Ultrasound Review 1

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60 IEEE RANSACTIONS ON SONICS AND ULTRASONICS, VOL. U-22, NO. 2, MARCH 19

Industrial Applications of Ultrasound - A ReviewI. Hish-Power Ultrasound

Abstract-The estimated worldwide sales of ultrasonic powerequipment for industrial uses total nearly $100 million a year. Theindustry had its beginnings shortly after WorldWar II and grewsteadily over the next two and a half decades.

Lower cost of ultrasonic power made possible by advances nelectromechanical power conversion materials and power semi-conductors has greatly contributed to the practicality of ultrasonicequipment. Yet the main reason behind the growth of power ultra-sound is the ability to perform some unique jobs that save moneyand have become indispensable in modern manufacturing.

Not all attempts to implement ultrasonic power devices have beensuccessful, butcommercial success is a function of technologicalstate of the art and the need for the process. Since both changewith time, surprises are likely. Who would have guessed the poten-tial of ultrasonic plastic welding, let lone that of ultrasonic

While stressing the more established applications, this articletakes a broader ookat the uses of high frequency mechanicalvibratory energy, outlining the advantages and the limitations ofeach process.

sewing?

I. GENERALIN CONTRAST o ultrasonic nondestructive esting,theobject of a macrosonicapplication is to exposethe workpiece to enough vibratory energy to bring aboutsome permanent physicalchange. This involves a flowof mechanical power from the source o he workpiece,which,dependingon heapplication,may ange roma few wattsper quare nch to tens of thousands ofwatts per square inch. Vibratory input, during the timeof exposure, is normally of thecontinuousRave ype.Macrosonicphenomenaextend well into hemegahertzrange, butmost practicalwork sdone at frequenciesbetween 20 and 60 kHz, somewhat above he range ofhuman hearing.A basic macrosonic systemonsists of an electro-mechanicalransducernd ighrequencylectricpower supply. The power supply converts the availableelectric inepower intohigh requency electricpowerwhich is used to drive the electromechanical transducer.The transducers are typically of a compound design, butat theirhear t use electrostrictiveor magnetostrictiveelements which changephysicaldimensions inresponseto an electric or a magnetic field. Mostmodern rans-ducers use piezoelectric ceramics f lead zirconate ti tanatedue to itsuperior electromechanical conversionfficiency,typically in the order f 95 % or better.

Manuscript received November 8, 1974.The author is with Branson Ultrasonics Corporation, Subsidiaryof Smith Kline Corporation, Eagle Rd., Danbury, Conn. 06810.

Just what are the limits of practical ultrasonic powertoday? If the application allows stacking of sonic powsources, no particular limit to the maximum t,otal powexists. The powervailablerom a single half-watransducer, however, is limited by he volume of thelectromechanicalconversionmaterial that canbe acommodated and varies inversely uith the square of thfrequency. As transducer design dependson the usexact power limits are not possible to pin down, but,4 kat 20 kHz could serve as a rough reference.

Bydefinition, the mechanical power transferred fromthe sonic source to the load is the product of sonic sourvelocity at the load nterface and he mechanical forresisting the sourcevelocity [l]. The force is produceby the medium on which the sonic source is acting.

Transducer output velocity and frequency can be usas primarysourceparameters. Theproduct of velociandrequency defines acceleration, andheatio velocity and requency defines the transduceroutputdisplacement. See Table I.As a point of interest, racticalltrasonic owersources are by nature velocity or displacement generatidevices, where due to high mechanical Q the motionsinusoidal, and hereareno practicalways of directgenerating ultrasonic forces.

The most commonly used transducers are of extensiontype where the output face of the transducer is a circulpiston area vibrat ing sinusoidally in the direction of ttransducer axis. Theransducer utput facean applied directly to the load, or coupled to ntermediatsonic resonators (Fig . 1). Extensionalransducersm-part compressional waves t o the load. Transducers caalso be designed to produceshear, orsional or flexuvibration, or tofocus vibrational intensity in fluid med

Contrary o hepopularmyth, ultrasonic treatmeisnormallynotdoneby focusing soundwaveson twork through the air. I n most cases a direct contact withe vibratory tool is needed, or liquid is used as a vehicNeither is therea commonmechanism esponsible orall sonic effects: ultrasonic metal welding is unrelatedultrasonic aerosol production, and plastic welding unrelated to ultrasonic cleaning.

Yet there are some peculiarities about the basic ultrsonic parameters, as shown in the following example.

A 20 kHzransducer perating a t a eak utputvelocity of 26 ft./sec. will havepeak-to-peak displacmentamplitude of 0.005 inches andpeak acceleratiof 10 X l@g. To load 8he transducer to 1kW the loa


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SHOE: INDUSTRIAL APPLICATIONS OF ULTRASOUND 61TABLE IEFFECTF FREQUENCYN TRANSDUCERARAMETERS

PARAMETER FREQUENCY FREQUENCY x 2Length L L/2Width W w/2Weight K W8Output surface S W 4Power P P/4Power density P PDisplacement D D/ZAcceleration A ZAOutput velocity V V

Fig. 1. Sonicandultrasonicpower ransducers: S kW, 10 kHz;1 kW, 20 kHz; and 40W, 40 kHz. Transducers are of piezoelectrictype.

must exert on he ransducerapeak force of 57 lbs.(excluding any reactive loading).Theworkperformedby this transducer in one second is equivalent to liftinga 740 lb. load to a height of one foot. What is so unusualabout these values?

First,powerultrasound is characterized by very highrepetitionates,mallisplacements, moderate po intvelocities, and very high accelerations. Second, large amountsof work can be done withou t app lication of high forces andlarge displacements. Theransducernhexample,incidentally, would weigh about 2 lbs.

