Issue 50

N. A. Fountas et alii, Frattura ed Integrità Strutturale, 50 (2019) 584-594; DOI: 10.3221/IGF-ESIS.50.49 593 turning parameters corresponding to these results are 1479 rpm for n ; 0.1709 mm/rev for f and 0.5000 mm for a . It is deduced that the results simultaneously satisfying all three objectives are not necessarily the values of upper or lower points of the problem’s intervals. These values for turning parameters occur according the interactions between them. It is also observed that the different solutions prioritize a different hierarchy among the objectives. The best result for Ra comes from the multi-objective solution of the delta wolf which is equal to 2.966 μm whereas the worst value for Ra comes from the multi-objective solution of the beta wolf which is equal to 3.108 μm. The best result for Rt comes from the multi- objective solution of the delta wolf which is equal to 16.594 μm whereas the worst value for Rt comes from the multi- objective solution of the beta wolf which is equal to 17.180 μm. Finally the best best result for Fc comes from the multi- objective solution of the beta wolf which is equal to 83.153 N whereas the worst value for Fc comes from the multi- objective solution of the delta wolf which is equal to 83.326 N. Whether the significance of these small differences among the results is of major or minor importance, it depends on manufacturing specifications and surface finish requirements. C ONCLUSIONS AND FUTURE RESEARCH n this work an experimental study on machinability parameters in turning of CuZn39Pb3 brass alloy was performed. Machinability was investigated with reference to arithmetic mean surface roughness Ra ( μ m), maximum height of the profile Rt ( μ m) and main cutting force Fc (N) which were considered as dependent responses affected by the cutting conditions; rotational speed n (rpm); feed rate f (mm/rev) and depth of cut a (mm). An L18 mixed-level Taguchi ortho- gonal design of experiments was set to build the design space according to the operational range of cutting conditions as well as their corresponding levels. The results obtained suggest that cutting conditions and their interactions differently affect the responses of Ra , Rt and Fc . Main cutting force is minimized by applying low speeds and moderate feeds whereas roughness parameters Ra and Rt are minimized by using high speeds combined to moderate feeds for a depth of cut equal to 1.0 mm. Full quadratic predictive models were generated via regression analysis and good correlation was achieved between experimental and predicted results for all responses. The resulting models were then considered as the objective functions for solving a multi-response optimization problem for turning of CuZn39Pb3 brass alloy. An advanced multi- objective intelligent algorithm following the behavior and social activity of grey wolves was applied to solve the problem. It was revealed that the algorithm is efficient in its heuristic search during all independent algorithmic runs with emphasis to the final recommended optimal parameters to solve the optimization problem. As a major future perspective the authors currently plan to further investigate soft computing methods and several intelligent algorithms for optimizing the turning of CuZn39Pb3 brass alloy and apply the same methodology to optimize the machining operations such as turning or milling of other engineering materials. A CKNOWLEDGEMENTS he authors are grateful to Dr.-Ing. G.A. Pantazopoulos of ELKEME Hellenic Research Centre for Metals s.a for the supply of CuZn39Pb3 brass specimens. N.M. Vaxevanidis wishes to thank the Special Account for Research of ASPETE for supporting the presentation of a preliminary version of this work in the “1 st International Conference of the GSEMM” through the funding program “Strengthening research of ASPETE faculty members”. R EFERENCES [1] Kuyucak, S., Sahoo, M. (1996). A review of the machinability of copper-base alloys, Can. Metall. Quart., 35(1), pp. 1-15. [2] Klocke, F., Nobel, C., Veselovac, D. (2016). Influence of tool coating, tool material, and cutting speed on the machin- ability of low-leaded brass alloys in turning, Mater. Manuf. Process. 31(14), pp. 1895-1903. [3] Nobel, C., Klocke, F., Lung, D., Wolf, S. (2014). Machinability enhancement of lead-free brass alloys, Proc. CIRP, 14, pp. 95-100. [4] Kato, H., Nakata, S., Ikenaga, N., Sugita, H. (2014). Improvement of chip evacuation in drilling of lead-free brass using micro drill, Int. J. Autom. Technol., 8 (6), pp. 874-879. [5] Nobel, C., Hofmann, U., Klocke, F., Veselovac, D. (2015). Experimental investigation of chip formation, flow, and breakage in free orthogonal cutting of copper-zinc alloys, Int. J. Adv. Manuf. Technol., 84(5-8), 1127-1140. I T