DC-Gain Layer-to-Layer Stability Criterion in Laser Metal Deposition Process

In Laser Metal Deposition (LMD), a blown powder metal additive manufacturing process, functional metal parts are fabricated in a layer-by-layer fashion. In addition to the inlayer dynamics, which describe how the process evolves within a given layer, the additive-fabrication property of LMD creates a second set of dynamics which describe how the process evolves from layer-to-layer. While these dynamics, termed layer-to-layer dynamics, are coupled with both the in-layer dynamics and the process operating conditions, they are not widely considered in the modeling, process planning, or process control of LMD operations. Because of this, seemingly valid choices for process parameters can lead to part failure – a phenomenon commonly encountered when undergoing the laborious procedure of tuning a new LMD process. Here, a layer-to-layer stability condition for LMD fabrications is given, based on the shape of the powder catchment efficiency function, which provides insight into the layer-to-layer evolution of LMD processes and can be useful in process planning and control. The stability criterion is evaluated for various operating points, allowing stable and unstable operating regions to be identified. Simulation results are presented showing both stable and unstable layer-to-layer LMD fabrications. The simulated behavior successfully predicts the results seen in both stable and unstable experimental depositions.