© Strojni{ki vestnik 48(2002)3,133-142 © Journal of Mechanical Engineering 48(2002)3,133-142 ISSN 0039-2480 ISSN 0039-2480 UDK 621.9.01:621.912 UDC 621.9.01:621.912 Pregledni znanstveni ~lanek (1.02) Review scientific paper (1.02) Prehod iz obi~ajne v zelo hitro obdelavo in analiza oblikovanja odrezkov The Transition from the Conventional to the High-Speed Cutting Region and a Chip-Formation Analysis Sabahudin Ekinovi} - Slavko Dolin{ek - Janez Kopa~ - Matja` Godec Zaradi najnovejših dosežkov razvoja na področju konstrukcije obdelovalnih strojev (glavnega vretena, podajalnih pogonov ipd.) je zelo hitra obdelava postala cenovno ugoden obdelovalni postopek za izdelavo izdelkov z veliko kakovostjo obdelane površine, zaradi manjših vplivov na obdelano površino in doseganja odličnih dimenzijskih natančnosti. S tem, ko poznamo tovrstne značilne prednosti zelo hitre obdelave pred običajno, je eno od ključnih vprašanj povezano z določitvijo ustreznih vrednosti rezalnih hitrosti, ki ustrezajo zelo hitremu območju. Vzrok za to lezi v dejstvu, da se vpliv na obdelovalne značilnosti povečuje, ko prehajamo v območje velike hitrosti. Po drugi strani pa prevelike rezalne hitrosti niso priporočljive zaradi povečanja obrabe orodij in večje porabe energije na obdelovalnih strojih. Za podporo pri reševanju teh problemov je v članku predstavljen postopek, ki sloni na analizi mehanizma oblikovanja odrezkov in njihove oblike na podlagi uporabe metalografskih metod. © 2002 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: stroji obdelovalni, obdelave visokohitrostne, oblike odrezkov, hitrosti rezanja) As a result of advances in machine-tool design (main spindle, feed drives, etc.), high-speed milling has become a cost-effective manufacturing process for making products with a high surface quality, low variations of the machined surface and excellent dimensional accuracy. Taking into account the evident advantages of high-speed machining over conventional machining, a key issue is to identify those cutting speeds that correspond to high-speed machining. The simple reason for this is that machining effects increase when entering the high-speed region but, on the other hand, an enormous increase in the cutting speed is not advisible due to the appearance of higher tool wear and machine-tool energy consumption. In order to solve the problem this paper describes a procedure based on a chip-formation mechanism and a chip-shape analysis, together with the use of metallographic methods. © 2002 Journal of Mechanical Engineering. All rights reserved. (Keywords: machine tools, high speed cutting, chip formation, cutting speeds) 0 UVOD Obdelava z veliko hitrostjo se šteje kot eno od novejših, perspektivnih izdelovalnih tehnologij zaradi višje produktivnosti, doseganja odličnih kakovosti obdelane površine, manjših vplivov na obdelano površino in ustreznih dimenzijskih obdelovalnih natančnosti. Od vseh zelo hitrih metod ima zelo hitro frezanje še najpomembnejši pomen ([1] do [3]). Zaradi prednosti, ki jih dajejo izboljšane karakteristike obdelovalnih strojev (glavno vreteno, podajalni pogoni ipd.), je zelo hitro frezanje postalo cenovno učinkovit izdelovalni postopek. Zaradi tega se zelo hitra obdelava veliko uporablja v letalski in avtomobilski industriji za obdelavo strojnih delov zapletenih oblik iz aluminija in njegovih zlitin. Zaradi napredka na področju rezalnih orodij in odrezovalnih tehnologij se v zadnjem času zelo hitro frezanje 0 INTRODUCTION