Numerical Simulation For Micro Laser Peen Forming Of Ultrathin Sheet Metal

The recent trends towards miniaturization cause the commercial demands for the part with very small dimensions. The formation of parts of made of very thin sheets has become increasingly important. Micro laser peen forming is a new type of sheet metal forming process. This new technology is based on shock waves as a source for the forming energy, which are created through laser pulses and brings plastic deformation to the ultrathin sheet. In this thesis, the laser shock processing was applied for micro-forming and the advantages of the laser shock processing and the micro plastic deformation were integrated. Based on the continuous medium mechanics, the crystal structure character of materials and plastic deformation mechanism have been taken into account. The grain structure of the milli-component has been expressed by two elements type, so called grain element and grain boundary element. They were described by different constitutive equation, using the computer language VC++ to compile the program for mesh division, and the simulation was done by the finite element software LS-DYNA. The simulation results agree well with the experimental results, thus the method of mesh division was reasonable and it can effectively simulate the process of micro laser peen forming.The finite element division program MicroMesh and the commercial program LS-DYNA are combined in this thesis and then the axisymmetric micro laser peen forming process is simulated. The impact of different laser parameters, material properties and size in the micro laser peen forming was researched and the process of several pulses being applied at one point was simulated. These are the valuable conclusions: (1) The grain boundary is significant in the micro laser peen forming. The concave deformation of the sheet increases as the thickness of the grain boundary decrease and it is nearly linear relationship between the two. The existence of the grain boundary hinders the concave deformation of the sheet. The thicker the grain boundary, the smaller the concave deformation of the sheet. (2) A program is developed to simulate the load of the impact of the impulsive pressure induced by explosion. The sheet deformation under different peak values is analysed. It is discovered that the peak value is significant in the micro laser peen forming. The deformation increases as the peak value increases. (3 )The influence of every process parameters to the deformation. Is studied. The results show that different material has different deformation when other technology parameters are the same. The increase of the thickness hinders the deformation. The more irregular the grain, the greater the deformation. (4) The effect of the diameter of the microdie was researched. The bigger the die diameter, the smaller the effect. (5) When several pulses were applied at one point, the deformation was the biggest at the first time and then gradually become smaller.