Large Diameter Seamless Steel Pipe Extrusion Upset Forming Process

Literature Overview

This paper by Guo Yongqiang, Xu Chunguo, Ren Weiwei, Chen Yujin, and Zhang Ya from the Beijing Institute of Mechanical and Electrical Engineering, published in Forging Technology in 2014, Volume 39, Issue 12, investigates the upset forming process for large-diameter seamless steel pipes using extrusion methods. Funded by the National High-Tech Research and Development Program (2012AA040202), the study employs finite element simulation software Deform-3D to analyze the relationships between various process parameters and optimize the upset forming capability of the pipe material. The research is classified under TG376.2 and addresses key parameters including semi-cone angle, heating temperature, forming speed, friction coefficient, and limit upset ratio.

Core Technical Findings

The primary objective of this research is to understand the variation laws of process parameters during upset forming of large-diameter seamless steel pipes and to improve the degree of upset deformation. The authors systematically analyze the interrelationships among semi-cone angle, heating temperature, forming speed, friction coefficient, and the limit upset ratio through numerical simulation.

The following table presents the key process parameters and their optimized values as determined in the study:

Analysis of Temperature Gradient Method

One of the most significant contributions of this paper is the proposal of a temperature gradient heating method to enhance the upset forming capability of large-diameter seamless steel pipes. The conventional approach uses uniform heating across the entire workpiece, which limits the achievable upset ratio. The authors demonstrate through both theoretical analysis and finite element simulation that applying a controlled temperature gradient, where the region to be deformed is heated to a higher temperature than the surrounding areas, can substantially increase the deformation capacity.

The temperature gradient value k is defined as the ratio of the maximum temperature to the minimum temperature in the heated zone. When k equals 1.67, the upset ratio m reaches approximately 0.67, representing a 15 percent improvement over uniform heating conditions. This improvement is attributed to the localized softening of the material in the deformation zone, which reduces the flow stress and allows for greater plastic strain accumulation without excessive force requirements.

The following table compares the upset forming performance under uniform heating versus temperature gradient heating:

Experimental Validation

The study validates the numerical simulation results through both scaled experiments and full-scale experiments. In the scaled experiments with a sample size ratio of 1:0.6, the experimental upset ratio m under uniform temperature conditions matches the numerical analysis results, confirming the accuracy of the finite element model. In the full-scale experiments with a 1:1 sample size ratio, when the temperature gradient value k is set to 1.67, the upset ratio m reaches approximately 0.67, demonstrating a 15 percent improvement in upset deformation degree.

The experimental results also confirm that the optimal semi-cone angle alpha of 23 degrees provides the best balance between deformation uniformity, force efficiency, and surface quality. Deviations from this angle in either direction result in either excessive force requirements or non-uniform material flow patterns that can lead to surface defects and internal cracking.

Engineering Practice Applications

This research has direct implications for the manufacturing of large-diameter pipe fittings, particularly elbows, reducers, and tees that require upset forming operations. The temperature gradient heating method offers a practical solution for achieving higher deformation ratios without requiring larger forming equipment or higher temperatures that could compromise material properties. For engineers involved in pipe fitting production, the key takeaways include:

• The semi-cone angle of 23 degrees should be adopted as the design standard for upset forming tools
• Temperature gradient heating with k values between 1.5 and 1.7 can significantly improve upset ratios
• Finite element simulation using Deform-3D is a reliable tool for predicting forming behavior and optimizing process parameters
• Quality control should focus on temperature uniformity monitoring, surface defect inspection, and dimensional accuracy verification

Study Insights and Reflections

This paper exemplifies the effective integration of numerical simulation and experimental validation in solving practical manufacturing challenges. The concept of temperature gradient heating is particularly elegant in its simplicity and effectiveness, offering a practical improvement that does not require major equipment modifications. For engineers in the pipe fitting industry, this research provides actionable guidance for improving production efficiency and part quality. The study also underscores the importance of systematic parameter optimization in metal forming processes, where multiple interacting variables must be balanced to achieve optimal results. The findings are especially relevant for the production of large-diameter pipe fittings used in oil and gas pipelines, power generation facilities, and chemical processing plants, where the ability to achieve greater upset ratios translates directly into reduced material waste and improved structural integrity of the final products.