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Control of a Shaped Metal Deposition Process

This paper deals with the study and the development of control strategies for a process of Shaped Metal Deposition (SMD) through robotic arc welding.
Such processes are used for rapid manufacturing of large components such as those used in the aerospace sector.
The work presented in this paper has been carried out in the frame of the RAPOLAC European project, which aims also to investigate upon an automatic control system, in order to free the operator from constant monitoring and manually acting on the whole process parameters.
SMD was developed and patented by Rolls-Royce in order to produce mechanical parts directly from a CAD model. The innovative aspect of the SMD process consists of reversing the production philosophy actuated up to now, by the traditional manufacturing methods, such as machining for example.
Machining is based on the material remove from the work piece, in order to obtain a desired final shape. There are several evident drawbacks in this process, like the large waste of material in scraps and the consequent increase of the costs, depending of the material used.
The SMD process works by adding progressively the material to the final work piece, in order to obtain the desired shaped component. This is achieved by adding the material required layer by layer. This means that effectively no process scraps are produced minimizing the material used to the strictly amount required by the final workpiece shape.
The different control strategies implemented are founded on properties of a Gas-tungsten Arc Welding (GTAW) process.
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