On-Line Condition Monitoring of Additive Manufacturing Based on Friction Induced Acoustic Emissions

Layer-by-layer superpositions are the primary way of additive manufacturing (AM). The layer can be formed by point-forming, line-forming, or surface forming. Each layer is integrated with the other to complete construction. The quality of each layer has an essential impact on the quality of the whole AM model. In particular, the excessive surface bulges in the construction process will affect the coupling quality of the next layer, which leads to the failure of part construction. However, due to the different construction parameters, materials, and equipment, the quality of print layer forming is not very uniform but changes greatly. This paper proposes a new method to monitor changes based on acoustic emission analysis. In this work, the main concern is detecting the bulge at different layers. The material bulges on the completed layer will increase the friction effects between the nozzle and the layer, forming random impulsive dynamic excitations and producing more significant acoustic emission responses. The time-frequency analysis shows that the AE waveform due to the bulges exhibit wideband with high amplitudes. It means moving waveform parameters such as moving root mean square (MRMS) value, energy, and so on can be a useful indicator to show the behaviors of the friction effect. Experimental studies show that the proposed MRMS values give accurate indications of the simulated part bulges at different layers, allowing the printing quality to be assessed based on the number of occurrences of the high MRMS value at each layer. In addition, this real-time information will provide feedbacks to terminate or adjust the printing process to ensure part quality.