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In recent years, with the rapid development of aerospace, military, automobile, motorcycle, shipbuilding and other industries, the demand for bending and rolling parts has increased sharply, and the requirements for rolling accuracy are becoming higher and higher. However, the traditional feeding solution of hydraulic cylinder cannot further improve the contour accuracy of rolled profiles. In addition, due to the characteristics of the profile, material properties and various random factors in the forming process, the existing forming formulas have limited application and are only suitable for profile processing under certain circumstances. In response to these problems, servo electric cylinder was introduced to replace the traditional hydraulic cylinder, and the mechanical structure of the four-roll bending machine was redesigned, which proved the feasibility of applying servo electric cylinder to the four-roll bending machine. CNC bending machine, which improves the control accuracy and response speed, providing a comprehensive design solution for the four-roll CNC bending machine. In order to solve the problem that the existing forming formula is not very versatile, the actual values of R (profile forming curvature) and d (servo electric cylinder feed) of the four-roll CNC bending machine are used, and the curve fitting method is used to establish a universal automatic control model. It has high performance and a wide application range, and as the number of tests increases, the forming accuracy is gradually improved.
Aluminum alloy profiles are widely used in the aerospace field due to their high specific strength, light weight and good formability. They are one of the main supporting structures of aircraft airframes. In addition, with the rapid development of coal power, hydropower, nuclear power, wind power, petrochemical and other industries, the design and development of sheet rolling machines and the research on forming methods of rolled profiles have also become hot spots. The bending process is widely used in metalworking in the oil and gas, shipbuilding, pipeline, automobile and other industries. However, since roll forming involves elastic deformation and plastic deformation, elastic rebound occurs, which has a negative effect on the final forming accuracy and fluidity of the bending part of the profile. Z-section is an important component of the aircraft fuselage bracket, and its bending quality has a significant impact on the overall quality of the aircraft fuselage. The four-roll sheet rolling process has high efficiency and low cost. The bending process parameters play a vital role in the quality of the profile bending.
During the daily maintenance of the four-high rolling mill, Li 7 found that after many years of operation and use, water entered the hydraulic system installed at the bottom of the hydraulic cylinder, which caused some problems for the equipment and affected the normal operation of production. The application fields of electric cylinders are becoming more and more extensive, and the market for electric cylinders is also growing8. Therefore, the use of electric cylinders is an experimental solution. In the research of the machine, Yue 9 established the relationship between the equipment force, bending moment and driving force, obtained a calculation method for the driving power of the main transmission system of the four-high rolling mill, and selected the power of the main motor based on this calculation result. Huang 10 used the finite element optimization design function of ANSYS software to carry out the simulation and optimization of the transmission components of the four-high rolling mill. Zheng 11 carried out a theoretical analysis of the force deformation of the lower roller, derived a calculation formula for the force deformation of the lower roller, designed an effective compensation scheme, and used the finite element analysis software ABAQUS to carry out three-dimensional dynamic simulation of the compensation state of the lower roller. Yao 12 introduced the equipment and design characteristics of the four-roll full hydraulic plate bending machine, focusing on the composition, working principle, key design points, etc. of the equipment. Yan 13 fully understood the mechanical behavior during the pre-bending process and analyzed the load on the working roll during the pre-bending process of the four-roll roll plate. As can be seen from the above, in the research of machine tools, some scholars focus on theory and calculation, while others focus on modeling and optimization. For machine tools, there is less experimental verification and machine tool design, so it is very important to replace the traditional hydraulic and electro-hydraulic systems with servo-electric cylinder systems and build machine tools.
Generally speaking, scholars mainly use the finite element method combined with experiments to analyze the influence of various factors on the forming of profile rolls. However, there are fewer studies on CNC bending machines and their automatic control systems, and more studies on a simple three-roller model and fewer studies on a more complex four-roller model. The hydraulic system currently used in bending machines limits the forming accuracy, and the forming method has serious limitations. Based on this, this study tests the rationality of using servo electric cylinders on roll bending machines, and uses the profiling curve (R) and servo electric cylinder feed (d) values as the basis for calculation, based on practical considerations. automatic control model that can be applied. Roll bending can be performed on products of any cross section and material.
