Evaluation of the cutting edge wear and of the technological speed for the 13H11N2V2MFS stainless steel turning.

Vlase, Auremia ; Ghionea, Ionut ; Munteanu, Gabriel 等

1. INTRODUCTION

The stainless steel properties, like a very good resistance to corrosion factor actions and to high temperature, made these materials suitable to be used for a wide range of application from chemical or energetic to the alimentary or health industries. Even though, some characteristics like the high toughness, low thermal conductibility and cold-hardening during the cutting processing, are reducing the workability ratio. Therefore, a disadvantage we shall mention is the low workability of stainless steels have a (Barlier, C., 1999) but to obtain an increase for this parameter, some alloyed materials like S and Se are used (Shaw, 1999). The above mentioned research continues the author concern regarding the workability of stainless steel (Ghionea, A., Vlase, A., Ghionea, I., 2007).

2. CUTTING CONDITIONS

In Table 1 are presented some chemical characteristics of the steel 13H11N2V2MFS and the most important mechanical characteristics are shown in Table 2. Other information about the elaboration by casting, thermal treatments, mechanical characteristics, metallographic study is available in standards (STAS 3583-87, DIN EN 10988, NF EN 10027). The determinations and measurements were made according to some experimental conditions. Thus, the following elements of the technological system have been used:

* the semi-products used for experimental determinations are obtained by casting under the shape of bar;

* the high-speed steel cutter is suitable for stainless steel that have high plasticity and low hardness properties;

* the cooling and lubricating fluid: P 20% emulsion environment improves the cutting processing;

* machine tool: turning machine, SNA 500 type, 24 speed steps ([D.sub.nc]: 16...1600 rpm), 21 feed steps ([d.sub.fL]: 0.028...5 mm/rot), motor drive power PME = 7.5 kW;

* turning tool STAS 350-82 from Rp5 STAS 7382-88, 6-5-2;

* for cutting: UAS-200 machine with special cutting device.

3. METHOD AND EXPERIMENTAL RESULTS

The method of parametric analysis was applied and the experimental data established were processed mathematically (Parakkal, G. & al., 2002), (Spur, G. & Stoferle T., 1979). In order to establish a suitable relation of assessment for the tool cutting edge wear on the side face, it is taken into consideration the relation from (Vlase, A., 1973), under the form:

VB = [C.sub.VB] x [d.sup.x.sub.L] x [f.sub.L.sup.y] x [v.sub.c.sup.z] x [[tau].sup.w] x [mm] (1)

where: [d.sub.L] is the depth of cut, in mm, VB--wear dimension, in mm; [f.sub.L]--feed, mm/rev, [v.sub.c]--technological cutting speed in m/min; t--working time, in min.; x, y, z and w--polytrophic exponents, CVB--the constant which depends on the piece's material and of the cutting tool.

The relation (1) becomes linear if we apply the logarithm function, as follows:

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

In equation (2) they were introduced five sets of values chosen among a greater number of data experimentally established and presented in Table 3.

The following restrictions were imposed: [d.sub.L] = 0.25...0.50 mm and [f.sub.L] [less than or equal to] 0.2 mm/rev.

[FIGURE 1 OMITTED]

In the Figure 1 is presented the equipment and the testing instruments used for measure the parameters (Vlase, I., 2001). The wear is measured using a microscope and the dimension is shown at different moments of wears expanding. Some other processes have been made by the preliminary determinations with [f.sub.ax] > 0.25 mm/rot.

In this last case the percent of the cutting edges' breaking was high.

Having the relation (2) and the data from the table 3 it can be formed a five equation system, where CVB, x, y, z and w are the unknowns.

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3)

Then, we have determined the numerical values for the five unknowns: [C.sub.VB] = 1.74 x [10.sup.-8], x = 0.91, y = 1.2 and z = 3.92, w = 0.89.

