Modeling of laser keyhole welding: Part I. mathematical modeling, numerical methodology, role of recoil pressure, multip
- PDF / 2,016,969 Bytes
- 14 Pages / 612 x 792 pts (letter) Page_size
- 74 Downloads / 236 Views
I. INTRODUCTION
LASERS, since their inception, have become critical in manufacturing processes involving joining, precision machining, and surface modification. Conventional manufacturing technologies, such as welding, cutting, and drilling, are continuously being replaced by new laser technologies. However, without a thorough understanding of the associated physics, the potential of lasers cannot be fully realized. Laser-aided materials processing is based on light-matter interaction and may result in four phases, such as solid, liquid, vapor, and plasma, over a wide range of temperatures. Hence, the involved physics has a wide spectrum ranging from heat conduction, melting, and fluid flow to vaporization, plasma formation, and laser-plasma interaction. Mathematical analysis of the process is computationally demanding and requires multidisciplinary approaches. One of the physics, the “keyholing” phenomenon, which occurs at high laser intensities, is critical to deep penetration welding. Upon irradiation with a high-intensity laser beam, the target material melts first, and subsequently, vaporization occurs. The vapor flux generates a recoil pressure on the evaporating surface. Also, there exists a huge temperature gradient on the liquid/vapor (L/V) interface due to the spatial distribution of laser-beam energy, which generates a thermocapillary force. Recoil pressure and thermocapillary force together provide the driving force for liquid ejection forming a vapor-filled cavity called the “keyhole.” As the keyhole deepens, the energy deposition pattern changes considerably due to the multiple reflections of the laser beam inside the hole. The major advantage of keyholing lies in its ability to 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
improve energy utilization and propagation tremendously. The existence of a keyhole, however, makes the process physics very complicated. The dramatic influence of the keyhole on the molten pool characteristics is illustrated in Figure 1. Figure 1(a) presents a high-speed charge coupled device (CCD) camera picture of the molten pool in the absence of a keyhole, i.e., in low-laser-intensity conduction-mode welding. Here, the melt pool is small with a shape close to a circle. The flow field, which is solely generated by the thermocapillary force, is very stable, and the free surface deformation is very small. In contrast, the presence of the keyhole dramatically changes the molten pool characteristics (Figure 1(b)). In keyhole mode (Figure 2), the melt pool is much longer and deeper, and the flow pattern is very complicated. Here, the difference and complexity
Data Loading...
