Influence of thermoelectric junctions on the electrical signals generated by the tool-workpiece thermocouple system in machining

This work investigates the influence of the electrical circuits on TMF (total thermoelectromotive force) response signals captured from the rotating workpiece generated by the tool-workpiece thermocouple system in turning process considering four different thermoelectrical circuits - Ec namely: C1 - bronze pin, C2 - aluminum pin, C3 - graphite brush and C4 - liquid mercury contact. The tests were carried out under different cutting conditions. A multifactorial analysis of variance was performed using the 2k factorial design, always considering the C4 as the lower level. In addition, a single factor analysis of variance was performed, keeping the cutting speed, Vc, the feed rate, f, the depth of cut, doc, and the lubri-coolant system, Lub, constants while varying the Ec in order to validate the results found with the factorial design. The results indicated that there was no statistical significant difference in the TMF responses of the tool-workpiece thermocouples C1 and C4 as well as C2 and C4. However, when comparing the TMF generated by C3 and C4 a significant difference was detected, indicating that graphite brushes is not recommended for such application, while the bronze and aluminum pins can be thought as an advantageous substitute for the laborious liquid mercury system.