Another useful characteristic is the ability to propagatethrough solids, liquids, and gasses and form a resonantpattern. This allows work to be done at areas away fromth e source and makes it possible to tr eat a large volumeof material.

Most uses of macrosound depend on compound vibra-tion-induced phenomena occurring in matter. These are

1) cavitation and microstreaming in liquids [ 2 ] , [3]2 ) surfacenstability occurring at liquid-liquid and3) heating and fa tigu ing in solids..Major uses of macrosound are discussed next in order

of commercial significance. Since hardacts re otavailable, the ranking is by necessity subjective. Sections

liquid-gas interfaces [4],

Sonics and Liquids and Sonics and Solids give an over-view of macrosonicapplications and highlightsome ofthe more intriguing developments.

11. FIVE MAJOR APPLICATIONSA . Cleaning

Ultrasonic leaning is the oldest industrial applica-tion of power ultrasound. Present-day uses span a widevariety of industriesangingrom castings to semi-conductors.Ultrasoniccleaning is oftencombined withother pre- and post-cleaning perations uch as pre-soaking or vapor rinsing and makes use of a variety ofdetergents nd cleaningolutions.Descaling and de-greasing are also done.

Themain dvantage of ultrasonic leaning lies inbrushlesscrubbing ue to cavitation, which inwell-designed cleaner is evenly distributed throughout thevolume of the liquid and is capable of reaching normallyinaccessible places.Ballbearings, carburetorparts,andvessels with complex internal cavities can be effectivelycleaned.Ultrasonicleaning works best,nelatively hardmaterialssuchas metals, glass,, ceramics, and plastics,which reflect rather than absorb sound. Cleaning equip-ment normally operates in the rangef 20-50 kHz.

The phenomenon responsible for ultrasonic cleaning iscavitation.Highrequencylternating pressure in aliquidforms microscopic voids whichgrow t o a certainsize, then collapse, causing veryighnstantaneoustemperaturesand pressures. This implosion of cavita-tionalbubbles does the ough work of loosening dir tand grease stuck t o the workpiece. Oscillation of stablecavitational bubbles. and he esultantmicrostreamingalso contribute to cleaning [ S ] .Cavitationcanbeproducedbyothermethods hanultrasonics and is commonwith underwater propellerblades and steam turbines. Ultrasonically induced cavita-tion, however, can be produced as a far field effect,, awayfrom the source, andwithoutany gross movement ofth e liquid. Far field effect. is achieved by resonating thetotal volume of the liquid in the cleaner. ,4t frequenciesof interest, the layers of maximum cavitational intensityrepeat every 0.5 to 1.5 inches producing fairly uniformcleaning throughout he volume. For moreuniformitythe parts may be moved during xposure.

Power density of ultrasonic cleaners s relatively low,usually below 10 watts per square inch of driving area.An attempt to overdrive t8he tank results in a loss ofthe far field effect and causes pronounced cavitation andwear at thedriving surface.

The choice of cleaner requency snormallydeter-minedyhe application. Since cavitationalhockintensity is higher at, lower frequencies, a 2.5 kHz cleanerwill havemorebrute cleaningability thana 40 kHzcleaner.However lower frequencies have eenounddamaging to somedelicate parts,and for cleaning ofsemiconductors, for instance, 40 kHz may be preferable.40 kH z cleaning is also quieter.


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62 IEEE TRANSACTIONS ON SOMCS AND ULTRASONICS, MARCH 19

Fig. 2. Monorailautomatedultrasonic cleaning system for clean-ing, rinsing, and drying automotive ring and inion gears.

Fig. 3. Smallultrasoniccleaners with power Buppliea mounted inthe base.

Standard ndustrial cleaners typically range inpowerfromone hundred oacouple of thousandwattswithcorresponding tank capacities of 1-44 gallons.Multi-kilowatt special syst,ems with tank capacities of severalhundred gallons arenotuncommon Fig. 2 ) . In recentyears, low power, low cost below $100) cleaners havebecomeavailable,which hasmade ultrasoniccleaningaccessible to m a l l shops and laboratories (Fig. 3 ) .

Modern ltrasonic leaners mployolid-state elec-tronic power supplies with automatic tuning and do notrequire operatorattention. A commonproblem to allultrasoniccleaners is gradualdeterioration of the ankdue to cavitational erosion. This depends largely on theapplication, and well-designed systems can give years ofsatisfactory service.It is hard to envision any dramatic breakthroughs inultrasonicleaning. Tankmaterialsnd design canprobably be further improved to extend life and enhancecleaning. Since cavitat ional ehavior isifferent fordifferent, olvents, and alsochangeswith emperature,

choice of optimum cleaning paramet.erscanbe trickand further advances in this area areikely.B . Plastic Welding

Probablywithout knowing it, most, people in thUnited States come in daily contact with ultmsonicallym-elded plastic parts. The processwasdeveloped in thlast ten years and was quickly accepted in asscmbly toys, appliances, and indust,rial thermoplastic parts. Thbig break came with discovery of far field welding, whimade welding of rigid thermoplastics possible and etended he echniquebeyond welding of plastic filmpracticed earlier.

Ultrasonic welding hasan ideal ombination of igredients sought in modern manufacturing. The proceis fast nd clean,equires o onsumables, does nneed a skilled operator, and lends itself readily t,o autmation. It is used extensively in the automotive industfor assembly of taillights, dashboards, heater duct,s, another components where plastics have replaced thc tradtional use of glass and metal.

