Modeling of laser keyhole welding: Part II. simulation of keyhole evolution, velocity, temperature profile, and experime
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I. INTRODUCTION
IN the Part I of this work, the authors have presented the model derivation for laser-keyhole welding, which considers three-dimensional fluid flow and heat transfer together with evolution of the liquid/vapor (L/V) and solid/liquid (S/L) interfaces. The numerical solution scheme adopted for this complex problem is also discussed in Part I. This article will present and discuss simulation results using practical welding parameters and interesting findings. This article also presents experimental comparison of the model. Due to such intrinsic difficulties as high temperature, high melt-flow velocity, and extremely bright plasmas, experimental studies and measurements on the keyhole welding process are very limited. Matsunawa and co-workers visualized keyhole movements and flow patterns and measured approximate melt velocities inside the melt pool using the high-speed X-ray transmission imaging method.[6,2] They observed the weld-pool configuration by burying Sn/Pt wire along the weld line. They also observed the liquid flow in weld pool by preplacing fine tungsten particles of 100 to 400 m in diameter between the two thin plates and analyzed the trajectories of W particles. However, it is still necessary to have velocity information on the melt surface, since the flow field is driven by surface phenomena, such as thermocapillary force and recoil pressure. In this study, an optical visualization method[11] has been used to measure the weld-pool geometry. The images captured by a high-speed charge coupled device (CCD) camera are accurately calibrated and processed by image analysis software. In addition to the melt-pool geometry, the flow field predicted by the model needs to be verified. To the best of the author’s knowledge, no experimental data are available regarding the melt-flow velocity on the surface. [4]
HYUNGSON KI, Research Fellow, and JYOTI MAZUMDER, Professor, are with the Center for Laser Aided Intelligent Manufacturing, Mechanical Engineering Department, University of Michigan, Ann Arbor, MI 481092125. Contact e-mail: [email protected] PRAVANSU S. MOHANTY, Assistant Professor, is with the Mechanical Engineering Department, University of Michigan-Dearborn, Dearborn, MI 48126-1409. Manuscript submitted November 8, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
In this study, a method of estimating the melt-flow velocity on the L/V interface is suggested. Instead of directly measuring the melt-flow velocity, an attempt is made to trace the motion of a hump (or a disturbance), which is created by the keyhole fluctuation and convected on a current. Such a hump is believed to have wave characteristics. Thus, it propagates outward from the keyhole region at the phase velocity. This study claims that the movement of the hump center point can represent the flow velocity at that point. Experimental observations and measurements are compared with the model predictions.
II. SIMULATION RESULTS The parameters for the simulations are chosen based on the capability of our experimental faci
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