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occurring at tool-chip-workpiece interfaces duringthe high speed dry cutting of a AISI 316L stainlesssteel with TiN coated carbide tools.(a)Fig. 2. Various technologies of tribometer (a) Olsson’stribometer [5], (b) Zemzemi’s tribometer [5], (c) Hedenqvist’stribometer [6].(c)2 EXPERIMENTAL SET-UP2.1 Material descriptionA cylindrical bar, made of AISI 316L, is fixed ontoa lathe chuck, as illustrated in Figure 3.4-Pneumatic jack6-DynamometerForcesmeas.FtFn2-Cutting toolrefreshingthe surface5-Pin holder(b)3- Pin :Carbide +TiN coating7-Thermistor1-Workpiece :316LHeat Fluxmeas.Fig. 3. Tribometer designed for cutting applications.A pin made of cemented carbide with a TiN coatingand having a spherical geometry Ø 9 mm is pressedonto the cylindrical surface by means of a jack.Thanks to the helical trajectory of pin, the surfacecontact is continuously regenerated. The pin ismaintained by an instrumented pin-holder able toprovide data about the instantaneous heat fluxentering into the pin [7]. It is fixed onto adynamometer, in order to provide the apparentnormal and tangential force (macroscopic forces).After each friction test, a cutting tool refreshes thesurface and a belt finishing operation is performed inorder to obtain a very low initial surface roughness.2.2 Testing conditionsTesting conditions have to be chosen in accordancewith the frictional conditions estimated along thetool/chip/workpiece interfaces. For instance, themachining of a AISI 316L with a TiN coated carbidetool in dry cutting conditions is around Vc~120m.min -1 . Based on Figure 1, it is of evidence that themacroscopic sliding speed at the tool-workpieceinterface is almost equal to the cutting speed ~ 120m.min -1 . On the chip-tool interface, the averagesliding velocity depends on the compression ratio β,which is around 2. So at this interface, themacroscopic velocity is 2 times lower than thecutting speed 60 m.min -1 . As a consequence, thecharacterization of the frictional properties at thetool/chip/workpiece interface needs performingfriction tests in the following conditions: slidingvelocity: 60-120 m.min -1 , pressure: 1-2 GPa [2].2.3 Experimental resultsThe sliding velocity was the single modifiedparameter in this work. A normal force equal toabout 1000 N has been applied onto pins, which leadto an average pressure of 1.8 GPa.The first output data provided by this set-up is theratio between the tangential and the normal force.This coefficient can be defined as an apparentfriction coefficient Ftµapp= . (1)FThe evolution of µ app versus sliding velocity isplotted in Figure 4. This confirms that it is notrelevant to consider the friction coefficient asindependent from sliding speed. Over 120 m.min -1 , amodification of the frictional behavior is observed.nWorkmaterial : AISI 316 L steelPin : Carbide + TiN coatingSphere diameter : 9 mmFig. 4. Apparent friction coefficient.