How does the process work? Essentially, high rc?qut*vibrationproducesheat whichmelts the plastic. Yultrasonically induced heat can be generated sclr:c:tivcprecisely at the int erface of the parts being joined witout indiscriminate heating of the surrounding materialLess weld energy is used, result ing in less dist,ortion amaterial degradation. Sinco tha heat is gctneratcd withthe plastic and not conducted from the t,oo1, welding cbe a.ccomplished in completely inaccessible placps.

Most hermoplasticshavecharacteristicssuitable orultrasonic welding [S]. This includes the bili tyotransmit and to absorb vibration, as ~vell as low thermconductivity to facilitate ocal build-upof heat,.

Heating n plastic s a function of ultrasonic tressand varies roughly as the square of stress amplitmud(;.Tmaximize the stress in the weld region, the cwntact arbetween the parts being joined is rcduced. Static: claming force is used to keep the parts together during wcing. A hold ime o f a fraction o f a second is addafter ultrasonic exposure to allow the plastic t8 0solidbefore unclamping. Typical welds arc don(. in less thansecond.

Compared to cleaning,ltrasoniclastic wddirequires much higher power densities, typically hundrcof watts per square inch at the weld, and a t t8he conof the toolwith the workpiecc. To deliversuch powdensities plastic welding horns operate at amplit,udcs0.001 to 0.005 inches (over ten times higher than cleing), and due to high energy storage exhibit very sha,rmechanical esonances.Additionally,dependingon tapplication, heymustaccomrnodatc a wide varietyloads, andduring he welding mechanical oadingmayvary. To satisfy these requirementjsa new breed of rqument ado e eveloped, raising ltrasonicowertechnology to a new level.

Modernltrasoniclastic welders operate prodminantlyaround 20 kH z at power outputss below 10


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SHOH: INDUSTRIAL APPLICATIONS OF ULTRASOUND 63

Fig. 6. Ultrasonic man welder for assembly of large plastic panels,such asused in plastic furniture.

Fig. 4. 700 W, 20 kH z ultrasonic pl&ic welder.

Fig. 5. Two ormore horns are ften usedorweldingarger arts. Fig. 7. Spot welding ribs nto lastic boat.Horns are slotted to produce uniform vibration.

watts, lock automatically on the horn esonance, andholdvibrationalamplitudeconstant orvarying mech-anical loads. Another useful innovation has been the useof mechanical amplitude transformers t o facilitate match-ing of equipment to the load.Ultrasonicexposure iscontrolled by accurate electronic timers (Fig. 4).

The mostvisibleprogressover the yearshasbeenmade in theize of plastic parts than can beltrasonicallywelded, primarily helped byhigher power equipmentandadvances n ultrasonic horndevelopment Figs. 5

and 6 ) . Improvements n oint design have xtendcdultrasonic welding to more difficult plastics and shapes.

Ramifications of ultrasonic welding processncludeultrasonic staking,spot welding, and inscrting of metalparts into plastic [7] (Fig. 7 ) .

An areadeservingspecialconsideration sultrasonicwelding of woven and nonwoven fibers [S], [S]. Thermo-plastic textiles with up to 35% natural fiber content canbe ultrasonically sewn. Thc advantages include absenceof thread and its color-matching problems, simultaneous


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64 IEEE TRANSACTIONS ON S O N IC S AN D ULTRSSONICS, M A R C H 19

Fi . 8 Ultrsllonicsewingmachine for joininghermoplasticvbrlcs withoutneedle or thread. Up to 5% natural fibre contentis acceptable.

Fig. 9. Stit ch pa ttern s possible with ultrasonic sewing.

execution of several stitches, and numerous variations ofsimultaneous cut and seal operations (Figs.8 and 9).

Further developments in ultrasonic plastic welding arelikely to be in the area of horn improvement to expandthe size andwear. Shift to lower frequencies s a pos-sibility ince many welding operations areautomatedand the noise can be conveniently shielded.C . Metal W e l d i n g

Commercial quipment for ultrasonic metal weldingwas introduced in t,he late 1950s. Originally the processfoundcceptancen the semiconductorndustry forwelding of miniature conductors,known asmicrobond-ing [lo]. lieccnt advances n equipment design and theneed for better ways of joining high conductivity metalshave evived he nterest n ultrasonic metal weldingand purred on furthermprovement of tho process.Standard cquipment is available to weld parts up to 1/8thickand larger,dependingon thematerialandpartconfiguration (Fig. 10).

Fig. 10. 1200 W , 20 kH z ultrasonicmetalwelder.Lapweldsareproduced by ultrasonic shear at the nterface.

Fig. 11. Automotive starter motor armature with armature wiings ultrasonically welded t o commutator segments; both metare copper (Courtesy of Ford Motor Co.).

The uniqueness of ultrasonic metal welding resides the fact t,hat theprocess is relat,ively cold. While somheating occurs, the welding dependsmoreoncleaningthan on material melting. Ultrasonic shear causes mutuabrasion of the surfacesbeing oined,breaking up andispersing oxides and other contamination. Th e exposeplasticized, metal surfaces arebrought ogetherunderpressure and solid-statebonding takes place [lo].thi s respect ultrasonic welding resembles spin welding, pressure welding, with the noted difference that the reno gross movement of parts or largedisplacement material.

Ultrasonic metal welds are thus characterized by loheat and relatively low distortion. Welding temperaturare typically below the meltingemperatures of tmetals, whichhelps to avoid embrittlement and forma-tion of high esistance intermetalliccompounds in dsimiiar metal welds.

Since electricalconductivity plays x0 rolc in theproceapplications that are difficult, or impossible,ith


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SHOE: INDUSTRIALAPPLICATIONS O F ULTRASOUND 65

Fig. 13. Large'ultrasonic tank fo r immersion soldering.

