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ORIGINAL ARTICLEState-of-the-art on vibratory finishing in the aviation industry:an industrial and academic perspectiveR. Mediratta1&K. Ahluwalia1&S. H. Yeo2Received: 25 May 2015 /Accepted: 4 October 2015# Springer-Verlag London 2015Abstract Vibratoryfinishingisaversatileprocessthatisusedin many industries globally for radiusing, brightening,deburring, fine finishing, cleaning, burnishing, and descalingof components. This state-of-the-art paper will discuss howvibratory finishing has evolved into what it is today and theadvancements in technology. The development of massfinishing, the importance of vibratory finishing in aviationindustry, the parameters involved in this process, and the pat-ent landscape of the advancements in vibratory finishing willbe elucidated. More importantly, the paper will dwell intoattempts made to understand the science behind this arcaneprocess. Empirical investigations, model developments, bulkand granular impact velocity studies, vibrostrengthening, andAlmen strip characterization are the research efforts that willbe discussed in particular. This work has identified gaps in thevibratory finishing process, some of them being media flowmeasurement and the need for a monitoring system to deter-mine the frequency losses from motor vibrations to the mediavibrations. Methods for calculating the frequency and ampli-tude of machine vibrations, the impact velocity of media, andthe force of media striking the workpiece are still under re-search. Literature points out that more work can be done interms of the quantification of process parameters, the relation-ship between them, and the effect they have on the surfacefinish. The industry is on the lookout for shorter cycle timeswithimprovedsurfacefinishingquality,andthusvarioustech-nological advancements in vibratory finishing, namely dragandspindlefinishing,havecomeintoexistence.Totheknowl-edge of the authors, there has been no comprehensive reviewworkdoneonvibratory finishing.Thispaperattemptstoservethe purpose of being a one-stop academic and industrial ref-erence for scientific communities and professionals workingin this field. The paper further endeavors to serve as a meansto initiate the development of a next generation vibratoryfinishing system with real-time monitoring and surface finishmeasurements.Keywords Vibratoryfinishing.Shortcycletime.Eccentricweights.Mediamotion.Modeldevelopment.Fixturing1 IntroductionVibratory finishing has become increasingly significantover the last decades in the value chain of product de-velopment in a variety of industries especially aviation.This is due to enhanced automation of the process aswell as due to the many different process engineeringapplications of modern vibratory finishing technology.Yabuki et al. adequately summed up the versatility ofthe process in one line: it can be aggressive enough forremoval of burrs in steel parts as well as sufficientlydelicate to polish plastics 1.Vibratoryfinishingisaprocessunderthebroadumbrellaofmass finishing. Mass finishing consists of abrasive industrialprocesses by which a substantial quantity of componentsmadefrommetal orother materials can beeconomically proc-essed in bulk to achieve one or several of a variety of surfaceeffects such as deburring, edge radiusing, brightening,* S. H. Yeomshyeo.sg1Rolls-RoyceNTU Corporate Lab, c/o School of Mechanical &Aerospace Engineering, Nanyang Technological University, 50Nanyang Avenue, Singapore 639798, Singapore2School of Mechanical and Aerospace Engineering, NanyangTechnological University, 50 Nanyang Avenue, Singapore 639798,SingaporeInt J Adv Manuf TechnolDOI 10.1007/s00170-015-7942-0removing surface roughness, and stress relieving amongothers 2. With such a wide variety of applications, the pro-cesses are used extensively by the manufacturing industries.The inherent economy, flexibility, and adaptability of massfinishing systems have made them unique methods for im-provement of a vast variety of industrial parts. The conse-quences of not performing mass finishing processes can bequite severe: parts will perform poorly due to decreased loadcapacity, poor corrosion, and fatigue resistance to name a few.Thispapergivesanoverviewofthemassfinishingprocess-es,howmassfinishinghasevolvedovertheyears,andfocusesmainlyonthe machinesand machine characteristics thatbringabout the surface finish particularly for the vibratory finishingprocess. The key process variables for vibratory finishing, itsimportance in the aviation industry, and technological ad-vancements particularly to do with lowering the long cycletimes in such a process and the efforts that have been madeso far to understand this empirical process will also bediscussed briefly.2 Mass finishing and its historical developmentMass finishing is a general term for abrasive industrial pro-cesses, with loose particles known as media, together withcompound, all within a container in which components aresubmerged. Barrel finishing, vibratory finishing, centrifugalfinishing,anddragfinishingaresuchprocessesincludedwith-in broad purview of mass finishing. Energy is imparted to thisabrasive media by a variety of vibratory-cyclical motions tocause it to interact with part surfaces. To date, vibratoryfinishing is the most widely known mass finishing process.Mass finishing processes established their place in the in-dustry in the 1900s. Barrel finishing is said to be the originalmass finishing method. The first demonstration of massfinishing process was tumbling barrels with natural stonesused by ancient Chinese and Egyptians to polish theirweapons and jewelry 3. Mass finishing processes haveevolved in technology and innovation. This has resulted inmany variantsbarrel finishing, vibratory finishing, centrifu-gal finishing, and drag finishing. Although the key processvariables (KPVs) of any mass finishing setup vary from pro-cess to process, they can be classified under four broad head-ings as shown in Fig. 1. Since these four KPVsmedia, com-pound, machine, and workpieceare highly interdependent,theycanbevisualizedasatetrahedroncalledthe“Tetrahedronof Interdependence” 4.The functions of the various process parameters are as fol-lows 4, 5:1.Media: Media is the main element responsible forimparting the necessary surface finish to the components.It can be abrasive as well non-abrasive.2.Compound: Compound is the water-based lubricant andcoolant in the process. It has a lot of usesdrainingabraded material, cleaning the surface to be finished,and controlling the pH of the process among others.3.Machine type: Mass finishing machines have evolvedsince the inception of the process. From barrels to dragfinishers, there has been a continuous evolution of tech-nology and efficiency. Different machines differ in theirfinishing actions and the media motion inside themachine.4.Workpiece: Workpiece is the most important of the pro-cess variables. The workpiece dictates all of the aboveparameters.Forexample,thesizeandmaterialofthecom-ponents to be processed dictate the type of the machineand media. A large component undergoing polishing willhave to be finished in a big machine with a suitablepolishing or non-abrasive media and compound.The factors inherent to the mass finishing processmedia,compound, and machine type have witnessed many improve-ments since the industrial deployment of mass finishing. Themost significant have been in terms of the machine type. Thisevolution of technology is shown in Fig. 2.3 Vibratory finishing in