From the relation (2) results the formula of the wear for the 13H11N2V2MFS steel as a regression function, as shown:

VB=1.74 x [10.sup.-8] x [d.sub.L.sup.0.91] x [f.sub.L.sup.1.2] x [v.sub.c.sup.3.92] x [[tau].sup.0.89] x [mm] (4)

In the stainless steel turning process it is recommended the admissible cutting edge tool wear in a range of 0.5 to 0.7 mm. At the limit condition of VB=0.7, the cutting speed formula is:

[v.sub.c] = 87.08/[T.sup.0.227] x [d.sub.L.sup.0.232] x [f.sub.L.sup.0.306] x [m/min] (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 t is replaced with the tool life, in minutes.

[FIGURE 2 OMITTED]

Based on the relations (4) and (5) there can be represented the variation curves of VB and [v.sub.c] parameters considering [D.sub.t], [f.sub.L] or [tau]. In Figure 2 are shown the graphical representations of the wear VB variation diagrams with the most important parameters D, and [v.sub.c]. The resulting chips are discontinuous. Also, a superior value of the cutting depth or speed causes an increase of the wear dimension, so the range shall be avoided.

[FIGURE 3 OMITTED]

Based on the proposed equation (5) we represent in the figure 3 the graphical representation of the speed [v.sub.c] variation diagrams with the parameters [d.sub.L] and [f.sub.L].

From these graphics we can observe that as the cutting depth [d.sub.L] or feed [f.sub.L] is increasing, the cutting speed will decrease; therefore, a lower speed is helpful to improve the quality of cutting.

4. CONCLUSIONS

The objective of this paper consist in the establishing of two regression functions for the analytical evaluation with experimental data of two specific parameters for the cutting process: edge wear and the technological speed, applied for wide use.

The model consists of two equations, (4) and (5) suitable for 13H11N2V2MFS stainless steel cutting tool wear behavior. The established equations have the accuracy comparable with other methods that requires a larger amount of materials and tools.

Therefore, we consider that an economic gain is obtained by using the current model and the tool manufacturer as well as the final users may find it very helpful in order to reduce the time for experimental determination and to low the amount of materials or tools.

All the results obtained and above mentioned are a contribution in order to establish the index of workability for the stainless steels and confirm the classification of 13H11N2V2MFS stainless steel 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

Ghionea, A., Vlase, A. & Ghionea, I. (2007). The wear evaluation of the cutting edge and the cutting speed in the drilling process of some manganese steels, Proceedings of the 18th International DAAAM Symposium, Katalinic, B., pp. 295-296, ISBN 3-901509-58-5, Vienna,[degrees]Ctober, 2007, Published by DAAAM International, Vienna

Parakkal, G. et al. (2002). Modeling of turning process cutting forces for grooved tools. International Journal of Machine Tools & Manufacturing 42 (2002), 179-191

Shaw, M. C. (1984) Metal cutting principles, Clarendon Press Oxford

Spur, G. & Stoferle Th. (1979) Handbuch der Fertigungstechnik, Band 3/1 Spanen, Carl Hanser Verlag, Munchen Wien

Vlase, A. (1973). Contributions regarding the genuine stainless steel workability, Ph. D. Thesis, University Politehnica of Bucharest

Vlase, I. (2001). Contribution regarding the determination of the assessment indicators concerning refractare steel workability, Ph. D. Thesis, University Politehnica of Bucharest

Tab. 1. Chemical characteristics

 C Mo Ni Cr Mn Si S P V N

0.12 2.0 2.5 11.5 0.7 0.9 0.02 0.03 0.3 0.02

Tab. 2. Mechanical characteristics

Tensile Flowing
strength Limit Elongation Hardness
[R.sub.m] [R.sup.02] [delta] HB
[N/[mm.sup.2]] [N/[mm.sup.2]] [%]

1080 788 9.2 185

Tab. 3. Experimental results

 Cutting Working
No. Depth, Feed, speed, time, Wear
 of [d.sub.L], [f.sub.l] [v.sub.c], [tau], VB,
det. [mm] [mm/rot] [m/min] [min] [mm]

 1 0.50 0.1 108.5 8 0.354
 2 0.50 0.2 105.5 8 0.729
 3 0.50 0.1 163.3 8 1.759
 4 0.25 0.1 101.0 8 0.142
 5 0.25 0.1 99.5 12 0.193