Applied Mechanics and Materials Vols. 592-594 (2014) pp 316-320 Online available since 2014/Jul/15 at www.scientific.net © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.592-594.316 Submitted: 25.04.2014 Revised: 17.05.2014 Accepted: 19.05.2014 EXPERIMENTAL INVESTIGATIONS ON CRYOGENIC COOLING IN DRILLING OF ALUMINIUM ALLOY Govindaraju. N1, a *, Shakeel Ahmed. L2,b and Pradeep Kumar. M3,c 1 Research Scholar, Department of Mechanical Engineering, Anna University, Chennai, India. 2 Research Scholar, Department of Mechanical Engineering, Anna University, Chennai, India. 3 Asso. Professor, Department of Mechanical Engineering, Anna University, Chennai, India. a *n_govindaraju@yahoo.com, bshakeel_mechanical@yahoo.com, cpradeep@annauniv.edu Keywords: Drilling, cryogenics, temperature, thrust force, hole quality, aluminium. Abstract. The usage of a conventional cutting fluid in the metal cutting operations gives harmful effect for environment and to the operator’s health. In this study, experimental investigations were carried out in a drilling operation on aluminium alloy material using a liquid nitrogen (LN2) coolant. The variables in the experiment were, cutting speed and feed, the drilling depth was maintained constant. For each feed rate (0.02, 0.05 & 0.08 mm/rev) three holes were drilled for cutting speeds 110, 130 & 150 m/min. The cutting temperature and thrust force were recorded. The cutting temperature and thrust force were reduced, when cutting speed was increased. The hole quality parameters like cylindricity, circularity and perpendicularity were analyzed using CMM. Introduction In metal cutting operations, a substantial percentage of the power used is transformed into heat at the machining zone. Such high temperature of the machining zone affects the tool life, surface finish and accuracy of the workpiece. Hence, to reduce the cutting temperature, a cutting fluid is used. When conventional types of cutting fluids are used, they create health hazards and also strict laws to restrict the pollution arising from the cutting fluid waste. Necessity arises to use an alternative coolant in metal cutting operations. LN2 has been tried as one of the alternatives as a cryogenic medium. It cannot be concluded that the cryogenic medium is beneficial for all types of machining operations. An attempt is made in the drilling operation to make holes in aluminium alloy material. As pointed out by Shokrani et al. [1] except for a few studies on drilling composite materials, to the best of his knowledge, there is no study on the effect of cryogenic cooling in drilling operations. Paul et al. [2] reported significant reductions in the cutting forces, when machining different types of steels, when LN2 is sprayed on the crater and flank faces of uncoated carbide tools. Dhar et al. [3] stated that cryogenic turning resulted in significant cutting force reduction in AISI 1040 steel. Contrary to these two papers, Dhananchezian et al. [4,5] indicated that the application of LN2 in the tool rake surface increased the cutting force by 15 % in orthogonal machining and also reduction in cutting temperature of 44-51 %, reduction in cutting force of 16 % and reduction in surface roughness of 22-34 % in turning process. It has been reported by Kalyan et al. [6] that LN2 spray on the cutting edge reduced the cutting force by 14.83 % while machining AISI 202 Stainless steel. Nalbant et al. [7] conducted experiments in milling AISI grade stainless steel. When LN2 was sprayed on stainless steel, the cryogenic temperature resulted in the workpiece material’s hardness and increased the cutting forces by 6.5 %, 5.6 %, and 3.3 % along the X, Y, and Z axis respectively. Uehara et al. [8] found that the cutting force increased by turning AISI 304 Stainless steel material when LN2 coolant was used. Many researchers have reported that the usage of a cryogenic coolant in the cutting process would result in increase of cutting forces. In machining 6061-T6 aluminium, maximum 38 % reduction of cutting temperature is reported when LN2 is sprayed onto the rake face of an uncoated tungsten carbide tool, by Dhananchezian et al. [4]. Uehara et al. [8] concluded that the application of LN2 would result in reduction of the All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 124.124.237.194-13/10/14,08:02:56) Applied Mechanics and Materials Vols. 592-594 317 cutting zone temperature. Ravi et al. [9,10] conducted the cryogenic milling experiment and found to be in the cutting zone temperature which was reduced to maximum of 57 % when