Research On Influence Of Friction Effect On Overlapping Sheets Viscous Medium Pressure Forming

Overlapping sheets forming process is one of the main methods to improve the plasticity of hard-to-deform materials.In forming process,the improvement of forming sheet deformation ability is related not only to the plasticity,strength and other properties of overlapping sheet materials,but also to interface friction between forming sheet and overlapping sheet.In this paper,the 5A02 aluminum alloy sheet with poor plasticity deformation ability was used as forming sheet and the SUS304 stainless steel sheet with good plasticity as overlapping sheet.The influence of different friction states of contract interface of 5A02/SUS304 on forming properties of forming sheet in overlapping sheets viscous medium pressure forming process was studied.First,lubricating materials of polytetrafluoroethylene(PTFE),silicone rubber,graphite,molybdenum disulfide and mechanical lubricating oil were used as lubrication respectively for contact interface of forming sheet and overlapping sheet.The plate sliding experiment was carried out to measure friction force between forming sheet and overlapping sheet under different lubrication and without lubrication conditions,different normal pressure and different sliding speed conditions.The influences of lubrication states,normal pressure and sliding speed on friction coefficients of 5A02/SUS304 interface were obtain based on coulomb friction law.Then,the stress states of forming sheet were analyzed in theory in overlapping sheets viscous medium bulging process.5A02/SUS304 overlapping sheets viscous medium bulging experiments were conducted to investigate the effects of lubrication states on fracture position,limit bulging height,bulging specimen thickness distribution of forming sheet.The changes of microstructure and fracture morphology of fracture zone material of limit bulging specimen under different lubrication condition was observed.The finite element analysis for overlapping sheets viscous medium bulging experiment was carried out to research the effects of different friction coefficients on equivalent stress,equivalent strain and wall thickness distribution of forming specimens.Finally,the finite element method was adopted to analyze overlapping sheets viscous medium hemispherical parts deep drawing process under three different blank-holder force curves,the optimum blank-holder force curve was identified by comparing the results.The equivalent stress,equivalent strain,wall thickness distribution and the material flow inflange zone of forming specimens were analyzed to investigate the influence of different friction coefficients of 5A02/SUS304 interface on forming property of overlapping sheets viscous medium hemispherical deep drawing parts.The overlapping sheets viscous medium hemispherical parts deep drawing experiments were carried out under different lubrication conditions based on the optimum blank-holder force curve,and the experimental results were in good agreement with numerical simulation results.