High-speed machining is a relatively new production technology that allows a higher productivity, an excellent surface finish and a good dimensional accuracy in the manufacturing process. High-speed milling is one of the most important of all high-speed cutting methods ([1] to [3]). Thanks to the advances in machine-tool performance as a result of improvements to the main spindle, feed drives, etc., high-speed milling has become a cost-effective manufacturing process that produces products with a high surface quality, low variations in the machined surface and dimensional accuracy. High-speed milling was first used successfully in the aircraft and automotive industries for machining complex machine parts made of aluminum and its alloys. Recently, with the advances in cutting-tool materials and gfin^OtJJIMISCSD 02-3 stran 133 IVUgfTMECl Ekinovi} S. - Dolin{ek S. - Kopa~ J. - Godec M.: Prehod iz obi~ajne - The Transition from uporablja tudi za obdelavo legiranih jekel v kaljenem stanju (trdote od 30 HRc pa do 60 do 65 HRc) ([4] in [5]). Kar nekaj kriterijev obstaja za definiranje območja zelo hitre obdelave oziroma kriterijev za določitev meje med običajno in zelo hitro obdelavo, takšni so npr. [6]: velikost rezalne hitrosti, število vrtljajev vretena ali vrtečega se orodja (hitrost vretena), DN število (DN je premer vretena v mm pomnožen s hitrostjo vretena v vrt/min), dinamično obnašanje in material obdelovanca. Najbolj ustrezna definicija zelo hitre obdelave je tista, ki sloni na vrsti materiala obdelovanca [6] (sl. 1). Na primer, vrednosti rezalne hitrosti med 500 do 700 m/min se nanašajo na zelo hitro območje za primere pri obdelavi legiranih jekel, po drugi strani se te vrednosti rezalne hitrosti šteje za počasnejše območje pri obdelavi aluminija. 7 <^ 6 <^ 5 <^I 4 iff J> - ¦ 100jm '100m 100um a) b) c) d) Sl. 2. Mikrostruktura obdelovanih jekel: a) Ck15 (156 HV), b) X5CrNi189 (221HV), c) X63CrMoV51 (zarjeno 282 HV), d) X63CrMoV51(kaljeno 629 HV). Fig. 2. Microstructures of the machined steel grades: a) Ck15 (156 HV), b) X5CrNi189 (221HV), c) X63CrMoV51 (annealed, 282 HV), d) X63CrMoV51(quenched, 629 HV). jeklo / steel (Ck15) jeklo / steel (XCrNi189) jeklo / steel (X63CrMOV51) zarjeno / annealed »L T> iff m jeklo / steel (X63CrMOV51) kaljeno / quenched KL %L z *>/ rezalna hitrost /cutting speed, vc (m/min) 50 150 300 1500 Sl. 3. Oblika odrezkov pri obdelavi različnih jekel Fig. 3. Chip shapes produced during machining X5CrNi189 in zarjeno jeklo X63CrMoV51, medtem ko smo za kaljeno jeklo X63CrMoV51 uporabili hitrosti 50, 150, 300 in 1500 m/min. Oblika odrezkov pri odrezovanju je prikazana na sliki 3. 2 REZULTATI IN RAZPRAVA Fotografije mikrostrukture odrezkov pri obdelavi jekla Ck 15 so prikazane na sliki 4. Pri rezalni hitrosti v = 150 m/min (sl. 4a) je povprečna debelina odrezka 0,34 mm, tako da znaša koeficient nakrčevanja odrezka k = 0,34/0,1 = 3,4. Struktura materiala ustreza običajni obliki deformacije z vzdolžno deformiranimi zrni. Na zunanji strani odrezka je mogoče opaziti drugotno deformacijsko plast. Glede na znano klasifikacijo oblike odrezkov [12] je to značilen primer zveznega odrezka. Ta oblika je značilna pri obdelavi deformljivih jekel pri uporabi majhnih rezalnih hitrosti. Pri rezalni hitrosti v = 1500 m/min (sl. 4b) je povprečna debelina odrezka 0,13 mm in koeficient nakrčevanja k = 0,13/0,1 = 1,3. Struktura je prav tako deformirana (stlačena), pojavlja pa se več izrazitih vrhov na zunanji strani odrezka (zob - označeno s X63CrMoV51 (annealed) steel. The X63CrMoV51 (quenched) steel was machined with cutting speeds of 50, 150, 300 and 1500 m/min. The chip shapes pro-duced during machining are presented in Fig. 3. 