LN2 is sprayed on the hardened steel material and also found that reduction in cutting temperature, reduction in cutting forces over dry and wet machining using AISI D3 steel. Benfredj et al. [11] reported a reduction in grinding zone temperature when LN2 is injected into the tool-workpiece interface in grinding steels. Many researchers found that regardless of the cooling technique, using LN2 as a cryogen is an effective method, in reducing the temperature between the chip – tool interfaces. Jerold et al. [12] by using CO2 cooling reported reduction in cutting temperature of maximum 35 % and increase in surface finish of 4 – 52 % in turning operation. Manimaran et al. [13,14] studied the effect of input process parameters in grinding operations. They observed that for effective grinding performance, LN2 environment was the significant parameter and also found that using LN2 as coolant produces surface roughness reduction of 43 % and 26 %, grinding force reduction of 24 % and 16 % over dry and wet grinding. Experimental Procedure Drilling experiments were conducted on aluminium (99.12% Aluminium) alloy with Physical Vapour Deposition (PVD) coated carbide indexable inserts clamped on the DRZ type tool which is locked in the BT 40 tool holder. The BT 40 tool holder assembly is rigidly located in the taper bore of the spindle of the Vertical Machining Centre (VMC). The drilling experiments were performed on an aluminium alloy flat work piece material of the size 164 × 80 × 20 mm. The workpiece is rigidly clamped on the top-base of the KISTLER dynamometer. Fig. 1 Experimental setup Figure 1 shows the experimental setup for cryogenic environment. The workpiece is finish machined to the size of 164 × 80 × 20 mm. A hole with a diameter of 3 mm is drilled from the side of the work piece for the insertion of a K - type thermocouple, such that a gap of 0.2 mm is maintained between the tip of the thermocouple and the wall of the proposed 16 mm diameter of the hole. Zeilmann et al. [15] used this technique to measure the temperature at three different heights, and they found that the peaks of the temperature were at the lowest level. Nine holes were made for a depth of 17 mm against the work piece height of 20 mm. The temperature values were recorded using a K - type thermocouple at the lowest depth of the drill. The cutting parameters are speed and feed. The speed levels are 110 m/min, 130 m/min and 150 m/min and the feed levels are 0.02 mm/rev, 0.05 mm/rev and 0.08 mm/rev respectively. Since aluminium alloys has a tendency to adhere to the tool while drilling holes a cryogenic cooling system was developed, to supply LN2 to the cutting zone. The available LN2 storage container is modified for a pressurized cryogenic coolant flow. LN2 is stored in the cryogenic container. The compressed air with a pressure of 3 bar forces the LN2, and it is directed to the toolchip interfaces through a nozzle. 318 Dynamics of Machines and Mechanisms, Industrial Research Results and Discussion An experimental study was conducted under LN2 environment involving the drilling of aluminium alloy with PVD coated carbide inserts. The experimental results of LN2 cooling, cutting temperature, thrust force were recorded. Hole quality parameters circularity, cylindricity and perpendicularity were measured in CMM. Effect of LN2 on Cutting Temperature Fig. 2 Temperature Vs. Cutting Speed Figure 2 shows the cutting temperatures recorded by a K - type thermocouple for three different cutting speeds and feed rates. It is known and empirically proved that increase of the cutting speed increases the cutting temperature. But in drilling operations, the pattern obtained was different. For a lower feed rate (0.02 mm/rev) when the cutting speed was increased from 110 to 130 m/min, there was a drop of 26oC (36.6% reduction). When the cutting speed was increased from 130 to 150 m/min, temperature dropped by 5oC (11.1% reduction). At all cutting speeds, there was a reduction in temperature for the LN2 coolant. When the feed rate was increased to 0.05 mm/rev and 0.08 mm/rev, temperature dropped in the same manner. Effect of LN2 on Thrust Force Fig. 3 Thrust Force Vs. Cutting Speed The thrust force and cutting speed at various feed rates under LN2 coolant supply are shown in Fig. 3. The thrust force was 754.4 N for a cutting speed of 110 m/min and feed rate of 0.02 mm/rev. When cutting speed was increased to 130 m/min for the same feed rate, thrust force recorded was 701.5 N, a reduction of 7 %. In 150 m/min cutting speed, thrust force recorded were 