A mathematical model for bend-allowance calculation in automated sheet-metal bending

Sheet-metal components are used extensively in the aerospace and the electronic industry, where high precision is an essential requirements for the final products. In precision components, the calculation of the bend allowance is important in arriving at the final dimensions of the developed length of the sheet metal. Bend allowance is defined as the length of the unstretched fiber in the bent portion of the sheet. Any inaccuracy in calculating the bend-allowance parameter during bending may result in increasing the inaccuracy in the final developed length of the sheet. This causes the blank size to be incorrect, which in turn causes the location of bend lines, slots, and holes to be inaccurate. This may cause mismatch in the final assembly also. In this paper an attempt has been made to first review the current industrial practice for the calculation of bend allowance. The current empirical methods used to calculate the bend-allowance parameter are examined and the drawbacks associated with them are identified. The highlight of this paper is on a mathematical model which has been developed to calculate the bend-allowance parameter accurately by assuming plane-strain deformation and a rigid-plastic material, considering thinning effects. The effects of temperature and friction are neglected. The bend-allowance parameter is calculated on the basis of material properties such as the yield stress and the strain-hardening exponent, and the tool geometry. The model has been tested with available data in the literature to assess its accuracy