A novel multi-axis parallel free-bending system for precision tube forming: Design, kinematic analysis, and experimental validation

Xia T., Cheng C., Chen L., Liu Y., Guo X., El-Aty A. A.

Journal of Manufacturing Processes, vol.176, pp.193-209, 2026 (SCI-Expanded, Scopus)

  • Publication Type: Article / Article
  • Volume: 176
  • Publication Date: 2026
  • Doi Number: 10.1016/j.jmapro.2026.09.005
  • Journal Name: Journal of Manufacturing Processes
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, ABI/INFORM, Compendex, INSPEC, Materials Science & Engineering Collection (ProQuest), Pharma Collection (ProQuest), Technology Collection (ProQuest)
  • Page Numbers: pp.193-209
  • Keywords: Directional error compensation, Forming consistency, Free bending, Multi-axis parallel mechanism, Spatial pose control
  • Ataturk University Affiliated: No

Abstract

Conventional free-bending forming (FBF) systems face limitations in lightweight design, structural stiffness, and kinematic flexibility when forming complex spatial tubular components. To address these challenges, a novel multi-axis parallel free bending forming (MAP-FBF) system is proposed and experimentally validated. A control-point-based pose computation method is first established by integrating tube-axis geometric reconstruction with the inverse kinematics of a parallel mechanism, enabling accurate transformation from a spatial tube-axis description to the six-degree-of-freedom (6-DOF) pose of the bending die. A multi-domain co-simulation platform incorporating pose computation, inverse kinematics, and multibody dynamics simulation is then constructed to evaluate trajectory-tracking performance. Simulation results demonstrate strong agreement with the theoretical target poses, confirming the proposed method's positioning capability. A functional prototype and dedicated control system are subsequently developed for experimental validation. The results show that although the bending die maintains high positioning stability under loading, significant directional inconsistencies occur during the forming process due to hinge clearances and assembly deviations. To address this issue, a workspace-wide directional error compensation strategy is proposed. After compensation, the coefficient of variation of the formed bend radii is reduced from 39.3% to 6.45%, significantly improving forming consistency. The proposed system and compensation strategy provide a practical framework for achieving high-precision and direction-independent forming in MAP-FBF technology.