504.5 N, 28.08 % reduction over the previous value. It shows for an increase in cutting speed, thrust force decreased. When the feed rate was increased to 0.05 mm/rev and 0.08 mm/rev for the same cutting speed condition, thrust force reduction was noticed. At all cutting speeds, there was a reduction in thrust force for the LN2 coolant. Applied Mechanics and Materials Vols. 592-594 319 Study of Hole Quality Fig. 4a Cylindricity Vs. Cutting Speed Fig. 4b Circularity Vs. Cutting Speed Fig. 4c Perpendicularity Vs. Cutting Speed The quality of the drilled holes is of prime importance in practical applications. Figure 4a, 4b and 4c shows the performance of the drilled holes. Cylindricity measurements showed that the highest measured values were for lower feed rate 0.02 mm/rev for three cutting speeds. When the cutting speed is increased to 130 m/min and 150 m/min, the cylindricity measurements decreased for the feed rates 0.05 mm/rev and 0.08 mm/rev. An increase in feed rates lead to degradation of the hole quality and circularity measurements showed that there was an increment in measurements for an increase in feed rate. This is due to chip dragging the surface of the hole. When the cutting speed was increased from 110 m/min, the perpendicularity measurements were either lowering down or decreasing at the same level. For higher feed rate 0.08 mm/rev, perpendicularity measurements were lower for all cutting speeds. Conclusions In LN2 cutting conditions, experiments on the drilling of aluminium alloy were carried out. Conventional carbide drills were replaced by an asymmetric indexable drill, in which there is no identical cutting edge. The major conclusions are: 1. The cutting temperature was reduced by 11 to 37 % when cutting speed was increased for different feed rates. 2. The drop in temperature is of the same pattern for all feed rates. The cutting temperature is maximum for a lower feed rate (0.02 mm/rev). 3. The thrust force was reduced by 2 to 28 % when cutting speed was increased. The thrust force as minimum for a lower feed rate (0.02 mm/rev). Here also the pattern is same for all feed rates. 4. The hole quality (circularity) was better for the lower feed rate. 320 Dynamics of Machines and Mechanisms, Industrial Research References [1] A. Shokrani, V. Dhokia, P. Munoz Escalona and S.T. Newman, State of the art cryogenic machining and processing. International Journal of Computer Integrated Manufacturing, Vol. 26 (7) (2013). [2] S. Paul and A.B. Chattopadhyay, Environmentally conscious machining and grinding with cryogenic cooling. Machining Science and Technology, Vol. 10 (1) (2006), p. 87-131. [3] N. 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Yildiz, Effect of cryogenic cooling in milling process of AISI 304 Stainless steel. Transactions of Nonferrous metals society of china, Vol. 21 (1) (2011), p. 72-79. [8] K. Uehara and S. Kumagai, Chip formation surface roughness and cutting force in cryogenic machining. Annals of CIRP, Vol. 17 (1) (1968), p. 409-416. [9] S. Ravi. S and M.P. Kumar, Experimental Investigations on cryogenic cooling by liquid nitrogen in the end milling of hardened steel. Cryogenics, Vol. 51 (9) (2011), p. 509-515. [10] S. Ravi and M. Pradeep Kumar, Experimental Investigation of Cryogenic Cooling in Milling of AISI D3 Tool Steel. Materials and Manufacturing Processes, Vol. 27 (2012), p. 1017–1021. [11] N. Benfredj and H. Sidhom, Effects of the cryogenic cooling on the fatigue strength of the AISI 304 Stainless steel ground components. Cryogenics, Vol. 46 (6) (2006), p. 439-448. [12] B. Dilip Jerold and M. Pradeep Kumar, Machining of AISI 316 Stainless Steel under CarbonDi-Oxide Cooling. Materials and Manufacturing Processes, Vol. 27 (2012), p. 1059–1065. [13] G. Manimaran and M. Pradeep Kumar, Multi-response Optimization of Grinding AISI 316 Stainless Steel Using Grey Relational Analysis. Materials and Manufacturing Processes, Vol. 28 (2013), p. 418–423. [14] G. Manimaran and M. Pradeep Kumar, Investigation of Cooling Environments in Grinding EN 31 Steels. Materials and Manufacturing Processes, Vol. 28 (2013), p. 424–429. [15] Rodrigo Panosso Zeilmann and Walter Lindol Fo Weingaertner, Analysis of temperature during drilling of Ti-6Al-4V with minimal quantity of lubricant. Journal of Materials Processing Technology, Vol. 179 (2006), p. 124-127. Dynamics of Machines and Mechanisms, Industrial Research 10.4028/www.scientific.net/AMM.592-594 Experimental Investigations on Cryogenic Cooling in Drilling of Aluminium Alloy 10.4028/www.scientific.net/AMM.592-594.316