Bending Limit Curves in Sheet Metal Bending Evaluation

Abstract

Bending and hemming process are used in automotive industries for assembling the car body panel.The main failure mechanism under bending loads is the intercrystalline fracture. This is due to the fact that the Forming Limit Curve (FLC) describes first occurrence of membrane instability and no material failure in consequence of an intercrystalline fracture at bending.The FLC fails to predict the formability in hemming processes since difference in failure mechanism. A new failure criterion, the so-called Bending Limit Curve (BLC) has been developed. In this work, the left hand side BLCs are experimentally determined for Advanced High Strength Steel grade DP1000, Stainless Steel grade SUS430 and Deep Drawing Steel grade SPCC having a thickness of 1.0 mm. The influence of various bending radii and level of pre-strain on the bending strains are investigated and discussed by using the Three Point Bending Test. Bendability of investigated materials are evaluated by using optical strain measurement system GOM-Aramis to determine maximal achievable bending strain on the specimens. The developed left hand side BLCs were found to be higher level than conventional FLCs. The bigger bending radius established lower bending limit strain. The higher bending strain was obtained from the higher pre strain level.

Bendability evaluation of sheet metals in three-point bending test by using acoustic emission features

“…The square shape workpiece (60 x 60 mm) with the thickness of 1.0 mm was prepared using shearing machine. The three-point bending tests according to VDA 238-100 (Saxenal et al, 2017;Panich, 2017) were conducted with varying punch plate radii (0.4, 1, and 2 mm) due to obtaining the sufficient difference of bendability levels ( Figure 3). The testing apparatus was set up on a 25 tons universal testing machine.…”

“…The classical material properties commonly used to assess the deep-drawing process can be used to describe the material failure in bending process although they have different failure mechanisms. However, the Bending Limit Curve (BLC) based on the assessment of deformation changes at the bending edge, is often used as mentioned in Panich (2017) and Saxenal et al (2017).…”