The profile is placed between the upper and lower rollers. The left and right lower rollers control the position of the rollers in accordance with the rolling radius. As the rollers rotate, the profile moves to feed and makes one or more feed movements until the profile is processed to the required curvature. The principle of four-roll bending, shown in Figure 1, is to control the profile through the upper roller. The friction force arising between the profile and the upper roller pushes the profile to complete the feed movement and sets the other rollers in rotation. The upper and lower rollers are the driving and driven wheels, respectively. The tangential force acting from the upper and lower rollers on the sheet material creates a driving moment causing the profile to move tangentially along the roller directed toward the profile offset, while the left and right rollers move in the direction opposite to the tangential direction of offset, causing friction in the tangential direction of the profile resistance moment. When bending starts, the lower roller presses the profile and clamps it between the upper and lower rollers, so that the profile is bent and deformed continuously and stably under the friction action of the rollers, effectively preventing the profile from being skewed or misaligned. After the lower roller presses the profile, the left and right rollers complete feeding according to the trajectory, and the profile is bent accordingly.
After the lower roller presses the profile, the left and right rollers complete the feed along the trajectory, and the profile is bent accordingly.
In the roll bending process, there is a certain center distance between the main and auxiliary rollers and the side bars. During the roll bending process, the main and auxiliary rollers with the largest center distance should compress each other to ensure the roll bending effect. However, due to the center distance between the rollers, part of the two ends of the profile cannot be compressed to the maximum center distance, and the problem of straight cross-section will occur, resulting in the loss of profiles. In order to reduce the waste of profiles, the pre-bending process is adopted. The process steps are shown in Figure 2.
The centering is shown in Figure 2a: By centering the profile in front of the bending roll, it is possible to ensure that the end face of the profile being processed is parallel to the tire of the side roller, thereby effectively avoiding distortions and deformations of the profile during the bending roll process.
The pre-bending is shown in Figure 2b. In the four-roll symmetrical sheet bending machine, the asymmetric distribution of the roller positions can be used to pre-bend the end of the part to reduce or even eliminate the remaining straight edges, so that the last field of the straight edge is 0. The basic process of pre-bending the profile is as follows: first, based on the centering, the left roller is lowered to the appropriate position, secondly, the upper roller is rotated back to return the profile to the position with the appropriate margin on the left side; finally, the right roller. When it rises to the appropriate position, the upper roller is rotated forward, causing the profile to be pre-bent.
The stationary roll bending process is shown in Figure 2d. Continuous roll bending is the main process of roll forming. During this process, the speed and position of the upper roller and the feed speed of the side roller need to be strictly controlled. As a result of pre-bending, the right roller is lowered to the appropriate position, the left roller is raised to the appropriate position, and the upper roller rotates forward, driving the profile feed for continuous roll processing. The process of bending the profile with a roll after centering, pre-bending and continuous roll bending is called the lifting roll bending process with the side roller before bending.
As shown in Figure 3, under the compressive action of the upper roller R1 and the lower roller R2, when the four-roller pre-bending roller is formed, the center of the forming curvature of the pre-bending roller section can be considered to be collinear with the center of the upper and lower rollers, and deformation is assumed. The curvature of the profiles in this region is the same, provided that the profiles always touch the straight edge during the pre-bending process14.
According to the geometric model of the opposite side process shown in Figure 3, the displacement of the lower roller is \(h_{1}\), the displacement of the left roller is \(h_{2}\), and the displacement of the right roller is \(h_{3}\). According to the geometric relationship (1), we can obtain expressions for the displacement of the lower, left, and right rollers. The schematic diagram of the opposite side is shown in Figure 2a:
The pre-bending process is the preparatory work for the roll bending of the profile. The right roller is lifted (dropped) to complete the pre-bending of the left profile. The subsequent roll bending process is carried out with the pre-bending position. The working roll for bending has remained almost unchanged, so the pre-bending process is as follows: The displacement of the working rolls during bending and normal bending of the rolls can be obtained together, and the lift before bending can also be used as a formula for the one-way displacement of the lifting roll. The bending process is shown in Figure 2b.
