| Laser shock forming with semi-mold(LSFwM) employs the shock wave pressure induced by laser to plastically deform the sheet laterally and longitudinally to reproduce the shape of mold cavity accurately. The LSFwM technology is a new plastic forming technology with ultra-fast and accurate characteristics, its can forms parts with high precision and high efficiency, which has a great potential in the field of aeronautics,astronautics and vehicles. In this paper, taking the 2024-T351 aluminum alloy sheet as the research object, the interaction between sheet and mold cavity and its detailed forming process were first investigated combined with numerical simulation and experiment methods. Then the forming characteristics was also analyzed, and the regular of the effects of some related critical parameters on forming performance were discussed. Afterwards,the dynamic failure process of sheet under ultra-high and ultra-strain-rate conditions was observed numerically in real time. Moreover, its failure mechanism was also analyzed.Finally, the feasibility and forming regular of multiple-pulse incremental LSFwM were investigated. Finally, the failure mechanism of sheet in the LSFwM was discussed. The main contents and conclusions are as follows:(1) The finite element model of LSFwM was first established. The sheet’s deformation process and forming mechanism, strain distribution, forming velocity,thickness variation, and the effects of shock wave pressure and sheet thickness on the morphology of formed part were studied in detail. Then, the springback deformation and residual stress distribution of sheet after unloading were discussed. The numerical results show that the sheet fitting the mold cavity is a dynamic successive deformation process,which can be divided into five stages specifically. Significant strain gradients around the mold entrance and laser spot edge are found. The downward velocity of sheet in deforming process reaches to 614 m/s, after the sheet impacts on the mold cavity bottom and then bounces off upward with velocity of 319 m/s. The thickness of sheet is non-uniform and the greatest reduction occurs at the mold bottom corner. The area of sheet fitting the mold cavity increases with increasing of shock wave pressure and decreasing of sheet thickness.However, a bigger shock wave pressure and thinner sheet can induce rebound deformation of sheet in the center. The sheet spingbacks and the residual stress redistributes after the unloading shock wave pressure and blank holder. The failure mode of sheet shocked by laser is stretch rupture.(2) The finite element model of multi-pulse increment LSFwM was then established.The deformation process and feasibility of increment forming of sheet were investigated utilizing ABAQUS/Explicit and ABAQUS/Standard codes. The laser shock region, the sequence of shocking and the effects of the diameters of mold opening on the deformation morphology were also studied. The numerical results show that it is feasible to form part with large area by utilizing some small laser spot in different locations. Moreover, its forming performance of sheet is superior than that of large area. The more large area of laser shocking is, the better forming precision of formed part is. Moreover, the better forming precision can be obtained by overlapped shocking sequence. The smaller of the diameter of mold opening is, the better forming precision of formed part is.(3) In order to validate the accuracy of numerical results, a series of experiments of single pulse and multi-pulse LSFwM were conducted. After the results obtained from numerical are verified by the corresponding experimental results, the effects of some relative laser parameters, including shock wave pressure, sheet thickness on the deformation morphology were discussed. The thickness distribution of formed part is analyzed by microscope. Moreover, the surface residual stress of formed part was measured by X-diffraction. |
