Machinability of inconel 718 during turning: Cutting force model considering tool wear, influence on surface integrity

Abstract

Machining accuracy can be compromised by elastic workpiece deformation and subsurface residual stress introduction during cutting. In order to anticipate the impact of cutting forces and surface integrity evolutions on finished surface and its geometrical errors, it is necessary to better understand the influence of cutting conditions and tool wear. In this study, machinability of Inconel 718 using a round carbide tool in finish turning conditions is assessed. Cutting forces evolution during tool life are analysed and accompanied by advanced investigations of cutting phenomena. An original mechanistic cutting force model is developed, identified and tested. It includes the effect of tool wear over time in its local formulation. This model allows predicting cutting forces evolution along tool pass for a wide range of finishing cutting conditions. Furthermore, a thorough analysis of residual stress profiles at different tool wear levels is led. It features quantitative results for fresh and worn tools. A study on the influence of cutting parameters and tool wear on residual stress profiles in the machining affected zone is highlighted.

Study of phenomena responsible for part distortions when turning thin Inconel 718 workpieces

“…The experiment involves machining tests on 6 discs with different conditions summed up in Table 1. The cutting conditions are consistent with semi finishing and finishing conditions identified in [17]. The tests consist in 3 consecutive face turning passes.…”

“…As mentioned in the introduction section, machining with a worn tool may create high tensile stresses close to the machined surface. However, the affected depth and magnitude of the compressive peak are also significantly increased compared to machining with a fresh tool [14,17]. Based on these bibliographic knowledge and experimental observations, it is deduced that the residual stress profiles obtained with a worn tool are highly compressive in the studied case.…”

“…This may mean that tensile stresses are predominant at this stage of the cutting process when using higher feed. Even though residual stress profiles significantly vary during tool life, several studies show that the effect of wear on surface integrity is moderate in Inconel 718 until the flank wear reaches a critical level [15,17]. Over this level, a major increase in cutting forces and machining induced residual stresses affected depth is observed.…”

“…When turning with a tool in the controlled wear region, XRD measurements show that the machining-affected area depth is inferior to 0.15 mm (cf. [17]). Considering the fact that the average effective depth of cut is always greater than 0.15 mm as shown in Fig.…”

Cutting Forces Assessment in CNC Machining Processes: A Critical Review

“…It was found that the Bayesian inference can predict cutting and ploughing forces with minimal initial data, which means that this method is a preferred approach when the initial data are very reduced and there is inherent uncertainty. In the recent study presented by Toubhans et al [48], a cutting force model for the turning of Inconel 718 was developed, which enables the prediction of cutting forces and their evolution along the tool pass, for a wide range of surface finish levels of quality. The authors found that including a component relative to the chip flow direction in the local force model allows for better force predictions.…”