Fig. 12. Low heat of ultrasonic metal welding allows sealing liquid-filled copper tubing. Typically no pre-cleaning is needed on highconductivity mehls.resistance welding caneoneltrasonically.hisincludes melding of high conductivitymetals, uchaselectric grade aluminum and copper (Fig. l l ) , also com-binations of metals of different esistivities ikecopperand steel.

Welding of parts widely differing inheatcapacity,such as foil to thicksections, is difficult withheat-de-pendent methods but can be done with ultrasound. Otheruses include sealing of liquid-filled containers Fig. 12 )and packaging of heat-damageable contents nd ex-plosives.

Ultrasonic metal welding as an industrial process hasthe desirable characterist,ics of ultrasonic plastic weldingbut also has more competition from other metal-joiningmethods. Besides microbonding, its applications aremainly n electric and electronic ndustries in assemblyof electric motors,ransformers, switches, and relays.Current trend to replace copper by aluminum is helpedby ultrasonic welding since there are not many reliablealternatives for joining aluminum conductors.

Since metal welding requiresshearultrasonicmotionparallel to t he plane of the weld, far field welding is notpractical. The method is essentially suitable for producingspot, welds and line welds. Continuous seaming of metalfoil and sheet is also possible.

Ultrasonic power densit'ies at heconta ct with thewelding tip are very high, in the order of 10,000 wattsper square inch. This causes tip wear and at resent makesultrasonic welding impractical for hard metals. hnotherlimitation is compatibility of materials which due orequirement ormutualabrading ab2it.y mustnotbetoo far apart inhardness.

The equipment orultrasonicmetal welding rangesfrom low power microbondersperatingetween 40and 60 kHzo machines of several ilowatt outputcapacity operating between 10 an d 20 kHz, for weldingof larger parts. t, should benoted hat, onhigh con-

Fig. 14. Ultrasonicallysolderedaluminum radiator ducts. No fluxwas used.

duct'ivitymaterialsultrasonic welding canbe over 20timesmore efficient compared to resistance welding.Thus a 5 k W ultrasonic welder may be equivalent to a100 kVA resistance welder. Automat ic uning and con-stan t amplitude control are a must on larger ultrasonicwelders.

Furtheracceptance of ultrasonicmetal welding d llargely epend on effective solutions to properointdesign and dissemination of this knowledge to potent ialusers. Toake fulldvant,age of ultrasonic weldingthepartsmustbe designed for the process. Improve-mentsn welding tip materials nd design are alsoprobable.D. oldering

Ultrasonic olderingcan tin without fluxes and im-proves wettability under most conditions. The process isfundament'ally similar t'o ultrasonic cleaning and has beentriedwith various degrees of success since the early1930's. Growing need for fluxless soldering of aluminumand a general striving for qual ity have given ultrasonicsoldering a new significance.

Applications of ultrasonic soldering [ ] include electricand electronic components where nickel, Kovar, and otherhard-to-tin metals are often used. Tinning of transformerleads, both copper and aluminum, is also effect'ive.


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66 IEEE TRANSACTIONS O N SONICS -4ND ULTRASONICS, M A R C H 197Continuoussoldering of printedcircuits C121 and con-tinuous wire tinning s another area of interest. Recentactivity in aluminum heat exchangers with the inherentproblem of tr apped flux has created an opportun ity forultrasonics in the air conditioning industry and inspireddevelopment of large ultrasonic soldering tanks (Figs. 13and 14).

Overall processing times with ultrasonic soldering canbe improvedecause pre-cleaning and post-cleaningoperations are usually eliminated. Also, the actual solder-ing is faster. Tinning is more uniform.

The principle of operation is simultaneous cleaning andtinning.avitationnmolten solder erodes surfaceoxides and exposes clean metal to solder. Design of ultra-sonic soldering quipment, however, ismorenvolveddue o highoperating emperat'ures.Presentultrasonicsoldering tanks operate at temperatures up to850F.

Both far field and near field soldering are done, rangingin power densities from a few watts to several hundredwat ts per square inch. Resistance to cavitat,ional erosionis an important consideration in the design of equipmentand is compounded by the requirement for metallurgicalcompat,ibility.

Future developments a re likely t o bring more efficientways of couplingultrasonicenergy t o the workpiece aswell asmprovementsnltrasonicankmaterials.Operating emperature imits will probably be raised,which may make volume treatment of high temperaturemetals practical.E. Machining

To da te, ultrasonic machining has proved most effec-tive on hard,rittlematerials, likelumina,therceramics, and glass. Two methods are currently n use.

The older method, knownas ultrasonic impact grinding,makesuse of abrasive lurry usuallyboron arbide,silicon carbide, or aluminum oxide) fed between the non-rotatingvibrating t oo l and he workpiece. Odd hree-dimensional shapes can be reproduced, wherehe resultingimpression is aegative o f the t,ool. Simultaneousmachining of clusters of holes is also possible. The methodis inherently slow and therefore has limited possibilitiesin th e industry.

In the more recent development, known as ultrasonicrotary machining, xial lt'rasonic ibration is super-imposedupon the rotary motion of the drill. Diamondimpregnated or plated core drills, water-cooled throughthe center, are used. The tools operate typically around5 000 rpm,and heoperation s essentially high speedabrasion (Fig. 1 5 ) .

Ultrasonic rotary machiningubst'antiallyncreasescutting rates, extends tool life, and due to the lower toolpressures used allows better dimensionalontrol andreduccs chipping. A simple explanation of the process iscontinuous cleaning of the tool by cavitation of thecoolant, urtheraidedbyultrasonic acceleration of thetool. T he tool loads less and cuts more efficiently.

