Investigation and optimization of the effect of machine vibrations on the dimensional surface quality in milling operations /

Abstract

Following an extensive literature review on the vibrations in machining operations, experimental work is undertaken in two main phases on the investigation and optimization of effects of machine vibrations on dimensional surface quality in milling operations. In Phase IA, forced vibrations are induced in the spindle of CNC machining center comparable to the older machines used in industry. This has been done using external weights with the help of purpose built gripper. Effects of external weight and spindle speed are found significant on vibration amplitudes. In Phase IB, industrial machines are selected to benchmark the vibration amplitudes induced in the machine under study. The selected vibration amplitude levels are used in Phase II to investigate the effects of spindle forced vibrations during milling operations. Phase IIA and Phase IIB are aimed to carry out experimentation using high speed steel (HSS)and solid carbide end mill cutters in order to investigate the effects of spindle forced vibrations along feed rate and axial depth of cut on dependent parameters including surface roughness and dimensional accuracy. Cutting speed, radial depth of cut, spindle speed, number of flutes and tool hang are taken as fixed parameters. A L9 Taguchi orthogonal array is used for design of experiments. The signal to noise ratio (S/N) analysis followed by analysis of variance (ANOVA) is used for analysis. It is revealed by ANOVA that spindle forced vibrations have strong effects on surface roughness in case of solid carbide end mill cutter. In Phase IIC, different tool wear patterns are evaluated for HSS and solid carbide end mills. It is found that higher levels of vibration amplitude and feed rate accelerate the propagation of tool wear. A tool failure is also observed at high vibration amplitudes in case of solid carbide end mill cutter. Based on the results obtained in Phase IIB, optimization is done on the basis of ANOVA and recommends preferred operating parameters for finishing operations using solid carbide end mill cutter.