As a profile becomes smaller, lighter, and more slender, maintaining straightness can become quite difficult, because, while a finished component may only be ~150 mm long, before it gets cut to 150 mm, the profile will be extruded, handled, and if anodising is required, then hung to be anodised (in lengths of a couple metres, at least), and that's where maintaining straightness becomes problematic.
When designing a small, bespoke aluminium extrusion, asking whether the shape can be extruded isn't enough. You have to consider whether the finished profile will remain straight enough to perform as intended once it has been processed.
Why straightness in small aluminium extrusions must be considered early
A short finished component may feel relatively rigid, but before it is cut to size, it will exist as a two or three metre extrusion. And at that length, the section will be a lot more flexible than you'd like.
If your aluminium profile needs to slide into another extrusion or align closely with another component, the straightness matters, because even a slight bow can be enough to affect function.
This is why straightness should be considered across the full manufacturing length, not only at the final cut length. Consider it into the final, finished product, because straightness, especially if the extrusion must be anodised, is very difficult to guarantee.
Can anodisation affect the straightness of a small aluminium profile?
Anodisation can absolutely affect straightness for small and slender profiles.
Anodising requires the extrusion to be supported and moved through several treatment stages. A larger, more rigid section may tolerate this easily, while a small aluminium profile will be more susceptible to movement or distortion.
Where straightness is critical and any bow is not tolerable, it can be useful to compare mill-finish and anodised samples before moving into full production. This way, you can check whether distortion is present immediately after extrusion or whether it is being introduced later during finishing and handling. If it is the latter, then you can decide if anodisation is more important, or straightness.
How can twist affect a small aluminium profile?
Unfortunately, straightness is not the only potential issue to consider.
A profile can also experience twist, where the cross-section gradually rotates along the length of the extrusion. The cross-sectional dimensions may still be within tolerance, but the profile as a whole no longer sits or moves as intended.
Twist can be influenced by metal flow during extrusion, cooling, and residual stresses within the section. Smaller, slender profiles can be more sensitive because they have less stiffness to resist this movement. For a bespoke aluminium profile that needs to slide or clip inside another component, even a small amount of twist can create issues down the line.
Designing for the finished component, not just the extrusion
It's important to have your aluminium profile drawing not just confirmed for extrusion, but for every part of the production process. A profile may be perfectly possible to extrude, but that does not automatically mean it will perform as expected in the final application.
For small aluminium extrusions, before moving to prod, it's worth discussing:
• Realistic straightness requirements
• Extrusion production length
• Final cut length
• Fit and clearance between other components if it is the case
It's often worth involving your aluminium profile supplier early to ensure that what is shown on the drawing translates successfully into production.
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