Enabling sheet hydroforming to produce smaller radii on aerospace nickel alloys

Abstract

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.

A state of the art review of hydroforming technology

“…Subsequent operations, annealing or pressure intensifiers can help tighten up the radii after the forming operation, but as a general rule keeping radii at least 3 to 5 times larger than the material thickness is advisable whenever possible for high pressure hydroforming operations, [12] and 10 times larger for low pressure operations [4]. That said, more recent work has shown that in certain circumstances the edging technique [89] or a subsequent coining operation can produce radii as small as 2 times the material thickness in certain circumstances (explained in detail in "Advanced hydroforming techniques"section).…”

“…This technique, as described by Triform presses (an equipment vendor) is called edging and allows for extra material to stretch in from the flange on the upwards stroke and be pushed into the corner when the punch travels back down. Bell et al showed that a flange radius could be reduced significantly by using the edging process and provided an empirically derived equation for calculating flange radii [89]. Edging, unlike a coining operation, does not require extra tooling or an additional forming cycle but it is not quite as accurate or repeatable.…”

“…Anisotropy causes variation in material properties depending on orientation which is shown most frequently in the literature as mechanical property changes with regard to rolling direction. At the macro scale this can lead to typical values like a 5.5% difference in yield strength depending on orientation [89] which could impact forming and on the micro scale these differences are more pronounced. Other technical concerns include: extreme tribological conditions caused by high surface to volume ratios, achieving tolerances [102], inapplicability of available lubrication products, excessive forces on miniature dies, and handling concerns, [103].…”

On the thinning variations in hydrostatic forming of sheet metal

“…Hydrostatic forming for sheet metal has many advantages such as improving the ability to shape complex parts, increasing surface quality, and especially suitable for shaping lightweight and thin sheet materials [12][13][14]. Because of its superiority, there have been many studies on this technology over the years with different aspects of materials, temperatures, and die structures [15][16][17][18][19][20]. In hydrostatic forming process, the workpiece is remarkably thinned because of bulging phase under the action of a high-pressure liquid.…”

Experimental Modeling of Pressure in the Hydrostatic Formation of a Cylindrical Cup with Different Materials

“…The working principle of this technology is shown in Figure 1. Moreover, this technology can be suitable for the shaping of a wide variety of materials, from high deformability materials, such as carbon steel material, to low deformability materials, such as stainless steel or some alloys [1,[8][9][10][11][12]. There are many impressive studies on forming technology.…”