Influence of lubrication modes on residual stresses generation in drilling of 316L, 15-5PH and Inconel 718 alloys

Abstract

Drilling is a very old and very complex process. As the tool is embedded in the part, neither the material removal phenomena, nor the evacuation of chips are well understood. As a consequence a bad choice of drilling tool or poor drilling conditions may affect the surface integrity of the machined part. The aim of this article is to bring a contribution to the understanding of lubrication modes on cutting phenomena and surface integrity when drilling a 316L austenitic stainless steel, a 15-5PH martensitic stainless steel and an Inconel 718 nickel alloy. Residual stress states in the hole have been analysed after drilling with three lubrication modes (internal high pressure coolant, external low pressure coolant, dry). Results have been analysed with regard to the thermal and mechanical actions of the drill on parts, thanks to temperature sensors along the hole, and thrust force+torque measurements. First this work has highlighted that residual stress state varies along a hole. Second, it has been shown that lubrication is a critical parameter on surface integrity. Whereas efficient cooling conditions enable to obtain compressive residual stresses and a limited affected layer, a lack of lubrication generates tensile residual stresses, a larger deviation in the results and an increase in the thickness of the affected layer.