Hydraulic System for 15000 kN Steel T-Tee Hydraulic Bulging Machine

Literature Overview

This paper, published in Hydraulics and Pneumatics (1995, Vol. 19, No. 3, pp. 26–29) by He Songqiao, Li Weimin, and Du Shaowu from the Hydraulic Teaching and Research Section of Liaoning Institute of Technology, describes the hydraulic system design of a 15000 kN steel T-tee hydraulic bulging machine. The system employs a programmable logic controller (PLC) for automated operation, utilizes a combined hydraulic cylinder configuration, and incorporates energy-saving measures. The paper also highlights the advantages of using CAD software for hydraulic manifold block design.

Machine Function and Process Description

The hydraulic bulging machine is designed for the manufacturing of steel T-tee fittings through the hydraulic bulging process. In this process, a steel pipe blank is positioned in a die cavity, and hydraulic pressure is applied internally to expand the pipe wall into the die shape, forming the T-branch. The 15000 kN force capacity indicates the machine is designed for heavy-duty applications, likely targeting large-diameter or thick-walled pipe fittings.

The bulging process involves several key stages:

Loading the pipe blank into the die cavity.
Applying internal hydraulic pressure to expand the pipe wall.
Holding pressure for a defined time to allow material flow and springback compensation.
Releasing pressure and extracting the formed fitting.
Trimming excess material and performing final inspection.

Hydraulic System Architecture

The hydraulic system is designed to deliver the required 15000 kN force with precise pressure and flow control throughout the bulging cycle. Key components and design features include:

Component	Specification	Function
Combined hydraulic cylinder	Dual-stage or multi-stage configuration	Delivers high force at low speed for bulging, and high speed for rapid retraction
Programmable logic controller (PLC)	Programmable control logic	Automates the bulging cycle sequence and monitors system parameters
Hydraulic manifold block	CAD-designed integrated block	Reduces leakage points and simplifies maintenance
Pressure control valves	Proportional or servo valves	Precise pressure regulation during bulging
Flow control valves	Adjustable or proportional	Controls bulging rate for dimensional accuracy
Energy recovery system	Regenerative circuit or accumulator	Recovers energy during retraction stroke

Combined Hydraulic Cylinder Design

The combined hydraulic cylinder is a critical component that addresses the fundamental challenge of hydraulic bulging: the need for high force at low speed during the forming stroke, and high speed during the retraction stroke. A dual-stage or multi-stage cylinder configuration achieves this by:

Using a large-diameter stage for the high-force, low-speed bulging phase.
Transitioning to a smaller-diameter stage for the high-speed retraction phase.
Incorporating pressure relief and cushioning features to prevent over-pressure and mechanical shock.

Energy-Saving Measures

The hydraulic system incorporates several energy-saving strategies:

Regenerative circuit: Energy is recovered during the cylinder retraction stroke by routing the displaced fluid back to the pump inlet, reducing pump power consumption.
Variable displacement pump: The pump displacement is adjusted to match the system demand, minimizing energy waste during low-flow phases of the cycle.
Accumulator pre-charge: A pre-charged accumulator provides rapid fluid delivery during the initial bulging phase, reducing pump load.
Idle power reduction: The PLC controls pump shutdown or low-power standby mode during non-operational periods.

CAD-Designed Hydraulic Manifold Block

The use of CAD software for hydraulic manifold block design offers several advantages over traditional hand-drawn designs:

Improved accuracy in port positioning and flow path design.
Reduced risk of design errors and rework.
Enhanced ability to optimize internal flow channels for minimal pressure drop.
Easier integration with the overall hydraulic schematic and control logic.
Documentation and maintenance benefits through digital design records.

Engineering Analysis and Practice Integration

The design of this hydraulic bulging system reflects several important engineering principles that are directly applicable to modern pipe fitting manufacturing:

Force and speed optimization: The combined cylinder design demonstrates the principle of matching hydraulic system characteristics to the process requirements. A single-stage cylinder would either be oversized (wasteful) or undersized (inadequate) for the dual requirement of high force and high speed.
Control system integration: The use of a PLC for automated control ensures repeatable, consistent bulging cycles, which is essential for producing fittings with uniform dimensional accuracy. The PLC also provides diagnostic capabilities for monitoring system health and detecting anomalies.
Energy efficiency: In industrial manufacturing, hydraulic system energy consumption is a significant operating cost. The energy-saving measures described—regenerative circuits, variable displacement pumps, and accumulator pre-charging—are now standard best practices in hydraulic system design.
Manufacturing quality assurance: The bulging process requires precise control of pressure, time, and temperature to achieve consistent mechanical properties and dimensional accuracy in the formed fittings. The hydraulic system design must support these quality requirements through accurate pressure regulation, stable flow delivery, and reliable cycle control.

Study Insights and Implications

This paper provides a valuable case study in hydraulic system design for a specific manufacturing application. The integration of mechanical design (combined cylinder), control engineering (PLC), and manufacturing technology (CAD-designed manifold) exemplifies the multidisciplinary nature of modern industrial equipment design. For pipe fitting manufacturers, the key insights are:

Hydraulic bulging is a viable and cost-effective process for manufacturing T-tee fittings, particularly for large-diameter or thick-walled applications where forging or welding may be impractical.
The hydraulic system design must be optimized for the specific process requirements, not merely selected from standard component catalogs.
Energy efficiency and automated control are essential for competitive manufacturing, as they directly impact operating costs and product consistency.
CAD-based design tools significantly improve the quality and efficiency of hydraulic system development, reducing design errors and development time.

The principles documented in this 1995 paper remain relevant in contemporary hydraulic bulging machine design, with modern implementations incorporating advanced features such as servo-controlled proportional valves, real-time pressure monitoring with closed-loop feedback, and predictive maintenance systems. The fundamental engineering challenges—force-speed optimization, energy efficiency, and process control—have not changed, but the tools and techniques for addressing them have evolved significantly. Engineers working on pipe fitting manufacturing should study such foundational papers to understand the evolution of hydraulic bulging technology and the enduring engineering principles that underpin its continued development.