Hollow parts are precisely extruded by employing specialized dies that incorporate a mandrel to form the internal void, enabling the creation of continuous, seamless profiles.
The Core Mechanism: Die Components
The ability to extrude a hollow section relies on a specially designed die that consists of two separate mating parts attached to each other. These components work in unison to define both the external and internal geometry of the extruded profile:
- Die Plate: This component is responsible for forming the outer shape of the profile. As the material exits the die, the die plate dictates the external dimensions and contours.
- Mandrel: This crucial component forms the inside shape of the profile, creating the hollow space. The mandrel is strategically placed within the die opening, forcing the material to flow around it.
This innovative two-part die system is fundamental to producing hollow sections, from simple tubes to complex multi-chamber profiles.
| Component | Function |
|---|---|
| Die Plate | Defines the external dimensions and shape of the extruded profile. |
| Mandrel | Defines the internal dimensions and shape, creating the hollow void. |
The Extrusion Process for Hollow Profiles Explained
The extrusion of hollow parts typically utilizes a process where solid billet material is pushed through a die under immense pressure.
Specialized Die Designs
For hollow profiles, specific die types are commonly used to facilitate the formation of the internal void and ensure material integrity:
- Porthole or Spider Dies: These are the most prevalent die designs for hollow extrusions.
- The billet material is forced into the die, where it encounters the mandrel, which is supported by "bridges" or "spider legs" extending from the die body.
- As the material flows, it splits around these supporting legs, momentarily becoming multiple streams.
- Crucially, these separate material streams then converge in a welding chamber located just before the final die opening. Under extreme pressure and temperature, these streams are forge welded back together, forming a continuous, monolithic (seamless) hollow section around the mandrel.
- Finally, the now-joined material passes through the remaining die opening, defined by the die plate and the mandrel, to achieve the precise final outer and inner dimensions.
This ingenious method allows for the creation of intricate hollow geometries without requiring subsequent welding or joining operations. Learn more about the general aluminum extrusion process at The Aluminum Association.
Material Flow and Pressure
The immense pressure exerted by the ram on the billet is critical. It ensures that the metal flows uniformly around the mandrel and its supports, providing sufficient force for the material streams to effectively re-weld in the welding chamber. The temperature of the billet is also carefully controlled to optimize material ductility and promote efficient flow and bonding.
Post-Extrusion Steps
After exiting the die, the hollow profile undergoes several finishing processes:
- Cooling (Quenching): The extruded profile is rapidly cooled, typically with air or water, to set its metallurgical properties and achieve desired hardness.
- Stretching: This process pulls the profile to straighten it, remove any minor twists or distortions, and impart specific mechanical properties through strain hardening.
- Sawing/Cutting: The long extruded profiles are cut to the desired final lengths.
Common Materials and Practical Applications
Hollow extrusion is a versatile process used across various industries due to its ability to produce lightweight yet strong components.
Materials
The choice of material depends on the required properties for the final product:
- Aluminum Alloys: By far the most common, especially alloys like 6061 and 6063, due to their excellent extrudability, high strength-to-weight ratio, and corrosion resistance.
- Copper Alloys: Used for electrical conduits, heat exchangers, and plumbing due to their conductivity and ductility.
- Magnesium Alloys: Increasingly used where extremely lightweight structural components are required.
Practical Applications
Hollow extruded parts are ubiquitous in modern manufacturing:
- Architectural and Construction: Window and door frames, curtain wall systems, structural supports, handrails, and decorative elements.
- Transportation: Components for automotive, aerospace, and rail industries, including chassis parts, structural members, and heat sinks.
- Consumer Goods: Bicycle frames, furniture, lighting fixtures, and electronic enclosures.
- Industrial: Heat exchanger tubes, pneumatic and hydraulic cylinders, electrical busbars, and various pipe and tubing applications.
Advantages of Hollow Extrusion
The hollow extrusion process offers significant benefits:
- High Strength-to-Weight Ratio: Especially beneficial with aluminum, creating strong yet lightweight structures.
- Design Flexibility: Allows for the creation of complex, multi-chamber cross-sections that would be difficult or impossible to achieve with other manufacturing methods.
- Cost-Effectiveness: Reduces the need for extensive machining or assembly operations, leading to lower production costs.
- Uniform Wall Thickness: Precise die design ensures consistent wall thickness throughout the profile, optimizing material usage and performance.
