Study On The Theory Of Producible Rolling Thickness And The Buckling Deformation Of Oblique Cross Wave In Ultra-thin Strip Rolling

The vigorous development of the micromanufacturing and microelectronic industries has given rise to pressing requirements for ultra-thin metal strips with a small thickness and high-dimensional accuracy and the manufacturing technology of ultra-thin metal strips is becoming more and more important.With the reduction of the thickness of the ultra-thin strip,the rolling process is becoming more and more difficult,which puts forward higher requirements for the precision of strip thickness control.Meanwhile,the problem of complex shape defects is prominent,which affects the quality of rolled strip products.Therefore,the theoretical and technical problems on thickness and shape control of strips need to be solved urgently.The conditional cold rolling theory of thin strip,represented by the Stone theory,assumes that the roll remains a circular profile in the contact deformation zone.However,experiments and actual production show that the Stone rolling force model has defects.This is because there is a neutral zone in the contact deformation zone under some rolling conditions,so the assumption of the circular profile is no longer applicable.In this paper,through the finite element analysis of the rolling process of strips with different thicknesses,the variation of deformation zone profile and the distribution of contact pressure under different reductions are obtained.The Stone minimum rolling thickness is taken as the critical thickness of the neutral zone exists in the contact deformation zone under a minimum reduction,the range of strip thickness is divided by taking it as the boundary point,and different rolling conditions are studied.When the ratio of initial strip thickness to Stone minimum rolling thickness is known,the critical single-pass reduction can be determined,and the applicable conditions of the Stone rolling force model can be determined,which provides theoretical guidance for the computation of rolling force in thin strip cold rolling process.In the rolling process of the ultra-thin strip,the existence of the neutral zone leads to the sharp increase of rolling force but the increase of plastic deformation of the strip is very small.In actual production,due to the productivity requirement,it is impossible to carry out infinite rolling to reach a certain thickness,so the computation of the contact deformation zone is particularly important.In this paper,based on the Fleck theory and elastic half-space theory,the maximum single-pass plastic deformation can be calculated according to the rolling force conditions and the initial thickness of the strip.The producible rolling thickness model of ultra-thin strip rolling is established.For a given unit width rolling force,the relationship between the single-pass reduction and the ratio of initial thickness to theoretical minimum rolling thickness is obtained.It also corrects the formula of conditional minimum rolling thickness and provides theoretical guidance for the existing mills to determine the product specification range and formulate the rolling schedule,and to determine the roller diameter and force energy parameters and the solution of rolling force when designing the rolling mill.In the production process of the precision ultra-thin strip,the problem of an oblique cross wave is prominent.The thickness distribution of defective strip and geometrical parameters of wave shape is given and the mechanism of the oblique cross wave is analyzed.It is considered that the comprehensive action of front tension and transverse stress at the roll gap exit leads to the highly periodic alternating wave peaks and troughs on the strip,and the adjacent wave crests and troughs are connected to form oblique cross or single rib oblique wave shape under the action of transverse shear stress.The rolling model of the ultra-thin strip was created by ABAQUS software,and the variation of in-plane transverse compressive stress and transverse shear stress with front and rear tension of strip at roll gap exit was studied.The theoretical computation model of geometric characteristic parameters of oblique cross wave shape was given,and the variation law of oblique cross wave shape with rolling process parameters was obtained.Secondly,the mechanics of the strip at the roll gap exit is abstracted and the finite element model is established by ABAQUS software.The eigenvalues and eigenvectors of linear buckling are extracted by subspace iteration method,and the obtained eigenmodes are introduced into the arc length method analysis model as the initial defects.The nonlinear analysis model of pre-buckling and post-buckling process of oblique cross wave is established,so the post-buckling morphology and the post-buckling equilibrium path of the strip under specific conditions are obtained.The results show that the analysis of the generation mechanism of oblique cross waves and the theoretical computation model of geometric characteristic parameters are correct.Finally,the rolling experiments of ultra-thin strip were carried out with 20 high rolling mill in the laboratory.The geometric characteristic parameters of oblique cross wave under different rolling conditions were measured,and the variation of geometric characteristic parameters with rolling process parameters such as front and back tension was obtained,which was in good agreement with the analysis results of generation mechanism,which verified the correctness of theoretical analysis and finite element model of oblique cross wave.On this basis,the control strategy of oblique cross wave is studied,and the technical ideas and effective measures to restrain the shape defects are given.