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Old 01-27-2011, 09:22 AM   #1
UKscooby
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Default Aluminum extrusions and anodizing

In the next month or so I plan on having my first aluminum extrusion tool made and I wondered if anyone here works in this industry.
Are there any golden rules when designing such as wall thickness, spacing and required tolerances etc?

Here is the first rough draft of an idea I'm working on. It's for a strip light using a 1 inch wide pcb with 12 LED's an inch apart, and a driver at one end.



This is the pcb that will go in there.



Once I have the extrusion done it will need to be anodized. I'll get them done in black, grey, clear and either a purple or violet for the UV version. Looking around online brought me to this page:

http://www.focuser.com/atm/anodize/anodize.html

Now I have the itch to try this myself. I have almost all the equipment already so I would only be into this ~$300 to set up a complete diy anodizing operation that would be perfect for the low volume of parts I need.
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Last edited by UKscooby; 01-27-2011 at 09:27 AM.
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Old 01-27-2011, 10:02 AM   #2
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you might take a look at alodine or similar conversion coating.

that's about all I have to offer. cool project!
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Old 01-27-2011, 10:08 AM   #3
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I'll show you an extrusion tool
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Old 01-27-2011, 10:10 AM   #4
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Does your shop need any black and white tile?
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Old 01-27-2011, 10:14 AM   #5
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I have no idea. That being said, I'm curious about your design (which I have now patented). Do LED's really get that hot? To require that big of a heatsink, I mean. Or is the heatsink there to dissipate the heat from something else in your gizmo device. Was there any math involved or did you just "wing it"? Make my Thursday slightly more interesting, please.
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Old 01-27-2011, 10:27 AM   #6
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Does your shop need any black and white tile?
You stole mah post!
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Old 01-27-2011, 10:30 AM   #7
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LED's do get hot - especially the high power ones. Your typically LED converts around 45% of the incoming energy into light, the rest is heat. That can add up to a lot of heat when you have multiple LED's in a small area.

In this example there are 12 LED's an inch apart from each other. Each LED is running at 800mA with a forward voltage of around 3.2V. So thats 2.56W per LED. 55% of that x 12 = 16.9W heater.

The heat sink design is an educated guess based on experience, a few calculations and bench top testing with various chunks of finned heat sink. I estimate it to heat up around 2.0 deg C per W above ambient. So, at room temp of 20 deg C, it will heat up to 53.8 deg C. Fairly warm but ok to touch and well within the LED and driver operating specs. It is designed to mount to a chassis or faceplate, or some other kind of structure which will also offer a small amount of heat sinking.
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Old 01-27-2011, 10:33 AM   #8
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Quote:
Originally Posted by UKscooby View Post
LED's do get hot - especially the high power ones. Your typically LED converts around 45% of the incoming energy into light, the rest is heat. That can add up to a lot of heat when you have multiple LED's in a small area.

In this example there are 12 LED's an inch apart from each other. Each LED is running at 800mA with a forward voltage of around 3.2V. So thats 2.56W per LED. 55% of that x 12 = 16.9W heater.

The heat sink design is an educated guess based on experience, a few calculations and bench top testing with various chunks of finned heat sink. I estimate it to heat up around 2.0 deg C per W above ambient. So, at room temp of 20 deg C, it will heat up to 53.8 deg C. Fairly warm but ok to touch and well within the LED and driver operating specs. It is designed to mount to a chassis or faceplate, or some other kind of structure which will also offer a small amount of heat sinking.
Is it being mounted vertically? That would get the most convection moving across/thru the fins.
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Old 01-27-2011, 10:35 AM   #9
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That would be up to the guy installing it in his equipment. It needs to work in any orientation.
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Old 01-27-2011, 10:44 AM   #10
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Quote:
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I have no idea. That being said, I'm curious about your design (which I have now patented).
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Old 01-27-2011, 11:49 AM   #11
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are you designing industrial LEDS

all me to OT tangent
i work for a ski area
we do night skiing aprox 1100 acres are covered ~500 fixtures with 1000w bulbs

we have looked at switching to LEDs (currently have a grant that is switching all or our interior lighting to LEDs ~$80k) outside but have run in to the issue of ice brine. The 1k bulbs kick off enough heat to melt the ice off but we are concerned that leds would not
99% of there use is during the winter use ~180 days per year but occasionally during the summer
thoughts comments suggestions?

a mild saturday

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Old 01-27-2011, 12:06 PM   #12
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Most of what I design is for industrial apps. The lights could be designed to heat up enough to melt off ice, or, a heater can be added to the housing and would still use less energy than a conventional light bulb.

