Rezalne sile in njihov vpliv na gospodarnost obdelave

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1 Strojni{ki vestnik 48(2002)3, Journal of Mehanial Engineering 48(2002)3, ISSN ISSN UDK : UDC : Pregledni znanstveni ~lanek (1.02) Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Preview Fores sientifi and Their paper Influene (1.02) Rezalne sile in njihov vpliv na gospodarnost obdelave Cutting Fores and Their Influene on the Eonomis of Mahining Janez Kopa~ Rezalne in posebej speifiène rezalne sile imajo znaèilen vpliv na stroške obdelave. Znanje in poznavanje prave tehnologije o obdelavi sta teoretièna podlaga za prihranek energije v proizvodnji. Poznamo teoretiène modele rezalnih in speifiènih rezalnih sil pri struženju, frezanju in vrtanju. Podane so kot vpliv obdelovanega materiala, postopka obdelave in tehnoloških parametrov Strojniški vestnik. Vse pravie pridržane. (Kljuène besede: obdelave z odrezavanjem, sile rezanja, prihranki energije, uèinki ekonomski) Cutting fores, and espeially speifi utting fores, have a signifiant influene on mahining osts. Having the right knowledge and the right mahining tehnology is a way of saving energy in the prodution proess. There are theoretial models of utting fores that speify the utting fores during turning, milling, and drilling. In this paper we give an explanation of the influenes of mahining material, mahining proesses and tehnologial parameters on utting fores and eonomial mahining Journal of Mehanial Engineering. All rights reserved. (Keywords: mehanial utting, utting fores, energy savings, eonomi effet) 0 UVOD Za obdelovalnost materiala so rezalne sile pri postopku pomemben kriterij. Zagotovljene informaije o prièakovanih komponentah rezalnih sil so pomembne zaradi spodaj naštetih razlogov. Od naèrtovanih rezalnih sil med postopkom odrezovanja je odvisna potrebna moè stroja. Vrednost komponente rezalne sile povzroèa, da se med postopkom odrezovanja deformirajo deli stroja, kar ima za posledio natanènost obdelave. Za razvoj sprotnega nadzora rezalnega postopka je pomembno poznavanje velikosti rezalnih sil v odvisnosti od materiala obdelovana. Poleg tega pa rezalne sile doloèajo tudi meje pri optimiranju. Prava izbira rezalnega postopka in optimalnih tehnoloških parametrov znatno prihrani energijo pri obdelavi, kar neposredno vpliva na stroške. Vplivni dejavniki na velikost komponent rezalnih sil si sledijo po pomembnosti: a) naèin odrezovanja: neprekinjen oziroma prekinjen rez b) rezalni parametri: 0 PREFACE When it omes to the mahinability of a material, the utting fores used in the proess are important riteria. Guaranteed information about the expeted utting-fore omponents is, moreover, partiularly signifiant for the following reasons. The fores ourring in the metal-utting proess provide information about the power requirements of the mahine and are therefore fundamental in the designing of the mahine tool drive. Data on the utting-fore omponents are required when designing the mahine parts as the fores ourring during a utting operation result in the deformation of ertain mahine elements, thus imparing the working auray of the mahine. For developments in the field of adaptive ontrol of the utting proess, knowledge of the material-dependent utting fore is also of major importane in defining the performane limit onfining the range of optimization. Choosing the right utting proess and the optimum tehnologial parameters results in signifiant savings of energy during mahining. Of the fators influening the utting-fore omponents, the following are very important: a) in the utting methods: onstant or varying rosssetional area of the ut hip frition b) in the utting onditions: stran 121

2 Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Fores and Their Influene podajanje (f) globina rezanja (ap) geometrijska oblika rezalnega roba rezalna hitrost (v) hladilna tekoèina ) material: kemijska sestava toplotna obdelava d) orodje: material orodja lomile odrezkov prevleka obraba orodja 1 VPLIV REZALNIH PARAMETROV PRI IZRAÈUNU KOMPONENT STATIÈNIH REZALNIH SIL Rezultanta rezalnih sil sila F se pojavi med postopkom odrezovanja in je odvisna od smeri gibanja orodja in obdelovana. Rezultanto rezalnih sil sestavljajo rezalna sila F, podajalna sila F f in odrivna sila F p (sl. 1). Obremenitev orodja pri struženju prikazuje slika 2. vrtenje obdelovana rotation of workpiee feed (f) bak engagement (ap) utting-edge geometry utting speed (v) utting fluid ) the material: hemial omposition heat treatment d) in the tool: tool material hip breaker oating tool wear 1 RELATIONSHIPS FOR THE CALCULATION OF THE STATIC CUTTING-FORCE COMPONENTS The utting fore F ating on the tool during the mahining operation an be divided in terms of the diretions