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Lock-In thermography is a useful Non Destructive Technique (NDT) for enhanceddetection of defects in components, as it amplifies the phase contrast wheredefects exist. This amplification was found to be around 2-3 times compared toconstant heating. The current used a Fuse Deposition Modelling (FDM) 3D printerto print samples with known defects, in order to characterise the relativeeffects of different variables on the Lock-In phase data. Samples were printedusing ABS (Acrylonitrile Butadiene Styrene) and PLA (Polylactic Acid) forcomparisons, and variables such as print direction, cameras, heating power,Lock-In frequency, as well as thickness, width and depth of defects wereexplored. It was found that different materials resulted in differentbaselines, but had similar phase contrast. A novel asynchronous technique wasderived to enable Lock-In measurements with 5 different infrared cameras, andsimilar results were found. Even cheap cameras like the Seek Thermal CompactXRwere proven capable of detecting the same defects as other cameras such as theFLIR SC7500. Heating power did not affect phase contrast, except for shallowerdefects up to 1.0 mm deep, where higher power resulted in better contrast. Asexpected, deeper defects could only be detected using lower Lock-Infrequencies, and there was better phase contrast with wider, thicker andshallower defects. It was shown that defects 4 mm in width could be detectedautomatically up to a depth of around 1.5 mm, based on the phase signal trends.Sub-sampling of frame data showed that at least 10 frames were required perLock-In period for minimal deviations in Lock-In phase contrast. Also, it wasshown that phase contrast was similar for shallower defects up to 1.5 mm deep,with data from 1 Lock-In period, as long as the first frame was synchronisedwith the heating cycle.

Asynchronous Lock In Thermography of 3D Printed PLA and ABS samples