Extrusion, channel, and profile bending: a review

The use of extrusions for stiff and lightweight design is widespread. Whilst many applications can be realised with straight extrusions, some applications demand the use of bent extrusions. By introducing the use of bent extrusions into automotive applications, the demands for higher accuracy as well as highly flexible methods were increased. This review gives a systematic overview about the existing processes for the bending of extrusions in small scale (e.g. rapid prototyping) and large scale production (e.g. automotive mass production). The methods are systematised in a 2×3 matrix. There are two main groups of processes, which are kinematic shaping, based on forming 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 tool. With respect to the moments in action, it can be differentiated between bending without a moment, bending with constant moment, and bending with position-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 reviewed. This includes two questions: the accuracy of the curvature; and the deviations in the cross section. Methods of open- and closed-loop control based on process modelling for an increase of accuracy are shown as well as the practical methods to avoid cross section deformation.