of motion of the tool and the workpiee into the utting fore F, the feed fore F f and the passive fore F p (Figure 1). The onditions of the tool s engagement are desribed in Figure 2 for the turning proess. [1] vrtenje obdelovana rotation of workpiee gibanje orodja motion of tool Sl. 1. Rezalne sile pri struženju Fig. 1. Cutting fore omponents during turning gibanje orodja motion of tool Sl. 2. Razmere pri struženju Fig. 2. Conditions of engagement during turning Rezalna sila F Potek rezalne sile lahko delimo z širino odrezka b in ga prikažemo v odvisnosti od debeline odrezka h v dvojnem logaritemskem diagramu. Dobimo linearno odvisnost: Cutting fore F The ourse of the utting fore F related to the width of the ut b is a funtion of the thikness of the ut h in the system of log-log oordinates as a straight line that is desribed by the equation: F = b k - b = 1.1 a p sin h= f sin 1 m (1) (2) (3). stran 122

3 Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Fores and Their Influene Zgornjo enaèbo je izkustveno razvil Kienzle in popisuje odvisnost rezalne sile F od prereza odrezka, kar prikazuje slika 3. Standardna speifièna rezalna sila je odvisna od širne odrezka b in debeline odrezka h, kjer je b =1mm 2, ter vplivnega koefiienta rezalne sile 1-m, kar je razvidno iz enaèbe. Standardna speifièna rezalna sila k 1.1 je v veliki meri odvisna od materiala, rezalnih parametrov, orodja in vpliva tehnološkega postopka. Poveèanje rezalne sile je odvisno od vplivnega koefiienta rezalne sile 1-m, karakteristik materiala obdelovana in materiala orodja ter razliène globine rezanja. Predstavitev izkustvene vrednosti rezalne sile F je odvisna od prereza odrezka b*h oziroma globine rezanja a p kot funkija debeline odrezka h. Rezultat je premia v dvojnem logaritemskem diagramu, ki je podana z enèbo: k k h 1-m = 1.1 = This equation was established by Kienzle aording to the empirially determined dependene of the utting fore F on the ross-setional area of the ut a p f or b, subjet to the turning data shown in Figure 3. The speifi utting fore k l.l related to the ross-setional area of the ut b = 1 mm 2 and the rise in the utting fore related to the nominal width of the ut 1-m are entered into the equation as harateristi data.[2] The speifi utting fore k l.l is, in this ase, largely dependent on the material, the utting onditions, the tool and the proedural influenes. The inrease in the utting fore related to the nominal width of the ut 1-m haraterises the utting-fore behaviour of a workpiee-material toolmaterial ombination for different thiknesses of ut. The representation of the experimentally determined utting-fore values F related to the ross-setional area of the ut b * h or a p* f as a funtion of the thikness of the ut h also results, under log-log oordinates, in a straight line, whih an be desribed by the equation: F b h (4). rezalna sila F širina rezanja b - KIENZLE enaèba / equation debelina odrezka h / Sl. 3. Grafièna predstavitev poteka rezalne sile in speifiène rezalne sile Fig. 3. Graphi determination of the utting fore and the speifi utting fore V tej zvezi je speifièna rezalna sila k podana kot funkija debeline odrezka h. Te povezave nas pripeljejo do enaèbe za rezalno silo F : Through this relation, the speifi utting fores k are given as a funtion of the thikness of the ut h. These onnetions lead to a further equation for the alulation of the utting fore F : F = bhk (5). stran 123

4 Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Fores and Their Influene Podajalna sila F f Za izraèun podajalne sile F f, vpeljemo enako zvezo kakor pri rezalni sili F, ta je definirana kot linearna funkija podajalne sile, ki je funkija širine odrezka b kot funkija debeline odrezka h, kar je predstavljeno v dvojnem logaritemskem diagramu: Feed fore F f For the alulation of the feed fore F f, a relationship an be established that is similar to that used for the utting fore F, whih is based on the linear behaviour of the feed fores related to the width of ut b as a funtion of the thikness of ut h as shown under log-log oordinates: 1 m f F = b k - f f1.1 (6). Znaèilen podatek: standardna speifièna rezalna sila je odvisna od prereza odrezka, ki je b = 1mm 2. Poveèanje podajalne sile je odvisno od vplivnega parametra podajalne sile, kar je upoštevano v enaèbi. Nasprotno kakor pri enaèbi rezalne sile, moramo v enaèbi za izraèun podajalne sile upoštevati, da je raztros pri podajalni sili F f /b=f(h) veèji kakor pri rezalni sili. As harateristi data, the speifi feed fore k f1.1 related to a ross-setional area of ut of b = 1 mm 2 and the inrease in the feed fore related to the nominal width of the ut 1 - m f are inluded in the equation. Unlike to the utting-fore equation, this equation to alulate the feed fore must be regarded as an approximate solution as the satter of the test values in the representation F f / b = f (h) is larger than with the utting fore [3]. Odrivna sila F p V skladu s pravili za izraèun podajalne sile F f, lahko odrivno silo F p izrazimo z enaèbo: Passive fore F p In aordane with the rules of alulating the feed fore F f, the passive fore Fp an be expressed as: 1 m p F = b k - p p1.1 (7). V preglednii 1 so zbrane vse enaèbe za izraèun rezalnih sil in torzijskih momentov za nekaj najbolj pogosto zastopanih postopkov obdelave. 