RESEARCH OF PROCESSED SURFACE ROUGHNESS FOR TURNING HARDENED STEEL BY MEANS OF CERAMIC CUTTING TOOLS V. P. DASIC High Technical School, R. Krstica 19, 37240 Trstenik, YUGOSLAVIA; e-mail: dasicp@ptt.yu SUMMARY In the paper is given the experimental research for processed surface roughness parameters R a and R max in depended to cutting time and elements of cutting regime for turning hardened steel by means of ceramic cutting tools. Correlation coefficient in all example is greater than 0,97. Keywords: metalworking, turning, ceramic cutting tools, processed surface roughness 1 INTRODUCTION In the basic phase of development, ceramic cutting tools was applied for processing of cast iron in multi-serial production with small part of hard iron and hard materials. According to the development of ceramic cutting tools in the direction of the greater hardness, it happened that application part of steel has accelerated tendency [2, 8, 9]. Ceramic cutting tools are produced as multi-bladed indexable inserts for application in turning, milling and planing of cast iron, almost all kinds of steel, high hardness tempering steel of 40-65 HRC. According to basic chemical structure of ceramic composite materials, it is not recommend to process aluminum, titan and their alloys. 2 TERM OF TESTING The experiment has been realized in the production conditions of the Industry "14. October" in Krushevac under the following conditions: operation: external finished turning, material: steel C.1730 (according to JUS standard) or C60 (according to DIN standard) or EN9 (according to BS standard), which characteristics are: R m = 800-950 N/mm 2 and 230-270 HB, machine for turning: CNC lathe MD10S from the firm Max Muller, cutting tools: tool holder CCLNL2525M16 and the indexable inserts CNGN160808 (and 12) T02020 made of mixed ceramic SH20F from the firm SPK- Feldmuhle, nose radius: r = 0,8 and 1,2 mm, elements of the cutting regime: a = 0,25-0,4 mm, s = 0,08-0,15 mm/rev and v = 450-600 m/min and processing without cooling or lubrication means. In flow testing have been registered processed surface roughness parameters R a and R max depended to cutting time and elements of cutting regime. 3 DEPENDENCE OF PROCESSED SUR- FACE ROUGHNESS PARAMETERS AND CONCENTRATED TOOLS WEARING Many researchers developed several mathematical models of dependence of tools wearing and processed surface roughness. In all developed models, as an important parameter, appeared values of concentrated tools wearing [2, 5, 7, 10, 12]. Dependence of surface roughness parameters and concentrated tool wearing could be mathematical represent by equation: R a = f(vb) (1) or equation: R a = f(t) (2) in which the concentrated tool wearing VB is replaced with cutting time t. The review of measured values of mean arithmetic deviation of the profile R a in [µm] depended to cutting time t in [min], for finished turning of steel C60 with cutting tool from mixed ceramic for elements of cutting regime a = 0,25 mm, s = 0,08 mm/rev and v = 600 m/min, is given in the table 1 [4, 5]. Dependence of R a = f(t) we will try to describe by power polynomial. Comparative analysis of the polynomial of the first to the fifth power, according to the methodology shown in the book [2, 4, 5], is presented at table 2 [5]. From the table 2, it could be noticed that the power polynomial of the first (t), the third (t 3 ) and the second (t 2 ) degree have the greatest influence to the total variation of the depended variable. That is the base for choosing the third power polynomial (the third regression equation from table 2) as the polynomial which can adecvatly describe function R a = f(t) and it is given in the form (figure 1) [4, 5]: R 2 3 a = 0,36735 + 0,12081 t - 0,0109 t + 0,00035 t (3) its index of nonlinear correlation is R = 0,97325.
Table 1: The table review of measured values of R a depended to t for turning in the steel C60 by ceramic cutting tools Figure 1: Graphic review of experimental data and calculated values of dependence R a = f(t) Table 2: The table review of the analyzing the approximated dependence R a = f(t) by power polynomial 4 DEPENDENCE OF PROCESSED SUR- FACE ROUGHNESS PARAMETERS AND ELEMENTS OF CUTTING REGIME Mathematical equation which shows function of maximum bumps height of profile R max is based on the well known equation in literature for a long time, and it considers the sharp tool process. It gives link between R max and the shape of the tool top and its step is [7, 10, 12, 13]: 2 s Rmax = 125 (4) r In many testing the processed surface roughness through cutting on the lathe with sharp tools, it is noticed that, because of the influence of the many factors, results calculated according to the equation (3) do not match the measured values for processed surface roughness parameters. The value of maximum bumps height of profile R max for different conditions can be shown in equation: n 2 s Rmax = k (5) r Researching the process of turning by sharp tools and with concentrated tools wearing, many researchers introduced, in the equation, several influential factors which characterize the cutting process on the lathe so the maximum bumps height of profile R max has the form: R max = f(c, a, s, v, r, VB, κ, α, γ, CAL,...) (6) or mean arithmetic deviation of the profile R a : R a = f(c, a, s, v, r, VB, κ, α, γ, CAL,...) (7) It is certain that the regression equation of processed surface roughness parameters R a and R max can be described as a degree function with or without interaction factors. The review of measured values of R a and R max in [µm] depended to elements of cutting regime a, s and v and nose radius r is given in the table 3 [1, 3].
