Page 20 - Апрель

METALWORKING EQUIPMENT AND TOOLS

In the literature it is noted that with an increase in the hardening of the treated surface,
the inhomogeneity of the properties of the surface layer also increases, even with the constancy
of all processing conditions. The heterogeneity of the surface layer manifests itself in a non-
uniform distribution of point defects; the surface areas are characterized by different chemical
properties. A micro relief is formed on the surface with depressions and protrusions of non-
uniform shape, with a random distribution of the height and pitch of micro roughness. This leads
to the appearance in the surface layer of foci with increased tendency to cracking, corrosion,
adhesion and abrasion [3, 5]. In the process of chip separation, the thickness of the layer crushed
by the cutting edge during chip separation changes randomly, creating preconditions for non-
uniform hardening of the surface layer and variations in the parameters of micro roughness.
The latent deformation energy accumulated by the surface layer as a result of hardening
can act as an integral characteristic of the stress-strain
state [5 - 7]. This energy is accumulated as a result
of elastic distortions of the crystal lattice caused by an
increase in the dislocation density; it is proportional to
the square of the average distortions of the crystal lattice.
The lower the latent deformation energy in the surface
layer, the higher the fatigue resistance of the part, even
at normal temperatures. When working at elevated
temperatures, this effect is especially pronounced. An
important consequence of the instability of the physical
and mechanical state of the surface layer after cutting is
the violation of the dimensional stability of parts some time
after processing. This problem is relevant not only for thin-
walled products, but also for precise parts, the dimensions of which can be distorted simply as a
result of aging [4 - 6]. An experimental assessment of the influence of technological parameters
on the accumulation of latent surface energy has shown that there is an ambiguous effect of
the same parameters on the level of latent energy when processing various materials. It was
experimentally found that wear of the cutting edge of tools affects the accumulation of latent
deformation energy sometimes to a greater extent than cutting modes [3, 5]. For example, in
[5] it is shown that for titanium alloy VT14 the power dependence of the latent deformation
energy UC on the cutting speed V, feed s, depth of cut t and tool wear hз has the form:
UC = const V0, 115s0, 25t0, 29hз 0,34.
It can be seen from this dependence that the effect of wear can be more significant in
comparison with cutting conditions. The influence of tool wear on the level of latent energy is
further complicated by the fact that there is no unambiguous assessment of the very nature
of wear. The accepted control of the flank wear does not guarantee its fair assessment of the
effect of deformations of the surface layer of the part on the accumulation of latent energy. In
works [9 - 13] it is shown that there are forms of wear when a tool with a larger wear chamfer
along the flank face creates less surface deformations than a tool with less wear, assessed by
the flank face. This suggests that the widespread periodic monitoring of the radial wear of the

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