EXPERIMENTAL INVESTIGATION AND PROCESS PARAMETEROPTIMIZATION OF EN31 STEEL WITH CHROMIUM COATED DRILLBITS USING ANOVAABSTRACT The metal cutting is very essential to try for high metal removing rate andthe best product quality. The major problem in achieving high productivity and best quality isshort life span of a tool. To enhance the life of tool many new materials are developed so has tomeet themarket demandandcompetitivepriceforthisthereshouldbepropercontrol overvariouscost involvedinmachiningnamedasmaterial cost labourcost andtoolingcost thematerial cost can be controlled by using special material which meet all required properties withreduced price. The methodology of Modified Taguchi optimization method for simultaneousminimization and maximization of Surface roughness !a"# machining time and material removalrate of $%&' (lloy steel affect the aesthetical aspect of the final product and hence it is essentialto select the best combination values of the )%) drilling process parameters to minimize as wellas maximize the responses. The experiments were carried out by a )%) lathe# using physicalvapourdepositioncoated)hromiumnitridedrillingtoolbitforthemachiningof$%'*. Theexperiments were carried out as per +* orthogonal array with each experiment performed underdifferent conditions of such as speed# type of drilling tool# and feed rate. The Taugchi method andanalysis of variance (%,-(" was employed by using M.%.T(/0'1 software to identify thelevel of importance of the machining parameters on Surface roughness !a"# Machining time andMaterial !emoval !ate M!!".1CHAPTER-11 INTRODUCTION2rilling is one of the basic machining process of making holes and it is essentially formanufacturingindustrylike automobile industry# medical industry# andaerospace industry.$specially drilling is necessary in industries for assembly related to mechanical fasteners. .t isreported that around 11#333 holes are drilled as a complete single unit production of the (.!/4S (&13 aircraft &" 2rilling of metals is increasing requirements for producing small productsandmorehighlyfunctional. 5ithincreasingdemandfor precisecomponent production# theimportant of drilling processes is increasing rapidly. /ecause of the requirement of deeper andsmaller holes required in the above said industries. .t is required for drilling process technologiestoachievehigheraccuracyandhigherproductivity.Thereareseveral convectional andnon0conventional manufacturing process by which drilling can be possible. 2rilling using laser beam#electron6s beam and electric discharge methods and also electrolytic polishing# electro chemicalmachining has been frequently used by industries and for experimental researches. 7owever# forgeneral application# conventional drillingprocess is preferredduetothehigher economicalbenefits than other processes and also it has highly productivity than other non 0convectionaldrilling processes. 8hysical vapour deposition8-2 " describes a variety of vacuum depositionmethods used to deposit thin films by the condensation of a vaporized form of the desired filmmaterial onto various work piece surfaces e.g.# onto semiconductor wafers". The coating methodinvolves purely physical processes such as high0temperature vacuum evaporation withsubsequent condensation# or plasmasputter bombardment rather thaninvolvingachemicalreaction at the surface to be coated as in chemical vapour deposition. $%&' is an important material with desirable properties# including high resisting in natureagainst wear and can be used for components which are subjected to severe abrasion# wear# highsurface loading. 7ence# $%&'promises fruitful development for applications in the automobilesector due to its high strength.1.1 CNC LATHE )omputer numerical controlled )%)" lathes are rapidly replacing the older productionlathes multi spindle# etc." due to their ease of setting# operation# repeatability and accuracy. They2are designed to use modern carbide tooling and fully use modern processes. The part may bedesigned and the tool paths programmed bythe )(29)(Mprocess or manuallybytheprogrammer and the resulting file uploaded to the machine# and once set and trailed the machinewill continue to turn out parts under the occasional supervision of an operatorFigure (1.1) CNC machineThe machine is controlled electronicallyvia a computer menu style interface: theprogrammay bemodifiedand displayed atthe machine# along withasimulated viewoftheprocess. Thesetter9operatorneedsahighlevel