While versatile, extrusion has constraints:
- Cross-Sectional Size: Limited by the press size (circle size). Very large profiles require enormous, expensive presses.
- Hollows: Hollow sections require a “bridge” in the die to support the internal mandrel. This creates a weld line where metal streams reunite, which is a potential weak point if not properly designed.
- Wall Thickness: Minimum wall thickness is proportional to the size of the profile’s circumscribing circle. Very thin walls are difficult to fill and can lead to dimensional instability.
- Tolerances: While good, tight tolerances (especially on thin walls) are more challenging and costly.
- Lead Time for New Dies: Custom extrusion dies require design, machining, and try-out, taking several weeks and incurring NRE cost.
- Alloy Restrictions: Not all aluminum alloys extrude well; 6063 is best for complex shapes.