Calculation of bend deduction in sheet metal air bending

Abstract Accurate prediction of flat pattern lengths is essential for achieving high dimensional precision in sheet metal air bending. Conventional approaches, such as the DIN 6935-based calculation implemented in CAD systems, often result in significant deviations due to their limited consideration of material behavior, bending angle, and tool geometry. This study presents a universal methodology for determining bend deduction based on controlled experimentation, dedicated measurement technology and systematic validation. A dedicated measurement fixture was developed and evaluated through Type-1 and Type-2 measurement system analyses to ensure reliable leg-length measurement over different bend angles. As a proof-of-concept application, bend deduction values were determined for EN AW-6082 T6 with a sheet thickness of 1.0 mm across bend angles from 45° to 135°. The experimentally derived values were transferred into a bend deduction table (BDT) by interpolation and implemented for CAD-based flat-pattern calculation. Validation against DIN 6935 predictions demonstrates that the proposed BDT significantly improves flat-pattern length accuracy, reducing deviations by up to 0.38 mm. The results demonstrate that an experimentally calibrated BDT can improve flat-pattern accuracy without requiring finite element simulations. The methodology can be transferred to other materials, sheet thicknesses, and bend radii through empirical calibration and is therefore suitable for broad industrial application.