Microstructural Alterations Associated With Friction Drilling of Steel, Aluminum, and Titanium

Friction drilling, also called thermal drilling, is a novel sheet metal hole-making process. The process involves forcing a rotating, pointed tool through a sheet metal workpiece. The frictional heating at the interface between the tool and workpiece enables the softening, deformation, and displacement of work-material and creates a bushing surrounding the hole without generating chip or waste material. The bushing can be threaded and provides the structural support for joining devices to the sheet metal. The research characterizes the microstructures and indentation hardness changes in the friction drilling of carbon steel, alloy steel, aluminum, and titanium. It is shown that materials with different compositions and thermal properties affect the selection of friction drilling process parameters, the surface morphology of the bore, and the development of a highly deformed layer adjacent to the bore surface.