When you start designing a new extruded aluminum piece, there are several important factors you should keep in mind. Here is a quick list of design tips to get you started:
1. Know the circle size of your vendor. If you don’t know the extruder’s limitations you’ll likely design a part they can’t produce and end up redesigning the part or shopping it around to find a fit. Additionally, the greater the circle size the more tolerance becomes an issue. Start working with an extruder early on. Some offer engineering support and some don’t.
2. Evaluate your tolerance requirements to that which your extruder can support. You can look to aluminum.org for design guidance in addition to your extruder. Aluminum.org’s information is somewhat technical however. So, for quick answers call/email your extruder or you can use Qualified Vendor’s quote service to find suppliers.
3. If your parts require secondary machining, make sure you design in indexing features. This can be as simple as an extruded groove in which the machinist can use to take a hole dimension off of.
4. Wall thickness – design them as uniformly as possible. This will prevent voids in the extrusion.
5. Designate critical and cosmetic surfaces. This will prevent unintended marring of critical surfaces.
6. Heat sinks – as a rule of thumb, fins should not exceed 10:1 length to thickness.
7. Screw bosses – keep a 60 degree opening otherwise the die will require a torpedo which will significantly affect the cost and life of the die. Use your machinery’s handbook for McMaster Carr for screw hole guidance. I recommend self cutting/starting thread forming screws. They’re inexpensive and yield a great strength, so much so that you need to be careful when inserting them so you don’t shear off the heads – use a driver with a clutch.
8. Make transition areas smooth with gentle radii.
9. Select the proper alloy for your application and make sure your extruder can use this alloy. Many only work with one or two series of aluminum – 2XXX or 6XXX are most common.
10. Lastly, consider your finish. Design with appearance and performance in mind. Don’t forget that the parts have to have secondary operations, packaged and shipped. Many finishes like anodizing will change your tolerances. Keep this in mind. Likewise, if you’re going to powder or wet paint your finished parts make sure you designate which features (holes, grooves, etc.) need to be masked off to prevent paint contamination. This may affect your final assembly.