Molten Pool in Welding Processes: Phenomenological vs Fluid-Dynamic Numerical Simulation Approach

The metallurgical and mechanical properties of fusion welded joints are influenced, among others phenomena, by the weld pool dimension and shape. Weld pool shape is important in the development of grain structure and dendrite growth selection process as well as in the development of residual stresses. For these reasons, significant advances have been made in recent years to understand, in greater detail, the dynamics of the heat and fluid flow in the weld and the subsequent development of the pool shape. In numerical simulation of welding processes, there are two different approaches used to model the fusion zone. If the prediction of distortions and residual stresses is the primary objective of the simulation (computational weld mechanics simulation), the phenomenological approach is the most suitable method used to model the fusion zone. Otherwise, when the weld pool shape has to be predicted, the fluid-dynamic equations must be solved at the expense of a significant ‘computational load’ increase. In this work, after a brief description of weld pool characteristics, such two different approaches are described and compared.

Weld Pool Weld Width Prediction Based on Artificial Neural Network

In the COgas shielded arc welding, the weld pool forms is closely related to the quality of welding,but weld pool shape is affected by the welding process parameters. By using BP neural network to predict weld puddle weld width, the results show that the experimental data are very close, thus indicating that prediction of weld width through this network method is very effective.

Weld Pool Shape Variations and Electrode Protection in Double Shielded TIG Welding

A new welding method named double shielded TIG welding has been investigated and is described in this paper. It is applicable to the TIG process and can improve the weld depth/width ratio and protect the electrode from oxidation during the welding process. A two pipeline structure is designed in the torch. Pure inert gas passes though the inner pipeline which keeps the arc stable and protects the tungsten electrode. A mixed gas containing an active gas passes through the outer pipeline. The active element which is decomposed from the active gas dissolves in the weld pool so as to change the Marangoni convection from an outward to an inward direction, and, as a result, the weld pool shape becomes deep and narrow. The double shielded TIG welding method increases the weld depth by about 2~3 times over the conventional TIG welding. The effects of the active gas (oxygen) in the outer pipeline on the weld pool shapes are discussed. Heavy oxide layer is considered to weaken the Marangoni convection and changes the weld pool shape.