The wear evaluation of the cutting edge and the cutting speed in the drilling process of some manganese steels.

Ghionea, Adrian ; Vlase, Aurelian ; Ghionea, Ionut 等

Abstract: This paper presents some data experimentally determinated in the drilling process of the manganese steels T70Mn140 and T105Mn120. It is elaborated a methodology to determine the relations of regression for the tool wear and for the cutting speed. Some determinations were taken into consideration, defined by values of the process parameters. The measurable data defining the cutting process is processed mathematically and they were transposed under the shape of a relation in order to determine the wear of the cutting edge and speed. Also, it is presented the form of the regression functions, as well the variation of the technological cutting speed in dependence of the drill diameter and of the tool's feed.

Key words: wear, cutting speed, relations of regression..

1. INTRODUCTION

The antiwear austenitic manganese steels (Hadfield) have a greater resistance than the carbon steels with the same yield strength [R.sub.m]. These steels have a good wear resistance in the abrasion process, combined with high ductility and tenacity, being used in the machining process of the parts submited to wear, especially: jaws, crusher rings, teeth and excavator buckets, chains for tracks, pieces for drilling. It is known the reduced machinability of these steels [Barlier, C., 1999]. To extend the utilization of the manganese steels on a large scale, owing to their mechanical and chemical properties, require some researches to determinate their properties of cutting [Research contract, nr. 574, 2000]. The work presents a parametric methodology applied to approximate the relations through regression functions.

2. INITIAL DATA

In table 1 are presented some chemical characteristics of the steels T70Mn140 and T105Mn120. Also, the most important mechanical characteristics of these steels are presented in Table 2. Other informations about the elaboration by casting, thermal treatments, mechanical characteristics and metallographic study of the semiproducts are presented in [STAS 3718-88; Research contract, nr. 574, 2000].

The determinations and the measurements were made according to some experimental conditions.

Thus, the following elements of the technological system have been used:

* machine tool: radial drilling machine, type RF 22/B, having 12 speed steps ([D.sub.nc]: 45 ... 2000 rpm), 9 feed steps of advances ([D.sub.fax]: 0.05 ... 1.25 mm/rot), motor drive power [P.sub.ME] = 7,6 kW;

* cutting tools: drill with drilling heads, with changeable bed plates mechanically attached, ordering code IDI 200-SG ISO M20-M30, IC908 [ISCAR METRIC Catalogs, 2000].

* the semi products used for experimental determinations are obtained by casting under the shape of bars or discs under conditions of laboratory.

3. METHODOLOGY

The method of parametric analysis was applied and the experimental data established were processed mathematically. To establish the relation of assessment for the tool cutting edge wear on the side face, it is taken into consideration the relation from in [Vlase, A., 2007], under the form:

VB = [C.sub.VB] x [D.sup.x.sub.t] x [f.sup.y.sub.ax] x [v.sup.z.sub.c] x [[tau].sup.w] (1)

where: [D.sub.t] is the tool's diameter, VB--size of the wear, in mm; [f.sub.ax] and [v.sub.c]--parameters of the cutting conditions; [tau]--working time, in min.; x, y, z and w--polytropic exponents, [C.sub.VB]--the constant which depends on the piece's material and of the cutting tool. The relation (1) is linearized by logarithmizing,

lg VB = lg [C.sub.VB] + x lg [D.sub.t] + y lg [f.sub.ax] + z lg [v.sub.c] + w lg [tau](2)

In equation (2) were introduced six sets of values chosen among a greater number of data experimentally established and presented in Table 3. The first five determinations reffers to the manganese steel T70Mn140 and the 6th is for T105Mn120. The following restrictions were imposed: Dt = 10 ... 20 mm and [f.sub.ax] [less than or equal to] 0.15 mm/rot. Some other processes have been made by the preliminary determinations with [f.sub.ax] > 0.3 mm/rot. In this last case the percent of the cutting edges' breaking was high.

All the experimental results were obtained with cooling conditions (Castrol Syntil R, 5% concentration). Having the relation (2) and the data from the table 3 can be formed a six equation system, where [C.sub.VB], x, y, z and w are the unknowns.

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3)

In the next stages there are determined the numerical values for these five unknowns.

Thus, subtracting the 4th equation from the 2nd equation, results: w lg 5.8 - w lg 13.4 = lg 0.388 - lg 1.218, from which: w = 1.365. In the same way, are deduced: x = -1.8, y = 1.12 and z = 3.82. Replacing the calculated values for x, y, z and w in equation (1) results: [C.sub.VB1] = 1.092 x [10.sup.-3], which corresponds to the T70Mn140 steel. Thus, the relation (2) become the relation (4) and represents the calculus of the wear for the T70Mn140 manganese, being a function of regression and has the form:

[VB.sub.1] = 1.092 x [10.sup.3] x [D.sup.-1.8.sub.t] x [f.sup.1.12.sub.c] x [v.sup.3.82.sub.c] x [[tau].sup.1.365] x [mm] (4)

To determine the value of the constant CVB2, for the manganese steel T105Mn120, in the 6th equation of the system (3), there are replaced the numerical values of x, y, z and w, resulting:

[C.sub.VB2] = 1.26 x [10.sup.-3].

