Roll Gap Control In Continuous Roll Forming And Its Numerical And Experimental Research

Continuous roll forming is a novel method of sheet metal forming process, it combinesthe traditional rolling technology with multi-point adjustment technology and takes twosmall deflection bending flexible rolls as the work roll. The theoretical foundation ofcontinuous roll forming is non-uniform thinning principle and transverse bendingdeformation mechanism. The transverse bending of flexible roll and roll gap can be adjustedby adjusting equipment, so as to realize the continuous forming of3D sheet metal parts withdifferent curvatures. Continuous roll forming has broad application prospect in areas such asautomobiles, aircraft, ships and buildings.Continuous roll forming surface shape is controlled by roll gap. In the forming process,the elastic deformation of work roll assembly makes roll gap change, and leads the actualroll gap to deviate from the designed roll gap, and result in the forming parts fail to achievethe target shape. There are one flexible roll and two wire soft shaft back-up rolls in workroll assembly. The wire soft shaft has small stiffness and produces large elastic deformationin forming process. The elastic deformation of wire soft shaft is the main reason of roll gapchange.In this paper, the elastic deformation of wire soft shaft back-up roll in forming processwas considered, a more realistic finite element model was established. The roll gap changeand influencing factor of continuous roll forming were studied by numerical analysis. Theroll gap correction method for the work roll assembly elastic deformation compensation,was presented and verified by numerical analysis and experiment. Instead of the roll gapcontrol method based on wire soft shaft back-up roll, the roll gap control method based onsteel axis back-up roll was proposed and verified by numerical analysis and experiment.The two kind of roll gap control method was compared and analyzed. The main contents and conclusions of this paper are as follows:(1) The influence of different process parameters on the roll gap change of continuousroll forming was studied. The results show that the roll gap relative variation increased withthe increase of sheet metal compression ratio. The higher the sheet metal strength is, thelarger the roll gap relative variation is. Under the condition of the same overall pressamount, the roll gap relative variation increased with the decrease of sheet thickness, theroll gap relative variation increased with the increase of the distance between adjacent wiresoft shafts. With the increase of overall press amount applied by upper roll, the quantity ofroll gap compensation was increased, the roll gap relative variation decrease gradually.(2) The variation law for convex surface and saddle surface was studied. Whenforming a convex curved surface parts, roll gap variation in the middle area is larger than inedge area. When forming a saddle curved surface parts, roll gap variation in the edge area islarger than in the middle area.(3) Amount of elastic deformation of part in work roll assembly was compared, themain factors to influence the roll gap change were analysed. The amount of flexible rollelastic deformation is small and it can be ignored compared with that of wire soft shaftback-up roll elastic deformation and the vertical distance variation between flexible rollcenter and wire soft shaft back-up roll center. The elastic deformation of wire soft shaftback-up roll, vertical distance variation between flexible roll center and wire soft shaftback-up roll center are the main reasons of the roll gap change.(4) The roll gap correction method was verified by numerical analysis and experiment.By using the elastic deformation of work roll mechanism as the first step correction, usingthe difference values of total elastic deformation in different correction step as a correctionof follow-up step, the roll gap was modified. Through numerical analysis and experimentalstudy the conclusion could be draw, the roll gap variation after modification is much lessthan that of before modification, roll gap achieved a high accuracy, the formed parts alsoachieved a higher surface quality and a better forming precision.(5) Improving the roll gap control method, the roll gap control method based on steelaxis back-up roll was put forward and verified by numerical analysis and experiment. Theresults show that when the steel axis back-up roll is used, not only the roll gap relative variation, but also the roll gap correction and times of correction decrease obviously. Afterseveral times corrections by using two kinds of roll gap control methods, surface can gethigher forming precision by far less times of corrections and and much smaller correctionvalue. The roll gap control method based on steel axis back-up roll is significantly superiorto the one based on wire soft shaft back-up roll.