Development of a flexible incremental forming process to manufacture asymmetric shafts

Abstract

This thesis is concerned with a new flexible incremental forging process to manufacture shafts having asymmetry or odd number of symmetry in the cross-section. Shafts having asymmetry or odd number of symmetry in the cross-section can not be simply manufactured by conventional incremental radial forging. In order to manufacture such shafts, the new concept of incremental forging with one punch and a flexible fixture is developed by suggesting a flexible fixture, instead of two opposed punches used in radial forging, so that the flexible fixture only supports the workpiece while the punch is moving during forming. A new flexible fixture is designed to support the workpieces having a variety of shapes as flexibly as possible. The flexible fixture is mainly composed of a half spherical rubber diaphragm filled with steel shots and an internal support. During incremental forging, the workpiece is supported by the clustered shots being subjected to the atmospheric pressure (due to the vacuum) and the internal support together. Since the height of the internal support and the shape of the half spherical rubber diaphragm are adjustable to a specific workpiece, the fixture supports the incremental forming load of the punch in the flexible manner. The flexible fixture can have different shapes in supporting the workpiece, and the shape of the support influences the stress distribution in the deformation zone. In order to have a better understanding of this phenomenon, support parameters which are basically normalized supporting depth and normalized projection area are defined. The effects of these two parameters are examined by performing the FEM analysis. It is seen that the normalized projection area does not have any significant effect on the stress distribution as long as the normalized projection area is larger than 2.25. The proposed manufacturing concept of incremental forging includes the use of one punch and a flexible fixture. Therefore, the approximate forming...