Experimental investigation of limit strains in single point incremental forming of St14-AA3105 bi-layer sheets

Bi-layer metallic sheets exhibit advantageous mechanical properties for automotive and aerospace applications, including enhanced sound and vibration damping, improved wear and corrosion resistance, and increased formability. However, the formability of laminated sheets is often limited by plastic instability and local necking. In this study, the limit strains of a St14-AA3105 laminated sheet were experimentally investigated using the single-point incremental forming (SPIF) process, and the effects of step size, tool diameter, feed rate, and spindle speed on the limit strains of the bi-layer sheet were examined. The results show that decreasing step size, tool diameter, and feed rate, as well as increasing spindle speed, lead to an increase in the limit strains of the laminated sheet, with step size exerting the strongest effect (up to 65 %), followed by spindle speed (up to 28 %), tool diameter (up to 12 %), and feed rate (up to 7 %). In addition, the forming limit diagram (FLD) of the St14-AA3105 sheet under conventional stamping conditions was theoretically predicted using the Marciniak-Kuczyński (M-K) model. A comparison shows that the limit strains obtained in the SPIF process are consistently higher than those predicted for conventional stamping.