Incremental sheet forming of steel/polymer/steel sandwich composites

Abstract

Formable three- or multi-layer metal/polymer/metal sandwich sheets are interesting functional materials replacing pure metallic sheets in various applications due to the arbitrary tailoring of their mechanical properties and thicknesses delivering the application-related properties. Forming of such sandwiches is often more limited compared to mono-metallic sheets due to the load conveying mechanism through their thin skin sheets. To extend and improve the forming potential of the sandwich sheets, single point incremental forming (SPIF) was used for the first tests shaping conical profiles with variable and constant wall angles in addition to semi-spherical ones. The forming limits were identified in terms of the limiting wall angle, part height and the surface strains determined by digital image correlation. The results reveal that shaping of the sandwich composites sheets is possible and similar to monolithic metal sheets, but with earlier failing of more than 30%. Failure of the sandwich sheets by cracking and delamination as well as galling is expected. Additionally, the sine law used normally to describe the thickness at failure of SPIF was applied and verified. Besides, the fracture forming limit curve could be used to describe their forming limits. Applying two-stage SPIF could extend the forming potential compared to the single-stage SPIF of the same part angle.

Keywords

• Incremental sheet forming
• Sandwich composites
• Steel/polymer/steel
• Strain analysis
• Fracture forming limit curve
• Sine law