[El Greco]

I need to machine some anodized aluminum. The slot drill I used in an experiment was ruined quite quickly.

Are there any special types of cutters (commercial) made for this application ?
Or do you have to make your own special tools ?

Or alternative/special techniques ?

(The aluminum I am using is 1.6mm angle)

[uscra112]

The anodize surface is very thin, but extremely hard. Carbide cutters will be required. You also don't say what alloy of aluminum is under the anodize. If it's an extrusion, the aluminum may be a soft alloy that doesn't machine well. In which case I'd use lower RPM, lots of coolant and a light feed. Contrary to what we're all taught about aluminum, but the conventional wisdom is for more friable alloys like 6061, 2024, and 7075.

[Anodizer]

I anodize for our department at Virginia Tech. Professors do not always remember all of the things they want when the aluminum is machined.
We mostly use 6061 and 6063 extrusions for machining. These can be machined after regular anodizing (Type II). If it is hard coat anodized (Type III) the surface has the hardness of sapphire and will deflect the bit!
Your problem is the metal is so thin it is moving under the bit. Back the angle with something hard , like a piece of hardwood or a scrap of Delrin. Make sure your bit is sharp and use something to keep the aluminum from sticking to the bit. We use WD40.
The metals that are impossible to machine are in the 2000 series, like electronic miniboxes. I have even tried subjecting them to dry ice to firm the aluminum, but no luck. This alloy has a high copper content.
I do get a sick feeling when I do a premo anodizing job then see it go back to the lathe/milling machine/drill press.

[Anodizer]

All extrusions are made for the 6000 series aluminum. We use 6061 and 6063.
I anodizes real well. I should know, I am the one that does it!
The problem is the piece has no rigidity because it is so thin. You need to support the piece to mill it. Also, a mill drill bit does not have enough slope for milling aluminum. Aluminum bits have a very slow ramp. You should use on for aluminum and a two cutter style. Use a lubricant as aluminum will weld itself to a bit because of its softness.
You piece is probably Type II anodized, the most common. If, by chance it is Type III, you will have problems as its surface has the hardness of sapphire.
To do anything with Type III you usually have to grind the anodize off of the area.
I makes me feel miserable when I do an A+ anodizing job and a professor made a mistake in his drawing. See the anodize being machined just does me in.

Fred Mahone

[cschmidt]

I haven't done a lot of milling of anodized aluminum but what I have done has never caused me a problem. I just use standard HSS end mills.

One thing to watch is what alloy of aluminum you are trying to mill. I have run into problems with the likes of 5052 grade alloys which are a bit softer so the can be bent without breaking. When I have tried to mill this, I end up gumming up the cutter and ruining them quite quickly. The best solution that I have found is to go a bit slower and use a lot of coolant.

[Rex Swensen]

How important is the anodizing in the area to be machined? You can quickly remove it by dunking it into a lye solution (caustic soda). This chemically eats away the anodized layer which is extremely thin. Do not leave it too long since it will continue into the underlying aluminum as well. Need some experimentation. Be very careful with caustic soda solution, it is very aggressive to clothing, skin, and especially eyes. Wear eye protection. Rinse the job well in fresh running water afterwards.

[rruybal]

HELLO,

I've machined a lot of alu. parts that were anodized and when we had very thin parts all we did is sandwitch the part between two pieces of alu., you can also use two pieces of scrap "anything" as long as it is ridged to support your part. If you are cutting a slot, use a carbide cutter with two flutes that is center cutting, and do a (ramp in) cut. keep plenty of coolant on the cutter and you won't have any problems. Your feed should be about half the recommended feed rate and the same sfpm, as a regular cut. If you can't sandwitch the part you'll have to use a cutter which is a right hand cut with a left hand helix, that's about the only chance you'll have to do this operation without getting felx, and having the part move away from the cutter.
Hope this helps
rruybal

[zeoncomp]

Hello,

I am trying to cut 3/16" AL H32 5052 and I was thinking to use this:

http://www.toolstoday.com/p-5801-alu...uter-bits.aspx

I was thinking about tool # 51508
What do you think about it? I am using a plasma table converted to a routing table.

Also - what kind of lubricant should I use and where to find it.
This would be my first time doing this and I'm sorry if I ask too many stupid questions.
Appreciate your help.