the aviation industryDavidson 7 duly summarized why edge and surface condi-tioning is critical: “Sometimes, to fully understand the signif-icance of edge and surface quality issues, it is important tounderstandthe magnitudeoftheconsequenceswhenedgeandsurface condition receive insufficient attention.” The end-products of the aviation industry operate with human life ona daily basis and thus there are stringent requirements on edgeand surface conditions when it comes to the processes in-volved in the industry.The aerospace industry demands very fine surface finishrequirements for parts such as fan and turbine blades. If thefan blades have smooth surfaces, the risk of deposits stickingto the airfoil surface is reduced. The smoother the airfoil sur-faces, the lower the engine operating temperatures. This allowsa greater margin to be achieved between the actual exhaust gasMass finishing KPVs Workpiece Machine type Compound Media Outcome (finished components) Fig. 1 Mass finishing KPVsInt J Adv Manuf Technoltemperature and the engine “red line”maximum exhaust gastemperature (MEGT) as shown in Fig. 3. This temperaturereduction improves the time between overhaul for aircraft en-ginesthey can remain in service longer before an overhaul isneeded 8. Improved surface finishing of turbine blades alsoenhancestheaccelerationandcompressionoftheairmassflowinturbines,resultinginlowerfuelconsumptionaninvaluabletechnical benefit with rising costs of fuels nowadays 9. Low-ering surface roughness also helps in increasing fatigue life 7.This is important as the airplane components are subject tovarying amount of stresses during operation.The stress concentration in components like fan blades orturbinebladesinanaircraftengineisincreasedbysharpcornersas well as burrs. Deburring and edge radiusing reduces stressconcentration, which further increases fracture resistance andfatigue life. It has been observed that most fatigue cracks areinitiated at the surface of a part rather than internally. Hence,surface conditioning becomes critical for the long and safe lifeofapart,especiallyintheaerospaceindustry.Duringassembly,roughsurfacesandsharpexterioredgescanalsodamagecoatedor painted surfaces. Sharp outside corners on a structure act aselectrical charge accumulators and can be a static dischargehazard. During flight operation, sharp edges may have an im-balance of electric charges and can become spark over pointswhenever voltage is applied. This potential difference can becaused by static charge and/or lightning strikes 7.Vibrating barrels produce better surface finish High speed rotating disc produces faster finishing action Fixturing the workpiece improves process cycle times Spindle/drag finishingVibratory finishingBarrel finishingCentrifugal disk finishingFig. 2 Evolution of mass finishing technology 5, 6Int J Adv Manuf TechnolVibratory finishing is one such widely used process whichcan result in attaining the surface finish requirements specifiedby the aviation authorities as well as conditioning the parts tocounter the potential disasters caused by the phenomena de-scribedabove.Theprocessisflexibleandcosteffectiveintermsofnumerouspartswithcomplexgeometry(whichis usuallythecase with aerospace parts) can be finished simultaneously withminimal effort in process planning. Vibratory finishing helpsdevelop beneficial compressive stresses as well provide a stressequilibrium enhancement throughout the part, as all part fea-tures are processed identically. These compressive stresses willcounteract the tensile stress caused by a crack and help to con-tain its propagation. Many machining and grinding processestend to develop residual tensile stresses in the surface area ofparts. These residual tensile stresses make parts susceptible topremature fracture and failure when repeatedly stressed. Vibra-tory finishing counters this by imparting residual compressivestresses 7. However, vibratory finishing requires long cycletimes associated with such a process. The lack of science andunderstanding of the mechanism behind the vibratory finishingprocess is a barrier to optimizing the process to its full potential.In component applications, a typical fan blade in the aero-space industry has a length of 1,200 mm and a width of500 mm. A tub vibrator is used to finish these blades. Smallerand rotatory aerospace components such as turbine blades,blisks, and compressor discs are finished in a vibratory bowl.During the finishing process, fixtures are used to mount thesecomponents to prevent any damage from nicking or other im-pingements on delicate edges 10. The role of fixturing will beelaborated further in Sections 4.2 and 6.4. The airplanes struc-tural fuselage components and wing spars undergo deburringand radiusing in bigger tub vibrators. Parts that are deburredand have smooth radii in contrast to sharp edges have higherresistance to fatigue crack initiation and propagation. Paint ad-hesion on part edges is improved as well, which is useful fordownstream manufacturing processes 8, 10.4 Vibratory finishing KPVsVibratoryfinishingisacomplexprocesswhereeachandeveryoperating parameter plays a crucial role in bringing out thedesired surface finish. Vibratory finishing machines come intwo major configurationsthe bowl and the trough. Thesetwo configurations address the variations in the size and vol-ume of components to be finishedfrom huge componentslike fan blades to small components like turbine blades. TheKPVs are the same irrespective of the machine. Each keyprocess variable is interdependent and one cannot be ignoredover the rest in bringing about the required surface finish. Asmentioned in Section 1, the Tetrahedron of Interdependencewill always be intertwined for any mass finishing process toobtain the finished product.Dependingonthetypeofcomponent,itsdesiredoutput,andpotential application, the KPVs can be ranked sequentially.Though frequency of the vibratory motor is the most importantparameter while selection of media is the next as the frequencyofvibrationsfromthemotoraretransmittedtothemediawhichprovide the main finishing action to the component, other as-pects such as the right amount of dosing of the compound forlubrication and cleaning apart from other machine parametersare also vital. These parameters are listed in Fig. 4.The literature review on the key aspects of the machinecharacteristics is summarized in Fig. 5. The motor and theeccentric weights collectively are referred to as the unbal-anced mass drive system and is the core of the vibratoryfinishing process. Sections 4.1 and 4.2 will elaborate moreon the unbalanced drive system and fixturing.4.1 Motor and eccentric weightsAt the heart of the vibratory finishing process is a motor witheccentric weights, hence the name “unbalanced mass drivesystem”. It is attached to the bowl or the tub which is fixedto the ground by means of springs. Eccentric weights are at-tached to the ends of the motor shaft which causes wobblingaction when it rotates, which in turn vibrates the assembly.The frequency is usually controlled by specifying the speedof the motor. The amplitude and direction of rotation arechanged by modifying the eccentric weights attached to themotor. These are referred to as the input parameters of theprocess in addition to the type of compound and media. Typ-ical ranges for frequency and amplitude are 2060 Hz and 210 mm, respectively 5.High-speed motors are also being implemented to reducecycle times 11, 12. The speed of the motor designed in 11was up to 40 Hz as compared to between 20 to 25 Hz operatingin similar machines and the time taken to reach roughness sat-uration reduced by approximately 40 %. In both the references11,12,thereisaconsensusonthefasteranduniformrotationalmovement of the media in a high-speed vibratory finishingMEGTExhaust gas temperature Smooth airfoils Rougher airfoils Fig. 3 The effect of surface finish on aircraft engine exhaust gastemperaturesInt J Adv Manuf TechnolVibratory finishing processCompoundCompositionGrit sizeGrit materialEmulsifying agentMediaShapeSizeMaterialCoarseness of the gritCompositionWeightMachineFrequencyAmplitudeBasic designShapeCapacityWork pieceMaterialInitial roughnessSurface areaToughnessGeometryLocationSizeWeightLoadingAmount of mediaAmount of abrasivesAmount of waterVolume of partsWeight of partsFig. 