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    (低温工程)不锈钢316表面磨削过程冷却降温的影响.pdf

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    (低温工程)不锈钢316表面磨削过程冷却降温的影响.pdf

    grindingIndiaMachininginvestigationenvironmentstainlesscooling. The enhancements realized by the delivery pressure of the cryogen, with respect to the grindingforces, and surface roughness were also studied.the grindingintoprocessing wheel and work material, resulting thermal damages to surfaceof the work material. Therefore, the use of a cutting fluid duringthegrinding operation is very essential. The coolant types, method ofsupply, and delivery pressure are critical for heat dissipation [2].The major problems with the oil based conventional wet coolantstechnique, inpressure air asof oil mistis alsosafe with reference to operator’s health and environmentaltion. The alternative method which has attracted attention isgenic machining using liquid nitrogen LN2 as a coolant [18]application of LN2as coolant in different machining processes liketurning [6,7], and milling [8] produced improvements in genera-tion of defect free surfaces, lower grinding forces and higher mate-rial removal rates MRR due to the effective control of grindingzone temperature.Ben Fredj and Sidhom [9] found that surfaces ground withcryogenic cooling produced fewer surface defects, and reduced⇑Corresponding author. Tel. 91 44 26811499; fax 91 44 26811009.E-mail addresses manimaran_mehotmail.com, manimaran_meyahoo.co.inG. Manimaran, pradeepannauniv.edu M. Pradeep kumar, principalCryogenics xxx 2013 xxx–xxxContents lists availableCryogenicssaveetha.ac.in R. Venkatasamy.the machining performance. The coolants applied to the machiningzone absorb the maximum heat, and transfer the remaining heat tothe work material and tool. The coolant supply is also difficult ingrinding process, due to the large contact area between the grind-alternative is the MQL minimal quantity lubricationwhich a small quantity of oil is applied, with highthe carrier. In the MQL technique, a large volumecharged into the environment. Hence, MQL technique0011-2275/ - see front matter C211 2013 Elsevier Ltd. All rights reserved.http//dx.doi.org/10.1016/j.cryogenics.2013.11.005Please cite this article in press as Manimaran G et al. Influence of cryogenic cooling on surface grinding of stainless steel 316. Cryogenics 2013,dx.doi.org/10.1016/j.cryogenics.2013.11.005is dis-notpollu-cryo-. Thetransformation of frictional energy into thermal energy. Externalfriction between the abrasive grain and work surface, as well as be-tween the chip and abrasive grain are partly responsible for theheat generation during grinding. However, heat also develops asa result of internal friction through displacement processes andplastic deformations [1]. The excessive heat affects the mechanicalproperties of the work material and grinding wheel, and reducesinfluence the formation of a thin layer of hard and brittle surfacecalled white layer. The layer appears white under an optical micro-scope whose properties are different from bulk material, so it isdetrimental to fatigue life and surface integrity [4]. Grinding indry conditions generates the cutting marks, micro-grooves, oxida-tion and subsurface damages [5]. There is a need for developing anew technology to avoid or minimize the use of cutting fluids. OneStainless steelGrinding1. IntroductionMechanical energy is produced byrelative movement between the grindingmaterial. This energy is mainly convertedremoval process, leading to a temperaturezone. Friction and plastic deformationC211 2013 Elsevier Ltd. All rights reserved.process duringwheel and the workheat during materialincrease in the grindingresponsible forare, environmental pollution due to the boiling of the cutting fluid,smoke, health of the operators and difficulties in storage and main-tenance [3]. The current industrial production uses about a fewhundred million gallons of harmful polluting cutting fluids. Thecryogenic coolant, if substituted as a cutting fluid, can avoid envi-ronmental problems associated with cleaning and disposal [16].In dry grinding, plastic deformation and high temperature canCryogenic coolingEnvironmenting forces compared to dry and wet cooling. The surface roughness under cryogenic cooling is found toproduce 59 and 32 lesser values and fewer defects, compared to surfaces ground with dry and wetInfluence of cryogenic cooling on surfaceof stainless steel 316G. Manimarana,⇑, M. Pradeep kumarb, R. VenkatasamyaDepartment of Mechanical Engineering, Saveetha Engineering College, Chennai 602105,bDepartment of Mechanical Engineering, CEG Anna University, Chennai 600025, Indiaarticle infoArticle historyReceived 9 February 2013Received in revised form 18 November 2013Accepted 22 November 2013Available online xxxxKeywordsabstractThe objective of the presentface roughness by the applicationCryogenic machining is anments were conducted oning. The experimental resultsbenefits in the machining performance.journal