The evolution of heat flux transmitted to the pin φ pinversus sliding velocity is plotted in Figure 5. Itappears that heat flow increases with the velocity,which is coherent with the fact that more energy isproduced and dissipated. The frictional behaviourmay be modified over a certain value (saturation).The Johnson-Cook parameters used have beenchosen thanks to the works of Umbrello et al. [8].Moreover our model considers the hypothesis fromBowden et al. [9] with: µ plast describes the plasticdeformation part of µ app and µ adh corresponds to theadhesive friction coefficient: µapp= µadh+ µ . (3)plastThe model uses thermo-dependent properties for theWC/Co substrate [6] and the AISI 316L workpiece:Workmaterial : AISI 316 L steelPin : Carbide + TiN coatingSphere diameter : 9 mmFig. 5. Heat flux measured into the pin.3 NUMERICAL POST-TRAITEMENTA finite element model, simulating the sameexperimental conditions of plowing and friction, hasbeen developed. Macroscopic experimental data µ appand φ pin are used to fit the numerical model for 3sliding velocities: 60-90-120 m.min -1 .3.1 Description of the modelVsVsTable1. AISI 316L workpiece propertiesParameter Temperature ValueSpecific heat 20 450(J.kg -1 .°C -1 ) 300 545500 570800 625Thermal Conductivity(W.m -1 .°C -1 )1100 67020 14300 18500 21800 241100 29Density (kg.m -3 ) 20 8000300 7890500 7800800 76601100 75103.2 Thermal boundaries conditionsThe model includes the heat generation induced bythe friction in addition to the heat dissipated by theplastic deformation (plowing) of the workmaterial.As shown by Figure 7, the frictional heat flux φ frictionis dissipated at the interface in a narrow layer,whereas the plastic deformation heat flux φ plast isdissipated only in the workpiece in a large volume.Fig. 6 Geometry of the numerical friction model.The 3D model (Fig.6) is based on the work ofZemzemi et Al. [5]. Considering the high strain andstrain rate, an explicit formulation has been chosen.A thermo-mechanical model has been programmedwith ABAQUS explicit.A Johnson-Cook flow stress model has been used tomodel the AISI 316L steel. This model is dependenton strainε p, strain-rate ε&pand temperature T so asto observe softening phenomenon:σeqm⎡ ⎛ & ε ⎞⎤⎡np ⎛ T − T ⎞ ⎤0= ⎣⎡ A + B( εp) ⎦⎤ . ⎢1 + C.ln . ⎢1−⎥⎜ ⎥ε ⎟ ⎜ ⎟⎢⎣ ⎝&0 ⎠⎥⎦ ⎢ ⎝ TF− T⎣0 ⎠ ⎥⎦(2)Plastic deform ationheat fluxTransm itted to part 1Plastic deform ationheat fluxD iffused in part 2Friction heat fluxtransm itted to part 1Friction heat fluxtransm itted to part 2Fig. 7. Heat flux sources during friction tests.3.3 Fitting methodFor each testing condition simulated, the indentationdepth h, the adhesive friction coefficient µ adh and theheat partition coefficient α have to be determined. Inthis aim, an iterative method, presented in Figure 8has been developed. The experiments has provided
Page 1: Development of a friction modelling
Page 6 and 7: 2.2 Toolkit and specimen geometryFi
Page 8 and 9: In general, the friction coefficien
Page 10 and 11: determining a relative movement bet
Page 12 and 13: force needed to move the pin (frict
Page 14 and 15: and specimens are parts of actual i
Page 16 and 17: 4.3 Effect of lubricant particle si
Page 18 and 19: 2 EXPERIMENTAL2.1 PSCT set-up and p
Page 20 and 21: found here only in a low strain rat
Page 22 and 23: pieces are scaled by the same scali
Page 24 and 25: the experimental one shows nearly n
Page 26 and 27: 2 NUMERICAL TOOL2.1 General descrip
Page 28 and 29: much better when rotating velocity
Page 30 and 31: transfer across the roll-strip inte
Page 32 and 33: egime, the contact behaviour is gov
Page 34 and 35: eJ / 2βD pD mr pJ / 2PunchFig. 2.G
Page 36 and 37: number of profiles, which has the a
Page 38 and 39: In spite of the predominance, galli
Page 40 and 41: other hand, it has not been observe
Page 42 and 43: corresponds to the minimum energy s
Page 44 and 45: 10.90.80.70.60.50.40.30.20.100 5 10
Page 46 and 47: 2 EXPERIMENTAL PROCEDURETwo lubrica
Page 48 and 49: can be described using the followin
Page 50 and 51: through an arc cathodic equipment.
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To verify the absence of coating in
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angle, and m 0 the constant frictio
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4 NUMERICAL MODELLING4.1 Upsetting
Page 58 and 59:
indenter. T-shape compression, a ne
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Tangential force / Normal force0.35
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