| Aiming at the problems of high cost,low efficiency and poor quality of manual laying during the course of floor tiles laying,a brick laying sand leveler is designed.Based on the basic theory of Discrete Element Method,the key structure and operation precision of the brick laying sand leveler are studied by EDEM simulation,ABAQUS simulation and test research.The main research contents are as follows:(1)The physical and mechanical characteristics of sand are studied and the parameters such as size,density,water content and static angle of sand pile are determined by experiment.Based on the dynamic characteristics of sand dump,the cantilever beam and lifting mechanism of sand leveler are designed,the structure calculation is completed,and the leveling control strategy is formulated.The discrete unit is calibrated and the mechanical analysis of particle-to-particle contact is carried out by establishing space global and local coordinate systems.JKR contact model is selected according to the operation environment of sand leveler.Simultaneously,the direct scraping process of sand leveler is simulated and analyzed based on EDEM.The tangential and normal resistance changes of the scraper under different factors are obtained,and the data are fitted with six polynomials to get the corresponding fitting function.Through the orthogonal test,the influence of different factors on the two-way force is analyzed and the optimum sand scraping thickness and speed are h=10.0mm,v=250.0mm/s respectively.The sand scraping angle is in the direction of vertical sand surface.Through the comparison test results,it is found that the angle of sand scraping has a significant influence on the accuracy,and the thickness of sand scraping is the second.(2)Based on the conclusion of the optimum working parameters,the internal stress and density distribution of the sand dump are studied and the simulation experiment of sand dump leveling is carried out.The simulation experiment of sand dump leveling shows that with the increase of the depth of the sand dump,the pressure stress of the sand grains increases and the horizontal distribution is uniform.Demonstration results of sand speed change during scraper travelling show that the upper surface of the scraper has fast sand speed,the first movement,and the middle layer has low sand speed.When the scraper moves in front of the sand dump,there are fewer low-speed sand grains due to the destroyed internal stress of the original sand dump.The structure of cantilever beam of sand leveler is topologically optimized according to the fitting function of the optimum parameters.The results show that the maximum displacement of cantilever beam after optimization is reduced from 4.21mm to 1.45mm,the maximum stress is reduced from 20.04MPa to 6.82MPa and the volume is reduced from 9.23e-3 m3 to 5.41e-3 m3.When the mass of the cantilever beam decreases by 41.4%,the first-order natural frequency of the cantilever beam increases by 2.48Hz and the second-order natural frequency increases by 2.60Hz.The natural frequency is higher than the external excitation frequency,which meets the natural frequency requirements and improves the anti-interference ability of the cantilever beam.(3)Conduct field tests.The results of displacement test on the front end of the cantilever beam show that the change of the front end displacement is 1.48mm,which is close to the simulation value of 1.45mm and less than 1.50mm required under operating conditions,thus meeting the requirements of cantilever accuracy.The precision test results of sand leveler show that the maximum elevation difference before and after operation of sand leveling system is reduced from 40.10mm to 5.70mm,the standard deviation is reduced from 7.41mm to 1.37mm,and the absolute difference is not more than 2.00mm.The sampling point of flatness is raised from 35.94%to 86.45%.The operation effect of sand leveling system is obvious and basically meets the production requirements. |
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