ofskill toperformtheprocess# however theknowledge base is broader compared to the older production machines where intimateknowledge of each machine was considered essential. These machines are often set and operatedby the same person# where the operator will supervise a small number of machines cell". The design of a )%) lathe varies with different manufacturers# but they all have somecommon elements. The turret holds the tool holders and indexes them as needed# the spindleholds the work piece and there are slides that let the turret move in multiple axes simultaneously.Themachinesareoftentotallyenclosed# dueinlargepart tooccupational healthandsafety,7;S"issues. 5ithrapidgrowthinthisindustry#different )%)lathemanufacturersuse3different userinterfaceswhichsometimesmakeit difficult foroperatorsastheyhavetobeacquaintedwiththem. 5iththeadvent of cheapcomputers# freeoperatingsystems suchas+inux# and open source )%) software# the entry price of )%) machines has plummeted. 1.1.1 LATHE OPERATIONS .n order to perform different operations in a lathe# the work piece may be supported anddriven by any one of the following methods < '. 7eld between centre6s and driven by carriers and clutch plates. =. 7eld on a mandrel which is supported between centers and driven by a carriers and catch plates. &. 7eld and driven by chuck with the other end supported on the tailstock centre. >. 7eld and driven by a chuck or a faceplate or an angle plate. The above methods of holding the work may be broadly classified under two headings < '. 5ork piece held between centre6s# =. 5ork piece held by a chuck or any other or any other fixture. 1.1.2 BASIC LATHE OPERATIONS '. 2rilling =. Turning &. Threading >. )hamfering 1. ?nurling @. Arooving B. Spinning C. /oring *. Tapping '3. Dacing41.1.2.1 DRILLING 2rilling in a lathe is to remove material from the work piece to produce a cone0shaped ora cylindrical hollow surface. 1.1.2.2 DRILLING PROCESS 2rilling is a cutting process that uses a drill bit to cut or enlarge a hole of circular cross0section in solid materials. The drill bit is a rotary cutting tool# often multipoint. The bit is pressedagainst the work piece and rotated at rates from hundreds to thousands of revolutions per minute.This forces the cutting edge against the work piece# cutting off chips swarf" from the hole as it isdrilled. 1.1.2.3 TYPES OF DRILLING PROCESS '. Spot drilling =. )enter drilling &. 2eep hole drilling a. Aun drilling b. Trepanning >. Micro drilling 1. -ibration 2rilling1.1.2.3.1 SPOT DRILLING The purpose of spot drilling is to drill a hole that will act as a guide for drilling thefinal hole. The hole is only drilled part way into the work piece because it is only used to guidethe beginning of the next drilling process.1.1.2.3.2 CENTER DRILLING The purpose of center drilling is to drill a hole that will act as a center of rotation forpossible following operations. )enter drilling is typically performed using a drill with a specialshape# known as a center drill. 1.1.2.3.3 DEEP HOLE DRILLING 2eep hole drilling is defined as a hole depth greater than ten times the diameter of thehole. These types of holes require special equipment to maintain the straightness and tolerances.,ther considerations are roundness and surface finish. 51.1.2.3.4 GUN DRILLING (nother typeof drillingoperationiscalledgundrilling. Thismethodwasoriginallydeveloped to drill out gun barrels and is used commonly for drilling smaller diameter deep holes.This depth0to0diameter ratio can be even more than &33. !educedgalling. 1. $xtended toolsK life. @. .ncrease in feed rate and cutting speed. B. +ess maintenanceand down time. C. )ost saving in new tools and dies.1.3 SUMMARY OF DRILLING PARAMETERS AND FORMULA 1.3.1 CUTTING SPEED The speed of the work piece surface relative to the edge of the cutting tool during a cut#measured in surface mm per minute. 1.3.2 SPINDLE SPEED Speed always refers to the spindle and the work piece. 