2 REZALNI PARAMETRI Podatki o obdelavi, kot sta globina rezanja a p in podajanje f, so namenjeni izraèunu povpreènega prereza odrezka a p f = b in nakazujejo prek znanih enaèb na velikost rezalne sile. Rezalna geometrija Rezalna geometrija ima preejšen vpliv na velikost komponent rezalnih sil. Po eni strani deformaija v strižni oni vpliva na geometrijsko obliko odrezka, po drugi strani pa je geometrijska oblika odrezka definirana z geometrijsko obliko orodja. Na velikost komponent rezalnih sil tako vplivajo razmere v strižni oni in geometrijska oblika orodja. Èe se spremeni epilni kot g (zmanjša ali poveèa), se spremenijo omenjene sile (poveèajo ali pomanjšajo) za naslednje vrednosti: rezalna sila F za približno 1,5 % podajalna sila F f za približno 5,0 % odrivna sila F p za približno 4,0 % za vsako stopinjo (1 ) spremembe epilnega kota. Èe je velikost prostega kota a 3 = a = 12, ta nima znaèilnega vpliva na komponente rezalnih sil. Table 1 shows some of the equations for omputing the utting fores and torques that our during mahining, suh as turning, drilling, milling, et. 2 CUTTING CONDITIONS The mahining parameters as data bak engagement a p and feed f pass over by way of the ross-setional area of ut a p f = b immediately into the utting-fore equations indiated. Cutting-edge geometry The utting-edge geometry has a major influene on the quantity of the utting-fore omponents. On the one hand, the deformation proesses in the zone of shear are affeted by it and, as a result, so is the geometry of the hip formation, on the other hand, the tool angles determine, for geometrial reasons, the relative quantities of the various fore omponents. As the rake angle g dereases (inreases), there is an inrease (derease) of the: utting fore F by about 1.5 % feed fore F f by about 5.0 %. passive fore F p by about 4.0 % for every degree of rake angle hange ompared to the test value. Within the usual range of learane angles a 3 = a = 12 no influene an be determined on the utting-fore omponents. stran 124

5 Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Fores and Their Influene Preglednia 1. Enaèbe rezalne sile in torzijskega momenta Table 1. Cutting-fore and torque equations Obdelovalni postopek Mahining proess Struženje Turning Enaèbe za izraèun Equation for the determination of Rezalna sila F Torzijski moment Md Cutting fore F Torque Md F = b k D + d Md = b k 1-m F = b k m h = f sin D + d Md = b k 1.1 a 4 p D - d b = ; a = sin 2 Skobljanje Planing Vrtanje Drilling Povrtavanje Boring Frezanje Milling Podobno kakor struženje Like turning Posamezen rezalni rob: Eah utting edge: F = b k F = b k m D s b = ; = 2sin 2 f h = sin 2 Posamezen rezalni rob: Eah utting edge: F = b k F = b k m D s b = ; = 2sin 2 f h = sin 2 Posamezen rezalni rob: Eah utting edge: F = b k F = b k h = b = f z m sinj sin a p sin s D Md = 2b k 4 Md = 2b k 1.1 Md = f k 2 D 8 1-m D 4 D + d Md = 2b k 4 1-m D + d Md = 2b k D - d Md = f k 8 Md = b k Md = b k 1.1 D 2 1-m D 2 Èe se spremeni strmina l (zmanjša ali poveèa), se spremenijo tudi sile (poveèajo ali pomanjšajo): rezalna sila F za približno 1,5 % podajalna sila F f za približno 1,5 % odrivna sila F p za približno 10,0 % za vsako spremembo strmine l za 1. Vpliv nastavnega kota je zajet v enaèbi (3) in (5) za izraèun rezalne sile F in odrivne sile F p pri znani širini b in debelini h odrezka. Medtem ko se rezalna sila F in odrivna sila F p zmanjšata z nastavnim kotom, se podajalna sila F f poveèa. Odvisnost podajalne sile F f od nastavnega kota ni popolnoma popisana v enaèbi (4), torej èisto matematièno bi bila popisana z nastavnim kotom, širino odrezka b in debelino odrezka h, torej z enaèbo (4) dobimo nepopoln rezultat. Za As the utting-edge inlination l dereases (inreases), there is an inrease (derease) of the: utting fore F by about 1.5 % feed fore F f by about 1.5 % passive fore F p by about 10.0 % for every degree of hanging the angle of inlination as ompared to the test value. The influene of the utting-edge angle is ontained in the equations (3) and (5) for the alulation of the utting fore F and the passive fore F p by the indiation of the width of ut b and the thikness of ut h. While the utting fore F and the passive fore F p inrease as the utting edge angle redues the feed fore F f dereases. The dependene of the feed fore on the utting-edge angle is, however, not desribed by the indiated equation, as a result, a purely mathematial onsideration of the utting-edge angle within the range width-of-ut b and thikness-of-ut h will lead to the stran 125

