The extrusion process
Direct and indirect extrusion
There are several different extrusion methods, but the most common are direct and indirect extrusion. Both are intermittent processes where factors such as ingot weights, profile weights, extrusion lengths and cycle times play an important role. The method used by ProfilGruppen is called direct extrusion.
For small profiles and simple tubes, continuous extrusion is also used. Whatever the method, what is common is that the material is shaped as it is pressed through profile-forming slots in the tool.
Achieving stable and accurate production requires careful adjustment of the tools and precise control of the process parameters.
Description of extrusion
Extrusion starts with an alloyed aluminum ingot being cut into custom lengths and heated to around 500°C. It is then pressed with high force through a tool that gives the profile its shape. The profile is then cooled with air or water, depending on the alloy. After cooling, the profiles are stretched and cut to the correct lengths before undergoing hot stamping. This process, which takes between five and eight hours at around 180°C, improves the strength of the aluminum.
Construction and design aspects
Drawbridge – a solution for tight tolerances
When a profile is difficult to produce with tight tolerances, a breakout bridge can be used. The profile is then produced as a hollow profile, where the gap opening is closed with a sealing part. After the final heat treatment, the bridge is removed, resulting in a profile with precise dimensions. For fragile profiles, the break bridge also serves as a transport safety device.
Bulk thickness – a balance between strength and design
The choice of alloy affects the thickness of material required for a profile. Generally speaking:
- EN AW-6005 requires approximately 15% more material thickness than EN AW-6060.
- EN AW-6082 requires approximately 25% more material thickness than EN AW-6060.
Larger profiles generally require a greater material thickness for the extrusion process to work optimally. For best results, profiles should have:
- Even thickness of the material
- Symmetrical shape
- Stable profile build-up
Corner radii – precision and limitations
Corner radii are often described as “as sharp as possible”, but there are limitations:
- Outside corners are created by inside corners in the tool and vice versa.
- It is not possible to extrude an outside corner with a radius smaller than 0.20 mm, due to the limitations of wire EDM technology and the filling capacity of the material.
- Internal corners can technically be made perfectly sharp, but tool wear leads to rounding over time.
Tongues – a challenge for semi-open profiles
In the construction of semi-open profiles, the partially enclosed section is formed by a tongue in the tool. This is subjected to high material pressure, which increases the risk of tool failure. By following recommendations for the ratio between the depth of the tongue and the opening of the profile, durability can be optimized.
Tongue form factor
Different types of tongues present different problems for the tool designer. In all conditions, a tongue with good support is preferable, but the problems can be solved by special design of the tools.
Executive summary
The extrusion process offers great opportunities to create customized aluminium profiles with high precision. At the same time, there are technical limitations that affect design and production. By understanding how factors such as break bridges, material thickness, corner radii and tongues affect the process, it is possible to develop profiles that are both durable and production-friendly. The right material selection and optimized design lead to efficient and cost-effective solutions for different applications.