The calculus relation of the cutting edge wear for this steel is:

[VB.sub.2] = 1.26 x [10.sup.3] x [D.sup.-1.8.sub.t] x [f.sup.1.12.sub.c] x [v.sup.3.82.sub.c] x [[tau].sup.1.365] x [mm] (5)

Relations (4) and (5) are used to determinate the calculus relations of the technological cutting speeds for different values of the admissible wear VB, in mm. The parameter [tau] is replaced with the tool life, in minutes. Thus, it results the calculus relation (6) of the technological cutting speed for each of the two considered steels (index 1, respectively, 2), as follows:

[v.sub.x1,2] = [([VB.sub.1,2]/[C.sub.VB1,2]).sup.0.262] x [D.sup.0.471.sub.t]/[T.sup.0.357] x [f.sup.0.293.sub.ax] (6)

The ratio [VB.sub.1,2]/[C.sub.VB1,2] differs by the value of [C.sub.VB1,2] constant (Table 4).

The shape of the drilling head cutting edges is a curve. Some values of the work parameters: rotation [n.sub.c] = 180 rot/min, feed [f.sub.ax] = 0.112 mm/rot. Total length of the eight holes of each piece is 203 mm, which represents 10 min work duration. The penetration rate, for each hole, is less than 2 x [D.sub.t], the maximal value indicated in [Research contract, nr. 574, 2000]. For each tool, on any cutting edge sitting face appeared a wear mark of 0.37 ... 0.4 mm wide.

The resulting chips are discontinuous (Figure 1). At hole's depth greater than 10 mm, the temperature in the cutting area increases, as well the friction between chips and the exhaust channels. Also, the chips are colored in blue and brown.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

Based on the relations (4), (5) and (6) there can be represented some variation curves for the VB and [v.sub.c] parameters for values of the [D.sub.[tau]], fax and [tau].

In Figure 2 is shown an example of a graphical representation of the speed [v.sub.c] variation diagrams with the parameters [D.sub.[tau]].

4. CONCLUSIONS

The method of the regression analysis has been used to settle the relations of calculus for the wear of the tool cutting edges for each of the two considered steels on the setting-up face and for the economical cutting rate. The intensification of the edges wear is revealed by increasing the chips forces and torque, the shape and color of the chips, the quality of the surface, the apparition and growth of a burr at the ends of the bore. The results obtained are a contribution in establishing the index of workability for the manganese steels and confirm the classifications of the respective steels within the class of materials with a reduced workability through cutting.

5. REFERENCES

Barlier, C. & Girardin, L. (1999). Memotech. Productique, materiaux et usinage (Memotech. Production, materials and machining), Editions Casteilla, ISBN 2.7135.2051.7, Paris.

Vlase, A.; Ghionea, A. & Ghionea, I. (2007). Determination of the calculus relations for the tool wear and the cutting speed in the turning of the manganese steel type T105Mn120, Proceedings of the 5th International Conference on Advanced Manufacturing Technologies ICAMaT 2007, Vlase, A. (Ed), pp. 337-342, ISSN 1843-3162, Romania, july 12-14, 2007, AGIR, Sibiu.

*** ISCAR METRIC CATALOGS (2000), (CD version), march.

*** Researches and realization of some optimal technologies for the machinability by cutting of the manganese steels. (2000). Research contract, nr. 574/7.09.2000, Relansin Program, AMCSIT Politehnica Bucharest, Romania.

*** STAS 3718-88, Marks and characteristics for the manganese steels, Romanian standard.

Table 1. Chemical characteristics

Steel mark C Si Mn Ni Cr

T70Mn140 1.70 1.05 13.8 1.90 0.17
T105Mn120 1.18 0.90 13.4 0.95 0.15

Steel mark Mo Cu Al Mn

T70Mn140 0.16 0.017 0.028 0.023
T105Mn120 0.05 0.019 0.038 0.027

Table 2. Mechanical characteristics

 Thermal treatment

 Quenched

 [R.sub.m] [A.sub.5] [R.sub.mi]
Steel mark [MPa] [%] [MPa]

T70Mn14O 890 50 278
T105Mn120 830 43 257

 Thermal treatment

 Quenched--tempered

 [R.sub.m] [A.sub.5] [R.sub.mi]
Steel mark [MPa] [%] [MPa]

T70Mn14O 327 29 157
T105Mn120 310 19 147

Table 3. Experimental results

 Tool
No. diam., Feed, Speed,
of [D.sub.t], [f.sub.ax], [n.sub.c],
det. [mm] [mm/rot] [rot/min]

1 20 0.075 250
2 10 0.075 500
3 14 0.112 355
4 10 0.075 500
5 20 0.075 355
6 10 0.075 355

 Cutting Working
No. speed, time, Wear
of [v.sub.c], [tau], VB,
det. [m/min] [min] [mm]

1 15.7 27.2 0.918
2 15.7 5.8 0.388
3 15.7 10.3 0.727
4 15.7 13.4 1.218
5 22.3 8.5 0.718
6 11.15 15.4 0.459

Table. 4. Values of the cutting speed constant [C.sub.vc1,2]

 Parameter
 Cutting speed
 [v.sub.c1,2] [m/min.] Diameter [D.sub.t], [mm]

Manganese steels: [v.sub.c1,2] = <12 12...18 19...25
T70Mn140, index 1 [C.sub.vc1,2] x
T105Mn120, index 2 [D.sup.0,471.sub.t] / Wear [VB.sub.1,2], [mm]
 [T.sup.0.357] x
 [f.sub.ax.sup.0,293] 0.40 0.60 0.80

 Constant [C.sub.vc1]

 4.69 5.20 5.62

 Constant [C.sub.vc2]

 4.51 5.02 5.41