SOME OBSERVATIONS OF SURFACE INTEGRITY OF DEEP DRILLING HOLES

The surface integrity produced by the gun deep drilling process is presented. The effects of drilling speed, drilling feed and work hole diameter on both surface and subsurface conditions of low and medium carbon steel are investigated. The results of the investigation show that the surface roughness decreases at high cutting speed, low feed rate, small length-to-diameter ratio and large hole diameter. In addition, the machined surface shows evidence of severe plastic flow and coarse scale surface damage. The microhardness at the machined surface region is larger than the bulk hardness of the work material for all conditions used. The subsurface region generally contains two distinct layers, i.e. a fragmented layer and a less heavily deformed layer. The results could be interpreted in terms of temperature rise during cutting, plastic deformation, drilling forces, vibration, lubrication, tool wear, built-up edge, chip form, and the interaction between the burnishing pads of the gun drill and the freshly drilled surface.