This article presents the results of experiments that concerned the verification of machined surface conditions of workpieces from a new austenitic stainless steel with Extra Low Carbon (ELC) Cr22Ni9MoTi compared with stainless steels Cr18Ni8. The results of cutting zone evaluation under cutting speed 80 m/min, depth of cut 2,75 mm and feed 0,08 mm per rev., a definition of shear level angle Φ1. For Cr22Ni9MoTi steel Φ1 is 36° to 39°. The acquired results are interesting in that for the defined conditions we can achieve a quality outer surface after cutting with roughness parameters down to around 0,65 μm at cutting speed 80 m/min and feed 0.08 mm per rev.Rad prikazuje rezultate eksperimentalnog istraživanja koji se odnose na verifikaciju uvjeta strojne obrade radnih komada od austenitnog nehrđajućeg čelika sa posebno niskim sadržajem ugljika (ELC) Cr22Ni9MoTi u usporedbi sa nehrđajućim čelikom Cr18Ni8. Rezultati ocjene rezne površine kod brzine rezanja 80 m/min, dubine reza 2,75 mm i posmaka 0,08 mm po okretaju definiraju vrijednost smičnog kuta Φ1. Za čelik Cr22Ni9MoTi Φ1 je 36° do 39°. Prikupljeni rezultati su zanimljivi za definiranje uvjeta pod kojim se može postići kvaliteta hrapavosti vanjske površine nakon rezanja do oko 0,65 μm kod brzine rezanja 80 m/min i posmaka 0,08 mm po okretaju

A. Panda

J. Jurko

M. Gajdoš

English

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J. JURKO, M. GAJDO[, A. PANDASTUDY OF CHANGES UNDER THE MACHINED SURFACE ANDACCOMPANYING PHENOMENA IN THE CUTTING ZONE DURINGDRILLING OF STAINLESS STEELS WITH LOW CARBON CONTENTReceived – Prispjelo: 2010-04-11Accepted – Prihva}eno: 2010-10-20Original Scientific Paper – Izvorni znanstveni radINTRODUCTIONPrecise and reliable information on the machina-bility of a material before it enters the machining pro-cess is a necessity, and hypotheses must be testedthrough verification of actual methods. This article pres-ents conclusions of machinability tests on austeniticstainless steels with low carbon content and describesappropriate parameters for the cutting zone during theprocess of drilling. These trends confirm that the cuttingprocess remains one of the basic manufacturing technol-ogies. In this study presents the conclusions of cuttingprocess analysis on a new austenitic stainless steel withlow carbon contents Cr22Ni9MoTi, which applicated infood processing industry, and describes study ofchanges under the machined surface and accompanyingphenomena the process of drilling. The content of thisarticle also focuses on the analysis of selected indicatorsof steel machinability by 1: it is quality of machinedsurface and their parameters (precisions of dimensionholes, morphology of surface, residual stresses, plasticdeformation, depth of hardening layer, surface rough-ness, microhardness, defects of surface). The results ofthe article are conclusions for working theory and prac-tice for drilling of stainless steels.Automated production of in the sense of machineproduction has characteristic features: a reduction ofproduction costs, stimulation of the development of cut-ting tools, and changes in the construction of machinetools, all of which work against the creation of optimaltechnological methods, which thrusts the technologicalprocess of cutting into a more important position by 2.Stainless steels are fundamentally subdivided by theirchemical composition and metallographic structure.Austenitic steels are the most extensive and thus themost important category of stainless steels.EXPERIMENTAL WORKThe experiments were performed in laboratory con-ditions and verified in real conditions during manufac-ture. The set-up used contained the following compo-nents: Machine: VMF-100 CNC machining