엔드밀 가공시 절삭력 및 표면조도 분석법에 관한 연구

Abstract

A Study on the Analysis of End-milling Force and Surface Roughness

Hee-Geun Cho

School of Mechanical Engineering, The Graduate School, Pukyong National University

ABSTRACT

In this paper, firstly, a new end-milling force modelling technique was suggested by considering runout, and its result was compared with real measured force. The specific cutting force is the multiplication of cutting force coefficient and uncut chip thickness. This parameter was used for experimental modelling and prediction of theoretical force. These coefficients, which can be obtained by fitting measured average forces in several conditions, were used for the formulation of theoretical force. The mechanism of end-milling force with runout was developed in this research and its result was verified by comparing the fluctuating theoretical force with its measured one. The fluctuation of force was incurred by a geometric shape of workpiece and its runout in holding. The result of suggested force considering runout shows a good consistency with measured one. So this modelling method can be used effectively for a prediction of end-milling force considering runout effect. Secondly, there are some analysing methods for surface roughness in end-milling. For this purpose, the fractal interpolation method was used to estimate and analyze the average surface roughness, Ra, in this study. Due to the chaotic behavior of dynamic property in surface roughness, a desirable method must be introduced to represent this property well. As a result, it was proved that the fractal interpolation is one method to analyze the surface roughness profile as well. The fractal analysis discussed in this study is within the scope of the fractal interpolation and its dimension. Also, in analyzing the fractal dimension, two methods have been introduced. Using these two methods, the fractal dimensions of roughness profiles at a given condition in end-milling were analyzed. In real measured roughness profile, there are many factors those affect on the behaviors of surface roughness characteristics. In this sense, a fractal interpolation of surface roughness was investigated in several conditions of end-milling. Thirdly, an average surface roughness, Ra, was measured by optical measurement and its mathematical model according to spindle speed and federate was obtained by least square method. Also, its result was compared and investigated with real measured average surface roughness. The optical measurement of surface roughness was performed by CLSM (confocal laser scanning microscope) and the captured HEI (height encoded image) data was used as an original data for the generation of average surface roughness and its mathematical plane or contour surface. Using this model with two independent variables, the behavior of an average surface roughness was analyzed with an experimental modeling of least square algorithm. And it can be used for the prediction of Ra in different condition of end-milling.

Key words : Average surface roughness, Chip thickness, Cutting force, CLSM (confocal laser scanning microscopy), End-milling, Fractal dimension, Immersion angle, Lead angle, Run-out, Scaling factor, Shifting factor, Tool dynamometer, Tooth passing frequency