Zhuojin Pipe Fitting Co., LtdNumerical Simulation and Experimental Study of 45 Degree Oblique Tee Extrusion Forming
Literature Overview
Zhao Hengliang and colleagues from the China Academy of Machinery Science and Technology, Hebei Hongrun Heavy Industry Co., Ltd., and Beijing Institute of Electromechanical Technology published a study in Forging & Stamping Technology (2016, Vol. 41, Issue 4) presenting a comprehensive investigation of 45° oblique tee extrusion forming using AFDEx finite element software. Funded by the National Science and Technology Major Project (2014ZX04014-051) and International Science and Technology Cooperation Program (2015DFA51740), the research combines thermomechanical coupled finite element modeling with experimental validation to characterize the forming process for a specific specification of 45° oblique tee fitting.
Core Technical Content
The study establishes a thermomechanical coupled finite element model for the extrusion forming process of 45° oblique tee fittings. The forming process involves three sequential stages: upsetting (镦粗), reverse extrusion (反挤压), and piercing (穿孔). The simulation reveals the distribution patterns of equivalent strain, load-time curves, and die stress throughout the forming sequence.
Process Parameters and Load Characteristics
| Process Stage | Simulated Forming Load (kN) | Experimental Forming Load (kN) | Deviation |
|---|---|---|---|
| Upsetting | 42,410 | 41,520 | -2.1% |
| Reverse Extrusion | 34,920 | 34,500 | -1.2% |
| Piercing | - | 34,500 | - |
The high strain values concentrate primarily in the region where billet metal flows past the vertical punch. The load-time curves show that during upsetting, the load rises slowly then increases rapidly until completion. During reverse extrusion, the load increases rapidly to approximately 23,000 kN, stabilizes for a period, and reaches a final forming load of 34,920 kN.
Metallurgical Analysis of the Forming Process
From my expertise in pipe fitting metallurgy, the extrusion forming of 45° oblique tees presents several critical metallurgical challenges that the study addresses through simulation. The thermomechanical coupling is essential because the forming temperature directly affects material flow stress, strain hardening behavior, and the resulting microstructure of the finished fitting.
The concentrated strain regions identified at the vertical punch interface represent zones of potential microstructural heterogeneity in the final product. In practice, these regions may exhibit:
- Enhanced grain refinement due to high strain accumulation
- Potential for strain-induced martensitic transformation in low-alloy steels
- Residual stress concentration requiring post-forming stress relief
- Variable mechanical properties across the cross-section
Material Selection Considerations for Oblique Tee Forming
| Steel Grade | Formability Assessment | Key Consideration |
|---|---|---|
| 10CrMo991 | Good | High temperature strength for power plant applications |
| P91/P92 | Moderate | Requires precise temperature control |
| 15CrMoG | Good | Common for boiler and pressure vessel applications |
| 20# Carbon Steel | Excellent | Baseline material for process development |
Process-Product Property Relationships
The load-time behavior observed in the simulation provides critical information for equipment selection and process optimization. The upsetting stage requiring approximately 42,000 kN establishes the minimum tonnage requirement for the forming press. The reverse extrusion stage, with its characteristic rapid load increase followed by stabilization, indicates a transition from initial deformation to steady-state material flow.
The close agreement between simulated and experimental loads (deviations of 1.2-2.1%) validates the finite element model and provides confidence in using simulation for process optimization and scale-up. This level of accuracy is achievable when the constitutive model, friction conditions, and thermal boundary conditions are properly calibrated.
Engineering Practice Applications
For pipe fitting manufacturers producing 45° oblique tees through extrusion forming, this study provides:
- Equipment sizing criteria based on peak forming loads for specific specifications.
- Process parameter windows that ensure complete material flow without excessive die wear.
- Die stress distribution data for optimizing die material selection and heat treatment specifications.
- Strain distribution predictions that inform post-forming inspection requirements, particularly for critical applications requiring ultrasonic testing of internal integrity.
The research methodology combining numerical simulation with experimental validation represents the current best practice for developing new pipe fitting forming processes. The approach enables rapid process optimization with reduced trial-and-error costs, which is particularly valuable when producing specialized fittings for demanding applications such as power generation, petrochemical processing, and nuclear industry.
Study Insights and Recommendations
The successful validation of the AFDEx model against experimental results demonstrates the maturity of finite element analysis for pipe fitting forming process development. However, several areas warrant further investigation: the effect of forming speed on product quality, the influence of initial billet temperature distribution on final product properties, and the long-term fatigue performance of extrusion-formed 45° oblique tees compared to their forged counterparts. For production applications, the simulation results should be supplemented with metallographic examination and mechanical property testing at multiple locations within the formed fitting to ensure uniform quality throughout the component.