Hemming process with counteraction force to prevent creepage

• A novel hemming process incorporating a counteraction force, in order to prevent the creepage phenomenon during the hemming process, is proposed.
• A sharp radius hem is achieved due to prevention of the creepage.
• The mechanics of creepage are analyzed, and provide fundamental of further hemming process development.
• The Finite Element Method is utilized to study mechanics of creepage, as well as to optimize the tooling geometry.

Creepage, a typical phenomenon in the hemming process, can be defined as undesired roll-in of the panel at the bending line. Creepage also reduces the final panel width and makes the hemming radius larger. In this study, experimental observations are reported, and a finite element model, based on the LS-DYNA® two dimensional plane strain solid formulation, is utilized to study the mechanics of how the hem flange bends and folds during the hemming process. A novel hemming process incorporating a counteraction force is proposed in order to prevent the creepage phenomenon during the hemming process. An experimental hemming tool was designed according to this concept, and optimization of the tooling geometry was carried out utilizing the finite element model. An experimental study was conducted to confirm that the new hemming process can prevent creep be employed to help retain a sharp radius during flanging operation.