Uses for ultrasonic rotary machining [13], C141 includemachining of precision ceramicomponents,rilling

Fig. 15. Ultrasonicotarymachine for drilling,milling, anthreading. Axial ultrasonicibration is added t o rotationmotion of th e drill.

small-diameter, eep,ntersecting holes i n quartzorlasers,machiningucleareact,ormatcrinls,lasmasprayed oatings and ferrite con1putc.r parts. Drillinmilling, andhreading rc possible. Tho tools rovarious shapes and sizes, from 0.02 to 1.5 inches in diameter. 20 kHz frequency is used (Figs. 16 and 17).

Drilling of boron-epoxy composites laminatcdwithsteel and t>itaniumsheet epresents an int,erestingcasandhas been esearched to someextent [15]. Convctional tools th at cut, boron fibres d o not work on metaand vice versa. Ultrasonic drilling promises a compromis

Ultrasonic rotary machining is a useful and, insomecases, indispensable process of somewhat 1imit)ed commercial potential due to the exotic nature of it s applictions.

111. SONICS AND LIQUIIIS:OTHER APPLICATIONSAn extensive ist o f applications is given in Tablc 1It is intcrosting to not'c that tl1c majority o f macrosonapplicationsnvolveiquids, nd wit,ll fen- cixcept,io

depend either on cavitation, or, like aerosol productioon surfacc nstability. It is also intercsting that to dano other liquid-related sonic appliration has had anthing vaguely resembling the commcwial succcss of ult rsonic cleaning.A . Extractim

?\lost popular here is thc us(: o f high intensity cavittion for biological cell disruption n esearch and lovolume processing.


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SHOH: INDUSTRIAL APPLICATIONS OF ULTRASOUND 07

Fig. 16 . Glass, aluminum oxide, anderrite arts rillednd Fig. 17 . Diamondmpregnated nd plated tools used in rotarymachined with ultrasound. Rotary method waa used. ultrasonic machining, Most areiquid ooledhrough the center.

TABLE I1MACROSONICPPLICATIONS-LIQUIDS

PROCESSPPLICATIONS ALSJANTAGESANKINGCLEANING

SOLDERING

EXTRACTION

HOMOGENIZING

ATOMIZATION

DRYING

DEGASSING

CHEMICAL PROCESSENHANCEMENT

PZIROUS MEDIA FLOWENHANCEMENTEROSION

CRYSTALLIZATION

TtD2FUG.L TPANSPORT

DEPOLYMERIZATION

Cleaning, degreasing, descalingindustrial parts. Cleaninghospital equipment.Fluxless aluminum soldering.Soldering and tinning electricand electronic components.Blological cell breakage forresearch. Antigen extraction.Extracting perfume, juices,plants.chemicals from flowers, fruits,

Emulsifying cosmetic toiletpreparations, essential andmineral oils. Waste treatment.Dye pigment andye dispersion.Insecticide preparation.Medical inhalatlon, nebulizing.

production.Fuel atomization, Metal powder

Drying heat sensitive powders,defoaming.food stuff, pharmaceuticals,

Beer and carbonated drinksolutlon agltatlon."fobbing". hotographic

Degassing molten metals andglass.Electroplatlng.

Aging alcoholic beverages.Filtering; Impregnation

Cavitation eroslon testlng.Deburring, stripplng.Metal treatment durrng astingand weldlng.Uistlllation and other chemicalprocesses.Extruding plastics. Plasticflbre manufacturing.

Saves time and manual labor.Cleans hard-to-reach areas.

Eliminates flux, pre- and post-cleaning. reduces rejects.

Simple to use. Reduces damageto contents.Speeds up extraction. Increasesyields. Allows lower temperatures.

Emulsifies without pre-mixing.Reduces or eliminates surfactants.

Fine, uniform dispersion. Noflocculation.

No gas used.Small particles, controlledlze.

More efficient burning.Small particles, controlled ize.

Lower temperatures. Preventsdamage to perishables.

Better control, safe for glasscontainers.

Reduces porosity.

Increases platlng rates. Denser,more uniform deposit.Speeds up process.

Better penetration.Increases flow rates.

Convenient to use.Saves labor.Refines grain, reduces stresses.

Speeds up heat exchange.

Lowers viscoslty.

A

B

B

B

BC

C

C

C

C

C

X

X

X

A - Established large-scale process C - Some industrial useB - Established small-scale process X - Experimental


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68 IEEE TRANSACTIOKS ON SONICS AND ULTRASONICS, MARCH 197Near field cavit'ation breaks down ell walls and releases

cell contents into the surrounding liquid. The method isused to extract active antigens for making vaccines andas a general tool for studying cell structure. Lltrasonicextraction is simple and, if cooling is used, causes minimaldegradation of contents.

The equipment is normally in the range of 100 t o 500watts,operatingaround 20 kHz.Highamplitudehornsare used, producing power densities in the order of 500watts per square inch. Batch and continuous processingare done.

Other extractionuses include extractionf perfume fromflowers, essential oils from hops, juices from fruits , andchemicalsrom plants [S],16]. The otential ereseems great,but' pplication progress, at east n heUnited States, has been slow. A review of high intensitmyliquid processing is needed n view of the powerful 10 kHzequipment and other equipment improvernents availabletoday.B . Atomization

Ultrasonic tomizers anproduce malldroplets ofpredictable size. Forgiven iquid,droplet size isfunction of atomizerfrequencyandgetssmalleras thefrequency is increased [4].

1 . Ultrasonic ebulizers for medicalnhalationhaveshown best commercial progress. Medical nebulizersoperate bet,ween 1 and 3 megahertz and produce dropletsbetween l and 5 microns. Mainadvantagesare smallparticle size, tight distr ibut,ion, and he absence of gas,which makes ultrasonic nebulizers suitable for anestheticsystems [17].2 . Fuelatomization by ult,rasound [ l71 hasbeer re-

searched to a considerable extent to improve combustionefficiency and reduce pollution. Several types of devices,both electronic andpneumatic, ren use, operatingbetween 20 and 300 kHz. Use n oil burners as well ascarburetorshas been onsidered bu t due to marginaleconomics has never caught on in a big way.

