DETERMINATION OF TECHNOLOGICAL CONDITIONS

BY ELECTRO-IMPULSE LATHE WORK HARDENING

S. Kovalevskyy1 V.Tulupov2

1DSEA, Kramatorsk, Ukraine,

2DSEA, Kramatorsk, Ukraine,

Summary: The analysis of methods of prognostication of quality of the processed surface is conducted for ultra high speed heat turning. Chosen as maximally exact and acceptable for determination of the modes of turning of the developed technological method of the electro-pip hardening by lathe turning, method in-use integral temperature-timeline description and developed algorithm in the software product of MathCAD allowing the model of evolution the thermal fields in real time depending on technological parameters.

Keywords: current, impulse, lathe work, thermal field.

1. INTRODUCTION

Decision influence on the structural changing and phases transitions do the kinetic and thermodynamics terms of turning of metal, forming the physical-mechanical state of superficial layer of detail, that influences on his operating properties here [1].

For the technological providing of the set hardness, structure and phase composition, strengthening depth, in the process of impulsive turning of working surfaces of details of machines, there is the issue of the day of estimation of dynamics of the temperature fields which depend on the power terms of the impulsive strengthening.

In the process of the electro-impulse lathe work hardening (ЕILWH) that includes tooling by the clean sharpening with the simultaneous key-in of impulsive current of rectangular form through the area of contact of cutting instrument with a detail [2, 3], which forms the regular discrete structure (RDS) of surface as the fixed fragments of white layer.

The fixed fragments form RDS, depending on frequency and pulse width current, and also modes of tooling (longitudinal serve and frequency of rotation of spindle), distributing of these fragments is set on a surface that is processed. Hardness of these fragments will depend on the temperature-timeline mode, brands of material that is processed and his initial state.

2. BASIC PART

Determination of method of pointing of the modes of ЕILWH is the purpose of work depending on the necessary depth of strengthening of surface and hardness of the fixed fragments that determines technological possibilities of this method of turning in public.

Author [1] based on the results of researches asserts, that at implementation of terms (1) to transformation of high-quality white layer is provided:

, (1)

where: КЕ – is power coefficient (set experimentally);

с – is the specific heat capacity of metal, that is processed, J/(кg×˚С);

Тз – is the temperature of temper of metal, ˚С;

Ро – is middle specific pressure on the local volume of metal, МPа;

τ – is time of thermal action on the local volume of metal, that is processed.

The offered method does not take into account the law of division of thermal stream and temperature-timeline description of process of turning, and that is why is not accomplished.

In [4], for determination of the necessary technological modes of electro-mechanics turning, authors use found by the critical temperature (by the veritable temperature of beginning of education) of Тк which suggest to find operating by the following empiric equalization of similarity of temperatures at different speeds of heating:

(2)

where: Т – is temperature of temper at the known mode;

Т1 – is temperature of temper at the sought mode after;

k – is a permanent size that depends on the brand of material;

nv – is the factor of similarity of speed of heating

and stalling speed of temper of Vк:

(3)

where: Ac – is temperature of critical point;

Тmin – is the temperature of minimum firmness of austenite;

τmin – is time of minimum firmness of austenite.

This method of determination of the modes of turning has also failings is small exactness of calculation.

The results of the conducted researches [5] show that to set synonymous connection of numeral values of thermal cycles indexes with the modes of turning and descriptions of quality of the fixed layer is not possible. Obviously, what the numeral values of thermal cycles indexes concerne by the size of the entered energy and character of its distributing in material.

On the basis of it is offered [6] at setting of the modes of hard-facing with the use of the concentrated sources of heating to use in place of two parameters: middle speed and maximal temperature of heating, one complex – integral temperature-timeline description of S (4), which allows completer to describe the thermal processes of education in a metal (Figure 1):

. (4)

By the compatible design of the temperature fields and process of processes of transformations austenite of steel the set numeral values of description of S, which provide the completeness of process of transformations austenite of steel, and also certain dependences of values of this description from maintenance of carbon at steel (Figure 2) and initial state of material, were an author [6] (Figure 3).

Figure 1. Kinetic curve of heating and cooling became in the process of hardening [6]

Curve 2 answers the uncompleted process of аустенитизації, at which in the stage of cooling can be fixed 50 % martensite, if in this layer there will be the attained values of description of S, proper to the curve 1, it guarantees the receipt in this layer of homogeneous shallow corn of austenite and, consequently, and shallow dispersion martensite in the process of the proper cooling of steel.

Thus, taking advantage of the built graphs of evolution of the thermal fields (Figure.4) which arise up in the process of ЕILWH and integral temperature-timeline description of S (Figure. 2, 3), during the lead through of their analysis possibility of prognostication of quality of flowing of process of turning appears with the purpose to getting of the necessary state phase-structural of surface layer of detail.

Figure 2. Dependence of temperature-timeline description on the concentration of carbon in steel (a0 = 0,8·10-3 mm) [6]
Figure 3. Dependence of temperature-timeline description on the structural factor of а0: 1 – is steel 45; 2 – is steel of У8; 3 – is steel of У10 [6]
Figure 4. Graph of evolution of the thermal field of compatible action of thermal streams from the process of cuttings and one impulse on the local fragment of surface, that is processed

So for example, at turning of ЕILWH detail from steel 45 ГОСТ-1050-88, critical point of what Ас1=730°С, with cutting speed v=100 m/min.; by the serve S=0,2 mm/rev.; by the depth of cut t=0,5 mm; by frequency of impulse current of f =100 Hz; by a pulse width τі = 5×10-3 s; by density of current j=1,25·103 А/mm2 matters τ1=1×10-4 s and τ3=4,2×10-3 s.

Figure 5. Graph of description in dependence on the values of τ1 and τ3, which concerne from the graph of evolution of the thermal field

Defining at a maximal temperature Tmax=1800°С value of description S=5,25, after the graph of dependence of temperature-timeline description from the concentration of carbon in steel (Figure 2) and after the graph dependence of temperature-timeline description on the structural factor of а0 (Figure 3), we draw conclusion, that the process of transformations austenite not is completed, here in the stage of cooling can be fixed 50 % martensite.

3. CONCLUSIONS

Thus using the model of the thermal field, which arises up in the process of ЕILWH description of S, that determines the integral temperature-timeline action on a metal in place of middle speed and maximal temperature of heating allows more precisely to forecast the general depth of receipt more shallow dispersion structures of the fixed layer and to appoint the modes of turning for this technological method.

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