On high-speed turning of a third-generation gamma titanium aluminide

Gamma titanium aluminides are heat-resistant intermetallic alloys predestined to be employed in components suffering from high mechanical stresses and thermal loads. These materials are regarded as difficult to cut, so this makes process adaptation essential in order to obtain high-quality and defect-free surfaces suitable for aerospace and automotive parts. In this paper, an innovative approach for longitudinal external high-speed turning of a third-generation Ti-45Al-8Nb- 0.2C-0.2B gamma titanium aluminide is presented. The experimental campaign has been executed with different process parameters, tool geometries and lubrication conditions. The results are discussed in terms of surface roughness/integrity, chip morphology, cutting forces and tool wear. Experimental evidence showed that, due to the high cutting speed, the high temperatures reached in the shear zone improve chip formation, so a crack-free surface can be obtained. Furthermore, the use of a cryogenic lubrication system has been identified in order to reduce the huge tool wear, which represents the main drawback when machining gamma titanium aluminides under the chosen process condition

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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 improvemen

High Performance Turning of Austempered Ductile Iron (ADI) with adapted Cutting Inserts

AbstractHeat treated Ductile Iron with austenitic-ferritic matrix (ADI) has a high potential for the substitution of forged steel and conventional Ductile Iron. Advantages of ADI compared to steel are good castability and lower density. In comparison to conventional Ductile Iron, the increased ratio of tensile strength/ductility with higher resistance against abrasive wear and durability are of advantage. In the industrial applications, the material sided advantages are counterbalanced by the higher costs of the demanding machining, especially in rough turning operations. In this presentation, the development of cutting inserts for high performance turning operations, which are adapted on the specific requirements of the machining of ADI 900, are described. In the first step, the particular machinability, which can be traced back to the metallic matrix, was specified. The characteristic, discontinuous chip formation in combination with the strong tendency of hardening of the austenitic− ferritic matrix was identified as a major wear mechanism, resulting in extreme peaks of cutting forces and high specific mechanical load on the insert edge. For an enhanced evaluation of chip formation and the resultant thermomechanical tool load, a 3D FEM simulation model was developed. By using this 3D simulation model of the longitudinal external turning process, the maximum cutting forces were specified in addition to the influence of the chip segment formation frequency. The obtained results from the simulation have been used to develop an optimised insert geometry. By using the optimised tool, an increased tool life of 70% could be observed. The shown results are part of the PhD Thesis authors Dissertation “Werkzeug− und Prozessauslegung zur Drehbearbeitung von austenitisch-ferritischem Gusseisen mit Kugelgraphit