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13 June 2005 Characterisation of high-density particle distributions for optimisation of laser cladding processes using digital holography
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Laser cladding is an innovative surface treatment process which has several advantageous properties like a reduced material distortion compared to conventional techniques. In this technique the cladding material is fed as a powder through the laser beam to the melt pool. For an optimisation of this process with respect to treatment time and efficiency a characterisation of powder size, distribution and velocity is crucial. Holographic particle image velocimetry is a powerful tool for characterisation of particle distributions with respect to size, 3D-position and velocity. Due to the holographic recording principle 3D-information can be evaluated from just one hologram. Its major drawback, the time-consuming development and repositioning of the hologram plates, can be avoided using the well-known technique of digital holography. In this case the hologram is recorded by a CCD-camera and reconstructed numerically. Common digital holographic particle measurements are performed using an inline configuration in order to minimise the experimental effort. In this case the measurements are limited to low-density particle fields due to increased noise generated by an overlap of real and virtual image in the reconstruction process. In this paper the application of off-axis digital holographic particle velocimetry to the characterisation of powder distributions in a laser cladding process is presented. Besides the experimental realisation special emphasis is given to the numerical reconstruction of the 3D-position and velocity of the particles. In extensive tests the suitability of the proposed technique is demonstrated. In the powder measurements up to 300 particles are detected with diameters of about 100μm and characterised with respect to position in a volume of about 1cm3 from just one hologram. In addition the speed of the particles is determined by double pulse measurements.
© (2005) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Volker Kebbel, Jurgen Geldmacher, Knut Partes, and Werner Juptner "Characterisation of high-density particle distributions for optimisation of laser cladding processes using digital holography", Proc. SPIE 5856, Optical Measurement Systems for Industrial Inspection IV, (13 June 2005);


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