Hemming with Pre-Bent Inner Sheet for Joining Ultra-High Strength Steel Sheets of Automobile Parts

Abstract

In order to join two ultra-high strength steel sheets with low ductility for automobile parts, a joining process by hemming with a pre-bent inner sheet was developed. In this joining, the pre-bent inner sheet instead of the conventional flat inner sheet was used to relax the deformation concentration of the outer sheet. Although 780 MPa steel sheets were joined without the pre-bent inner sheet, a fracture in the outer sheet occurred in joining the 980 MPa sheets due to the low ductility of the sheets. The 980 MPa and 1180 MPa sheets were successfully joined by hemming with the pre-bent inner sheet. In this process, the deformation of the upper sheet was relaxed by contacting with the inner sheet, and then the strain on the outer surface reduced. Although softening around a weld nugget occurred by heating in the conventional welded joint, work-hardening occurred in the hemmed joint. The joint strength was investigated and then the peel strength of the hemmed sheets was about a half of the welded one. It was found that the hemming process with the pre-bent inner sheet was effective for joining ultra-high strength steel sheets with low ductility.

Improving Press Bending Production Quality through Finite Element Simulation: Integration CAD and CAE Approach

“…The plate is bent to produce an angle according to the work design requirements using a punch as a press tool and a die as a holding and shaping tool (Boljanovic, 2014; Jain and Sharma, 2016). Sheet metal bending is classified depending on the bending shape of the plate, which includes v-bending, r-bending, u-bending, and hemming (Abe et al, 2020;Hai et al, 2020). In a study by (Hai et al, 2020), the v-bending shape is the most often employed plate formation in bending.…”

Joining sheets made from dissimilar materials by hole hemming

“…In order to prevent fracture on the outside surface of the bend zone, a large bend radius for the outer sheet along with a pre-bent inner sheet was employed in the final hemming stage. 14 Despite the capability of the joining of dissimilar materials, the hemming process has attracted less attention than the other joining processes by plastic deformation that goes back to the fact that it can be only applied to sheet edges.…”

“…In order to prevent fracture on the outside surface of the bend zone, a large bend radius for the outer sheet along with a pre-bent inner sheet was employed in the final hemming stage. 14 Despite the capability of the joining of dissimilar materials, the hemming process has attracted less attention than the other joining processes by plastic deformation that goes back to the fact that it can be only applied to sheet edges. Under these circumstances, the objective of this article is to develop a new hemming-based joining process, called 'hole hemming', which enables to joining of dissimilar materials with different mechanical properties, and without limitation in the joint position.…”