Extrusion quick guide for designers
In order to take advantage of the unique benefits of aluminium, in combination with the extrusion process, and to make a cost-effective product with optimal functionality and which looks good, it is important to understand the basics of extrusions.
Finding the right wall thickness depends on the strength requirements and the desire to create a cost-effective profile. Profiles with uniform wall thickness are the simplest to produce. However, where necessary, wall thickness within a profile can easily be varied. For example, a profile's bending strength can be increased by concentrating weight/thickness away from the neutral axis.
The main factors affecting wall thickness are extrusion force and speed, the choice of alloy, the shape of the profile, the desired surface finish and tolerance requirements.
That said, it is perfectly acceptable to have a range of wall thicknesses within a single profile. This could be the case for profiles where, for strength reasons, it may be best to concentrate weight/thickness away from the center of gravity.
Profiles with varied wall thickness are less easier to extrude than profiles with uniform wall thickness.
Other points to consider:
- The extrusion process cannot achieve razor-sharp corners without additional fabrication. Corners should be rounded. A radius of 0.5 – 1mm is often sufficient.
- As far as possible sharp tips should be avoided. The tip can easily become wavy and uneven. Tips should therefore also be rounded.
- Following extrusion, a profile with large variations in wall thickness cools unevenly. This gives rise to a visible structural unevenness that is particularly marked after anodizing. Always use soft lines.
- Solid profiles reduce die costs and are often easier to produce.
For economic reasons, you should always aim to design a profile that is as easy to produce as possible.
A profile is easier to extrude if it has simple, rounded shapes with radius corners, has little variation in wall thickness and is symmetrical. Profiles are more difficult to extrude if they have deep, narrow channels.
Further, where a profile has, for example, legs and screw ports, there may be process-induced shadowing (heat zones) opposite such features. Using decoration, these heat zones can be completely masked.
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