Abstract: This paper describes the transformation of the HWS static pressure molding line, introduces the system composition, network structure characteristics, hardware composition and main hardware structure characteristics of the Siemens PROFIBUS fieldbus system, and briefly introduces the various system software used to develop the system. Keywords: HWS static pressure molding line; PROFIBUS-DP; hardware; software 1 Project Introduction The HWS static pressure molding line is a second-hand casting production line with advanced international standards from the late 1980s, manufactured by HEINRICH WAGNERSINTO in Germany and imported by Weifang Diesel Engine Factory in 1992. The line consists of molding machines, box-separating machines, box-closing machines, box-turning machines, bottom plate adding machines, upper and lower box sections, pouring sections, and cooling sections. The entire process connection is completed by 5 transfer trolleys and 4 lifting platforms. Before the transformation, the molding machine and box-separating machine were controlled by two Siemens S5-115 PLCs respectively, while other parts were controlled by conventional relays, which was a semi-automatic line control method. After years of operation, the line experienced frequent mechanical and electrical failures, and various parts failed to meet process requirements. In 2001, we assessed and began implementing a technical upgrade. The upgrade plan included adding a cooling channel, one box-turning machine and one lifting platform, extending the upper and lower box sections, completely redesigning and updating the box-closing machine and bottom plate adding machine, and upgrading the electrical control system to achieve full-line联动 (interconnection/coordination). For electrical control, we selected a system composed of Siemens PLCs, industrial PCs, OP control panels, and PROFIBUS fieldbus. This system greatly enhanced the flexibility of on-site control, reduced design and construction costs, minimized cable laying, and facilitated maintenance and expansion. After the project was implemented, the system operated stably and reliably, achieving considerable economic benefits. 2. System Composition The upgrade of the electrical control system for the HWS static pressure molding line adopted Siemens SIMATIC fully integrated automatic control technology. It uses an S7-400 high-speed processor and a distributed I/OET200M structure, and selects the PROFIBUS-DP fieldbus communication protocol to form a high-speed, reliable industrial control network. The monitoring section of the entire control system is divided into field-level monitoring using OP170B computers and upper-level monitoring using high-performance industrial PCs and the WINCC monitoring software. The high-performance CPU414-2DP central processing unit, installed in the central control room, is the core of the entire control system. It communicates with each substation (ET200M), OP170B, and the upper-level computer, while simultaneously collecting and processing data signals to achieve automatic control of the entire system. Distributed ET200Ms, installed in each substation, use a PROFIBUS-DP network to perform data acquisition, data processing, process control, fault alarms, and interlocking protection operations and controls. Each substation is equipped with a visual operation panel (OP170B) that exchanges data with the central processing unit via a PROFIBUS-DP network, providing a user-friendly operation and monitoring interface for field operators. The upper-level monitoring station in the central control room uses the SIEMENS PCBOX840 industrial PC and SCM1995-R industrial monitor, specifically designed for industrial applications, offering high data processing performance, stability, and strong anti-interference capabilities. The industrial control computer is equipped with a CP5611 communication card for connecting to the PROFIBUS-DP fieldbus, enabling data communication with the main PLC. The WINCC monitoring software provides timely, accurate, and visual displays of the field equipment status to the control room staff, facilitating monitoring and management of the entire production line. The network structure of the HWS static pressure molding line control system is shown in Figure 1. 3. Network Structure Characteristics The PROFIBUS fieldbus is an open fieldbus based on the international standard EN5017. It uses a token-based scheduling principle for data communication and mainly includes the high-speed bus PROFIBUS-DP (H2) with a maximum baud rate of 12 Mbps and the intrinsically safe low-speed bus PROFIBUS-PA (HI) for process control. The perfect combination of DP and PA makes the PROFIBUS fieldbus superior to other fieldbuses in both structure and performance. PROFIBUS is suitable for communication between automation systems and field signal units. It can also directly connect to transmitters, actuators, drives, and other field instruments and equipment with interfaces to acquire and monitor field signals. Furthermore, it replaces a large number of traditional transmission cables with a single twisted pair or fiber optic cable, significantly saving cable costs and correspondingly reducing construction, commissioning, and post-system maintenance time and costs. 