5hen it is stated in revolutions perminuterpm" it tellstheir rotatingspeed. /ut theimportant featurefor aparticular turningoperation is the surface speed# or the speed at which the work piece material is moving past thecutting tool. .t is simply the product of the rotating speed times the circumference of the workpiece before the cut is started. .t is expressed in meter per minute m9min"# and it refers only tothe work piece. $very different diameter on a work piece will have a different cutting speed#9even though the rotating speed remains the same. - L M2%9'333 m9min 7ere#v is the cuttingspeed in turning# D is the initial diameter of the work piece in mm# and N is the spindle speed in!8M. 1.3.3 FEED RATE The speed of the cutting toolKs movement relative to the work piece as the tool makes acut. The feed rate is measured in inches per minute and is the product of the cutting feed .8!"and the spindle speed !8M". Deed always refers to the cutting tool# and it is the rate at which thetool advances along its cutting path. ,n most power0fed lathes# the feed rate is directly related tothe spindle speed and is expressed in mm of tool advance" per revolution of the spindle"# ormm9rev. Dm L f.% mm9min 7ere# D is the feed in mm per minute# f is the feed in mm9rev and % is the spindle speed in !8M. 1.3.4 MATERIAL REMOVAL RATE The material removal rate M!!" in turning operations is the volume of material9metalthat is removed per unit time in mm&9min. Dor each revolution of the work piece# a ring shapedlayer of material is removed. MRR L v. f .d N'333" in mm3 9 min 1.4 CUTTING TOOL FOR LATHE 1.4.1 DRILL TOOL ( rotary end cutting tool having one or more cutting lips and having one or more helicalor straight flutes for the passage of chips and the admission of a cutting fluid. 1.4.2 HIGH SPEED STEELS "HSS# 7SStoolsaresonamedbecausetheyweredevelopedtocut at higherspeeds.2eveloped around '*33 7SS are the most highly alloyed tool steels. The tungsten T series" wasdeveloped first and typically contains '= 0 'CO tungsten# plus about >O chromium and ' 0 1Ovanadium. Most gradescontainabout 3.1Omolybdenumandmost gradescontain>0 '=Ocobalt. .t was soon discovered that molybdenum smaller proportions" could be substituted formost ofthetungstenresultinginamoreeconomical formulationwhichhadbetter abrasionresistance than the T series and undergoes less distortion during heat treatment. )onsequentlyabout *1O of all 7SS tools are made from M series grades. These contain 1 0 '3O molybdenum#10'.1 0 '3O tungsten# ' 0 >O vanadium# >O )hromium and many grades contain 1 0 '3O cobalt.7SS tools are tough and suitable for interrupted cutting and are used to manufacture tools ofcomplex shape such as drills# reamers# taps# dies and gear cutters. Tools may also be coated to improve wear resistance. 7SS accounts for the largest tonnage of tool materials currently used. Typical cutting speeds< '3 0 @3 m9min. 1.5 DRILL BIT NOMENCULTURE AXIS The imaginary straight line which forms the longitudinal center line of the drill. BAC& TAPER ( slight decrease in diameter from point to back in the body of the drill. BODY o The portion of the drill extending from the shank or neck to the outer )orners of the cutting lips. BODY DIAMETER CLEARANCE o That portion of the land that has been cut away so it will not rub against the walls of the hole. CHISEL EDGE ANGLE 11The angle included between the chisel edge and the cutting lip# as viewed from the end ofthe drill. CLEARANCE DIAMETER o The diameter over the cut away portion of the drill lands. DRILL DIAMETER o The diameter over the margins of the drill measured at the point. FLUTES o 7elical or straight grooves cut or formed in the body of the drill to provide cuttinglips# to permit removal of chips# and to allow cutting fluid to reach the cuttinglips. FLUTE LENGTH o The length from the outer corners of the cutting lips to the extreme back end oftheflutes. .t includes thesweepof thetool usedtogeneratetheflutes and#therefore# does not indicate the usable length of the flutes. HELIX ANGLE o The angle made by the leading edge of the land with a plane containing the axis ofthe drill. LAND o The peripheral portion of the body between adjacent flutes. SLIP RELIEF ANGLE o The axial relief angle at the outer corner of the lip. .t is measured by projection into a plane tangent to the periphery at the outer corner of the lip. NEC& o The section of reduced diameter between the body and the shank of a drill. OVERALL LENGTH o The length from the extreme end of the shank to the outer corners of the cuttinglips. .t does not include the conical shank end often used on straight shank drills#nor does it include the conical cutting point used on both straight and taper shankdrills.o PERIPHERAL RA&E ANGLE o The angle between the leading edge of the land and an axial plane at the drill point. POINT ANGLE 12o The angle included between the lips projected upon a plane parallel to the drill axis and parallel to the cutting lips. SHAN& o The part of the