2 RESULTS AND DISCUSSION The microphotos of the chips produced during the Ck15 machining are shown in Fig .4. When the cutting speed (vc) was 150 m/min, Fig. 4a, the average chip thickness was 0.34 mm, so the chip compression coefficient (l) was 0.34/0.1 = 3.4. The structure of the material suggests a classical type of deformation with elongated grains. A secondary deformation layer appears on the inner side of the chip. According to the classification of chip types given in [12] this is an example of a steady-state continuous chip. This type of chip is characteristic of ductile steel grades that are machined with low cutting speeds. When vc = 1500 m/min, Fig. 4b, the average chip thickness was 0.13 mm, with l = 0.13/0.1 = 1.3. The structure is also deformed (elongated) but with more intense chip peaks (teeth): see arrows A in Fig. 4b. By analyzing the elongation of the grains in VBgfFMK stran 136 Ekinovi} S. - Dolin{ek S. - Kopa~ J. - Godec M.: Prehod iz obi~ajne - The Transition from puščico A na sliki 4b). Na podlagi analize deformacije strukture zrn lahko opazimo posamezne deformacijske proge, ki nakazujejo možnost segmentacije odrezka, če bi se rezalna hitrost zvečala prek 1500 m/min (puščica B, sl. 4b). Po obliki odrezka in njegove strukture lahko kljub vsemu sklepamo, da razmer pri obdelavi žarjenega jekla Ck 15 (mikrotrdote 156 HV) z rezalno hitrostjo v = 1500 m/min še ne moremo šteto za zelo hitro obdelavo. Tudi drugotna deformacijska cona je tanjša kakor pri prejšnjem primeru. the structure we can see some lines that point to the possibility of chip segmentation if the cutting speed increases over 1500 m/min: see arrows B, Fig. 4b. Nevertheless, the chip shape and its structure definitely show that milling with a cutting speed of 1500 m/min cannot still be considered as high-speed machining in the case of annealed Ck 15 with a microhardness of 156 HV. The secondary deformation layer is not as thick as in the previous case. drugotna deformacijskal plast secondary deformation layer L !*\ Y ¦ B drugotna deformacijskal plast secondary deformation layer_______ a) rezalna hitrost 150m/min cutting speed 150 m/min b) rezalna hitrost 1500m/min cutting speed 1500 m/min Sl. 4. Prečni prerez odrezkov, nastalih pri obdelavi jekla Ck 15 Fig. 4. Cross-section of chips produced during machining of Ck 15 Slike mikrostrukture odrezkov, nastalih pri obdelavi nerjavnega jekla X5CrNi189, so prikazane na sliki 5. Pri rezalni hitrosti v = 150 m/min so odrezki podobni žagasti obliki, toda z močno povezanimi segmenti. Vendar tovrstna oblika odrezkov ni rezultat segmentacije, ampak močne plastične deformacije materiala. To je tudi prikazano v povečanem izrezu na sliki 5a. V tem primeru se notranji lomi pojavijo zaradi intenzivne deformacije. V strukturi tega jekla so poligonalna avstenitna zrna očitno plastično deformirana. Slika 5b pa kaže neobičajno obliko odrezka pri obdelavi tega jekla s hitrostjo v = 1500 m/min. Kljub veliki rezalni hitrosti s slike ni mogoče opaziti segmentacije odrezka kot posledice plastične deformacije. Na zunanji strani odrezka se pojavi neka vrsta nabiranja materiala. Očitno je, da je to neenakomerna zvezna oblika odrezka. Nabiranje materiala in spremenljivost deformacijskega postopka je mogoče tudi