Numerical Simulation and Experimental Verification of Hot Pressing Forming of TC4 Titanium Alloy T-Type Tee Fittings

Literature Overview

This paper by Han Shihao, Duan Mingde, Zhang Zhuangya, Li Chong, Hou Shizhe, and Ba Mingchao, published in Heat Processing Technology (2026, Vol. 55, No. 5, pp. 166-173), investigates the hot pressing forming process for TC4 titanium alloy T-type tee fittings using a combined numerical simulation and experimental approach. The work is supported by the National Key R&D Program of China. The authors are from Henan University of Science and Technology and the 725th Research Institute of China Shipbuilding Group Corporation.

Core Technical Parameters

The study systematically examines three critical process parameters: hot pressing temperature, hot pressing rate, and die entrance fillet radius. These parameters directly influence the final wall thickness distribution and bulge height of the formed tee fitting, which are critical quality indicators for structural integrity and dimensional accuracy.

The optimal conditions for maximum bulge height are identified at 750°C, 7.5 mm/s, and 60 mm fillet radius. This combination represents a balance between material flow capability and dimensional control, achieving the desired geometry with acceptable wall thickness uniformity.

Forming Mechanism Analysis

The hot pressing forming process for T-type tee fittings involves complex material flow patterns governed by the interplay of temperature-dependent material properties, strain rate sensitivity, and die geometry constraints. At elevated temperatures, TC4 titanium alloy exhibits reduced yield strength and enhanced ductility, facilitating the necessary material redistribution for tee formation. However, excessive temperatures may lead to grain coarsening and reduced mechanical properties in the heat-affected zone.

The die entrance fillet radius plays a crucial role in controlling material flow direction and strain distribution. A larger fillet radius promotes more uniform material flow but reduces the forming force, potentially leading to incomplete forming at lower temperatures. Conversely, a smaller fillet radius concentrates strain at the die entrance, increasing forming force but potentially causing material thinning and cracking.

Experimental Validation

The experimental results confirm the numerical simulation predictions with good agreement, validating the simulation model's accuracy for process optimization purposes. The key quality indicators examined include:

The experimental verification demonstrates that the numerical simulation approach is reliable for predicting forming quality and optimizing process parameters, significantly reducing the need for costly trial-and-error experimentation.

Engineering Practice Implications

For manufacturers of titanium alloy tee fittings, this research provides a systematic approach to process optimization. The identified optimal parameters (750°C, 7.5 mm/s, 60 mm fillet radius) serve as a starting point for production process development, with subsequent refinement based on specific material batches and equipment capabilities. The combined simulation-experimental methodology offers a cost-effective path to process qualification, reducing development time and material waste.

The findings also highlight the importance of die design in hot pressing forming. The fillet radius, often treated as a secondary design consideration, significantly influences forming quality and should be carefully optimized during die development. Additionally, the temperature-rate interaction demonstrates that process parameter optimization requires a holistic approach rather than isolated parameter tuning.

Key Questions and Reflections

Several aspects merit further investigation. First, the effect of multi-step forming sequences, where the tee is formed in stages with intermediate reheating, could potentially improve wall thickness uniformity at the expense of production speed. Second, the influence of material microstructure, particularly prior beta grain size, on forming quality should be studied, as microstructural variations can significantly affect material flow behavior. Third, the scalability of the process to larger tee fittings requires investigation, as geometric scaling may introduce additional challenges related to temperature uniformity and force capacity.

The research also raises questions about the long-term mechanical properties of hot-pressed tee fittings. While the forming process achieves the desired geometry, the microstructural evolution during hot pressing, including grain refinement and texture development, must be evaluated for fatigue and fracture resistance in service applications.

Study Insights and Implications

The most valuable contribution of this research is the establishment of a validated simulation-experiment framework for hot pressing forming of titanium alloy tee fittings. For engineering practice, the key insight is that process parameter optimization requires simultaneous consideration of temperature, rate, and die geometry, with interactions between parameters often being more significant than individual parameter effects. The identified optimal conditions provide a practical starting point for production development, while the simulation methodology enables rapid evaluation of design alternatives. This work demonstrates that numerical simulation, when properly validated, can significantly accelerate the development of complex forming processes while maintaining quality and reliability.