Research On Metal Foil Indirect Shock Micro Forming Under Laser Driven Flyer

With the continuous development of micro and nanotechnology, the manufacture of MEMS (Micro-Electro-Mechanism System) and its micro parts have become present research hotspot in micro manufacturing field. Because micro plastic forming technology has special advantages in large scale batch production, it has an increasingly extensive application on the manufacture of metallic microstructure. And it has already become the subject frontier of modern manufacturing field both at home and abroad. Based on the analysis of micro forming both at home and abroad, combining laser-driven flyer technology, a novel laser indirect shock micro forming is presented, which uses laser-driven flyer to load the sheet metal. Based on the theory analysis of the mechanism of laser-driven flyer and metal foil forming, a systematical study on the deformation property of metal foil indirect shock micro forming under laser-driven flyer were carried out from experiment and numerical simulation in this article. The main contents are as following:The mechanism of laser-driven flyer loading and metal foil forming were investigated, involving laser induced shockwave, shock force mathematical model, flyer target structures, influencing factors of laser-driven flyer, analytic representation of laser-driven flyer, impact dynamics of laser indirect shock forming, temperature rise of collision process and high strain rate plastic forming. This study laid a foundation for reasonable selection of the micro forming process parameters and numerical simulation of forming process.An experimental system for metal foil indirect shock micro forming under laser-driven flyer was developed. Through the research of micro forming based on micro channel networks mould, circular hole mould and circularity micro-channel mould, it analyses the effect of laser energy, workpiece thickness and defocusing on the deformation. The surface topography and roughness of the workpiece was investigated experimentally. And the theoretical strain distributions on typical formed parts were analyzed. It is found that the work piece has a high spatial resolution at the micron-level and the good surface quality is accomplished when process parameters are reasonable. The research results have shown the possibility of realizing sheet metal micro forming. The research on laser indirect shock micro forming showed that increasing the laser energy could increase the deformation depth, but may induce fracture when the laser energy is too high. Further studies proved that laser-driven flyer is also very suitable for micro punching technology.This paper also reports an investigation into laser indirect shock micro forming process through finite element simulation. ANSYS/LS-DYNA is an explicit dynamic analysis program, which is used to simulate the forming process. Comparing the simulated results with experiments, the precision and reliability are validated. The energy history, the displacement history and residual stresses field of the model are analyzed. The effect of laser energy, the die radius and the frictional coefficient on the deformation was numerically studied. The numerical simulation research provides means for optimization of process parameters, prediction and control of deformation shape.The microstructures of the treated samples were examined by transmission electron microscopy (TEM). The microstructures of the workpiece under laser-driven flyer loading are characterized by nano-sized grains and a small fraction of mechanical twins. And multiple mechanical twins appeared inside many grains. In the grain, twin boundaries are parallel to each other and they subdivide the grain into a thin twin-matrix (T-M) lamellar structure, of which the thickness varies from several to several tens of nanometers. The two structural refinement mechanisms are introduced: the dynamic recrystallization and the twin-matrix (T-M) lamellar refinement mechanism. Laser-driven flyer loading provides a new way for grain refinement.This paper uses the method of smoothed particle hydrodynamics and the model of Johnson-Cook tensile cumulative damage to simulate the spall induced by the laser-driven flyer loading. The change law of internal stress distribution and the extreme value of spall under laser-driven flyer are obtained. These results could offer some useful messages for the study on the failure criterion and controlling of laser indirect shock micro forming.