EXPERIMENTAL INVESTIGATIONS FOR PERFORMANCE ENHANCEMENT OF ECDM PROCESS

Abstract

Miniaturization is a trend to fabricate small-sized products. Over the past few years, the exponential evolution of miniaturized products in microfluidics has earned the attention of industrialists, manufacturers, researchers, and academicians across the globe. The basic structure of microfluidic devices consists of several micro features such as micro-channels, micro holes and micro slits that are integrated on a common platform. Glass is one of the most commonly used material to fabricate the microfluidic devices. A solution for fabrication of micro-features on glass material can be use of hybrid non-conventional micromachining process that is an Electrochemical discharge machining (ECDM). Electrochemical discharge machining (ECDM) is an emerging micromachining process that integrates the features of two non-conventional machining processes such as electrochemical machining process and electric discharge machining process. The flexibility to machine the micro features, i.e. micro holes, microchannels, micro slits, and micro textures on glass material using ECDM makes it popular machining process. Notwithstanding the benefits of ECDM process, it provides low material removal rate (MRR) and has limited ability for high aspect ratio drilling and deep depth machining. The need for high productivity, accuracy, and repeatability during micro-fabrication using ECDM insists further modifications in ECDM system. In view of the above, In the present research endeavor, to improve the performance of ECDM process, several modifications in ECDM system based on tool electrode, work material feeding system, and electrolyte have been carried out. These modifications have been carried out in the existing facility of ECDM process. The main motive of these modifications was to enhance the performance of ECDM process without involving any major modification and manufacturing complexity in the existing facility of ECDM process. So, In future, these modifications can be easily incorporated in the existing machines of ECDM process. After modifications, exhaustive experimentation has been performed to investigate the effect of different process parameters associated with these modifications on response characteristics. To establish the relationship between input process parameters and response characteristics, regression modeling was performed. Multi-objective optimization was performed to optimize the process parameters to achieve high productivity and accuracy with good surface quality. The fabricated micro features were characterized using an optical iv microscope, stereo microscope, field emission scanning electron microscope (FE-SEM) and surface roughness tester. In ECDM, gas film thickness plays a key role as it controls frequency and intensity of spark discharges. To improve the performance of ECDM process, the basic understanding of gas film formation mechanism is essential. Thereby, in the present research endeavor, the behavior of gas film was experimentally investigated. The experimental results recommended the formation of thin and stable gas film over the tool electrode to effectively channelize the electrochemical discharge energy to work material. In the first step, a pressurized feeding system was developed. The objective of this modification was to ensure the constant zero working gap between tool electrode and work material. The concept to maintain zero working gap between tool electrode and work material was further extended to machine microchannels and slits on glass material by using ECD milling and W-ECDM process with rough tools, respectively. The performance of rough tools for micro-channeling with ECDM is superior over smooth surfaced tools. In addition to the concept to maintain zero working gap between tool electrode and work material, the assistance of abrasion action was also provided in the ECDM system. The abrasive coated tool electrode performed the abrasion action with rotary motion. Along with the advantages of micro gaps generated between tool electrode and work material, the rotary motion of abrasive coated tool electrode helps to flush out the sludge from machining zone. Apart from the modifications mentioned above in ECDM system, the electrolyte based modifications were also performed in this research work. In the present research work, a new electrolyte supply system named titrated flow method was incorporated in the existing facility of ECDM process. The objective of this development was to prolong the discharge regime up to deep depths. The incorporation of titrated flow of electrolyte in ECDM system eliminates the accumulation of bubbles from hole entrance and ensures the continuous supply of electrolyte towards tooltip. The application of titrated flow of electrolyte in ECDM process fabricates the micro through holes in 1350 μm thick work material in approximately 30 seconds. In another modification, a new hybrid electrolyte is used to fabricate the microchannels on glass. This hybrid electrolyte contains a mixture of sodium hydroxide and potassium hydroxide in same proportion along with the graphite powder. The use of powder mixed hybrid electrolyte found very effective at higher applied voltage. The modifications mentioned above in ECDM system improves the overall process performance and open several research avenues to extend this work for the fabrication of complex micro features on glass material.