4 Vibratory finishing KPVs3Machine characteristicsMotorPositionSpecification (frequency)Eccentric weightsPositionMass (amplitude)FixturesStatic/ dynamicShapeIntegrated/ separateVibratory vesselCapacityShapeBowlTroughOthersUnbalanced mass drive system Fig. 5 Vibratory finishingmachine characteristicsInt J Adv Manuf Technolmachine in comparison to a conventional one. However, therehave been contrasting observations made pertaining to mediasamplitude of vibrations. In the machine designed in reference11,theamplitudeofmediavibrationsreducesathigherspeedsand the media maintains a much more consistent contact timewith the component. These result in lower surface impinge-ments and a more homogeneous surface finish on the entiresurface of the components in a shorter cycle time. Rawlinson12attributesfastercycletimestouniformandincreasedmediaspeed and a precise control of high amplitude of vibrations.Further research can be conducted to ascertain which level ofamplitudelow or highis responsible for faster finishing athigh frequency of vibrations. Changes in eccentric weights toalter the amplitude will play a crucial role in understanding therole of high/low amplitudes in a high-frequency machine.For a vibratory bowl, the motion of the workload in themachine is considered as helical. There are two types of mo-tions“roll”motioninwhichmediarisesattheouterdiameterwall and falls down toward the center hub and the “feed”motion in which the workload travels clockwise or counter-clockwise lapping path around the bowl channel as illustratedin Fig. 6 by Domblesky et al. 13. Roll motion is determinedby the mass of the lower eccentric weight, whereas feed mo-tion is determined by the mass of the upper eccentric weight.By convention, the bottom eccentric weight always leads thetop weight in the direction of rotation of the drive shaft,whereas the media always rotates in the direction opposite tothe drive shaft rotation. The angle between the two eccentricweights, known as the lead angle, controls both roll and feedmotions 5. This concept is well illustrated by Nebiolo 14and is shown in Fig. 7.Foravibratorytrough,themethodofinducingvibrationsisthe same as in vibratory bowls. The motion is simplerit isrotatory as shown in a cross section of a trough in Fig. 8 3.4.2 Fixturesan upcoming trendThere has been limited research work in the literature withrespect to immobilization of the workpieces by deployingfixtures which offers another research approach. 15, 16.For high-value components such as turbine blades, it be-comes important to immobilize the workpieces to preventthem from colliding into one another. The other advantagesof fixturing include faster cycle times, finer surface finishes,and prevention of damage to the bowl liner from the sharpedges of parts 3.Fixturing of components is rather a relatively new conceptinthefieldofvibratoryfinishing,wherethecomponentisheldby suitable means and immersed into the media container.This type of fixtured vibratory finishing is also referred to asvibrostrengthening 16. These fixtures can be static (fixed onthe vibratory setup) or dynamic (freely floating). Both theconfigurations are known to speed up the finishing processproducing desired Ravalues in lesser cycle times. This is be-cause the force flow of media against the components is saidtoincreaseconsiderably and there isan increase in the relativevelocities between the media and the workpiece 1517.In a way, drag finishing, spindle finishing, and streamfinishing are advanced forms of fixtured finishing. In boththese methods, the parts that are to be finished are clampedby suitable means. These methods are known to reduce cycletimes by almost 33 % compared to conventional vibratoryfinishing 5.5 Patent analysisA thorough patent search related to vibratory finishing wasalso carried out in this work in order to determine the innova-tions that have come about pertaining to the various KPVs ofvibratory finishing. A general trend that was observed wasthat most of the patents dealt with improving the vibratoryfinishing process in terms of improving cycle times and pro-ducing quality surface finish.Going along the lines of high-speed vibratory motors re-ducing cycle times discussed in Section 4.1, Hammond Ma-chinery18patentedahigh-speedmassfinishingsystemwithspecial arrangement of the eccentric weights and increasedhorse power of the motor causing the spinning shaft to rotateat 2,000 rpm or more 11. Innovative fixturing methods havegottheirfairshareofpatentsaswell.VanKleefandSothornintheir patent 19 refer to a spindle fixturing method along withmixing of media through means of a plate which can be liftedup or down vertically through the abrasive media. WaltherTrowals patent in 2012 20 is to do with electromagneticmeans of fixturing ferromagnetic workpieces. A patent onmagnetic fixture by REM technologies 21 and vibratory fix-ture by MERMARK INC. 22 are other patents to do withFig. 6 Roll and feed motions in a vibratory bowl 13Int J Adv Manuf Technolfixturing. Rolls-Royce Deutschlands patent deals withstrengthening elements (media) and the shape for these ele-ments. REM technologies have also patented the chemicallyaccelerated finishing process 23. Apart from this, patentspertainingtotheuseofdividersandmeansforseparatingpartsfrom media for faster process times were also seen.Based on the patent search that was conducted, the authorscame up with the patent map as shown in Fig. 9. The patentmap clearly establishes that most of the patents pertain to theunbalanced mass drive system and special means of fixturingthe workpieces in order to reduce cycle times. Patents relatedto other operating parameters such as media, compound, andseparation means of media from the components were alsoseen in the patent search conducted iterating the fact that vi-bratory finishing is a process which involves multiple param-eters and one parameter cannot be ignored over the other inorder to bring about the optimal surface finish.6 Research efforts in vibratory finishingTodate,vibratoryfinishinginvestigationsarelargelybasedontrial and error in order to determine the optimal parameters tobringaboutthedesiredsurfacefinishofacomponent3,9,13,2428. The mechanism behind vibratory finishing still re-mains unclear in spite of various studies that have beenconducted.Themainresearchareasareshown inFig.10.Thissection discusses the main findings from these research stud-ies briefly. These can be applied bypersonnel operating vibra-tory finishing machines such as in the aviation industry andscientists working on the process in order to better understandand optimize their processes and experiments, respectively.6.1 Empirical investigationsDoody 29 mentioned in his research on microprocessor-control techniques