Micro-milling of Ti-6Al-4 V with controlled burr formation

Abstract

• A methodology is proposed to suppress the burr generation by tailoring compressive residual stress on the workpiece during the micro-milling process. • The burr formation is reduced by 63% by incorporating compressive surface residual stress of 589 MPa at the material surface. • The cutting marks at the machined side-wall are investigated and found to depend on the frictional behaviour between the tool and the workpiece. • Dynamic recrystallization is captured by EBSD on the micro-milled slot. • User-defined constitutive flow and friction models are proposed to capture the mechanism of the burr formation and morphology of the chip. Burr generation is expected to be a function of the state of stress and microstructure of the material before micro-milling. Burr formation may be hindered by cold working process such as peening, as peening leads to grain refinement and the induction of residual stress at the material surface. The novelty of the present work is the numerical modelling and experimental verification of control of burr formation in micro-milling of Ti-6Al-4 V by introducing compressive residual stress on the surface of the workpiece. The practical significance of the current study is that the compressive residual stress suppresses the burr generation by up to 63% in terms of burr width and height. The resultant cutting forces are found to be 13% higher for pre-stressed material, compared to the ones without pre-stress. As the cutting-edge radius and grain size of the material are of comparable magnitude in the case of micro-milling, a strain gradient-based dynamic recrystallization constitutive flow model is developed and incorporated into a finite element model in Abaqus. In addition, the cut marks at the machined wall of the material, are modelled with a proposed friction model and verified with experiments. The results of the FEM model are found to agree with the experimental finding by up to 12%.