<p>Modeling the strongly localized thermal effects in high-energy beam welding directly using finite element based methods is still a challenge. This paper presents an adaptive isogeometric framework for transient heat-transfer analyses that utilizes truncated hierarchical B-splines (THB splines). The application of this method is the simulation of the temperature fields that are induced by the intense heat sources used in fusion welding processes. By exploiting a spline descriptions for the weld parts, a Gaussian-type heat-source model was easily imposed in the newly developed local curvilinear system for the weld trajectory. Various nonlinear behaviors, including temperature-dependent material properties and radiation boundaries, were considered during this study. A recovery-based error estimator was applied to the THB splines to enable local mesh refinement, which was needed to resolve the temperature field with sharp gradients that surrounds the welding pool. By considering the locally high temperature field caused by the welding heat source, a combined criterion was designed to determine which elements should be coarsened. Furthermore, lumped forms of the heat-capacity matrix and the corresponding term from the convection boundary were developed. Numerical examples of various application scenarios, including those involving laser and electron-beam heat sources, were designed to verify the proposed method. The size of the numerical model using proposed method is reduced by over 95% compared to the commercial software to obtain comparable temperature field around weld pool. The results revealed the capabilities and versatility of adaptive Isogeometric analysis (IGA) when it is used for welding process modeling.</p>