Manufacture of vertical walls with asymmetric incremental sheet forming

Abstract

Single point incremental forming (SPIF) is a dieless sheet metal forming technique that can manufacture customised sheet metal components in a cost-effective manner. However, the process is still in the developmental phase and hasn't been utilised industrially due to low geometrical accuracy, fracture at high wall angles and long cycle times. The goals of this research are to study the feasibility of the already existent strategies to eliminate geometrical errors and enhance formability and to, introduce a methodology to successfully generate vertical walls with the least geometrical errors and thickness variation within the manufactured component.

The impact of friction on sheet interface and formability is reported by recording the temperature obtained by increasing the tool rotation speed and feed rate. A flat tool is used in the study and an upper limit of the tool rotation speed is reported. The limit is much lower than the hemispherical tool reported in the literature and two heat generation zones is the justification. High tool rotation speed and feed rate are found to reduce the geometrical errors but still are unacceptable.

Multi-stage strategies such as the conventional downward, DDDU and IO-OI are implemented to manufacture a C-channel designed to support a plane fuselage for vibration testing. Tunnel strategy is also employed. Vertical walls are only conceivable using a conventional downward strategy and a series of steps followed for the toolpath development are reported in the form of an algorithm. The results show that the developed component is affected by severe geometrical inaccuracies and extreme thickness variation. Cost analysis reveal high costs associated with multi-stage forming in the design stage.

Finally, it is concluded that cost-effective and industrially acceptable flat base geometries are inconceivable through SPIF. The apparatus of Two Point Incremental Forming (TPIF) is modified and a new tool path strategy is developed to manufacture the vertical walls. The results show that the novel strategy is capable of manufacturing vertical walls with much lower thickness variation and geometrical errors. The developed method is cost-effective and easy to implement but requires a die.