Abstract
For the purpose of improving the productivity of laser metal deposition (LMD), the focus of current research is set on increasing the deposition rate, in order to develop high-deposition-rate LMD (HDR-LMD). The presented work studies the effects of the powder stream on HDR-LMD with Inconel 718. Experiments have been designed and conducted by using different powder feeding nozzles—a three-jet and a coaxial powder feeding nozzle—since the powder stream is mainly determined by the geometry of the powder feeding nozzle. After the deposition trials, metallographic analysis of the samples has been performed. The laser intensity distribution (LID) and the powder stream intensity distribution (PID) have been characterized, based on which the processes have been simulated. Finally, for verifying and correcting the used models for the simulation, the simulated results have been compared with the experimental results. Through the conducted work, suitable boundary conditions for simulating the process with different powder streams has been determined, and the effects of the powder stream on the process have also been determined. For a LMD process with a three-jet nozzle a substantial part of the powder particles that hit the melt pool surface are rebounded; for a LMD process with a coaxial nozzle almost all the particles are caught in the melt pool. This is due to the different particle velocities achieved with the two different nozzles. Moreover, the powder stream affects the heat exchange between the heated particles and the melt pool: a surface boundary condition applies for a powder stream with lower particle velocities, in the experiment provided by a three-jet nozzle, and a volumetric boundary condition applies for a powder stream with higher particle velocities, provided by a coaxial nozzle.
Highlights
Laser metal deposition (LMD)— known as direct metal deposition (DMD), direct laser deposition (DLD), and laser engineered net shaping (LENS)—is one of the laser additive manufacturing (LAM) processes
In laser metal deposition (LMD), a laser beam is used as the power source to generate a melt pool on the base material, normally a metal substrate, and to melt the metal powder that is injected by a powder nozzle into the melt pool
In this work we have investigated the effects of the powder stream on high-deposition-rate laser
Summary
Laser metal deposition (LMD)— known as direct metal deposition (DMD), direct laser deposition (DLD), and laser engineered net shaping (LENS)—is one of the laser additive manufacturing (LAM) processes. In LMD, a laser beam is used as the power source to generate a melt pool on the base material, normally a metal substrate, and to melt the metal powder that is injected by a powder nozzle into the melt pool. The powder feeding nozzle and the laser optic together form the LMD processing head. Metals 2017, 7, 443 solidifies and a single track is deposited. A layer is formed by the overlapping of single tracks, and a. LMD has advantages in comparison to other deposition welding processes, such as the defined low heat input, which enables an accurate control of solidification. Due to the small heat affected zone (HAZ) and non-equilibrium rapid solidification, a fine microstructure can be obtained, leading to improved mechanical properties
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