Study On Mechanism Of Interaction Between Laser And Powder Stream During Coaxial Fiber Laser Additive Manufacturing

Laseradditive manufacturing(LAM) is an advanced manufacturingtechnology withthe features of low energy, short procedure, high flexibility,and controllable shape andstructure.LAM involves building a complex objectlayer by layer directly andrapidly.The fiber laser has remarkable advantages for LAM due to short wavelength(λ=1.06μm~1.07μm), high beam quality, high flexibility, and low running costIthas been foud that the interaction between laser and powder affectsthe structurequality significantly.In this thesis, we built a model first to clarify the effects of uniformity of powderon laser beam attenuation based on the Mie scattering theory. The model was thenverified by the fiber laser and Ni45self-fluxing alloy powder. The scattering loss lawwas obtained from the above experiments.The results showed that with higher powderconductivity, smaller powder particle and longer laser wavelength, the scattering lossof laser power increased.The mathematical and physical model of the shape and concentration of thecoaxial powder stream was established. Associatedwith the above attenuation model,we proposed a new model for laser beam attenuation when using coaxial powderdelivery. The results showed that the variation of powder feed rate and the volume ofcarried gas affected the laser power density after passingthrough the powderstream(referred to the rest laser powder density) and hardlyaffected the distribution oflaser power density. In addition, the relative position of waist of coaxial powderstream and laser beam had great impacts on the distribution of laser powerdensity.Based on the modelwhen the waist of laser beam was33mm above the waistof powder stream, the distribution of the rest laser power density was the Gaussiandistribution; moreover, when the relative position was53mm, the rest laser powerdensityisdistributionas similar as the flat-top. Furthermore, the parameters of fiberlaser collimating and focus system also influenced the distribution of the rest laserpower density.When the focus length of collimating lens reduced orthe focus length offocus lens elongated, the distribution of the rest laser power density was flat-top.Therefore, we suggest to applythe short focus length of collimating lens and longfocus length of focus lens in LAM to obtain the relatively homogeneousdistribution ofthe rest laser power density.