Chatter Investigation on Machining of Gray Cast Iron Considering the Damping Effect

Everton Ruggeri Silva Araujo,João Álvaro Belo Pantoja Junior,Giovanni De Souza Pinheiro,Salomão Levy Neto

doi:10.3991/ijes.v7i3.11376

Abstract

In recent years, the study of chatter vibrations has been intensifying in the machining of materials. In this paper an investigation of this phenomena was conducted for gray cast iron (CGI). The chatter vibrations in machining process can considerably compromise the workpiece surface finish, tool wear and in some cases provide severe damage to the machine-tool. Thus there is an imminent need to expand the theory of chatter vibrations for the class of brittle materials. To analyze the vibrations of the process of machining and zones where the process is stable, and where it is unstable, the stability lobes diagram was used. This diagram is constructed at low speed cutting, where the phenomenon of damping arises. The damping is a crucial factor in the process, it increases system stability. This effect was considered in the formulation of chatter vibrations using the indentation model of Wu. For experimental validations the signals of cutting force were acquired and analysis was conducted in frequency domain to identify where the vibrations emerged allied with a roughness analysis of the workpiece. The results demonstrated perfectly the consequences of chatter vibrations in surface finish of grey cast iron and proved that the stability lobes diagram provides good results to detect these vibrations, determining the areas where the material removal should be avoid.

Highlights

Chatter vibration is the one of the types of vibrations existing that has been gaining prominence on the part of the researchers in the area of the machining, due to the numerous problems that this provides, such as poor surface finish of the manufactured parts, excessive tool wear and damages for machine-tool
In order to validate the stability lobes diagram, the tests were conducted under different cutting conditions using the test force signals from kistler dynamometer to prove the occurrence of chatter vibrations To accomplish this the Fast Fourier Transmission (FFT) was used to analyze the signal of force in frequency domain to detect whether there will be vibration peaks near to the peaks of the natural frequency of the system
Using the FFT power spectrum of force for tests 1 and 2, was verified a frequency of 612 Hz with an amplitude equal to 4,1x104 N is modulated nearest from the natural frequency of system corresponding to 606 Hz, this behavior implies that in this experiment the chatter vibration act making the system unstable, which is will compromise the tool, the workpiece surface finish and the machine-tool

Summary

Introduction

Chatter vibration is the one of the types of vibrations existing that has been gaining prominence on the part of the researchers in the area of the machining, due to the numerous problems that this provides, such as poor surface finish of the manufactured parts, excessive tool wear and damages for machine-tool. [2] states that these vibrations in the machine tool set play an important role for poor productivity in the industry, accelerating the wear of mechanical components, compromising chip formation, causing poor surface finish of the part, and damaging the bearings of the spindle. This type of vibration arises due to the low structural rigidity of the parts in the machining process associated to a self-excitation mechanism where the process frequencies are close to the natural frequency of the system.

Methods

Results

Conclusion