Zhuojin Pipe Fitting Co., LtdNumerical Simulation and Process Optimization of CuNi90/10 Socket-Weld Tee Hot Forming
Literature Overview
This paper by Yang Qingyun, Yuan Wei, Ma Junpu, and Zhang Zhiyuan (China Shipbuilding Industry Corporation, Institute 725, published in Materials Development and Application, Vol. 36, No. 6, 2021) presents a thermo-mechanical coupled finite element analysis of the hot forming process for CuNi90/10 socket-weld tee fittings using the Deform-3D software. The study systematically investigates the effects of punch geometry, push speed, initial temperature, and friction conditions on forming quality, providing actionable process optimization recommendations for nickel-copper alloy tee production.
Material and Process Context
CuNi90/10 (Cupronickel 90/10) is a corrosion-resistant alloy widely used in marine applications, including seawater piping systems, heat exchangers, and submarine pressure hulls. Socket-weld tees are critical components in these systems, requiring precise geometry for both mechanical integrity and gasket sealing. The hot forming process must balance material flow, dimensional accuracy, and surface quality.
| Parameter | Value/Range |
|---|---|
| Material | CuNi90/10 (C70600 equivalent) |
| Simulation software | Deform-3D |
| Model type | Thermo-mechanical coupled FEA |
| Punch shapes evaluated | Multiple configurations including cylindrical convex |
| Push speed range | Multiple speeds tested |
| Optimal push speed | 40 mm/s |
| Initial temperature range | 950–1000°C |
| Friction coefficient | Lower values preferred |
Process Parameter Analysis
Punch Geometry
The study evaluates different punch profiles, with the cylindrical convex punch emerging as optimal. This finding is consistent with general hot forming principles: a convex punch promotes uniform material flow and reduces localized thinning at critical junctions. Flat punches tend to create more abrupt material displacement, leading to higher stress concentrations and potential cracking in the branch pipe wall.
Push Speed
The optimal push speed of 40 mm/s represents a balance between:
- Too slow: Excessive oxidation, prolonged exposure to high temperature leading to grain coarsening, and reduced productivity.
- Too fast: Insufficient time for material flow to fill complex geometries, increased forming loads, and potential die wear.
At 40 mm/s, the strain rate is sufficient to maintain favorable flow stress behavior while allowing adequate material redistribution.
Initial Temperature
The 950–1000°C range corresponds to the optimal forging temperature window for CuNi90/10. This temperature range ensures:
- Sufficient plasticity for complete die filling
- Favorable grain structure without excessive grain growth
- Acceptable oxidation rate during forming
- Adequate flow stress for manageable forming loads
Friction Conditions
Lower friction coefficients improve forming quality by reducing surface drag effects that cause:
- Uneven material flow across the die surface
- Surface defects and roughness
- Increased forming loads
- Potential cracking at free surfaces
Practical friction reduction methods include proper die lubrication with graphite-based or ceramic-based lubricants suitable for nickel-copper alloys at forming temperatures.
Engineering Practice Integration
Several practical considerations arise from this study:
- Die design: The cylindrical convex punch design must be carefully manufactured with appropriate surface finish (typically Ra 0.8–1.6 μm) to minimize friction and surface transfer defects.
- Heating control: Uniform heating of the CuNi90/10 billet is critical. Temperature gradients within the billet can cause asymmetric deformation and dimensional inaccuracy. Infrared heating with temperature monitoring is recommended.
- Post-forming operations: Socket-weld tees typically require subsequent machining of the socket bore, face, and sealing surfaces. The hot forming process must leave adequate machining allowance (typically 2–5 mm) while minimizing material waste.
- Quality verification: Formed CuNi90/10 tees require:
- Dimensional inspection per applicable standard (e.g., ASME B16.11 for socket-weld fittings)
- Surface quality assessment (no cracks, laps, or excessive oxidation)
- Chemical composition verification
- Corrosion resistance testing per ASTM B150 or equivalent
- Hydrostatic testing after machining
Common Defects and Countermeasures
| Defect | Cause | Countermeasure |
|---|---|---|
| Branch wall thinning | Excessive material flow into branch | Reduce punch speed; optimize punch radius |
| Surface cracking | High strain rate or insufficient temperature | Increase initial temperature; reduce push speed |
| Incomplete filling | Insufficient forming force or poor lubrication | Increase temperature; improve lubrication |
| Surface roughness | Poor die finish or excessive friction | Polish die; apply proper lubricant |
| Dimensional inaccuracy | Asymmetric material flow | Ensure uniform heating; optimize die geometry |
Study Insights and Implications
This study provides valuable quantitative guidance for the hot forming of CuNi90/10 socket-weld tees, a process that is challenging due to the relatively narrow forging window of nickel-copper alloys. The systematic parametric analysis approach using Deform-3D is well-suited for process development and optimization, allowing engineers to identify optimal conditions before committing to physical trials. The finding that lower friction is consistently beneficial reinforces the importance of die surface quality and lubrication strategy in nickel alloy forming operations. For shipbuilding and marine engineering applications where CuNi90/10 tees are critical components, this research provides a solid foundation for process standardization and quality improvement. The thermo-mechanical coupled modeling approach should be adopted as standard practice for developing forming processes for other nickel-based alloys used in marine and offshore applications.