Development of Mathematical Equation for Chip Serration Frequency in End Milling of Titanium Alloy (Ti6Al4V) under the Influence of Magnetic Field from Permanent Magnets

Abstract

Machining of metals is generally accompanied by a violent relative vibration between work and tool, known as chatter. Chatter arises due to resonance when the vibrations of the instability of chip formation and the natural vibration modes of the machine-system components coincide. This paper focuses on a novel approach of minimizing chatter in end milling of Titanium alloy (Ti6Al4V) under magnetic field from permanent magnets. The method consists of two ferrite permanent magnet bars (dimensions: 1′′ x 6′′ x 3′′), mounted 5mm from the cutting tool using a specially designed fixture, to provide a uniform magnetic field of 2500-2700 Gausses (approximately). A titanium alloy Ti6Al4V block was then end milled using uncoated WC-Co inserts.The experiments were designed using the Design Expert software with three independent variables; cutting speed, feed, and depth of cut. Machining tests were conducted for two different conditions – with and without the application of magnets. Scanning Electron Microscope (SEM) was used to measure the chip segmentations.The SEM analysis of chip serrations demonstrated that the chip formations were more stable while cutting under the presence of permanent magnets due to lower intensity of chatter. Keywords: Chatter, Chip Serration Frequency, Permanent Magnet, Titanium Alloy.

Influence of damping coefficient from permanent magnets on chatter formation during end milling of titanium alloy (Ti-6Al-4V)

“…Cutting under the presence of magnets made the chips more stable with comparatively higher frequency of primary serration teeth as compared to normal cutting. From this observation, chatter appears in the system when these serrated teeth get amplified and their frequencies are lowered and coincides with the natural frequency of any one of the system components, leading to resonance [9]. The increment in chip serration frequency is due to the damping effect of the magnets on the oscillatory motion of the tool.…”

“…Chatter occurred due to the resonance between the chip serration frequencies with any prominent mode frequency of the different machine components [9]. Since these high peaks are caused by resonance and the amplitude of vibration in resonance is a function of the damping coefficient of the system, so any factor that would lead to the increase in the damping factor is expected to lower the amplitude of chatter.…”

“…Identification of chip frequency is important since chatter is thought to occur when the chip serration frequency (primary or secondary) coincides with or get close to, or becomes an integer multiple of any of the natural frequencies of a system [7] . Chatter occurred at nearly constant frequencies, close to the natural frequencies of prominent system components over a range of cutting speed for a given set of cutting conditions [8] Chatter is an abnormal tool behavior which it is one of the most critical problems in machining process and must be avoided to improve the dimensional accuracy and surface quality of the product [9]. Chatter arising during end milling and turning is a result of resonance, caused by mutual interaction of the vibrations due to serrated elements of the chip and the natural vibrations of the system components, e.g.…”