| Gradient material parts are widely used in key parts of aerospace,ship,automobile,nuclear energy and other equipment.Gradient material is one of the kinds of functionally gradient materials,which is characterized by the uniform change of each component along the gradient direction,so as to obtain the gradual transition of material performance and the stable combination of various gradients.As an additive manufacturing rapid prototyping technology,laser energy deposition technology can melt the powder rapidly under the action of laser and realize the material layer by layer accumulation,which provides a new way for the forming of gradient materials.At present,the research on the preparation of gradient materials by laser cladding mainly focuses on the composition,phase content and performance of the materials,but there are few studies on the distribution uniformity of each component powder in the same gradient and the transition of material content between different gradients.This kind of problem can be attributed to the conveying stability and mixing uniformity of powder.In the mixing problem of two or more groups of powder,the existing research mostly uses ball mill,mixer and other mechanical operation for premixing,or uses powder feeding equipment to directly transport multi-component powder,and the mixing timeliness and uniformity are ignored.In order to solve the above problems,this paper establishes the powder mixing model of selfdesigned powder mixer based on the gas-solid two-phase flow theory,simulates the effect of gas flow and particles in different powder mixer structures by using CFD-DEM coupling method,and explores the real-time and uniform powder mixing problem in the rapid prototyping process of gradient material parts.The specific research contents are as follows:(1)The theoretical analysis model of gas particle two-phase flow is established.The particle phase is considered to be a pseudo fluid,and the gas and solid phases are modeled by a two fluid model,in which the gas phase is a continuous phase.According to the Navier Stokes equation,the particle phase is a discrete phase.The contact force and the interaction force between the particle and the gas phase can be described by Newton’s second law of motion,and solved by DEM model,The influence of porosity on the stability of numerical analysis is also considered.(2)The structure of the mixer was designed and the internal flow field and particle system were simulated.The cavity size of the powder mixer is Φ eighty × Through the spoiler structure to change the flow channel,ANSYS-Fluent was used to analyze the change of flow field parameters in the transportation pipeline and the powder mixer,and the structure optimization design of the powder mixer was completed.CFD-DEM coupling analysis method was used to explore the interaction law of gas-solid two-phase fluid in the cavity,and the influence of different process parameters on powder mixing was simulated.(3)Build the powder mixer and complete the mixing experiment of laser cladding powder.The single factor and orthogonal experiments were designed for the dynamic detection of powder mixing uniformity,and the detection method of powder mixing uniformity was established.With the help of high-speed camera,the movement characteristics of particles in the pipe,in the powder mixer and at the outlet of cladding head were observed.The effectiveness of powder mixer was verified by combining simulation results and experimental data,and the process parameter window of real-time powder mixing control was obtained.(4)Based on the rapid,uniform and stable mixing of heterogeneous alloy powder by powder mixer,the laser cladding rapid prototyping experiment of gradient material parts was carried out.The microstructure of the gradient section of the single pass multi-layer thin-walled parts was analyzed.The element content of each gradient was detected by field emission SEM,and the mechanical properties of the gradient material parts were analyzed. |
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