Strojniški vestnik - Journal of Mechanical Engineering 56(2010)3, StartPage-EndPage Paper received: 02.04.2009 UDC xxx.yyy.z Paper accepted: 00.00.2010 An Experimental Investigation on Effect of Cutting Fluids in Turning with Coated Carbides Tool Yahya Isik University of Uludağ, Department of Technical Science, Vocational School of Higher Education, Turkey The major needs in machining are high material removal rate, good work surface finish and low tool wear. These objectives can be achieved by reducing tool wear using proper cooling system of the tool during machining. The work aims to seek conditions in which dry cutting is satisfactory compared with the flood of fluid usually used. The cutting tool used in this research is CVD coated carbide TiC+AI2O3+TiN insert (ISO P25). The type of inserts is DNMG 150608. During the experiments flank wear, cutting force and surface roughness value were measured throughout the tool life. The results have been compared with dry and wet-cooled turning. The results of the present work indicate substantial reduction in tool wear, which enhanced the tool life; this may be mainly attributed to reduction in cutting zone temperature and favorable change in the chip-tool interaction. ©2010 Journal of Mechanical Engineering. All rights reserved. Keywords: flank wear, tool life, cooling, cutting forces, tool wear 0 INTRODUCTION this moment, completely dry cutting is not suitable for many machining processes. Since In metal cutting process, the condition of cutting fluid is necessary to prevent the chips from the cutting tools plays a significant role in sticking to the tool and causing its breakage [4]. achieving consistent quality and also for High temperature in cutting zone has been controlling the overall cost of manufacturing. The traditionally tried to control by using cutting main problem caused during machining is due to fluids. The coolant effect reduces temperature in the heat generation and the high temperature cutting zone and the lubrication action decreases resulted from heat. The heat generation becomes cutting forces. Thus the friction coefficient more intensified in machining of hard materials between tool and chip becomes lower in because the machining process requires more comparison to dry machining [5] and [6]. The energy than that in cutting a low strength aims of cutting fluid applications were material. As a result, the cutting temperatures in determined as cooling and lubrication in metal the tool and the work-piece rise significantly cutting. In addition, cutting fluids can help to during machining of all materials [1]. At such disposal of the chips from hole and control chip elevated temperature the cutting tool if not formation. Because they decrease contact length enough hot hard may lose their form stability between chip and tool, and this situation has a quickly or wear out rapidly resulting in increased positive effect on chip breaking. Thus, they can cutting forces, dimensional inaccuracy of the help to achieve better tool life [7] and [8]. The product and shorter tool life. The magnitude of cost of cutting fluids is approximately 7 to 17% this cutting temperature increases, though in of the total cost in machining process [9]. As different degree, with the increase of cutting cutting fluid is applied during machining velocity, feed and depth of cut, as a result, high operation, it removes heat by carrying it away production machining is constrained by rise in from the cutting tool/work-piece interface [10]. temperature. This problem increases further with This cooling effect prevents the tool from the increase in strength and hardness of the work exceeding its critical temperature range beyond material [2] and [3]. which the tool softens and wears rapidly [11]. In dry cutting operations, the friction and Cutting fluids are used throughout industry in adhesion between chip tool tend to be higher, many metal cutting operations and they are which causes higher temperatures, higher wear usually classified into 3 main categories: neat rates and, consequently, shorter tool lives. Up to cutting oils, water-soluble fluids and gases [12]. *Corr. Author's Address: Uludag University, Vocational School of Higher Education, 16059 Görükle, Bursa, Turkey, yahya@uludag.edu.tr 1 Strojniški vestnik - Journal of Mechanical Engineering 56(2010)3, StartPage-EndPage The major needs in machining are high radius were considered. In fact, the roughness material removal rate, good work surface finish similarly deteriorated under wet machining in and low tool wear. These objectives can be some of tests. achieved by reducing tool wear using proper cooling system of the tool during machining. The 1 EXPERIMENTAL DETAILS main objective of using cutting fluids in machining operations is the reduction of 1.1 Cutting Tool Materials temperature in the cutting region to increase tool life. The cutting fluids are used in machining Carbides are the most common tool operations in order to material for machining of castings and alloy (i) Reduce friction at the tool-chip and tool- steels. These tools have high toughness, but poor work-piece interfaces, wear characteristics. To improve the hardness and (ii) Cool both chip and tool, and surface conditions carbide tools are coated (iii) Remove chip. carbide with hard materials such as TiN, TiC, Furthermore, they have a strong effect on TiAlN, and TiCN by chemical vapor deposition the shearing mechanisms and, consequently, on (CVD). the work-part surface finish and tool wear [13] Currently, the most popular CVD coatings and [14]. are titanium carbide (TiC), titanium