Optimized Tooling Design Algorithm for Sheet Metal Forming over Reconfigurable Compliant Tooling

Abstract

FE Robustness: comparing sheet metal forming variation and finite element models AIP Conf. Proc. 712, 958 (2004); Abstract. New forming technologies based on compliant "discrete-die" reconfigurable tooling are available for production of sheet metal parts, but there is a need for a formalism that can accurately predict the three-dimensional shape of the required tooling, a priori. An optimized tooling design algorithm has been developed based on a methodology that uncouples the effects due to springback and those due to the compliance of the polymeric layer. A springback compensated die shape is initially predicted for the case of stretch forming over smooth rigid dies based on an iterative approach using the finite element method. The tooling design algorithm is based on an inverse springback approach that uses the elastic-plastic stress state prior to unloading to elastically deform the sheet in a direction opposite to springback. A procedure has been developed to improve the convergence behavior of the inverse springback approach utilizing an interpolation scheme. The interpolation scheme uses prior iterations to predict the desired die shape by fitting spatially varying quadratic relationships between the tool shape and the part shape error histories. The optimized tooling design algorithm is extended to compliant dies by developing a method that corrects the die shape for polymer through the thickness compression. The algorithm is applied to stretch forming of large-scale airframe skin parts commonly found in aerospace structures. Two shapes are investigated, a 90-inch radius cylindrical cap and a 90inch radius spherical cap.

Magnetic smart material application to adaptive x-ray optics

“…The amount of springback is highly coupled with the stress distribution in the formed part prior to unloading, the applied boundary condition and material deformation behavior. This problem can be corrected by adjusting the tooling shape to the appropriate shape, i.e., the "springforward" method 12,13,14,15,16 , and/or using active process control of external forces during the loading stage 17,18,19 .…”

Numerical simulation of deformation in multi-point sandwich forming

“…Using finite element analysis, Boyce and Anagnostou investigated the ability of a polymer pad to smooth out the local pressure and predicted the springback of an unloaded workpiece. Through experiment and simulation, it was discovered that the key variables in dimple suppression by polymeric pad were thickness and compressive modulus [4,5].…”

“…This type of tooling is expensive to manufacture and is uneconomic for small batch quantities. For this reason, some flexible reconfigurable tool designs have been suggested such as the discrete die tool [1,2], the reconfigurable stretch forming tool [3][4][5] and rubber pad tool [6,7]. There tool design can be used to form a number of different part shapes and can be used economically for small batch quantity production.…”

Numerical simulation on the local stress and local deformation in multi-point stretch forming process

“…After the 1980s, the concept of reconfigurable tooling for flexible fabrication was proposed by Hardt and Gossard [6]. In the previous of Nakajima and the others, a discrete die mechanical design was explored, which can rapidly fabricate sheet metal parts [5][6][7][8][9][10][11][12][13][14][15][16][17]. A shape control algorithm was proposed which based on the concept of the deformation transfer function, and it can be used to compensate for springback and other production variables [8,17].…”

“…MIT, Grumman Aerospace, and Cyril Bath Company developed a reconfigurable stretch forming die, which measures 1.83×1.20 m (6×4 ft) and consists of 2,688 pins, with 42 pins along one side and 64 along the other [13]. A survey analysis revealed that a single reconfigurable die could replace hundreds of fixed tools that are currently in use [15]. In MPF, plenty of studies and progresses were made in recent years [18][19][20][21][22][23][24].…”