Analysis of tool deflection errors in precision CNC end milling of aerospace Aluminum 6061-T6 alloy

Abstract

Especially with increased cutting forces using complex-shape tools such as long end milling tools, deflection in machining significantly affects the dimensions and geometry. This kind of error in end milling may be efficiently reduced by controlling the cutting parameters and properly selecting a suitable lubrication mode. The target of this research is to study the mechanism of deflection error and find the optimum condition for the cutting process to minimize deflection error. In this research, lubrication mode is considered one of four factors affecting deflection error in traditional flood lubrication, Minimal Quantity Lubrication (MQL), nanolubrication and dry cutting, which are used in the machining process with end milling tools. The three other parameters are axial depth of cut, radial depth of cut, and feed of cut. The workpiece material used in this research is AL 6061-T6, the cutting tool used is HSS end milling with diameter 4 mm, and the mode employed is side milling. The experiment is designed according to the Taguchi method, and it includes sixteen samples. The cutting fore and deflection error on a workpiece are recorded and then analyzed by S/N response analysis and analysis of variance (using Pareto ANOVA). The results indicate that radial depth of cut affects nearly 95% to deflection error. The effect of the other factors is not considerable. The optimum deflection error (31.22 μm) is attained at the lowest level of radial depth of cut (0.32 mm) and feed of cut (250 mm/min), and the second level of axial depth of cut (10 mm) and Minimal Quality Lubrication. A model of tool deflection named Instantaneous Deflection is defined and used to explain the phenomenon of deflection error. This model can explain the mechanism of deflection in end milling much better than average cutting force models. It proves that cutting force and distance between tool holder and cutting point are two parameters affecting deflection error. Between these two factors, cutting force has a much more significant effect. Cutting force is also proven to have a strong linear relationship with deflection error.