nitride (TiN), The positive effect of the use of fluids in titanium carbon nitride (TiCN), and alumina metal cutting was first reported in 1894 by F. (Al2O3). The first successful CVD coating, TiC Taylor [15], who noticed that by applying large offers high hardness and excellent wear amounts of water in the cutting area, the cutting resistance. A later development, Al2O3 coatings, speed could be increased up to 33% without offers superior thermal stability, oxidation wear reducing tool life. Since then, cutting fluids have resistance, and high-temperature hardness. High- been developed resulting in an extensive range of temperature characteristics of Al2O3, when it's products covering most work-piece materials and deposited as a single layer or alternating multi- operations. According to Kress [16], the costs layer, provide increased productivity in high- associated with the use of cutting fluids represent speed machining of steels and cast irons. approximately 17% of the finished work-piece DNMG 150608 (with an ISO designation) cost against 4% spent with tooling. Kwon [17], carbide inserts, clamped on tool holders CSBNR studied flank wear by incorporating cutter 2525 M12. As cutting tools, CVD coated carbide temperature and physical properties of coating TiC+AI2O3+TiN insert (ISO P25) were used in and work materials. The objective of this paper is the experiments. Inserts possesses, a coating to investigate the effects of internal cooling on the consisting of a TiCN under layer, an intermediate tool flank wear in orthogonal metal cutting. Diniz layer of Al2O3 and a TiN out layer, all deposited and Micaroni [4], carried out other experiments in by CVD (Fig. 1). turning operations of AISI 1040 steel, also using coated carbide tools and cutting conditions typical of finishing operations. Their goal was to compare dry cutting with cutting with abundant fluid at different feeds, cutting speed and tool nose radius. The present work deals with experimental investigation in the role of cutting fluids on cutting temperature, cutting forces, tool wears, and surface roughness value in machining AISI- Fig. 1. CVD coating layers of insert 1050 steel at industrial speed-feed condition by CVD coated carbide TiC+AI2O3+TiN insert as compared to completely dry machining. This 1.2 Work-piece Material study indicated that cutting fluid did not show a The work-piece material is AISI 1050 significant improvement on surface roughness steel. The chemical composition of work-piece particularly when cutting tests with 0.8 mm nose material are 0.52%C, 0.86%Mn, 0.040%P, 2 Isik, Y. Strojniški vestnik - Journal of Mechanical Engineering 56(2010)3, StartPage-EndPage 0.050%S. Cylindrical work-pieces wear was measured. The work-piece surface (Ø80×340 mm) were fixed between the chuck roughness was measured by a profilometer and the tailstock and were pre-machined by using (Taylor Hobson Talysurf Series 10). Oil based a separate insert. coolant was pumped at rate of 3 liter/min on the tool-work interface, so as to flood the cutting 1.3 Machinability Test zone along with surrounding area in wet turning tests. The process parameters as indicated in Machining tests were carried out according Table 1 were selected on recommendation of tool with Standard ISO 3685 [18] which involves manufacturers for machining AISI 1050 steel. turning of a bar at a constant cutting speed (Vc) In the experiments, CVD coated carbide and the identification of the cutting time (Tc) TiC+AI2O3+TiN cutting tool was taken into necessary to obtain a specific value of tool flank consideration throughout the tool life at certain wear. Since conventional 5.5 KW TOSS lathe cutting conditions. Parameter on tool life, was was used in the tests, in order to have a constant determined with respect to the recommendations cutting speed, in the turning operation 190 to 260 advised by the tool manufacturers for the coated m/min of various cutting speed, 0.14 mm/rev of tools. For all tools, only the flank wear was taken feedrate, 0.5 mm and 1 mm of depth cut values into consideration in the comparisons. The result were used in all cases. As the tool life criteria, a of experimental data is given in Table 2. value of 0.3 mm of average flank wear land (IB) that was established by ISO 3685, was used (Fig. 2). Coated carbide inserts, ISO DNMG 150608 (K10), clamped on tool holders CSBNR 2525 M12 were used in the tests, Cutting forces, flank wear and surface roughness values were measured until the tool expires. The cutting forces were measured by a three-dimensional force dynamometer, Kyowa TD-500. The flank wear of the tool was measured by means of Nikon104 microscope with a magnification of X10 and the cutting process was Fig. 2. Geometry of wear of turning tools [19] paused in every 60 mm and the average flank Table 1. Experimental condition Machine tool : TOSS, 5.5 KW, Lathe Work specimens materials : AISI-1050 steel (0.52%C, 0.86%Mn, 0.040%P, 0.050%S.) Size : (Cylindrical workpieces Ø80×340 mm) Cutting tool : CVD Coated carbide, DNMG 150608(K10) Coating : TiC+AI2O3+TiN Tool holder : CSBNR 2525 M12 (ISO specification), Working tool geometry : Inclination angle: 6, rake angle: 6, clearance angle: 6, cutting edge angle: 75 Principal nose radius: 0.8mm Force dynamometer : Kyowa TD-500, Microscope : Nikon104 with a magnification of X10 A profilometer : Taylor Hobson Talysurf 10 Process parameters Cutting velocity, V : 190, 220, 240 and 260 m/min Feed rate, f : 0.14 mm/rev Depth of cut, a : 0.5, 1.0 mm Environment : Dry, and wet cooling An Experimental Investigation on Effect of Cutting Fluids in Turning with Coated Carbides