for vibratory finishing that the characteris-tics of vibratory energy transferred to the processing mediadepends on: rotation speed of the motor shaft, relative posi-tions of the eccentric masses, total eccentric mass fitted to theshaft, and the radial distance between the centers of top andbottom masses. This can be related to the discussion in Sec-tion 4.1 on motors and eccentric weights. The change invibratory characteristics can be observed in a vibratoryfinishing machine by simply increasing the speed of the mo-tor or modifying the configuration of eccentric weights. In-creasing the frequency of vibrations of the machine can beaccomplished by increasing the motor speed on the controlpanel of the vibratory machine. The amplitude of vibrationscan be altered by changing the weights/orientation of theweights on the vibratory motor. Most conventional vibratorymachines come with an amplitude label attached on themfrom which the amplitude of vibrations can be determined.This method is not a very robust one and is based on visualinspection of the label. The amplitude resolution of 0.5 mm isused within an operating window of 2 to 8 mm. A morecomprehensive displacement sensor or amplitude meter needsto be devised to increase the reliability of amplitude measure-ments. Studies on the effect of media amplitude on vibratoryfinishing are limited. Precise monitoring of amplitude is re-quired to investigate the effect of different levels of amplitudeon the finishing process.Fig. 7 Eccentric weights in avibratory bowl 14Motion of mediaFig. 8 Media motion in a cross section of a vibratory troughInt J Adv Manuf TechnolWang et al. 25 devised a special load cell to measurenormal contact forces between the media and the workpiecein a vibratory bowl finisher. Fourier transform offorce signalsexhibited that most of the energy occurred at the same oper-ating frequency of the finisher. This means that most of theforce transferred from media to the component occurred at themachines operating frequency. Comparable results were ob-tained when the sensor was placed facing forward as well asbackward in the workpiece spiraling around the bowl. It wasconcluded that impact wear conditions were relatively con-stant against all of the workpiece surfaces. Fixed workpiecetrials were also carried out and it was observed that contactforces were greater in this configuration as compared to afreely moving workpiece in the media. This goes in tandemwith the concept of fixturing as discussed in Section 4.2.Fixturing has thus become increasingly emphasized in vibra-tory finishing as cycle times are considerably reduced. Anincreasing trend of average impact forces and the averageimpulse with increasing media size was observed for dry con-ditions, but not significantly for wet conditions. Wang et al.also observed that as the amount of lubrication increases fromdrytowater-wettodetergent-wet,boththeabsoluteworkpiecespeed and the speed of the media relative to the workpiecedecreases,and hence,concludedthatlubricationconditionhasa greater relative effect on the speed of the media than that ofthe workpiece. The hardness and roughness changes weremostly influenced by the degree of lubrication, the media sizeand its roughness. This is because the plastic deformation perimpact is affected by the interaction between the media andthe workpiece 25. Parameters such as lubrication (type andquantity) through a suitable compound and media propertiescannotbeignoredtobring aboutthe requiredsurface finishoncomponents, thereby reinforcing the Tetrahedron ofInterdependence.Yabuki et al. 1 devised a new force sensor to measurenormal and tangential contact forces of media in vibratorybowl. They also videotaped media contact modes. The sche-matics of the three contact modesfree impact, rolling ofindividual media, and adjacent media rolling over a stationarypiece of mediaare shown in Fig. 11. Scanning electron mi-crographs and force sensor measurements showed that a freeimpact (Fig. 11a) produced a relatively small crater and forcesignal; rolling of individual media (Fig. 11b) produced a trackof small craters and a force signal burst with multiple distinctpeaks separated by complete unloading and adjacent mediarolling over a stationary media (Fig. 11c) produced the largestsingle crater and a force burst with a higher average contactforce and incomplete unloading 1. A key finding is that theFig. 9 Patent mapVibratory finishing research areasEmpirical investigationsModel developmentsBulk and granular impact velocitiesVibrostrengtheningAlmen strip characterizationFig. 10 Vibratory finishing research areasInt J Adv Manuf Technolcomponent shouldbemounted in a fixture ina way thatitisinthe direction of media flow for the greatest impact and fasterfinishing. It was also observed that in the dry condition, themaximum impact force and frequency of impact occurrencewere much higher than in the water-wet condition. The fol-lowing factors were stated as the causes of the above obser-vationthatwasrenderedunexplainablebyWangetal.25:(i)reduced coefficient of friction in the finisher due to waterwetting and hence lower energy transfer efficiency from thewall to the media; (ii) a water film on the media promotesadhesion and acts to dissipate impact energy; and (iii) in-creased lubrication reduced the speed of media relative toworkpiece. It can therefore be concluded though lubricationaids in the vibratory finishing process, excess lubricant canreduce the speed of media impact and increase finishing time.Baghbanan et al. 30 experimented with the same forcesensor as developed by Yabuki et al. 1 in a vibratoryfinishing trough. It was observed that the pattern of normaland tangential forces and the surface property changes in atrough finisher were similar to that in a bowl finisher ob-served by Wang et al. 25 and Yabuki et al. 1. The relation-ship between hardness and finishing time was also reported tobe similar for the small, low energy bowl finisher and thelarge, high-energy trough. However, a different mountingmethod for the workpieces in the troughclamping insteadof adhesive bonding that was used in case of the bowlwasattributed for minor variations of the results. Lubrication con-dition was also experimented with and it was found that itsignificantly affected the workpiece hardness and surfaceroughness 30 similar to the observations made by Wanget al. 25 and Yabuki et al. 1 Hence, it was concluded thatvibratory finishing follows a general pattern that is irrespec-tive of the type of machine, vibration frequency andamplitude. Similar conditions of vibratory finishing are seenacross the different types of vibratory equipment- be it a bowlor trough type. Fixtures are used in both the configurations;however the design of the fixture will depend on the compo-nent being finished. One significant difference between thebowl and the trough that was characterized through Almenstrips was higher impact energy of media in the tub. This canbe explained by the fact that the machines were operated atdifferent frequencies30 Hz for the bowl and 47 Hz for thetub. Higher impact energies with increasing frequency mayalso explain the reduced cycle times with high-speed motorsdiscussed in Section 4.1.Domblesky et al. 13 conducted experiments with the vi-bratory bowl finisher and investigated the changes in materialremoval rate and surface finish of workpiece materialsalu-minum, brass, and steel as a function of media, workpiecematerial, bowl acceleration, and finishing duration. It wasmentioned that