A FEATURE-BASED FLAT PATTERN DEVELOPMENT SYSTEM FOR SHEET-METAL PARTS

Sheet metal fabrication requires flat pattern development to determine blank shapes and sizes. For a 2D design, bend allowances resulting from metal stretching at bends must be accommodated. In addition to bend allowances, flat patterning for a 3D design involves unfolding of calls and mapping of features such as slots, cutouts, etc., onto unfolded walls. Manual determination of flat patterns is time-consuming and error-prone, especially for intricate parts. Integrated CAD/CAM packages for sheet metalworking that incorporate flat patterning modules can significantly shorten the design cycle. However, these packages are often supported on expensive systems and only concentrate on geometry processing, overlooking design and production rules that can cause fabrication failures. We developed a PC-based flat patterning system that runs on AutoCAD. The system includes a high-level design module that allows parametric design and modification of parts using standard features. Unfolding and folding are performed in a progressive manner, i.e., bend-by-bend. As design and flat patterning proceed, possible fabrication failures are checked against using geometric reasoning. After unfolding, mould lines and bend lines are displayed for manual dimensioning. The flat pattern data can be generated in the formats of DXF and IGES for integration with software that perform other operations such as nesting, cutting and bending.