homepage www.elsevier.com/loais to evaluate the improvements in the grinding force and sur-of LN2liquid nitrogen as a coolant in the cryogenic grinding process.concerned green manufacturing process. The grinding experi-steel 316 in three environments, namely, dry, wet and cryogenic cool-show that a reduction in the grinding zone temperature leads to excellentThe cryogenic coolant offers 37 and 13 reduction in the grind-at ScienceDirectcate/cryogenicshttp//2 G. Manimaran et al./Cryogenicsgrinding forces. Fathallah et al. [10] conducted experiments undercryogenic cooling and conventional cooling, with the objective offinding the effects of the cooling mode on the ground surface integ-rity of hardened AISI D2 steel. It was found that the material re-moval rates could be increased several times without affectingthe surface residual stresses under cryogenic cooling. The surfaceroughness, residual stress and sub-surface damages are reducedto a great extent with the application of cryogenic cooling.Venkatrao [11] summarizes that cryogenic machining with li-quid nitrogen is safe and environment friendly. Nitrogen is anon-hazardous gas, that constitutes about 79 of the atmosphericFig. 1. The experimental setup with LN2delivery.Table 1Grinding conditions.Machine 2.25 KW Hydraulic surface grinderGrinding wheel Aluminum oxide Al2O3 A60K5VDiameter of wheel 250 mmWidth of wheel 25 mmWork piece Stainless steel 316Wheel speed VS 31.4 m/sDepth of cut DOC 10–40lm in steps of 10Table speed Vw 0.1, 0.125 and 0.15 m/sFeed 10lmEnvironments C15 Dry.C15 Soluble oil.C15 Liquid nitrogen.Dressing Single point diamond dresserDressing depth 10lmabFig. 2. The variations in the a Tangential force b normal force with depth of cutwork speed 0.125 m/s, pressure 3 bar.Please cite this article in press as Manimaran G et al. Influence of cryogenic coodx.doi.org/10.1016/j.cryogenics.2013.11.005abxxx 2013 xxx–xxxair. Cryogenic gases have a wide variety of applications in indus-tries such as health, electronics, manufacturing, automotive andaerospace industries, particularly for cooling purposes. Liquidnitrogen is the most commonly used element in cryogenics. It isproduced industrially by the fractional distillation of liquid air.Nitrogen melts at C0210 C176C and boils at C0198 C176C. It is the mostabundant gas, colorless, odorless, tasteless and non-toxic. Hencethe nitrogen discharged into the atmosphere in cryogenic processwas safe with regard to the operator’s health, and had an insignif-icant impact on the environment.Bhaduri et al. [12] conducted experiments with white, grey alu-mina and cBN cubic boron nitride grinding wheels, with neat oiland cryogenic cooling. They found that neat cooling oil is moresuitable for grinding low carbon steel compared to cryogenic cool-ing. The main reason is the large scale adhesion and breakage ofgrits. Cryogenic cooling is also not effective when grinding Ti–6Al–4 V titanium material with the monolayered brazed typecBN grinding wheel. The chemical interaction between the workFig. 3. The variations in the a Tangential force and b normal force with workspeed depth of cut 40 lm, pressure 3 bar.abFig. 4. The variations in the a Tangential force b normal force with deliverypressure at various depth of cut work speed 0.125 m/s.ling on surface grinding of stainless steel 316. Cryogenics 2013, http//material and grinding wheel could not be improved by the applica-tion of LN2as coolant [13]. The cryogenic cooling seems to be cool-ant of the future and mainly environmentally safe; and hence, it isa cooling technique to be further examined for applications inmanufacturing processes. Stainless steels are difficult to machinedue to work hardening, high toughness, high ductility and lowthermal conductivity. Hence, in this study, experimental workhas been carried out to investigate the influence of cryogenic cool-ing and delivery pressure, on the grinding of stainless steel 316 interms of the grinding forces and surface roughness.Fig. 5. The variations in the specific grinding energy with depth of cut workspeed 0.15 m/s, pressure 3 bar.aabFig. 7. The variations in the surface roughness with a depth of cut workspeed 0.15 m/s, pressure 3 bar b work speed depth of cut 40lm,pressure 3 bar.G. Manimaran et al./Cryogenics xxx 2013 xxx–xxx 3bcFig. 