Experimental Investigation of the Thickness Distribution in a Three-Layer Aluminum-Polyethylene Sheet During Two-Point Incremental Forming Using Central Composite Design

Abstract

The two-point incremental forming (TPIF) process is an advanced and flexible method for manufacturing complex metal parts without the need for dedicated molds. In this study, the thickness distribution of three-layer aluminum–polyethylene (Al–PE–Al) sheets formed using TPIF was experimentally investigated. The sheets, measuring 180 × 180 mm and consisting of 1 mm aluminum 1050 layers and a 1 mm HDPE core, were formed into truncated pyramid geometries on a CNC machine. Using a central composite design methodology, input parameters including tool rotation speed, feed rate, and vertical step depth were varied, with thickness distribution measured as the output parameter. After forming, samples were cut using waterjet cutting to prevent thermal damage to the polymer layer. Thickness at various points along a central path was precisely measured using a vision measuring machine (VMM). Results showed that the top aluminum layer experienced greater thickness reduction than the bottom layer (23.30–39.75% vs. 12.71–32.75%) due to direct tool contact and higher local stresses. The bottom layer, protected by the polymer core, exhibited less thinning. Overall, the three-layer sheet (26.05–44.83%) showed greater thickness reduction than either aluminum layer individually, reflecting strain redistribution through the viscoelastic HDPE core and interaction between the polymer and aluminum layers. These findings emphasize non-uniform stress distribution and the importance of process parameter optimization for controlling layer-specific deformation and overall thickness uniformity.