The use of carbide and particle-damped bars to increase tool overhang in the internal turning of hardened steel

Abstract

Vibrations are very prejudicial to machining as they directly affect the dimensional accuracy and surface roughness of the machined part. Excessive vibration must be avoided or at least reduced. This can be achieved in several ways, including the use of dampers and more rigid material for tool holders. Tool vibration is stimulated in internal turning by the cantilever shape of the tool and the large tool overhang used, impairing the quality of the turned part. This is a serious problem in the turning of hardened steel because internal turning is usually the last operation carried out on the surface, making tight tolerances and low surface roughness values necessary. Excessive vibrations would harm the surface finish and could lead to tool breakage because of the low toughness of the tool materials used for this kind of application. The main objective of this work was therefore to identify alternative approaches for finishing internal turning of long holes in hardened steel parts. Different tool holder materials (steel and cemented carbide) and a particle impact damped steel tool holder were tested to determine the longest overhang that could be achieved in each configuration. The results showed that carbide bars reduced vibrations and allowed longer overhangs to be used. Particle impact dampers may be a simple alternative to the more expensive carbide bars.