Online Melt Pool Temperature Control for Laser Metal Deposition Processes

Melt pool temperature is of great importance to deposition quality in Laser Metal Deposition processes. To control the melt pool temperature, an empirical process model describing the relationship between the temperature and process parameters (i.e., laser power, powder flow rate, and traverse speed) is established and verified experimentally. A general tracking controller using the Internal Model Principle is then designed. To examine the controller performance, three sets of experiments tracking both constant and time-varying temperature references are conducted. The results show the melt pool temperature controller performs well in tracking both constant and time-varying temperature references even when process parameters vary significantly. However an experiment of multi-layer deposition indicates that maintaining a constant melt pool temperature does not necessarily lead to uniform track morphology, which is an important criteria for deposition quality. The reason is determined to be that different melt pool sizes may have the same temperature depending on the dynamic balance of heat input and heat loss.