jasno opaziti na posnetku SEM (detajl na sliki 5b). Glede na dobljeno obliko odrezka za ta material ne moremo postaviti sklepov o tem, ali je hitrost odrezovanja v = 1500 m/min že v območju zelo hitre obdelave ali ne. Slike mikrostrukture odrezkov, dobljenih pri obdelavi žarjenega jekla X63CrMoV51, so prikazane na sliki 6. Pri rezalni hitrosti v = 150 m/min (sl. 6a) je odrezek podoben tistim, dobljenih pri obdelavi jekla Ck15 (sl. 4a), le da je koeficient nakrčevanja manjši (k = 0,17/0,1 = 1,7). Opaziti je tudi večji kot nagnjenosti The microphotos of chips produced during the machining of XcrNi189 are shown in Fig. 5. When vc was 150 m/min the chip had a saw-tooth shape with strongly bonded segments. However, this type of chip is not the result of chip segmentation, rather, it occurs because of severe plastic deformation of material, which is shown in detail in Fig. 5a. In this case the initial crack appears due to intense deformation. The polygonal austenite grains are evidently elongated in the structure of this particular steel grade. Fig. 5b shows an unusual shape of chip, which was produced with a cutting speed of 1500 m/min. No chip segmentation appears as this steel passes through the plastic deformation region, even at high cutting speeds. There is some kind of material “accumulation” on the outer side of the chip; this is obviously an unsteady-state continuous chip. The accumulation of material and the unsteadiness of the process are clearly visible on the SEM photograph (detail in Fig. 5b). By looking at the chip shape it is not possible to conclude whether the cutting speed of 1500 m/min belongs to the high-speed machining region for this type of steel grade. The microphotos of the chip produced during the machining of X63CrMoV51 (annealed) are shown in Fig. 6. When vc was 150 m/min (Fig. 6a) the chip looks like the one produced by machining Ck15 (Fig. 4a), only with a lower chip compression coefficient (l = 0.17/0.1 =1.7) and a higher grain texture angle (i.e. gfin^OtJJIMISCSD 02-3 stran 137 iMlglTMlGCl Ekinovi} S. - Dolin{ek S. - Kopa~ J. - Godec M.: Prehod iz obi~ajne - The Transition from - 1 T m w - m t ¦ lomi cracks 9 f ¦ 20Vm 1-----------1 a) rezalna hitrost 150 m/min cutting speed 150 m/min b) rezalna hitrost 1500 m/min cutting speed 1500 m/min Sl. 5. Prečni prerez odrezka, nastalega pri obdelavi nerjavnega jekla X5CrNi189 Fig. 5. Cross-sections of chips produced during X5CrNi189 machining strukture (kot med drugotno deformacijo zrn in strižno ravnino). Ta oblika odrezka je tudi značilen primer enakomernega, zveznega odrezka. Pri obdelavi tega jekla z rezalno hitrostjo v = 1500 m/min (sl. 6b) pa je odrezek segmentiran c in nazobčan. Nastaja na podlagi intenzivnega striga vzdolž mej med posameznimi segmenti, zato je to tudi tipičen primer segmentnega odrezka, nastalega na podlagi lokaliziranega striga. Segmenti so skoraj enake širine (povprečje 0,06 mm) in oblike, kar kaže na stabilnost postopka deformacije odrezka. Natančno je to prikazano na fotografiji SEM na sliki 6b. Preostali detajli na fotografiji pa prikazujejo deformiran in nedeformiran del odrezka. Iz oblik odrezkov na sliki 6 lahko sklepamo, da rezalna hitrost v = 150 m/min ustreza običajnem območju, hitrost v c = 1500 m/min pa zelo hitrem območju obdelave. c Slika 7 prikazuje mikrostrukture odrezka, nastalega pri obdelavi kaljenega jekla X63CrMoV51. Pri rezalni hitrosti v = 50 m/min (sl. 7a) je mehanizem oblikovanja odrezkov enak kakor v primeru