Model-based temperature feedback control of laser cladding using high-resolution hyperspectral imaging

Laser cladding is a technique that is frequently used for the coating and repair of metallic components. More recently, the technology is used in the additive manufacturing domain for building freeform three-dimensional parts. A lot of attention is dedicated to the optimization of process parameters and to real-time feedback control strategies. This paper presents a feedback control scheme in which a hyperspectral camera is used to provide absolute temperature measurements of the melt pool surface with a high spatial resolution of 12 μm/pixel. A combined linear state feedback and proportional-integral controller actuates the laser based on the measured temperature profile in order to maintain a constant melt pool width. The controller includes a model-based state observer for suppressing the noise introduced by powder particles that are present in the laser cladding process with coaxial powder feeding. The performance of the controller is evaluated by creating beads with varying thicknesses on a base plate of AISI 316L stainless steel. The experimental results demonstrate that the controller is able to successfully regulate the melt pool size with a standard deviation that is smaller than 10 μm during laser melting (without powder) and 50 μm during laser cladding (with powder).