abrasive wear and grinding are fundamentallyrelated to mass finishing from a material removal perspective.This is because in both processes, minute asperities abradematerial from a workpiece surface by scratching the surfaceon a microscopic scale. In the experiments carried out,Domblesky et al. hypothesized that based on their respectivemechanical properties, aluminum would have the maximummaterialremovalrateandsteelthelowest.Itwasobservedthatbrass had the highest material removal rate (MRR) and alumi-num the lowest. This observation was attributed to the similardensities of the media and aluminum which would result inlower relative motion between the two. Further investigationswere called for to comprehend the reason behind the MRR ofbrass being twice that of steel. It was noted in the experimentsthat the resultant bowl acceleration is highly affected by thetotal roll weight (bottom eccentric weight) as compared to thefeed weight (upper eccentric weight). This observation buildsontheroleofrollandfeedweightsasdiscussedinSection4.1.It was suggested that for deburring and edge radiusing appli-cations, roll setting should be used as the primary means tocontrolandoptimizecuttingactionandMRR.Thissuggestionis useful for personnel involved in deburring and edgeradiusing of aerospace components through vibratoryfinishing. One potential limitation that the authors of thisState-of-the-Art study note is that whether the suggestionsmade by Domblesky et al. can be implemented in other vibra-tory bowls since different machines come with varying con-figurations of eccentric weights. MRR was found to be direct-ly related to the resultant bowl acceleration and the differencein density between media and workpieces 13. MRR alsodiffers from material to material, but for a given material, itwasconstantovertime.Workpiecehardnesswasalsofoundtobe a factor in influencing material removal rate with softerworkpieces having higher material removal rates.Kumar et al. 28 devised a simple 1D simulator for thevibratory finishing process. Titanium workpieces were testedFig. 11 Contact modes of media in vibratory finishing: a free impact, brolling ofindividual media,and c adjacentmedia rollingovera stationarypiece of media 1Int J Adv Manuf Technolfor material removal rates, surface roughness and contactforces were measured in two different arrangements.Through experimental investigations, it was found that sur-faces which are placed deeper in the media and perpendic-ular to the vibratory motion demonstrated higher MRRs.Media flow can be visualized as layersmedia deeper inthe container move with the weight of media layers aboveit and hence strike the component with a different force thana media layer on the surface, thereby causing higher materialremoval. Modeling of contact forces of the media and work-piece was carried out using multibody dynamics simulation.While it proved to be a suitable method, Kumar et al. statethat it must be optimized further to be used along with aprediction model. More accurate predictions of peak contactforces and other relatively small forces need to be done inorder to render the simulation results useful for materialremoval prediction of the workpiece.6.2 Vibratory finishing processmodel developmentsSofronas et al. 31 were one of the earliest researchers todevelop a comprehensive model for vibratory finishing pro-cess in 1979. They used a statistical tool known as responsesurface methodology to investigate the effect of hardness,projection width, processing time, media size, and vibrationfrequencies on workpiece projection height reduction, edgeradiusing, and surface finish reduction 31. These three de-pendent variables are well illustrated in Fig. 12. It was notedthat the reduction in height of projections was accomplishedby a “hammering” or “peening” action with a subsequentplastic deformation in bending. It was also claimed that asimilar mechanism was responsible for the radiusing and sur-face finish reduction as opposed to an abrasive metal removalmechanism. It was concluded from experiments that the vi-bratory frequency was the most significant process variablewithhigherfrequencies increasingthe responses ofthe depen-dent variables illustrated in Fig. 12, followed by media sizeand processing time. The implementation of high-speed mo-tors to reduce cycle times as discussed in Section 4.1 are inaccordance with the findings from this study by Sofronas.Hashimoto 24 followed suit and established fundamentalprinciples of the vibratory finishing process and proposedmathematical models using differential equations forpredicting surface roughness and stock removal. Three ruleswereproposedfor the vibratory finishingprocess basedontheexperimental results obtained. First, the roughness of theworkpieces subject to vibratory finishing will exponentiallydecline to a constant value known as “roughness limitation,”which is dependent on the inherent surface texture of theworkpiece. Second, the higher the difference between theroughnessofworkpieceanditsroughnesslimitation,thefasterthe roughness changes of the workpiece. Lastly, Hashimotoproposed that in the steady state, the vibratory finishing pro-cess has a constant stock removal rate. He used two bowlvibrators with varying capacity, frequency of 21 Hz, and am-plitude of 5 mm for his experiments. Hashimotos experimen-tal results matched well with the predictions of his mathemat-ical models. The proposed rules are universally observed in avibratory finishing setup and the vibratory finishing operatorscan use the models proposed to optimize the process cycletimes as well. The rules can be extended to machines withhigh-speed motors that are available in the industry today assimilar saturation curves were observed in 11.Domblesky et al. 26 followed up their experimental in-vestigation of vibratory bowl finishing 13 and proposed amaterial removal model using cutting forces as the startingpoint for the model development. The model was validatedwith experiments and it was established that MRR is timeindependent, reinforcing Hashimotos 24 third rule. Al-though the results appeared to support the proposed MRRmodel, further work can be done to affirm the effect of differ-ent media and workpiece mass on MRR. The authors of pres-ent State-of-the-Art study opine that Domblesky et al. madecertain simplifying assumptions for the development of theirmodel. Firstly, the peening mechanism proposed by Sofronaset al. 31 was neglected as it was claimed that that would notinfluence the rate of material removal. It was observed thatMRR is proportional to bowl acceleration, indicating an ag-gressive cutting action at high acceleration levels. It was fur-ther implied that high acceleration should reduce cycle timesfor edge radiusing applications where a high level of materialremoval is needed. This contradicts the peening and plasticdeformation mechanism explained by Sofronas et al. 31 foredge radiusing. Secondly, media was assumed to be self-sharpening and the cutting action was insignificant over time.However, in actual processes, media is influenced over timeand a suitable assumption for the change of media could havebeen implemented. These observations and contradictionsmade can be corrected and implemented for further researchon understanding vibratory finishing.Naeini et al. 32 took modeling to the next step and devel-oped a discrete element model (DEM) to simulate bulk spher-ical steel media flow in a 2D vibrationally fluidized system.Fig. 12 Projection height reduction, surface