centrumTool: a new screw drill design with TiAlN layer, di-ameter d=5,5 mm, and corner angle 2r=120o, Solid car-METALURGIJA 50 (2011) 2, 113-117 113This article presents the results of experiments that concerned the verification of machined surface conditionsof workpieces from a new austenitic stainless steel with Extra Low Carbon (ELC) Cr22Ni9MoTi compared withstainless steels Cr18Ni8. The results of cutting zone evaluation under cutting speed 80 m/min, depth of cut2,75 mm and feed 0,08 mm per rev., a definition of shear level angle 1. For Cr22Ni9MoTi steel 1 is 36° to 39°.The acquired results are interesting in that for the defined conditions we can achieve a quality outer surface af-ter cutting with roughness parameters down to around 0,65 m at cutting speed 80 m/min and feed 0.08 mmper rev.Key words: steel, surface, tool, drilling, cutting zoneStudija promjena ispod obra|ene povr{ine i pridru`eni fenomeni u zoni rezanja tijekom bu{enjanehr|aju}eg ~elika s niskim sadr`ajem ugljika. Rad prikazuje rezultate eksperimentalnog istra`ivanja kojise odnose na verifikaciju uvjeta strojne obrade radnih komada od austenitnog nehr|aju}eg ~elika sa posebnoniskim sadr`ajem ugljika (ELC) Cr22Ni9MoTi u usporedbi sa nehr|aju}im ~elikom Cr18Ni8. Rezultati ocjene rez-ne povr{ine kod brzine rezanja 80 m/min, dubine reza 2,75 mm i posmaka 0,08 mm po okretaju definiraju vri-jednost smi~nog kuta 1. Za ~elik Cr22Ni9MoTi 1 je 36° do 39°. Prikupljeni rezultati su zanimljivi za definiranjeuvjeta pod kojim se mo`e posti}i kvaliteta hrapavosti vanjske povr{ine nakon rezanja do oko 0,65 m kod brzinerezanja 80 m/min i posmaka 0,08 mm po okretaju.Klju~ne rije~i: ~elik, povr{ina, alat, bu{enje, zona rezanjaISSN 0543-5846METABK 50(2) 113-117 (2011)UDC – UDK 669.14.018:621-4:621.9.02:621.954=111J. Jurko, M. Gajdo{, A. Panda, Faculty of Manufacturing Technologies,Tu Ko{ice, Pre{ov, Slovakiabide drill were clamped on high accuracy collet hydrau-lic holder.Workpiece: the materials to be machined were typeof austenitic stainless steels with chemical compositionlisted in Table 1. The dimension of each piece was bxhxl(50x50x100) mm. The cutting process employed wasdrilling with dry machining (DM), and the cutting speedwas defined at intervals of vc=50 to 100 m/min, the feedwas advanced from intervals of f=0,04 to 0,2 mm perrev., and cutting depth ap=2,75 mm.Table 1 Chemical composition of stainless steelsType of Stainless SteelChemicalcomposition/mas.%CHE Cr18Ni8 Cr22Ni9TiMoC 0,6 0,04Cr 18,0 22,0Ni 8,0 9,0Mn 2,2 1,6Ti - 0,6Mo - 1,8P 0,03 1,2S 0,03 0,03RESULTS AND DISCUSSIONCutting zone (shows in Figure 1) is a summary termfrom the region during cutting. To properly describe thecutting zone it is necessary to describe the regions andtest parameters: primary plastic deformation zone (pri-marily an examina-tion of phenomena associated withthe creation and formation of chips, with the effect of thecomponents of cutting force-the state of strain deforma-tion, the location of the angle of the shear level, chipcompression, the temperature field, chip shape, chip for-mation and separation, the effect of the components ofcutting force) by 3-5.Secondary plastic deformation zone (primarily anexamination of phenomena associated with friction andcutting wedge wear, and also with the generation of heatand temperature - the location of the grain angle, thecontact length of the cutting wedge and the face plate,friction stress and creation of Built Up Edge (BUE),friction, the generation of heat and temperature and themechanism of tool wear. Tertiary plastic deformationzone (primarily an examination of the phenomena asso-ciated with the shaping creation of the machined sur-face, its profile, morphology, qualities and