Physical influences of the plasma during metal powder irradiation using different wavelength laser systems

Abstract

The plasma effect of the irradiated metal powder surface is a physical phenomenon which can give significant information about the composition created in the melt pool and also it indicates the range of temperatures involved in the process. It was observed that the Direct Laser Deposition (DLD) process is not completely free from plasma effects. Whilst DLD parameters, shielding gas and deposited material composition can have a major influence, small plasma effect can also support significant modeling and process control. Understanding this is essential if the process is to be fully controlled for a manufacturing environment. The research presented in this paper brings together the current theories as to why this occurs and offers a coherent picture of the degree of influence of each factor and at which point in the process each is active based on the empirical data presented. The work reported here centres on initial studies performed with different wavelength laser systems and their irradiation impact on the various metal powders. A Ytterbium fiber laser, CW (λ = 1.070 µm) and a CO2 slab laser, CW (λ = 10.600 µm) systems were used. The in situ plasma monitoring was done via a portable fiber optic spectrometer combined with fast digital imaging.The plasma effect of the irradiated metal powder surface is a physical phenomenon which can give significant information about the composition created in the melt pool and also it indicates the range of temperatures involved in the process. It was observed that the Direct Laser Deposition (DLD) process is not completely free from plasma effects. Whilst DLD parameters, shielding gas and deposited material composition can have a major influence, small plasma effect can also support significant modeling and process control. Understanding this is essential if the process is to be fully controlled for a manufacturing environment. The research presented in this paper brings together the current theories as to why this occurs and offers a coherent picture of the degree of influence of each factor and at which point in the process each is active based on the empirical data presented. The work reported here centres on initial studies performed with different wavelength laser systems and their irradiation impact on...