Finite Element Simulation and Experimental Investigation of Conventional and High Speed Machining of Al 6061-T6 Alloy

Abstract

Aluminium based alloys are important industrially, owing to their high machinability, corrosion resistance, and strength to weight ratio. These properties make them highly suitable to be used in automotive, aerospace and food processing industries. Due to its high industrial importance, minimal tool wear and superior machining characteristics, Aluminium 6061-T6 alloy has been selected as the workpiece in many research works. Many research studies have been conducted in the past for the experimental and numerical investigation of cutting forces, temperatures, residual stresses and tool wear etc. during machining of Al 6061-T6 alloy. A close agreement was found between experimental and simulated results, however, the available FE models for aluminium based alloys have generally been limited to low and medium cutting speed ranges (i.e. below 1600 m/min). It was observed that the experimental cutting forces were dropped suddenly during High Speed Machining (HSM) condition of Al 6061-T6 alloy. This sudden drop in the experimental cutting forces due to adiabatic heating and reduced coefficient of friction at HSM, was not captured accurately by existing models. An effective predictive model which can numerically investigate the effects on Al 6061-T6 alloy in the high speed machining regime (i.e. above 1600 m/min – 2000 m/min) at the feed rates (f) of 0.1-0.4 mm/rev has previously not been reported in the literature. The current research therefore aimed towards the development and testing of an effective FE model that is capable of simulating the machining of Al 6061-T6 alloy at conventional as well as high speed regime. In the current research work, extensive experimentation and numerical investigations were carried out covering low, medium and high speed/shear rate machining regimes using a dynamic coefficient of friction and thermal softening effect at HSM condition. This approach considerably improved the predicted cutting forces obtained through the existing sets of Johnson-Cook (J-C) material constants. The maximum error of (Fc) were reduced to 19.1% and 23.7% at higher cutting conditions for both existing data sets of material constants, compared to earlier predictions of 36% and 41%, respectively (at higher coefficient of friction and without considering adiabatic heating effect). The current research work adopted a new method for measuring cutting forces using a power meter through specific cutting energy approach, by carrying out extensive experimentation and literature validation, which is more economical than commercially available force dynamometers. Besides, for the first time, low, medium and high speed ranges during machining of Al 6061-T6 alloy were defined accurately during the current research work. Finally, a suitable set of J-C material constants were selected through inverse methodology which was found to be as accurate as existing sets of J-C material constants in LSM and MSM regimes but was also found to be more accurate in the HSM range. Therefore, the set of J-C material constants selected in this research work can be used in a consolidated model for the entire cutting range with accuracy greater than the sets of J-C material constants available prior to this research.