A computer-implemented method computes an unfolded part of a modeled bended 3D object in a 3D scene of a computer-aided design system. The method a) provides the 3D object; b) selects a fixed portion (FP) of the 3D object; c) selects a mobile portion (MP) of the 3D object; d) determines a 1D interface (INT) forming an intersection between the fixed portion (FP) and the mobile portion; e) computes a transformed portion resulting from a linear transformation of the mobile portion (MP) according to an drawing direction (DD); f) trims the transformed portion in the vicinity of the 1D interface (INT), thereby forming a trimmed transformed portion (TTP); g) creates a fillet (FI) between the 1D interface (INT) and the trimmed transformed portion (TTP); and h) defines the unfolded part as an union of the fixed portion (FP), the trimmed transformed portion (TTP) and the created fillet (FI).