Hole-making processes and their impacts on the microstructure and fatigue response of aircraft alloys

Dan Sun,Xuda Qin,Yan Jin,Daniel Keys,Qing Zhao,Savko Malinov,Patrick Lemoine,Patrick Doyle

doi:10.1007/s00170-016-9850-3

Abstract

A comparative study on conventional drilling and helical milling has been reported under the context of aircraft alloy hole making. The impacts of these two different machining processes on the microstructures and the fatigue performance of different aircraft alloys have been elaborated. Results show that both alloys undergo more severe surface/subsurface plastic deformation under conventional drilling comparing to helical milling process. Helical milling leads to a longer coupon fatigue life compared to conventional drilling for both alloys. The fatigue life of Al 2024-T3 is significantly longer than that of Ti-6Al-4V under all machining conditions. The use of coolant generally produces less damaged surface and leads to enhanced fatigue performance of the machined alloys. In addition, the machined surface roughness has been studied to further elaborate the effects of different machining processes.

Highlights

Ensuring the reliability of aircraft is a primary concern for aircraft designers and manufacturers
The helical milling significantly improved fatigue life comparing to conventional drilling process
For Al 2024-T3 alloy, the use of helical milling resulted in 63% longer fatigue life under dry condition and 18% longer fatigue life under lubricated condition comparing to conventional drilling

Summary

Introduction

Ensuring the reliability of aircraft is a primary concern for aircraft designers and manufacturers. Fastener holes are made by hand using the conventional drilling process, whereby a rotating drill feeds into the fuselage skin. Conventional drilling involves a rotating cylindrical tool bit which has two cutting edges at the working end and feeds into the workpiece. During the conventional drilling process, the material is removed when the chips are transported laterally and evacuated through the flutes. This translates into a high thrust force and effective dissipation of heat is difficult [3]. Chip and fuselage skin can increase the surface roughness of the hole which can provide stress concentration zones from which fatigue cracks can initiate [4, 5]

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Results

Conclusion