Multi-directional Dieless Incremental Flanging Of Sheet Metals

As the basic process of sheet metal forming,flanging is widely used in production of thin-walled tubes. The characteristics of the traditional flanging process is difficult to adapt to the rapid new product development with the improvement of people's living standard and the increase of product update speed, so we need a fast and efficient technology in production.This paper describes a flexible and versatile flanging method based on the single-point incremental sheet forming, hole-flanging and flanging was carried out utilizing modified tools, The deformation mechanism and various factors that influence the forming quality were analyzed, The main conclusions are as follows:(1) Physical experiment and numerical simulation show that Various forward/backward stretch and shrink flanging as well as hole-flanging with arbitrary shape can be executed by this flexible method without dedicated die. Thus, a more complete forming chain based on ISF can be established, which saves considerable time and cost in the production of required dies for flanging via conventional press working.(2) Compared with traditional ISF, the different forces and deformation modes during dieless incremental flanging can lead to special defect types, including buckling and warpage of plates, depending on the geometrical features of workpiece and tool, processing parameters, etc. Warpage presents a tilting flange wall and large transition radius. This occurs in the flanging of plates with relatively smaller structural stiffness, example, planar plates with free lateral sides and less surrounding constraint or convex bending lines. Warpage in hole flanging is lower, but instability phenomena such as buckling might occur at the onset of the flanged lips.(3) The inclination angles of the tool shoulders have significant influence on the warpage and buckling. Meanwhile it only slightly affects the thickness distribution of the flange. If the ?-value is small, the pressure that the tool exerts on the plate rim during pre-flanging stage is large. This might cause buckling at the lip. The analytical expression deduced from Euler's formula of instability indicates that the minimum critical ?-value increases with increasing friction, yield stress s, distance l between the bending line and clamping position. It decreases with increasing Young's modulus E and thickness t. If the ?-value is large, warpage of the plate is prone to occur. The recommended ?-value for incremental round-hole-flanging is 20–30?. As for sheet flanging with lower structure stiffness, the suitable ?-value is smaller.(4) In addition to normal factors such as tool path, feeding rate, and material properties, etc., the flanging type, tool geometry, and fixing state of the blank should also be comprehensively considered in the process planning of dieless incremental flanging. Appropriate modification of tool geometry can be utilized to control specific deformation of plates, which will minimize the occurrence of forming defects.