inheritedtraits-contact of the machined surface and the worn sideplate). Cutting surface, its properties and integrity. Thegradually - deformed region of the cut layer.In tested cutting zone area was defined this areas:non-deformed material structure, plastic deformationzone with defined width (shear volume, central part ofthe chip, displaying a high level of strain hardening, re-gion of the chip deformed by the action of friction, theloose central part of the chip, irregular in shape, cuttingsurface of the tool, the contact region between chip andcutting tool face, built up edge on the cutting tool corner,the contact region between the machined surface andcutting tool flank.Researching the cutting zone (the interaction be-tween the tool, the workpiece, and the chips) is to cap-ture its state at the moment of the creation of the chip(the so-called root of the chip). Cutting zone testing andanalysis under a Semi Electron Microscope (SEM), thatdifferent regions of smoothly-formed chips can be de-scribed. It is important to define the shear level in thecutting zone. The first zone between the chip and theworkpiece, called the shear layer, divides the non-de-formed region from the deformed chip under the angleof the shear layer, (indicated by 1) which is defined asidentical to the boundary angle of deformation. The sec-ond zone is the zone where cracks arise and widen.Cracks arise as a result of the strength of the material onthe cut level and are caused by the dividing of the mate-rial in the form of chips. A chip arises along the entiresurface of the tool, and the third zone is the zone of in-tensive friction between the chip and the cutting tool.The engaged cutting wedge is subject to intensive stressnot only in the face plate, but also on the side plate in thefourth zone. The results of cutting zone evaluation undercutting conditions (vc=80 m/min, ap=2,75 mm andf=0,08 mm per rev.) are a definition of shear level angle1 and the texture angle 2. For Cr22Ni9MoTi steel 1is 36° to 39°, 2,I is 28° to 30° and 2,II is 38° to 44°.Also important are the values of the depth of the plastic-ally-deformed material (of the chip), the Flow zone andthe strain hardness of the machined surface. For the de-114 METALURGIJA 50 (2011) 2, 113-117J. JURKO et al.: STUDY OF CHANGES UNDER THE MACHINED SURFACE AND ACCOMPANYING PHENOMENA ...Figure 1 Cutting zone in drilling – chip formatting, vc=80 m/min, ap=2,75 mm and f= 0,08 mm perrev.fined experimental conditions cutting speed vc=80m/min, depth of cut ap=2,75 mm and feed f=0,08 mmper rev., the values stated in Table 2 were achieved.Table 2 Cutting Zone ParametersParametersCr22Ni9TiMoCr18Ni8Cutting widthht /mmh1 /mm (15-18) %.ht (20-22) %. hth2 /mm (75-80) %. ht (60-56) %. hthFZ /mm (5-7) %. ht (20-22) %. htDepth of the hardenedmachined surf. hh / mm0,05 0,12Depth of the shear layerhSP / mm0,01-0,020,02-0,04Where ht is the cutting width, ht=hPD+ hFZ, h1 is thedepth of the I. zone, h2 is the depth of the II. zone, hFZ isthe depth of the flow zone, hPD is the depth of the plastic-ally-deformed material, hPD=h1+ h2, hh is the depth ofthe hardened machined surface and hSP is the depth ofthe shear layer, by 6,7.The thickness of the cut layer continually varies chipthickness. Chip formation is described through the the-ory of plasticity. The presence of strain lines in chip for-mation is depicted in Figure 2. The strain line field ex-tended to the region of plastic deformation, the ma-chined surface, and the cut layer (the chip). Strain linesrepresent an extensive high-intensity deformation. Theprocess of cutting is the mutual interaction between thetool and the workpiece, which is controlled by manyphenomena, which creates a synergistic effect. The edgepreparation