6 Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Fores and Their Influene nastavne kote manjše od normalnih, lahko podajalno silo izraèunamo z matematièno enaèbo, vrednost podajalne sile pa je manjša od dvakratne velikosti te pri normalnih nastavnih kotih (F f = 2F f (=70 ) - F f (<70 ) ). Velikost radija konie ima znaten vpliv na velikost komponent rezalnih sil, pri èemer mora biti najmanjša globina rezanja a p = 2 r. Rezalna hitrost Rezalna hitrost vpliva na komponente rezalnih sil, njen vpliv je razlièen glede na material obdelovana in orodja ter vrsto obdelave. Hitrorezno jeklo se uporablja za rezalne hitrosti do 25 m/min, to pa je tudi hitrost v = 25m/ min, pri kateri se doloèi standardno speifièno rezalno silo. Da prepreèimo nastajanje nalepka pri rezalnih hitrostih v < 30m/min, uporabimo orodje iz karbidne trdine. Upoštevati pa moramo, da se pri odrezovanju pojavljajo tudi rezalne hitrosti do v > 1000m/min, kar vpliva na velikost rezalne sile. Hladilna tekoèina Vpliv hladilne tekoèine je bistvenega pomena pri velikih rezalnih hitrostih. Pri majhnih rezalnih hitrostih, se rezalne sile zmanjšajo zaradi prodora hladilno-mazalne tekoèine v dotikalno obmoèje, kar povzroèi zmanjšanje trenja med odrezkom in orodjem. Pri veèjih rezalnih hitrostih ima hladilno-mazalna tekoèina v strižni oni samo hladilni uèinek. Pri sodobnih rezalnih materialih ni nujno potrebna uporaba hladilno-mazalne tekoèine, ker imajo nove prevleke rezalnih orodij dobre znaèilnosti. Sodobne in naravi prijazne metode obdelave s hladilno-mazalno tekoèino so metode minimalnega hlajenja, pri tem za mazanje uporabljajo sistem razprševanja naravnega olja s stisnjenim zrakom. Kemièna sestava 3 OBDELOVANI MATERIAL Èe poznamo kemièno sestavo obdelovalnega materiala, lahko le oenimo velikost rezalne sile pri obdelavi. Vendar pri tem ni pravila in so zato potrebne meritve sil. wrong results. For utting-edge angles smaller than those on whih the test value is based, the feed fore an be determined by alulation in suh a way that the mathematial value of the feed fore for the smaller uttingedge angle is subtrated from the double test result (F f = 2F f (=70 ) - F f (<70 ) ). Within the range of the usual values for the orner radius, no appreiable influene on the utting-fore omponents an be determined as long as the term 2 r = a p is fulfilled. Cutting speed The influene of the utting speed on the utting-fore omponents must be differently assessed for the various workpiee materials and the tool materials with their speifi ranges of appliation. The appliation range for high-speed-steel tools is, in general, for utting speeds of about 25 m/ min; so that for this material the utting behaviour is desribed with suffiient auray by the indiation of the speifi utting-fore value at v = 25 m/min. To prevent built-up-edge formation, no utting speeds of v < 30 m/min are normally used for arbide utting tools. As regards the utting-speed-dependent behaviour of the utting fores in turning operations in the range of v < 1000 m/min, fundamental examinations are available. Cutting fluid The influene of utting fluids varies depending on the utting speed. At low utting speeds, the utting fores are redued owing to the penetration of the lubriant into the ontat zones and the diminished frition between hip and tool. At higher utting speeds within the range of the formation of ontinuous hips, the utting fluid only has a ooling effet. Modern and eologial methods use neardry utting with a minimum amount of natural oil dispersed with pressurised air. Chemial omposition 3 WORKPIECE MATERIAL Aording to the present state of knowledge, the hemial omposition of the workpiee materials is only suggestive of the size of utting-fore omponents in exeptional ases, beause definite laws relating to this influene are quite rare. stran 126