Tool 3 Strojniški vestnik - Journal of Mechanical Engineering 56(2010)3, StartPage-EndPage Table 2. Results of experimental data Flank The rate of The volume Tool Cutting parameters wear flank wear of material life [mm] [mm/min.] removed [min.] Cutting speed Feed rate Depth of Cutting [cm3/tool life] [m/min] [mm/rev] cut [mm] condition 0.35 0.0173 783.65 20.13 1.0 Dry 0.33 0.0146 814.35 22.55 260 0.14 Wet 0.35 0.0080 627.20 43.60 0.5 Dry 0.37 0.0063 705.63 58.27 Wet 2 RESULTS AND DISCUSSION as the average wear (mm) divided by the effective tool life [min] [23]. The major advantage of wet- 2.1 Tool Wear and Flank Wear cooled turning seems to be reduction of tool wear at high speed. Fig. 3 shows the progression of Cutting tools may fail by brittle fracture, flank wear in dry and wet-cooled turning and plastic deformation or gradual wear. Turning volume of material removed is shown Fig. 4. carbide inserts having enough strength; toughness and hot hardness generally fail by gradual wear. With the progress of machining, the tools attain crater wear at the rake surface and flank wear at the clearance surfaces [19], the principal flank wear is the most important because it raises the cutting forces and the related problems. Flank wear is a major form of tool wear in metal cutting. When machining using tools under typical cutting conditions, the gradual wear of the flank face is the main process by which a cutting tool fails [20] to [22]. Fig. 3. Flank wear vs. cutting time (v=260 According to ISO standard 3685 to tool m/min, f=0.14 mm/rev, a=1 mm) life testing, the life of carbide tools, which mostly fail by wearing, is assessed by the actual machining time after which the average value (VB) of its principal flank wear reaches a limiting value of 0.3 mm [24]. In tool life evaluation turning processes were paused in every 60 mm and the average flank wear was measured. If the tool was not expired (which means it does not reach to a value of 0.3 mm of average flank wear land) at the end of the first bar, second bar of the same structure was used for the rest of the process. This was necessary for the constant cutting speed as explained previously. Tool life estimation involves a number of tests to be carried out at various cutting Fig. 4. Volume of material removed (v=260 conditions till the failure of the cutting tool. In m/min, f=0.14 mm/rev, a=1 mm, a=0.5 mm) general, as the tool life criterion, amount of flank wear is used. Flank wear (VB) is an important 2.2 Surface Finish factor in determining the tool life. The cutting test was started with a new cutting tool, and the Surface finish is one of the most stringent machining process was stopped at certain requirements placed on finish operations; its intervals of cutting length in order to measure the degradations are usually due to the tool wear. For width of flank wear. Flank wear rate is calculated this reason, the work-part surface finish and the 4 Isik, Y. Strojniški vestnik - Journal of Mechanical Engineering 56(2010)3, StartPage-EndPage tool flank wear were used to evaluate the tool reduces the coefficient of friction at the interface performance. In particular, the wear criterion of the tool and chip over the rake face. This is adopted in the finish turning tests was based on a achieved through lubrication, and by lowering the maximum allowed value imposed to the average strength of welded junctions between the tool and surface roughness (Ra), according to the ISO chip. 3685 [15]. Two important performance parameters in turning process are tool life and surface roughness of the machined surface. For most tests, cutting speed and cutting fluid did not show a significant effect on surface roughness for both dry and wet machining conditions. The effect of the cutting speed is negligible. Figs. 5 and 6 shows the variation of surface roughness at different cutting speeds, and flank wear with time for dry and wet-cooled turning. Fig. 7. Tool life at different cutting speeds (f=0.14 mm/rev, a=1 mm, a=0.5 mm) Fig. 5. Flank wear vs. surface roughness (v=260 m/min, f=0.14 mm/rev, a=1 mm) Fig. 8. Tangential cutting force versus cutting time with dry and wet cooled condition 2.3 Cutting Forces Fig. 6. Cutting speeds vs. surface roughness The magnitude of the cutting forces is one of the most important machinability indices The major advantage of using cutting because that plays vital roles on power and fluids in machining operations is reduced of tool specific energy consumption, product quality and wear at high speed. The other advantage is the life of the salient numbers of the machine– lowering of cutting forces. Fig. 7 illustrates the fixture–tool systems. Fig. 8 shows the variation of tool life at different cutting speeds and constant main cutting force with the machining time for depths of cut at a feed rate of 0.14 mm/min with certain cutting conditions. The cutting force in dry and wet-cooled turning. When cutting speed dry turning was found compared to wet-cooled increases, Tool life decreases as is expected. But, turning. In all the cases of cutting-speed turning, tool life more decreases for wet cutting than dry the cutting force is less in wet-cooled turning due cutting. This is because application of flood fluid to less flank wear. The relative advantage in cutting force offered by flood fluid cooling over An Experimental Investigation on Effect of Cutting Fluids in Turning with Coated Carbides Tool 5 Strojniški vestnik - Journal of Mechanical Engineering 56(2010)3, StartPage-EndPage the dry cutting can also be seen from Fig. 8. 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