Pyrometry-based closed-loop control of the melt pool temperature in Laser Metal Deposition with coaxial wire feeding

Laser metal deposition with coaxial wire feeding is a directed energy deposition process that enables near-net-shape and direction-independent additive manufacturing of metal parts. However, the high sensitivity of the process to disturbances poses a major challenge, as this frequently leads to defective components and rejects. To counteract this, a pyrometer was coaxially coupled into the beam path of the laser processing head to accurately determine the melt pool temperature without limiting accessibility. Applying deterministic test signals, a system model describing the dynamic relationship between the temperature and the laser power was identified. Based on this model, a closed-loop process control was designed. The control system was validated by introducing various disturbances, for which the reference temperature could be tracked with good approximation. The designed temperature control results in reduced effort for tuning the deposition process as well as a lower probability of defects, which saves manufacturing time and cost.