Machining home cast aluminium.

[NeoTech]

So well, now were at the stage, machining the lump of metal one just created..

First off, i mainly use indexable tips. WNMGand DCMT is my goto tips, cuz they are easy to source..
So right off the bat i went with the WNMG.. its my "cut everything" tip..  Lets say i got suprised (and scared as hell) when the tip hooked into the cast aluminium and ripped it out of the chuck.. This stuff doesnt cut well.. Its like chewing gum blended with cheezedoodles..

So in went the DCMT tip, the standard tip i use is  08 tip.. well that was a repeat story, out came the lump after the tip bit in.. So i went through my collection of tips and i found these 005 tips (0.05mm) they ar for finishing stainless.. Really nice tips, i dropped the speed to 200rpm.. And voila now i could cut the piece, slowly.. It doesnt form strings just small chips, and its gets really rough finish..

I never bothered to dig through my HSS tool bin, but im starting to think, a round formed HSS toolbit like a spade fly cutter is the way to go here? Or how do you get around the rough cut surface finish?! (Without heat treating it to a T4 or similar).

[awemawson]

Aluminium alloys can be very 'gummy' particularly in the 'as cast' state rather than heat / solution treated. Also aluminium is a very reactive metal and will stick to tool tips, actually welding on, creating a bigger tip which gets more build up . . .etc etc .. and you end up with a dig in (or pull out in your case).

First off try a little WD40 on the work as you machine it. It will reduce the adhesion of the aluminium to the tip to quite a large extent.

[NeoTech]

Hmm yeah i figured the WD40 would do the trick, i have something similar X40, it cuts easier, but it still leaves a horrible surface finish, and i dont dare to go any faster atm.. my lathe took a real beating from that pull out.. im just glad i didnt ran the cut on the autofeed, that would have ended badly..

So.. solution treating it is then.. I wonder where i can conjour up some heating elements or an old kitchen oven.. Seems like to get a T4, you only need, several hours at like 240C.. thats not impossible. =)

[sparky961]

Isopropyl alcohol works well to keep things cool too, just don't forget how flammable it is.  Stay away from carbide tools, and keep your HSS as sharp as possible.

Relatively high SFM, low feed for hobby machines is what I've found works best.

[NeoTech]

It was the high SFM that scared the crap out of me though.. but i will give it a go again.. gonna crack out my Sandvik HSS blanks and make some tool bits tomorrow unless my better half will interfere with my vacation and wanna do.. things..

[PekkaNF]

Yesh. IPA (Isopropyl alcohol) is pretty common in nordic counties as a winter Windshield Washer Fluid (de-icer).

And if you got welding it produces rough finish. More speed and polished aluminium insert. Works wonders.

This works me (CCGT060204 NAG-H1):
http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Indexable-Turning-Tools

when Lamina doesn't (and usually this works on everything I chuck into lathe).
https://www.lamina-tech.ch/eng/catalog/family/ccmt

I hate the cheap inserts, most of them are waste of money.

Pekka

[NeoTech]

Is WNMG and DCMT considered cheap? I use Sandvik inserts mostly.. really easy to source from local metal working shops..

edit:
Hmm those CCxx's have a really different geometry than mine.. think im gonna picke one up and try it out.. *soo many inserts*

[vtsteam]

I only ever used HSS with cast aluminum. But most castings from automotive aluminum like pistons and cases, etc. was never alloyed to leave a shiny machined surface like you can get from say 6061. Actually, I find that those auto casting alloys have a stiffer, harder feel and make smaller chips than the high strength numbered wrought aluminum varieties -- which seem well. . . . wrought. Cast aluminum alloys have lots of silicon in them -- particularly pistons, which is mostly what I use.

Definitely if you get tip welding on a tool bit it will really mess up your finish -- not to mention your dimension.

I never got as fine a finish on cast alloys as I did on manufactured wrought alloys. It's just a different material.

[PekkaNF]

Is WNMG and DCMT considered cheap? I use Sandvik inserts mostly.. really easy to source from local metal working shops..

Nope. Sandvik is great, if you have a huge surplus I'll pack my car next summer and visti you The thing is is they really like to make them in many very optimized variation, all different angle, chipbreakers, coatings etc..The chances are that the one you get is optimized 7mm DOC, 15 min lifespan on paricular steel and does not perform well with your alichewinggum.