finish reduction, and edgeradiusing in a workpiece 31Int J Adv Manuf TechnolDEM is used to simulate the collisions and subsequent veloc-ities of the media, container, and workpiece. The DE modelemployed a linear contact model with contact parameters asfollows: normal and tangential stiffness (k), normal and tan-gential damping (), and sliding friction (). It was highlight-ed that further improvements in the model predictions can bemade by treating normal and tangential stiffness and dampingparametersasdistinctratherthanequalasdonebyNaeinietal.The extent of plastic deformation and erosion of the work-piece surface is controlled by the media impact forces whichin turn are controlled by the media impact velocities. TheDEMpredictedthatnormalcontactvelocitycomponentsweresix to eight times larger than the tangential components. Ex-perimentally, it was found that the normal contact forces be-tween media and sensor were approximately ten times higherthan tangential forces 1, 32. This paper combines the mech-anisms proposed by Domblesky et al. (abrasive material re-moval) 26 and Sofronas et al. (peening) 31 and attributes itto normal impact forces and velocities of the media. The au-thors of the present State-of-the-Art study concur with Naeiniet al. in that vibratory finishing has dual mechanisms operat-ing to give the necessary surface condition: plastic deforma-tion by media impacts and material removal by relative mo-tion of media and workpiece.Naeini et al. 33 modelled the development of single-cellbulk circulation of two different media in vibratory bedsusing a 2D discrete element method. The bed of sphericalparticles was modeled as a single layer of disk with the as-sumption that all collisions and motion occurred in the xyplane. The vital difference between this study 33 and thatdone by the same authors in 32 was the spacing of glasspartition plates used to hold media in the vibratory troughs. Inthe previous experiment 32, the glass plates were spaced toaccommodate only a single layer of particles as compared to aspacing of 100 mm in the present setup, which led to themedia flow having a greater 3D component. Naeini et al.wanted to determine to what extent the 2D DEM can repre-sent such a nominally 2D flow. It was mention that resultantshear forces between the container walls and media wererelated to the behavior of the system. Model predictions wereconfirmed with experimental results. It was found that withgreater depth of the media in the container, the magnitude ofthe bulk circulation increased and hence, components placeddeeper in the media will be subject to harsher finishing ascompared to components placed near the surface of the me-dia. This was further substantiated by Kumar et al. 28 in2012. Naeini et al.s modeling attempts can be carried for-ward by considering how the shear forces at the finisher wallsare transferred between particles into the bulk. As technologyand research have evolved, more insights are being gainedinto vibratory finishing. The findings from Naeini et al.s ex-periments will help to determine the optimal position to placethe component in a vibratory finisher for best results.Uhlmann et al. 34 investigated and developed a geometry-based model for prediction of changes in surface roughness-profile for the transient period of vibratory finishing. Accordingto Hashimotos rules 24, the transient period is defined as thetime it takes for the initial roughness value to exponentially de-cline to reach the “roughness limitation” value. Uhlmann et al.sstudyaimedtopredictsurfaceroughnessthroughtheformulationof the empirical process model as a quantitative method. Themodel was based on the hypothesis that during the transientperiod, the MRR is proportional to the improvement in surfaceroughness. The models predictions were verified with measure-ments after different process times through a profilometer and itwas shown that the models predictions seemed to fit the mea-surementsfairlywellwithmeanresidualsrangingfrom0.7to+2.1%.Forthegivenprocessparameters,itwaspresentedthatthemodel could also be transferred to a workpiece with differenttopographical features. Systematical forecast errors in the modelwere found to increase with process times. It was suggested thatthese errors were due to the change of material removal mecha-nism during the transient period. Further research in underlyingmaterial removal mechanisms of vibratory finishing and on thetransferability of the developed model to different workpieceshapes, initial roughness, materials, and media can be carriedout. Uhlmann et al.s observations reinforce the disadvantagesof vibratory finishing highlighted in Section 3the lack ofknowledge of the exact material removal mechanisms at playintheprocess.Existingresearchhasuncoveredsomeknowledge,but an overall picture is yet to be painted.Uhlmann et al. 27 also investigated vibratory finishingand determined a process model combining the geometricmodeldevelopedinreference34,withDEMandexperimen-tal results. Experimental investigations on vibratory and dragfinishingwerecarriedouttoestablishtherelationshipbetweenvibratory finishing processes and process parameters such asprocessing time, workpiece speed, excitation frequency, abra-sive media, and initial surface roughness of workpieces. Ex-perimental results were utilized for the model developed.Transient MRRs in vibratory finishing were found to bestrongly dependent on the initial surface roughness. Thecauses for different material removal mechanisms were statedas follows: for abrasion and micro-cutting mechanism, rela-tive velocity between workpiece and media is the primaryfactor in controlling the MRR; for a predominantly cutting-like material removal mechanism, the intensity of media im-pact is the primary factor in controlling the MRR. Experi-ments for drag finishing, which is an advanced form offixtured vibratory finishing, also showed a steady increase insurface roughness improvement for spherical media with arise in energy input. This high-energy input is given by anincrease in excitation frequency and workpiece speed. Theobservations provide relevant experimental evidence to thediscussion of high-speed motors and fixtures in improvingcycle times as mentioned in Sections 4.1 and 4.2.Int J Adv Manuf Technol6.3 Bulk and granular impact velocitiesCiampini et al. 35 measured surface-normal impact velocitydistributions,frequencies ofimpactand impactpower per unitarea using a piezoelectric impact force sensor. The work wasan extension of Wang et al. 25 and Yabuki et al. 1 in termsof developing a method to extract normal impact velocityfrom the impact force signals. One notable difference fromearlier studies was that the sensor was fixed as opposed tofreely flowing with the media. This fixed support providedimpact velocity data that was independent of the workpiecesize, shape, and material. Porcelain and steel spheres weredropped onto the sensor cap from known heightsthis wasused to determine the relationship between impact velocityand force signal. Two modes of contact between media andthe sensor were observedshort duration direct impact con-tacts and longer duration non-impact contacts. The impactmodes are well illustrated in Fig. 13, which showed periodi-cally within time frames called “bursts” and the lengths ofthese burst periods were in correspondence with the finishersdriving frequency. It was proposed that the infrequent, high-velocity impacts may have a higher significance in the me-chanics of vibratory finishing as compared to the