Numerical Analysis of the Multi-Point Stretch Forming Process of Aircraft Outer Skin Part

Abstract

As a flexible manufacturing technique, Multi-point stretch forming (MPSF) is a suitable method for forming aircraft outer skin part. The traditional solid stretching die is replaced by the discrete multi-point die (MPSD), and the sheet metal is stretch-formed over the MPSD generated by serial adjusting mode or parallel adjusting mode. The MPSF can be used to form the parts of different shape and reduce the cost and leading time of stretching die fabrication for aircraft outer skin part. A series of numerical simulations on typical MPSF processes of aircraft outer skin part were carried out. The thickness of elastic cushion and free length are important factors to influence on the stretch forming results of stretch-formed parts. The numerical simulation results show that the thicker the elastic cushion is, the more valid the dimple will be suppressed .The longer the free length is, the easier the wrinkle will be brought.

Component specific elastic cushion design to enhance the accuracy with the usage of reconfigurable tools in stretch forming

“…It is well known from earlier studies 15,16,18 that higher cushion thickness results in less waviness in the thickness strain, but increases the shape error. Therefore, the thickness of cushion (t c ) is selected (at which the thickness strain distribution and accuracy are reasonably good) by performing FEA using different thicknesses.…”

“…Possibility of wrinkle formation is high with the longer transition length. 16 The global shape error (i.e. deviation between ideal and formed profiles after unloading) of components decreased either with the decrease in the cushion thickness (due to lower reaction moments at the clamping edges leading to less elastic recovery) 12,15,16,18 or an increase in the pin head radius.…”

“…16 The global shape error (i.e. deviation between ideal and formed profiles after unloading) of components decreased either with the decrease in the cushion thickness (due to lower reaction moments at the clamping edges leading to less elastic recovery) 12,15,16,18 or an increase in the pin head radius. 17 However, usage of a larger pin head radius restricts the range of curvatures of the components to be formed.…”

“…17 However, usage of a larger pin head radius restricts the range of curvatures of the components to be formed. 17 All the above studies [15][16][17][18] carried out analysis (FEA) with the cushion of constant thickness.…”

“…Comprehensive literature review presented above indicates that cushion deformation plays a prominent role in enhancing the shape accuracy (quantified using the local and global shape error) of the MPSF sheet metal components. Majority of attempts [15][16][17][18][19] in the stretch forming with reconfigurable tooling used the cushion of constant thickness. The partial conformability between cushion and pin head surfaces resulted in non-uniform deformation in the cushion, thereby increasing the height of dimples on the component.…”