Are these bulbs 110V or 220V?
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Old 01-27-2011, 12:07 PM   #13
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Whats the length of the extruded part? I'd say send it out to get plated. you dont want to deal with all that nasty stuff. Make friends with the anno shop. We sent out TONS of stuff each week to be plated. Note that you will most likely be charged a "lot" charge minimum for each color. Sometimes you can tell them that you are not in a huge rush and when they do a specific color you can have them throw them in the tank with the others.
good luck with your parts.
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Old 01-27-2011, 12:14 PM   #14
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If you plan to anodize stuff yourself, I believe you must have a shop which is commercial or industrial zoned and have EPA permission to run baths of caustic substances. Plus the appropriate permits for disposal of waste and filters to prevent air pollution.

It's not completely legal to just do this in your garage. Take a look at this and research about it in your area:

http://www.finishing.com/346/00.shtml
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Old 01-27-2011, 12:23 PM   #15
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you could just tumble/vibrate it - or sandblast it.

does it NEED to be finished in a color?

Also, will you be using some tape or paste under the board for thermal transfer?
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Old 01-27-2011, 12:40 PM   #16
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Does it have to be an extrusion? Custom ones are expensive, especially for low volume. You couldn't find an existing one you could use out of the Tierny (sp?) Metals catalog?

Home anodizing would take some dedicated space and definitely isn't a trvial thing to set up. Could you, as someone else suggested, use alodine? Although alodine is fairly nasty stuff too.
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Old 01-27-2011, 12:47 PM   #17
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Quote:
Originally Posted by f4phantomii View Post
Does it have to be an extrusion? Custom ones are expensive, especially for low volume. You couldn't find an existing one you could use out of the Tierny (sp?) Metals catalog?

Home anodizing would take some dedicated space and definitely isn't a trvial thing to set up. Could you, as someone else suggested, use alodine? Although alodine is fairly nasty stuff too.
yeah, I can't imagine an extrusion extremely similar to the drawing isn't available. Even if some minor change to his PCB width were needed, or even sending the extrusions to be milled a little differently, cut to length, de-burred, cleaned and alodined - cheaper than a custom extrusion and DIY. Of course, it can be fun to do stuff yourself. Just be careful with the chemistry.
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Old 01-27-2011, 01:00 PM   #18
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For your Extrusion profile: you need radii in the corners. For your fins, I would make the bottom of the slot a full radius, and also make the end of each fin a full radius.

An extrusion machine will make like 6' long bars, which you will then have to get bandsawed to length, and take a finish machine cut on either end.

Then you will need to have mounting holes (depending on your design) machined into the extrusion to hold your components. These are usually just tapped holes. (4-40, 6-32, maybe larger).

I looked again at your design. It looks like you've set it up to have the PCB board slide into a slot, then you are using end plates to secure the PCB with screws. I would recommend you change your design to have the PCB mount from the top with screws. Why? Because the way you have it designed now, you are going to have to stand the heatsink up on end, then machine a face and tap some holes. Then you will have to flip the part around and do the same to the other end. This is two separate machining operations, and it will add cost to your part.

If you redesigned the part to mount from the top, you could load the raw heatsink into a vise, have the milling machine trim both ends to the correct length, then machine the mounting holes (drill and tap).

Now you have gone from two machining steps down to one.

Also, Extrusion tolerances can be loose sometimes. +-.01 is a common tolerance. So for where the PCB board mounts to the heatsink chassis, I would not extrude that mounting slot, I would have that slot machined into the heatsink during the machining operation that trims the end and drill/taps the holes.

If you need more help I do Design For Manufacturing consulting...