Generally for aluminium you need a special insert, lot of speed (you want that heat to fly away with chips and not dwell around to weld on the tip) and plenty of coolant.

I had plenty of problems turning mystery aluminiums before, but I used methanol/ethanol (sort of T-röd), Ground HSS bits to classical aluminium angles and polished it shiny. With plenty of speed I got very good succes rate. Then I swiched over inserts and had to study this thing over again Same thing with the mill, it's old and low rpm. Have to hook up something like 60 mm two insert face mill, before inserts works. Sharp 12 mm Swedish polished HSS roughing mill works fine.

You know that all alcohols are pretty flammable and methanol is pretty poisonous to breathe. Nevertheless I have used them in well ventilated spaces and used respirator. I use liquid specially for finnish therefore not great amount is flung aroud, but there is a definate swif of it after turning/milling. Most of the time IPA winshield anti freeze (-40C or sometimes even -20C)seems to work and it should be whole lot safer, but sometimes specially with pocket milling it sort of turns grey and mushy, probably should just flood it? Could be also that it reacted badly with water based cutting emulsion? Generally I don't like the idea of mixing different cutting fluids at all, but sometimes you are milling one thing and then next...

This is great oppurtunity to learn more.

Pekka

[NeoTech]

vtsteam, i see. you are of course right, the cast alloys are not meant to be machined more than a hole drilled and a bearing pressfitted. I shouldnt really expect it to behave like my stock materials. I have a bunch of old stock sandvik HSS (C40 through C60) in larger dimensions (15x15 to 20x20) i will try to machine with that see if i can get it to behave differently. I made a large slug cause i need to make a bunch of pulleys.  And like you my main sources is pistons, and casings from autoparts.


PekkaNF, hehe well i dont have a huuge surplus, but i go to my local shop that uses dcmt for lie 3min and then changes them..  So i get a bag of around 200 carbides for a couple of packs of coffe and a cake.. They are used but they are sharp enough for my use most of the times.. fine tipped ones break easily though.. but cost me more or less nothing..

I think though i will go get myself a spraybottle and som "T-Röd" it seems the easiest to source.. i use X40 from "Biltema" for WD40 substitute but i guess that just makes it more greased up than cooled down. 

But as stated above, i shouldnt maybe expect it to machine like the 6068-T6 or 7075-T6 i usually use for parts.  (6061 is really hard to find in Sweden). Im a happy camper if it only stops being all rugged up and sharp to handle after i have turned it actually. =)

[NormanV]

My main source of raw material has been cast aluminium wheels, it machined ok, threads were a bit "gritty" but ok.
Norman

[vtsteam]

Probably you can test for about how good a finish you can get machining with a particular aluminum alloy by filing a piece of it with a fine file. Some stock shines up more than others. Of course you can always polish it to mirror gloss with a buffing wheel, etc. but for normal machining, a file will give you a pretty good idea.

If you're getting a lot of digging in, maybe reduce the top rake of the tool, as is done with brass, which is also grabby. Nice thing about HSS is you can easily grind it differently and quickly try your modification out. HSS is a lot harder than aluminum, so tool wear isn't an issue like it is on hard spots in cast iron, etc.

[sparky961]

HSS is a lot harder than aluminum, so tool wear isn't an issue like it is on hard spots in cast iron, etc.

Mostly true, but the aluminum oxide skin that's on there after casting can very quickly wear your tool if you aren't cutting underneath it. 

[NeoTech]

I may have got the skin of it off by using my indexable tools.. what im trying to get here is a non thorny surface.. And thats prob. tool + sfm issue it seems.. I know more tomorrow though..  Gonna try the common variations i found about tools cutting castings.  =)

[vtsteam]

HSS is a lot harder than aluminum, so tool wear isn't an issue like it is on hard spots in cast iron, etc.

Mostly true, but the aluminum oxide skin that's on there after casting can very quickly wear your tool if you aren't cutting underneath it.

Haven't had that problem in 11 years of casting and machining those castings. Maybe our castings are different. Sand inclusions can do that. But oxide? My castings come out shiny as a new dime, with less oxide than the metal that went into them. All aluminum except freshly machined stock has an oxide coating -- I haven't noticed any difference in tool wear because of it.