will determine the residual stress patternnear the machined surface in Figure 3.Every tool is damaged in the process of cutting by8,9. Wear mechanisms are activated in the cuttingzone during the interaction of the elements of the cuttingedge of the tool and the workpiece, and under the influ-ence of temperature, and by the fact that friction de-pends on the interaction of the clean metal surface be-tween the front plate of the cutting edge of the tool andthe chip, as stated by 10. According to DIN 50321 it isrecognized four fundamental mechanisms of tool wear:adhesive wear, abrasive wear, fatigue wear, triboche-mical reaction wear. The mechanism of wear means thesynergistic effect of factors that create a change in mat-ter, a change in volume, i.e., a change in cutting edge di-mension by 11. Sintered carbide tools are not as sensi-tive to temperature on touching plates as high-speedsteel, and can be used to attain higher performance, butin this case they have greater pressure stress, which di-rectly influences the process of adhesive wear by 12.The criterion VBk=0,3 mm was applied during evalua-tion. The cutting process conditions were designedbased on the needs of the material and on the operationof the finished surface. The results of the long-term testafter exhaustive analysis is the Taylor Tool Life Equa-tions for individual types of stainless steels:Tvc121522 1042 4552,,for steel Cr22Ni9MoTiTvc1052 36 1042 3905,,for steel Cr18Ni8Damage to the cutting edge of the tool in conditionsgreater than vc=80 m/min, ap=2,75 mm and f= 0,08 mmper rev. is shown in Figure 4. Face plate tool damage isdefined by belts that are consistent with the temperaturefields on Figure 5.The micro geometry of the outer surface is character-ised by micro geometric chipping. For evaluating theMETALURGIJA 50 (2011) 2, 113-117 115J. JURKO et al.: STUDY OF CHANGES UNDER THE MACHINED SURFACE AND ACCOMPANYING PHENOMENA ...Figure 3 Dependence residual stresses – machined sur-face, vc= 80 m/min, ap=2,75 mm, f= 0,08 mmper rev.Figure 2 Strain lines in chip formation, vc= 80 m/min,ap=2,75 mm, f= 0,08 mm per rev.outer surface after drilling and defining the cutting pro-cess conditions, the following parameters were used inthe investigation: the outer surface roughness parameterRa and Rz was measured on measuring tool - Talysurf.Morphology of the outer surface after cutting were eval-uated after careful analysis using an SEM.The acquired results are interesting in that for the de-fined conditions we can achieve a quality outer surfaceafter cutting with roughness parameters down to aroundRa=0,65 m. When drilling, it is not an advantage to afeed of lower than 0,1 mm for the roughness criteria ofthe outer surface. Very good results were mainlyachieved when cutting speed was 80 m/min and the feedwas 0,08 mm per rev. The roughness value for the outersurface, Ra, reached around 0,65 m. Similar roughnessin the outer surfaces of the individual type is not basedon differences in the quality of the outer surface. Thevalue of Rz (following ISO 4287, it is the upper limit ofunevenness in outer surfaces) did not exceed a value of3,0 m. Before drilling, the hardness of the basic struc-ture of Cr22Ni9MoTi steel was measured at 195 HB.After drilling, outer surface hardness was measured andthe results is outer layer hardness increased by 15 to 20% for Cr22Ni9MoTi steel. It is very significant that thehardness of the outer surface after cutting increases withan increase in cutting speed and decreases with an in-crease in feed value.CONCLUSIONIt is important for both theory and practical applica-tions that essential conclusions come from measurementand analysis. Results were acquired under laboratoryconditions and