Deformation Behavior And Affecting Factors Of Sheet Metals During Incremental Hole-Flanging With Inclined Axis

As a common process in sheet metal forming,hole-flanging forming is widely used in the production of thin-walled parts.In the traditional sheet metal hole-flanging methods,the conventional forming method is stamping.It can obtain higher forming efficiency,forming precision and material utilizing rate,so it suitable for mass production.But the stamping mould design and manufacturing cycle is long,and the processing and maintenance costs are also very high.In particular,the mould needs to be replaced when the product changes slightly and lack of flexibility.With the improvement of people's living standard,products update faster and faster.Hole-flanging process based on the traditional stamping method has been difficult to adapt to the development of new products and user customization requirements.In practice,it is urgent to develop a fast and efficient hole-flanging technology.As a kind of flexible forming method with large flexibility,hole-flanging by incremental sheet forming has some practical applications at present.However,the existing technology is mainly aimed at flanging the axial symmetry hole and its generatrices length along the circumferential direction are equal.Its deformation is relatively simple.For the more general case,namely,the non-axisymmetric hole-flanging with inclined axis,we still lack of in-depth understanding.It is necessary to carry out related research in order to master the deformation mechanism and law,so as to reduce the hole-flanging defect and ensure the forming quality.In this paper,the deformation behavior and its influence factors of sheet metals during incremental hole-flanging with inclined axis were studied.Two different processing paths were presented: continuous forming path and intermittent forming path.And the forming results were compared from the aspects of stress and strain distribution,thickness distribution and forming force.At last,we analyzed the influence of spiral trajectory pitch ?Z,tool diameter d and oblique angle ? on the shape and size precision during incremental hole-flanging with inclined axis by response surface method.Main conclusions are as follows:(1)Incremental hole-flanging with inclined axis has the deformation behaviour of bilateral symmetry and up-down asymmetry.Under the same processing conditions,with the increasing of the inclination angle for axial hole-flanging,the neck of the flanging-hole is thinner and thinner along the circumferential direction.Along the circumferential direction of 0~90°,thickness reduction speed is relatively slow,but when more than 90°,thickness reduction speed is faster and faster.And the greater the inclination angle is,the faster the thickness reduction speed is.(2)By analyzing the stress and strain,thickness distribution and forming force,it can be found that the continuous forming path process can get more uniform stress and deformation,the forming quality is better than intermittent forming path.(3)The shape and size of the precut hole and the relative position of the mould have a great influence on the results of incremental hole-flanging with inclined axis.The size and position of the precut hole can be calculated according to the geometric relationship dimension of the radial development of the flanging hole.The initial shape can be assumed to be elliptical,then the optimization is carried out by numerical simulation.(4)Because of the non-axisymmetric deformation of the axial flanging hole on the inclined plate,the springback of each position is different.The larger the folding angle is,the greater the springback is,also the dimension deviation of the flanging hole is larger.The spiral trajectory pitch ?Z,tool diameter d and inclination angle ? are important factors affecting on the maximum springback angle ??.By response surface analysis,the final results show that the magnitude of their influence on the maximum springback is inclination angle ? >tool diameter d>spiral trajectory pitch ?Z.