Quantitative Near Infrared Thermal Imaging of Laser Based Additive Manufacturing of Metals

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Research question:Can existing thermal imaging technologies be used to measure the thermal fields in additive manufacturing of metals. Additive manufacturing of metals requires a small rapidly moving heat source, usually either a laser or an electron beam. Measurement of the thermal fields around the heat source would be a great boon to materials scientist working in the field. An online measurement of the thermal field would also facilitate closed loop feedback control of the process. Accurate measurement of the thermal fields is challenging. Throughout the course of the PhD I have gained the skills and expertise necessary to implement high speed thermal microscopy in a modified commercial and pure research environment. I have developed novel methodologies to characterise and overcome limitations of the thermographic instrument components available on the market. I have used commercial silicon based cameras with various optical arrangements to acquire videos of the metal additive manufacturing process. My thesis is concerned with the steps required to convert these images into accurate maps of the thermal fields. In attempting to quantify the thermal fields I have utilised:Optical design theory.Radiometric temperature measurement theory including radiative properties.Imaging system characterisation. Including novel methodologiesDigital signal processing in two dimensions, including novel applications of methodologies from other fields.I have implemented coordinate system transforms to correct for geometric distortions.I have used image processing techniques to extract quantitative measurements, pertinent to the field of additive manufacturing.