Measurement and analysis of the thermal load in the bore subsurface zone during BTA deep hole drilling

Abstract

To machine bores with larger diameters (D > 40mm) and a length to diameter ratio greater than ten (lb/D > 10) the BTA deep hole drilling process is often used. The cutting action of the cutting edge and the burnishing of the guide pads influence the resulting surface and the subsurface zone of the machined bore. The guide pads support the BTA drill head against the machined bore to prevent straightness deviations. A thermo-mechanical load, which results from the cutting and burnishing, influences the surface of the bore and effects the surface integrity, i.e. micro hardness, residual stress state, microstructure or the surface roughness, of the bore. In this paper, a measurement strategy to determine the thermal load in the subsurface zone using thermocouples is presented. Furthermore, a fiber-optic ratio pyrometer was used to measure the temperature in the contact zone between the cutting edge and the wall of the bore. The experiments were carried out using different workpiece materials, tool coatings and cutting parameters. The measurements are analyzed and set in context with previous studies.