Microsoft Word - B_23_R.doc HUNGARIAN JOURNAL OF INDUSTRIAL CHEMISTRY VESZPRÉM Vol. 38(2). pp. 169-173 (2010) RESEARCH OF ROUGHNESS OF HARD TURNED BORES K. SZAKÁCS Department of Production Engineering, University of Miskolc, 3515 Miskolc, Egyetemváros, HUNGARY E-mail: kati873@freemail.hu This paper reports an extensive characterization of the surface roughness generated during hard turning operations performed with conventional PCBN tools and during combination turning and grinding machining. Hard turning has been applied in many cases such as producing bearings, gears, axles and other mechanical components. The PCBN is widely used for finish machining of hardened steel parts (HRC 45–65). The special condition of dry hard cutting is the required cutting speed must be ranged from 90 to 180 m/min. After the hard turning and combination machining tests, the relevant changes of surface profiles and surface roughness parameters were successively registered and measured by a profilometer. Based on the experimental results, this paper shows and analyse the modification of the surface roughness parameters in case of hard turning and combination machining[1]. Keywords: hard turning, grinding, surface roughness, combination machining Introduction This work aims to investigate the machining of hardened steels using cubick boron nitride (CBN) The combining of processes in the machining of high-precision hardened workpieces is catching on. Since the introduction of the first combined turning and grinding center at Metav 1998 the new technology has found wide-ranging acceptance. One of the leading exponents is the Emag Group Experimental set-up, cutting parameter control is shown by Fig. 1. Table 1 contains the parameters of surface roughness and the tool edge geometry [2, 3]. Table 1: Nomenclature ap – cutting depth (mm) f – feed rate (mm/rev) vc – cutting speed (m/min) Ra – arithmetical roughness (μm) Rm – equivalent mechanical resistance (ηm) Rz – rougness (ηm) Rq – quadrotic roughness (ηm) Kr – tool cutting edge angle (°) αr – rake angle (°) γr – relief angle (°) VB – flank wear (mm) Work piece Material Geometry Machined surface Cutting operation Cutting speed Feed rate Cutting depth Lubrification Tool Wear Coatingl Geometry Machine tool Power Precision Rigidity Cutting forces Wear Figure 1: Experimental set-up, cutting parameter control [4] Experimental conditions Work pieces All the tests were carried out with parts machined under industrial. The cutting parameters were taken from the practice. The machined material was the steel DIN 20MnCr5, quenched to 62 HRC. The machined work piece was on gear with a cylindrical section with a diameter of 53 mm and length of 49.3 mm and the other gear was diameter of 60 mm and length of 45.3 mm. 170 Table 2 shows the chemical composition of the material [2]. Table 2 Cemical Composition % C 0.17/ 0.22 Mn 0.15/ 0.40 P 0.02 0.035 S 0.035 max. Si 0.15/ 0.4 Cr 1.00/ 1.30 Al 0.020 min. Tool The inserts conformed to the ISO cod. Hard turning: conventional MITSUBISHI: NP-CNGA120408TA2 MB8025 (roughing) and the tool holder C5-PCLNR/L- 17090-12 and smoothing wiper: NP-CNGA120408GSW2 MBC010 and the tool holder C5-PCLNR/L-17090-12. Combinated machining: SOMITOMO: 4NC- CNGA120412, and the tool holder C5-PCLNR/L- 17090-12 Grinding wheel: 97A 602 I 5 V112 CNC turn It was employed a turn PVS Pittler, this equipment presents the stiffness and accuracy enough for the demands of the hard turning operations. Combinated turn and grinding machine Improved component and end product quality, as the workpiece is machined in a single setup, whereby the rough hard turning operation leaves a grind-finishing allowance of just 0.02 mm (relative to the diameter). Compared to conventional grinding methods the minute grinding allowances required for the application of HDS-technology allow you to grind with a minimum of coolant and even dry, in which case there is no need for costly grinding sludge disposal measures [3]. Figure 3: PGK 120 prfilometer [2] Surface roughness measurements After each individual test, part surface finish was measured with a stylus profilograph. In this investigation, a shop floor PGK 120 profilometer (Fig. 3) with a 5 μm diamond stylus radius was used. I used a special computer programs. Conclusion Significant difference could be found among the surface roughness number as the function of number of pieces on the worpieces surface machined by hard turning and by combined machining (Fig. 4). In case of hard turning significant fluctuation can be seen in the values of surface roughness, which makes uncertain the planning of the machined roughness. This manifestation can be disadvantageous in case of production certain machine elements. This can be explained by the tool wear mechanism of PCBN single point cutting tools, because the tool is machining on one point, and its geometrical errors can be copied into the workpieces. In spite of this in the case of combined machining roughness height mad by hard turning can be grinded by the grinding wheel truined at each worpiece (Fig. 5). So, the surface roughness to be produced can be regular, can be planned. Furthermore the micro-thread can be avoided which occurs in hard turning. However, hard turning can be pretend to quasy absolute environmentally friendly procedure for neglecting of coolants and lubricants, but because of fluctuation of surface roughness its change to combined machining is suggested, which involves a little load of environment. 171 0 0,1 0,2 0,3 0,4 0,5 1 10 20 30 40 50 60 70 80 90 100 110 120 Ra work pieces combined machinig hard turning a, 0 0,1 0,2 0,3 0,4 0,5 1 10 20 30 40 50 60 70 80 90 100 110 120 work pieces Rq combined machinig hard turning b, 0 0,5 1 1,5 2 2,5 1 10 20 30 40 50 60 70 80 90 100 110 120 work pieces Rz combined machinig hard turning c, 0 0,5 1 1,5 2 2,5 1 10 20 30 40 50 60 70 80 90 100 110 120 work pieces Rm combined machinig hard turning d, Figure 4: Roughness parameters as a fuction of work pieces for different machining conditions 172 Hard turned profile Combining machined profile Workpieces 1 Workpieces 40 Workpieces 50 Workpieces 90 Workpieces 120 Figure 5: Charasteristic surface profiles 173 REFERENCES 1. W. GRZESIK: Influence of tool wear on surface roughness in hard turning using differently shaped ceramic tools, Wear, 265 (3-4), 2008, 327–335. 2. G. DE S. GALOPPI, M. S. FILHO, G. F. BATALHA: Hard turning of tempered DIN 100Cr6 steel with coate and no coated CBN inserts, Journal of Materials Processing Technology, 179, 2006, 146–153. 3. http://www.emag.com/de/maschinen/schleifmaschi nen/innenrundschleifen/vsc-dsdds-baureihe.html 4. M. REMADNA, J. F. RIGAL: Evolution during time of tool wear and cutting forces in the case of hard turning with CBN inserts, Journal of Materials Processing Technology, 178 (1-3), 2006, 67–75. 5. Acélkalauz, Szabványkiadó, Budapest, 1983, p.110. 6. R. PAVEL, I. MARINESCU, M. DEIS, J. PILLAR: Effect of tool wear on surface finish for a case of continuous and interrupted hard turning, Journal of Materials Processing Technology, 170 (1-2), 2005, 341–349. 7. J. KUNDRAK, K. GYANI, V. BANA: Roughness of ground and hard-turned surfaces on the basis of 3D parameters, International Journal of Advanced Manufacturing Technology, 38 (1-2), 2008, 110–119. 8. J. KUNDRAK, A. G. MAMALIS, A. MARKOPOULOS: Finishing of hardened boreholes: Grinding or hard cutting? Materials and Manufacturing Processes, 19 (6), 2004, 979–993. 9. J. KUNDRAK, K. GYANI, V. BANA: Qualification of hard bored surfaces with 3D parameters, DAAAM International Scientific Book, Vienna 2005, 371–384. 10. A. G. MAMALIS, J. KUNDRAK, K. GYANI: On the surface integrity of precision-ground steel cylindrical parts, Materials and Manufacturing Processes, 18 (5), 2003, 835–845. 11. J. KUNDRAK, V. BANA: Investigation of surface roughness in turning of hardened and cylindrical surfaces. 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