7 Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Fores and Their Influene Toplotna obdelava Raziskava vpliva toplotne obdelave na rezalne sile je pokazala, da vpliv toplotne obdelave ni natanèno definiran glede na rezalne sile. Pri obièajnih rezalnih orodjih, kakor sta hitrorezno jeklo in karbidna trdina, je treba vpliv toplotne obdelave na podatek k 1.1 in 1-m izmeriti za vsak primer posebej. Pri preskusih odrezovanja toplotno obdelanih materialov s hitroreznimi jekli so izmerjene rezalne sile manjše kakor pri mehko žarjenih obdelovanih. Ta ugotovitev velja tudi za potek rezalne sile v povezavi z 1-m. Meritve rezalnih sil pri odrezovanju z orodji iz karbidne trdine so pokazale, da primerjava toplotno obdelanih proti mehko žarjenim vzorem kaže veèje vrednosti za k 1.1 in1-m. Medtem ko primerjava med normalizaijo in žarjenjem na mehko ni pokazala znaèilnih sprememb rezalnih sil. Odvisnost speifiène rezalne sile k 1.1 in poveèanj rezalne sile glede na širino odrezka preko vplivnega eksponenta 1-m je povezana z napetostmi in deformaijskimi karakteristikami obdelovanega materiala. Zato ni natanèno definirana povezava in lahko prièakujemo veèje raztrose rezultatov. 4 ORODJE Dogodki v rezalni oni, kjer potekata strig in nastanek lamel odrezka, prvinsko vplivajo na podajalno in odrivno silo. Tudi tu je znaèilen raztros glede na zvezo sila / debelina odrezka. Linearni popis komponent rezalne sile, kot funkije debeline odrezka je izveden kot približna rešitev. Materiali za rezalna orodja Èe uporabimo rezalno keramiko (Al 2 O 3 ), so rezalne sile proti karbidni trdini za okoli 10% manjše. Vzrok so boljše torne razmere pri drsenju odrezka po epilni ploskvi rezalne plošèie. Lomilnik odrezkov, ki je v moderni obliki že integriran na rezalni plošèii je dimenzioniran tako, da je polmer za iztek odrezka èim veèji. S tem lomilnik nima bistvenega vpliva na rezalne sile; zmanjšana pa je tudi obraba segmenta lomilnika. Na splošno se priporoèa, da je odmik lomilnika od rezalnega robu v vrednosti okoli 10 f (torej desetkratnega pomika orodja). Obraba orodja Obraba orodja je zanesljivo v povezavi z velikostjo rezalnih sil. Deli se na dve znaèilni, in sier na obrabo proste ploskve, ki jo povzroèa Heat treatment Investigations aimed at defining the influene of heat treatment on the utting fores have led to the result that there is no definite dependene of the main utting fore on heat treatment. However, as regards high-speed-steel tools and arbide utting tools, the qualitative effets of heat treatment on the data k l.l and 1-m an be determined separately. Under the experimental onditions, heat-treated materials for the high-speed-steel tool material generally show muh lower utting-fore values than for soft-annealed steels. This statement also applies to the inrease in the utting fore related to the nominal width of the ut 1 m. The utting-fore measurements onduted with arbide utting tools showed that heattreated materials, as ompared to soft-annealed materials, frequently reveal higher values for k l.l and 1-m. A omparison of the utting fores for normalised and soft-annealed materials, however, does not result in any appreiable differenes. While the dependene of the speifi utting fore k 1.1 and of the inrease in the utting fore related to the nominal width of the ut 1-m on the strength and deformation harateristis within the entire range of materials examined may be shown, no definite relationship an be attributed to this influene owing to the wide range of satter. 4 TOOL The deformation onditions in the shear zone of the tool some of whih varied for different thiknesses of the ut and made themselves felt in the position and size of the shearing plane and in the amount of hip rowding had an effet on the feed fores and the passive fores. In view of the range of satter of the various test results, a linear desription of these fore omponents as a funtion of the thikness of the ut must therefore be regarded as an approximate solution. Tool material When aluminium-oxide tools (utting eramis) are employed as a tool material, the resulting utting fores are about 10 % lower than with arbide metal beause with a erami utting material there are more favourable fritional onditions on the true rake or hip fae. The size of the hipbreaker b sp should be dimensioned so that the radius of hip urvature is as large as possible. This is to ensure that on the one hand the size of the hip breaker will not have any major influene on the utting-fore omponents, and on the other hand, the wear ation on the true rake is as low as possible. The rule-of-thumb value hip former = 10 times the feed an generally be regarded as favourable. Tool wear Numerous results are available onerning the influene of tool wear on the utting-fore omponents. As a onsequene of the inreasing frition areas between the stran 127

