Machinability in drilling : mechanistic approach and new observer development

Abstract

This paper focuses on machinability especially in drilling. It is usually estimated experimentally based on thrust force and torque measurements, chip morphology analysis, surface quality and tool wear tests. A specific experimental procedure has been developed and tested for many steel grades. However wear tests are probably the most critical point. Wear tests are essential for an industrial application since they lead to know the cost per hole nevertheless they are highly time and work material consuming. Wear pattern and wear rate depend on the thermo mechanical stresses exerted on the cutting tool in the contact zones. A mechanistic approach enables to estimate the mechanical stress distribution along the drill lip. A new observer based on the mechanical thrust and force measurements is proposed to estimate stress distribution dissymmetry and rapidly rank the machinability in drilling. His relevancy is checked for several steel grades and drilling conditions: metallurgical structure and hardness are different, cutting material and coating and cutting conditions vary. Experiments are performed without lubricant.