Papers by Keyword: Optical Diagnostics

Abstract: The processes occurring during selective laser melting were studied with a high-speed CCD camera. In order to record all optical in-homogeneities, the camera was integrated into optical arrangement, that realized the Schlieren-method. Within the experiment three parameters were estimated, such as powder particles opening angle, their velocity and the outflow velocity of vapor-gas jet. The influence of laser setup parameters is given. It is shown that particle size and material composition, together with laser power, affect greatly on the opening angle and velocity of powder particles emission, respectively.

Abstract: The objective of this study is to restore the true temperature in during the process of Selective Laser Melting (SLM) of metal powder (in the present case INOX 316L), that is the actual problem in laser assisted additive technologies. To meet this objective, at the first stage, the temperature was measured on the surface of metal substrate INOX 304L without a powder layer. Based on the results of studies the method of temperature measurementof the molten pool surface on metallic plates and during melting of metal powder layer, that were exposed to laser radiation, using an infrared camera (IR), in the present case FLIR Phoenix RDAS TM, was proposed. To restore the true temperature based on the brightness temperature values measured by IR camera, the results of temperature measurements were compared with the width of the molten track on the surface of the plate in the absence of powder. In case of SLM, the results of IR camera measurements were compared with the width of a welded track (bead). The true temperature profiles and temperature gradients values were determined along the axis of the laser beam for melting of plates without powder. In the case of powder melting, the developed method allows to determine the influence of several key SLM parameters on the molten pool shape.

Abstract: It is known that the micro-structure of coatings produced by low pressure plasma spraying (LPPS) is significantly different from the one produced by atmospheric plasma spraying (APS). Because of the different pressures between the inside and the outside of the plasma gun, the exiting plasma jet experiences unconventional behavior related to supersonic expansion at reduced pressure. In this work, the DPV 2000 system was used to measure in-flight particle velocity and temperature. Alumina powder was injected as sprayed particles under 150 mbar conditions. These preliminary researches are the starting points for development and optimization of this process.

Abstract: Shock waves are indispensable tools for medical applications, and hence their interactions with human tissue become one of the most important basic research topics. In this paper, the determination of shock Hugoniot curves for liquids that can model human tissue, namely water, castor oil, and aqueous solutions of sodium chloride, sucrose and gelatin, at 10 and 20 weight percent are presented. Underwater shock waves were generated by ignition of 10 mg silver azide pellets and time variations of over-pressures were measured and simultaneously the shock speed was measured by the time of flight technique. Then shock Hugoniot curves were obtained, by assuming the Tait type equation of state, to relate the estimated density and measured pressure values. Results show in the cases of aqueous solutions that increasing amount of additives into water causes only a very minute decrease in the compressibility of the solution. This difference was more pronounced in the case of sodium chloride, less for gelatin, and almost none for sucrose aqueous solution.