A Novel Single-Step Superfinish Hole Making Process for Maximum Fatigue Life

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A hole is the most common feature in machining. The conventional process for making quality holes consists of many steps: centering drill, rough drill, hardening, boring, reaming, grinding, burnishing or cold expansion. A hole gives rise to severe stress concentration. As a result, fatigue failure often originates at the hole in cyclically loaded structures such as aircraft and automobiles, which can be catastrophic as well as costly. A new concept of using single-step machining to pre-stress the machined surface, which was previously shown to have the capability of improving the fatigue life of rolling contact over thirty times, is applied in this research project. The objective of the project is to realize the significant potential benefits of using single-step machining to pre-stress the machined surface in hole drilling for maximum fatigue life at a reduced cost. The tasks to be performed include: (1) developing a process model that relates the drilling conditions to the residual stress distribution; (2) developing a performance model that relates the residual stress distribution to fatigue life; and (3) linking the process model to the performance model so the final residual stress distribution, thus the fatigue, can be optimized. The research results will benefit the industries manufacturing aircraft, automobiles, and other structures subject to cyclic loading. Because of the vast scale on which drilling operations are carried out, even a slight increase in the efficiency would yield important practical and economic benefits.