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(11) or lager grade of tolerance the task can be solved. If calculated tolerance i corresponds to the ninth (9) or more exact grade of tolerance it is necessary to change ...

calculated tolerance i in the table of tolerances corresponds to the eleventh

(11) or lager grade of tolerance the task can be solved .

If calculated tolerance i corresponds to the ninth (9) or more exact

grade of tolerance it is necessary to change locating (technological datum)

without attempts to solve a dimensional circuit since in a workpiece machining

the probability of deriving of reject (invalid part) is great .

REFERENCES

1. .. : . 2- .

: , 2009. -90 .

2. .., . 1. - , 2003. 943 .

CONTACT LOADS ON SURFACES OF WORN OUT CUTTER IN

STEEL MACHINING

Zhang Jiayu, Kozlov Victor Nicolaevich, Guo Yingbin, Sabavath Sai Kiran Scientific supervisor: Victor Nicolaevich Kozlov, Ph.D. (Engineering), Associate Professor of NR TPU National Research Tomsk Polytechnic University, Tomsk, Russia For calculation of a cutting tool strength, it is necessary to know not only component forces of cutting, but also distribution of contact loads on rake and flank surfaces [1-5]. This task is especially important for rough cutting by the worn out cutting tool. Wear on a flank surface leads to appearance of a chamfer on a flank surface (flank-land) and the big contact loads leading to a tool failure .

The method of a section tool is used for research of contact stresses distribution [1-5]. It is very labour-consuming and demands the use of rigid, special four-component dynamometer. Therefore research was carried out for defining the parametres of contact loads distribution which can be used for loading of cutting tool for calculation of cutting tool strength .

Research of force dependences was executed in turning a workpiece made from a steel 40 with hardness 220 and ultimate tensile stress VIII -

UTS=1000 MPa by a cutter with a cutting plate made from cemented carbide T15K6. The principal edge angle in the plan =45 , the end cutting-edge angle 1=45 , the side-rake angle = +5 , the side-relief angle = 12 , the angle of the principal cutting edge inclination =0 , artificial chamfer length hf was varied from zero to 0.95 mm with a constant clearance angle h=0 .

For elimination of a variance in the depth of cut t after each cutting the real (actual) depth of cut tact (mm) was calculated. Actual specific force of

cutting was calculated for tangential component Pz:

   

This precisely determined force Pz pr was used for construction of graphs of cutting force dependence from the feed rate s, the depth of cut t and the length of a chamfer on a flank surface hf .

For research of influence of feed rate s on a specific tangential component of cutting force qPz act (P) corresponding graphs have been constructed (Fig. 1). Similar equations were used for calculation of more precisely determined components Px pr and Py pr .

In our research the precisely determined resultant force of cutting force





components, acting in horizontal plain XOY, Pxy was also calculated:

   

Graph of this specific cutting force qPxy pr dependence on feed rate s is presented in Fig. 1. Increasing feed rate s causes reducing the specific cutting forces qPz and qPxy .

   

Fig. 1. Influence of feed rate s (mm/r) on specific cutting forces (MPa) in steel 40 machining. t = 2 mm; v = 2 m/s; hf = 0.29 mm By results of graphs of cutting force components Pz and Pxy, the forces Pz r, Pxy r, acting on the rake surface of the cutter, have been selected by the method of extrapolation on a zero chamfer of a flank surface (hf 0 mm) .

Using these components of cutting force Pz r and Pxy r the normal N and the tangential (shear) F forces on the rake surface were calculated with the account of the principal angle on the plan and the side-rake angle .

These forces were used to create epures of normal and shear contact stresses on the rake surface of the cutting tool (Fig. 2) based on the law of contact stresses distribution, received by us [1, 3] and other scientists [2, 4, 5] .

When constructing the drawing, the condition to be met is as follows :

c N xi dx (N), (5) c F xi dx (N), (6) where xi is normal contact stress in a considered point i from a cutting edge on a rake surface of a cutting tool (P); xi shear contact stress in a considered point i from a cutting edge on a rake surface of a cutting tool (P);

is length of contact of a chip with a rake surface of a cutting tool (mm) .

By results of our experiments it was acknowledged that the greatest normal contact stress on the rake surface max 19002300 MPa, depending on feed rate s, that is approximately 2 times more than ultimate tensile strength of a steel 40. The parametres max, const, max, l0 and l1 of contact stresses on the rake surface of a cutter (Fig. 2) were calculated .

