Partitioned Differential Lubrication Effects on 5A02 Aluminum Alloy Tee Tube Forming Quality

Literature Overview

This research by Xu Yong and colleagues from North China University of Science and Technology, Institute of Metal Research of the Chinese Academy of Sciences, and Shenyang Aerospace Complex Component Precision Manufacturing Key Laboratory was published in China Mechanical Engineering (2025, Vol. 36, No. 5, pp. 1094-1102). The study proposes a partitioned differential lubrication method for hydraulic forming of 5A02 aluminum alloy tee tubes, addressing the challenge of achieving uniform wall thickness distribution in complex tubular fittings. The work is supported by the National Natural Science Foundation of China (52405439) and the China Postdoctoral Science Foundation (2024M763339).

Forming Process and Technical Challenge

Hydraulic forming of tee tubes involves expanding a tubular blank using internal fluid pressure to form branch outlets, creating a complex three-dimensional geometry from a simple tube. The fundamental challenge lies in the non-uniform material flow requirements: the branch arms require significant axial and circumferential stretching, while the main body sections require minimal deformation. Traditional uniform lubrication strategies cannot accommodate these conflicting requirements, leading to either excessive thinning at the branch locations or excessive wrinkling in the main body.

The 5A02 aluminum alloy, a high-strength Al-Mg-Si-Zr alloy, exhibits specific forming characteristics including moderate strain hardening behavior and sensitivity to lubrication conditions. Its application in aerospace structures demands high forming precision and minimal material waste, making the optimization of lubrication strategies particularly important.

Partitioned Differential Lubrication Method

The proposed method divides the forming surface into two distinct zones with different lubrication conditions:

1. Expansion zone (branch arm region): Enhanced lubrication is applied to facilitate material flow into the branch arms, reducing friction resistance and allowing more uniform material distribution during the forming process.
2. Non-expansion zone (main body region): Artificially roughened surfaces are created to increase friction, which restricts excessive material flow and promotes material accumulation toward the transition zones between the main body and branch arms.

Finite Element Simulation Results

The finite element simulation results demonstrate clear advantages of the partitioned differential lubrication approach over traditional uniform lubrication:

• The wall thickness thinning rate at the branch arm sides and top is effectively reduced, improving structural integrity of the formed tee.
• The side feed material quantity is decreased, thereby lowering the risk of instability and wrinkling in the main body section.
• As the expansion zone lubrication area increases, the axial tensile stress on branch arm elements gradually decreases, directly reducing the thinning rate at the branch arm sides.
• As the non-expansion zone artificial roughness area increases, the axial compressive stress on the tee tube side wall elements decreases, while circumferential tensile stress gradually increases. This stress redistribution promotes material flow toward the transition zones between the main body and branch arms, preventing material accumulation in the main body center and reducing wrinkling risk.

Engineering Practice Integration

From a pipe fitting manufacturing perspective, this research provides actionable guidance for hydraulic forming process optimization. The partitioned lubrication approach can be implemented through:

• Selective application of lubricant films using masking techniques or patterned surface treatments on the forming die.
• Creating controlled surface roughness on non-expansion zones through mechanical texturing or chemical etching.
• Integrating the optimized lubrication strategy with existing hydraulic forming equipment without requiring major capital investment.

The FMEA (Failure Mode and Effects Analysis) perspective reveals that the primary failure modes in tee tube hydraulic forming—excessive thinning at branch arms and wrinkling in the main body—are directly addressed by the differential lubrication strategy. By tailoring friction conditions to local deformation requirements, the method simultaneously mitigates both failure modes, representing a significant advancement in forming process reliability.

Study Insights and Implications

This research exemplifies the principle that process parameter optimization should be spatially tailored rather than uniformly applied. The partitioned differential lubrication concept demonstrates that different regions of a forming component have fundamentally different material flow requirements, and a single global parameter setting cannot satisfy all local conditions simultaneously. This insight extends beyond hydraulic forming to other manufacturing processes such as welding, where heat input and cooling rates must be varied across different weld sections to achieve uniform properties. The ability to control local deformation through surface treatment offers a non-invasive approach to improving forming quality without modifying tooling geometry or material properties, making it particularly valuable for existing production lines seeking quality improvements.