Numerical simulation of a pyramid steel sheet formed by single point incremental forming using solid-shell finite elements

in Key Engineering Materials [=KEM] (2013)

Single Point Incremental Forming (SPIF) is an interesting manufacturing process due to its dieless nature and its increased formability compared to conventional forming processes. Nevertheless, the ... [more ▼]

Single Point Incremental Forming (SPIF) is an interesting manufacturing process due to its dieless nature and its increased formability compared to conventional forming processes. Nevertheless, the process suffers from large geometric deviations when compared to the original CAD profile. One particular example arises when analyzing a truncated two-slope pyramid. In this paper, a finite element simulation of this geometry is carried out using a newly implemented solid-shell element, which is based on the Enhanced Assumed Strain (EAS) and the Assumed Natural Strain (ANS) techniques. The model predicts the shape of the pyramid very well, correctly representing the springback and the through thickness shear (TTS). Besides, the effects of the finite element mesh refinement, the EAS and ANS techniques on the numerical prediction are presented. It is shown that the EAS modes included in the model have a significant influence on the accuracy of the results. [less ▲]

Towards fracture prediction in single point incremental forming

in Key Engineering Materials [=KEM] (2013), 554-557

The stress state in metal forming processes usually implies low values of triaxiality. It is well known that damage models based only on triaxiality fails to capture the damage behavior properly, and ... [more ▼]

The stress state in metal forming processes usually implies low values of triaxiality. It is well known that damage models based only on triaxiality fails to capture the damage behavior properly, and recent articles have stressed the effect of the Lode parameter in describing damage. Moreover, in some process like incremental forming, the through thickness shear could dominate the rupture mechanism making the description, using solely the triaxiality, inaccurate. In this paper, a preliminary study of the stress state is carried over a near-to-failure single point incremental forming (SPIF) formed cone, through finite elements simulations using a newly developed solid-shell element. The results provide a basis for further studies into damage development in SPIF. [less ▲]

Study of the geometrical inaccuracy on a SPIF two-slope pyramid by finite element simulations

in International Journal of Solids and Structures (2012)

Single Point Incremental Forming (SPIF) is a recent manufacturing process which can give a symmetrical or asymmetrical shape to an undeformed metal sheet by using a relative small tool. In this article, a ... [more ▼]

Single Point Incremental Forming (SPIF) is a recent manufacturing process which can give a symmetrical or asymmetrical shape to an undeformed metal sheet by using a relative small tool. In this article, a two-slope SPIF pyramid with two different depths, which suffers from large geometric deviations when comparing the intended and final shapes, is studied. The article goal is to detect if these divergences are due to new plastic strain while forming the second angle pyramid by using finite elements simulations. To validate the numerical results, both the shape and the forces are compared with experimental measurements. Then, an analysis of the material state is carried out taking the equivalent plastic strain, von Mises effective stress and yield stress distribution through a cut in the mesh. It is noticed that there is plastic deformation in the center of the pyramid, far from the tool neighbourhood. Also, high values of stresses are observed under the yield stress in other parts of the sheet. As a strong bending behaviour plus membrane tension is found in some sheet elements, these elastic stresses are due to a bending action of the tool. It is concluded that the main shape deviations come from elastic strains due to structural elastic bending, plus a minor contribution of localized springback, as no plastic deformation is observed in the angle change zone. Future developments in toolpath designs should eventually consider these elastic strains in order to achieve the intended geometry. [less ▲]