Study on tool wear and chip shapes in deep drilling OF AISI 4150 steel

Abstract

Deep drilling process is widely used in the manufacturing of diesel injection components such as the injection holder, used to transport fuel from the high-pressure pipe to the combustion chamber of the engine. The material used in the manufacturing of these components is low-alloy steel AISI 4150. This high percentage chrome (~1 %) and molybdenum (~0.2 %) steel attains its high resistance through heat treatment (quenching and tempering), which allows this material for working with high injection pressures up to 2300 bar. However, it presents problems in deep drilling operations. This is due to the high rate of drill bit breakage, high tool wear and ribbon-like chips. This work studies deep drilling of AISI 4150 steel by analyzing through the method of design of experiment, the influence of the following machining factors: cutting speed, feed-rate and tool coating. Tool wear, machining drilling torque and shape of the machined chips were considered for the analysis. Evidences were found that the uncoated tool shows a cyclical wear mechanism of adhesion removal workpiece material on the tool, where material is welded onto the cutting edge forming the built-up edge. The results showed that TiNAI-coated tool did not present this wear mechanism and it outperformed the uncoated tool.