Aluminum Extrusion Advice 2

[liegev]

Good Afternoon,

Our products in the past have had a folded, stamped and anodized aluminum chassis. I'm working on a new chassis design and we want to use an extrusion process. I've never design for that process and wonder if there are any good resources out there for me to use in order to avoid huge errors. The chassis is for an electronic device the size of a pack of cigarettes. It's a consumer product and it just needs to protect the electronics inside. It does not need to dissipate heat or anything.

Any advice would be tremendously appreciated.

Thanks,
C.

 

[BillPSU]

You need to find an extrusion vendor to make your parts. Go find a good one and ask them to help you with the design. Many years ago I was involved in changing a solid round engine fan spacer to an extrusion. At the time aluminum bar was about $1.00 per pound and an extrusion was about $1.15 per pound. I reduced the fan spacer weight by over 60%. The original fan spacer was 7" OD and about 4" long. The extruder we used was Alumax however that was about 30 years ago.

Good Luck
Bill

 

[MikeHalloran]

As of 40 years ago, the last time I looked at it in detail, the largest extrusion press in the world was in Arkansas and could accept a die with a hole about 13 inches in diameter. It could make any part you could fit in that circle (even if you had to roll it up: big flat extrusions can be extruded as a partial circle or a spiral and unrolled while they are still soft). That's no problem for you.

The minimum order for that press was about 5000 lbs, which is basically one stroke. There are smaller presses that can accept smaller minimum orders, but you have to make it worthwhile to change the die and insert the ingot.

Most any extrusion house will be glad to provide a design guide that includes suggestions to minimize complexity and cost, and also includes achievable tolerances.

In general, a closed hollow extrusion will cost you a lot more, for the extrusion and for the die, than something that can generally be described as an angle. Fear not; you can design an angle that's self-conjugate, so you can take two pieces of the same length and slide them together to form a closed perimeter, and use the end plate retaining screws (self- threaded into C shaped features) to lock them together. You will still need end plates to make a closed box; they can be stamped sheet metal or molded plastic.

As-extruded shapes are too soft to handle much without damage, so the extruder will recommend a standard temper.

Do not forget to include the cost of cutting the extrusions to a precise length, and especially the cost of deburring the cut surfaces. Some houses will do this for you, but you still get to pay for it.

Don't forget to make room to store a couple thousand pounds of (20 feet long, probably) extrusions from the mill, and protect them from bird poop and roof leaks until you use them up.

... By now you are having second thoughts, right? Extrusions can pay for themselves if they eliminate parts like spacers and standoffs for circuit boards (but you have to design the board to fit into the extrusion and keep the components away from the slot features in the exrusions), and especially if you can use them for more than one end product, so before rejecting them, do take a look at your overall product roadmap and do preliminary designs for the next couple versions or derivative products, and include features for those future products if you can reasonably predict what they will be like.

You may not need fins for cooling, but you might consider adding stubby fins or linear bosses to the exterior surface, so you don't have to worry about tiny scratches being obvious, and so you have trim/finish options like color anodizing the entire part and then sanding or milling off part of the fin/boss surface to add bright highlights or a durable logo.





Mike Halloran
Pembroke Pines, FL, USA

 

[IFRs]

There are lots of smaller extruders, with 1000 pound minimums. Go with one close to you. The Aluminum Association has published some guidelines, check their web site. While you can extrude anything, there are things that increase cost. Good luck!

 

[liegev]

Hey Guys,

Thank you all so much for your feedback. It was immensely useful.

Take care,
C.

 

[jmarkus]

Mind if I tack on a question related to designing for extrusions?

I understand that for hollow extrusions, the wall thickness is dependent on the alloy being extruded and the circumscribed diameter (CCD?) of the profile, among other things. But I've seen many different charts which suggest different minimum thicknesses for the same alloy. Is there some kind of calculation that can be done to determine what the minimum thickness would be if, say, I knew the tonnage of the press it would be run in (in addition to the alloy and CCD information)?

Thanks,
Jeff

 

[MikeHalloran]

I think you're getting into an area where what's achievable depends on the skill of the individual die designer, the die maker, and probably the press operator too.

I.e., think twice before painting yourself into a corner where only one house in the world can make your parts.



Mike Halloran
Pembroke Pines, FL, USA