As can be seen from Figure 3, the displacement of the lower roller is \(h_{1}\), the displacement of the left roller is \(h_{2}\), and the displacement of the right roller is \( h_{3}\). According to the geometric relationship, we can obtain expressions for the displacement of the lower, left, and right rollers. Three points that do not lie on the same line define a circle, \({\mathrm{OO}}_{1}\), \({{O}_{1}O}_{2}\), \ ({\ mathrm{OO}}_{2}\) are three non-collinear points. According to the Pythagorean theorem, we can obtain formula (3). The positional relationship of the three points is shown in Figure 3.
In the process of developing the sheet metal rolling machine, various sheet metal rolling machines on the market were investigated, and innovative machine specifications were proposed through analyzing the advantages and disadvantages of different machines. Choose four-roller feeding instead of the more mature three-roller design. Compared with three-roller sheet rolling, four-roller sheet rolling can reduce the straight edge reserve, but increases the control difficulty. Using servo electric cylinder instead of traditional servo cylinder achieves higher control accuracy, which helps improve the profile accuracy and reduce the machine size. The left and right lower rollers of the machine are driven by servo electric cylinders. The position control accuracy can reach ±0.01mm. High repeatability ensures the consistency of profile processing. The fast response of the servo electric cylinder ensures accuracy. profile bending. The pusher joint uses spherical bearings, which can simultaneously bear radial load, axial load or combined radial and axial load. The rollers are installed on a specially designed T-shaped machine to realize smooth feeding and processing, and the integrated bed is used to achieve smoother bending and rounding of the profile. The integration of VS software with GTS-800 motion controller can turn the PC into a motion controller with the ability of real-time motion control. The automatic control design uses the actual R and d values of the CNC four-roll bending machine, adopts the curve fitting method, and selects the basic curve equation as the basis of the control model. Overall, it can be regarded as a major improvement and upgrade of the four-roll bending machine.
The motion system, as shown in Figure 4a, has three numerically controlled motion coordinate parameters, namely the parameters of the main rotational motion and the synchronous control of the motion in two directions.
The upper roller is a fixed wheel, which mainly plays the role of transmission and direction; the lower roller is a clamping wheel, which can move up and down, and the clamping pressure P can be controlled by numerical control to complete the interaction; radial bending, and the moving directions of the left and right rollers are X1 and X2 respectively.
The geometric relationships and position dimensions of the control structure of the four-roll CNC sheet metal bending machine designed and manufactured in this study are shown in Figure 4b. The position of each roller in the dotted line in the figure represents the maximum stroke position during its movement.
The functional relationship between the stress distribution along the height of a steel plate and the true stress on the plate cross-section during linear purely plastic bending can be expressed as:
In the formula, \(\sigma\) is the workpiece stress, \(\sigma_{s}\) is the yield strength of the material, \(\varepsilon\) is the workpiece deformation, \(E_{2}\) is the linear reinforcement model of the material. This sum can be obtained by referring to the relevant manual.
In the formula, b is the maximum width of the steel plate rolled on a sheet rolling machine, and the initial deformation bending moment \(M_{0}\) is equal to
The top roller of a four-high sheet rolling machine is the driving roller. The total drive moment acting on the top roller is the sum of the torque consumed in the deformation process and the torque required to overcome friction. torque consumed by the roller rolling on the curved plate. Frictional resistance, and frictional moment consumed by the roller bearings.
The torque consumed during the deformation process can be determined using the condition that the work of the internal bending force is equal to the work of the external force acting on the upper roller:
In the formula \(W_{n}\) is the work of the internal bending force, \(W_{w}\) is the work of the external force acting on the upper roller, \(L\) is the length of the plate corresponding to the bending angle.