Annodizing: Aluminum will oxidize in normal Air, which forms a protective Oxide layer that protects the rest of the metal below the skin. Annodizing is a process where they dip the parts in a tank that contains different types of minerals. An electric current is run through the tank and an Oxide layer of a specific color forms on the outside.

I also would not try Annodizing at home, if you are going to sell these products. The EPA will come busting down your door very quickly. Send them out to a shop that does it for a living. Money well spent.

I would also advise against trying to machine and manufacture these units in your garage, unless you have a machining background. Not that you can't learn, but you won't be very efficient at it, especially in the beggining. Focus on what you know, and what you are good at: Design, and the Electronic portion.

Just my two cent$,

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Old 01-27-2011, 01:22 PM   #19
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I appreciate your input. I did know there needs to be radii on corners, I just drew this quickly to get what was in my head on the computer.

So this shape is basically a U. The pcb fits inside the bottom of the U and is screwed down to the alu. Under it will be thermal gap filler. At the top you can see a groove either side. A .118in piece of diffusing plastic slides down those grooves and forms the cover. 2 end plates are fitted, one with an extra cutout for the power connector to fit through.

As far as machining the heat sink, there will be 4 holes in each end, several under neath for mounting and 3 on the inside bottom to screw down the pcb.

I've been quoted based on this drawing $1500 for the die. Obviously that can change with a final drawing.

As for other similar extrusions out there - the key here is how high that grove for the diffusing plate is above the top for the LED reflectors and lenses. Too low and you will see hot spots, too high and you will see rings and a reduced output.
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Old 01-27-2011, 01:31 PM   #20
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Ok, cool, that makes a lot more sense now. Where the bottoms of the fins meet the wall of the Groove, you will want to make the wall about 1.5 times as thick as the fins. That should provide enough strength. I'd allow at least .06 on either side of the PCB for clearance. Also, you'll need a small radius at the bottom of the Groove. The typical smallest internal radius for an extrusion would be .03, and external radii should be no smaller than .015. There are exceptions to this general rule, but they increase the cost of building the extrusion die.
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Old 01-27-2011, 01:59 PM   #21
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Quote:
Originally Posted by UKscooby View Post
I appreciate your input. I did know there needs to be radii on corners, I just drew this quickly to get what was in my head on the computer.

So this shape is basically a U. The pcb fits inside the bottom of the U and is screwed down to the alu. Under it will be thermal gap filler. At the top you can see a groove either side. A .118in piece of diffusing plastic slides down those grooves and forms the cover. 2 end plates are fitted, one with an extra cutout for the power connector to fit through.

As far as machining the heat sink, there will be 4 holes in each end, several under neath for mounting and 3 on the inside bottom to screw down the pcb.

I've been quoted based on this drawing $1500 for the die. Obviously that can change with a final drawing.

As for other similar extrusions out there - the key here is how high that grove for the diffusing plate is above the top for the LED reflectors and lenses. Too low and you will see hot spots, too high and you will see rings and a reduced output.

Similar to CC's advice, consider having the slot for the diffuser milled in - perhaps to some existing extrusion design. basically, make certain you exhaust all existing extrusion designs that can just be modified with 1 or 2 machining operations before you get a custom extrusion. Also, consider finding a way to use standoffs/split/slotted fingers of some type to support the diffuser from the top of your PCB and eliminate the slot for it in the ext. completely (I admit there may be good optical reasons not to do that).

Seems like I've seen power switching and audio amp stuff with heatsinks of a similar profile. Just cut off shorter.
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Old 01-27-2011, 02:05 PM   #22
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Betterer?

I'll take another look around and see what I can find that might work.
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Old 01-27-2011, 02:07 PM   #23
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I wouldn't anodize at home.

You are going to run into a truck-load of problems including chemical storage, management and disposal, consistent quality, fumes, environmental laws, zoning laws, heath issues, safety issues and so on.

Getting consistent good quality takes robust calibrated equipment and experience.
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Old 01-27-2011, 02:08 PM   #24
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i have minimal experience with any of this, but i remember reading (and have seen) that using extruded C-shaped channels instead of drilled and tapped holes for mounting the end plates can reduce your machining costs. Sort of like the lower left corner in this drawing:

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Old 01-27-2011, 02:12 PM   #25
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