Effect of Various Media on Composite Bulging Process of Equal Tees

Literature Overview

The paper by Liu Ling et al., published in Forging & Stamping Technology (2007, Vol. 32, No. 5, pp. 40–43), investigates the influence of different bulging media on the composite bulging process of equal tees. Bulging is a key forming process for manufacturing tees from pipe blanks, and the selection of bulging medium significantly affects the forming quality, dimensional accuracy, and surface finish of the final product.

Composite Bulging Process Overview

Composite bulging combines the advantages of different bulging methods to achieve improved forming quality. In the context of tee manufacturing, the process involves:

1. A pipe blank is cut to the required length.
2. The blank is positioned in a die cavity shaped to the tee geometry.
3. A bulging medium is introduced into the pipe cavity and pressurized.
4. The internal pressure forces the pipe wall to conform to the die cavity shape.
5. The formed tee is removed and finished as required.

The bulging medium serves as the pressure-transmitting element that contacts the inner surface of the pipe. Its properties directly influence the forming pressure distribution, metal flow pattern, and final product quality.

Media Comparison and Performance Analysis

The study evaluated five different bulging media:

The key finding is that all media can achieve the required bulging ratio, but they differ significantly in surface quality and economic characteristics.

Selection Criteria and Engineering Guidelines

Based on the experimental results and metal flow analysis, the following selection guidelines are established:

For high inner surface quality requirements:

• Nylon, polyurethane rubber, or silicone rubber are recommended.
• These elastomeric media conform closely to the inner surface, providing uniform pressure distribution.
• The smooth surface of these media transfers minimal surface defects to the formed product.

For low inner surface quality requirements or no inner surface specification:

• Paraffin wax is recommended.
• The wax medium is cost-effective and recyclable, reducing production costs.
• The slightly rougher inner surface is acceptable for applications where internal surface finish is not critical.

Metal Flow Analysis

The metal flow behavior during bulging is influenced by the medium's compressibility and surface characteristics. Elastomeric media (nylon, silicone rubber, polyurethane rubber) are nearly incompressible, providing uniform radial pressure on the pipe wall. This uniform pressure promotes consistent metal flow and reduces the risk of local thinning or wrinkling.

In contrast, paraffin wax exhibits some compressibility and may flow slightly during the forming process. This can lead to non-uniform pressure distribution, particularly at the intersection zone where the tee geometry changes. However, for applications where inner surface quality is not critical, this non-uniformity is acceptable.

Key Reflections

This work provides practical guidance for tee manufacturers on media selection, which is a critical but often underappreciated process parameter. The economic considerations are particularly important, as the bulging medium represents a consumable cost in production. The ability to recycle paraffin wax significantly reduces material costs for applications where surface quality is not critical.

For pipeline engineers, this literature underscores the importance of process parameter selection in manufacturing quality. The same principle applies to other forming processes: the choice of forming medium, lubrication, and process parameters directly influences the final product quality and service performance.