| Additive Manufacturing(AM,also known as 3D printing)is a technology that allows for the machining of complex shapes and structural parts by laying down powder material layer by layer and laser scanning and sintering it to obtain prefabricated parts,which are now more widely used in industrial production.Throughout the 3D printi ng process,the processed powder material is of critical importance.The difference in fluidity in the powder spreading process will seriously affect the uniformity of the powder layer,resulting in laser sintering after the appearance of holes,surface co nvexity or the appearance of pits,parts of the density of not up to the requirements of the situation.Therefore,the influencing factors of powder flow performance should be studied to improve the accuracy of the parts.In addition,the process parameter s of the powder laying process will also seriously affect the uniformity of the powder layer,such as the scraper speed,laying powder thickness.How to lay out a flat,uniform,high density powder layer has been an important topic of research by scholars.In this paper,based on the background of SLS,nickel-based high-temperature alloy powder is selected as the object of study,from the powder flow and laying powder quality related research.The main research contents are as follows.(1)First of all,the microscopic morphological measurement and flow characteristics of nickel-based high-temperature alloy powder test experiments.The scanning electron microscope was used to observe the topography of the surface,to provide a basis for the subsequent simul ation of the numerical model;the laser particle size analyzer was used to measure the size distribution range,to understand the cumulative volume distribution of particle size;the integrated powder tester was used to measure the flow performance index of the powder;the quadruple straight shear instrument was used to measure the internal friction coefficient and internal friction angle of the powder.The powder was heated in a constant temperature box to study the change of resting angle at different tem peratures;the powder was screened by a sieving instrument to analyze the effect of different particle sizes on the resting angle.(2)Discrete element software was used to model and calibrate the parameters.First,the Hertz-Mindlin elastic model and the JKR model were selected as contact models;then the rest angle values were used The model and the straight shear numerical model are calibrated after comparison with the measured data from the experiment,and the parameters are tuned to a Reasonable parameters can then be used to continue the next simulation study.(3)By putting in the calibration parameters obtained from the above simulation,the numerical model of the powder spreading process is constructed,and the powder spreading quality is studied from the scraper speed and powder spreading thickness.Firstly,the particle velocity distribution field and the variation of stacking angle in the powder spreading process are analyzed.Then the filling characteristics of the powder layer are analyzed and the study is carried out from the morphology and filling rate of the particles on the surface of the powder layer.Finally,the homogeneity of the powder layer is analyzed,characterized in terms of the apparent density as well as the apparent density deviation.(4)An experimental setup for testing the quality of powder spread was designed and built to analyze the quality of powder spread specifically.Two variables were designed to be studied by varying the squeegee translation speed and powder spreading thickness.The powder spread quality of the powder layer was characterized by measuring the powder mass in each box on the experimental set-up.The standard deviation of each data set is then analyzed to derive differences in the uniformity of the powder layer,and finally the effect on the quality of the powder layer in the direction of the powder movement is analyzed. |
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