CLADDING TECHNOLOGY SHANXI CO., LTDComposite Bulging Process for Equal-Diameter Copper Tee Tubes
Literature Overview and Technical Context
The research by Cai Lifang, Zhang Yanmin, and Sun Aixue (2003) from Henan University of Science and Technology addresses the composite bulging process for equal-diameter copper tee tubes. Published in the Journal of Henan University of Science and Technology (Natural Science Edition), this work focuses on a specific forming technique — composite bulging — applied to copper tee tubes of equal diameter. Copper tee tubes are used in electrical connectors, heat exchangers, and fluid systems where thermal conductivity, corrosion resistance, and formability are important material properties.
The composite bulging process combines internal pressure bulging with external mechanical forming to produce the tee geometry in a single operation. This approach is advantageous for copper tubing because copper has excellent formability and ductility, making it well-suited for hydroforming or pneumatic bulging processes. The work contributes to the understanding of tubular forming processes that are relevant to pressure vessel fabrication, particularly for small-diameter tubing and branch connections.
Process Mechanism and Forming Analysis
Composite bulging of tee tubes involves the simultaneous application of internal pressure and external mechanical deformation to form the branch opening in the tube. The internal pressure (typically hydraulic or pneumatic) causes the tube to expand outward, while the external mechanical element (such as a plug, punch, or die) controls the shape and position of the branch opening.
The forming sequence for an equal-diameter tee tube typically involves the following stages:
- Initial inflation of the tube to create a local bulge at the intended branch location.
- Insertion of a mechanical plug or punch to define the branch opening geometry.
- Further inflation to expand the tube wall into the die cavity, forming the tee shape.
- Depressurization and removal of the formed part.
The key process parameters include the internal pressure level, the plug insertion depth and rate, the die geometry, and the lubrication conditions. The interaction between these parameters determines the final geometry, wall thickness distribution, and mechanical properties of the formed tee tube.
| Process Parameter | Typical Value | Effect on Forming |
|---|---|---|
| Internal pressure | 50–200 MPa | Controls bulge diameter and wall thinning |
| Plug insertion depth | 2–10 mm | Defines branch opening size |
| Plug insertion rate | 1–20 mm/min | Affects strain rate and temperature rise |
| Die surface roughness | Ra < 0.8 µm | Minimizes surface marking and friction |
| Lubricant viscosity | 50–200 cSt | Controls friction and surface quality |
Material Behavior and Forming Limitations
Copper, particularly copper tubing in the annealed (O) condition, has excellent formability with elongation values typically exceeding 30%. This makes copper well-suited for bulging operations, but the forming limit must still be carefully managed to avoid excessive thinning or cracking. The forming limit diagram (FLD) for copper defines the safe strain region in terms of major and minor strain, and the forming process must be designed to keep the strain state within this safe region.
For tee tube forming, the strain state at the branch junction is typically biaxial, with both major and minor strains being tensile. This is generally a favorable strain state for formability, but the strain magnitude can be high enough to cause thinning beyond acceptable limits. The acceptable thinning ratio is typically defined by the application requirements, with electrical connectors requiring tighter tolerances than fluid system applications.
Quality Control and Inspection
The quality of copper tee tubes formed by composite bulging is assessed through dimensional inspection, wall thickness measurement, and mechanical property testing. Critical quality attributes include the branch opening diameter and position, the wall thickness at the thinnest point (typically at the branch junction), the surface finish, and the tensile strength and elongation after forming.
Non-destructive testing methods applicable to copper tee tubes include ultrasonic testing for wall thickness measurement, eddy current testing for surface and near-surface defect detection, and visual inspection for surface quality. For applications requiring high reliability, such as electrical connectors or pressure systems, 100% inspection may be required.
Study Insights and Engineering Relevance
The work by Cai et al. provides valuable insights into the composite bulging process for copper tee tubes. The study demonstrates that the combination of internal pressure and external mechanical forming can produce complex tee geometries in a single operation, reducing the number of manufacturing steps and improving production efficiency.
For engineers working in pressure vessel and bimetal fabrication, the relevance of this work lies in the understanding of tubular forming processes and the principles of composite forming. The same principles of strain control, pressure management, and tool design that apply to copper tee tubes are applicable to steel, stainless steel, and alloy tee tubes used in pressure vessel branch connections. The key lesson is that composite forming, when properly designed, can produce high-quality tubular components with minimal defects and excellent mechanical properties.