Analysis of the evolution of the Built-Up Edge and Built-Up Layer formation mechanisms in the dry turning of aeronautical aluminium alloys

Abstract

Tool wear is one of the main parameters employed for evaluating tool life, due to its influence in the loss of quality of the manufactured parts. So, minimising tool wear is possible to maximise tool life and to optimise the manufacturing performance. Different mechanisms can cause the tool wear in a specific machining process. Adhesion wear is one of the tool wear mechanisms that can be present in a wider range of cutting temperatures. This type of tool wear can be produced by two different ways. On the one hand, direct adhesion wear is caused by the incorporation of tool particles to the chips. On the other hand, secondary adhesion wear is caused by the incorporation of fragment of the workpiece material to the tool. This affects to the tool wear in two ways. First, tool geometry changes by the material incorporation. In a second place, when these fragments are removed, they can drag out tool particles causing tool wear. Indirect adhesion can be located in the tool edge, giving rise to the Built-Up Edge (BUE) and/or in the tool rake face giving rise to the Built-Up Layer (BUL). BUL and BUE formation and their evolutions affects to the workpiece quality. In this paper a study of the BUL and BUE formation mechanisms, their evolution and their influence on the dry turned aeronautical workpieces surface quality has been achieved. In particular, this study has been developed using aerospace aluminium alloys such as UNS A92024 (Al–Cu) and UNS A97050 (Al–Zn). Results have shown that BUE is formed by mechanical adhesion mechanism. On the other hand, BUL is initially formed by thermo-mechanical causes. However, a secondary BUL has been detected as a consequence of the extrusion process of the BUE. Changes in BUL and BUE have been related with the changes observed in the roughness profile of the machined pieces and evaluated through the average surface roughness, Ra. So, a first relationship between the adhesion effects and the surface finish of the worked samples has been found. Obtained results have confirmed that BUE changes the tool position angle giving rise to a reduction of Ra.