| In the context of new era,the national strategic development plan has put forward new requirements for intelligent level,energy saving and emission reduction of manufacturing industry.Deep drawing process of sheet metal(DDP)has met with new challenges and development opportunities,and it is necessary to explore the process optimization scheme on the basis of satisfying the "Forming & Performance".Friction is the key factor affecting the forming performance and quality of DDP,reasonable utilization of beneficial friction and suppression of harmful friction will play a crucial role in the process.The microscopic contact condition and dynamic friction between sheet and die are the decisive factors for process lubrication.Establishing the relationship between micro contact friction and macro process parameters,will be helpful to comprehensively understand the friction and lubrication mechanism in DDP,and will provide theoretical reference for the exploration of new forming technology conforming to the national strategic needs.This paper focused on the friction and lubrication in DDP of cylindrical parts,the following issues are mainly researched in the paper:(1)The effect of friction on drawing force in DDP of cylindrical parts.The approximate analytical model of DDP is established and the analytical expression of drawing force is derived by using energy method.Through the quantitative analysis of the elements in drawing force,the approach to control the friction force in different contact areas which can effectively reduce the drawing force and improve the forming performance has been studied.(2)The mechanism of microscopic contact and friction in DDP of cylindrical parts.The microscopic contact and friction mechanism between sheet metal and die are analyzed under different pressure,strain,material and surface topography,combining with the typical lubrication process in engineering practice,the formation principle of various lubrication states has been studied.(3)The mechanism of friction reduction by vibration and the hydro-pulsating lubrication technology(HPLT).The effect of high and low frequency vibrations on the friction coefficient in DDP is studied through friction experiment and theoretical analysis.The quantitative relationship between vibration parameters and the reduction ratio of friction coefficient is deduced.Based on the mechanism of friction reduction by vibration,the HPLT is proposed and the process principle are introduced in detail.(4)Finite element numerical models of dynamic friction coefficients based on contact and lubrication.By using Abaqus user subroutine module,the theoretical models are imported into the finite element numerical simulation by Fortran code,and the accurate description of friction coefficient in DDP of cylindrical parts can be realized.(5)Experiments on HPLT of cylindrical parts.The forming die,the pump station and the hydraulic system devices for hydro-pulsating lubrication are designed and manufactured.BUSD,DC04 and SS304 sheets are chosen to carry out the tests under different process parameters and lubrication conditions.The experimental data,theoretical results and simulation results are validated each other.The results show that the HPLT have effectively suppressed the friction,improved the forming limit,wall thickness uniformity and surface quality of the workpiece.The theoretical and numerical model are proved to be scientific and accurate by comparison. |
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