frequent,low velocity impacts since the former is the main cause forplastic deformation and hardening of the impact site. The im-portance of frequent, low velocity impacts depends on theapplication. In one application of vibratory finishing ma-chinesdrying with nimble, absorptive mediainvolveslight contact and hence low-velocity impacts become impor-tant as opposed to burnishing, where high-energy contacts arerequired to create plastic deformation. By varying the mediamasses, it was found that increasing the media mass had theeffectofreducingtheamplitude withoutaffectingthefrequen-cy. This happened because the eccentrically weighted shaftwhich generates the vibratory motion of a finisher was sup-ported by ball bearings attached to the tub. Measurementstaken from the sensors showed that finishing became moreaggressive as the parts move closer to a wall and on reducingthe total media mass in the vibratory finishing equipment.Ciampinietal.sstudygaveinsightsintomonitoringvelocitiesin a vibratory finishing setup and uncovered details on howimpact velocities play a role in the material removal mecha-nism.Onthevibratoryfinishingmachine,thevelocitiescanbealtered by changing motor RPM (frequency). Combined withthe results of Kumar et al. 28, more experiments can becarried to determine the best possible position for fixing aworkpiece in a vibratory finisher for ideal results for variousapplicationsfinishing, drying, and burnishing amongothers. Ciampini only stressed on the plastic deformationmechanism in vibratory finishing. Further research can beconducted to identify if the infrequent, high-velocity impactshaveaneffectonmaterialremovalbymeasuringtheweightofthe samples periodically.Hashemnia et al. 36 refined on measuring the impactvelocities of media and developed a new laser displacementprobe. It was noted that the media in a vibratory finisher havetwo types of velocitiesa large scale bulk flowvelocityand asmall scale impact velocity. The workpieces immersed in themedia encounterrepetitive,high-frequencyimpactsofthesur-rounding media. The main factors affecting the erosive wearand plastic deformation of workpieces were attributed to thevelocity, frequency, and direction of the impacts of the mediaparticles. Extreme values of impact velocities have their dis-advantageshigh-velocity impacts can cause fracture andfragmentation while low velocity impacts can reduce the effi-ciency of the process. The challenges of measuring impactvelocities between vibrating particles in a vibratory finisherwere highlightedsmall scale of motion and difficulty in de-signing probes which can measure velocities on such a scalewithout affecting the media. The objective of the Hashemniaet al.s study was to develop a high-speed laser displacementsensor probe to determine the surface-normal impact veloci-ties in a vibratory finisher. The graphical methods used byNaeini et al. 32 and Wang et al. 25 to measure bulk flowproperties had limited spatial resolution and hence hamperedwithmeasurementsofimpactvelocities.Theimpactvelocitieswere determined by conducting graphical analysis of the laserdisplacement sensor signals with MATLAB. Hashemniaetal.sstudy had one experimentinconsistency with thestudyby Ciampini et al. 35 which allowed a comparison of thesensors usedthe placement of the sensors at one particularposition in the trough. Ciampini et al. used impact force sen-sors whereas the present study involved laser displacementsensors to determine impact velocities. The present study byHashemnia et al. 36 had velocities ranging between 50 and100 mm/s and the previous study by Ciampini et al. 35 hadvelocities ranging between 0 and 20 mm/s. The most signifi-cant reason behind this difference was that in the Ciampiniet al.s study, a linear correlation was assumed between mea-sured impact force and the impact velocity. Other reasonswere difference in the size of the probes in the two studiesand that “non-impact” contact events were excluded in thepresent study by Hashemnia et al. due to the nature of laserdisplacement sensornon-contact method. It was observedthat the depth in the flow influenced the impact velocities ofthe media particlesvelocities were much higher fartherFig. 13 Impact modes of media: a) longer duration non-impact contactsand b) short duration direct impacts 35Int J Adv Manuf Technolaway from the free surface. This can be linked with Kumaret al.s 28 findings of higher MRRs at deeper locations with-in the media. In the present set of experiments, spherical me-dia was used. It was highlighted that measurement of the bulkflow velocities for irregular shaped media will be challengingdue to the variation in the average displacement signal fromthe laser sensors.Hashemnia et al. 37 carried forward their earlier work36 on impact velocities and developed a DEM to predictlocal impact and bulk flow velocities in a vibratory troughusing high-speed laser displacement sensors. These valueswere then correlated to the measured values for spherical steelmedia. Hashemnia et al. mentioned that the link between sen-sitivityofparticleimpactvelocitiesandtheuncertaintiesinthecontact coefficients used in DEMs was unknown. Hence thecoefficients of restitution and friction corresponding toparticle-particle and particle-wall interaction were includedin DEM analyses. The impact and bulk flow velocities wereobserved to be relatively insensitive to the uncertainties in thecoefficients of friction and restitution. The reason for impactvelocities being greater at a deeper location was unclear,highlighting the inherent variability and unpredictability ofthis process as highlighted in Section 3. It was concluded thatDEM was reasonably accurate in its predictions of local andbulk velocities of media in vibrationally fluidized beds withthe maximum differences being 20 and 30 %, respectively.6.4 VibrostrengtheningSangid et al. 16, 38 carried out two sets of work in the fieldof vibrostrengtheningone on experimental investigation offixturingtheworkpieceandthesecondoneonitsvisualizationand modeling. Vibrostrengthening is a variant of the vibratoryfinishing process, which serves the dual purpose of impartingcompressive residual stresses and improving surface finish.The process can be considered as a potential alternative tothe shot peening process. In this process, the workpieces arefixedandthemediaactsuponthemasdiscussedinSection4.2.This results in aggressive mechanical working of the surfaceof the workpiece. It was observed that vibrostrengthening re-sultedinsignificant fatigue enhancements onmachined work-pieces. A sub-surface compressive residual stress produceddue to plastic deformation by media action along with a bettersurface finish were said to improve the fatigue strength of theworkpiece. As highlighted in Section 3, this fatigue enhance-mentisextremely beneficialfor aerospace components. Itwasalso observed that within the range of frequencies tested,higher the machine frequency and amplitude, the greater thefatigue life enhancement. A useful insight into variation ofmedia action with depth was given, thereby correlating obser-vationsmadebyKumaretal.28.On the one hand, the mediaare less packed at the top of the tub and move as individualparticles. On the other hand, media are densely packed deeperin the trough due to the mass of the particles on top of themand hence they move as a single mass. This results in greatermedia impact on the workpiece and an increased mechanicalworking of the workpiece material. While testing the influ-ence of processing conditions