Research On Key Technology Of Straight Seam Welded Pipe Roll Bending

In order to meet the needs of the automobile industry for energy conservation,emission reduction,safety,comfort and other aspects,automotive lightweight has become an important trend in today’s automobile manufacturing industry.Automobile lightweight can be realized in many ways,one of the important ways is to use high-strength steel instead of traditional ordinary steel for automobile parts production.With high strength steel as raw material,straight seam welded pipe formed by roll bending began to be gradually applied to the structure of automobile body,chassis structure and exhaust pipe structure,through improving the strength and stiffness of the body,reducing the weight and fuel consumption of the body,and then improve the vehicle handling,stability and environmental protection.Compared with ordinary steel,high strength steel has the characteristics of large yield strength,poor shape,large rebound,difficult welding and so on.In the process of roll bending,it is easy to appear the problems such as excessive residual stress,obvious stress concentration,large errors in wall thickness and size,and poor welding quality at the edge.In view of the above problems,it is necessary to explore the high strength steel roll bending forming process,reveal the sheet forming law,find the causes of quality defects,optimize the forming process and unit parameters,in order to improve the high strength steel straight seam welded pipe forming performance.The main research contents of this paper are as follows:(1)The forming principle of sheet roll bending is introduced,and the roll pass is designed by the comprehensive double radius forming method;A simplified numerical simulation model of high strength steel roll bending was established,and the boundary conditions of sheet and roll were reasonably set in combination with the actual situation.The finite element numerical simulation analysis based on explicit dynamic algorithm was carried out to analyze the forming process.The accuracy of the numerical simulation results was verified by measuring the plate opening degree and section shape.(2)The stress and strain distribution law of sheet metal in different forming stages and the change law of typical joint stress and strain with time were analyzed,and the forming law of sheet metal and the causes of forming defects in the process of roll bending were obtained;The effects of rolling speed,frame spacing and other technical parameters on the longitudinal strain of sheet edge were investigated.In order to solve the problem of high strength steel roll bending and forming process,the springback calculation method of sheet metal and springback compensation are put forward.(3)Optimize the design of the forming roll by using different change coefficients;In order to improve the insufficient deformation of the center of sheet metal,a W-shaped roll is introduced to reverse bend the center of sheet metal.The forming quality evaluation index of steel tube was established based on the Angle,wall thickness deviation and uniformity,outside diameter deviation and uniformity,and the forming quality of steel tube was evaluated comprehensively and objectively.The orthogonal test of "multi-variable" and "multi-index" was designed to explore the effects of bending Angle,frame spacing and rolling speed on molding quality.Based on the results of range analysis and variance analysis in orthogonal experiment,the optimal molding scheme was determined.According to the optimal results,the molding unit was rearranged and the numerical analysis was carried out.The comparative analysis shows that the optimized forming scheme can improve the forming quality of straight seam welded pipe.(4)Based on the forming characteristics of high-strength steel,the forming process of high-strength steel straight seam welded pipe is planned and designed,and the key process is modular analysis;In view of the low efficiency of roll replacement,low precision of adjustment and low degree of automation existing in the production process of roll bending forming unit,a roll quick change device for roll bending forming was proposed,and the key parts were selected and checked,which provided a new idea for the design and improvement of roll bending forming unit.