Research on the Mechanism of Rotary Drawing Tee Tubes

Literature Overview

This 1998 paper published in "Tool Engineering" presents an early and fundamental study of the rotary drawing mechanism for producing tee tubes, which are used in heat exchangers and refrigeration systems. The authors from the Department of Mechanical and Electrical Engineering at South China University of Technology investigated the forming characteristics and conditions of tee tubes produced by the rotary drawing process. The study was supported by the Guangdong Provincial Natural Science Foundation. The experimental results demonstrated that the drawing force increases with the inclination angle of the die, the rotary drawing allowance, and the feed rate, while the height of the side hole is primarily determined by the rotary drawing allowance. This work provides valuable insights into the mechanics of complex tube forming processes and has implications for the design and optimization of rotary drawing operations for production tee tubes.

Core Technical Analysis

Rotary Drawing Process Fundamentals

The rotary drawing process for tee tube production involves the simultaneous rotation and axial feeding of a tube blank through a die set. The die set consists of a main die that shapes the outer contour of the tee and a plug or punch that forms the internal cavity and the side hole. As the tube rotates, the material is gradually drawn and formed into the tee geometry, with the side hole being formed by the interaction of the plug and the die.

The key process parameters that influence the rotary drawing of tee tubes are:

Forming Mechanism Analysis

The forming mechanism of tee tubes during rotary drawing can be understood through the following stages:

1. Initial contact: The tube blank is positioned in the die set, and the plug begins to advance axially while the tube rotates.
2. Material deformation: As the plug advances, the tube material is forced outward against the die walls, causing radial expansion and axial compression.
3. Side hole formation: The plug geometry creates a localized deformation zone that forms the side hole in the tube wall. The height of the side hole is determined by the amount of material displacement, which is controlled by the rotary drawing allowance.
4. Steady-state forming: Once the plug has fully advanced, the tube continues to rotate and feed through the die set, maintaining the tee geometry.
5. Final forming: The completed tee tube exits the die set with the desired geometry and surface finish.

Drawing Force Analysis

The drawing force in the rotary drawing process is influenced by several factors:

• Friction between tube and die: The friction coefficient between the tube surface and the die surface is a major contributor to the drawing force. Proper lubrication is essential to minimize friction and reduce the required drawing force.
• Material flow resistance: The resistance of the tube material to plastic deformation depends on the material's yield strength, strain hardening behavior, and the severity of the deformation.
• Die geometry: The inclination angle of the die affects the component of the drawing force that acts in the axial direction. A larger inclination angle increases the axial component of the friction force, thereby increasing the drawing force.
• Rotary drawing allowance: The allowance represents the amount of material deformation required to form the tee geometry. A larger allowance requires greater material displacement, which increases the drawing force.
• Feed rate: A higher feed rate increases the strain rate in the material, which can increase the flow stress due to strain rate sensitivity, thereby increasing the drawing force.

Side Hole Height Determination

The height of the side hole in the tee tube is primarily determined by the rotary drawing allowance. The allowance controls the amount of material that is displaced outward to form the side hole. A larger allowance results in a taller side hole, while a smaller allowance produces a shorter side hole. This relationship is direct and predictable, making the rotary drawing allowance the primary process parameter for controlling the side hole geometry.

The side hole height must be carefully controlled to ensure that the tee tube meets the dimensional specifications required for its intended application. In heat exchanger applications, the side hole height affects the flow distribution and heat transfer performance of the tee. In refrigeration applications, the side hole height affects the pressure drop and flow characteristics of the tee.

Engineering Practice Implications

Process Optimization

The findings from this study have direct implications for the optimization of the rotary drawing process for tee tube production:

1. Drawing force minimization: To reduce the drawing force and improve process efficiency, the inclination angle of the die should be kept as small as practical, the rotary drawing allowance should be minimized while still achieving the required side hole height, and the feed rate should be optimized to balance productivity with drawing force.
2. Side hole height control: The rotary drawing allowance should be carefully selected to achieve the desired side hole height. Process trials should be conducted to establish the relationship between allowance and side hole height for the specific tube material and die geometry being used.
3. Lubrication optimization: Proper lubrication is essential to minimize friction and reduce the drawing force. The lubricant selection should be based on the tube material, the operating temperature, and the required surface finish.
4. Die design optimization: The die geometry should be designed to minimize the drawing force while maintaining the required dimensional accuracy. Finite element analysis (FEA) can be used to simulate the forming process and optimize the die geometry before production trials.

Quality Control

The quality of tee tubes produced by rotary drawing must be controlled through the following measures:

• Dimensional inspection: The side hole height, tee angle, and overall dimensions must be measured and verified against the specified tolerances.
• Surface finish inspection: The internal and external surfaces of the tee tube must be inspected for surface defects such as scratches, wrinkles, and die marks.
• Wall thickness measurement: The wall thickness at the side hole and at the main body of the tee must be measured to ensure that the material deformation is within acceptable limits.
• Mechanical property testing: Tensile tests and hardness tests should be performed on representative samples to verify that the mechanical properties of the tee tube meet the specified requirements.
• Leak testing: Pressure leak tests should be performed to verify the integrity of the tee tube, particularly at the side hole where the wall thickness is reduced.

Study Insights and Reflections

This paper provides a foundational understanding of the rotary drawing mechanism for tee tube production. The systematic experimental approach and the clear identification of the key process parameters and their effects on the forming process are valuable contributions to the field of tube forming technology. The finding that the side hole height is primarily determined by the rotary drawing allowance is particularly useful for process design and optimization.

One important reflection from this study is the recognition that the rotary drawing process for tee tubes is a complex three-dimensional forming operation that involves simultaneous rotation, axial feeding, and material displacement. The interaction between these deformation modes makes the process challenging to model and optimize, and experimental validation remains essential for process development.

Another insight is that the drawing force is a critical process parameter that affects both the productivity and the quality of the tee tubes. Minimizing the drawing force not only reduces the energy consumption of the process but also reduces the risk of material defects such as cracking and excessive thinning. This highlights the importance of process optimization in achieving high-quality tee tube production.

Summary

The rotary drawing process for tee tube production is a complex forming operation that requires careful control of process parameters to achieve the desired geometry and quality. The study demonstrates that the drawing force is influenced by the die inclination angle, the rotary drawing allowance, and the feed rate, while the side hole height is primarily determined by the rotary drawing allowance. These findings provide a solid technical foundation for the design and optimization of rotary drawing operations for tee tube production. Engineers involved in tee tube manufacturing should use these insights to optimize their processes, improve product quality, and reduce production costs.