[rruybal]

Hi,
Before you buy this tool go to the link below and take a look at this tool it has a very high helix which is great for cutting AL. and it won't cost you as much. The problem with routers is the way their ground.

http://www.use-enco.com/CGI/INSRIT?P...PARTPG=INLMK32

As you can see this cutter has a great deal of clearence which is what you need to cut ALUMINIUM cleanly. If the part isn't ridged you'll need to stiffen it up. There are several coolents you can use, but I recommend Hangstfers S500 CF, you'll find it at the link below.
http://www.hangsterfers.com/

Good Luck and let me know how it works out for you.
rruybal

[zeoncomp]

rruybal

Thank you for the input. It all looks good except the fact that I need to be able to make holes too. The one that you recommend has a square end. Any ideeas?

Thank you

[rruybal]

Hi Bud,
I forgot to mention that this tool is called a center cutting endmill, that means the flute on one side is ground past the center. So it will cut easelly on a plunge cut or ramp cut without building up preasure in the middle of the tool. These endmills are designed to work in this application. When you use it to make holes just take it easy when you plunge straight down and you won't have any problems. I've used these endmills for a very long time and never had any problems with them, except when I've stacked parts together and tried to plunge through 5 or 6 parts. The endmill leaves a round thin slug that may get between the parts if there stacked. (Not good if your trying to hold a total tolerence of .0005 on location and size.)

Hope this Helps
rruybal

[zeoncomp]

It absolutely did .... I will go for this no question about. I will not stack the material so I'm not worry about it.

Now so I understand - what is the main difference between what I was looking for - and what you showed me. I am just trying to undestand.
According to these guys this gives you a "mirror" finish. can this be achieved ?

The router that I use is a B&D 1 1/4hp 25,000 rpm max who accepts 1/4 tools. Is this any good ?

Funny - I thought that I will be thrilled with plasma - but I guess the router part is nicer

Thank you

[rruybal]

Hi Bud,
If you look at the two tools side by side you'll see so much more clearence and space between the flutes on the high helix end mill than on the router bit. This is why we use these cutters to machine aluminium.
There are so many factors to consider when trying to mill a mirror finish, as far as I know you'll get a mirror finish when you use the right tool, speed and feed and cutting fluid. Cutting fluid is very important, it not only cools the part and cutter but is also a lubricant. It keeps gummy materials from binding to the cutter for a better finish. In the machining world finiches are graded by Micron. If you attain a 2 micron finish it is considered a mirror finish because it has the smothness of glass. If you get a 16 finish it's considered an ecceptionally good finish. Usually most machining is in the range of a 32 finish which is considered a standard finish throughout the industry. The High Helix on the endmill is ground so that more of the tool is engaged with the surface of the part ellimating vibration, which greatly deminishes the finish. This undesirable condition is called "CHATTER", and you'll be able to hear it as it increases propotional to the the ridgidity (or lack of) in your setup. A high helix endmill is designed to eliminate the (bounce) of the cutter as one flute disengages and the other digs in along the suface of the part as you machine.
You have more than enough RPM, so you must make sure that you have plenty of coolant. This is why you'll see CNC machining centers' totaly enclosed. If your machining head is ridged and your set up is ridged, you're half way there. Can you control the RPM. If so you may want to experiment with the RPM and feed rate. you may want to keep a
.004 load on on the cutter. A lot of people think that the slower you go the smother the finish. This is true to a point. But not always and not in every situation. Let me know how this goes, and good luck.

rruybal

[zeoncomp]

Thank you for the explanation ... I understand perfectly what you're saying except the ".004 load on on the cutter" .... and yes . I can control the speed

Thank you again
--remy

[rruybal]

Hi Bud,
The .004 load is actually the feed rate. Here is the formula;

Cutting Speed in inches per minute = 3.14159 X Diameter of tool X Spindle RPM
Divided by 12.

So if your RPM is 2000 and your cutter Diameter is .1875 = 2000 x .1875 = 375 X 3.14159 divided by 12 = 98.17 ft. per minute. this is the formula for a feed rate of .012 inches per revolution. This is the standard from the Machinery's Handbook. So if you want to drop it down to .004 per. revolution just divide it by 3 and you have 32.72333 ft. per minute. If you don't have a big machine that is ridged you'll want to cut this feed rate to about
.002 per revolution which is 16.361665 or 16.4 ft. per minute.

I don't want to confuse you with a lot of this stuff, but feeds and speed rates are important. they are the thing that gives you the finish your looking for.

Hope this helps, and good luck
rruybal