Full-Automatic Extrusion Machine for Conical Pipe Fitting Production

Literature Overview

The paper by Zeng Yihui, Bai Chunwang, Zeng Xianjun, and Chen Shengli, published in Machine Tool and Hydraulics (Volume 32, Issue 9, 2004, pages 133–135), describes the development of a fully automatic extrusion machine for manufacturing conical pipe fittings. The research was conducted jointly by the Department of Mechanical Engineering at Hunan Normal University and the Jiangnan Machinery Factory. The machine integrates preheating, extrusion forming, and core rod extraction into an automated production cycle controlled by a Programmable Logic Controller (PLC).

Technical Design and Process Description

Conical pipe fittings (such as reducers and conical tees) are traditionally manufactured through forging, machining, or welding processes, each of which has limitations in terms of material utilization, production efficiency, and dimensional accuracy. The proposed extrusion-based approach offers a material-efficient alternative by forcing heated pipe stock through a forming die to achieve the desired conical geometry.

The machine design incorporates several key technical features:

1. Tube-type preheating furnace: The pipe stock is preheated to the appropriate forming temperature before entering the extrusion zone. The tube-type design ensures uniform heating along the length of the pipe, which is critical for achieving consistent extrusion force and material flow.
2. Extrusion forming die: The die geometry is designed to progressively deform the cylindrical pipe stock into the target conical shape. The die profile determines the final geometry of the fitting and must be carefully designed to avoid material thinning or cracking.
3. Dual-piston core rod and ejector mechanism: After the pipe stock is extruded through the die, the core rod (mandrel) and the ejector rod must be withdrawn to release the formed fitting. The dual-piston design enables independent control of the core rod extraction and the ejector action, ensuring clean separation without damaging the formed part.
4. PLC-based automatic control system: The PLC coordinates the entire production cycle, including material loading, preheating, extrusion, core rod extraction, and unloading. The control system ensures precise timing and sequence control for each operation.
5. Loading and unloading manipulators: Robotic manipulators handle the loading of raw pipe stock and the removal of finished fittings, enabling unattended operation and high production throughput.

Process Analysis and Performance Evaluation

The extrusion process for conical fittings involves several critical process parameters that must be carefully controlled:

• Preheating temperature: Must be high enough to reduce the flow stress of the material but not so high as to cause excessive oxidation or grain growth. For carbon steel fittings, typical preheating temperatures range from 700°C to 900°C, depending on the specific steel grade.
• Extrusion speed: The rate at which the pipe stock is forced through the die affects the deformation rate, flow stress, and final material properties. Higher speeds may lead to uneven deformation and potential cracking, while lower speeds reduce production efficiency.
• Die geometry: The angle of the die taper, the land length, and the entry angle all influence the material flow pattern and the quality of the formed surface.
• Lubrication: Appropriate lubrication reduces friction between the material and the die, lowering the required extrusion force and improving surface finish.

The authors report that the machine achieves high automation, high production efficiency, material savings, and excellent product quality. These advantages make the extrusion process competitive with traditional forging and machining methods, particularly for medium to high-volume production of conical fittings.

Engineering Practice Considerations

From a practical standpoint, the development of this machine addresses several real-world manufacturing challenges:

• Material utilization: Extrusion is a near-net-shape process that minimizes material waste compared to machining from bar stock. For high-value alloy fittings, this translates into significant cost savings.
• Production scalability: The fully automatic design enables continuous production with minimal operator intervention, which is essential for meeting the high-volume demands of pipeline and pressure vessel manufacturing.
• Quality consistency: Automated control of preheating temperature, extrusion speed, and cycle timing ensures consistent product quality across production batches, which is critical for meeting specification requirements such as ASME B16.9, ASTM A234, and API 5L.

However, several practical challenges must be addressed in production deployment:

• Die wear and maintenance: Extrusion dies are subject to high temperatures and pressures, leading to wear and potential deformation. Regular die inspection and replacement are necessary to maintain product quality.
• Material surface quality: The extrusion process may introduce surface imperfections such as scale, oxidation, or die marks. Post-extrusion finishing operations (such as pickling, grinding, or machining) may be required for critical applications.
• Process window optimization: The optimal combination of preheating temperature, extrusion speed, and die geometry must be determined through trial production for each specific fitting geometry and material grade.

Study Insights and Reflections

This paper represents a practical engineering achievement in the field of pipe fitting manufacturing. The integration of multiple process steps (preheating, extrusion, core rod extraction, material handling) into a single automated machine demonstrates a systems engineering approach to manufacturing process design. The PLC-based control system ensures reliable and repeatable operation, which is essential for industrial production environments.

The dual-piston design for core rod extraction is a particularly interesting engineering solution. In extrusion processes, the clean removal of the core rod and the formed part is critical to avoid damaging the finished product. By using independent pistons for the core rod and the ejector, the machine achieves precise control over the extraction sequence, which is difficult to accomplish with a single-actuator design.

The material savings aspect is worth emphasizing. In traditional machining of conical fittings from bar stock, a significant portion of the raw material is removed as chips. For alloy and stainless steel fittings, where material costs are high, the extrusion approach can reduce material waste by a substantial margin, directly improving the economic viability of the manufacturing process.

Summary

This study presents the successful development of a fully automatic extrusion machine for conical pipe fitting production, integrating preheating, extrusion forming, core rod extraction, and material handling into a single automated system. The machine offers significant advantages in terms of automation, production efficiency, material utilization, and product quality. Manufacturing engineers involved in pipe fitting production should consider this extrusion-based approach as a viable alternative to traditional forging and machining methods, particularly for medium to high-volume production scenarios where material efficiency and process consistency are critical.