# System Design and Experimental Study of a Four-Roll Bending Machine
## 1 Introduction  
The four-roll bending machine, as a core piece of equipment in the field of metal plastic forming, plays an irreplaceable role in aerospace, rail transit, new energy equipment manufacturing, and other sectors due to its high forming efficiency and capability to process complex curved surfaces [1]. However, with the growing demand for high-precision, multi-specification bent components in modern industry, the limitations of traditional rolling machines in terms of mechanical architecture and control systems have gradually become apparent: the rigid coupling design of mechanical structures leads to insufficient scalability and adaptability, while single-level motion control modes struggle to meet the requirements for multi-axis coordination and high dynamic response during machining. This is particularly pronounced when dealing with highly malleable aluminum profiles [2], where the coupling effects of material springback and dynamic load disturbances often induce forming precision degradation and surface quality defects (such as localized indentations,periodic ripples, and micro-cracks), severely constraining product quality and production efficiency [3; 4]. Therefore, addressing the urgent need for precision innovation in high-end equipment manufacturing, conducting in-depth research on key technologies for four-roll bending machines holds significant scientific value and engineering importance. Recent years have witnessed the irreplaceable engineering significance of CNC bending machines in precision processing of complex bent components [5; 6]. For instance, [PERSON] et al. developed a semi-automatic bending machine addressing manual operation inefficiencies through automation strategies that reduced production cycles by over 40%, lowered costs by 25%, and simultaneously improved product quality and output volume [7]. [PERSON] et al. designed a cost-effective motorized three-roll plate bending machine capable of efficiently bending 6 mm thick mild steel plates at a manufacturing cost of $1363.64 using a 10 HP electric motor and specialized component assembly processes [8]. [PERSON] et al. validated the feasibility of servo-electric cylinder implementation in four-roll profile bending machines, proposing an adaptive control model based on curve fitting between actual forming curvature (R) and servo cylinder feed (d) values to enable precision processing of various profile specifications with progressively enhanced forming accuracy through iterative testing [9]. [PERSON], [PERSON] et al. developed the world's first fully automated metal rod bending system by integrating augmented reality (AR) and robotic technology, enabling precise digital shaping of implant rods in spinal fusion surgery. This innovation significantly reduced residual stress at the bone-screw interface (\(p\) = 0.0015), shortened operational time, and decreased the number of reduction device engagements (\(p\) = 0.0037) compared to the manual gold standard, providing an innovative solution to overcome technical limitations of traditional handheld shaping methods [10]. [PERSON] et al. introduced a novel multi-functional bending machine combining 6-DOF parallel kinematic mechanisms (PKM) with hydraulic servo drives for flexible control of bending radii and angles through dynamic modulation of die motion trajectories and tube feed lengths without requiring tooling changes, significantly improving process adaptability for designer furniture and universal product manufacturing [11]. In the research paradigm combining theoretical breakthroughs with enhanced rolling precision and mechanical performance, [PERSON] et al. proposed an upgrade scheme for the upper roll drive system of plate bending machines integrating dynamic load adaptation, intelligent friction compensation, and multi-objective genetic algorithm optimization, significantly improving sheet metal forming accuracy and equipment service life [12].