Determination of chatter-free cutting mode in end milling

Abstract

Chatter accompanies the cutting process and is the main obstacle to achieving precision and productivity in milling operations. To reduce the amplitude of vibrations, it was proposed to use a stability lobes diagram (SLD) when assigning cutting modes. The machining system in end milling was represented by a two-mass dynamic model in which each mass has two degrees of freedom. The behavior of such a system was described by a structure with two inputs, in-depth and cutting feed, and a delay in positive feedback on these inputs. A new criterion was applied to design the SLD based on an analysis of the location of the machining system Nyquist diagram on the complex plane. The algorithm for designing a stability chart was developed into an application program, a tool for the technologist-programmer when assigning cutting modes. A method for parameter identification necessary for designing the dynamic system “tool – workpiece” was proposed. The effectiveness of the developed method was proven experimentally when the choice of spindle speed during end milling allows one to reduce the roughness parameter Ra from 3.2 µm to 0.64 µm at the same feed rate of 650 mm/min.