Multivariable adaptive modeling and control of geometry in GMA welding material deposition with application in solid freeform fabrication

Rapid Prototyping (RP) is an emerging technology for fabrication of 3-D models, and involves a collection of processes in which physical prototypes are quickly created directly from computer generated models.; This research is to develop a rapid prototyping technology, which will produce functional objects from stainless steel, ready for use, without or with very little necessity for postprocessing, while using conventional, high deposition rates and inexpensive GMA welding equipment.; This research addresses the issues of geometric modeling and control of the weld-based metal deposition in GMAW processes for solid freeform fabrication. In particular, a dynamic, lumped parameter model of the solidified surface shape is developed, based on linear, time-varying, multi-input and multi-output formulation. The deposited bead profile is measured in-process by a trailing 3-D laser scanner following the GMAW source, as well as a leading similar sensor in front of the torch. Their measurements serve for feedback and feedforward in the SISO implementation. The parameters of the geometric model are adapted in real time through measurements of the bead width and height in the MIMO system.; These geometric features are modulated by one-step-ahead controller with a Smith predictor, which deals with the measurement delay. In addition to the one-step-ahead controller, PI filtering is also used to eliminate the steady-state error which comes from the imperfect process model.