Numerical Simulation and Process Optimization of CuNi90/10 Socket-Weld Tee Forming

Literature Overview and Context

The paper by Yang Qingyun, Yuan Wei, Ma Junpu, and Zhang Zhiyuan (2021), published in Materials Development and Application (Vol. 36, No. 6, pp. 26–30), presents a comprehensive numerical simulation study of the hot forming process for CuNi90/10 socket-weld tees using the Deform-3D finite element software. CuNi90/10 (copper-nickel alloy, 90% Cu, 10% Ni) is a widely used material for seawater service applications in shipbuilding, marine engineering, and offshore platforms due to its excellent corrosion resistance in marine environments. The authors systematically investigate the effects of punch shape, pushing speed, initial temperature, and friction coefficient on the forming quality, with the objective of identifying optimal process parameters.

Finite Element Model and Simulation Setup

The authors establish a thermo-mechanically coupled finite element model using Deform-3D, which is a specialized software for metal forming simulation. The model accounts for the interaction between the thermal field (temperature distribution and heat transfer) and the mechanical field (stress, strain, and material flow) during the hot forming process.

The forming process involves heating a CuNi90/10 blank to a forging temperature, placing it in a die, and using a punch to push and form the tee geometry. The simulation captures the material flow, stress distribution, temperature evolution, and forming force throughout the process.

Key Simulation Results and Analysis

Punch Shape Effects

The authors compare three punch shapes: cylindrical flat, convex cylindrical, and concave cylindrical. The results demonstrate that the convex cylindrical punch produces the best forming quality, characterized by:

• More uniform material flow distribution
• Lower horizontal load (forming force)
• Reduced risk of material folding or cracking at the branch opening
• Better dimensional accuracy of the formed tee

The convex geometry promotes gradual material flow into the branch cavity, reducing the peak strain rate and associated thermal softening effects.

Pushing Speed Optimization

The optimal pushing speed of 40 mm/s represents a balance between forming efficiency and material quality. At lower speeds (<20 mm/s), the forming time is excessively long, leading to significant heat loss and increased forming force. At higher speeds (>60 mm/s), the rapid deformation generates excessive adiabatic heating, which can lead to local overheating and potential microstructural degradation.

Temperature and Friction Effects

The optimal initial temperature range of 950–1000°C is consistent with the recommended hot working temperature range for CuNi90/10 alloy, which exhibits peak thermal softening in this range. Below 950°C, the material flow stress is too high, requiring excessive forming force. Above 1000°C, there is a risk of grain coarsening and surface oxidation that degrades the final product quality.

The friction coefficient analysis reveals that lower friction is always beneficial for forming quality. This is achieved in practice through the use of appropriate die lubricants (such as graphite-based or ceramic-based coatings) and die surface treatments.

Engineering Practice Integration

The simulation results have direct practical value for manufacturers of CuNi90/10 socket-weld fittings used in marine and offshore applications. Several engineering considerations arise from the findings:

1. Die Design: The convex cylindrical punch shape should be adopted as the standard for CuNi90/10 tee forging operations. This requires corresponding modifications to existing die tooling, but the improvement in forming quality justifies the investment.
2. Process Control: The pushing speed should be controlled within the 35–45 mm/s range, with 40 mm/s as the target. This requires hydraulic press speed control systems with sufficient accuracy to maintain consistent forming conditions.
3. Temperature Management: The initial temperature should be monitored and controlled within the 950–1000°C range. In practice, this is achieved through furnace temperature control and in-process temperature measurement using infrared pyrometers.
4. Friction Management: Die lubrication and surface treatment programs should be implemented to minimize the friction coefficient. Common approaches include applying borax-based coatings to die surfaces or using press lubricants during the forming operation.

Study Insights and Reflections

This paper demonstrates the value of finite element simulation in optimizing hot forming processes for specialized alloys. The systematic parametric study approach—varying one parameter at a time while keeping others constant—provides clear insights into the relative importance of each process variable.

I find the friction coefficient finding particularly noteworthy. In practice, friction management is often underemphasized in hot forming operations, with operators relying on generic lubrication practices rather than optimized friction control. The simulation results confirm that even modest reductions in friction coefficient can lead to meaningful improvements in forming quality and load reduction.

The work also highlights the importance of material-specific process parameters. The optimal temperature range for CuNi90/10 differs from that of carbon steels or stainless steels, and applying generic forging parameters without material-specific optimization can lead to suboptimal results or even product failures.

In conclusion, this paper provides valuable process optimization guidance for CuNi90/10 socket-weld tee forging, with clear recommendations for punch geometry, forming speed, temperature, and friction management that can be directly implemented in manufacturing operations.