Extrusion, channel, and profile bending: a review

The use of extrusions for stiff and lightweight design is widespread. Whils t many applications can be realised with straight extrusions, some applicat ions demand the use of bent extrusions. By introducing the use of bent extr usions into automotive applications, the demands for higher accuracy as wel l as highly flexible methods were increased. This review gives a systematic overview about the existing processes for the bending of extrusions in sma ll scale (e.g. rapid prototyping) and large scale production (e.g. automoti ve mass production). The methods are systematised in a 2 x 3 matrix. There are two main groups of processes, which are kinematic shaping, based on for ming by defined relative motion of the tool and workpiece, and forming with shape-defining tools, i.e. forming by adapting the raw part to a shaping t ool. With respect to the moments in action, it can be differentiated betwee n bending without a moment, bending with constant moment,and bending with p osition-dependent moment. Further, some considerations are given as to how to develop the process design for the bending operation, In addition, some of the important features of working accuracy in bending extrusions are rev iewed. This includes two questions: the accuracy of the curvature; and the deviations in the cross section. Methods of open- and closed-loop control b ased on process modelling for an increase of accuracy are shown as well as the practical methods to avoid cross Section deformation. (C) 1999 Elsevier Science S.A. All rights reserved.