
between l and 5 microns. Mainadvantagesare
small
particle size, tight distribut,ion, and the
absence of gas,
which makes ultrasonic nebulizers suitable for anesthetic
systems [17].
2. Fuelatomization by ult,rasound [l71 hasbeer researched to a considerable extent t o improve combustion
efficiency and reduce pollution. Several types of devices,
both electronic andpneumatic,arein
use, operating
between 20 and 300 kHz. Use in oil burners as well as
carburetorshas beenconsidered
but due to marginal
economics has never caught on in a big way.
3. Dispersion of molten metals for production of powders
and metal spraying has been demonstrat)ed. Spraying of
molten lead, tin, zinc, bismuth, aluminum, and cadmium
has been reported, but cost justification is questionable
~ 1 7 1[W.
,
There is apat,terntotheseapplications:Greatest
success has beenachievedwhere
the requirement for
quality supersedescost, andthethroughput
needcdis
low. As theproductgetscheaperand
t.hP processing
rates increase, ultrasonicatomizat,ionbecomes
less desirable.
Some of t.his is likely t,o change.Fuel, for instance,
costs more today, and ultrasonic atomizers can be built
for less. 3hltenmetal
dispersion withits
formidable
equipment prob1c:nls may become practical as a result of
the progress in ultrasonic soldering.
Cavitation-induced microst'irring can decreasethe thermal boundary layer and improve heat transfer in a variety
of systems.References datebacktotheearly
1960Js,
and uses indistillationandother
chemicalprocessing
have been suggested. Present concern with efficiency has
made the topiconce more popular.
B. Crystallization
Finer grain has been prod~lctdin aluminum and other
nletalsbyinsonationduringthc
solidification stage.
E. Flow Enhancement
Liquid flow ratesthrough porousmediacan
be increased byultrasound. Uses in filtering [22], [a31 and
is
impregnation
have
been
suggested.
The
subject
intriguing because low amounts of vibratory power can
be effective.
IV. SONICSANDSOLIDS:
OTHER APPLICATIONS
An ext'ensive list of applications is given in Table 111.
A . MetalForming
Over the years there has
been a considerable interest
by the controversies about the
in this area, heightened
mechanism of the process.
The benefits o f vibration-asxistcd formingtypically
include lower forming forces, larger percentage deformation without t,earing, and improvements in surface finish.
Dueto highpowerrequirementsthe
successful work
performed to date has beenlimited to objectssmall in
size or cases where the area to be affected is small.
1. Tube clra?uing withultrasound C241 has beenused
in manufact,uringfor about, ten years and is most
effective
on thin wall tubing having an initial diameter of about
4 inch or less. TJsually the plug is vibrated in the direction of drawing. The advantages are faster drawing rates,
better size control, and ability to producedifficult shapes,
such as rectangular tubing with sharp
corners, or tubes
500: 1 ) .
with
large
diameter-to-wall
ratios
(up
to
Aluminum, copper, iron,and nickel based alloy, have
been drawn.
69
SHOE: INDUSTRIALAPPLICATIONS OF ULTRASOUND
TABLE 111
MACROSONIC
APPLICATIONS~OLIDS
PROCESS
WELDING
APPLICATIONS
RANKING
PLASTICS - Welding rigidt h e m plastics. Seam welding film and
fabric. Metal-in-plastic insertlon.
Staklng.
ADVANTAGES
Fast, clean, economical, good
weld integrity. Welds inaccessible areas.
A
B
METALS - Mlcrobonding. Lap welding
Low heat, no pre-cleaning.
high electrical conductivity and dis-Insensitive to electrical
similar metals. Seam welding sheet.
resistivity and heat capacrty
mismatch.
MACHINING
DENTAL
-
Prophylaxis teeth treatment. ~ a s yto use, less discomfort
compared to hand scrubbing.
-
HARD, BRITTLE MATERIALS
Vlbratlonasslsted rotary machining.
B
Faster rates, longer tool life. B
better dimensional control.
Impact grinding using abrasive slurry.
Makes multiple hole
patterns,
odd, three-dimenslonal shapes.
METALS - Vlbration-assisted drilling, Faster rates, longer tooll l f e .
tapping, turning.
better finish.
C
METALS - Drawing thlnwall tubing of
large diameter to
wall ratios.
Higher drawlnq rates. Allows
drawing difficult shapes.
C
Drawing small diameter wire from
difficult-to-form metals.
Faster drawlng, less breakage,
better surface.