like media and compound onthe process, it was noted that precise control is critical forcompound dosing and sufficient time should be allowed be-tween processing samples to ensure that the lubricant drainsout of the system and the media dries up. Further experimentsand methods would be needed for lubricant introduction, con-trol and removal to obtain a “balance between the effective-ness of the process and wear rates of the vibrating medium”16. As discussed in Section 4, these experiments highlightthat the vibratory finishing process is incomplete without anyone of its KPVs.In the second study by Sangid et al. 38, high-speed videorecordings and computational models to predict the fatiguelife were developed in order to understand thevibrostrengtheningprocess better. A Plexiglasfixture attachedto the side of the trough to observe the particle motion wasused as the experimental setup. The media motion was ob-served to have two components: a high-frequency oscillatorytrajectorythatiscompletedpervibrationalcycleofthetubanda slower drift trajectory that is observed to shift the oscillatorytrajectory. Sangid et al. noted that the oscillatory trajectorywas responsible for the outcome of the process and the driftmotion was responsible for the redistribution of media anddraining away the lubricant and workpiece remnants. It wasobserved that increasing the vibratory frequency resulted inthe increase of media velocity, thereby leading to forcefulmediaworkpiece interactions, beneficial higher residualstresses and also an increased fatigue life. The high-speedcamera recordings helped in calculating the effective impactforce between a media particle and the workpiece. The effec-tive force was found to be 5.3 N and this was in accordancewith previous calculations of approximately 4 to 6.5 N byBaghbanan et al. 30. This force was found to be sufficientin order to induce a residual stress and cause plastic deforma-tion within the realms of the experimental study. The compu-tational model was developed to predict the fatigue life of acomponent based on experimentally measured values of re-sidual stress profile and surface characteristics. This was pri-marily for shot peening applications. These two studies con-ducted by Sangid et al. highlight the versatility and potentialof the vibratory finishing process beyond what it was origi-nally designed for.6.5 Almen strip characterizationCiampini et al. 39 characterized the vibratory finishing pro-cess parameters using the Almen system. The Almen systemis a well-established process that is used for the characteriza-tion of shot peening process. Standardized strips made ofInt J Adv Manuf Technolmetal are clamped to a rigid support and bombarded with ashot peening stream. On being released from the clamp, thestrips curve due to the residual stresses created by plastic de-formation. This degree of curvature and its rate of change arerelated to the process variables of the shot peening process.Aluminum Almen strips were finished in the same vibratorytrough and media as used by Ciampini et al. 35. A vacuumholder was used in the trough to ensure that the strip remainedflat, providing a constant boundary condition. Almen satura-tion curves for two contact conditions which were previouslycharacterized using impact velocities in 35 were obtained. Itwas observed that higher plastic deformation and greaterAlmen strip deflectionwas causedbylargestimpactvelocitiesand hence, the suitability of Almen strips to characterize theaggressiveness of the vibratory finishing process wasestablished. Based on a novel normal impact simulator appa-ratus constructed by the authors 39, they provided furtherevidence that normal impacts are the dominant mechanism ofvibratory finishing as observed by other researchers 32.Ciampini et al. 40 also developed a model for the plasticdeformation of Almen strips subject to vibratory finishingand to reinforce the role of Almen strips to characterize thevibratory finishing process.7 ConclusionsVibratory finishing has proven to be a particularly effectiveform of mass finishing despite the advancements that havebeen seen in the mass finishing industry. Today, it occupies apivotal position in the production line of many industries andis considered a highly efficient and repeatable process withminimal usage of manpower as well as other resources.The key issue pertaining to vibratory finishing which stillplagues many researchers is got to do with solving the blackbox that encompasses the entire process. This entails clearlyestablishing the mechanism of the material removal and therelationshipbetweenprocessparametersandthesurfacefinishobtained. This relationship between input and output parame-ters of the process is not clear due to the complexity of mate-rial removal mechanism and uncontrollable nature of the vi-bratory finishing process.For instance, there islimited knowl-edge on how changing an input parameter such as media andcompound would positively or negatively impact the surfacefinish or material removal of the component. Thus, the designof this process for new components is still undertaken on atrial and error basis and largely depends on the expertise ofsuppliers and operators.A number of analytical, empirical and numerical modelshave been developed with regards to the vibratory finishingprocess. Based on the literature reviewed in this work on vi-bratory finishing, the key findings are as follows:1.Frequency of vibrations is the most important parameterin a vibratory finishing process with high frequency ofvibrations leading to shorter cycle times.2.There are two main mechanisms at play in a vibratoryfinishing process: plastic deformation by media impactsand material removal by relative motion of media andworkpiece.3.Fixturing the components to be finished increases theforce flow and relative velocity of the media against thecomponent, thereby decreasing cycle times. This is thereason why advancements in fixtured vibratory finishingfor example spindle finishing have arisen.4.Selection of media and the amount of compound play acritical role in bringing about the right surface finish.5.Material removal rates for a particular material remainconstant over time and are known to be higher whenthe component is perpendicular to and deeper in themedia flow.6.Normal forces and high-velocity impacts of media havebeen stipulated as the main causes of plastic deformationin a vibratory finishing process.7.Three main contact modes of media in vibratory finishinghave been observed: free impact, rolling of individualmedia and adjacent media rolling over a stationary pieceof media.However, quantifying the range of vibrational frequenciesthatisnecessarytoreducecycletimesconsiderablyforagivencomponent still remains. The right frequency with the appro-priate amplitude is the key to imparting the desired surfacefinish. The strict regulations in the aviation industry have alsomade it necessary that components meet the high standards ofquality and customer satisfaction. Although fixturing of com-ponents can help reduce cycle times considerably, there arechances that it damages the components and the repair timewill counter the advantages gained by fixturing. A novelfixturing means which reduces cycle times considerably aswell as one which does away with impingement on the com-ponent is still to be delved into. Researchers are also on thelookout for a smart media that can help bring about materialremoval as well as surface roughne
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