Combining Layer-to-Layer and In-Layer Feedback Control for Wire Arc Additive Manufacturing

Wire Arc Additive Manufacturing is a metal additive manufacturing (AM) process that deposits material layer-by-layer by melting wire feedstock with an electrical arc.  The ability to deposit layers of non-uniform (but controlled) height can be leveraged for building geometries with overhang features without needing support material. However, this requires precise process planning of the torch speed and feedrate to generate the appropriate varying-height profile within a single layer. In this work, we propose augmenting layer-to-layer planning of the torch speed with in-layer feedback control to reduce the error in the height of deposited material. Using an infrared camera, the error in the deposition height is measured throughout the welding process. The torch speed for each layer is planned using a model-based approach to correct for error in the previous layer by solving a constrained optimization problem. This plan is then used as a feedforward along with in-layer proportional control to further correct for errors in-process. This approach demonstrated an improvement of 15% in the average layer RMS error over pure layer-to-layer control.