Development of sensing and control system for robotized laser-based direct metal addition system

Laser-based direct metal addition (LBDMA) is a promising directed energy deposition technology that is well suited for the production of complex metal structures, low-volume manufacturing, and high-value component repair or modification. LBDMA is finding wide application in the automotive, biomedical, and aerospace industries. However, the process reliability and the repeatability of finished components are still problems. This work offers a solution by developing a sensing and control system for the robotically controlled 8-axis LBDMA system developed at the Research Center for Advanced Manufacturing of Southern Methodist University, Dallas, TX. The developed system consists of sensing and control units for the powder flow rate and the molten pool size. An optoelectronic sensor was developed to sense the powder flow rate. It is a main component in an on-line control system of powder flow rate in a LBDMA system. An infrared imaging setup was installed on the laser head to monitor the top full-field view of the molten pool. A simple proportional integral derivative (PID) controller, combined with feed-forward compensation was used to build a closed-loop control system for achieving a uniform molten pool size. Two L-shaped single-bead walls were built with and without closed-loop control, respectively. A good performance on achieving uniform geometry by closed-loop control of the molten pool size was approved.