performed in praxis. The conclusions areas follows: defined tool life equation following Taylor,defined the equation for the cutting strength compo-nents, confirmation of surface strain hardening (changein mechanical properties) after cutting. Defined coeffi-cients for kinetic machining of austenitic stainlesssteels, whereby Cr22Ni9MoTi steel Kv=0,68-0,72, forCr18Ni8 steel, the coefficient of kinetic machining wasKv=0,65-0,68. It is very important information for pro-cess machining.Acnowledgments: The authors would like to thank inthe VEGA grant agency for supporting research workand co-financing the projects: #01/3173/06, #3/7166/09and #1/0048/10.REFERENCES1. V. Tipnis, R.A. Joseph Testing for machinability. Interna-tional sympo-sium on influence of metallurgy on machina-bility. Deaborn Ohio, 1975, 11-30.2. H. Zum Gahr Microstructure and Wear of Materials.Amsterdam, 1987.3. J.H. Dautzenberg The Minimum Energy Principle for theCutting Process in Theory and Experiments. Annals of theCIRP, 32, 1, 1983, 223-227.4. W.R. DeVries Analysis of material removal processes. NewYork, 1991, 254.5. J. Jurko Monitoring and Diagnosis of Drill Wear and theThermodynamic Phenomenas of Material Removal by dril-ling of Stainless Steels. Experimental Analysis of Nano andEngineering Materials and Structures. Atheny, 2007, 77-78.6. J. Jurko, A. Panda, M. Gajdo{ Accompanying phenomenain the cutting zone machinability during turning of stainlesssteels. International Journal Machining and Machinabilityof Materials, 5 (2009) 4, 383-400.7. J. Jurko Verification of cutting zone machinability duringdrilling of austenitic stainless steels. Proceedings ofSPIE-The international Society for optical Engineering.Nanjing, 2008, 7375 (2) 2009.116 METALURGIJA 50 (2011) 2, 113-117J. JURKO et al.: STUDY OF CHANGES UNDER THE MACHINED SURFACE AND ACCOMPANYING PHENOMENA ...Figure 4 Damage to the cutting edge of the tool, vc=80 m/min, ap=2,75 mm, f= 0,08 mm per rev.Figure 5 Face plate tool damage, vc= 80 m/min,ap=2,75 mm, f= 0,08 mm per rev.8. Nam,P. Suh New Theories of Wear and Their Implicationsfor Tool Materials. Wear, 62 (1980), 1-20.9. P. L. B. Oxley Mechanics of Metal Cutting. Internationalconference in production engineering, Pittsburg, (1963),50.10. J. Tlusty, Z. Masod Chipping and Breakage of Carbide To-ols. Journal of Engineering for industry, 109 (1987) 3,403-412.11. E. Usui, A. Hirota Analytical Prediction of Three Dimensio-nal Cutting Process. Journal of Engineering for industry 100(1978) 2, 236-243.12. P. K. Venuvinod et all Tool Life in Oblique Cutting as a fun-ction of Computed Flank Contact Temperature. Journal ofengineering for industry, 112 (1990) 4, 307-312.Note: The responsibile for English language is the lecturer from TUKo{ice.List of symbolsap depth of cut, (mm)b width, (mm)d diameter, (mm)f feed (mm per rev.)1 shear angle (°)2 texture angle (°)h high, (mm)hFZ depth of the flow zone, (mm)hh depth of the hardened machined surface, (mm)hPD depth of the plast.-def. mat., (mm)hsm width of machined surface, (mm)hSP depth of the shear layer, (mm)ht cutting width, (mm)h1 depth of the I. zone, (mm)h2 depth of the II. zone, (mm)l length, (mm)Ra surface roughness - mean arithmeticaldeviation, (m)Rz surface roughness, (m)VBk tool wear criterion, (mm)vc cutting speed , (m/min) r corner angle (°)AbbreviationsCHE – Chemical ElementAcronymsDM - Dry MachiningSEM - Semi Electron MicroscopeMETALURGIJA 50 (2011) 2, 113-117 117J. JURKO et al.: STUDY OF CHANGES UNDER THE MACHINED SURFACE AND ACCOMPANYING PHENOMENA ...

Studija promjena ispod obrađene površine i pridruženi fenomeni u zoni rezanja tijekom bušenja nehrđajućeg čelika s niskim sadržajem ugljika

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