Study On The Contact Friction And Its Effect In Free Bending Of Aluminum Sheet

With the development of society,the requirements for the surface quality of bending parts are becoming higher and higher.At present,most of the research on sheet bending is focused on the theory of forming,and the research on contact friction is relatively less.The practice shows that the contact friction has a significant effect on the surface quality of the sheet bending parts,and the surface quality can be greatly improved by improving the contact friction condition.Therefore,it is necessary to study the effect of contact friction on the surface quality of the bending parts.In this paper,the V shape three point bending process of 1060 pure aluminum sheet with a thickness of 6mm is taken as the research object,the force situation of the contact friction zone between the die fillet and sheet is analyzed through theoretical analysis and finite element simulation,and the effect of different friction conditions on the surface quality of bending parts is studied by experiments,the effect of contact friction on the surface indentation of the bending parts and the formation mechanism of the indentation are studied.The main contents of this paper are as follows.Firstly,the theory of sheet bending,mechanics characteristics,contact model and friction model are briefly introduced,and the contact friction problem in sheet bending is emphatically analyzed.Secondly,sheet metal bending forming process is simulated by ANSYS LS-DYNA,and the changes of effective plastic strain,contact pressure in the contact area between the die fillet and sheet are emphatically analyzed to provide a reference for further experimental research.Then,the experimental device of bending forming and friction parameter test is designed,and the experimental scheme is determined,and the bending force,friction coefficient and other parameters of sheet metal bending are measured.Scanning electron microscope on the bending parts under sliding contact and rolling contact friction are carried out respectively,from macroscopic and microscopic perspectives,the action mechanism and effect rule of different contact friction forms and different die surfaces on bending parts' surface are studied.The factors affecting contact friction are analyzed,and the way to eliminate contact friction and improve the surface quality of bending parts is discussed.The research shows that the contact friction forms and the surface quality of the die fillet have a significant effect on the surface quality of the bending part in the V shape three point free bending experiment of 1060 pure aluminum sheet.1)The effect of the contact friction form on the surface indentation of the bending parts mainly lies in the shape and distribution of the indentation,which has little effect on the surface quality of the indentation.The indentation caused by sliding contact friction is deeper,and the indentation distribution is uneven.It mainly concentrates on two ends.There is material accumulation at both ends of the driving edge and the edge of the guide edge.The indentation caused by rolling contact friction is generally shallow,and the width direction of the strip is distributed evenly,which is basically narrow and long strip.Rolling friction can weaken the metal slip accumulation phenomenon.2)The effect of die surface on the surface indentation of the bending part mainly lies in the surface condition of the indentation itself,which has little effect on the distribution of the indentation.When the surface of the die is rough,the surface of the indentation has a uniform,dense and fine groove,which weakens the accumulation and slip of the material.3)The sliding contact friction is the interaction of metal material adhesion effect and furrow effect,will cause significant slippage and packing phenomenon of metal materials;The plough is almost non-existent in the rolling contact friction.