Melt pool boundary extraction and its width prediction from infrared images in selective laser melting

Selective laser melting (SLM) involves periodic processes of rapid temperature rise and drop, so it is of great interest in evaluating the quality of the melted powders by real-time thermal information. In this study, a LumaSense MCS640 thermal imaging camera in coaxial system, which can track the location of melt pool, was used to real-time monitor the surface temperature during Ti-6Al-4V forming and predict an average melt width by extracting the boundary of the melt pool in each infrared image. The characteristics of the temperature gradient distribution around a melt pool instead of the temperature itself was analyzed, the boundary of a melt pool was determined then by the maximum (or minimum) temperature gradient point in space. Straight melt samples were obtained by a fixed laser scanning direction in this study, the extracted boundaries of the moving melt pool in the direction perpendicular to the laser scanning direction were compared with the measured melt width from a microscope. A best width divergency between the prediction and measurement around 5% is achieved. [Display omitted] •An infrared thermal imager in the coaxial system is used to track and monitor the melt pool temperature.•The boundary of the melt pool is extracted according to the characteristics of temperature gradient distribution.•The width of the single track is predicted by the boundary of the melt pool.