Zhuojin Pipe Fitting Co., LtdManufacturing Process and Force Analysis of Drawn Tee Pipes
Literature Overview
This paper by Lin Weizhong from Guangzhou Petrochemical General Plant Construction and Installation Company, published in 1998 in Pipe Technology and Equipment (Vol. 1998, No. 2, pp. 25–29), provides a comprehensive practical guide to the manufacture of tee fittings through the drawing (pulling) process. The paper details the manufacturing process, working principles, die design methodology, drawing force calculation, and practical considerations for production.
Drawing Process for Tee Pipe Manufacturing
The drawing process for tee pipes involves pulling a pipe blank through a shaped die that progressively forms the branch opening. Unlike hydroforming or forging, this method uses tensile forces to draw the material through a converging die geometry, creating the tee shape through controlled plastic deformation.
The typical process sequence includes:
- Selection of appropriate pipe blank with sufficient wall thickness
- Pre-forming of the pipe blank to approximate the tee geometry
- Progressive drawing through a series of dies to achieve final dimensions
- Post-forming operations including trimming and dimensional correction
- Heat treatment if required by material specification
Die Design Methodology
The die design is the critical element of the drawing process. The paper describes a die system that includes:
| Die Component | Function | Design Consideration |
|---|---|---|
| Main body die | Shapes the main pipe section | Must maintain dimensional accuracy under high loads |
| Branch forming die | Creates the branch opening | Requires precise cavity geometry matching final dimensions |
| Pilot die | Guides and aligns the blank | Must accommodate material flow without binding |
| Support die | Prevents buckling during drawing | Provides reaction surface for drawing force |
The die material selection is critical: tool steels such as H13 or D2 are typically specified for their combination of hardness, toughness, and wear resistance. Die surface treatment through nitriding or chromium plating further extends service life.
Drawing Force Calculation
The paper provides methodology for calculating the drawing force required to form the tee:
The basic drawing force equation considers:
- Deformation resistance of the material (yield strength adjusted for strain hardening)
- Friction between the pipe blank and die surfaces
- Die geometry factors (reduction ratio, land length, entry angle)
- Material flow resistance at the branch formation zone
| Parameter | Typical Value | Influence on Drawing Force |
|---|---|---|
| Material yield strength | 250–450 MPa (carbon steel) | Directly proportional |
| Reduction ratio | 10–30% per pass | Higher ratio increases force exponentially |
| Die friction coefficient | 0.05–0.15 (with lubrication) | Higher friction increases force significantly |
| Die entry angle | 5–15 degrees | Optimal angle minimizes force |
| Branch diameter ratio | 0.3–0.8 of main diameter | Larger branch requires substantially more force |
Practical Considerations and Problem Solutions
The paper addresses several practical issues encountered during production:
- Material flow control: Ensuring uniform material flow into the branch requires careful die geometry design. Asymmetric flow can result in uneven wall thickness at the branch.
- Surface quality: Drawing can introduce surface defects including scratches, scoring, and dimensional irregularities. Proper lubrication and die surface finish are essential.
- Springback: After removal from the die, elastic recovery can affect final dimensions. The paper recommends over-forming by 1–3% to compensate for springback.
- Strain limitation: The maximum achievable reduction per pass is limited by the material's formability. Exceeding this limit causes cracking or tearing.
- Equipment requirements: Drawing machines must provide sufficient tonnage (typically 200–2000 tons depending on pipe size) and stroke length to accommodate the full forming sequence.
Comparison with Alternative Manufacturing Methods
| Method | Advantage | Limitation | Applicable Material |
|---|---|---|---|
| Drawing | Low cost, good surface finish | Limited to thin-walled pipes | Carbon steel, stainless steel |
| Hydroforming | Complex geometries achievable | High equipment cost | Wide range of metals |
| Forging | Full penetration, high strength | High energy consumption | Carbon steel, alloy steel |
| Welding | Any size achievable | Weld quality critical | All pipe materials |
Engineering Practice Recommendations
For engineers considering the drawing process for tee fitting production:
- Conduct formability testing on the specific material grade to determine maximum reduction limits.
- Design die systems with modular components to allow rapid changeover between different tee specifications.
- Implement in-process dimensional checking at intermediate forming stages to detect deviations early.
- Establish lubrication systems with appropriate temperature control to maintain consistent friction conditions.
- Develop acceptance criteria based on wall thickness uniformity, dimensional accuracy, and surface quality.
Study Insights
This paper represents practical manufacturing knowledge that bridges the gap between theoretical forming mechanics and shop-floor reality. The drawing process for tee fittings remains economically attractive for small to medium production volumes where hydroforming or forging equipment costs are prohibitive. The paper's systematic treatment of die design, force calculation, and practical considerations provides a valuable reference for engineers entering this manufacturing domain. The emphasis on practical problem-solving rather than theoretical development reflects the applied engineering tradition of Chinese manufacturing industry publications.