cast iron, aluminum bronze, stainless and machinability?

Recently have worked with a couple of guys who are rebuilding some machinery by building up cast iron and machining true. I have heard from numerous sources that aluminum bronze is a real good material to build up with and machine down for heavy industrial use in many different applications. I tried welding it once and did everything wrong and had all sorts of problems. I finally called the tech service from mfg and got straightened out. Didn't have big enough machine so never finished my learning with the wire. On this latest project another person is Tig welding an aluminum bronze alloy and is finally learning to do it well enough. The problems that came later was machining the aluminum bronze. Never heard or read about problems with it? I am told it is harder than woodpecker lips and is miserable to machine. Does one have to use carbide? Is it a matter of feeds and speeds? Same with a project using stainless 316. Put the casting on the horizontal mill and it just ate up cutters. I am mystified by this as I would never of guessed that these materials would be so hard on tooling. Is there a secret I can pass on the the guys to make their jobs easier. The hi speed tools are not cutting it, have had some luck with carbide but it has been a real fight to find out what works as even some of the carbide attempts have not been successful. Any hints would be appreciated. I cannot give accurate descriptions of cutters and feeds as I am not machining any of this, but I do know the high speed tooling has not been working at all. So what can I pass along to help? Regards, John.

Since we can only guess at the actual feeds and speeds, I'm going to guess that the cutter SFM is too high or the feed per tooth is too small. Both aluminum bronze (C954, I would guess) and stainless 316 are moderately difficult to work with, for a rather wimpy definition of "moderately difficult". Neither is anywhere as difficult to machine as some of the nickel exotics or superalloys. Proper feeds and speeds with sharp cutters will do the job. Even HSS will do the job! I've cut 316 with a manual hacksaw and HSS drill bits, so it's no super-metal.

You need low enough SFM that you are not burning your tools.
You need sufficient feed per tooth that you are not rubbing.

Since we had to guess at the aluminum bronze alloy, it's possible you're actually working with C955 or something similar with 5% nickel. That would be distinctly more difficult to machine than C954.

Old rule of thumb test - if you can mark it with the square corner of a smooth file, you can machine it with HSS

From Clarkson Osborn's book that I have to hand - these are guideline figures

Austenitic stainless steels (inc 316) 40 - 50 ft / min for milling, 30 - 60 for drilling.

Tough bronze - as yours sounds 50 - 100 ft / min for both milling and drilling, however bronzes can vary greatly especially on build up work, so lower speeds could be needed.

Bronzes by their nature are not easy to cut, they are abrasive and require sharp tooling, which will go off quickly if you get it wrong!

On my very limited experience, it's much safer to err on the slow side and taking more aggressive cuts (and there the 3 Rs come into play) than the opposite.
When one of those materials works harden, it's the surface that does that, while the "layers" underneath are softer.
Like when cleaning up a piece of cast iron: if you don't break through the skin completely, you're just chewing-up tool after tool.

Paolo

Limy Sami said:

Old rule of thumb test - if you can mark it with the square corner of a smooth file, you can machine it with HSS

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Should continue: ..but your cutter might need resharpening every 30 seconds.
Good file will cut HRC55 armor plate... do I want to machine it with HSS tooling? Hell no

MattiJ said:

Should continue: ..but your cutter might need resharpening every 30 seconds.
Good file will cut HRC55 armor plate... do I want to machine it with HSS tooling? Hell no

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Not if you run it slow enough Matti, ..........but I can only agree with you on armour plate. FTFAGOS.

On this latest project another person is Tig welding an aluminum bronze alloy and is finally learning to do it well enough.

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Might see if the tig is puddling ANY of the iron - which will chill and be hard

Happened to me with Silicon Bronze

The process needs to be exactly like brazing - no iron melting going on

Thumbnail shows nice Silicon Bronze bead - but the iron on each side is dead hard where the TIG melted same

You can tig-braze on cast iron with large filler rod (like 1/4”) but it’s really uncomfortable compared to torch brazing where your hands are farther away from the big hot lump… As said above if you bring any of the iron up into the solution, that part of the weld as well as the nearby CI parent will be too hard to machine with any economy. You can fix the CI with a 1600°F thermal treatment but any ferro-bronze you create will never behave.

For good repairs I’d rather just use CI rod & then toss things in the furnace. The rod is hard to find and prolly nuts expensive if you do however.

Good luck,
Matt

Because I am not near as involved with this project I cannot give the info some of you would like to know. I have emailed both machinists a link to this thread. I am hoping they will chime in and ask questions.

The one is machining stainless on a shaper and was having problems but seems to be doing better with some different tools. I think he has to dress it once in a while but is making headway. Seems like of slow going to me but he is satisfied that it is machining ok. He has been taking to me what seems like very light cuts. Not trying to second guess what they are doing but this just seems very slow and time consuming?

The bronze is A2 Bronze that was recommended and has been used on the one box. That guy started using a carbide insert cutter and was making some headway. But again very slow going. Hopefully they will chime in and can explain better what they have been experiencing. Some people would rather struggle than ask, but I am much more wimpy than that. I will ask. I don't like taking a lifetime to do a simple job and I get impatient if I do not see progress. So I ask to see if I can't speed things up and make life easier. Thanks and hope someone here learns something. Maybe even me! Regards, John.

316 on a shaper should be cake. It machines well with HSS unless you run too fast or let it run at to low feed and it work hardens. Aim for no more than about 50-60fpm on 316 with HSS. That and some kind of cutting oil or coolant will do wonders.

Coolant on stainless seems like a must, since it doesn't dissipate heat as well as plain carbon steel.

Yes, the heat runs into the tool as fast or faster than it dissipates into the work. That's why you run half the speed of steel. I generally run HSS unless the material is too hard for HSS to cut it (hardened or similar). Only then will I switch to carbide cutters.

And yes, a properly brazed cast iron repair should not have a hard spot near the repair. If you get it too hot and melt the iron, THEN you get white iron mixed in, and that will be pure misery. Brazing is just high temp soldering, if done properly. You heat the work only enough to melt and flow the brazing metal. It adheres to the parent metal like hot glue or solder.

handsome devil said:

Because I am not near as involved with this project I cannot give the info some of you would like to know. I have emailed both machinists a link to this thread. I am hoping they will chime in and ask questions.

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The 316 by nature wants a positive rake (any type tool) and likes some approach angle (if you can) to cut right.

Shaping and planing are slower by nature, a LOT slower… I tend to use my sheldon only for stock reduction when I can do other things while the machine putts away, or keyseating & other weird things that it just does well using cheap tooling while I stay at the machine.

Years back I did have a sort of production re-man part where I’d get ductile iron parts that needed the bores welded (in all of them) and a few would have a flat side wear surface that needed to be reestablished. So I turned what was a 15min setup and a 45 second mill job on 3-4 parts into a 5min setup and a 20-30 minute shaper job & just left the machine set up until needed. When I did use it I’d go bore parts while the shaper motored away.

These parts were welded with E70 filler and the flat part was welded at very high settings (over 200amps) so it would float some CI into the puddle around the (copper dam at the edges). They were then placed in a furnace, brought up to 1600°F for an hour and the furnace shut down.

I’ll attach a vid showing the shaper at work, near the end on the finish pass (maybe 1/64th) you can hear the tool bark slightly at these edges.


Good luck,
Matt