Numerical Simulation Of Laser Forming For Sheet Metal With Different Laser Source Modes

Laser forming is a new type of flexible sheet metal forming technology using laser induced thermal stress to produce plastic strain by metal material localized heated. Temperature field which directly determines the quality and forming efficiency is the dominant factor in laser forming process,and can be decided by the energy distribution of laser beam in time and space.Laser forming is a new type of flexible sheet metal forming technology using laser induced thermal stress to produce plastic strain by metal material localized heated. The magnitude and distribution of thermal stress directly affect the quality and forming efficiency of laser forming, and the thermal stress depends on the temperature distribution in sheet metal. Therefore, temperature fields are the dominant factor in laser forming process.The point of view of laser source modes served as a point of departure, the 3-D elastoplastic thermal-mechanical finite element model was established with finite element analysis software MSC.Marc, and validated with temperature and bending angle measurement results. Aiming at the manners of energy distribution and shapes of laser spot, numerical simulation of laser forming for pure aluminum sheet metal with the four different laser source modes, circular laser spot with Gaussian energy distribution, square laser spot with average energy distribution, rectangular 1/4 laser spot and rectangular 4/1 laser spot with average energy distribution, was investigated. For the same energy input, the temperature field, stress field and strain field of concave bending with different laser source modes were analyzed, Furthermore, the characteristics of convex bending were researched, and primary application of laser forming was realized.The relationship between bending characteristics and laser spot dimensions was studied in this paper, and the results show that it owns wider processing range with circular laser spot and square laser spot, while narrower processing range with rectangular 1/4 laser spot and rectangular 4/1 laser spot. There is a critical spot area corresponding to every kind of laser spots. Concave bending will turns to convex bending while the laser spot area reaching the critical spot area and it owns the biggest critical spot area with circular laser spot compared with other laser source modes. The results of temperature field and strain field indicate that the temperature gradient in the thickness direction only exists in the sheet width within the dimension of laser spot, and it appears nearly Gaussian distribution with circular laser spot, while average distribution with other laser source modes. The value of plastic strain difference between upper and lower surface and the width of plastic strain zone determine the magnitude of bending angle together. Higher plastic strain difference between the upper and lower surface is acquired with circular laser spot and square laser spot, and higher width of plastic strain zone is available with rectangular 1/4 laser spot.Based on a comprehensive analysis of the conclusion drawn above, the maximal bending angle is realized with rectangular 1/4 laser spot in both concave and convex bending, hence it is more efficient for laser forming with rectangular 1/4 laser spot. width of high temperature zone and average temperature difference between upper and lower surface have important influence on the bending angle, and the magnitude of stress becomes another significant factor for bending angle in laser forming process when large laser spot is used. Finally, the validity of the laws summarized from numerical simulation is verified by the experiments of concave bending and convex bending with the same sheet dimensions and the same processing parameters in the FEM.