CHINESE JOURNAL OF PHYSICS VOL. 47, NO. 4 AUGUST 2009 Theoretical Comparison of Oxygen Assisted Cutting by CO 2 and Yb:YAG Fiber Lasers B. Ahmadi, 1 M. J. Torkamany, 1 B. Jaleh, 2 and J. Sabaghzadeh 1 1 Laser Science and Technology National Center, Tehran, Iran, P.O. Box 14665-576 2 Department of Physics, Bu Ali Sina University, Hamedan, Iran (Received September 27, 2008) A mathematical model has been reported for oxygen assisted mild steel cutting by cw CO 2 and Yb:YAG fiber lasers. The model originates from the conservation equations of mass, momentum, and energy in a steady state. This physical approach leads to numerical predictions of kerf width, cutting speed, and contribution of oxidation power, which are consistent with experimental findings. PACS numbers: 42.62.-b I. INTRODUCTION The laser cutting of metals is an important field in laser material processing. A laser beam heats the work piece up, while an intense gas jet transfers momentum to the melt re- gion, in order to vertically accelerate the melt to eject at the bottom of the kerf. If the gas jet is chemically inert the process is called laser fusion cutting, otherwise oxygen gas is used to assist the process. In fusion cutting the energy necessary for cutting must be provided only by the laser beam. But in laser oxygen cutting the oxidation of the metal releases exother- mal energy in addition to the absorbed laser power. The previous mathematical models of laser beam cutting have involved fluid dynamics and heat transfer phenomena [1]. Reactive heat for oxygen cutting mechanism has been studied by Sh¨ uocker [2]. The beam parameters and the Fresnel absorption have been investigated by Schultz et al. [3]. Considering the basic phenomena involved, an important result was obtained by Schultz [4], who described thermal losses owing to heat diffusion in the sample. Cutting gas properties and dynamics have also been discussed in Refs. [5–8]. A simple analytical model for laser cutting with oxygen and inert assist gases was described by Kaplan [9]. Chen et al. proposed a model for roughness formation [10]. Their model implies a reaction rate that is limited by oxygen dif- fusion in the gas. The growth and decay periods of the oxide layer is related to temperature fluctuations and correlates with experimental data. The new generation of Yb:YAG lasers, fiber type, has recently been the focus of interest in laser material processing, specifically in laser cutting [11]. Here is a comparison between oxygen assisted cutting by CO 2 and Yb:YAG fiber lasers, that has done through a mathematical model for mild steel plates (2 and 3 mm thickness). We also try to calculate the maximum cutting speed to obtain the best quality of cut surface by neglecting vaporization [12]. For lower speeds it’s not allowed to ignore vaporization. Kerf widths and extracted oxidation powers are calculated http://PSROC.phys.ntu.edu.tw/cjp 465 c  2009 THE PHYSICAL SOCIETY OF THE REPUBLIC OF CHINA