8 Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Fores and Their Influene drsenje rezila po že obdelani površini obdelovana, in na obrabo epilne ploskve orodja, prek katere drsi odrezek. Znaèilen vpliv na veèanje obrabe pa ima seveda èas uporabe orodja. Tudi tu oene poveèanja obrabe niso mogoèe v zadostni natanènosti, zato so potrebne meritve. Le približne oene povedo, kakšna sta vpliv in povezava med obrabo orodja in poveèanjem rezalne sile: rezalna sila F se poveèa za 10% za vsak 0,1 mm obrabe W podajalna sila F f se poveèa za 25% za vsak 0,1 mm obrabe W odrivna sila F p se poveèa za 30% za vsak 0,1 mm obrabe W Kot definiija kriterija izloèilne obrabe rezalnega orodja pa seveda ne more biti pravkar omenjena povezava med rezalno silo in obrabo proste ploskve orodja W. 5 DINAMIÈNA REZALNA SILA Temeljita raziskava dinamiènih rezalnih sil pri struženju je pokazala, da ima poleg statiène komponente rezalne sile tudi nastanek odrezka velik vpliv na komponente rezalnih sil. V strižni oni in v podroèju nastanka nalepka na rezalnem robu, se lahko dinamièna komponenta rezalne sile F poveèa za 20%, podajalna sila F f in odrivna sila F p pa se lahko poveèata za 50%. V podroèju zveznega nastanka odrezka se lahko dinamièna komponenta rezalne sile zmanjša za 5 do 10 odstotkov (sl. 4). Znaten vpliv na dinamièno rezalno silo ima tudi lega lomilne stopnièke b sp, ki je lahko odvisna že od oblike sintrane plošèie. Majhna oddaljenost lomilne stopnièke poveèa gostoto odrezkov v taki meri, da je dinamièna sila v strižni oni v smeri podajalne in odrivne sile lahko veèja za 100 odstotkov od statiène. ut surfae and the flank of the tool or between the hip and the hip fae, on the one hand and the hanging onditions of engagement of the tool on the other, a substantial inrease in the utting-fore omponents with inreasing utting time is registered. In view of the number of fators, a quantitative statement on the inreasing fore in relation to the inreasing tool wear an only be an approximation. Numerous experimental results have shown that for an inrease of the utting-fore omponents as the tool wear inreases the following orretive values should be introdued: utting fore F : inrease of about 10% per 0.1-mm width of land wear W feed fore F f : inrease of about 25% per 0.1-mm width of land wear W passive fore F p : inrease of about 30% per 0.1-mm width of land wear W As a definition of the total wear is impossible, the inrease in the utting fore was related to the width of the land wear W. 5 DYNAMIC CUTTING FORCE Fundamental examinations of the dynamis of utting fores during turning have shown that in addition to the fators influening the stati uttingfore omponents the hip formation has a major influene on the utting-fore omponents. In the range of shear-hip formation, built-upedge formation and the rigidity of the proess, a high dynami utting-fore omponent ours in mahining, whih may aount for a utting fore F of up to 20%, and for the feed fore F f and the passive fore F p up to 50% of the stati omponents. In the range of ontinuous hip formation, the dynami utting fores drop to 5 10 % of the stati share, see Figure 4. A onsiderable influene on the dynami utting fores is exerised by the hip-breaker distane b sp, whih an be made diretly by shape-sintering of the utting insert. With a short distane and thus heavy rowding of the hip flow, the share of the dynami fore in the diretion of the feed fore and the passive fore an amount to as muh as 100 % of the stati share. F [N] F [N] [N] [N] statièna sila - povpreèje dinamièna komponenta average of statial fore t [s] dynami dinamial omponent t [s] Sl. 4. Povpreèje rezalne sile in dinamièna komponenta Fig. 4. Average utting fore and dynami part of the utting fore stran 128

9 Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Fores and Their Influene 6 PRAKTIÈNA PREDSTAVITEV Praktièna uporaba eksperimentalno dobljenih rezultatov je prikazana na sliki 5. Speifièna rezalna sila vpliva na energijo, potrebno za obdelavo. Za prihranek energije in stroškov je ekonomièna izbira najveèjega možnega podajanja. Najveèje tehnološko mogoèe podajanje je izbrano glede na postopek in zahtevano hrapavost (Ra). Kratka primerjava pokaže, kako lahko s pravilnim naèrtovanjem tehnoloških parametrov dosežemo 2- kratni prihranek energije in èasa obdelave ter tako zmanjšamo stroške. Iz primerjave finega struženja in postopka brušenja vidimo, da je speifièna rezalna sila pri struženju 2-krat manjša (prej omenjeni prihranek). 6 PRACTICAL DEMONSTRATION The pratial use of the experimental results is shown in Fig. 5. The speifi utting fore has an influene on the energy needed for mahining. With regard to saving energy and osts it is best to hoose the maximum possible feed rate. The maximum tehnologially justifiable feed rate is hosen based on the limits of the proess or the speimen roughness (Ra). The short omparision shows that using the right tehnologial parameters an save more than 2x the equivalent of energy: shortening the mahining time and reduing the osts. Fine turning of the final surfae of the workpiee in omparision with grinding bring about the mentioned 200% lower speifi utting fores. Some of the F/b [N/mm] k k [N/mm2] [MPa] NiCrMoV7V, HR=43 GG 20, HB=178 k F/b F/b 0,1 0,5 h[mm] Sl. 5. Eksperimentalni rezultati rezalnih in speifiènih rezalnih sil Fig. 5. Experimental results of utting and speifi utting fores poliranje - polishing brušenje - grinding log k [MPa] VHO fina obdelava - HSC finishing struženje - turning Sl. 6. Speifiène rezalne sile, odvisne od postopka obdelave Fig. 6. Speifi utting fores during the proess stran 129

