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

Machining thin workpieces is a challenging task as geometrical errors may result from the combination of several phenomena. Among these, elastic workpiece deformation and machining induced residual stresses may be predominant sources due to low part stiffness. There is a lack of studies trying to quantify the influence of machining induced residual stresses on the total geometrical errors. A thorough experimental methodology is developed to quantify the influence of both phenomena separately by comparing the workpiece shape and dimensions, in-situ, before and after machining, using laser sensors. The proposed methodology can also be used to quantify the geometrical errors linked to clamping or stress rebalancing following material removal. The case study is the finish turning of thin Inconel 718 workpieces using carbide tools. In the studied case, machining induced residual stresses are responsible for 3-32 % of the total geometrical errors depending on tool wear and cutting parameters.