| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 107 === This research built up a relatively low cost lateral off-line high-speed imaging system to observe the melt pool and the spatter behavior in selective laser melting with stainless steel 316L powder. The (1) melt pool geometry including melt pool length and width (2) spatter size distribution (3) total spatter volume comparing to the evaporation volume over 3200K with the simulation, which is the evaporation point of SS316L material. These three objectives are studied.
The imaging system is constructed on the side of the melt pool and therefore the image taken from the camera exists an angle of view. Thus, the perspective transformation is applied to transform the image from the side view to the top view mathematically and the spatial resolution was calculated. The melt pool was recognized using the liquid to the solid transition point of the material and used the second derivative method to identify the transition point. However, the transition point in the image was not clear enough to be identified because of the noises. As a result, the automatically detect algorithm to identify the transition point to measure the melt pool length and width was developed. The monitored length showed the maximum average error 15% while the error of the measured width was 24%.
A large number of spatters eject from the melt pool with very high speed during the process. Therefore, it is necessary to perform spatter tracking so as to get the spatter size distribution in a certain period. The tracking algorithm based on Kalman filter was developed. The result shows that the higher energy density, the more spatters generate. The volume of the spatter was also compared to the evaporation zone in the simulation. The result showed that the spatter volume was smaller than the evaporation volume in the simulation. This result should be further studied because of the contrary to physics.
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