drill by which it is held and driven.1. MATERIAL REMOVAL RATE The material removal rate M!!" in turning operations is the volume of material9metalthat is removed per unit time in mm&9min. Dor each revolution of the work piece# a ring shapedlayer of material is removed. MRR L v. f .d N'333" mm& 9 min 1.! TOOL WEAR Tool wear in machining is defined as the amount of volume loss of tool material on thecontact surface due to the interactions between the tool and work piece. Specifically# tool wear isdescribed by wear rate volume loss per unit area per unit time" and is strongly determined bytemperature# stresses# andrelativeslidingvelocitygeneratedat thecontact interface. Metalcutting tools are subjected to extremely arduous conditions# high surface loads# and high surfacetemperatures arise because the chip slides at high speed along the tool rake face while exertingvery high normal pressures and friction force" on this face. The forces may be fluctuating due tothe presence of hardparticles inthe component microstructure# or more extremely# wheninterrupted cutting is being carried out. 7ence cutting tools need< Strength at elevated temperatures 7igh toughness 7igh wear resistance 7igh hardness .t is common to assume that all the energy used in cutting is converted to heat a reasonableassumption" and that C3O of this is carried away in the chip this will vary and depend uponseveral factors0particularlythe cutting speed".Thisleaves about =3O of theheat generatedgoing into the cutting tool. $ven when cutting mild steel tool temperatures can exceed 113o)#the maximum temperature high speed steel 7SS" can withstand without losing some hardness.)utting hard steels with cubic boron nitride tools will result in tool and chip temperatures inexcess of '333o). 131.% SURFACE ROUGHNESS Surface roughness is an important measure of product quality since it greatly influencesthe performance of mechanical parts as well as production cost. Surface roughness has an impacton the mechanical properties like fatigue behavior# corrosion resistance# creep life# etc. .t alsoaffects other functional attributes of parts like friction# wear# light reflection# heat transmission#lubrication# electrical conductivity# etc. /efore surface roughness# it is also necessary to discussabout surface structure and properties# as they are closely related. 1.%.1 THE PRINCIPAL ELEMENTS OF SURFACE ROUGHNESS The principal elements of surfaces are discussed below< 1. SURFACE' Thesurfaceof anobject is theboundarywhichseparates that object fromanothersubstance. .ts shape and extent are usually defined by a drawing or descriptive specifications. 2. PROFILE' .t is the contour of any specified section through a surface. 3. ROUGHNESS' .t is definedas closelyspaced# irregular deviations onascalesmaller thanthat ofwaviness. !oughness may be superimposed on waviness. !oughness is expressed in terms of itsheight# its width# and its distance on the surface along which it is measured.4. WAVINESS' .t is a recurrent deviation from a flat surface# much like waves on the surface of water. .tis measured and described in terms of the space between adjacent crests of the waves wavinesswidth" and height between the crests and -alleys of the waves waviness height". 5aviness canbe caused by# 2eflections of tools# dies# or the work piece# Dorces or temperature sufficient to cause warping# 4neven lubrication# 14 -ibration or any periodic mechanical or thermal variations in the system during manufacturing operations. Dig.'.C.'=3 Surface characteristics 5. FLAWS' Dlaws# or defects# are random irregularities# such as scratches# cracks# holes# depressions#seams# tears# or inclusions. . LAY' +ay# or directionality# is the direction of the predominant surface pattern and is usuallyvisible to the naked eye. 1.%.2 FACTORS AFFECTING THE SURFACE FINISH (" The machining variables which include a" )utting speed b" Deed# and c" 2epth of cut. /" The tool geometry Some geometric factors which affect achieved surface finish include< a" %ose radius b" !ake angle c" Side cutting edge angle# and d" )utting edge. )" 5ork piece and tool material combination and their mechanical properties 2" Puality and type of the machine tool used# $" (uxiliary tooling# and lubricant used# and D" -ibrations between the work piece# machine tool and cutting tool.1.%.3 MEASUREMENT OF SURFACE ROUGHNESS'. 2irect measurement methods =. )omparison based techniques &. %on contact methods 15>. ,n0process measurement DIRECT MEASUREMENT METHODSDigure '.C.