If possible, maintain a uniform wall thickness throughout your section. Large differences can cause extrudability problems. If your design does include thick and thin dimensions, try to ensure the transitions are streamlined with a radius rather than a sharp corner. Big differences in wall thickness can also cause a difference in surface appearance after anodising.
As a rule, corners should rounded or radiused. Rounded corners are much stronger and easier to extrude. Normal radii are 0.4 to 1.0mm. If the design requires sharp edges a radius of 0.2mm is normally the smallest that can be extruded.
Fewer cavities (or hollows) in your section can ease production and reduce metal weight thereby reducing cost. It also simplifies the die design and may lead to a lower die cost.
By introducing decorative lines on your extrusion, you may conceal irregularities in surface appearance as well as protecting the surface against handling and marks incurred during general use. These are particularly useful where you have a wide flat surface.
Too deep a narrow channel can lead to a die breakage and is therefore best avoided. The general rule is that in any channel feature the depth of the channel should be no more than three times its width. This is however is just a general guide and we will be able to advise on any specific requirement.
When dimensioning your design try to specify dimensions and any particular tolerances from metal point to metal point rather than to a centre line or hole. Metal dimensions can be extruded to closer tolerances than the norm whereby dimensions to an open space are mere problematic as they cannot be measured during the production process.
Symmetrical sections are easier to extrude as the flow of material through the die is more balanced and the pressure load on the die is evenly distributed. The extrusion shape is more accurate, and the risk of the die breaking is significantly reduced.
If your section is going to require drilling, punching or assembly after extrusion you may want to make the machinists job easier by including index lines to ensure accuracy.
Introducing a web (or strut) into typically deep channels allows for better dimensional control and may allow for thinner walls to be specified, reducing the weight per Mtr of the section and therefore the cost.