Table 3: The table review of the measured values of R a and R max depended to a, s, v and r for turning in the steel C60 by ceramic cutting tools According to the previous methodology [1, 3, 6] for mean arithmetic deviation of the profile R a depended to a, s, v and r it was chosen regression equation as follows (figure 2) [1, 3]: 0,1136 1,2005 a s Ra = 62,1369 (8) v 0,3017 r 0,7525 its correlation coefficient is R = 0,99835 and mean relative error of the experiments is α rel = 2,1757 %. surface roughness parameters and influential factors for certain kind of material and cutting tools, too. The review of experimental value of the interactive dependence of processed surface roughness parameters R max = f(r a ) for different values of the elements of cutting regime is given in the table 4. And for maximum bumps height of the profile R max depended to a, s, v and r it was chosen regression equation as follows (figure 3) [1, 3]: 0,1476 0,9279 a s Rmax = 220,1837 (9) v 0,2827 r 0,6674 its correlation coefficient is R = 0,99756 and mean relative error of the experiments is α rel = 1,8613 %. 5 INTERACTIVE DEPENDENCE OF PROCESSED SURFACE ROUGHNESS PARAMETERS Numerical links between mean bumps height of the profile R z and mean arithmetic deviation of the profile R a are given by standard JUS M.A1.020, and those ones between maximum bumps height of the profile R max and mean arithmetic deviation of the profile R a are given by standard DIN 4667-70, mentioning that there are approximate. More correct link between maximum bumps height of the profile R max and mean arithmetic deviation of the profile R a is given by exponential dependence [2, 11], and it is not depended to the conditions and the kind of the processing. Using the experimental methods it could be possible to establish regression dependence between the processed Table 4: The table review of experimental values of the interactive dependence of parameters R max = f(r a ) for turning in the steel C60 by ceramic cutting tools Analyzing the dependence of the mean arithmetic deviation of the profile R a and maximum bumps height of the profile R max for different values of the elements of cutting regime it was chosen complex power-exponential regression equation (figure 4): 0,9341-0,2263 R R a max = 7,8192 Ra e (10) its correlation coefficient is R = 0,99578 and mean relative error of the experiments is α rel = 2,5017 %.
Figure 2: Graphic review of experimental data and calculated values for the chosen regression equation of dependence R a = f(a,s,v,r)
Figure 3: Graphic review of experimental data and calculated values for the chosen regression equation of dependence R max = f(a,s,v,r)
Figure 4: Graphic review of experimental data and calculated values of dependence R max = f(r a ) 6 CONCLUSION Passing trough the time parameters of processed surface roughness R a and R max change, and they depend on many factors among which the tools wearing are the most influential. Parameters of processed surface roughness R a and R max depend on many factors among which the elements of cutting regime (in the first place feed), nose radius and etc. are the most influential. Interactive dependence of processed surface roughness parameters could be adequately approximated by complex power-exponential regression. 7 REFERENCES [1] Dasic P.: Analysis choice of regression equations of the roughness of processed surface for turning by means of ceramic cutting tools, International Tribology Conference ITC - Nagasaki 2000, 29. Oct. - 02. Nov. 2000, Nagasaki, Japan [2] Dasic P.: Research of harder materials for finished turning by means of ceramic cutting tools, Monograph, (in preparation) [3] Dasic P.: Research of machinability functions for finished turning by means ceramic cutting tools, X International Technical Science Seminar High Technologies: Development and Personnel Provision INTERPARTNER - 2000 (Proceedings p. 29-36), 14-20. September 2000, Kharkov, Ukraine [4] Dasic P.: Statistical processing of experimental data, Book 1: One-factoring regression analysis, Monograph, Institute IMK 14. October, Krusevac, Yugoslavia, 2001-250 p. [5] Dasic P.: The analysis of possibilities of the approximation of machining process characteristics by power polynomial, 16th International Conference on Production Research - ICPR-16, 29. July - 03. August 2001, Prague, Czech Republic [6] Dasic P.: The Choice of regression equation of machinability functions as the part of technological data base, 27th Council of Production management in metalworking industry (Proceedings p. 4.87-4.94), 9-12. February 1999, Belgrade, Yugoslavia [7] Dasic P., Radonjic S., Jecmenica R., Nedic B.: Research of the Regression Functional of Processed Surface Roughness at the Turning by Means Modern Cutting Tools, X th International Conference on Tools ITC 2000 (Proceedings p. 155-158), 06-08. September 2000, Miskolc, Hungary [8] Dworak U.: SPK Schneidkeramik, Die Entwicklung zum Hochleistungs-Schneidstoff für die tägliche Praxis, In: Referate SPK Schneidkeramik Tage '84, Dusseldorf, 1984., p. 4-10 [9] Momper J. F.: Untersuchung zum Standvermögen keramischer Werkzeugschneiden beim Drehen unter besonderer Berücksichtigung der Schneideneingriffsverhältnisse, Dissertation, Vom Fachbereich Maschinenwesen der Universität Kaiserslautern, 1985. [10] Radonjic S.: Further supplements to investigating finish processing on lathe, dissertation Ph, Belgrade, Yugoslavia, 1986. [11] Sekulic S.: Correlation between the largest height of roughness and the mean arithmetic deviation of the profile from the middle line of the machined surface, Journal of Tribology in industry, Kragujevac, Yugoslavia, Vol. XIII (1991) No. 2, p. 46-50 [12] Solaja V.: On some correlations of the cutting process and the quality of generated surface, XIV Yugoslav Council of Production Engineering (Proceedings p. 279-294), 1980, Cacak, Yugoslavia [13] Spur G., Stoferle T.: Handbuch der Fertigungstechnik, Spanen, Carl Hanser Verlag, München, Wien, 1980.