&" Schematic diagramof surface roughness measurement technique by stylus$quipment 2irect methods assess surface finish by means of stylus type devices. Measurementsare obtained using a stylus drawn along the surface to be measured. The stylus motionperpendicular to the surface is registered. This registered profile is then used to calculate theroughness parameters. This method requires interruption of the machine process# and the sharpdiamond stylus can make micro0scratches on surfaces.CHAPTER-22. LITERATURE REVIEW 16CHAPTER ( IILITERATURE REVIEW2.1 INTRODUCTIONThe behaviour of a material is greatly dependent upon its surface# the environmentandits operating conditions. Surface engineering can be defined as the branch of sciencethat dealswithmethodsforachievingdesiredsurfacerequirementsandbehaviour inservice for engineering components H=1I. The surface of any component may be selectedon the basis of texture and colour# but engineering components generally demand a lotmore than this. $ngineering components must perform certain functions completely andeffectively under various conditions# possibly in aggressive environments. Modemprocess environments# whichcontribute towear# canbe verycomplex# involvingacombination of chemical and physical degradation. Surface properties of the componentused in a particular workingenvironment have to be designed with that environment inmind. P.VEN&ATARAMAIAH H'I et al has .nvestigated on the controllable parameterscutting speeds# feed rates# type of drill tool# cutting fluids" of drilling operations withinfluence the response of torque# cutting force# surface roughness# material removal rate#power" in $nC. 2rilling is undertaken 7SS tool only# by using taughi method. .t consist oftwo phases artificial neural network (%%" continued to that (%% is analyzed with S9%ratioofTaughiapproach.Thisworkisuseful inpredictingthemultiresponseswhilecutting different materials in different drilling parameters. A.NAVANTH) T. &ARTHI&EYASHARMAH=I (studyof taguchi methodbased optimization of drilling parameter in dry drilling of al =3'> alloy at low speeds:.nternational Qournal of $ngineering Sciences ;$merging Technologies# (ugust17=3'&..nternational Qournal of $ngineeringand(dvancedTechnology.Q$(T" .SS%* R C*1C# -olume0=# .ssue0'# ,ctober =3'= M. MONTOYAH&Ietalthispaperaimstoestablishthewearmechanismsofcoated and uncoated tungsten carbide drills when drilling carbon fiber reinforced plastics)D!8"9aluminum alloy (l" stacks. 2uring the drilling experiments# thrust forces weremeasured. Dorbothcoatedanduncoateddrills# abrasionwasthedominant tool wearmechanism# affectingtheentirecuttingedgeshigherwearwasobservedonuncoatedtools which caused a significant increase in thrust force during drilling both (l and )D!8materials. YOGENDRATYAGIH>I et al .n this paper the drilling of mild steel with )%)drilling machine by using a tool high speed steel by applying Taguchi methodology. ( +*array# taughi methodandanalysis of variance(%,-(" areusedtoformulate theproceduretriedonthechangeof parameter. 2esignoffers asystematicmethodforoptimization surface finish as well as high material removal rate M!!". TURGAY&IVA&H1I et al this paper focuses ontheoptimizationof drillingparameters using the Taguchi technique to obtain minimum surface roughness !a" andthrust force Df". (number of drillingexperiments were conductedusingthe +'@orthogonal array on a )%) vertical machining centre. The experiments were performedon (.S. &'@ stainless steel blocks using uncoated and coated M&1 7SS twist drills underdry cutting conditions. .t was found that the cutting tool was the most significant factoron the surface roughness and that the feed rate was the most significant factor on thethrust forceA.I. FERN*NDEZ-ABI( H@I et al analyzed the market of turning tools is copedmajoritybyhardmetal toolswith)-2coating. 7owever# availabilityof toolswithsharpcutting edges is essential in light turning of small parts. .n this context# 8-2 process18is optimum for obtaining sharp edges.Therefore# a methodology is presented to evaluatethe performance of 8-2 advanced tools for turning of difficult to machinematerials. Dourcoatings were tested< (lTiSi% n()oS"# (l)rSi% n()!oS"# (lTi% and Ti(l)r%. Theanalysiswasdevelopedcarryingoutweartestsandanalyzingdifferentsignalssuchascutting forces# $2T analysis of inserts# part roughness and insert image analysis. !esultsindicate that the best coatings for turning of difficult to machine materials as austeniticstainless steelsaren()oS and (lTi% coatings# since they offer the best performance. MUSTAFA &URTHBIet al theaimoftheworkreportedherewastoutilizeTaguchi methods to optimize surface finish and hole diameter accuracy in the dry drillingof (l =3=> alloy. (lthough modern metal0cutting cutting speeds &3# >1# and @3 m9min"#feed rates 3.'1# 3.