Comprehensive analysis of laser cladding by means of optical diagnostics and numerical simulation

Laser cladding is known as flexible and efficient method for elaboration of diverse protective coatings including functionally graded, multilayered, etc. Robotic laser cladding with coaxial powder injection is often referred to as Direct Metal Deposition (DMD). Development of on-line monitoring and process control, and its integration with DMD machines is a priority task.The objective of the present study is to demonstrate the advantages of comprehensive optical monitoring of DMD technology applying diverse and complementary optical diagnostic tools: pyrometers and infrared camera are applied to measure brightness temperature that is useful to define the shape of molten pool, to control melting/solidification and to avoid thermal decomposition when complex powder blends are used.The CCD-camera based diagnostic tool is useful for a particle-in-flight visualization, for a control of particle jet stability, and for a real-time measurement of particle-in-flight velocity. Numerical simulation of the carrier gas and particle flow in a coaxial nozzle of TRUMPF 505 DMD is carried out. Argon serving as carrier and shielding gas is supplied into an axial and two annular channels of the nozzle. Two-phase jet flowing toward the substrate and particle focusing mechanism are analyzed. Radial distribution of the particle mass flow over the substrate versus conditions of particle collision with nozzle walls is calculated. The developed software is used to analyze peculiarities of the particle heating and melting by the laser beam. This way, trajectories and thermal history are calculated for particles of different size.

► Comprehensive optical diagnostics in laser cladding.
► Brightness temperature measurements, true temperature restoration.
► Particle-in-flight monitoring.
► Calculation of mass and temperature profiles of powder jet.