Design Of Powder-feeding Nozzle Based On Beam Oscillation And Optimization Of Laser Additive Manufacturing Process

As an advanced manufacturing technology,additive manufacturing is widely used in important industrial fields such as aerospace,shipbuilding and automobile.As a new extension of laser additive technology,oscillating beam has obvious advantages of flexible and adjustable.Under the condition of introducing the oscillation beam,this article focus on the design of coaxial powder-feed nozzle and optimization of forming process parameters.The main research content is as follows:(1)A set of coaxial powder-feed nozzle which are easy to replace and flexible to adjust are designed for narrow range and wide range scanning respectively.At the same time,the state of powder and gas is simulated by taking the cavity clearance,tilt angle and the length of guide zone as the structural parameters.Results show that with different clearance,angle can significantly change the distribution of the powder and argon.However,the influence of the guiding district is limited.Finally,the nozzle structure parameters suitable for narrow range and wide range are found by analyzing corresponding indexes.(2)In the experiment of narrow range scanning forming,the macroscopic forming is mainly studied.The influence of laser amplitude,powder feeding amount,laser power and beam oscillation speed on the quality of narrow range scanning forming is analyzed.At the same time,the microscopic characteristics of typical narrow range scanning forming samples are described.It is found that the increasing of laser range worsens the forming effect.Small amount of powder can improve the quality of side wall.When the laser power is higher,the layer convex and collapse are more obvious,and the quality is better under the condition of low power.The beam oscillation speed has little effect on the macro effect of narrow scanning forming.In addition,the grain distribution accords with the microstructure characteristics of typical additive forming.(3)For wide range scanning forming,through the collection and analysis of powder flow images,it can be seen that when the flow rate of powder carrier gas is 8L/min and the flow rate of central protective gas is 12L/min,a large range of powder state can be obtained.On this basis,the powder spot defocusing and laser defocusing experiments were carried out respectively.The results show that when the defocus amount of powder spot increases to-6mm,the ladder-shaped stacking phenomenon is improved obviously,and the forming effect is improved significantly.However,the effect of laser defocus on the forming size is relatively small.(4)For wide range scanning forming,the microstructure and properties of focused and defocused samples were compared and analyzed.The grain size increases from 41.25?m to55.98?m before defocus,and the preferred growth trend of regional grain in the layer is more obvious,which finally leads to the decrease of hardness.(5)The microcosmic characteristics and properties of typical wider-ange and narrowrange forming specimens were analyzed.The results show that the average grain size is41.25?m under wide-range forming,which is smaller than 51.15?m under narrow-range forming,and the grain growth is more disorderly,the mechanical properties are more isotropic,and the hardness is higher than that of narrow-range forming.