Computer modeling of arc welds to predict effects of critical variables on weld penetration Page: 3 of 21
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methods to obtain time-dependant solutions for theoretical models that describe the
welding process.1'11 Numerical methods can be employed to predict the transient
development of the weld pool as an integral part of the overall heat transfer conditions.
The structure of the model allows each phenomenon to be addressed individually,
thereby gaining more insight into their competing interactions.
WELD POOL CONVECTION
The development of the weld pool is influenced by the simultaneous occurrence
of several important physical processes. These include the amount of heat transferred
from the heat source to the workpiece, the fluid flow in the weld pool, and the
accompanying convective heat transfer. Convection is an essential and important part
of the mechanism that controls weld penetration. The magnitude and direction of the
flow of molten metal in the weld pool can significantly alter the local heat transfer
conditions and, consequently, the fusion zone geometry and weld properties. In order
to understand the convective behavior in a weld pool, it is instructive to examine the
driving forces for fluid flow.
The driving forces for fluid flow in the weld pool fall into two categories. First,
the volume-forcing terms that include the buoyant (thermal/gravity) body forces and
electromagnetic body forces and, second, the shear and pressure acting on the weld
pool surface due to surface tension gradient and surface curvature.
Buoyancy Force: Heat flux from the arc generates spatial and temporal density
gradients in the metal. The buoyancy forces resulting from the spatial and temporal
density gradients within the weld pool result in an upward flow at the center of the
Electromagnetic Body Force: Electromagnetic forces are generated due to the
interaction of the divergent current path in the weld pool and the self-induced magnetic
field. These forces are present only during arc welding processes and is absent under
laser welding conditions. The forces generated result in a downward flow at the center
of the pool.
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Zacharia, T. & David, S.A. Computer modeling of arc welds to predict effects of critical variables on weld penetration, article, January 1, 1991; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1071861/m1/3/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.