Springback behavior of a metal/polymer laminate in incremental sheet forming: stress/strain relaxation perspective

Metal/polymer laminates are important lightweight construction composite materials. In search of economical alternatives of expensive traditional processes, feasibility of Single Point Incremental Forming (SPIF) to process laminates is being analyzed nowadays. Poor accuracy is one of the major drawbacks of this innovative process. Therefore, the present study aims at investigating the accuracy and identifying the mechanism controlling the springback in SPIF of the laminates. The High-Density Polyethylene (HDPE) sheets of varying thickness are adhesively bonded to Al–1060H24 sheet to build metal/polymer laminates. These laminates and the constituting monolithic sheets are subjected to SPIF and relaxation tests to identify the relevant springback mechanism (s). The results reveal that the magnitude of relaxation modulus of the laminate interestingly decreases as the polymer-to-metal thickness ratio increases. As a result, agreeing with the mechanics intuition, stress relaxation increases but amazingly strain relaxation decreases due to metal/polymer intactness thereby resulting in reduced springback in the formed components. The monolithic polymer sheet on the contrary experiences an increase in the relaxation modulus upon increasing thickness resulting in decrement in both the stress and strain relaxations thereby causing reduction in the springback. From analysis of the property–error correlations, strain relaxation is identified as the main springback controlling property in the laminates. On the other hand, both the stress and strain relaxations and modulus are detected as the springback controlling properties in polymers. The laminates are witnessed to experience a way lower profile error than the polymer attributing to lower strain relaxation. `