obdelave konstrukcijskega jekla Ck15 (sl. 4a) in žarjenega orodnega jekla X63CrMoV51 (sl. 6a). Ugotovimo lahko, da so hitrosti obdelave v območju običajnih rezalnih hitrosti. Pri obdelavi z rezalno hitrostjo v = 150 m/min (sl. 7b) nastaja tipično nazobčana, segmentirana oblika the angle between the secondary grain elongation direction and the shear plane). This kind of chip is also a typical example of a steady-state continuous chip. However, when machining with vc = 1500 m/ min (Fig. 6b) the chip is segmented and saw-tooth shaped. In this case the chip is formed by an intense shear along the boundaries between adjacent segments, and this is a typical example of a shear-localized segmental chip. These segments are almost of equal width (average 0.06 mm) and shape, which points to the stability of the chip-formation process. The SEM photograph shown in the detail of Fig. 6b also demonstrates this. The other detail of the same figure clearly shows the undeformed and deformed parts of the chip. On the basis of chip shapes shown in Fig. 6 we can conclude that a cutting speed of 150 m/min is in the conventional speed range, and a cutting speed of 1500 m/min is in the high-speed range. Fig. 7 shows the microphotos of a chip produced during X63CrMoV51 (tempered) machining. When vc = 50 m/min (Fig.7a), the chip-formation mechanism is the same as in the case of Ck15 (Fig. 4a) and X63CrMoV51 (annealed, Fig. 6a) machining. Obviously, this is the conventional cutting-speed region. During machining with a cutting speed of 150 m/min (Fig. 7b) the chip is segmented and possesses VBgfFMK stran 138 Ekinovi} S. - Dolin{ek S. - Kopa~ J. - Godec M.: Prehod iz obi~ajne - The Transition from b) rezalna hitrost 1500 m/min cutting speed 1500 m/min nedeformiran material undeformed material deformiran . material deformed material Sl. 6. Prečni prerez odrezka pri obdelavi žarjenega jekla X63CrMoV51 Fig. 6. Cross-sections of chips produced during (annealed) X63CrMoV51 machining odrezka. V nasprotju z obdelavo tega jekla v žarjenem stanju s hitrostjo v = 1500 m/min (sl. 6b) se v tem primeru pojavi tako imenovana bela plast, ki kaže, da se v postopku oblikovanja odrezka pojavlja postopek termičnega mehčanja. V splošnem je žagasto oblikovanje odrezkov povezano z oblikovanjem odrezkov pri obdelavi trdih materialov. To lahko povezujemo s krhkostjo materiala in nastajanjem velikih tlačnih napetosti na obdelovancu. Med odrezovanjem namesto plastičnega tečenja materiala nastajajo lomi na površini obdelovanca. Ti lomi sproščajo notranjo energijo, s tem delujejo na dele materiala kot drsne ravnine in omogočajo posameznemu delu odrezka da odteka med stičnimi površinami. Zaradi visokih vrednosti lokalnih temperatur nastanejo bele plasti martenzita. Termalno mehčanje materiala zatorej postaja vse pomembnejši vpliv na plastične lastnosti materiala v primerjavi z učinki deformacijskega utrjevanja. Deformacijsko utrjevanje je prevladujoč postopek med obdelavo teh vrst jekel z majhnimi rezalnimi hitrostmi (v = 50 m/min), ko pa rezalna hitrost doseže vrednosti 150 m/min, prevladujoč proces postane oblikovanje notranjih razpok in termičnega mehčanja. To se posebej izrazito kaže na slikah strukture odrezka pri rezalni hitrosti v = 300 m/min in 1500 m/min (sl. 7c in 7d). Ko se rezalna hitrost povečuje, se pojavlja hkrati več izrazitih plasti in a typical saw-tooth shape. In contrast to the machin-ing of this annealed steel grade with a cutting speed of 1500 m/min, Fig. 