10 Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Fores and Their Influene Podatki, zbrani v diagramu na sliki 6, kažejo razliko med postopki obdelave v odvisnosti od debeline odrezka h. Nasproten postopek pokaže, kako je speifièna rezalna sila manjša pri veèjem podajanju [4]. Da predstavimo in primerjamo teoretiène rezultate s praktiènimi vplivi, je treba pogledati sliko 7. Razvidna sta vpliv obdelovalnega materiala in vrsta obdelave na stroške obdelave. Èe primerjamo obdelavo mehkega materiala, npr. aluminij ali jeklo, s trdimi materiali, na primer nikljeve zlitine, opazimo, da je razlika v stroških obdelave kar 4-kratna. Pri tem je seveda opazen tudi vpliv rezalne sile, ki v povezavi s hitrostjo narekuje moè stroja, kar pa je tudi eden od stroškov.razvidna je tudi razlika glede na vrsto postopka; struženje povzroèa znatno veèje stroške kakor frezanje, èe gledamo glede na odvzem enake prostornine materiala. results olleted in the diagram in Fig.6 show diferenes between proesses, suh as turning, HSC, grinding soft material and hard steels, depend on h (thikness). The reverse observation shows how the speifi utting fore is lower with a higher feed rate [4]. Comparing the theoretial and measured results with the pratial effet shows, in Fig. 7, how great is the influene of the type of mahined materials, refleted in the utting fores and the mahining osts. The produt of the utting fore and the utting speed provides the power needed for the proess: this is the energy osts. As first, the relative osts between soft (Al, steel) material and hard (nikel-based alloys) materials are a fator of four different for mahining. Another influene is the hosen type of mahining: the turning proess is muh more expensive than milling, whih means the tehnologist has to be very areful when preparing the offer for the ustomer. struženje, turning frezanje, milling stroški obdelave (s) mahining osts (s) Sl. 7. Relativni stroški obdelave mehkih in trdih materialov Fig. 7. Relative osts of mahining soft and hard materials 7 VHO OBDELAVA Z VELIKIMI HITROSTMI Uporabno obmoèje debeline odrezka (h) pri obdelavi z velikimi hitrostmi je omejeno. Za primerjavo rezultatov (poglavje 6 obièajna obdelava) z rezultati sodobne obdelave v trdo je mogoèe videti, da je odvisnost enaka. To pomeni, da sta rezalni postopek in rezalna geometrija (a,b,g,r,) teoretièno še vedno enaki. Klasièna in sodobna obdelava VHO imata skupno to, da je njun izid odrezek in da se za oba postopka uporablja isti matematièni model. S slike je razvidno, da je pogosto odrivna sila pri odrezovanju v trdo elo veèja od glavne rezalne 7 HSC MACHINING CONDITION The usable (h) thikness by HSC mahining is expliitly limited in this proess. By omparing the result shown before (setion 6: lassial mahining) with the results of modern HM (hard mahining) we an see that the relationship is the same. It means that utting proesses with an exat utting geometry (a,b,g,r,) are still in the same theoretial area. The lassial utting and modern HSC mahining both have as a produt, therefore the same models and equations are used for both proesses. Figure 8 shows that the passive fore an be larger than the utting fore. In pra- stran 130

11 Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Fores and Their Influene speifièna rezalna sila k [MPa] speifi utting fore k [N/mm 2 ] rezalna sila utting fore fore normalna rezalna sila normal utting utting fore fore obdelovani material: mahining mahining material: mat.: 100CR6 rezalno orodje: 100Cr6 PKB utting tool: frezanje utting tool: PKB dry up dry milling up milling Rezalni Cutting pogoji: ondition: Cutting onditions: a p = 5 mm a e = 0,1 mm f z = 0,1 mm v = 50 m/min d = 40 mm, z = 1 a = 10 g = 0 r e = 1,2 mm sile. To v praksi pomeni odmik orodja od naèrtovanega obrisa obdelovana in s tem napake na izdelku. Zato v praksi zmanjšamo debelino odrezka. imenska debelina odrezka h nominal thiknes of ut h [mm] Sl. 8. Sile pri frezanju v trdo [5] Fig. 8.Hard mahining (HM) and fores [5] tie, it auses failure on a dimension of the produt, as a result, we have to redue the feed rate. 8 SKLEP Nepoznavanje podroèja rezalnih sil ima lahko za posledio slabo obdelavo, lome orodja, in veèje obdelovalne stroške. Obièajni obdelovalni postopki še vedno ponujajo banko tehnoloških podatkov, v kateri so podatki o rezalnih silah glede na obdelovalni material, postopek, rezalno