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Multi-criteria Optimization of Hole Geometry for the Laser Trepanning of the Titanium Alloy Ti-6Al-4V
R. Goyal and A.K. Dubey

Titanium and its alloys are extensively used materials in aerospace industry due to their remarkable metallurgical and mechanical characteristics; however, superior mechanical properties, poor thermal conductivity and higher chemical affinity of titanium alloys make them difficult-to-cut by conventional machining methods. The present research investigates the possibility of machining quality improvement in Ti-6Al-4V by applying the laser trepan drilling. The drilled hole quality in terms of hole taper, and circularity at top and bottom sides have been considered for multi-criteria optimization. Authors have applied a new hybrid approach of modelling and multi-objective optimization of hole geometry in laser trepan drilling of difficult to cut Ti-alloy. The hole quality comprising taper and circularities are represented by a common performance index in mathematical form using artificial neural network modelling coupled with grey-entropy measurement technique. Optimization of the performance index function using genetic algorithms show considerable improvements in hole quality. The parametric effect show that high chemical reactivity and low thermal conductivity of Ti-alloy play important role in deteriorating the hole geometry.

Keywords: Nd:YAG laser, titanium alloy, Ti-6Al-4V, laser trepanning, hole geometry, artificial neural network (ANN), and genetic algorithm (GA), multi-criteria optimization

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