The torque required to overcome friction can be determined using equation (13). Friction torque for asymmetrical arrangement of shaft rollers
In the formula \(f\) is the coefficient of rolling friction, we take \(f = 0.8\;{\text{mm}}\ \(\mu\) is the coefficient of sliding friction on the journal, \( \mu = 0.05\sim 0.1\) \(d_{a}\), \(d_{b}\), \(d_{c}\) are the diameters of the journal of the upper roller, lower roller and side roller, respectively.
In the formula, \(v\) represents the linear velocity, \(r\) represents the radius of the drive roller, take \(r = {{D_{a} } \mathord{\left/ {\vphantom {{ D_{a} } 2}} \right \kern-0pt} 2}\); \(\eta\) represents the transmission efficiency.
Servo electric cylinder is a new modular product that integrates servo motor and ball screw or roller screw, converts the rotary motion of servo motor into linear motion, achieves precise control of speed, rotation speed and torque, and makes full use of the advantages of precise control of servo motors to accurately control speed, position and thrust. It is a revolutionary solution for high-precision linear motion applications.
The servo-electric cylinder system is controlled by a servo motor. Using the feedback control characteristics of the servo motor, precise control of thrust, speed and position can be achieved.
Electric cylinders have many advantages over traditional hydraulic cylinders, such as higher actuation reliability, higher precision and stability, and more advanced control functions.
Servo-electric cylinders have the characteristics of long service life, strong adaptability to the environment and powerful starting and stopping capabilities. Through the integration of servo motor and electric cylinder technology, excellent environmental performance, energy-saving effect and high-precision motion control capabilities are achieved.
The structure of the servo electric cylinder is relatively simple and mainly consists of four parts: drive mechanism, reducer, linear transmission mechanism and transmission mechanism. There are two structural forms of servo motors and electric cylinders. One is the direct-coupling electric cylinder, as shown in Figure 6a. The direct-coupling servo motor is directly connected to the motor through a coupling. The other is a parallel structure, as shown in Figure 6b. The motor is installed in parallel with the electric cylinder through a high-strength synchronous belt, which is also called a parallel structure or a folding structure. In addition to the characteristics of the series electric cylinder, the parallel electric cylinder has a relatively short overall length, making it more suitable for installation in limited space.
The selection of suitable parameters of servo electric cylinder mainly depends on various factors such as cylinder load, cylinder service life, number of cycles, stroke distance, installation space, etc.
Accurate knowledge of the load is critical to selecting the most cost-effective and reliable electric cylinder solution.
The relationship between the motor output torque and the electric cylinder output force is
In the formula, \(F\) is the output force of the electric cylinder, \(T\) is the output torque of the engine, \(R\) is the gear ratio, \(L\) is the propeller stroke (mm), \(\eta\) is the mechanical efficiency, typically 85–90%.
Equation (17) can be used to estimate the size of the engine required to meet the load requirement. In addition to the maximum force applied during operation, the critical factor to consider is the change in force throughout the stroke. The average load can be obtained from the change in force throughout the entire working cycle and is the basis for calculating the service life of the cylinder.
In the context of electric cylinders, the term “service life” usually refers to the service life of the screw used inside the cylinder. This service life can be divided into two different parts: the fatigue life of the screw (which can be quantified by calculation) and the service life (which depends on various conditions of use, including temperature, average load, type of lubrication, frequency of relubrication and other relevant factors).
In the formula \(L_{10}\) is the service life of the electric cylinder, \(C_{a}\) is the basic nominal dynamic load of the screw road surface, \(F_{m}\) is the average load perceived by the electric cylinder, L is the load on the screw stroke.
The optimal electric cylinder can be selected by specifying the acceleration and speed of the drive or by specifying the cycle time and the required distance.
The selection of the electric cylinder is closely related to its working stroke, installation location, etc. When the electric cylinder is working, it is necessary to ensure that the mechanical limit is not exceeded. Therefore, safety strokes must be added to both ends of the working stroke S to make part of the stroke longer. The sum of these two strokes is the working distance S of the electric cylinder, that is, \(S = S_{{{\text{work}}}} + 2S_{{{\text{safe}}}}\), as shown in Figure 7. According to the requirements of the installation space, electric cylinders of series or parallel design can be selected.
