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METALWORKING EQUIPMENT AND TOOLS METALWORKING EQUIPMENT AND TOOLS

RELIABILITY OF TOOLS WITH CARBIDE COMPOSITE technological mode. In this case, although
the coefficients of variation of the tool life
COATINGS with coatings have low values, they have a

The industrial applicability of tools made using new technologies is rather noticeable effect on the real average
determined by the stability of their operating conditions, that is, the reliability statistical tool life, and with a large production
carrying out a technological operation. Studies of the properties of carbide program, this provision must be taken into
coatings with intermediate copper-nickel films, made by electric pulse account.
technologies, show that, along with high wear resistance, they are The total statistical durability T0.9 is
characterized by increased fragility and high sensitivity to lower than the average durability T. When
sharp cyclic changes in temperature and load. In practice, processing stainless steels, the actual
the stability of the performance properties of coated tools durability decreases by 25 ... 35%. If,
can be characterized by the standard deviation σ or the when choosing the processing modes, it is
coefficient of variation Kvar of tool life. Tool life in this case necessary to guarantee the tool life with a
is considered as the time of failure-free operation with a given given level of probability (Tr / Tн), then the
probability P, which for a metal-working tool must be at least cutting speed can be determined from the
0.9. dependence, where
Industrial tests of high speed pen drills and coated circular
cut-off tools show that tool life stability with Kvar ≤ 0.2 Tн - standard period of durability;
can be considered good. With a Kvar of 0.2 ... 0.35, the U - the standard cutting speed;
resistance stability can be considered satisfactory. When m - indicator of relative durability: for steel
the coefficient of variation is outside 0.5, the process 0.2 ... 0.35, for marble 0.1 ... 0.15.
can be considered unstable and measures must be
Evaluation of the performance of tools

taken to improve the resistance indicators of the tools with coatings by the time of waste-free operation has a significant drawback as this method does
used. not allow assessing the influence of each technological factor or mechanical characteristics of
To a large extent, the coefficient of variation of the materials used separately. Therefore, from the point of view of the possibility of influencing
resistance is associated with the quality manufacture
of hard-alloy coating. In this case, the stability of the the processing process, this method is not efficient enough.

The relative change in the values of the input technological parameters is small, which
mechanical properties of multilayer coatings mainly fits
into the laws of the electrical potential of materials. The makes it possible to use the principles of linearization of functions of random variables when
finding the initial technique. An analysis of various methods for determining the mean time
creation of multilayer intermediate coatings significantly
improves the sintering ability of the carbide powder to the between failures shows that in terms of identifying the dominant factors affecting a technological
steel substrate of traditional tool steels by creating a large operation, it is quite convenient to use graphical methods of evaluation using Pareto diagrams
for express assessment. For a batch of 64 feather drills and 28 circular saws in the processing of
diffusion zone that is more resistant to shock and bending loads.
A statistical test of the performance of multilayer coatings has shown marble, granite, titanium alloy and stainless steels, when constructing the Lorenz curve, it was
found that 80% of failures can be associated with changes in the deformation characteristics of
that these tools have not only greater durability, but also a lower coefficient
of variation. The latter is due to a significantly greater difference in the the coating.
The study of the deformation characteristics of coatings, which, other things being equal,
values of the time of wasteless work (Tp) with a given probability (0.9) characterize the durability of the material, was carried out by assessing the resistance of hard
relative to the values medium durability (T). Experiments have shown that with an increase in alloys to plastic deformation in the area of developed plastic deformation. The change in the
T 2.5 ... 3 times, T0.9 increased 5.4 times. The assessment was carried out according residual stresses of the first kind in hard alloys was determined by the layer-by-layer etching
to the dependence method according to standard techniques.

Тр = Т (1 - Uр •Кvar),

where Uр − normal distribution quantile, for р = 0,9 Uр = 1,28. Table 1.1.

In practice, for tools such as drills and saws, which are designed Physical and mechanical properties of hard-alloy coatings.
for dimensional processing within 12 ... 14 precision grades, this means
5 ... 6 times the savings of tools with a
simultaneous reduction in their cost for tool Alloy coating grade Flexural strength σизг Compressive strength Hardness HV, Mpа
steels. MPа σсж MPа
Insufficient assessment of tool BK6 1250/1600 4800/5500 11600/14300
performance only by the average value ВК15 1370/1800 3200/3625 9010/11280
leads to overestimation of the average tool ТN20 1230/1875 3470/3640 8730/9120
life values. The recommended ranges of
cutting speeds were determined from the The denominator contains data for alloys with intermediate coatings.
condition that the standard tool life when
processing steels is equal to the average
tool life when working in the selected

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