Heat management in solid free-form fabrication based on deposition by welding

Abstract

Solid free-form fabrication (SFF) based on gas-tungsten arc welding (GTAW) is one of the few rapid prototyping techniques that has the capability to build three-dimensional metallic parts. For this application, a mild steel (AISI 1018) was used. The most important problem in this process was to find the optimal process parameters. The goal is to build complex three-dimensional parts by depositing metal by welding in a form of layers. The building of a three-dimensional part by welding is especially sensitive to inadequate heat input. The traditional way of manually adjusting the heat input cannot be used because of the dynamic changes in the underlying substrate geometry. To investigate this problem a finite element model (FEM) has been developed that correlates the influence of the different underlying substrate geometry to the quality of the welding-based deposition process. The results from the FEM suggested that influence of the geometry is significant and cannot be neglected. Extensive experiments were designed and performed in order to verify the conclusions derived from the results of the FEM. A real-time adaptive controller of the welding parameters is proposed. This controller performs heat management in real time according to the volume changes of the material of the underlying layers in the vicinity of the heat source. In addition, the overall system performance was monitored and recorded by through-the-arc sensing in order to demonstrate the versatility and robustness of the controller.