A MATHEMATICAL-MODEL FOR BEND-ALLOWANCE CALCULATION IN AUTOMATED SHEET-METAL BENDING

Sheet-metal components are used extensively in the aerospace and the e lectronic industry, where high precision is an essential requirement f or the final products. In precision components, the calculation of the bend allowance is important,in arriving at the final dimensions of th e developed length of the sheet metal. Bend allowance is defined as th e length of the unstretched fiber in the bent portion of the sheet. An y inaccuracy in calculating the bend-allowance parameter during bendin g may result in increasing the inaccuracy in the final developed lengt h of the sheet. This causes the blank size to be incorrect, which in t urn causes the location of bend lines, slots, and holes to be inaccura te. This may cause mismatch in the final assembly also. In this paper an attempt has been made to first review the current industrial practi ce for the calculation of bend allowance. The current empirical method s used to calculate the bend-allowance parameter are examined and the drawbacks associated with them are identified. The highlight of this p aper is on a mathematical model which has been developed to calculate the bend-allowance parameter accurately by assuming plane-strain defor mation 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 t he yield stress and the strain-hardening exponent, and the tool geomet ry. The model has been tested with available data in the literature to assess its accuracy.