Spinning Process And Properties Of Stainless Steel Based Bimetal Tubes

With the rapid development of science and technology,the application of tubes is facing a more severe service requirement and a more complex load condition.Single metal tubes are difficult to meet higher performance requirements due to the limitation of their properties.Therefore,more and more attention has been paid to bimetal tubes because they possess the excellent properties of two materials and have relatively low cost.Spin forming as a low cost,low load,high efficiency plastic forming technology has great potential in manufacturing high performance bimetal tubes.In this study,the spinning forming technology was adopted to manufacture 304/Ti and 20#/304 bimetal tubes.The composite forming mechanism of bimetal tubes in spinning forming process was studied.Moreover,the study investigated the influence of process parameters on the dimensional changes and tube performance by finite element simulations and experiments.In addition,a method to improve the bonding strength was developed.The main contents and conclusions were listed as follows:(1)Based on the theory of elastoplastic mechanics,a plane mechanics model for spinning bimetallic tubes was constructed.The research revealed the forming mechanism through analyzing the stress condition of each component and the innfluencing factors of forming.Simultaneously,we proposed a criterion to evaluate whether a bimetal tube undergo spin composite forming.(2)This study clarified spinning method and designed the toolings for 304/Ti and 20#/304 bimetal tubes.In addition,the range of spinning process parameters for the bimetal tube of corresponding material was defined by referring geometry,bimetal tubes' structure and spinning forming characteristics.(3)Through numerical simulation,it was found that there was an instantaneous stress attenuating on the interface of two metals.The feed rate and spindle speed had little effect on the wall thickness variation of bimetallic tube.And the control of the base tube and the lining tube wall thickness could be achieved by adjusting the pressing amount.Contemporary,the results showed that the feed rate,spindle speed and pressing amount had great influence on the variation of wall thickness deviation.Furthermore,in forming process of subsequent passes,reducing the fluidity and deformation of the material was important to ensure the dimensional accuracy of bimetal tube.(4)The influence of forming parameters on the bonding performance was carried out.The results indicated that the bonding strength of bimetal tube was mainly affected by the pressing amount.Moreover,the multi-pass spin forming process could be divided into three stages: the fitting phase,the performance improvement phase and the performance reduction phase.The spinning bimetal tube with 3~4 passes had better bonding performance.And decreasing pressing amount with passes was also beneficial to the bonding performance.Furthermore,putting the brazing filler between the base tube and the lining tube could improve the bonding performance of bimetal tube furtherly.