Duplex Peening and Smoothing Process

Author:  J. W. Neal, J. W. Sullivan, J. F. Loersch
Source:  US Patent 4,428,213
Doc ID:  1984128
Year of Publication:  1981
Abstract:  
Disclosed is a two step process of peening for workpieces having small radii fillets or fragile edges, such as gas turbine airfoils have. In the first step, relatively small size shot of less than 1mm dia is used to impart a first peening intensity to a workpiece. This results in a first relatively rough surface finish. In the second step, shot of substantially uniform diameter in range 1-2.5 mm is impacted with uniform velocity to provide a surface finish smoother than 30AA (10 to the -6inch). When fillets are peened, improved fatigue life results from the duplex process. When used on edges, where direct edge impact is avoided in the second step, deformed edges are avoided by the process. Yet the workpiece is substantially smooth and the edges have the requisite residual stress distribution.