Investigation On Methods And Effects Of Reducing Friction During Incremental Sheet Forming Of TA1 Sheets

As a advanced dieless forming process,Incremental sheet forming(ISF)owns extremely high flexibility,rapidly forming efficiency and huger plastic deformation capacity.So,ISF is especially suitable for small-batch and personalized sheet forming.However,poor surface finish and excessive forming load are problems in present times,particularly for some difficult-to-form materials such as titanium and titanium alloys.Titanium has numerous excellent characteristics such as high specific strength,strong heat resistance,corrosion resistance,etc.It has been widely used in aerospace and other fields.During the ISF process,the forming tool is controlled by the computerized numerical control machine and continuously squeezes the sheet layer by layer to make it deformed.As a crucial component,the forming tool directly contacts the sheets during forming.A friction pair is comprised of the forming tool and sheets,and the contact condition significantly affects the forming load and the performance of the formed part.The lubricating can form a thin file between the forming tool and the sheet to avoid direct contact between them.Traditional lubricants such as mineral oil are difficult to form a stable lubricating film when the forming load is large,which results in lubrication failure.In this paper,the contact conditions are changed by changing the surface characteristics of the forming tool and the sheet respectively,so as to reduce the friction,improve the surface finish and improve the material flow to make the material deformation more uniformFirstly,commonly used solid lubricant molybdenum disulfide was adapted in high-load ISF process.The effects of plasma spraying parameters on the mechanical properties of nickel-clad molybdenum disulfide coatings and TA1 substrates were investigated.The tensile test.Vickers hardness test and powder deposition rate were carried out respectively.The results show that the yield strength of the coated sheet increases with the decrease of the spraying distance and the increase of the spraying power;the microhardness drops with the spraying distance and spraying power increase.It rises with the main gas flow increase.The powder deposition rate and microhardness show consistent results,the huger the deposition rate,the higher the microhardnessThen,the ISF experiments were carried out by using the prepared coated sheets.The effects of self-lubricating coating on reducing friction force were analyzed in terms of forming force,surface finish and forming temperature.It was found that the friction coefficient during forming was dramatically reduced except for the self-lubricating coating prepared at main gas flow of 1800L··h-1.The friction coefficient of self-lubricating coating decreased by approximate 80%compared with the traditional lubricant oil of them.The temperature results are roughly the same as the analysis of the forming force,which further illustrates the accuracy of the forming force analysis The self-lubricating coated sheet has higher contact surface roughness after forming,but exhibits lower surface roughness values on the non-contact surface.The wear rate indicates that there is still self-lubricating coatings on the surface of the formed components,which shows that the self-lubricating coating can not only play the role of reducing friction and lubrication during ISF process,but also continue to play a lubricant role in the subsequent service of the formed component.Finally,a large-angle roll forming tool is designed.The effects of hemispherical sliding forming tools and rolling forming tools in the reduction of friction,thickness reduction and equivalent strain during the forming process were compared by using the finite element simulation software ABAQUS.It was found that compared with sliding friction tools,rolling friction tools can significantly reduce the friction force.At the same time,as the reduction of friction force is more conducive to the flow of the material,which results the strain of the sheet more uniform.The maximum thickness reduction rate of sheets is also reduced,which is contributed to increase the forming limit of the sheet.In this paper,the purpose of decreasing friction during ISF process of TA1 sheets was achieved by adopting solid lubricants and rolling forming tools.In order to further enhance the bonding strength between the solid lubricants and the sheets,a plasma spraying technology was used to prepare a nickel-clad molybdenum disulfide self-lubricating coating on TA1 sheets.The effects of spraying parameters on TA1 the mechanical properties of sheets and anti-friction effect in ISF process were investigated.Due to the advantages of finite element software in difficultly obtained date,for instance strain.The finite element method was employed in comparing the difference of two type forming tools.In the current works propose two methods that can effectively decrease the friction in 1SF of TA1 sheets.And provide theoretical basis and measures for reducing the forming load and enhancing the quality of formed component,which has certain application potential.