Theoretical analysis, finite element modelling, and experimental investigation of manufacturing convoluted spiral tubes through free bending forming technology

The free bending forming (FBF) technology is a new die-less forming process suitable for bending complex-shaped thin-walled tubes with several bending radii. A new theoretical model of convoluted spiral tubes manufactured through FBF technology is proposed in this investigation for revealing and understanding the parameters of manufacturing the spiral tubes using FBF technology. After that, finite element modelling and experimentation were performed to verify the accuracy and reliability of the proposed theoretical model. The max error determined by comparing the experimental results with those acquired from the theoretical analysis is less than 7%. This verifies the reliability and the accuracy of the new theoretical analysis. Afterwards, the forming limit of a convolute spiral tube manufacturing by FBF technology is explored. It is realized that the spiral diameter (D) was affected by distance A which is the distance between the front end of the guide mechanism and the centre of bending die in Z direction; and eccentricity (U). In addition, it is detected that D is directly proportional with distance A and inversely proportional with distance U, where D increased by increasing distance A and decreasing U.