High performance cutting of gamma titanium aluminides: Influence of lubricoolant strategy on tool wear and surface integrity

Heat resistant gammatitaniumaluminidesareintermetallicalloysplannedtobewidelyusedinhigh- performanceaircraftengineswithinthenextfewyears.Thisapplicationfieldisascribedtothe exceptionalmaterialproperties,especiallythelowdensityandauniquestrength-to-weightratiofor titanium-basedalloys,goodoxidationbehaviourandthermalstability,limitedductilityandfracture toughnessbelowbrittle-to-ductiletransition,andgoodcreepresistance. The demandingmachinabilityofgammatitaniumaluminidescanbetracedbacktothesedesirable materialproperties.Consequently,cuttingprocessadaptationisessentialtoobtaincomponents suitabletosatisfystrongregulationsregardingsurfaceintegrity,withoutneglectinganeconomical production.Previousresearchactivitiesconfirmedthatthermalmaterialsofteningduringcuttingdue to thehighspeedmachiningisakeytoreachhighqualitysurfaces,buttoolwearwasidentifiedasthe limitingfactor. The relativelyhighcuttingspeedresultsinhightemperaturesintheshearzoneandthelowthermal conductivityofthe g-TiAl workpiecematerialleadstoanextremethermaltoolload.Furthermore,in combinationwiththeformationofsaw-toothchipsandthediscontinuousflowofthechipalongthe rake face,adhesiveweariscaused. The influenceofconventionalfloodcoolingandhighpressurelubricoolantsupply(wetconditions), cryogeniccoolingwithliquidnitrogen,andminimumquantitylubrication(MQL)wereinvestigatedin longitudinalexternalturningoperations.Toolwear,cuttingforces,chipmorphologyandsurface roughnesswereevaluated.Surfaceintegritywasanalysedintermsofmachinedsurfacedefectsand sub-surfacealterations. The investigationsindicatethatcryogeniccoolingisthemostpromisinglubricationstrategy, meaningthatthethermodynamicalimpactoftheexpandingliquidnitrogenapplieddirectlyclose to thecuttingzonesuccessfullycounteractthehugethermalloadonthetoolcuttingedges,providing potentiallyenormousbenefitsintermsoftoolwearreductionandconsequentsurfacequality improvement