# System Design and Experimental Study of a Four-Roll Bending Machine
## 2 Methods  
### Overall Structure and Main Technical Specifications  
This study focuses on the development of a PC-based multi-axis controlled vertical four-roll bending machine. Initially, based on the structural characteristics of existing four-roll bending equipment, a 3D parametric model of the core mechanical system was established using SolidWorks 2020. This model encompasses a reinforced base frame, three sets of servo-electric cylinders (controlling the left lower roll, right lower roll, and upper roll), and a stepper motor-driven upper roll positioning mechanism. Furthermore, No. 45 steel, recognized as a high-quality carbon structural steel, is characterized by its high strength, high rigidity, and considerable density. During the rolling process, the rolling of steel becomes more challenging due to the greater force exerted [18]. Therefore, by conducting an in-depth analysis of the stress conditions experienced by 45# steel (elastic modulus 200 GPa, Poisson's ratio 0.28, yield strength 355 MPa) as the workpiece during the roll bending process (as detailed below), we can ensure that the machine's mechanical framework possesses sufficient strength and stiffness to meet the roll bending requirements of various complex profiles, thereby guaranteeing the versatility of rolled profiles. The rollers, fabricated from 45 Cr alloy structural steel (quenched and tempered to HRC 40 hardness, yield strength 750 MPa), exhibit significantly superior performance compared to 45# steel. When the rollers contact the profile, the contact stress remains well below the yield limit of the 45 Cr alloy structural steel. Furthermore, 45 Cr alloy structural steel demonstrates excellent contact fatigue resistance, enabling it to withstand microscopic deformation accumulation under long-term cyclic loading. Consequently, the rollers themselves do not induce deformation that would affect the roll bending results. The control system comprises a host computer human-machine interface (developed using the C# language), responsible for inputting process parameters and monitoring real-time status; a Googol GT-800 motion control card, executing multi-axis trajectory planning and position command generation; Delta ASDA-B3 series servo drives connected to the servo-electric cylinders; a stepper motor facilitating material feed; and a terminal board for I/O signal conditioning and safety interlocking. The technical route adopted in this study is illustrated in Figure 1.  
A PC-based multi-axis controlled vertical four-roll bending machine was designed based on the requirements of bent components and the overall architecture of the rolling machine. The machine primarily consists of working rolls, a base frame, guide devices, a spindle drive system, side roll drive systems, lower roll drive systems, a drive system, a measurement and control system, and a transmission system, with its overall 3D mechanism illustrated in Figure 2. Equipped with an industrial control computer as the core control unit, the machine enables dual-mode operation through an integrated human-machine interface (HMI). In manual mode, operators can directly adjust the axial displacement of the side rolls via the interface to precisely execute single-pass rolling processes. When switched to automatic mode, the system supports parameterized input of target curvatures, automatically calculating and controlling the coordinated movement of all actuators based on predefined mathematical models to achieve high-precision single-pass rolling of metal profiles. This control architecture ensures stable process execution through real-time position feedback from servo cylinders and spindle photoelectric encoders, coupled with the real-time responsiveness of the servo system, thereby significantly enhancing machining efficiency and process repeatability. Based on the functional positioning and process requirements of the rolling machine in the material forming process, the technical specifications formulated for the rolling machine are presented in Table 1.