3. Dispersion of molten metals for production of powdersand metal spraying has been demonstrat)ed. Spraying ofmolten lead, tin, zinc, bismuth, aluminum, and cadmiumhas been reported, but cost justification is questionable

There is a at,ternohese pplications:Greatestsuccess has been chievedwhere th e requirement forquality supersedescost, and he hroughput needcd slow. As theproductgets heaper nd t.hP processingrates increase, ultrasonicatomizat,ionbecomes less de-sirable.

Some of t.his is likely t,o change.Fuel, for instance,costs more today, and ultrasonic atomizers can be builtfor less. 3hltenmeta l dispersion withts formidableequipment prob1c:nls may become practical as a result ofthe progress in ultrasonic soldering.

~ 1 7 1 ,W .

B. CrystallizationFiner grain has been prod~lctd n aluminum and other

nletals ynsonation uringhc solidification stage.

Degassing and emoval of residual tresseshave alsbeen reported.

In spite of a large volume of reference material on thisubject [19], there is no evidence of commercial mplementation.Theremaybe some installations neasternEurope [53.

The obvious difficulties here are the severe environmfor the ultrasonicequipmentand he equirement fotreating a large volume. These, again, may be helped bcurrent research in ultrasonic soldering.C . Emulsification

The main advantage of ultrasonic emulsification is the ability bo mix some immiscible liquids wit'hout addtives (surfactants). Recent publicity has called attentioto he emulsification of water in heating oil for bet'tfuel economy and less pollution [20]. Fuel saving seemuncertain, but here may besome substance to cleaneburning, and it is an interesting development to watch.D. eat Transfer [all

Cavitation-induced microst'irring can decrease he themal boundary layer and improve heat transfer in a vof systems.References dateback o heearly 1960and uses indistillationandother chemicalprocessinghave been suggested. Present concern with efficiency hmade the topiconce more popular.E. Flow Enhancement

Liquid flow rates hrough porousmediacan be icreased byultrasound. Uses in filtering [22], [a31 animpregnationaveeenuggested.heubjectintriguing because low amounts of vibratory power cabe effective.

IV . SONICSANDSOLIDS:OTHER APPLICATIONS

An ext'ensive list of applications is given in Table 11A . MetalForming

Over the years there has been a considerable interein his area, heightened by the controversies about thmechanism of the process.

The benefits of vibration-asxistcd formingypicallyinclude lower forming forces, larger percentage deformation without t,earing, and improvements in surface finisDue o highpower equirementshe successful woperformed to date has been imited to objectssmall size or cases where the area to be affected is small.1. Tube clra?uing withultrasound C241 has beenusedin manufact,uring or about, ten years and is mostffection thin wall tubing having an initia l diameter of abo4 inch or less. TJsually the plug is vibrated in the diretion of drawing. The advantages are faster drawing ratbetter size control, and ability to producedifficult shapesuch as rectangular ubing with sharp corners, or ubewithargeiameter-to-wall ratiosupo 500:1Aluminum, copper, iron,and nickel based alloy, havbeen drawn.


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SHOE: INDUSTRIALAPPLICATIONS OF ULTRASOUND 69TABLE 111MACROSONICP P L I C A T I O N S ~ O L I D S

PROCESSWELDING

MACHINING

FORMING

CU l T I N G

FATIGUING

CLEAVAGE

FRICTIONWDUCTION

DENSIFICATION

APPLICATIONSPLASTICS - Welding rigid h e m -plastics. Seam welding film andStaklng.fabric. Metal-in-plastic insertlon.

METALS - Mlcrobonding. Lap weldinghigh electrical conductivity and dis-similar metals. Seam welding sheet.

DENTAL - Prophylaxis teeth treatment.HARD, BRITTLE MATERIALS - Vlbratlon-asslsted rotary machining.Impact grinding using abrasive slurry.

METALS - Vlbration-assisted drilling,tapping, turning.METALS - Drawing thln all tubing oflarge diameter toall ratios.Drawing small diameter wire fromdifficult-to-form metals.Vlbration-assisted cutting ffibrous and spongy materials.Destructive testing and qualltycontrol.Cleaving crystals and laminatedobjects.Vibrating sieves and hoppers.TorquingCompactrng powders, sintering.

ADVANTAGESANKINGFast, clean, economical, goodweld integrity. Welds in-accessible areas.

Low heat, no pre-cleaning.Insensitive to electricalresistivity and heat capacrtymismatch.~ a s y o use, less discomfortcompared to hand scrubbing.

better dimensional control.Faster rates, longer tool life.

Makes multiple holeatterns,odd, three-dimenslonal shapes.Faster rates, longer tool l f e .better finish.

drawing difficult shapes.Higher drawlnq rates. Allows

better surface.Faster drawlng, less breakage,

acceleration, or melting.Better cutting ue to blade

Saves testing time. Findshidden flaws.High Impact, high rate.

Speeds up material flow.Tighter joints

molds. Increases density.Improves uniformity in complex

A

B

B

B

C

C

C

C

C

CXX

A - Established large scale process C - Some industrial useB - Established small scale process X - Experimental

2. Ultrasonic wire drawing allows faster drawing rates,and educes surface mperfections. Many investigationswere reported in the arly 1 9 6 0 ~ ~ith particular mentionof advantages for drawing small diameter ire from hard-to-form materials like tungsten and molybdenum. Therehas been little commercial act ivity. Improved equipmentis now available and may rejuvenate the interest in theprocess [%I.

