4. Re-designoftherivettools Fig. 11 showsthemajorcomponentsofaconventionalrivet hammer.Thevibrationofarivethammerisgeneratedattwo
hits theslidingairvalveandtheslidingairvalvehitsattherearend of thebarrel.Therefore,inordertoreducethevibrationtransmitted tothehumanoperator,vibrationcontrolmeasuresmustbeapplied tothesetwoplaces.Theergonomicandmechanicalmodifications madeontherivethammerwereasfollows: _ Movethehandletothepositionwherethecenterofgravityof the hammerislocated.Thiswillsignificantlyreducethe bending momentactingontheoperator’swristjoint.
Changetheangleofthehandlefromapproximately901 of a conventionalhammertoapproximately701 to aligntheaxisof the forearmandhand. _ Insert a‘‘nosebushing’’tothetipofthecylinder.Fora conventionalrivethammer,thecylinderhasaninnerdiameter about thesamediameteroftherivetset.Byenlargingtheinner
diameterofthecylinderandinsertingarubber-basebushing, about 2.5cm(1.0in)inlength,intothefrontendofthecylinder as shownin Fig. 12, adampingdeviceisplacedatthemost critical locationofthehammer. _ Add adampedrecoillessspringattherearendofthecylinder. Twotypesofdesignsweremanufacturedandfieldtestedas shownin Fig. 13(a) and(b).Type‘‘a’’wasanembeddedspring with aspecialpolymerthatwasdevelopedspeciallytomeet the temperatureandfrequencyrequirementsoftheoperation. The springwasmoldedwiththepolymerduringtheprocess and themoldhadtobecutopentoreleasetheembedded spring. ItwasproducedbytheRubberDevelopmentCo. locatedatLosAngels,CA,USA.Type‘‘b’’wasdevelopedby the 3MCorporation,USA,anditisaco-axialsheardamping device whichisadoptedforitseffectivenessaswellastheease of manufacturing.Itissimplyahollowcylinderfilledwith polymerdampingmaterialandasteelshaftembeddedinthe centerofthecylinder. _ Add arubbercushionattheendoftheslidingairvalve. Therefore,theaccelerationfromthepistoncanbereduced after ithitstheslidingairvalve. _ Add adampingcoatingtothesurfaceofthecylindertoreduce the transmittedvibrationfromthecylindertothehousingof the handle. Conventionalbuckingbarsarehardenedsteelbarswithoneor morepolishednormalsurfaces.Whenthebuckingbarisheld against theendofrivetshank,mostofthetransmittedenergyis consumed atthecontactpointtoflattentherivetshank.The person whoisholdingthebuckingbar,unfortunately,absorbsthe restoftheenergy. The ergonomicandmechanicalmodificationsmadeonthe buckingbarwere _ Changethesquareedgesofaconventionalbuckingbarintoa cylindricalshapethatwithadiameterof63.5mm(2.5in)can fit comfortablywithinahuman’spalm. _ Use apolisheddollyheadwithastemandadoublecylinder design toreplaceflatsurfacesofthebuckingbar.Basedonthe job requirement,theoperatorcanexchangeadifferentdolly head orthesizeofthehandle. _ Insert the3Mdampingdevice,asintherivethammer,intothe inner cylinderofthebuckingbar.