In situ detection and control of wrinkle formation during rotary draw bending

Abstract

Rotary draw bending (RDB) is a profile bending process which is preferably used for small wall thicknesses and small bending radii. The limits of the process are cracking on the outside of the arch and wrinkle formation on the inside of the arch. Cracking is predicted by comparing the calculated strains with a forming limit curve. Wrinkle formation is an instability which can only be calculated to a limited extent due to the variety of influences. It can be corrected by changing process parameters. Due to the geometry of the RDB tools, which fully enclose the bending component, the process is poorly observable, so that component defects are not already detectable during bending. The parameter corrections are therefore only possible for the subsequent component.The aim of the investigation is to measure the wrinkle formation of tube bends during RDB by means of an in situ measurement and to adapt and control the tool forces and axis displacements on the basis of developed adjustment rules. For the in situ measurement of wrinkles, measuring systems are tested and compared by means of practical bending tests of different bending tasks. By integrating a laser line sensor in the wiper die as well as a force sensor in the mandrel, early detection of wrinkles is successfully achieved.The development and elaboration of the missing components of a wrinkle formation control is a new method to capture quality characteristics during bending, to highlight their dependence on the process parameters and to build a controller to achieve the best possible component quality.