No. 4, 1998 - Tribology in Industry

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Figurc 13. Awiliary f,;ttction gt for deternination of tlrc ratio beh+'een energia consunted on frictiort betwcen the cleaing fuce and tlrc nnchined piece, and betw,een the chip and the rake face Figure 14. ALatilian, functiort g t for detenninatiorr of tlrc ratio bet l,een encryics consutncd ott fticliott betv'een tlte cleating face and tlrc nnchined piece, and bctw,et:n tlre clip and the rake face Figure 15. Atuilicry functiort gt for detenrination of the ralio hetv,een energies cotrswtted on fricliort betv,eetr the clzaring face and tl;e nucltined piece, and bef,ueen qilr,7) = {).76327 9z@):1'933' IJy substituting thc ubove uumerical values into the equation, we obt;lin: A"t 0.0:0 ,,- ) )" ='' i..j' . 0.76-127. 1.933 = 0.05901 6 and the expression further gives: /' ';; = 0.23529 .(1 + 0.05901A = 0.249176 n^. so we conclude that in the above example the energy of friction over the clearing face is 5.97o of the energy of friction over the rake face, and that the enerry offriction on the contact surfaces on lire rake and the clearing faces rs 24.9Vo, and the energy for overcoming the internal friction is 75.1V of the energy needed for chip formation. Relatively high normal stress on the contact surface between the chip and the rake face, has as a consequence lowering of the friction coefficient, and thus the real contact surface is increased, over which the micro welding will occur betlr,een the asperities on the chip surface that is sliding over the tool rake face. The friction conditions cu tire ruke face, as it is shown, are complicated due to appearance of friction on the clearing face. Earlier, simplified force schematics, enables determination of the averzrge value of the friction coefficient on the rake face. It is based on the assumption about equality and collineariry of the resultant force and forces in the shearingplane and the rake face (Figure 16). The friction coef-ficient determined in this way has not many comrnon points with real condition. The more realistic scheme is that presented in Figure 3. Considering the complexity of the tribological conditions in metal cutting, to
- ilittasl\-il 'iii.!il.i!l(iri " a^.::lsitrit o lii:siiiLtt-rr.rn u clirloelition of hai;l pirrricles . ti:,;SC;C!:iiit)n * th:rit;ll 1n.: tra::Jhar-iicir! fatigue G nhi:se,/sirufiural tl ansfornraticits " rniqrc-chipf,i;ig . i"',,.t. - ,. Lroiltii.'l-,.,1 f i:r-'illriii n:r:titl, nui this ec;riing has no impor- :,t:ncre !tt rir:r:hiq:ilt ihe tttttr-,iirm aiioys, rvitlt respeci to h.:r(l tr',';; i r,. il hit,;l a:.)ating. lir otiic:'st:;;-liss is concluded that at cerfain machining reginle. tho riorni:ianf infl.rrence has at least one of the wear nrcchiiuisms. By clianging the regirne, the dominant infiucr';': i:l we;il is also changed, Frgure 18. o e rtiialn oi tire elri-r.liaior " i :irlttic.l;l elie ul:,. iio''vevir iitcrr: :.it: ren;rrks aboui applicaL.tiity ot'sorne ci ihesc, nrcrhi,rrisnr,,. sinse t!re',' Co not belong into the r!,r;-.ii',it ill ; g11l i- tjtt:n!: fepilitC:.. l jrc .r"'.i,tn,.-r',;D is thc ;rc:cel ni 'j:e ciiffusive wear. th;ii i5 .;';1;lnilili' ihe ,ippelrrri;ir:e of lie tool rvear, Fiowever, :i)Rre!'e!r.,.tri hen point Out thitt ih..'re are physical foun- ,.1:,.iol,s tbr ercihe.i.,c anci
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No. 4, 1998 - Tribology in Industry

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