Evaluation of monitoring methods for electron beam melting powder bed fusion additive manufacturing technology

In-process process sensing and monitoring is being incorporated across additive manufacturing technologies due to the need for part qualification. Implementation of additively manufactured end-use parts has been hindered by the inherent process variability and anisotropy that adversely affect part performance. Process monitoring methods have the potential to ensure fabrication integrity is achieved and part isotropy is maintained across the entirety of a part. This manuscript compares two methods (pyrometer and infrared thermography) that have the potential to monitor layerwise surfaces of a powder bed fusion process. Measurement of surface temperatures during fabrication can be useful for parameter development of novel materials, prediction of resulting microstructural architectures, and ultimately as feedback used in a closed-loop control system to allow full spatial and temporal control of melting and microstructure. A multi-wavelength pyrometer was externally mounted atop an electron beam melting (EBM) additive manufacturing system to observe and record surface temperatures during the fabrication process. The multi-wavelength pyrometer used in this study was a non-contact device that was emissivity independent and capable of taking fixed spot sized measurements. An infrared camera was also installed atop an EBM system to monitor the fabrication surface and was used to measure temperature variations across the entire build area. Although the IR camera produces spatial measurements of an entire part, temperature data is emissivity dependent. Parts with variations in processing were fabricated and monitored using each instrument. Thermal variations between parts were identified with each instrument and related to microstructure. The advantages and disadvantages of each monitoring device were documented and are discussed in this manuscript.