Machining of fluidic channels on borosilicate glass using grinding-aided electrochemical discharge engraving (G-ECDE) and process optimization

Abstract

Electrochemical discharge machining (ECDM) has already been identified as a novel process for machining advanced ceramics and glass. The major limitations of this process are high overcut of the machined channels and the difficulty in controlling the roughness of the channel. This paper presents a novel technique which uses diamond-impregnated engraving tool as the tool electrode for machining accurate and smooth channels on borosilicate glass using ECDM. This technique can be called as grinding-aided electrochemical discharge engraving (G-ECDE). The new method utilizes both the grinding action of diamond grits and the thermal and chemical effects of ECDM for material removal. Preliminary experiments are performed using Placket–Burman design with center points to study the effect of machining parameters like voltage, electrolyte concentration, pulse-on time, tool rotational speed and tool feed rate on channel overcut and surface roughness of the channel. With the significant factors identified from the preliminary experiment, the main experiment was performed using a widely used response surface design called Box–Behnken design to develop second-order response models for surface roughness and channel overcut. Response surface plots are used to identify the effect of parameters and their interactions on the responses. Technique for order preference by similarity to ideal solution (TOPSIS) is used to optimize this multi-response problem. The optimum factor levels obtained from TOPSIS are a medium feed of 2 mm/min, a low voltage of 80 V, a medium pulse-on time of 0.0011 s and a low concentration of 2 M which produced channels with a surface roughness of 0.872 μm and overcut of 0.293 mm. From the microscopic images of machined channels, material removal mechanisms of G-ECDE are confirmed to be a combination of thermal melting due to electrochemical discharges, grinding action of diamond grits and high-temperature chemical etching action of the electrolyte. The performance of G-ECDE is compared with die-sinking ECDM and electrochemical discharge milling for producing channels and found that G-ECDE is the most suitable process to produce fluidic channel on glass which is free from recast layer and heat-affected zone. The results obtained from this study proved the potential of G-ECDE in producing smooth, accurate and complex fluidic channels on the glass.