Development of Computer-Controlled Hydraulic Press for Pipe Fitting Hydroforming

Literature Overview

This paper by Yang Bing, Zhang Weigang, Lin Zhongqin, and Chen Guanlong, published in Forging & Stamping Technology (2006, Vol. 31, No. 5, pp. 93-96), presents the design, development, and testing of a computer-controlled hydraulic press specifically designed for pipe fitting hydroforming operations. The research was conducted at the School of Mechanical Engineering, Shanghai Jiao Tong University, representing a significant contribution to the advancement of hydroforming equipment technology in China.

Core Technical Content

The development of this hydraulic press was driven by the need for specialized equipment capable of meeting the unique requirements of pipe fitting hydroforming processes. The paper analyzes the fundamental process requirements of pipe hydroforming, identifies the basic equipment requirements, reviews the state of existing forming equipment, and presents the design methodology, operating principles, and implementation details of the new computer-controlled hydraulic press.

Process Requirements Analysis

The pipe hydroforming process imposes several demanding requirements on the forming equipment:

1. High Pressure Generation: The system must generate and maintain internal pressures ranging from 200 MPa to 600 MPa to achieve the necessary material deformation.
2. Pressure Control Precision: Accurate pressure control is essential for achieving consistent dimensional accuracy and wall thickness distribution across production runs.
3. Synchronized Motion Control: The axial and radial forming motions must be precisely synchronized to achieve the desired deformation path and avoid forming defects.
4. Rapid Pressure Response: The system must respond quickly to pressure changes to accommodate the dynamic nature of the forming process and enable real-time process adjustments.
5. Safety Features: High-pressure systems require comprehensive safety features including pressure relief valves, emergency shutdown systems, and protective enclosures.

System Architecture

The developed hydraulic press integrates three major subsystems:

Control System Design

The computer control system represents the core innovation of this equipment development. The control system architecture includes:

• Process Programming: Operators can program forming cycles including pressure profiles, axial motion sequences, and timing parameters.
• Real-Time Monitoring: Sensors monitor pressure, temperature, axial position, and force throughout the forming cycle.
• Adaptive Control: The system can adjust process parameters in real-time based on sensor feedback to maintain consistent forming quality.
• Data Logging: All process parameters are recorded for traceability, quality assurance, and process optimization purposes.
• Safety Interlocks: Comprehensive safety interlocks prevent equipment operation under unsafe conditions including overpressure, overtemperature, or unauthorized access.

Engineering Practice and Implementation

From an engineering implementation perspective, the development of this computer-controlled hydraulic press addresses several critical challenges in hydroforming equipment design:

Mechanical Design Considerations

The mechanical system must withstand the extreme pressures generated during hydroforming while maintaining the precision required for accurate part formation. Key design considerations include:

• Frame Rigidity: The press frame must have sufficient rigidity to minimize elastic deformation under forming loads, which could affect dimensional accuracy and die life.
• Die Change Capability: Rapid die change capability is essential for production flexibility and minimizing downtime during product changeovers.
• Clamping Force: The clamping mechanism must securely hold the pipe blank during forming to prevent axial movement and ensure consistent forming conditions.
• Cooling System: Adequate cooling is required for both the hydraulic fluid and the forming zone to manage heat generation and maintain material properties.

Hydraulic System Design

The hydraulic system is the power source for the forming process and must be designed for high efficiency, precision, and reliability:

• High-Pressure Pump: A high-pressure pump capable of generating the required forming pressure with sufficient flow rate for rapid cycle times.
• Accumulator System: Pressure accumulators provide rapid pressure response and energy storage for peak demand periods.
• Precision Control Valves: Proportional or servo valves enable precise pressure control with response times suitable for real-time process adjustment.
• Fluid Conditioning: Filtration, cooling, and contamination control systems ensure fluid quality and system reliability.

Control System Implementation

The computer control system enables the advanced process capabilities that distinguish modern hydroforming from earlier manual or semi-automatic approaches:

• Process Window Definition: Operators define process windows including minimum and maximum pressure limits, forming speed parameters, and cycle time targets.
• Real-Time Feedback: Sensor data is processed in real-time to enable immediate process adjustments and defect detection.
• Process Optimization: Historical data analysis enables continuous process improvement through parameter optimization and trend analysis.
• Quality Assurance Integration: The control system interfaces with quality management systems for automated quality documentation and traceability.

Test Results and Validation

The paper reports test results obtained using simple test pieces to validate the hydraulic press's application effectiveness. The testing program demonstrates:

1. Pressure Generation Capability: The system achieves the designed maximum pressure with acceptable precision and repeatability.
2. Motion Synchronization: The axial and radial motions are synchronized within acceptable tolerances for forming applications.
3. Control Response: The control system responds to process parameter changes within the required time frame for effective process control.
4. Forming Quality: Test pieces exhibit acceptable dimensional accuracy, wall thickness uniformity, and surface quality.

Performance Verification

Study Insights and Implications

This research represents a significant contribution to the development of specialized hydroforming equipment in China. The computer-controlled hydraulic press developed in this study demonstrates the technical capability to meet the demanding requirements of pipe fitting hydroforming processes, providing a platform for industrial applications.

For engineers involved in hydroforming equipment selection and implementation, this work highlights the importance of integrated system design where mechanical, hydraulic, and control subsystems are developed as a cohesive whole rather than as independent components. The computer control system is not merely an add-on feature but is integral to achieving the precision, flexibility, and quality capabilities required for modern hydroforming applications.

The test validation approach using simple test pieces is appropriate for initial equipment qualification but should be supplemented with comprehensive production trials using actual production parts to fully validate the equipment's capability for industrial applications. The test program should include a range of materials, geometries, and process conditions to establish the equipment's capability envelope and identify any limitations or optimization opportunities.

In conclusion, this study demonstrates the successful development of a computer-controlled hydraulic press specifically designed for pipe fitting hydroforming applications. The integrated approach to mechanical, hydraulic, and control system design enables the precision, flexibility, and quality capabilities required for modern hydroforming production. The equipment provides a foundation for industrial hydroforming applications and contributes to the advancement of metal forming technology in China. Future development should focus on enhancing equipment capability through advanced control algorithms, expanded process monitoring, and integration with manufacturing execution systems for comprehensive production management.