Minor cutting edge–workpiece interactions in drilling of an advanced nickel-based superalloy

• Published in: International journal of machine tools & manufacture 2009-06, Vol.49 (7), p.645-658
• Main Authors: Kwong, J., Axinte, D.A., Withers, P.J., Hardy, M.C.
• Format: Article
• Language: English
• Subjects: Acoustic emission; Acoustical measurements and instrumentation; Acoustics; Applied sciences; Drilling; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Industrial metrology. Testing; Inelasticity (thermoplasticity, viscoplasticity...); Material drag; Mechanical engineering. Machine design; Nickel-based superalloy; Physics; Residual stresses; Solid mechanics; Structural and continuum mechanics
• ISSN: 0890-6955; 1879-2170
• DOI: 10.1016/j.ijmachtools.2009.01.012

Drilling is one of the key machining operations for manufacturing safety critical components that must comply with strict surface quality standards. The influence of major flank wear of drilling tools on workpiece surface quality has been well established; however, similar information concerning minor cutting edge is currently missing from literature. This paper presents a comprehensive analysis and discussions of the influence of the drill's minor cutting edge to workpiece surface integrity and residual stress distribution for RR1000, a newly developed nickel-based superalloy. These effects are critical to the acceptance of this new material in relation to tool geometry and machining strategies. The thickness of material drag in the hoop direction has been found to be the highest at the top and the least at the bottom of the hole, which is directly related to the contact duration between the minor cutting edge and workpiece surfaces; moreover this difference increased at higher levels of wear of the minor cutting edge. On-line process monitoring techniques have been employed to further understand the material drag phenomena, including feed force, torque and acoustic emission. Compressive axial and tensile hoop stresses at the surface of the holes have been measured as a function of depth and correlated both with metallurgical analysis of drilled surfaces and the process monitoring signals. It was found that the increased material drag associated with a worn tool resulted in compressive hoop surface residual stresses near the entrance hole in correspondence with trends in the processed acoustic emission signal. This work suggests that material drag increases with the duration of the minor cutting edge–workpiece interaction such that plastic deformation is the greatest near the drill entrance holes and that process monitoring of the degree of material drag in hoop direction can be practicable.