Enabling sheet hydroforming to produce smaller radii on aerospace nickel alloys

This paper presents the first academic study of a hydroforming process known as edging. An edging process allows a smaller radius to be produced with a lower pressure than a standard sheet hydroforming process and is currently developed by trial and error that relies heavily on operator experience. This paper reports the first systematic investigation of the edging process that concludes in a new analytical model which can be used to enable the design of edging processes. It was found that in each of the three aerospace nickel alloys tested, the edging technique was effective in sharpening the flange radius from 10 mm to 4 mm or from 6 mm to 2 mm in thicknesses of 2.1 mm and 1.2 mm respectively. This radius is equivalent to between 1.5 and 1.8 times the material thickness (1.5 t to 1.8 t). These results were achieved by using edging heights of between 2.5 to 5 mm (2.5 t to 3 t). At the limits of successful edging operations, (under 2 t) three different kinds of phenomena were observed: crushing of the top of the component, radii which were pushed inwards, and the generation of an underside lip which protruded from the bottom of the samples. This paper discusses the benefits of hydroforming with an edging operation, explores the limitations of the edging process, derives an equation which can be used to estimate the sharpness of an edged radius and finally defines a model which enables the design of an edging operation. The work reported here is particularly relevant to aerospace applications because it will enable lighter components to be formed with lower pressures with nickel based superalloys.