Machining Aluminum Bronze

[home-tek]

Anyone has experience machining aluminum bronze AMS4640?

[take a cut]

Yeah on manual machines and its not fun, what type of machining? I have had luck using ceramic in a lathe. Heavy cutting i find a good chipbreaker and small rad on the nose slow and medium to heavy feed. good luck

[handlewanker]

Hi, Been cutting ally bronze on and off for 30 years. A bit of advice, don't touch this material with a blunt tool, or if you've been cutting ferrous metals.
This material work hardens quickly with a blunt tool and gets a vey hard skin that will further blunt HSS tools.
If you drill with HSS drills make sure that the drill has the cutting edges of unequal lengths, about .010" difference for a 1/2" drill will help. This will make the drill cut a hole .020 bigger than the drill size and so will not seize up in the hole due to rapid expansion and rapid contraction when coolant gets down to the point.
Reaming ally bronze is the height of masochism.
Turning is pretty straight forward, but don't use carbides that are blunt as workhardening will happen.
Castings and forgings tend to "walk about" a bit due to internal stresses being relieved when machining.
A good tip is to leave a bit on for final finishing to size when all the rough turning has been done, and using newly sharpened tooling.
Milling can be a nightmare using blunt endmills, and side & face cutters will deflect like a dogs back leg, unless really sharp.
The material can become very springy and physically deflect if not supported well.
Coolant must be copious.
Characteristics similar to 316 stainless.
Ian.

[DareBee]

I agree with (more or less) with handlewanker.
In my experience I don't think it is quite as bad as you make it sound.

ALWAYS take healthy cuts try to be at 0.020 minimum

The scariest process IMO is trying to tap this stuff.

[Geof]

Originally Posted by DareBee ....The scariest process IMO is trying to tap this stuff.

Cutting a 1.25 dia. acme thread 20 or so inches long on a manual machine is a bit of fun as well. Operating screw for big gate valves.

[Mcgyver]

If you drill with HSS drills make sure that the drill has the cutting edges of unequal lengths, about .010" difference for a 1/2" drill will help. This will make the drill cut a hole .020 bigger than the drill size and so will not seize up in the hole due to rapid expansion and rapid contraction when coolant gets down to the point. Reaming ally bronze is the height of masochism. .

good tip on the drilling, new one for me. It always seems like the bloody material is shrinking around the bit - so its expanding so much from cutting and and cinching right in as it cools? miserable. wonder if drilling in smaller increments might help, obviously not appealing for production though

[handlewanker]

Hi Mac, the same goes for working most of the bronzes, but ally bronze has a mind of it's own.
The worst operation is reaming, and a close second to that tapping, and bringing up the rear our old friend parting off.
This last operation will drive you to drink, and if your nerves can take it, good show.
Here you really must have a SHARP freshly ground tools, if they've cut steel previous to this, kiss them goodbye.
It will go in and as it rubs a hard skin, just gets tighter and tighter.
Even carbide tipped stuff has the same problem.
The friction from a blunt tool generates enough local heat to expand the job and as it rapidly cools........gotcha!
The other problem is it's ability to "walk about".
The expansion rate and locked in stresses play havoc with dimensions.
Drilling in increments is a problem as the first drill will go in easy, cutting off centre and oversize, but the others that follow it will centralise and cut to size and if a bit blunt will seize up big time.
Anybody who contemplates working on alluminium bronze must face the fact that ANY, and that means ANY tool that is going to be used must be freshly ground.
For coolant in tapping, reaming and dieing we always used that thick dark brown cutting oil that stinks and looks like thin mollasses, but for turning and single point boring then the soluble oil/water mix was OK.
If you want to hand tap, then try Trefolex, if it's available, a sort of greenish yellowy, stinks like old currey,sulphur and brimstone, greasy compound
Apart from all it's troublesome characteristics it's tougher than a Greek wrestlers jock strap and the corosion resistance is also good.
It casts well, especially in investment casting, and I would use it in preference to cast iron for many small machine items.
Needless to say the chips come off like steel chips and are razor sharp.
Ian.

[john k]

We cut alum bronze on a HMC all the time. Drilling we use solid carb thru coolant drills no peck with high pressure coolant (800 psi). For mills use one with varable geo they wont chatter on a full dia cut. As far as tapping goes try thread milling its very consintent.

[handlewanker]

Hi john k, this is exactly the problem, unless you go for it with the correct equiptment then you'll have a nightmare on your hands.
Alluminium bronze is a totally unforgiving material to work with and the outcome of sloppy tooling is trouble.
Ian.