There are challenges in the conventional sheet metal folding for mass production; those are summarized by high tooling and energy costs and lack of dimensional accuracy. High cost per product is due to the need of specific manufacturing tools and equipment like dies and molds that are shape dedicated to certain product range and specifications. Lack of high accuracy is resulted from involved forming process, machine structure and springback effects in workpiece.
Origami-based Sheet Metal (OSM) folding fabrication process has been utilized to overcome these challenges. This novel approach is an extension of the origami technique to sheet metal folding process and it requires creating numerous features along the bend line, called Material Discontinuities (MD). MD are fabricated by removal of material completely or partially through thickness direction of sheet metal along the bend line using laser cutting process or progressive stamping. MD can also be created by stamping where no material removal is present, rather stamping creates deformed pattern along the bend line to guide the folding. MD controls the material deformation during bending and results in reduced bending force, minimal tooling and machinery requirements. Despite the promising potential of OSM, there is little understating of the effect of the selected MD shape and geometry on the final workpiece, specifically this is of interest when comparing the energy and cost allocations for OSM with a well-establish process for sheet metal such as stamping.
In this work, the effect of several types of MD on sheet metal folding process is investigated using Finite Element Analysis (FEA). In particular, wiping die bending of aluminum sheet with different MD shapes and geometries along the bend line is compared to the traditional sheet bending of final part in terms of stress distribution along the bending line and required bending force. FE simulations are carried out using structural and thermo-mechanical FE solver Code_Aster. Aluminum 2036-T4 is chosen as sheet metal material. Constitutive model in the simulation is J2 flow theory plasticity with isotropic hardening. The FEA results are validated by comparing it to the available empirical models in terms of bending forces.
This study finds that the OSM technique reduced the required bending force significantly, which has important significance in energy and cost reduction. It also ranked the MD in terms of the required force to bend the same sheet metal type and thickness for further future investigation. However, the MD leads to localized high stress regions along the bending line, which may affect load-bearing capability of the final part. In addition, it may lead to cracks or fractures of sheet metal part in the high stress region, especially if MD are densely arranged along the bend line.
