Analysis of form Error and Roughness of Hardened Steel Workpieces Internally Turned with Different Tools in Long Overhangs

Internal turning process is a very important and widely used process for enlarging and finishing holes. Especially for the components that work with external members, this operation needs to assure surface and geometric quality. In that case, the correct definition of working parameters will directly contribute to the quality of component. Aim of the current research was to analyse the form error and the roughness of workpieces submitted to internal turning process using boring bars in long overhangs with three different internal tools (steel, carbide and antivibrating tool). For the experiments, heat-treated DIN EN 1.2842 (ISO 90MnCrV8) steel with 58 HRC of hardness was submitted to boring process using CBN (cubic boron nitride) inserts, and a boring bar with the most possible rigid clamping system (Easy Fix). The workpiece roughness and circularity were measured using a profilometer and a form error measuring machine. The measurements provided the data to identify the boring bar levels of stability, and the workpiece micro and macro geometric errors. The experiments allowed to conclude that, for all toolbars, the evaluated errors kept constant with increasing L/D ratio during stable clamping conditions, without any vibration. On the other hand, higher values of overhangs, limited to L/D>4.25 for steel tool, can cause serious damages in the cutting system if the antivibration tools or the carbide will be not used.