Research On Improving The Forming Ability Of The Sheet Metal Incremental Forming

CNC incremental forming is a new flexible machining method of the sheet metal forming, the target parts could be obtained by pressing the metal sheet layer by layer through the forming tool movement controlled by the computer program. The formability and forming precision are higher than those of the traditional forming method, complex surface modeling of local area which can not be processed by conventional means can be formed in incremental forming, and it has high flexibility.These advantages are adapted to the current market demands for varieties of parts.However, the thickness change of incremental forming follows the cosines law of costt?0?(28), when the wall angle of part is larger, sheet thickness reduction is larger than the largest thickness reduction of the sheet forming limit angle, parts will appear rupture, for the straight wall parts machining, it can't be completed by incremental forming. These limit the forming ability of sheet incremental forming.Meanwhile, the final deformation of incremental forming is accumulated by several small deformation, forming tool presses the metal sheet layer by layer, compared with the traditional stamping process, the forming time is longer and the processing efficiency is lower. Therefore, in order to improve the forming limit and efficiency of sheet metal incremental forming, incremental forming method of local heating sheet outside machining position and incremental forming combined with bulge forming method are presented.By studying the strain change of the deformation region and unprocessed region of the fixed wall angle parts, the forming limit of the changed wall angle parts of local heating sheet incremental forming, it is concluded that incremental forming is a small local deformation, even if the sheet unprocessed region is heated to 250?, the tensile strength and yield strength of aluminum sheet are reduced to 31 MPa and 24 MPa, and the elongation increases to 75%, under the action of forming force, the sheet unprocessed region only generates the flow trend to the deformation region without the occurrence of plastic deformation. The incremental forming method of local heating sheet outside machining position has not played a positive role in improving the forming ability of sheet incremental forming.Comparative analysis of the strain change and the forming limit angle ofincremental forming combined with different bulge preforming parts and the incremental forming parts, the conclusions are obtained: spherical part bulge preforming combined with incremental forming, the position of maximum thickness reduction of spherical part is in the range of the local incremental forming region of the compound forming process, and the directions of the two maximum thickness reduction are opposite, the forming ability of sheet incremental forming can be improved significantly; straight wall part bulge preforming combined with incremental forming, the forming limit of sheet incremental forming and the machining efficiency of parts have been improved, with the increase of the preforming height of the straight wall parts, the increase degree of the sheet thickness of “thinning band” in incremental forming is decreased, therefore, the increase degree of the forming limit of sheet incremental forming will be decreased.The forming method of bulge preforming combined with incremental forming not only can greatly improve the incremental forming limit angle but also can improve the forming efficiency.