| The wide application of ultra-high strength steel in automobile production makes its processing technology be close watched.Hot blanking is a process of heat treatment and stamping,which can reduce blanking force and improve mechanical properties of parts.The purpose of this paper is to discuss the optimal parameters of the hot blanking process of medium thickness of boron steel BR1500HS by using small die gap through conventional blanking process.And in this paper,the hot blanking process of boron steel is studied with two kinds of punch(common cylindrical punch and gear punch).First,a cylindrical punch with a bilateral clearance ratio of 3?11%and a blanking temperature of 600?800? were used to conduct hot blanking test on boron steel BR1500HS,and the microstructure transformation,mechanical properties,dimensional precision and fracture quality of boron steel were studied.The results show that when the blanking temperature is 700?800?,the structure of the blanking parts is complete martensite and the hardness is about 560 HV.When the blanking temperature is constant,the maximum blanking force decreases with the increase of the clearance ratio of the die.When the clearance ratio of the die is same,the maximum blanking force decreases with the increase of the blanking temperature.When the blanking clearance ratio is same,if the blanking temperature increases,the width of the burnish of the blanking section increases,and the fracture quality becomes better.When blanking at 800? blanking,the ratio of the burnish width can reach 72.5%of the thickness of the blanking section.When the blanking clearance ratio is 6?8%,the dimensional accuracy of blanking parts is better,and the section quality is also better.When the blanking temperature is 800?,the dimensional accuracy of the blanking part is highest.Therefore,the optimal process parameters of the hot blanking process of boron steel BR1500HS plate are the blanking temperature of 800? and the clearance ratio of the die is 6?8%.The surface quality,mechanical properties and dimensional accuracy of the shear area of the blanking parts are generally better.Finite element simulation of hot blanking of boron steel BR1500HS plate with medium thickness is carried out by DeformV11.0,choosing three ductile fracture models(Brozzo fracture criterion,Freudenthal fracture criterion and Oyane fracture criterion)and the blanking temperature of 700?,750? and 800?.And a two-dimensional axisymmetric finite element model was established to analyze the hydrostatic stress,material flow and stress-strain in the hot blanking process.Then analyze material flow and stress and strain,etc.,and by comparing the simulation and experiment of fault location,and the fracture section shape,find out the optimal fracture model and the fracture threshold.The results show that Oyane fracture criterion is suitable for finite element simulation of hot blanking of boron steel BR1500HS.Gear punch with die clearance ratio of 6%was selected for hot blanking test of boron steel BR1500HS plate,the gear parts obtained can be used in the production of automobile gear and sprocket.The maximum blanking force,the surface morphology,the width of the burnish and the dimensional precision of the gear-shaped drop parts were measured.The maximum blanking force decreases with the increase of blanking temperature.For the shear zone morphology and dimension precision of gear shape blanking parts,the results showed that,with the increase of the blanking temperature,the burnish width of tooth surface increases,the surface is more smooth,and the addendum and dedendum have the same trend with tooth surface.At the same blanking temperature,the width of burnish is largest at dedendum and least at addendum.When the blanking temperature is 800?,the gear-shaped blanking parts have the highest dimensional accuracy.Therefore,when the punch is gear shape,the best blanking temperature is 800?.And we can obtain higher dimensional precision and wider burnish of blanking parts. |
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