Simulation of Deeppenetration Welding of Stainless Steel Using Geometric Constraints Based on Experimental in Formation

\Ye present a general overview of a method of numerically modelling deep penetration welding processes using geometric constraints based on boundary information obtained from experiment. We consider general issues concerning accurate numerical calculation of temperature and velocity fields in regions of the meltpool where the flow of fluid is characterized by quasi-stationary Stokes flow. It is this region of the meltpool which is closest to the heat-affected-zone (HXZ) and which represents a significant fraction of the fusion zone (FZ). IN X PREVIOUS REPORT (1). we introduced a method based on geometric constraints for the inclusion of experimental information concerning steady-state weldpool shape into a model system. X feature of this method is that it tends to compensate for either the unavailability of experimental measurements of material properties or gaps in knowledge concerning the general character of the keyhole. In this report. we present a general overview of the geometric-constraints method and issues concerning accurate numerica l calculation of temperature and velocity fields in regions of the meltpool where the flow of fluid is characterized by quasi-steady Stokes flow. The underlying motil-ation of our development is that it is transport in these regions of the meltpool which couple most strongly and direct ly to the heat-affected-zone (HXZ), and which, because of the rapid onset of viscous effects, represents a significant fraction of the fusion zone (FZ). The physical characteristics of all other regions of the meltpool. as well as the keyhole itself. are considered with respect to the relative strength of their coupling to regions of the meltpool that are close to the solidification boundary and within the Stokes-flow regime. Regions of the meltpool that are close to the keyhole present a particular problem because of the sharp rise in temperature. With respect to numerical discretization. these regions can be characterized effectively as Lam brakos , Milew ski 1 DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED 7 numerical singularities resulting from the type of stiffness that occurs in the integration of shocklike structures. However. regions of the meltpooi that are close to the solidification boundary are characterized by fluid properties which provide a means of overcoming any ill-conditioning due to the numerically singular character of regions near the keyhole and a more accurate specification of the flow. Because the character of the flow in regions that are close to the trailing solidification boundary is not coupled to the details of the character of the flow in regions near the keyhole. a well posed input condition is a set of upstream boundary values of the temperature and fluid-flow fields. The geometric-constraints method presented in this report entails the specification of a consistent set of upstream boundary values of temperature and flow velocity rather than explicit specification of the beam energy source. Physical Model of Deep Penetration Welding In the context of using geometic constraints. it is the solidification boundary and top surface boundary which determine the solution rather than the boundary corresponding to the vapor-liquid interface associated with the keyhole. Given this, it follows that the flow characteristics of the liquid in regions of the meltpool near the solid-liquid boundary must be modelled accurately. The keyhole boundary or keyhole source term. depending on the fashion of implementation, is only used to adjust the characteristically monotonic flow field along the top surface and solidification boundaries. Therefore. in our present model. it is not considered a true boundary of the system. or more precisely. of the solution domain. In our present model we adopt the approximation that the flow character of the liquid region is mostly that of quasi-steady Stokes