6b, the so-called white layer ap-pears, indicating a thermal softening process during chip formation. Generally, saw-toothed chip formation is an inherent feature when machining steels in their hardened state. It can be related to the brittle-ness of the material and to the generation of high compressive stresses on the workpiece during cut-ting. Instead of the material flowing plastically dur-ing cutting, a crack will begin on the workpiece sur-face. This crack releases the stored energy and acts as a sliding plane for the material segments, allowing the chip segment to be forced out from between the parting surfaces. Because of the high local temperature the white layers of martensite are formed. Therefore, the thermal softening of material becomes increasingly important and more and more influential on the plastic behaviour of the material in comparison to the effect of the strain hardening. Strain hardening is the dominant process during machining of this type of steel with a cutting speed of 50 m/min, but when the cutting speed reaches 150 m/min the formation of an initial crack and the thermal soften-ing process are dominant. This is especially visible on photographs of the chip produced at cutting speeds of 300 m/min and 1500 m/min (Fig. 7c and 7d). gfin^OtJJlMlSCSD 02-3 stran 139 iMMgfTMECl Ekinovi} S. - Dolin{ek S. - Kopa~ J. - Godec M.: Prehod iz obi~ajne - The Transition from a) rezalna hitrost 50 m/min cutting speed 50 m/min b) rezalna hitrost 150 m/min cutting speed 150 m/min ¦ nedefromiran material ¦ >¦- ^_^B Eea ^ white layerI J 100^m ;. ¦ ^n i—f c) rezalna hitrost 300 m/min cutting speed 300 m/min d) rezalna hitrost 1500 m/min cutting speed 1500 m/min Sl. 7. Prerez odrezka pri obdelavi kaljenega jekla X63CrMoV51 Fig. 7. Cross-sections of chip produced during X63CrMoV51 (tempered) machining tanjših odrezkov z manjšimi segmenti. Med obdelavo kaljenega jekla X63CrMoV51 (trdote 629 HV ali 52 HRc) torej preidemo v območje zelo hitre obdelave v primerih, ko znaša rezalna hitrost 150 m/min. To je mogoče skleniti na podlagi analize fotografij strukture in oblike odrezkov, dobljenih pri obdelavi z različnimi vrednostmi rezalnih hitrosti. 3 SKLEP Med običajno in zelo hitro obdelavo naslednjih jekel: ogljikovega jekla Ck15, nerjavnega jekla X5CrMoV51 in legiranega jekla X63CrMoV51 z rezalnimi hitrostmi v območju od 50 do 1500 m/min se pojavljajo različni mehanizmi nastajanja in oblikovanja odrezkov. Pri manjših rezalnih hitrostih pri vseh vrstah jekel nastajajo enakomerne zvezne oblike odrezkov, značilna je tudi manjša ali večja plastična deformacija. Ko obdelujemo bolj deformljiva jekla z manjšimi hitrostmi, so le ta izpostavljena večji plastični deformaciji. Glavna značilnost teh primerov obdelave je enakomerno deformacijsko utrjevanje. Pri obdelavi omenjenih vrst jekel z večjimi hitrostmi, posebno hitrostmi, ki ustrezajo območju velikih hitrosti, se pojavlja mehanizem oblikovanja odrezkov v obliki nastajanja razpok z večjim ali manjšim When the cutting speed increases more obvious lay-ers and a thinner chip with smaller segments appear simultaneously. It is clear that during machining of X63CrMoV51 (tempered, 629 HV, 52 HRC) the highspeed region is entered when the cutting speed is 150 m/min, which can be concluded on the basis of the chip shape. 