Simulation And Experiment Study On Press Hemming Dimensional Deviation For Aluminum Alloy Auto Panels

Hemming is a common process in white body manufacturing.As aluminum alloy is being used more and more widely in automobile,dimensional deviation,namely roll-in and roll-out,for aluminum alloy in press hemming process is completely different from that for steel due to process parameters change.Lacking experience in aluminum alloy hemming design,the domestic manufactures need a thorough understanding of dimensional deviation for aluminum alloy.Based on 6016-T4 aluminum alloy,roll-in/out is studied in press hemming process via both simulation and experiment.A calculation method for flanging length and hemming width is processed.A feature panel is designed for curved surface curved edge press hemming,experiment platform is constructed,and experimental verification is performed.The main content of this dissertation is as detailed below.1)Key parameters study for roll-in/out in aluminum alloy press hemming processThrough mechanics analysis for blank in hemming process,it is found that torque on blank in pre-hemming process is the main cause of roll-in/out.Regarding flat surface straight edge hemming,flanging die radius,Young’s module,outer blank thickness and gap between outer and inner panel are key parameters affecting roll-in/out.As for curved surface curved edge hemming,flanging blank size,convexity and curvature have a combined effect on roll-in/out.2)Flanging length and hemming width calculationFlanging length and hemming width are two crucial parameters in hemming process design.Based on fixed length of neutral level,existing method is inaccurate regardless of plastic deformation.Through strain analysis of the material in bending process,in consideration of sheet thinner in bending area and deformation in flanging area,a flanging length and hemming width calculation method is established with high precision,which is then verified by experiment.3)Aluminum alloy press hemming feature panel design and experiment studyIn summary of hemming size factors through investigation and literature review,based on steel hemming design in actual panels,a feature panel is designed and it combines flat surface flat edge,flat surface curved edge,curved surface flat edge,concave surface convex edge and concave surface concave edge hemming.Furthermore,corresponding press hemming platform is constructed.Through reasonable flanging-(pre-hemming)-hemming process design,hemming process for 6016-T4 aluminum alloy is studied.4)Roll-in/out and hemming height study in aluminum alloy rope hemmingWith a large bending radius,rope hemming reduces fracturing problem for aluminum alloy.Flanging die radius,gap between outer and inner panel and pressing distance of pre-hemming die are the key process parameters influencing roll-in/out of rope hemming,though hemming height is mainly determined by flanging die radius.In summary,the present study gives useful instructions in press hemming process design for aluminum alloy.