Research of Closed-Loop Control of Deposition Height in Laser Metal Deposition

In laser metal deposition (LMD), fixed process parameters are mostly used during the deposition. The actual deposition height of each layer is generally fixed and uncontrollable. In order to improve forming stability and accuracy of the forming parts, and compensate the error of deposition height, a real time closed-loop control system of deposition height with variable process parameters is development. The actual deposition height is controlled by means of the feedback of the error between actual deposition height and the set desired layer height. Both P-controller and PI-controller are designed, and scanning speed and laser power as input variables are implemented respectively to control the actual deposition height. The experimental results indicate that the variable scanning speed control is better than variable laser power control. The best fluctuation range of the actual deposition height is ±0.015 mm. The total deposition height can achieve the desired total layer height using PI-controller. If the powder feeding rate changes abruptly, the P-control system has a nice robustness. The sectional view of cladding layer texture shows the variable deposition heights, which are in accord with the step response curve of P-controller. The system provides a new method to control deposition height and to compensate deposition error.