orodje itn. S tehnološko pripravo lahko inženir izbere in doloèi najboljši postopek in s tem debelino odrezka (h). Le ta mora biti vedno najveèja po vsem obrisu obdelovana, glede na zahtevano hrapavost površine. To je prvi korak, ko lahko tehnolog prihrani energijo in zmanjša izdelovalne stroške. Sodoben naèin napovedi velikosti rezalnih sil je model analitiènega simuliranja. Program je pomoè, ki omogoèa napovedati potek dogodkov med obdelavo na osnovi nastavitev tehnoloških parametrov, orodja, obdelovana in stroja. Sodobni obdelovalni stroji imajo moèno raèunalniško podporo s programom za visoko podajanje, kar omogoèa obdelavo s konstantno rezalno silo in nespremenljiv prostorninski odvzem [6]. V tem primeru so dinamièni uèinki manjši, odrezovalni postopek pa je stabilnejši. Èe upoštevamo vse povzetke o rezalnih silah, so rezultati naslednji: manjša obraba rezalnega robu, boljša hrapavost obdelane površine, veèja natanènost in gospodarnejša proizvodnja. 8 CONCLUSION With a little knowledge of the utting fores we an expet worse mahining with tool breakages and higher prodution osts. Conventional mahining is stil based on a tehnologial data bank, where utting fores are provided for various mahining materials, mahining proeses, utting tools, et. By tehnologial preparation the enginer has to hoose and find the best proess with regards to the thikness of the ut (h). H has to be a maximum value with regard to the all-over ontour of the workpiee to the required surfae roughness. In this way we make the first step in reduing the energy and the mahining osts. The modern onept is a model of analytial simulation for the predition of the utting fores[6]. The program is an aid enabling us to foreast the ourse of events during the mahining proess with given initial onditions suh as the tehnologial parameters, the tool, the workpiee and the mahine. Modern mahine tools (HSM) with strong software and programs suh as high feed are working on a onept of onstant utting fores regarding the onstant mahining volume rate [6]. In this ase the dynami effet is lower and the utting proess muh more stable. To onsider all the summarized effets on the utting fores the results are: redued wear on the utting edge, better workpiee-surfae roughness, greater auray and eonomi produtivity. stran 131

12 Kopa~ J.: Rezalne sile in njihov vpliv - Cutting Fores and Their Influene globina rezanja širina odrezka lega lomilne stopniène notranji premer rezanja zunanje premer rezanja rezultanta rezalnih sil rezalna sila podajalna sila odrivna sila debelina odrezka speifièna rezalna sila standardna speifièna rezalna sila standardna speifièna podajalna sila standardna speifièna odrivna sila vplivni eksponent rezalne sile vplivni eksponent podajalne sile vplivni eksponent odrivne sile torzijski moment polmer plošèie podajanje podajanje na zob rezalna hitrost prosti kot strmina epilni kot nastavni kot kot konie kot oprijema (frezanje) natezna trdnost meja elastiènosti podaljševanje redukija površine trdota po Vikersu (število) 9 SIMBOLI 9 SYMBOLS a p mm bak engagement b mm nominal width of ut b sp mm hip breaker distane d mm inner diameter of ut D mm outer diameter of ut F N resultant utting fore F N utting fore F f N feed fore F p N passive fore h mm nominal thikness of ut k MPa speifi utting fore k 1.1 MPa speifi utting fore unit k f1.1 MPa speifi feed fore unit k p1.1 MPa speifi passive fore unit 1-m oefiient of utting fore 1-m f oefiient of feed fore 1-m p oefiient of passive fore Md Nm torque r mm orner radius f mm feed f z mm feed per tooth v m/min utting speed a learane angle l utting-edge inlination g rake angle tool utting-edge angle e tool inluded angle j s utting motion angle (milling) R m MPa tensile strength R e MPa yield point A 5 % elongation Z % redution of area HV10 Vikers hardness (number) 10 LITERATURA 10 REFERENCES [1] König, W., K. Essel, L. Witte: Speifi utting fore data for metal utting, Verlag Stahleisen MBH, Düseldorf. [2] Dolinšek, S., J. Kopaè (1992) Odrezavanje, dopolnitveno gradivo za predavanja in vaje, Fakulteta za strojništvo, Ljubljana. [3] Milfener, M., F. Èuš (2001) Analitial model of utting fores simulation in end milling. ICIT 2001, Slovenija. [4] Muren, H. (1976) Odrezavanje, Tehniška založba Slovenije. [5] Shultz, H. (1996) Hohgeshwindigkeitsbearbeitung, Carl Hanser Verlag. [6] Kopaè, J., G..Peterlin (2001) Novi pristopi pri visokohitrostnih obdelavah na osnovi CAM, Orodjarstvo Avtorjev naslov: prof.dr. Janez Kopaè Fakulteta za strojništvo Univerza v Ljubljani Aškerèeva Ljubljana janez.kopa@fs.uni-lj.si Author s Address: Prof.Dr. Janez Kopaè Faulty of Mehanial Eng. University of Ljubljana Aškerèeva Ljubljana, Slovenia janez.kopa@fs.uni-lj.si Prejeto: Reeived: Sprejeto: Aepted: stran 132