=3# and 3.=1 mm9rev"# depths of drilling '1 and =1 mm"# and differentdrilling tools uncoated and Ti%0 and Ti(l%0 coated" with a ''CF point angle.)onfirmation tests with the optimal levels of machining parameters are carried out. A. RIVERO HCI et al (s a result of the need to automate assembly in the aircraftindustry. The main difficulties6 in dry drilling are accelerated tool wear due to work piece.2ry drilling tests were performed usinguncoateddrills andtwodifferent coatingsproducedbymeans of anarc $vaporation8-2process. $xperiments consistedofmachiningwitha'30mmdiameter three0edgeddrill toproduce=10mmdeepjoiningprocess in aircraft manufacturing .Tool wear evolution and burr size were analyzed# aswell astheimpact of theprocessparametersontorque# power# feed# forceandtooltemperature.SONNYIRAWANH*I et al has investigatedon2rillingoptimizationaims tooptimize controllablevariables during drilling operationsuch as weight onbitandbitrotation speed for obtaining maximum drilling rate. Drom the research the constants thatrepresented several drilling variables had been determined. The rate of penetration for thefield had been predicted based on constants for every data vs. 2epth. Dinally# optimized19weight on bit had been calculated for several data points. .n the end# drilling simulator2rill0Sim 133" was used to prove the results based on actual field data.N.NELSION) R.T.RA&OWS&I) +. FRAN&S)P.WOOLIAMS) P.WEAVER)B.+.+ONESH'3I et al 8otential applicationsof diamond0likecarbon2+)" coatingsrangefromprecisiontoolsandbiomedical implantstomicromechanical devicesandenginecomponents. 5hereuniformcoatingsarerequiredonsubstrateswithcomplexgeometries# plasma enhanced chemical vapour deposition 8$)-2" is often a preferreddeposition method. (s a non0line of sight process# the geometry of the substrate is oftenconsidered negligible. Dor this reason analysis of 8$)-2 coatings# such as amorphouscarbon# has mostly beenconcernedwithreactor deposition variables# such as biasvoltage# pressure and gas ratios. Samples are therefore usually prepared and positioned tominimise the influence of other variables. /y depositing nominally similar 2+) films onsilicon samples positioned horizontally and vertically on the reactor cathode plate it waspossible to examine the variations in the coating characteristics and mechanicalproperties that occur due to the geometry of the substrate being coated. Topographic measurements and analysis of bonding structures revealed significantheterogeneity in the coatings. $lectron microscopy showed variation in surfacestructureaswell as thickness disparities of up to 13Oin the vertical sample. (tomic forcemicroscopy showed roughness# !a# varied from 3.&B nm to '1.> nm between samples.!amanspectroscopyhighlightedvariationsinthesp=9sp&bondingratioswhilstmicrowear tests demonstrated how these variations reduce the critical load performance. Theseeffectsareexplainedintermsofthedepositionmechanismsinvolvedandarerelatedtovariation in deposition species and geometrical field enhancements within thedepositionchamber. .mprovedunderstandingof theselocal variationswill aidintheoptimization of coatings for complex substrate geometries.2.2 CONCULSION 20Drom the above literature survey it is found that the minimum surfacewear2&alloysteels is not yet analyzed. 7ence# in this investigation an attempt has beenmade to study the process parameter (nalysis on7igh carbon steels. This $xperimentalstudyisveryusefulforcarryingoutfurtherstudiesonmetallurgicalpropertiesofthecoated materials.3. TAGUCHI APPROACH /asically# experimental design methods were developed original fisher. 7oweverexperimental design methods are too complex and not easy to use. Durthermore# a large numberof experiments have to be carried out when the number of the process parameters increases# tosolve this problem# the Taguchi method uses a special design of orthogonal arrays to study theentire parameter space with a small number of experiments only. The experimental results arethen transformed into a signal R to R noise S9%" ratio H'IH=I to measure the qualitycharacteristics deviating from the desired values. 