Research On Friction Characteristics Of Ultra-High Strength Steel B1500HS During Hot Stamping

Hot stamping technology can effectively overcome the difficulties brought by traditional cold stamping technology,such as low formability of steel,large amount of spring back and short service life of die.However,in the process of forming,high temperature and high stress make the contact between sheet metal and die complex and changeable,and the friction and wear behavior of contact surface will directly affect the forming quality of stamping parts and the wear of stamping die.In this paper,the friction characteristics of no-coating,hot-dip galvanized(GI),alloyed hot-dip galvanized(GA)ultra-high strength steel B1500 HS and die steel H13 in hot stamping process are studied from the aspects of experiment and finite element simulation.The specific research work is as follows:1)Firstly,the morphology parameters and profile height distribution statistical parameters of the friction pair surface are introduced,and the contact between the rough peaks of the friction pair surface is analyzed.Secondly,the important friction theories involved in the process of hot stamping friction and wear are analyzed:adhesion theory,heat conduction of friction system,stamping friction mechanism and high temperature friction surface effect.Finally,the three stages of the friction pair wear process are introduced,and the theory of adhesion wear,abrasive wear and oxidation wear which will be involved in the hot stamping friction wear are analyzed..2)A series of high temperature pin disk friction tests were carried out on ultra-high-strength steel with no-coating,hot-dip galvanizing(GI),alloying hot-dip galvanizing(GA)and die steel H13.The variation trend of friction coefficient with time under different test temperatures was analyzed,and the wear mechanism under different test temperatures was explored.The wear rate of die steel under different test temperatures was compared and analyzed.The results show that the high temperature friction coefficient of the three materials decreases with the increase of the test temperature,i.e.the forming temperature from 650℃ to 850℃.As a whole,the wear rate of the no-coating plate to the die steel is significantly higher than that of the GA plate and the GI plate.3)The finite element simulation software Deform is used to simulate the hot stamping process of U-shaped parts.The influence of friction coefficient on the stress-strain evolution of key area nodes and the thickness distribution of sheet metal after forming is analyzed.The influence of friction coefficient change between sheet metal and punch,die and blank holder on the maximum thinning rate,thickness nonuniformity and comprehensive forming performance evaluation is discussed The impact of indicators.The results show that the change of friction coefficient between sheet metal and die has a significant effect on the maximum thinning rate,thickness inhomogeneity and comprehensive formability after sheet metal forming.