Research On Laser Forming Process For Undevelopable Plates

Three-dimensional curved plates are widely applied in the field of aerospace,shipbuilding and transportation.As a dieless and flexible forming method of hot accumulation,laser forming can effectively avoid the springback and surface wrinkling and is pretty suitable for the forming of curved plates with small batch and various shapes.However,due to complex shape,it is inefficient and complicated to be formed from flat plates directly.Oriented to process planning of laser forming,this paper puts forward twostep forming method,in which the flat plate is formed by roll bending firstly and then laser heated,and studies the surface development algorithm,heating path planning and process parameters determination.The specific research contents are as follow:(1)Build up optimal development model of double-curved surface and compute the shape of single-curved plate.Based on the theory of large deformation and FEM method,the strains of elements and total strain energy are calculated by comparing the shape before and after deformation.Then the optimal shape is got by minimizing the strain energy with optimization algorithm.(2)Put up method of heating paths planning to form geometric features of undevelopable plates.According to temperature gradient and upsetting mechanism of laser forming,the calculated strain is divided into in-plane strain and bending strain.And the characteristic strain field is formed by comparing the magnitude of strains.The heating paths are set to be perpendicular to the direction of characteristic strain and the total layout is planned.(3)Complete process parameters determination and improve forming accuracy.Firstly,the database of process parameters and bending angle is built up through laser forming experiments and measurements.According to optimal developed shape and planned heating paths,the deformed angles are calculated and then the process parameters of every heating path are determined.Pillow-type surface and twisted surface are taken as two kinds of typical undevelopable plate,and the optimal shape of single-curved plate,layout of laser heating paths and heating parameters of every path are calculated and planned by optimal development algorithm,characteristic strain field and database of process parameters,respectively.Furthermore,the experimental verification and shape error analysis are carried out on experimental platform of laser forming.The mean square error of shape is 495?m for pillow-type surface and 421.2?m for twisted surface,which proves the validity of laser forming process planning mentioned above and provides a technical method for laser forming.