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2 EXPERIMENTAL PROCEDURETwo lubricants were chosen for the investigation asin [5]. These are the lubricant based on industrial oil(IO+G) and based on synthetic oil (SO+G). Bothlubricants contain colloidal graphite particles aslubricant’s components and the size of particles isless than 15 µm. The chemical composition of alloysunder study is given in Table 1 [5]. The bold type inTable 1 indicates the amount of the basic impurities,which the investigated alloys contain.The sizes of the ring samples were as follows: innerdiameter = 20 mm; outer diameter = 40 mm; height= 14 mm. The ring samples were heated totemperatures of 200, 350, 430, 450, and 470°C in anelectric furnace. Deformation of the heated sampleswas carried out on flat dies that were warmed up totemperature of 120°C. Samples were compressedwith lubrication. Die velocity was constant at V≈400mm/s (screw press with nominal load = 10 MN andmaximum load = 16 MN), which corresponded to aninitial strain rate of 28.6 s –1 . This value of strain ratebelongs to the strain rate interval (10 0 -10 2 s -1 ) withinthat the massive hot forging is usually carried out.Table 1. Chemical composition of alloys [5]Element Percentage, %A95456 A92618Al base baseCu 0.04 2.12Si 0.16 0.20Mn 0.63 0.03Mg 6.80 1.56Ti 0.1 0.05Zn 0.2 0.06Fe 0.22 1.0Ni - 0.80Cr - -The values of height h exp and inner diameter d expwere determined after compression of the ringsamples. The inner diameter was measured in threelocations along the height of the rings. Finally, thevalue of the inner diameter was determined asd exp =(d top +d mid +d bot )/3, where d top , d mid and d bot arerespectively inner diameter at the top, middle andbottom along the height of the ring, accordingly.3 NUMERICAL SIMULATION OF RINGUPSETTINGA numerical simulation of the ring test was carriedout by means of the FE system QFORM-2D(QuantorForm Ltd., Russia). The aims of thesimulation were to determine the values of thefriction factor based on the obtained experimentaldata for the lubricants under study, and further toconstruct calibration curves. Levanov’s frictionmodel [6, 7] was implemented by the QFORMsimulation software.Levanov’s friction model can be considered as acombination of Coulomb’s friction law and constantfriction law. It gives almost the same results asCoulomb’s friction law for low value of contactpressure σ n . In case of high contact pressure,Levanov’s friction model and constant friction lawallow us to obtain approximately the same values offriction shear stress.Fig. 1. Scheme of calculationFigure 1 illustrates the scheme of numericalcalculation performed. Here d exp and d fem are theinner diameter of the ring sample obtainedexperimentally and by FEM, respectively.The variable parameter in the simulation was thefriction factor. The simulation was carried out forthe same values of temperature as the experimentshad been done.Stress–strain curves of alloys under study were takenfrom the handbook [8]. These curves were obtainedunder the conditions given in Table 2.Table 2. Identification of flow stress-strain curvesAlloy type T, °C ε ε& , s -1A92618 200-470 0-3 0-3A95456 150-450 0-0.8 0.01-100To perform the simulation, we assumed that thecontact friction was constant at the definedtemperature of deformation within the investigatedrange.4 RESULTS4.1 Effect of temperature, strain rate andlubricant’s compositionAccording to scheme (see Fig.1), one parameter
should be compared. That is the inner diameter ofthe deformed ring specimen.Comparing the volumes of a ring before and afterthe FE simulation showed that the loss in volumewas approximately equal to 0.5%. As a result, it isuseless to control the outer diameter before and aftereach simulation trial. That is why the inner diameteris only controlled.The determined values of the friction factor k n aregiven in Table 3. Figures 2 and 3 show therelationships between the friction factors and thetemperatures for the lubricants under study.Moreover, in Table 3 the value of friction factortaken from [5] are given. These data correspond tothe upsetting of rings made from the same Al-alloyswith the help of hydraulic press. The deformationprocess was isothermal in those tests. It means thatthe initial temperature of a specimen and tools wasequal to each other. The initial strain rate was0.14 s -1 .Table 3. Friction actors k n valuesFriction factor k nT, °C Strain rate, s -10.14 s –1 28.6 s –1 0.14 s –1 28.6 s –1A95456 A95456 A92618 A92618IO+G200 0.171 0.41 0.25 0.21350 0.153 0.287 0.236 0.202430 0.155 0.245 0.146 0.179450 0.118 0.216 0.15 0.17470 0.11 0.21 0.138 0.143SO+G200 0.245 0.45 0.19 0.34350 0.206 0.396 0.223 0.32430 0.15 0.37 0.143 0.26450 0.12 0.31 0.114 0.24470 0.143 0.285 0.133 0.235Figures 2 and 3 illustrate the effect of twoparameters on friction factor, i.e. temperature andinitial strain rate. It can be seen that the moretemperature of deformation, the less friction factorvalue is. It is valid for both investigated alloys.On the other hand, using two different presses interms of their design allowed to investigate theeffect of strain rate on friction factor value.Unfortunately, we could not perform thiscomparison within the whole range of investigatedtemperatures. The reason for that is linked to the factthat the conditions of deformation in each casesdiffered from each other. In case of using of thescrew press for deformation the isothermal conditionwas approximately observed at the temperature of200°C.Taking it into consideration it can be concluded thatat temperature of 200°C the effect of strain rate ismore significant for Al-Mg alloy. Moreover, it isindependent from the lubricant’s composition.Increasing the strain rate from 0.14 to 28.6 s -1 givesrise to increase in friction factor in over two times. Itis valid for both lubricants.Fig. 2. Deformation of A92618 alloy: solid and dash lines –regression; points - experimentFig. 3. Deformation of A95456 alloy: solid and dash lines –regression; points - experimentOn the other hand, for Al-Cu-Mg-Fe-Ni alloy theeffect of strain rate on friction factor value is not soobvious. For the lubricant based on synthetic oil(SO+G) the influence of initial strain rate on k n isalmost the same. The increase in friction factor valueis over 1.5 times. For IO+G lubricant the effect ofstrain rate is opposite to it. The difference betweenthe values of friction factor for both initial values ofstrain rate is inessential.4.2 Regression for friction factor vs temperatureThe temperature dependence of the friction factor
Page 1 and 2: Development of a friction modelling
Page 3: The evolution of heat flux transmit
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 48 and 49: can be described using the followin
Page 50 and 51: through an arc cathodic equipment.
Page 52 and 53: To verify the absence of coating in
Page 54 and 55: angle, and m 0 the constant frictio
Page 56 and 57: 4 NUMERICAL MODELLING4.1 Upsetting
Page 58 and 59: indenter. T-shape compression, a ne
Page 60: Tangential force / Normal force0.35

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