Selective electrochemical boring of thin-walled tubes: Methodology, mechanism, and characteristics

Corrugated tubes having internally turbulated surface find intensive application in heat-exchangers. Fabrication of thin-walled tubes with turbulated internal surface using conventional machining processes is difficult due to the inability of tube wall to withstand the cutting force. With non-contact type machining processes, a methodology is yet to be developed for selective boring of thin walled tubes. In this research, we propose a novel approach to bore a thin-walled tube at selective locations using electrochemical route and the operation is termed as selective-electrochemical boring (SECB). Machining centre is fabricated in-lab and experiments are carried out using a partially-insulated single-point tool. Experiments are performed to study the influence of process parameters on different characteristic features of a groove profile. With the developed machining centre and the proposed machining methodology, multiple internal grooves with sub-micron level surface roughness are fabricated and subsequently characterized. Minimum surface roughness (Ra) of 0.064 & mu;m is achieved inside the groove on SS-304 tube. The unique feature of this invention is its ability to machine internal as well as external grooves at the selected location without the need for a specifically-shaped tool. Application of the proposed methodology can be extended to machining of turbulated profile on pre-drilled holes in turbine blades for enhancing heat transfer rate.