CUlTING
Vlbration-assisted cuttingof
fibrous and spongy materials.
Better cuttingdue to blade
acceleration, or melting.
C
FATIGUING
Destructive testing and quallty
control.
Saves testing time.
hidden flaws.
C
CLEAVAGE
Cleaving crystals and laminated
objects.
High Impact, high rate.
C
FRICTION
WDUCTION
Vibrating sieves and hoppers.
Speeds up material flow.
C
Torquing
Tighter joints
X
Compactrng powders, sintering.
Improves uniformity in complex X
molds. Increases density.
FORMING
DENSIFICATION
A
B
-
Established large
Established small
scale process
scale process
C
X
-
Finds
Some industrial use
Experimental
2. Ultrasonic wire drawing allows faster drawing rates,
[as]. To duplicate the effect on a 3 inch diameter slug,
andreduces surfaceimperfections. Many investigations close to one million watts of sonic power would be needed.
The use of macrosoundfordeformation
of a large
were reported in theearly 1 9 6 0 ’ ~with
~ particular mention
wire from hard- volume of metalmaynotbejustaroundthe
of advantages for drawing small diameter
corner.
to-form materials like tungsten and molybdenum. There
But small-scaleapplications are practical. Simultaneous
has been little commercial activity. Improved equipment metal welding and crimping, for instance, is being done.
is now available and may rejuvenate the interest in
the
B . Metal Drilling
process
3. Ultrasonic riveting hasbeen of interesttoaircraft
Rotary ultrasonic
drilling
tried
with
conventional
manufacturers. Experiments on aluminum and titanium
twist drills produced interesting but uneven results. Axial
rivets showed a possibility of a substantial reduction in
ultrasonic vibration was added to rotary motion of the
formingforce,andinsome
cases a largerdeformation
drill.
without cracking. Another set of experiments concerned
Faster driiling rates
and
longer drill life were
aluminum leak-tightriveting. The important question h e reobtained on titanium using small-diameter
cobalt drills,
is the effect of vibratory forming on fatigue life of the but nosignificantimprovement
was noticedonseveral
rivet and is largely unanswered.
other metals [26]. A number of portable drills are in use
As asoberingthoughton
sonic metalforming,it is for titanium drilling intheaircraftindustry.
A special
interestingtomentionanexperimentontitaniumand
short ultrasonic drill adapter was developed to make the
severalgrades of stainlesssteel,designed
to show the process practical (Fig. 18).
effect of sonics on volume deformation obscured
in drawing
C . Dental Treatment
operations by high surface friction.
An interesting success story, not quite fitting into the
Cylindrical slugs& of an inchin diameter were flattened
400-600% reductions in static industrial world,concernsanultrasonic“machinetool”
with and without sound.
force were possible for equivalent deformation, but sonic designedfor use inprophylaxistreat8ment, periodontia,
power densities were over 100 000 watts per square inch and other areas of operative dentistry (Fig. 19).
[%I.
70
Fig. 18. PortableQuackenbush drill, usedin aircraftmanufacturing, equipped with ultrasonic drill adapter. Faster drilling rates
and better drill life were demonstrated on titanium.
IEEE TRANSACTIONS ON SONICS AND ULTRASONICS, MdRCH
1975
Fig. 19.Ultrasonicdentalequipment
fordescaling teeth(prophylaxis), and other
uses
in
operative
dentistry.
(Courtesy
of
Cavitron Ultrasonics, Inc.).
This equipment is becoming popular and is apparent,ly of types of things power ultrasound can do that would be
liked by dentists and patients, who prefer it over the old representative of the present state of the art and inspire
manual scrubbing. Descaling of teeth is accomplished by further thought’ on the subject.
a linear, or elliptical, reciprocating scrubbing a t 25 kHz,
ACKNOWLEDGMENTS
aided by cavitation of the water spray.A variety of interTheauthor
wishes to
thank
Cavitron
Ultrasonics
changeableinsertsareavailable
for variousscrubbing
CorporationandFord
l\/lot,or Companyforthe
use of
operations.
photographs and B. L. Mims for reading the manuscript.
B. Crystal Cleavage C271
The illustrations are courtesy of Branson Ultrasonics
Crystal cleavage by ultrasound proved to be a valuable Corporation unless otherwise noted.
method of maintaining particle balance in a continuous
REFERENCES
chemicalprocessing installation.Ultrasonicallydisinte[l]
Hueter,
T.
F.,
and
R.