VIII -

Fig. 2. Parametres of contact stresses epures on the rake surface of the cutter. Abscissa is distance from a cutting edge along a rake surface x i (mm). Ordinate is contact stress on a rake surface (MPa) On Fig. 3 experimental points are presented and graph, after their calculation by program MathCAD to rectilinear dependence is constructed .

Fig. 3. Feed rate s (mm/r) influence on magnitude of the greatest normal contact stress at a cutting edge in steel 40 machining .

Shear contact stress on a rake surface in steel machining on the area with length l1 = c1 (mm) does not vary at moving far from the cutting edge, which confirms plastic character of a chip contact with a rake surface .

Magnitude max 200 MPa is equal to shear strength of this steel at a temperature nearby 700 that corresponds to knowledge about the processes occurring on a rake surface [1, 3, 4, 5] .

In our opinion, equations experimentally determined for steel 40X are possible to use also for other brands of steel when the continuous chip is forming. A major factor which influence on contact stresses is ultimate tensile strength UTS (UTS) (MPa) .

   

Considering that in our experiments the steel with UTS = 1000 (MPa) was being machined, we offer for calculation of epures parametres on the rake

surface of the cutting tool (see Fig. 3) to use following equations:

   

VIII -

At a cutting edge contact stresses are almost equal to zero, and at moving far from the cutting edge they are essentially increased on an exhibitor. It is connected with a sag mn1j of cutting surface under the influence of a radial component cutting force on the rake surface Py r in machining of the materials forming a discontinuous chip (Fig. 5) [3] .

Fig. 5. The sag of the reference surface mn1j under a radial component of cutting force on a rake surface Pyr (Pyn) With increasing feed rate s the radial force on a rake surface Py r is increased, but a length of projection of a conditional shear plain on a transient surface l is also increased .

   

where is shear angle () .

Specific normal load qPy r = Py r / (l b) (MPa) is thus diminished, and the wave length of a sag is increased. This in appearance, a paradoxical hypothesis proves to be true by results of our experiments, i.e. with increase of feed rate s contact stresses at a cutting edge are diminished .

Acknowledgments The research is carried out at National Research Tomsk Polytechnic University within the framework of National Research Tomsk Polytechnic University Competitiveness Enhancement Program grant .

   

2. Hu J., Chou Y. K. Characterizations of cutting tool flank wear-land contact // Wear, 2007, v. 263, (7-12 SPEC), pp. 1454-1458;

3. Kozlov V. N. Flank Contact Load Distribution at Cutting Tool Wear // Proceeding of the7th International Forum on Strategic Technology, IFOAT2012, 2012, v. 2, pp. 147-151 .

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. : , 1969. 148 .

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8. Artamonov E.V., Chernyshov M.O., Pomigalova T.E. Improving the Performance of Composite Bits with Replaceable Inserts // Russian Engineering Research, 2017, v. 37, No. 4, pp. 348350 .

9. Proskokov A. V. and Petrushin S. I. Chip Formation with a Developed Plastic-Deformation Zone // Proceeding of the7th International Forum on Strategic Technology, IFOST2012, 2012, v. 2. pp. 173-177 .

10. Afonasov A. and Lasukov A. Elementary Chip Formation in Metal Cutting // Russian Engineering Research, 2014, v. 3, pp. 152-155 .

Artamonov E. V., Vasilev D. V., Kireev V. V., and Uteshev M. Kh .

11 .

Mechanics of Chip Formation in Cutting // Russian Engineering Research, 2017, Vol. 37, No. 5, pp. 450454 .

CALCULATION OF TECHNOLOGICAL DIMENSIONS

Sabavatch Sai Kiran, Otokuefor Jerome Tzeyi, Okang Imeiba Victor Scientific supervisor: Victor Nicolaevich Kozlov, Ph.D. (Engineering), Associate Professor of NR TPU National Research Tomsk Polytechnic University, Tomsk, Russia The designation of TP represents a multialternative task, the correct solution of which requires realization of a number of calculations. In the beginning of designation kinds of processing of blank surfaces and methods of achievement of their accuracy appropriate to the requirements of the drawing, type of manufacturing and equipment, existing in the machine shop, previously are defined or established.




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