Investigations into machining accuracy and quality in wire electrochemical micromachining under sinusoidal and triangular voltage pulse condition

Abstract

• Application and optimization of novel pulsed voltage waveforms for improving the process accuracy in Wire-ECMM. • A mathematical analysis of the evolution of machining gap with time under the application of different voltage waveforms. • Finite element modelling for the visualization of current density distribution in the machining zone. • Evaluation of machining quality using three dimensional optical profilometer and SEM images of machined features. • Optimization of triangular pulsed voltage waveform by varying its rise and fall time for improving the process accuracy. Since the past two decades, improving machining accuracy, precision, and quality of machining in Wire-ECMM has been a prime focus of researchers across the globe. Application of high frequency pulse voltage for machining has served the purpose to a large extent. However, with high frequency pulse voltage, machining rate is compromised. Often, the use of very high frequency also necessitates the application of high voltage amplitude which consequently, leads to increased power consumption. To solve this problem, this research proposes the use of sinusoidal voltage waveform (SVW) and triangular voltage waveform (TVW) instead of a conventionally used rectangular voltage waveform (RVW) for machining. A mathematical analysis of the machining gap in the process using a mechanistic approach suggests that accuracy in terms of kerf width improves significantly when SVW and TVW are used for machining. Experiments are conducted to investigate the impact of pulse voltage waveform on different characteristic features of a kerf profile which are kerf width, edge fillet radius, corner radius, and taper angle. These waveforms are generated using a function generator with the help of a rectification cum amplification electronic circuit. Roughness of the surface machined using these three waveforms are also measured using optical profilometer. Experimental results suggest that the percent reduction in the kerf width for the three waveforms considered by changing the frequency of voltage pulse from 100 kHz to 200 kHz is significantly lower than that obtained by switching from RVW to TVW and keeping other pulse parameters such as frequency, amplitude, and duty ratio same. Using a wire (tool) made of tungsten and a diameter of 30 μm, minimum kerf width of 60 ± 2 μm, edge fillet radius of 11 ± 1 μm, and a negligible corner radius is obtained when TVW is used for machining. For the above stated parameters, profile roughness (R a ) & area surface roughness (S a ) of machined kerf are 1.43 μm and 1.55 μm respectively for RVW, which are reduced to 0.44 μm and 0.57 μm respectively, for TVW. To understand the reason behind the reduction of kerf width, corner radius, and edge fillet radius in case of TVW, as indicated by the experimental observations, numerical simulations are performed. For a comparative study, current density distribution pattern over the workpiece surface is plotted for the three waveforms. Later, TVW is further optimized by varying its ‘rise’ and ‘fall’ time. For this, a factor termed as Pulse Rise Factor (PRF) is defined and is varied in 5 steps. Experimental results suggest that kerf width is minimum 55.4 μm when PRF is zero and is maximum 71.8 μm when PRF is one. In the end, different micro features are machined using the optimal machining conditions.