No. 4, 1998 - Tribology in Industry

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