6. Force measurement profiles of the surfaces ground at a dry, b wet and c cryogenic conditions Vw 0.15 m/s, DOC 10 lm, pressure 3 bar.Please cite this article in press as Manimaran G et al. Influence of cryogenic cooling on surface grinding of stainless steel 316. Cryogenics 2013, http//dx.doi.org/10.1016/j.cryogenics.2013.11.0052. Experiment workThe cryogenic cooling system consists of a jet of LN2, supplied atthe grinding zone at a distance of 40 mm from the cutting zone,and an angle of 20C176. The liquid nitrogen jet was produced by sup-plying pressurized air to the LN2container, and fitting a properlydesigned nozzle at the end of the stainless steel delivery line. Thepressure of the LN2jet delivered to the machining area is fixed as3, 4, and 5 bars. Conventional cooling consists of 20 coolant oilin water, applied directly at the grinding wheel work materialinterface at 7.2 L/min. For dry grinding no coolant is used.A hydraulic surface grinding machine was used to carry out thegrinding tests under cryogenic cooling and oil based conventionalcooling. The surface grinder used in the experiment with liquidnitrogen delivery was shown in Fig. 1. To conduct the experiments,the work material is cut into 100 C2 50 C2 8 mm plates, and then theplates are fastened to the upper side of a piezo-electric transducerbased dynamometer type Kistler 9257B. Standard aluminumoxide Al2O3 grinding wheel of size 250 mm outer diameter,72.5 mm bore and 25 mm width was used throughout the experi-ment. The surface roughness is measured by the contact type Sur-tronic3, Taylor Hobson with a cutoff length of 0.8 mm andsampling number of 5 traverse length is 0.8 C2 5 4 mm. Thenon-contact 3D surface roughness measurements were taken withthe Tally-Surf CCI profilometry equipment. The temperature wasmeasured by a non-contact type IR pyrometer accuracy 1. Allthe grinding experiments were conducted at a constant feed andwheel speed. The grinding wheel speed was maintained at31.4 m/s and cross feed at 10 lm for all the trials. The dressingof grinding wheel was done after each trial with a diamond dresserat constant depth of 10 lm. The values were recorded after fivepasses for all the trials. The roughness values were taken at threelocations close to one another, and the average values wererecorded.The grinding forces are measured by the Kistler piezo-electricdynamometer and recorded continuously by the dynawaresoftware interfaced with dynamometer. The average value of aFig. 8. Variations in the surface roughness with delivery pressure under cryogeniccooling work speed 0.125 m/s.a4 G. Manimaran et al./Cryogenics xxx 2013 xxx–xxxbRa1.07 m cdFig. 9. The characteristic profile generated by the grinding under dry conditions Vw 0.15in the waviness c corresponding 3D model of the surface d SEM image of the work material.Please cite this article in press as Manimaran G et al. Influence of cryogenic coodx.doi.org/10.1016/j.cryogenics.2013.11.005m/s, DOC 40 lm, pressure 3 bar a variations in the roughness b variationsling on surface grinding of stainless steel 316. Cryogenics 2013, http//particular trial was used for the analysis. The details of the grindingconditions are listed in Table 1.3. Results and discussion3.1. Effect of grinding forcesFig. 2 illustrates the variations of the tangential and normalforce, with the depth of cut DOC at a work speed of 0.125 m/s.The tangential grinding forces reduced by 22–37 compared todry and around 13 compared to wet grinding. The reduction is15 and 11 when normal forces are considered. The grindingforces depend on the sharpness and fracturing of grits, as theyare developed due to the shearing action of the grits on the workmaterial during the grinding process [3]. The sharpness of the gritdepends on temperature at the grinding zone and adhesion of workmaterial. The adhesion also depends on the grinding temperaturedue to the freshly machined surface and chips formed are chemi-cally active at high temperature. Dry grinding generates dulling,followed by the breakage of grits. The wet coolant is not effectiveat higher DOC and speed. The control of the temperature at thegrinding zone improves the mechanical strength of grits, resultingsharper grits and leads to lower grinding forces.The increased work speed also generates higher grinding forcesas is evident from Fig. 3. The improvements realized from theapplication of cryogenic cooling are 12 and 23 compared todry and wet cooling, when grinding at 0.15 m/s. The flow of workmaterial around the grits of the grinding wheel was less duringcryogenic cooling leading to lower grinding forces. This is mainlydue to the lower temperature generated by cryogenic coolingresulting in less rubbing and ploughing action by the sharper grits.The Fig. 4 illustrates the improvements in the tangential and nor-mal grinding forces when grinding under various LN2deliverypressures. The influence of the delivery pressure is much less atlower DOC. The grinding forces reduced by 7 and 9 for the tan-gential and normal forces at 40 lm DOC. The increased deliverypressure contributes to a moderate reduction in the forces. Theability of the coolant to reach the machining zone is enhanced bythe coolant pressure, and better lubrication at the grit edges,resulting reduced forces.The frictional effects between the wheel and work material sur-face was indicated by Grinding force, and specific grinding energy[5]. The specific grinding energy Esis calculated by the followingequationEs FtVsVwapb 1where Esis the specific grinding energy, Ftis the Tangential force, Vsis the wheel speed, Vwis the work piece table speed, apis the depthof cut, b i

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