Process And Experimental Study On Preparation Of Profile Strips With Variable Thicknesses In Lateral Direction By Symmetrical Stack Rolling

In the trend of energy saving and emission reduction strategy,in order to reduce the quality of components and improve the bearing capacity of products,the concept of the blanks with variable thicknesses appeared in the Industrial field.At present,the preparation method of the profile strips with variable thicknesses in lateral direction are mainly welding?strip profile rolling or Bending-spreading rolling.The principle of welding is to weld a plurality of blanks with different thickness together to obtain a blank with variable thickness,but the products prepared have weld seams and sudden changes in thickness which reduce performance.And the principle of strip profile rolling and Bending-spreading rolling is to design a suitable shape for upper and lower rolls which makes blank metal unevenly flow in the width direction,but the uneven deformation of the products prepared in the rolling process will cause various defects such as waves,bends,tearing and so on.Besides,the maximum thickness difference of rolled profile strips is generally can't exceed 1:2.The purpose of this paper is to develop a new process for the preparation of profile strips with variable thicknesses in lateral direction by symmetrical stack rolling in view of the deficiencies of the existing production technology,and explore the causes of sliding misalignment during rolling process and several factors affecting the size of sliding misalignment for wedge-shaped blanks by methods of force analysis,experiment and numerical simulation.The main progresses are as follows:(1)A new process for preparing profile strips with variable thicknesses in lateral direction by symmetrical stack rolling has been developed.The new process mainly includes five key steps:die forging,surface treatment,superimposition,rolling,cutting and separation.And its main advantages include strong adaptability to raw materials,larger thickness difference of products,greater plate shape and so on.(2)Verification of the feasibility of the new process has been made.In the feasibility test,Q235 steel profile strip products with a thickness difference of about 3.5 were obtained by multi-pass hot rolling,which verified the feasibility of this new process.(3)The reasons for the sliding misalignment during the rolling process have been explored.Through the ABAQUS finite element simulation,it is found that in the upper and lower blanks during rolling process,the metal flows from the thin zone to the thick zone in the width direction,which is the cause of the sliding misalignment.(4)The influence of the inclined angle of blanks,the friction coefficient between two blanks and the number of rolling passes on the size of sliding misalignment have been investigated.The size of sliding misalignment increases with the increase of the inclined angle of blanks.When the inclined angle of blanks is 3° the size of sliding misalignment is 0.9 mm,which is reduced by two-thirds compared to 2.7 mm when the inclined angle of blanks is 6°.The size of sliding misalignment decreases with the increase of the friction coefficient between two blanks.When using the viscous paint for anti-sticking treatment,the size of sliding misalignment is only 0.15 mm,which is even reduced by 88.5%compared to 1.3 mm when using graphite paper for anti-sticking treatment.And the size of sliding misalignment generally decreases with the increase of the number of rolling passes.By four rolling passes,the size of sliding misalignment is 1.4 mm,which is reduced by about 54.8%compared to 3.1 mm by two rolling passes.(5)Several methods for reducing the sliding misalignment during rolling process are given.The reduction of the sliding misalignment can be achieved by varying the friction coefficient between blanks like using materials with rough surface for anti-sticking treatment or designing reasonable rolling procedures like appropriately increasing the number of rolling passes.