H. Bolt,“Sonics”, p. 41,Wiley, New
grated crystals are split along cleavage planes in contrast
York (1955).
to random breakage produced by mechanical means. While[2] Noltingk, B . E., and E. A. Neppiras,Proc.Phys. Soc., 63B,
No. 9, 674-685 (1950).
ultrasonic disintegration takes place in a super-saturated
[3] Elder, Kolb and Nyborg, Phys. Rev., 93, 364(A) (1954).
liquid,studiesshowed that cleavageresultsfrom
direct
[4] Doyle, A. W., B. V. Mokler, and R. R. Perron, API Research
Conf. Paper CP62-1‘$1962).
collision of particles with ult’rasonic horn and with one
[5] Neppiras, E. A.,
Macrosonics
in
industry”, Ultrasonics,
another [28]. It is likely that the principle would also
Januarv (1972).
[6] “Guide tb Ultrasonic Welding of Plastics”, Appliance Manuwork in a gas medium.
V. T H E F U T U R E
Unheralded by scientific publications, ultrasonic plastic
welding has become a large-scale industrial process while
the considerably
researched
metallurgical
and
metal
working areas have resulted in relatively little. Equally
disappointinghavebeen“catalytic”uses
of ultrasound
inchemistry.Theattentionpaidtoa
givenultrasonic
area is largely influenced by the topic of the day, as evidencedby currentinkrestinult’rasonic
fuel treatment
[ Z O ] , wastetreatment [as], oilwell rejuvenation, et’c.,
and is not always related to the true worth
of the process.
Thus taught by experience, the author will refrain from
any specific predictions save for pointing out two general
factors. The cost of an acoustic watt has been declining
and following t8he general technologicaltrend will continue
to do so in the future. This will make ultrasonic power
more competitive with convent’ional processes. The second
factor is thatmore ultrasonic equipment is now in use and
more people are working with it. This increased exposure
will undoubtedly lead t’o new uses.
Rather than compiling an all-inclusive list of ultrasonic
applications, the author has tried to show a cross section
facturer, April (1974).
[7] Sherry, J. R., “Assembling Plastic Parts”, Automation,November (1973).
[8] Creegan,H.
K., “TheThermal JoiningMachine”,Modern
Textiles, June (1073).
[9] “SonicStitching
inColor”,Apparel
Manufacturer,August
(1973).
[lo] Hulst, A. P., “Ultrasonic welding of metals”,Ultrasonics,
November (1972).
[l11 LeGrand,Rupert,“Ultrasonicsgets
3 new jobs”, American
Machinist, Februarz 8, 1971.
[l21 Gootbier, E. A., Ultrasonics in masssoldering”,Western
Electric Engineer, January 1969, Vol. XIII, No. 1.
[l31 Dallas,Daniel B., “The new look of ultrasonicmachining”,
Manufacturing Engineering and Management, February (1970).
[l41 “Tiny holes with a tliameter/length ratio of 1:300 successfully
drilled in glas“,, Industrial Diamond Review, March (1973).
[l51 Grauer, W . , Ultrasonic
Machining”,
Grumman
Aerospace
Corp. Technical Report AFML-TR-73-86, April (1973).
1161 Skauen, D. M,, J. Pharm. Sci., 56, No. 11, November (1967).
117) Topp, M. N., and Eisenklam, P., “Industrial and medical uses
of ultrasonicatomizers”,Ultrasonics,
Vol. 10, 127-133, May
(1972).
[l81 Pohlman, R., Conf. Proc. Ultrasonics Int. (1973) sponsored by
J. Ultrasonics.
[l91 Rosenberg, L. D.,“PhysicalPrinciples
of UltrasonicTechnology”, Vol. 2, 145-273.
[20] “Oil and Water Alchemy”, Time, February 11, 1974, p. 3.
[21] Rosenberg, L. D., “PhysicalPrinciples
of UltrasonlcTechnology”, Vol. 2, 3?;-409.
[22] Semmelink, A., Ultrasonically
enhanced
liquid
filtering”,
Conf. Proc. Ultrasonics Int. (1967) sponsored by J. Ultrasonics.
[23] Ibid., “Use of ultrasound to increase filtration rate”, Fairbanks,
H. V., p. 11.
[24] Jones, J. B., “Ultrasonic metal deformation processes”,Proc.
IEEE TRANSACTIONS
ox
SONICS AND ULTRASONICS, VOL.
su-22, NO. 2, MARCH 1975
71
Int. Conf. Manufacturing Technology, September (1967),
1972, Shoh, A.