3 CONCLUSIONS During conventional and high-speed milling of the following steels: carbon steel (Ck15), stainless steel (XcrNi189) and alloy tool steel (X63CrMoV51), with a cutting-speed range from 50 to 1500 m/min, different mechanisms of chip-formation appear. When the cutting speed is low, the steady-state continuous chip is characteristic for all the investigated steel grades, and more or less plastic deformation occurs. When more ductile steel grades are machined with lower cutting speeds they undergo more plastic deformation. The main characteristic in this case is uniform strain hardening. When machining the steels with higher cutting speeds, especially those speeds that belong to the high-speed region, the chip-formation mechanism is crack initiation along with more or less influence from the shear-localized mechanism. The consequence of VH^tTPsDDIK stran 140 Ekinovi} S. - Dolin{ek S. - Kopa~ J. - Godec M.: Prehod iz obi~ajne - The Transition from vplivom lokaliziranega striga. Posledica tega je nastanek žagaste oblike odrezkov z medsebojno ločenimi lamelami, oziroma pojav nedeformiranega in deformiranega območja (bela plast). Pojav bele plasti je tesno povezan z obdelavo trdih materialov. To dejstvo je mogoče razložiti s povečanjem temperature v rezalni coni, zaradi česar se povečuje vpliv termičnega mehčanja in plastičnih lastnosti materiala v primerjavi z učinkom deformacijskega utrjevanja. Zahvala Avtorji se zahvaljujejo Slovenski znanstveni fundaciji za finančno podporo omenjenih raziskav. this is the formation of a saw-toothed chip with apparent chip parts, i.e. an undeformed part and an extremely deformed part (white layer). The appearance of the white layer is closely associated with machining of hard materials. This can be explained by an increase of the temperature in the cutting zone, which makes the thermal softening more influential on the plastic behaviour of material in comparison to the effect of the strain hardening. Acknowledgement The authors are grateful to the Slovenian Science Foundation for providing financial support for this research. 4 LITERATURA 4 REFERENCES [I] Fallbohmer, P., C.A.Rodriguez, TOzel, TAltan (2000) High-speed machining of cast iron and alloy steels for die and mold manufacturing, Journal of Materials Processing Technology, Vol. 98, 104-115. 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Kneisel (1994) Turn-milling of hardened steel - an alternative to turning, Annals of the CIRP, Vol43/1, 93-96. [12] Vyas, A. M.c. Shaw ((1999) Mecanics of saw-tooth chip formation in metal cutting, Transactions of the ASME Journal of Manufacturing Science and Engineering, Vol.121, 163-172. gfin^OtJJlMlSCSD 02-3 stran 141 IVUgfTMECl Ekinovi} S. - Dolin{ek S. - Kopa~ J. - Godec M.: Prehod iz obi~ajne - The Transition from Naslovi avtorjev: dr. Sabahudin Ekinovič Authors’ Addresses: Dr. Sabahudin Ekinovič Fakulteta za strojarstvo v Zenici Faculty of Mechanical Eng. in Univerza v Sarajevu Zenica sekinovic@mf-ze.unsa.ba University of Sarajevo sekinovic@mf-ze.unsa.ba dr. Slavko Dolinšek prof.dr. Janez Kopač Dr. Slavko Dolinšek Fakulteta za strojništvo Prof.Dr. Janez Kopač Univerza v Ljubljani Faculty of Mechanical Eng. University of Ljubljana 1000 Ljubljana slavko.dolinsek@fs.uni-lj.si 1000 Ljubljana, Slovenia janez.kopac@fs.uni-lj.si slavko.dolinsek@fs.uni-lj.si janez.kopac@fs.uni-lj.si dr. Matjaž Godec Inštitut za materiale in tehnologije Dr. Matjaž Godec Lepi pot 11 Institut of Metals and Tech. 1000 Ljubljana Lepi pot 11 matjaz.godec@imt.si 1000 Ljubljana, Slovenia matjaz.godec@imt.si Prejeto: 18.12.2001 Received: Sprejeto: 23.5.2002 Accepted: VBgfFMK stran 142