高出力 다이오드 레이저를 이용한 窒化硅素세라믹의 레이저 豫熱旋削에 관한 硏究

Abstract

Abstract

Driven by development of science, factory automation is establishing itself widely since the Industrial Revolution. So, the interest in instrument life span and management time and cost increased, that on-going researches on materials like ceramics, plastics and new materials are in progress. In particular, the engineering ceramics which have been used long time by human being are one of the materials advantageous in various conditions with high strength, endurance at high temperature, abrasion resistance and corrosion resistance etc. However, due to high strength and high brittleness of ceramics, a finishing process required after sintering is difficult. Recently, the diamond grinding is generally considered as the only method economically feasible for machining of materials for industrial application. The grinding can produce products with excellent surface finishing and measurement precision, but has low material removal rate and insufficient machining flexibility, and thus is difficult to be applied to ceramics parts of complex shape.

Accordingly, this study focused on laser assisted machining (LAM) of silicon nitride ceramic that efficiently removes the material through machining of softening zone by local heating. In this study, the textual characteristics of SSN and HIP treated silicon nitride ceramics by the temperature were researched as one of basic research on such laser machining. And, the effects of laser-assisted machining parameters were studied for cost reduction, and active application in processing of silicon nitride ceramics.

Laser assisted machining of silicon nitride allows effective cutting using CBN tool by locally heating the cutting part to the softening temperature of YSiAlON using the laser beam. If silicon nitride is sufficiently preheated, the surface is oxidized and N2 gas is formed and escapes from the material, thereby making the cutting process more advantageous. During laser assisted machining, high power results in reduced cutting force and increased tool life, but excessive power brings oxidation of the surface. Increased feed rate also increases cutting energy during laser assisted machining and feed rate shows greater influence on cutting force than oxidation of the surface. Once appropriate cutting conditions are found by controlling the laser power and feed rate, silicon nitride ceramic can more efficiently be cut.

The surface temperature and cutting force were measured by pyrometer and dynamometer at real time respectively. And the surface and cross section of material were observed with video microscope and SEM, and oxidation of surface was analyzed using EDS and XRD. Using the results of these experiments, mechanism of laser assisted machining was ascertained.