Meshless Method And Its Application In Metal Forming Process With Contact Interface Of Arbitrary Shape

Metal plastic forming process has extremely important position in machinery manufacturing industry. Numerical simulation can improve the controlling level of metal plastic forming process and is a powerful tool for optimizing the process parameters and the structure of die. By numerical simulation, quality of the work-pieces couled be ensured; material consumption and developing time could be reduced, finally the cost coule be cut down.Among many numerical simulation methods, Finite Element Method (FEM) is the one which is the most widely used and proved to be valid. But so far, there have been some considerable difficulties in metal forming process simulation with FEM, such as distortion of grid and poor accuracy of stress field.There is no grid in Meshless Method, so it can avoid the difficulties resulted from the limitation of grid in FEM. The Meshless Method has better accuracy but less calculating difficulty than FEM. Therefore, it has both theoretical and practical significance to research and apply meshless method in metal forming process. Considering the contact interface of arbitrary shape is very common in metal forming, the meshless method is used to simulate the metal forming process with arbitrarily-shaped contact interface in this thesis.Computation efficiency is a big problem for Meshless Method. Integral computing and the processing algorithm of contact interface are the two key reasons for the poor efficiency of Meshless Method. So in this thesis, we will focus on these two respects to figure out some solutions to improve the efficiency.In this thesis, the Element-Free Galerkin Method (EFGM), based on the Moving Least Square approximation (WLS), was used as the numerical method, and elastic-plastic material was used as the material model. Regarding of the treatment to contact interface, the following works were carried out:presentation of mold cavity; search algorithm for contact interface pairs; calculation method for normal contact force and tangential friction force. And then the controlling equation of the forming process of elastic-plastic material, based on Updated Lagrange method (U.P), and relevant matrix were studied. Solve the equation using Dynamic Explicit Method based on Central Difference Algorithm.This thesis has the two following innovative jobs:(1) Meshless Method using Particle Integral Method was used in simulating metal forming process under arbitrarily shaped die and achieved high efficiency with good accuracy. Particle Integral Method is a stable integration method with high efficiency. In this thesis, after in-depth study on processing algorithms of contact interface with arbitrary shape, Particle Integral Method was used to simulate the forming process of a copper brick under extrusion of a ball-shaped punch. The results were compared with those gotten from FEM using ANSYS/LS-DYNA, It showed that the approach raised in thesis was correct and feasible.(2) Raised a new algorithm for contact surface searching, after in-depth study on Master-Slave Surface Method and Integration Algorithm, which were named "Projection Sub-domain Method" by the author. In this algorithm, the master contact piece on the surface of die and the slave contact point on the surface of work-piece were all projected to the plane which was vertical to the direction of movement of the punch. And then the projection area was divided into small rectangular sub-domains. With the help of these sub-domains, matching process to the master contact pieces and slave contact points became easy and quick. So the testing pair and contacting pair were then determined easily and efficiently. The final numerical simulation example showed that this algorithm has high processing speed and is easy of implementation.