4. Hardware Composition and Structural Characteristics 4.1 Central Processing Unit (CPU) As the core component of the electrical system, we selected the CPU4142DP as the central processing unit of the field control programmable controller, responsible for controlling the entire production line's process flow and acquiring and processing all field signals. The CPU414-2DP is a powerful SIMATIC S7-400 CPU with the following main performance specifications: Model: 6ES7414-2XG03-0AB0; Execution time: 0.1ms/k instruction; Integrated RAM: 128KB program; 128KB data; Load memory: expandable up to 64MB; Data backup: lithium battery; Total digital I/O channels: 65536; Total analog I/O channels: 4096; Timers/counters: 256/256; PROFIBUS-DP baud rate: maximum 12Mbit/s. 4.2 Distributed I/O ET200M Composition and Main Functional Parameters Since the entire system adopts a distributed control structure, each substation is equipped with a distributed I/O ET200M communication module and digital/analog input/output modules for acquiring and transmitting field signals. The entire line has 9 distributed I/O ET200M substations, including 2 on the molding machine. The ET200M distributed I/O substation mainly consists of the following parts: SITOP DC power supply; DIN mounting rack; IM153-1 communication interface module; and high-reliability I/O signal interface module. 4.2.1 Main Functions of ET200M The distributed I/O ET200M of the field control substation communicates in real time with the S7-400 central control station via PROFIBUS-DP fieldbus. Its main functions are: to acquire field I/O signals, transmit field digital or analog signals to the central control station through the ET200M's I/O signal interface module, and simultaneously transmit control signals from the central controller to the field devices. 4.2.2 Main Technical Parameters of the ET200M Communication Interface Module: Model: 6ES7153-1AA03-0XB0; Communication Interface: 9-pin Sub-D socket; Transmission Protocol: PROFIBUS-DP; Maximum Transmission Rate: 12Mbit/s; Maximum Address Space: 128 bytes input, 128 bytes output; Maximum Number of Modules: 8. 4.3 Graphical Display Operation Panel (See Figure 2): The OP170B is selected as the field operation platform, which can reflect the field operating conditions in a timely manner and allow operation of the equipment via soft buttons on the panel. Through the PROFIBUS-DP industrial control network, this operation panel can exchange data with the main PLC in the central control room. While providing timely and accurate feedback on the status of the field equipment to the operator, it also feeds back the control commands issued by the field operator to the main PLC, enabling the operator to adjust the equipment status in a timely and accurate manner. The upgraded HWS static pressure molding line is equipped with eight OP170B field operation panels. Each panel is configured with an intuitive field operation station for controlling and displaying the status of field equipment. In addition, each panel is configured with comprehensive equipment fault alarms and password-protected system parameter setting screens. The main performance specifications of the OP170B are as follows: Model: 6AV6542-0BB15-2AXO; Resolution: 320~240 pixels; Processor: 32-bit, 66MHz; Operating System: Windows CE; System Memory: 512KB Flash Memory; Communication Ports: RS232, RS422/RS485 serial communication ports, printer port; Display: 5.7” graphic display screen with high-brightness backlight. 4.4 As the monitoring station's industrial computer, we selected the SIEMENS PCB0X industrial computer, specifically designed for industrial applications, as the upper-level monitoring computer in the central control room. The industrial computer is equipped with a CP5611 card for connecting to the PROFIBUS-DP network, enabling networking and data exchange with the central PLC. The main configuration of the industrial computer is as follows. PIII 866MHz Central Processing Unit; 256MB RAM; 10.2GB Hard Disk; 24x CD-ROM; 1.44MB Floppy Drive; 10M/100M (RJ45) Ethernet Card; CP5611 PROFIBUS/USDP Network Card; 2 Serial Interfaces, 2 PS/2 Interfaces, 2 USB Interfaces, and 1 Parallel Interface; Windows NT 4.0 Operating System; Equipped with a 21” industrial-grade color monitor SCM1995-R. 5. System Software Introduction 5.1 Upper-Level Monitoring Software WinCC WinCC is a world-leading industrial control software jointly developed by Siemens and Microsoft in the field of automation. WinCC, or Windows Control Center, is a 32-bit Windows-based monitoring software. WinCC is a powerful and fully open monitoring system that can be used for both small-scale, simple process monitoring applications and complex applications. In any situation, WinCC can generate a beautiful and convenient human-machine interface, enabling operators to clearly manage and optimize the production process. 5.2 HMI Software Protool/Pro SIMATIC Protool/Pro is a PC-based visual HMI programming software that runs on Microsoft Windows 95/98/ME, Windows NT 4.0/2000, and Windows XP. SIMATIC Protool/Pro includes powerful runtime software (Protool/ProRT) and general configuration software (Protool/ProCS), suitable for configuring all Siemens operator panels. 5.3 Hardware Configuration and Control Programming Software STEP7 STEP7 programming software is the standard tool for SIMATIC C7, SIMATIC M7, and SIMATIC C7 programmable controllers. STEP7 is used for hardware configuration and parameter setting, communication, programming, testing, debugging, and documentation. STEP7 provides PLC control functions for various tasks and allows switching freely between programming language statement lists, ladder diagrams, and control system flowcharts. 6. Summary By adopting a typical distributed I/O control structure based on PROFIBUS-DP fieldbus technology, the control of the entire production line is centralized on a single PLC, and the monitoring and operation of field devices are completed using a Siemens OP operator panel. This significantly reduces costs while meeting control requirements. After nearly three years of production, the reliability and rationality of the entire casting production line control and monitoring system have been verified. Application of PROFIBUS bus to upgrade the HWS static pressing molding line.