Burnishing method and apparatus for providing a layer of compressive residual stress in the surface of a workpiece

A method of inducing a compressive stress on the surface of a workpiece with a minimal amount of cold working and surface hardening, the method comprising the steps of:

• defining a surface area for receiving compression stress;
• performing a burnishing operation by a burnishing apparatus comprising a socket having a tip member incorporating a ball seat and a freely rotating burnishing ball disposed within said ball seat;
• forcing the forwardmost tip of said burnishing ball against the surface of the workpiece;
• and
• rolling said burnishing ball over said defined surface area to induce a deep layer of compression within the surface with cold working of less than about 3.0 percent.

An apparatus for inducing a compressive stress on the surface of a workpiece with a minimal amount of cold working and surface hardening, the apparatus comprising:

• a socket having a generally cylindrical tip member integrally formed with a generally cylindrical rod member, and a socket support for supporting said socket on a conventional tool holder, wherein said tip member comprising a ball seat having an essentially spherical shape adapted to the surface of a burnishing ball disposed within said ball seat;
• a removable retainer cap for retaining said burnishing ball within said ball seat;
• and
• means for directing lubrication fluid from a reservoir to said ball seat to force said burnishing ball outwardly toward the surface of the workpiece and for providing said lubricating fluid around the outer surface of said burnishing ball to permit said burnishing ball to float continuously upon a thin film of said lubricating fluid;
• wherein said socket support comprises a slide having a longitudinally extending bore having a first end for receiving said rod member and a threaded end having a threaded inner surface, wherein an adjustment screw is received in said threaded inner surface of said bore, and wherein said adjustment screw includes an inner end coupled to said rod member through a mechanical spring means.