Figure 8-1 shows the installation of the guide rail on the bed, Figure 8-3 shows the installation of the spindle motor and coupling, Figure 8-3 shows the installation process of the servo cylinder and side roller shaft, and finally the installation of the complete machine.
The four-roller CNC bending machine is mainly composed of three parts: mechanical equipment, pneumatic system and CNC system. The mechanical structure of the machine is composed of four rollers, including the upper roller, left and right side rollers, lower center roller, servo electric cylinder, spindle motor and frame. The upper roller is fixed on the frame, and the left and right side rollers are driven by servo electric cylinders and perform feeding movement along the guide rail. The three-dimensional model of the four-roller CNC bending machine is shown in Figure 9a, and the real object is shown in Figure 9b.
From the comparison of Figures 10a and 10b, it can be seen that the mechanical structure of the servo-electric cylinder is simpler, and the use of pure electric control improves the safety of the machine during operation. The specific comparative analysis is shown in Figure. Table 1.
(a) Sheet metal bending machine controlled by hydraulic system; (b) Sheet metal bending machine controlled by servo-electric cylinder.
According to the requirement of the control system of the four-roll CNC bending machine, the PLC motion control card system solution is adopted and the hierarchical modular design method is adopted, as shown in Figure 11. The control system solution is an open architecture, portable and customizable, built on the Windows Forms application module of Microsoft Visual Studio software (.NET Framework). The Windows Forms application module provides the functionality required to write a complete motion control solution including the host interface. The Goodco GTS-800-PV-PCI series embedded PC motion controller is selected as this control system due to its ability to provide high-speed point motion control. The controller core is composed of DSP and FPGA, which achieves high-performance control computing. GTS-800 is widely used in various fields such as robots, computer numerical control (CNC) machines, woodworking machinery, printing machines, assembly lines, electronic processing machines, laser processing machines, PCB drilling and milling machines, etc. The combination of Visual Studio software with the GTS-800 motion controller turns your computer into a motion controller with real-time motion control capabilities. Visual Studio software complements the motion control function and replaces the traditional hardware control, thereby overcoming the limitations of the incompatibility of traditional hardware, making the control system more open and easily expandable with functions to meet diverse needs. The system can also utilize various resources of the Windows system to make it more modular, hierarchical and standardized, while shortening the development cycle of customized products. Microsoft Visual Studio (VS) is a series of development toolsets from Microsoft Corporation of the United States. VS is a nearly complete set of development tools, including most of the tools needed throughout the software life cycle, such as UML tools, code management tools, integrated development environments (IDEs), etc.
According to the control process of sheet rolling machine, the control system schematic diagram is developed, as shown in Figure 12.
In order to achieve the lightweight structure of the aircraft, large-section Z-shaped profiles are used in new large aircraft to form the frame and edge parts, which are mainly produced by the roll bending method12. The aluminum alloy profiles, which are an important component of the fuselage support, need to be processed into bent parts of a certain curved shape to ensure the support of the streamlined fuselage skin. Therefore, it is of great significance to study the profile bending formation process to improve the capabilities of aircraft manufacturing. As an important part of the aircraft fuselage support, the Z-shaped bent parts are generally rolled and bent from Z-shaped straight materials with a thickness of 2 mm and a length of 1300 mm, as shown in Figure 13a. Based on this cross-sectional data, the rollers involved are shown in the figure, and the dimensions of the rollers are shown in Figure 13b.
The finite element modeling method has the advantages of short test cycle and low cost. At the same time, it can more accurately analyze the laws and relationships between variables in the forming process. It has been widely used in various fields of profile roll bending analysis15. and is considered to be the most advanced profile bending study. The most effective method16,17. Based on this, the finite element software ABAQUS was used to establish a dynamic finite element model of four-roll bending to test whether the calculated roller position can bend the profile.
Post time: Jan-13-2025