[27] Midler, United
M.,States
Patent
number
3,510,266 (May 6,
Am. Soc. Tool and Mfg.
Engineers.
[25] Langenecker, B., Illiewich, S., and Vodep, O., “Basic
and
1970).
ap lied research on metal deformation in macrosonic fields at (281 Klink A., Midler M., and Allegretti J., “A Study of Crystal
P\ PL-Austria”. Conf. Proc. Ultrasonics Int.
(1973)
Cleavage bv SonifierAction”,ChemicalEngineeringProgress
.
.~ sDonsored
.~
.
by J. Ultrasonics.
Sympoiium”Series, No. 109, 1971, Vol. 67.
(261 “New Developments In Metal Working Procmes”, paper, 83rd
(291 “The Silent Treatment”, Time Magazine, February 11, 1974,
Meeting
Acous.
SOC.
Am.,
Bu5al0,
New York, 18-21 April
pp. 74-75.
Industrial Applications of Ultrasound-A Review
II. Measurements, Tests, and Process Control
Using Low-Intensity Ultrasound
LAWRENCE C. LYNNWORTH
Abstract-Thefollowingapplications
are reviewed:ultrasonic
measurement of flow, temperature,density,
porosity, pressure,
viscosity andothertransportproperties,level,
position, phase,
thickness,composition,anisotropy
andtexture, grain size, stress
andstrain,elasticproperties,bubble,
particle andleakdetection,
nondestructive testing, acoustic emission, imaging and holography,
and combinations of these. Principles, techniques, equipment,
and
application data are summarizedfortheseareas.Most
of the
measurements utilize approaches designed to respond primarily to
sound speed, but some depend on attenuation effects. Most equipment in use involves intrusive probes, but noninvasive, externallyBoth
mountedtransducersarebeing
promoted in severalareas.
are widelyused.Limitations
due
pulse and resonance techniques
to the influence of unwanted variables are identified in some cases.
A bibliography andlist of vendors providesources
for further
information.
INTRODUCTION
T
HE MAIX purpose of this review is to identify the
breadth,depth,pract,icality,andlimitations
of industrialapplications
of small-signal ultrasound.Additionally, we will attempt to identify patterns of emerging
ultrasonic technology.
In general, the scope of this review will be limited
toindustrialapplications
wherein the transductionor
propagation of low-intensity
ultrasound
responds
to
t,he properties, state, or quality
of the medium or prrt
in question. By restrictingt’he
scope to “indust.ria1”
applications we choose to omitnumerousinteresting
and important applications in
research, and in medical,
dental,
and
biological areas.
“Low-intensity”
avoids
macrosonic and nonlinear acoustic areas such as ultrasonic
Manuscript received November 8, 1974.
The author is with Panametrics, U‘altham, MW. 02154.
cleaning,machining, wire drawing, welding, atomizing
cavit’ating, emulsifying, influencing of chemical reactions
shock-wave measurements, and therapy. By limiting the
scope to cases where the objective is measuring uItrasound
transduction or propagation to indicate the value of some
variable parameter, we intend to detour around devices
such as quartz clocks, ultrasonic garage door openers, TV
channel selectors, delay lines, filters, and signal processors
despite the obvious industrial significance of such devices.
I n view of all these omissions, the reader may rightfully
ask, “What’s left’?” For the answer see Table I.
This review generally makes no attempt t’o identifythe
earliest demonstration of the entries in Table I, nor to
compare with competing technologies. Readers interested
in the origins of acoustical measurements of sound speed,
attenuation, polarization, or related quantities arereferred
elsewhere.’
Standard commercial equipment,particularizedfor
a
specific application, is available for almost every iten1 on
the list. Additionally, since virtually any ultrasonic measurement can be analyzed in terms of observations related
to transit t,ime or wave amplitude, general-purpose electronic measuringequipmentsuch
as digital processing
oscilloscopes, computingcounters,timeintervalometers,
peakdetect’ors, etc.,may also be used to perform the
industrialmeasurement,s or tests to be discussed below.
The items in TableI could be categorized into two major
groups in terms of instrument response being associated
primarilywithsoundspeed
c or attenuation coefficient
R. B. Lindsay,ed., Acoustics-lfislorical and Philosophicul Deuelopment (1973); Physical Acoustics (1973), Dowden,Hutchinson
and Ross Inc.,Stroudsberg, Pa. See also: D. M. Considine,ed.,
Encyclopedia of Znstrumentation and Control, McGraw-Hill, New
York (1971).