Study On Forming Holes By Thermoplastic Flanging In Sheet

Forming holes by thermoplastic flanging in sheet is different from the traditional cold flanging process,it is a green and environmentally friendly process with no need of coolant processing,small residual stress after flanging and small deformation after hole forming,the process uses friction contact between drill bit and workpiece to generate heat under spinning feed to soften workpiece material for thermoplastic flanging and forming holes.Cold flanging requires high roughness of prefabricated holes,which directly affects the tearing defects on the edges of flanged holes,the residual stress in the sheet after cold flanging is large,which affects the mechanical stability of the hole forming;The roughness requirement of prefabricated holes for thermoplastic flanging is low,after friction heating,the material structure in flanging area is softened,the deformation resistance of material is reduced,and the structure streamline after flanging and pore forming is good by friction spinning feed.Friction heat keeps the temperature in a certain range,and the mechanical properties of the workpiece after dynamic recrystallization of grain structure are stable.The main contents of this paper are as follows:A theoretical model for calculating the heat generated by friction between hot flanging punch and workpiece is established,and the theoretical analysis of friction is carried out,it lays a foundation for the analysis of the microstructure of flanging pore forming with temperature change;By choosing suitable simulation material and bit shape model,according to the physical properties of the material,with the help of software DEFORM-3D,the process of thermoplastic flanging of sheet metal is simulated,and the simulation parameters that affect the morphology of sheet metal under different thickness and prefabricated aperture conditions are obtained;Controlling the comparative analysis of single variable by simulating the morphological results,the results of flanging pore-forming morphology under the same plate thickness and different prefabricated holes and the same flanging pore-forming morphology under the same prefabricated aperture with different plate thickness are obtained.The factors affecting the flanging pore-forming morphology and the better parameter law of the flanging pore-forming morphology are obtained,finally,the reasonable processing parameters are found by comparison;In the process of thermoplastic flanging of sheet metal,real-time changes of grain structure occur,the variation of metallographic composition and grain refinement at different positions of the material were studied by simulation results,through the analysis of the stress,strain and load changes during the material deformation process,the variation rule of the thickness and prefabricated aperture parameters in the hot flanging pore morphology results is obtained.Through the analysis of the simulation results and the changes of micro-structure,the processing parameters affecting the pore-forming morphology and the distribution of residual stress in the workpiece after processing are obtained,it lays a foundation for further research on hot flanging.