Ultrasonic Vibration Assisted Turning of a Nickel-based Superalloy: Acoustic Horn Design, Experimental Investigations and Numerical Analysis

Abstract

The applications of nickel-based superalloys in different industries, like aviation, defense, marine, automobile and petrochemicals sectors, etc. have been increasing remarkably due to its distinctive properties such as corrosion resistance and high strength to the weight ratio. It has been noticed that the Conventional Turning (CT) process yields critical machining problems for cutting the nickel based superalloy due to the decreased thermal conductivity of the material. A lot of advanced manufacturing techniques have been investigated sensibly in the recent years to improve the machining quality. Ultrasonic Vibration Assisted Turning (UVAT) method is one of such processes that has gained a lot of attention due to its intermittent cutting mechanism. The central aim of the present research work is to examine (theoretically and experimentally) the machinability of the nickel-based superalloy (Inconel 825), which is one of the hard to cut material, using UVAT process. More emphasis is given to design and fabricate an UVAT experimental set-up because of unavailability of such type commercial one. Sonotrode or acoustic horn is a vital component in UVAT system. Hence, a lot of interest has been taken to design and model the acoustic horn using Finite Element Analysis (FEA). FEA has been done for designing the tool (sonotrode with cutting insert) and analyzing its performance. This analysis confirms the resonance frequency of vibration and working amplitude of the proposed UVT, which remain at f ≈ 20±0.5 kHz and amplitude a ≈ 35 μm respectively. The performance of the UVT has been examined under the modal and harmonic conditions to check its suitability for the machining operations. After manufacturing the UVT and experimental set-up, the experimentation has been carried out taking Inconel 825 (nickel-based superalloy) as the workpiece material. The experimental investigation is divided into two parts; the first one is L25 orthogonal array Taguchi's design of experiments (DOE) for both CT and UVAT processes to compare and analyse the results; and the second one is the L125 full factorial design of experiments for UVAT process to understand the effect of different process parameters on responses more deeply. The Grey Fuzzy-based Taguchi approach (a hybrid method), a Multi-Objective Optimization (MOO) method has been used to obtain the best optimal parametric setting for both CT and UVAT processes. The ANOVA has been performed to investigate the influence of input parameters on the output responses in the UVAT process. The ANFIS (a hybrid prediction tool) method has been used to predict and to validate the UVAT responses. The numerical study is performed for both the CT and UVAT processes (at optimal parametric settings) and the results are validated with experimental ones. The surface integrity of the workpiece, chip morphology and cutting tool wear are also studied. It is found that UVAT process reduces the surface roughness and cutting forces in comparison with CT process. The results also confirm the suitability of the UVAT process to machine the hard materials such as Inconel 825 and to obtain the best machinability characteristics.