3. Ultrasonic riveting hasbeen of interest oaircraftmanufacturers. Experiments on aluminum and itaniumrivets showed a possibility of a substantial reduction informing orce,and nsome cases a largerdeformationwithout cracking. Another set of experiments concernedaluminum leak-tight iveting. The important question hereis the effect of vibratory forming on fatigue life of therivet and is largely unanswered.

As asobering houghton sonic metal orming, t isinteresting omentionanexperimenton itaniumandseveralgrades of stainless teel,designed to show theeffect of sonics on volume deformation obscuredn drawingoperations by high surface friction.

Cylindrical slugs& of an inch n diameter were flattenedwith and without sound. 400-600% reductions in staticforce were possible for equivalent deformation, but sonicpower densities were over 100000 watts per square inch

[ a s ] . To duplicate the effect on a 3 inch diameter slug,close to one million watts of sonic power would be needed.The use of macrosound ordeformation of a large

volume of metalmaynotbe ustaround he corner.But small-scaleapplications are practical. Simultaneousmetal welding and crimping, for instance, is being done.B . Metal Drilling

Rotary ultrasonicrilling triedwithonventionaltwist drills produced interesting but uneven results. Axialultrasonic vibration was added to rotary motion of thedrill.

Faster driiling ratesnd longer drill life wereobtained on itanium using small-diameter cobalt drills,but nosignificant mprovement was noticedonseveralother metals [ 2 6 ] . A number of portable drills are in usefor titanium drilling in heaircraft ndustry. A specialshort ultrasonic drill adapter was developed t o make theprocess practical (Fig. 18).C . Dental Treatment

An interesting success story, not quite fitting in to theindustrial world,concernsanultrasonicmachine ooldesigned or use inprophylaxis reat8ment, periodontia,and other areas of operative dent istry (Fig. 19).


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70 IEEE TRANSACTIONS ON SONICS AND ULTRASONICS, M d R C H 19

Fig. 18. PortableQuackenbush drill, used n aircraftmanufactur- Fig. 19.Ultrasonicdentalequipment fordescaling teeth prophying, equipped with ultrasonic drill adapter. Faster drilling rates laxis), and othersesnperativeentistry.Courtesyand better drill life were demonstrated on titanium. Cavi tron Ultrasonics, Inc.).

This equipment is becoming popular and is apparent,lyliked by dentists and patients, who prefer it over the oldmanual scrubbing. Descaling of teeth is accomplished bya linear, or elliptical, reciprocating scrubbing a t 25 kHz,aided by cavitation of the water spray.A variety of inter-changeable nserts re vailable for various crubbingoperations.B. Crystal Cleavage C271

Crystal cleavage by ultrasound proved to be a valuablemethod of maintaining particle balance in a continuouschemicalprocessing installation.Ultrasonicallydisinte-grated crystals are split along cleavage planes in contrastto random breakage produced by mechanical means. Whileultrasonic disintegration takes place in a super-saturatedliquid,studiesshowed th at cleavage esults rom directcollision of particles with ultrasonic horn and with oneanother [28]. It is likely th at he principle would alsowork in a gas medium.

V. THE FUTUREUnheralded by scientific publications, ultrasonic plastic

welding has become a large-scale industrial process whilethe considerablyesearchedmetallurgical andmetalworking areas have resulted n relatively ittle. Equallydisappointinghavebeencatalyticuses of ultrasoundinchemistry.Theattentionpaid oa givenultrasonicarea is largely influenced by the topic of the day, as evi-dencedby current nkrest nultrasonic fuel treatment[ Z O ] , waste reatment [ a s ] , oilwell rejuvenation, etc.,and is not always related to the true worthf the process.Thus taught by experience, the author will refrain fromany specific predictions save for pointing out two generalfactors. The cost of a n acoustic watt has been decliningan d following t8he general technologicalrend will continueto do so in the future. This will make ultrasonic powermore competitive with conventional processes. The secondfactor is thatmore ultrasonic equipment is now in use andmore people are working with it. This increased exposurewill undoubtedly lead tonew uses.

Ra ther than compiling an all-inclusive list of ultrasonicapplications, the author has tried to show a cross section

of types of things power ultrasound can do that would brepresentative of the present state of the a rt an d inspifurther thought on the subject.

ACKNOWLEDGMENTSTheuthor wishes tohankCavitronUltrasonics

CorporationandFord l\/lot,or Company or he use photographs and B. L. Mims for reading the manuscrip

The llustrations are courtesy of Branson UltrasonicCorporation unless otherwise noted.

REFERENCES[l]Hueter, T. F.,andR. H. Bolt,Sonics, p. 41,Wiley, NeYork (1955).[2] Noltingk, B . E., and E. A. Neppiras,Proc.Phys. Soc., 63[3] Elder, Kolb and Nyborg, Phys. Rev., 93, 364(A) (1954).[4] Doyle, A. W., B. V. Mokler, and R. R. Perron, AP I Resear[5] Neppiras, E. A. , Macrosonicsn indu stry , Ultrasonic

No. 9, 674-685 (1950).Conf. Paper CP62-1$1962).Januarv (1972).[6] Guide tb Ultrasonic Welding of Plastics, Appliance Manu-facturer, April (1974).[7] Sherry, J. R., Assembling Plastic Parts, Automation,November (1973).[8] Creegan,H. K., TheThermal JoiningMachine,ModernTextiles, Jun e (1073).[9] SonicStitching inColor,Apparel Manufacturer,August(1973).[lo] Hulst, A. P., Ultrasonic welding of meta ls,Ultrasonics,November (1972).[l11 LeGrand,Rupert,Ultrasonicsgets 3 new jobs, AmericMachinist, Februarz 8, 1971.[l21 Gootbier, E. A., Ultrasonics in massoldering,WesternElectric Engineer, January 1969, Vol. XI II , No. 1.[l31 Dallas,Daniel B. , The new look of ultrasonicmachiningManufacturing Engineering and Management, February (19[l41 Tiny holes with a tliameter/length ratio of 1:300 successfudrilled in glas,, Industrial Diamond Review, March (1973)

