Keng Soon Woon

The influence of drill geometric accuracy on steady tool wear development and catastrophic tool failure in high aspect ratio gundrilling of Inconel-718

The performance of gundrilling and its stability are governed by the accuracy and repeatability of critical drill geometries for precision self-guiding such as the inner approach angle, outer approach angle and drill apex. Through a performance evaluation study of Inconel-718 drilling, it was determined that inaccurate approach angles with large geometric errors could deflect and bent the rotating drill in both radial and axial directions, resulted in severe whipping and vibrations that damage the carbide drill tips. As the deflected drill is advanced continuously, the drill apex deviates towards other directions from the original drilling path, leading to the formation of sectional straightness error. Consequently, accumulation of multiple sectional errors of each drilling cycle throughout an exhaustive deep hole drilling operation induces irrecoverable straightness misalignment on the hole.

The Effects of Resharpening Accuracy on Drill Failure and Hole Straightness in High Aspect Ratio Gundrilling of Inconel-718

This paper presents a pilot study on the consistency of high aspect ratio gundrilling of Inconel-718 that involves the drilling of three holes of 8mm in diameter and 1600mm in depth, under constant drilling conditions. But high degree of straightness variations among these holes indicates that critical drill geometries could not be accurately regenerated through the drill resharpening operation. As a result, vast variability is introduced to the process which has severe detrimental effects on the stability of the drilling process and degradation and failure modes of the drill as well the straightness accuracy of the holes.

A Non-Dimensional Analysis of Tool Edge Radius Effect on the Mechanics of Micromachining

The effect of tool edge radius on the mechanics of micromachining, both in terms of plasticity and tribology is significant. Through an experimental study, the responses of normalized process variables namely tool-chip contact length, deformed chip thickness and machining force were evaluated for varying relative tool sharpness. A non-dimensional analysis of the interrelationship among the process variables indicate a transformation in chip formation mechanism under an extreme condition is reported.

Numerical and experimental analysis of the tool edge radius effect in micromachining of ferrous materials

The tool edge radius effect in micromachining of ferrous materials was investigated extensively using advanced numerical and experimental approaches. The results revealed that the best surface finishing could be obtained at a critical combination of undeformed chip thickness and tool edge radius where material is removed through severe plastic deformation associated with an effective negative rake angle. The chip formation exhibits an extrusion-like behaviour as driven by intense deviatoric and hydrostatic stresses that are highly localised around the deformation zone. The changes in the chip formation behaviour over the range of a/r = 0.05-2.0 are indicated by four stages of machining force distributions. It is worth noting that the tool edge radius effect has a great influence on material deformations and contact interaction in tool-based micromachining. Thus, an analytical contact length model for tool-based micromachining is proposed.