Optical monitoring of Nd:YAG laser cladding

A bi-dimensional monochromatic (0.860 μm wavelength, 2.5×2.5 mm2 vision zone, 1.7 ms acquisition time) and 1-spot multi-wavelength (12 wavelengths in the spectral range 1.0–1.573 μm, 800 μm vision zone, 50 μs acquisition time) pyrometers are applied for surface temperature monitoring in Nd:YAG laser cladding. The experiments are carried out for cladding of wear resistant coatings varying laser power and powder feeding rate. Two different cases are studied: (a) wide cladded bead with lateral powder injection; (b) narrow cladded bed with coaxial powder injection. Temperature evolution corresponding to pulsed-periodic laser mode as well as two-dimensional steady-state temperature distributions corresponding to the CW-mode are analysed. Multi-wavelengths pyrometer is applied to restore the true temperature that is useful to control melting/solidification and to avoid thermal decomposition when complex powder blends are used. The CCD camera based diagnostic tool is applied for on-line monitoring of particle-in-flight velocity and size distributions in coaxial powder injection.