4-roll CNC plate rolling machine with Siemens PLC control system

A modern 4-roll CNC plate rolling machine is a high-precision, high-efficiency sheet metal forming equipment, widely used in manufacturing curved workpieces such as cylinders and cones. Siemens PLCs (such as the S7-1500 series) serve as its control core, working in conjunction with the drive system, human-machine interface, and measurement system to achieve fully automated, high-precision control of the rolling process.

I. System Overall Architecture A typical Siemens PLC-based 4-roll plate rolling machine control system adopts a distributed control architecture, with clear hierarchy and high reliability.

Control Layer (Brain):

Core Controller: Typically uses a Siemens S7-1500 series PLC (such as CPU 1515-2 PN). This series of PLCs has strong processing capabilities, rich communication interfaces, and supports PROFINET industrial Ethernet, making it an ideal choice for implementing complex motion control and logic control.

Functional Modules: May be equipped with a TM counting module (for receiving high-precision encoder signals) and analog input/output modules (for processing pressure and displacement sensor signals).

Drive and Execution Layer (Limbs):

Drive System: Employs Siemens SINAMICS series servo/frequency converter drive systems (such as S120 servo drives or G120 frequency converters).

Actuation Motors: AC servo motors are used for the upper roller (lifting and rotating) and side rollers (tilting movement of the left and right side rollers). The lower roller rotation is typically driven by a high-power frequency converter motor.

Hydraulic System: Pressure control of the upper roller's balancing cylinder and main cylinder is achieved through proportional or servo valves, controlled by the PLC's analog output module.

Human-Machine Interface Layer (Face):

Operator Panel: Employs a Siemens SIMATIC HMI intelligent panel (such as the TP1200 Comfort). It provides an intuitive graphical interface for parameter input (plate thickness, material, target diameter), process monitoring, manual operation, fault diagnosis, and program management.

Detection and Feedback Layer (Sensory):

Encoders: Installed on each roller shaft and lifting screw, providing real-time feedback of position and speed, forming a fully closed-loop control system.

Tilt sensor: Mounted on the side rollers, accurately measures the tilt angle of the side rollers.

Laser rangefinder/position sensor: Used to measure the real-time bending curvature of the sheet metal or the roll gap.

Pressure sensor: Monitors the hydraulic system pressure.

Communication network (neural network):

Backbone network: PROFINET Industrial Ethernet. PLC, HMI, drives, and remote I/O stations are all connected via PROFINET, enabling high-speed, deterministic data exchange.

Other interfaces: May connect to an external computer via PROFIBUS-DP or Ethernet TCP/IP (for advanced programming or data management).

II. Detailed Explanation of Core Control Functions Siemens PLCs, programmed through the integrated TIA Portal platform, implement the following core functions:

Axis motion coordinated control:

Using Process Objects (TOs) and Motion Control function blocks, the upper roller, lower roller, and left and right side rollers are defined as synchronous axes.

The system utilizes electronic gears/cams to synchronously move the lower roller (rotation) as the main axis, with the upper roller lifting and the side roller tilting as secondary axes. This ensures consistent linear velocity of the sheet metal during rolling, preventing slippage or scratches.

High-Precision Position Control:

Each servo axis undergoes full closed-loop position control. The PLC reads high-resolution encoder values, compares them with the target position, and adjusts the driver output in real time using a PID algorithm, ensuring a roller system positioning accuracy of ±0.1mm.

Precise control of the side roller tilt angle is crucial for the 4-roll plate rolling machine, directly affecting the straightness of the workpiece and the forming accuracy of the cone.

Intelligent Rolling Process Calculation and Flow Control:

Pre-bending, centering, rolling, and straightening are all fully automated.

Process Model Calculation: The PLC, either built-in or programmed in a high-level language, automatically calculates the following based on the input sheet metal parameters (thickness, width, material yield strength) and target diameter:

The downward pressure of the upper roller (deflection compensation)

The tilt and stroke of the side rollers

The motion trajectory and speed curve of each roller

The required number of rolling passes and pressure

Workflow:

Feeding and Centering: The PLC controls the automatic centering of the sheet metal through the cooperation of the side rollers and support rollers.

End Pre-bending: By precisely controlling the downward pressure of the upper roller and the position of the side rollers, the ends of the sheet metal are progressively bent multiple times to eliminate straight edges.

Rolling: The PLC executes the calculated motion program, and the three rollers (lower roller + two side rollers) work together to roll the sheet metal into the desired cylindrical shape. For conical cylinders, the side rollers dynamically tilt according to the calculated curve.

Rounding: After closing the cylinder, multiple rounding operations are performed to improve roundness accuracy.

Deflection Compensation Control:

For long-shaft plate rolling machines, the upper roller undergoes elastic deformation (deflection) under stress, resulting in a large gap in the middle and a "waist-shaped" formed cylinder.

Solution: The PLC controls multiple tilting cylinders of the upper roller or an external deflection compensation roller to dynamically adjust the local downward pressure of the upper roller based on the real-time rolling force, keeping its working axis straight.

Safety and Diagnostic Functions:

Integrated Safety: Safety functions (such as Safe Torque Off - STO, Safe Stop) of Siemens fail-safe PLCs (e.g., CPU 1516F) and drives can be used to directly implement safety circuits via PROFINET, replacing traditional hard-wired safety relays.

Comprehensive Diagnostics: Real-time monitoring of PLC, drive, and network status is achieved through the integrated diagnostic functions of TIA Portal. Clear alarm information (such as overtravel, overload, and communication failure) is displayed on the HMI, guiding maintenance personnel to quickly troubleshoot.

III. Software and Programming Environment
Platform: Siemens TIA Portal (Total Integrated Automation Portal).

Software Packages:

STEP 7 Professional: For configuring and programming S7-1500 PLCs. Uses SCL (Structured Control Language) to write complex process calculation algorithms and LAD/FBD to write logic control.

WinCC Professional: For configuring the SIMATIC HMI screen.

SINAMICS Startdrive: Integrated into TIA Portal for setting and optimizing servo drive parameters.

Advantages: All software operates under a single project and unified database, greatly simplifying programming, debugging, and maintenance.

IV. Summary of Key System Advantages
High Precision and Consistency: Thanks to the Siemens closed-loop motion control system and powerful process calculations, the rolled workpiece has high precision and good repeatability.

High Efficiency: Automated processes reduce manual intervention and trial-and-error time, especially significant in end pre-bending and tapered cylinder rolling.

High Reliability: Siemens industrial-grade hardware and distributed architecture ensure stable system operation in harsh industrial environments.

Powerful Communication and Integration Capabilities: The PROFINET network enables seamless data integration, facilitating future integration with factory MES/ERP systems for intelligent manufacturing.

User-Friendly Development and Maintenance: The TIA Portal platform significantly reduces engineering development complexity, and its powerful diagnostic functions make troubleshooting and routine maintenance more convenient.

Flexibility: By modifying process parameters in the PLC or calling different machining programs, it can quickly adapt to the processing of workpieces of different sizes and materials.

Conclusion: The 4-roll CNC plate rolling machine using a Siemens PLC control system represents the current high-end technology level in this field. It perfectly integrates precise mechanical design with advanced electrical automation technology, not only improving processing capabilities and product quality but also laying a solid foundation for the digital and intelligent transformation of metal forming processes.