Study On The Mechanical Trimming Technology Of Hot Stamped Part And The Design Of The Cutting Edge

In recent years,hot stamped parts are increasingly used in B pillar of vehicles and other structure parts.Nowadays,the removal process was main accomplished through laser cutting.The mechanical trimming has become the research direction because of the lower cost.Compared with the cold formed parts,hot stamped parts have higher strength and hardness.There are always some problems like high residual stress and delayed cracking during mechanical trimming process.Hence,suitable technology parameters and cutting edge outline play a crucial role in enhancing the cut surface quality and avoiding delayed cracking.In this thesis,the research comes from the mechanical trimming technology of hot stamped parts and the optimization of the outline of cutting edge.Based on the sheets with different phase components,the influences of the blanking clearance on the cut surface topography and the blanking force were studied.At the same time,the influences of sheet phase components on residual stress and delayed cracking were also studied.Based on a series of tension tests,a ductile fracture criterion which introduces phase volume fraction were established.The optimization of the trimming clearance and cutting edge outline were carried out based on the finite element model of the mechanical trimming of a featured part of B pillar.The main contents of this thesis:1)Based on a surface temperature controllable mold system,the temperature paths of completely austenitizing boron sheets under 930℃ were controlled accurately,then the sheets with full martensite,full bainite and mixtures with different phase volume fractions were got.The blanking experiments of sheets with different phase components were carried out under three kind clearances and the best one was confirmed.At the same time,the research of the influence of the phase components on the residual stress and delayed cracking was conducted under three clearances.2)Concerning the mixtures of martensite and bainite that may exist in the hot stamped B pillar,a series of tension tests were carried out,and the fracture criterion which introduces phase volume fraction were eatablished.A mechanical trimming model of a featured part was established based on ABAQUS/Explicit and it was verified through the comparison of the force in experiment and simulation,it also becomes the basis of the optimization of the technology.3)Based on the mechanical trimming model established before,an optimization under three blanking clearances was carried out.At the same time,the optimization of blanking sequence and the tool angle was conducted.Then,the outline of the cutting edge of hot stamped part was proposed.At last,the mold hardness design concerning sheets with different phase components was carried out to offer some instructions for the blanking of hot stamped sheets.