4sually# there are three categories of qualitycharacteristics in the analysis of the S9% ratio# i.e.# the R lower R better# the R higher R better# andthe R nominal R better. The S9% ratio for each level of process parameter is compared based ontheS9%analysis. !egardlessofthecategoryofthequalitycharacteristic# agreaterS9%ratiocorresponds to better quality characteristics. Therefore# the optimal level of the processparameters is the level with the greatest S9% ratio Durthermore# a statistically significant with theS9%and (%,-(H&I analyses# the optimal combination of the process parameters can bepredicted. Dinally# a confirmation experiment is conducted to verify the optimal processparametersobtainedfromtheparameterdesign. Thereare&Signal0to0%oiseratiosH1IH@Iofcommon interest for optimization of Static 8roblems. The formulae for signal to noise ratio aredesigned so that an experimenter can always select the largest factor level setting to optimize thequality characteristic of an experiment. Therefore a method of calculating the Signal0To0%oiseratio we had gone for quality characteristic. They are '. Smaller0The0/etter# =. +arger0The0/etter# 21&. %ominal is /est.1. SMALLER IS BETTER Thesignal0to0noiseS9%" ratiois calculatedfor eachfactor level combination. Theformula for the smaller0is0better S9% ratio using base '3 log is< S9% L 0'3UlogS V="9n" 5hereV L responses for the given factor level combination and n L number of responses in the factorlevel combination. 2. LARGER IS BETTER Thesignal0to0noiseS9%" ratiois calculatedfor eachfactor level combination. Theformula for the larger0is0better S9% ratio using base '3 log is< S9% L 0'3UlogS'9V="9n" 5here VL responses for the given factor level combination and n L number of responses in the factorlevel combination. 3. NOMINAL IS BEST The signal0to0noise S9%" ratio is calculated for each factor level combination.The formula for the nominal0is0best . S9% ratio using base '3 log is< S9% L 0'3Ulog s=" 5here sL standard deviation of the4 EXPERIMENTAL SETUP .n the present work# )%) lathe is used to drill holes on $% &': the machining setup isshown in figure 224.1 HIGH SPEED STEEL "HSS# .t is subset of tool steels# commonly used in tool bits and cutting tools. .t is often used inpower0saw blades and drill bits. .t is superior to the older high carbon tools used extensivelythroughthe '*>36sinthat it canwithstandhigher temperatures without losingits temperhardness". This property allows 7SS to cut faster than high carbon steel# hence the name highspeedsteel at room. .nthisstudy#wewereperformedusing'1.CB0mmdiameter7SStwistuncoated drills# 7SS Ti(l%0coated drills# and 7SS )r(l%0coated drills. .t shows thedimensional properties of the drilling tools. To guarantee the initial conditions of each test# a newtool was used in each experiment.4.2 COATED DRILL BITSThe most common methods of chromiumnitride thin filmcreation are physical vapordeposition 8-2# usually sputterdeposition# cathodicarcdeposition or electronbeamheating"and chemical vapor deposition )-2". .nbothmethods# chromiumis sublimated andreactedwith nitrogen in a high0energy# vacuum environment. )hromiumfilm may also be produced onworkpieces by reactive growth for example#annealing" in a nitrogen atmosphere. 234.3 WOR& MATERIAL DETAILS5ork material R $%&' 5ork material thickness 0 '1mmDigure >.&" 5ork material 4.4WOR& MATERIAL PREPARATION Theworkpiecematerial was $%&'# whichis extensivelyusedinthe(utomobileindustry and aerospace industry. The chemical and mechanical properties of $% '* are shownrespectively.4.5 CHEMICAL PROPERTIESC,-./012 C3.435/6/37 C,-./012 C3.435/6/37F-F- 8.%9CC $.3%9S/S/ $.219M7M7 $.819PP $.$19S S $.$19C:C: 1.$49M3M3 $.239N/ N/ $.239A2 A2 4.21924Steel grade and Chemical compositionSteel grade: BS EN 19C( ):0.36 0.44Si( ): 0.10 0.35Mn( ): 0.70 1.00P( ): ! e "S( ): ! e "Cr( ): 0.90 1.20Ni( ): #M$(): 0.150.35%&her():4'P(Sn0.15! ) P0.035* S0.040e) P0.035* S0.025 + 0.050") P0.025* S0.015 + 0.0404. PHYSICAL PROPERTIESHeat TreatmentTensile Strength Rm N/mmYield Stress Re N/mma% on 5.665SoImpact Izod Impact !"# $roo% Stress rp&.'Hardness H(Size mmR 700/850 495 15 34 28 480 201/225>100250S 775/925 555 13 27 22 540 223/277>150250S 775/925 585 15 54 50 570 223/277>63150T 850/1000 680 13 54 50 665 248/302 >2910025U 925/1075 755 12 47 42 740 269/331 >1363V 1000/1150 850 12 47 42 835 293/352 >629W 1075/1225 940 12 40 35 925 311/375 >619Table >.@" 8hysical properties4.! SURFACE FINISH MEASUREMENTSS;: