Size effect on surface generation of multiphase alloys in ultra-precision fly cutting

摘要

Ultra-precision fly cutting (UPFC) is a typical discontinuous cutting process where a cutting tool flies simultaneously with the rotation of a spindle and cuts the surfaces of a workpiece intermittently. To obtain good surface roughness with an acceptable productivity, it is crucial to investigate the influence of cutting chips and tooling movement during the cutting process. In UPFC, it is found that the surface rough patterns (SRPs), which are affected by submillimetre-size cutting chips, are generally formed at the tool-out area of each tool feed imprint on the machined surface. The formation of SRPs in UPFC is assumed to be affected by the size effect that is critical in new surface generation in the micromachining process. In this process, the tooling cuts through both the surface layer and inner layer grains of the workpiece during chip formation, thus resulting in the formation of an SRP. In this research, the influence of cutting parameters on the SRP is investigated; a hybrid constitutive Johnson Cook model is established and a finite element simulation using the established constitutive model is conducted to analyse the generation of the SRP. Experimental and simulation results indicate that when surface grain ratio is larger than 35 %, the inconsistent fracture strain between the surface and inner layers is the primary reason of the fracture inside the uncut chip in UPFC. SRPs are thus formed owing to the void formation and tooling movement marks on the machined surfaces. Increasing the spindle speed and reducing the feed rate minimise the occurrence probability of the SRP. Upon addressing the issues described above and with informative findings, this research provides an in-depth understanding of SRP generation affected by size effect in UPFC, and further presents a basis for improving the quality of machined surfaces.