Mechanistic models for additive manufacturing of metallic components

Plasma arc welding: Process, sensing, control and modeling

Calculations of fluid flow and heat transfer in the weld pool are strongly influenced by the values of effective thermal conductivity and effective viscosity of the liquid metal. The values of these variables are uncertain since the welding conditions and the fluid flow characteristics within the weld pool influence them. Following an inverse modeling approach, the present work develops a smart model that embodies a multivariable optimization scheme within the framework of a phenomenological heat transfer and fluid flow model to estimate the uncertain parameters necessary for weld pool modeling. The optimization scheme considers the sensitivity of the calculated weld geometry with respect to the unknown parameters. To avoid unrealistic optimized solutions, the smart model is internally guided to look for only the physically significant solutions. The model could estimate the effective thermal conductivity and effective viscosity for conduction mode laser welding as a function of nondimensional heat input ...

A smart model to estimate effective thermal conductivity and viscosity in the weld pool

It is a key issue to establish an appropriate model of the heat source in the simulation of keyhole plasma arc welding (PAW). It requires that the model account for the keyhole effect and have the characteristic of volumetric distribution along the direction of the plate thickness. For available heat source models, neither Gaussian nor double ellipsoidal modes of heat source is applicable to the keyhole PAW process. Considering the force of the high-speed plasma jet and the associated strong momentum, a modified three-dimensional conical heat source model is proposed as the basis for the numerical analysis of temperature fields in the keyhole PAW process. Further, a new heat source model for quasi-steady state temperature field in keyhole PAW is developed to consider the "bugle-like" configuration of the keyhole and the decay of heat intensity distribution of the plasma arc along the direction of the workpiece thickness. Based on this heat source model, finite-element analysis of the temperature profile in keyhole PAW was conducted and the weld geometry was determined. The results showed that the predicted location and locus of the melt-line in the PAW weld cross section are in good agreement with experimental measurements.

A new heat source model for keyhole plasma arc welding in FEM analysis of the temperature profile

Estimation of the parameters of a Gaussian heat source by the Levenberg–Marquardt method: Application to the electron beam welding

An inverse finite element computer code was developed to facilitate the experimental analysis of two-dimensional stationary arc welding processes. The method uses transient temperature data from thermocouples inbedded in the solid region of the work piece to determine through a Newton-Raphson interpolation procedure the transient position of the solid-liquid interface and the transient temperature distribution in the solid region of the work piece. The accuracy of the method was demonstrated through comparison with results obtained with a direct finite element code and through comparison with experiments.

An Inverse Finite Element Method for the Analysis of Stationary Arc Welding Processes

A study was performed on the heat transfer and the fluid flow during transient melting of a metal plate subjected to stationary, penetrating plasma-arc heating. An integral method of solution was used for this simplified, first-order simulation of plasma-arc metal processing. The results of the study reveal the importance of the workpiece thickness, plasma-penetrating hole size, and gravity on the melting process and the molten fluid flow. The study also shows that plasma-arc metal processing seems to be a low-efficiency manufacturing process with only 7% of the plasma energy contributing to the melting.

Y. F. Hsu

Papers

An Inverse Finite Element Method for the Analysis of Stationary Arc Welding Processes

Transient Melting of a Metal Plate by a Penetrating Plasma Arc