The Analysis Of Shearing Principle And Blade-shape And Parameters Of Drum Flying Shears

Among all cutting-off machines, the drum type chopping machine is equipped with advantages including simple structure, high productivity, low energy fluctuation and easy operation etc. It has shown a strong tendency to replace a multilink chopping machine since it was invented, and indicated blockbuster potential. However, major risks leading to failure in the gear box during real productions are often found due to the excessive shearing force. This thesis focuses on the frequent problems, such as gear box failure, incomplete chopping and damaged shear blades, which happen to the drum type chopping machine in Chongqing Iron&steel company. It also analyses the principle of the drum type chopping machine, determines the scientific methods for calculating the shearing force, investigates the influential factors concerning the shearing force, and provides approaches to reduce the shearing stress and prolong the life time of facilities.First, the microscopic mechanism of how materials are elastically deformed, plastically deformed and broken during the process of metal cutting is investigated, and the elastic deformation, plastic deformation and broken stages of using the drum type chopping machine to cut plates are analyzed. This analysis offers infallible theoretical supports for the validity of finite element modeling and the reliability of the modeling results. Starting with the dynamic process of the metal cutting using a drum type chopping machine with a spiral blade, via the study of an instantaneous shear plane, the acquisition of the characteristics of the spiral blade shearing dynamics, and the determination of the shearing angle during processes of stable shearing, a mechanical model of the metal cutting using a drum type chopping machine with a spiral blade is constructed.Furthermore, this thesis adopts rigid-plastic finite element method, utilizes the nonlinear finite element software DEFORM-3D to statistically model the process of cutting using the spiral blade, obtains the travel curve of the shearing force that is then fitted in MATLAB. and through the comparison of the results from finite element modeling and theoretical calculations, a modification of the theoretical model for the shear force is given and a conclusion that shows the process of the drum type spiral blade shearing shares similar properties with that of an inclined blade is drawn. Simultaneously, finite element models using different shapes of blade in the drum type chopping machine are established, which analyses the influence of blade shapes on the shearing force and proves a conclusion that the maximum shearing force using spiral and round blades is largely reduced compared with that of linear blades.Besides, on the basis that using spiral blades and inclined blades in the cutting process have similar properties, the spiral blade is discretized as infinite numbers of inclined blade elements, whose blade parameters including front angle, rear angle and blade round angle are also defined. Using a method of sliding curves, the mathematical model concerning the shearing force and blade parameters is derived and then gives the relationships between the front angle, the rear angle and the shearing forces. In addition, a simulation of the shearing process using the Unite element model with the inclined blade is carried out in DEFORM-2D, and the simulation results show the relationship between blade parameters and shearing forces. This model is then compared with a theoretical mathematical model. Both the theoretical model and the finite element analysis demonstrate that, an increase in the front and rear angles will reduce the maximum shearing force, and the round blade can relieve the stress concentration on the blade to some extent to reduce the maximum shearing force. However, too large round angles may blunt the blades and cause problems such as squeezing, warp and tearing, which in turn will largely increase the maximum shearing force.To sum up, the obtained conclusion showing the relationship between the blade shape, blade parameters and the shearing force has universal relevance, which also acts as a guide to reduce the maximum shearing force and prolong machine’s life time for other types of chopping machines. Therefore, this project has certain reference meanings for the design and usage of the chopping machines in our national production practice.