Influence of tool vibrations on tool wear mechanisms in internal turning of hardened steel

Abstract

Hard turning is becoming an usual way to replace grinding operations and is performed with ceramics and cubic boron nitride tools. However, tool inserts are brittle and may be subjected to wear and damage mechanisms like chipping and breakage. The damages are intensified in internal turning operations, where the tool holder presents lower rigidity than in external turning, making it subjected to higher vibrations. Most works analyze chatter (unstable cut) conditions, and a gap remains over the effects of stable cut vibrations. Therefore, this work conducted internal turning tests of hardened AISI 4340 steel in a 24 full factor design (tool holder material, overhang, cutting speed and feed) in order to verify the effects of these factors on tool vibration, tool life and wear mechanisms. Under stable cut, tool accelerations were 2 times higher for steel bars, when compared to carbide bar. Tool life (in terms of volume of material removed) was not affected by tool vibration and remained around 120,000 mm3 of material removed. The main conclusion of this work was that tool vibration, in the levels obtained in this work, did not influence tool life, but its growth made tool wear mechanism to change from diffusion to abrasion.