[l51 Grauer, W . , UltrasonicMachining,GrummanAerospaceCorp. 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., Industri al and medical usof ultrasonicatomizers,Ultrasonics, Vol. 10, 127-133, M(1972).[l81 Pohlman, R., Conf. Proc. Ultrasonics Int. (1973) sponsoredJ. 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 UltrasonlcTech[22] Semmelink, A., Ultrasonicallynhancediquidiltering,nology, Vol. 2, 3?;-409.

[23] Ibid., Use of ultrasound t o increase filtration rate, FairbanConf. Proc. Ultrasonics Int. (1967) sponsored by J. Ultrasoni[24] Jones, J. B., Ultrasonic metal deformation processes,ProcH. V., p. 11.


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IEEE TRANSACTIONS ox SONICS AN D ULTRASONICS, VOL. su-22, NO. 2, MARCH 1975 71Int. Conf. Manufacturing Technology, September (1967), 1972, Shoh, A.Am. Soc. Tool and Mfg.ngineers. [27] Midler, M.,nitedtatesatentumber 3,510,266 (May 6,[25] Langenecker, B ., Illiewich, S., and Vodep, O . , Basicnd 1970).ap lied research on metal deformation n macrosonic fields at (281 Klink A., Midler M ., and Allegretti J. , A Stu dy of Crysta lP\PL-Austria. Conf. Proc. Ultrasonics Int. (1973) sDonsored Cleavage bv SonifierAction,ChemicalEngineeringProgressby J. Ultrasonics.Meetingcous.OC.m.,u5al0, New York, 18-21 April pp. 74-75.

. .~ SympoiiumSeries, No. 109, 1971, Vol. 67. .~ .(261 New Developments In Metal Working Proc mes, paper, 83rd (291 The Silent Treatment, Time Magazine, February 11, 1974,

Industrial Applications of Ultrasound- A ReviewII. Measurements, Tests, and Process Control

Using Low-Intensity UltrasoundLAWRENCE C. LYNNWORTH

Abstract-Theollowingpplications ar e reviewed: ltrasonicmeasureme nt of flow, temperature, ensity , porosity, p ressure,viscosity and therransport roperties,evel, position, phase,thickness,composition,anisotropy and exture , grain size, stressandstrain,elasticproperties,bubble, particle and eakdetection,nondestructive esting, acoustic emission, maging and holography,and combinations of these. Principles, echniques, equipment, an dapplication data are summarized orhese reas.Most of th emeas urem ents utilize approaches designed to respond primarily tosound speed, but some depend on attenuation effects. Most equip-ment in use involves intrusive probes, but noninvasive, externally-mounted ransducersarebeing promoted in severalareas. Bothpulseandresonance echniques are widelyused.Limitations dueto the influence of unwanted variables are identified in some cases.A bibliography and ist of vendors provide ources for furtherinformation.

T INTRODUCTIONHE M A I X purpose of th is review is to identify th ebreadth,depth,pract ,icality, nd imitations of in-dustrial pplications of small-signal ultrasound.Addi-tionally, we will atte mpt to identify patterns of emergingultrasonic technology.

In general, the scope of this review will be limitedto ndustr ial pplica tions wherein the transductionorpropagation of low-intensityltrasoundesponds tot,heproperties,state,orquali ty of the medium or prrtin question. By restrictinghe scope to indust.ria1applications we choose to omit umerousnterestingand mportant applications n research, and in medical,dental,nd biological areas.Low-intensityvoidsmacrosonic and nonlinear acoustic areas such as ultrasonic

Manuscript received November 8, 1974.The author is with Panametrics, Ualtham, MW. 02154.

cleaning,machining, wire drawing, welding, atomizingcavitating, emulsifying, influencing of chemical reactionsshock-wave measurements, and therapy. By limiting thescope to cases where the objective is measuring uItrasoundtransduction or propagation to indicate the value of somevariable parameter, we intend to detour around devicessuch as quar tz clocks, ultrasonic garage door openers, TVchannel selectors, delay lines, filters, and signal processorsdespite the obvious industrial significance of such devices.I n view of all these omissions, t he reader may rightfullyask, Whats left? For the answer see Table I.This review generally makes no attempt to identify heearliest demonstration of the entries n Table I, nor tocompare with competing technologies. Readers interestedin the origins of acoustical measurements of sound speed,attenuation, polarization,or related quantities are eferredelsewhere.

Standard commercial equipment,particularized or aspecific application, is available for almost every iten1 onthe list. Additionally, since virtually any ultrasonic meas-urement can be analyzed in terms of observations relatedto transit t,ime or wave amplitude, general-purpose elec-tronic measuringequipment uch as digital processingoscilloscopes, computingcounters, ime ntervalometers,peakdetectors, etc.,may also be used to perform theindustrialmeasurement,s or tests to be discussed below.

The items in Table could be categorized into two majorgroups in terms of instrument response being associatedprimarilywithsoundspeed c or attenuation coefficient

uelopment (1973); Physical Acoustics (1973), Dowden,HutchinsonR. B. Lindsay,ed., Acoustics-lfislorical and Philosophicul De-and Ross Inc.,Stroudsberg, Pa. See also: D. M. Considine,ed.,Encyclopedia of Znstrumentation and Control, McGraw-Hill, NewYork (1971).

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