Friction And Wear Of Ultra-high Strength Steel During Hot Forming And Its Effects On Forming Properties

When the high-strength steel is formed by the conventional cold stamping process,there are problems such as poor forming property of sheet,large amount of springback of the formed part,and low mold life.During hot stamping process,the sheet is formed at a high temperature and after forming is completed,the pressure-hardening is performed in the mold to obtain a high-strength formed part,which effectively solves the problem of cold stamping.However,the contact between the sheet and the mold in high temperature is complicated,and the friction and wear behavior between the interfaces seriously affects the surface quality of the product and the wear of the mold.In this paper,ultrahigh-strength steel B1500 HS and hot tool steel H13 are taken as research objects.The effects of temperature,load and sliding speed on the high temperature friction coefficient and wear behavior of B1500HS/H13 are systematically studied by three-factor and three-level orthogonal experiments.Abaqus finite element software was used to study the influence of the friction coefficient of key areas of hot stamping box on the forming performance.The specific research contents are as follows:1)The morphological parameters of the solid rough surface and the statistical parameters of the height distribution are introduced,and the contact characteristics of the rough surface are analyzed.Secondly,based on the rough surface contact theory,the important friction mechanism involved in the high temperature friction process is analyzed: Adhesive friction mechanism,deformation friction mechanism,friction coefficient under oxidation and heat conduction and flash temperature phenomenon.Finally,three stages of general wear history were introduced,and the abrasive wear,adhesive wear and oxidative wear model existing in high temperature friction process were analyzed.2)The high temperature friction and wear properties of the B1500HS/H13 friction pair involved in the hot forming process were investigated.Firstly,three-factor and three-level orthogonal experiments considering temperature,load and sliding speed and their interaction were designed.The influence of various factors on the friction coefficient and wear mechanism of ultra-high strength steel B1500HS/H13 was analyzed.The level of significance that the factors affects the coefficient of friction were tested : temperature and sliding speed have a significant effect on the friction coefficient.3)Through the numerical simulation of hot drawing of ultra-high-strength steel box,the influence of the friction coefficient of the four key contact areas between the mold(the convex corner,the convex right angle,the concave corner and the die blanking zone)and sheet on the sheet forming properties of ultra-high-strength steel during the forming process were studied.The box mold model was established in Abaqus software,and the orthogonal numerical simulation experiment was designed.The simulate experimental results were analyzed by using the range and variance.The influence of the friction coefficient of the key area of the mold on the maximum thinning rate,thickness distribution non-uniformity index and crack tendency of formed parts is discussed.Studies have shown that the coefficient of friction between the die fillet and the die blanking zone has a significant effect on the sheet forming properties.