On the comparison of formability of roll-bonded steel-Cu composite sheet metal in incremental forming and stamping processes

The laminates of dissimilar metals are roll bonded to engineer composite in order to satisfy specific industrial needs. In the present study, the steel-Cu roll-bonded composite sheet is annealed to reduce the hardening effects and subjected to various characterization tests including formability tests in pressing (stamping) and incremental forming (single-point incremental forming (SPIF)). The hole drill tests show that the magnitude of residual stresses reduces from −40 to −1 MPa as the temperature increases from 0 to 700 °C. Besides the stresses, annealing is observed to affect the interfacial microstructure of laminates. The formation of an intermetallic Cu80Fe20 is detected through electron-dispersive spectroscope (EDS) analysis. However, the thickness of its layer is measured to be too small (i.e., 5 μm) to influence the mechanical properties/formability of the composite sheet, clarifying that any variation in the composite properties, if occurs due to annealing, would be a sole effect of corresponding change in the stress magnitude. Further, the formability in both of SPIF and stamping is found to increase as the annealing temperature increases. Comparing the formability in the two processes, the minimum increase in the formability offered by SPIF is recorded to be 923 %, a way greater than that reported for the monolithic sheets in the literature. This mega difference between the formability of the two processes, as per microscopic observations, is attributed to a fact that the formability of steel-Cu composite sheet in stamping is limited by delamination and coalescence of voids whereas these failure processes do not visibly appear in SPIF of the said sheet. These findings lead to a conclusion that SPIF can be a promising alternative of stamping to produce roll-bonded composite sheet components.