Thermal near infrared monitoring system for electron beam melting with emissivity tracking

This paper presents the design of a high speed, high resolution silicon based thermal imaging instrument and its application to thermally image the temperature distributions of an electron beam melting additive manufacturing system. Typically, thermal images are produced at mid or long wavelengths of infrared radiation. Using the shorter wavelengths that silicon focal plane arrays are sensitive to allows the use of standard windows in the optical path. It also affords fewer modifications to the machine and enables us to make use of mature silicon camera technology. With this new instrument, in situ thermal imaging of the entire build area has been made possible at high speed, allowing defect detection and melt pool tracking. Melt pool tracking was used to implement an emissivity correction algorithm, which produced more accurate temperatures of the melted areas of the layer.