Machining Aluminium Bronze

I am about to machine a casting that, I am told, is Aluminium Bronze. The metal is a light bronze colour and although harder than gunmetal can be filed with ease.

My thoughts are to treat it as bronze: That is to use cutting speeds slightly faster than one would for mild steel with a tool having a minimal top rake and use a neat cutting oil.

I have no experience of machine such material and would welcome comments from those who have.

JA

I would machine dry

Roy

I must admit I do not know the details of how to machine it as it's done by an external machine shop. We use about 50kg of AB2 castings in each of one type of container we do, and we've sold over 2000 of them.

Initially, until the machine shop found out how to machine it, they had huge difficulty. It's very dense & tough. I think they need to lubricate it (vaguely remember paraffin being mentioned but I may be wrong), and I think the feeds were a fair bit lower than steel. The problem is a moderately low yield, high elongation & moderate strength, leading to a heck of an energy input when cutting. AB2 doesn't chip well.

Sorry I can't be more help.

Regards,

Richard.

I have machined aluminum bronze, I used a fairly slow speed and no lubrication.

Thor

I have machined alu/bronze and I found kero quite good, beware reaming it will grab hard! Bore as close as you can then ream. It is not good for bearings and that should be avoided as it also tends to grab. Lots of clearance if you do.

I do know that BOC use alu/bronze on tap heads that deal with sub zero temperatures.

Clive

Ja - I have just finished machining some components for a small loco from aly bronze. I am not sure what grade the material is as I bought a job load of 3.5" diameter billets on ebay and the grade was unspecified. I found that although it was tougher and harder than PB / brass / gunmetal it was machinable as long as the tool bits/cutters were kept very sharp. I did not use lube except for reaming and tapping where I used tapping grease - I expect cutting oil would have been as good. I used cutting oil on the band saw when chopping the bits out of the billets. Sizing of the bits was done on my shaping machine using good quality vintage British HSS tool bits.

I had read somewhere that this material can work harden especially if trying to machine it with a blunter tool but I had no experience of this and all bits machined up OK.

I only made my bits from this stuff as I had no brass, PB or gunmetal of the right size to hack the bits from so it was a bit of an experiment - but it worked!

This material would make very wear resistant solid bearing surfaces due to its obvious toughness and a little googling shows that it is used extensively for this purpose.

I hope you machine your bits OK from this fairly esoteric (for us lot anyway) material.

Rik

Many thanks for the replies. I will inform you of my attempts, success or failure.

JA

Due to its wear resistance this material is used for mandrels and wiper dies on pipe bending machines when bending stainless steel, it avoids cross contamination of the stainless with ordinary steels.

Martin C

Edited By Martin Connelly on 22/03/2017 18:13:45

Also useful for worm wheels on powered rotary tables. Works with a hardened steel worm in full cnc tables.

There are several Copper Development Association publications dealing with Aluminium Bronze are available on-line.

e.g. **LINK**

Best regards,

Swarf, Mostly!

There's quite a range of Al bronze alloys, and some of them can also chill cast, becoming quite hard. Many years ago, I alloyed some that was approximately Cu9Al2Fe, and the ~7 mm thick sections were clearly chill cast, because a big angle grinder skated across the surface without much effect, and I had to regrind a new HSS drill after drilling 1.5 times through the section. I think I was drilling it dry, on the basis that "bronze is bronze, right?"

These days I'd just use TCT tooling, and google for cutting speeds & feeds. (I use some German TCT drills on brass, for their zero rake, and on the lathe, the crumb-like swarf pours out the flutes like sawdust - at a rate of knots. It would be fun to try them on Al bronze, not just the lathe/mill tooling.)

Something I forgot to mention. When I machined the stuff on the shaper (1mm deep cut at a time) it made a screeching noise as it cut. Only other time that I got a similar noise was shaping an old case hardened lathe tool shank

Rik

Hi JA, machined a lot of this stuff many years ago mainly for submarine seawater services equipment, most has been said but I would use either suds or paraffin as a lube and HSS cutters. Quite difficult to tap--make sure you use top quality and sharp taps. Actually machines nicely but you need a rigid machine and forget carbide.

Plus one for Clive's warning not to used for bearings--tried it to make a crank bearing for an old Atco mower about 50 years ago it rand for maybe 15/20 seconds and seized !! There is along story but not for now!

John
PS I believe the material was inspired as a more corrosion resistant material with a colour very close to Admiralty Brass -- how true I know not -- anyone else heard this ?

Edited By JohnF on 26/03/2017 13:22:56

Just reporting my machining of the Aluminium Bronze casting.

The six holes are tapped 6BA. After locating the holes positions with a centre drill a drill with its rake relieved for drilling brass was used. The material was uniformly hard without a really hard skin. However there was a hint of work hardening when drilling. Tapping was done with a thread cutting paste. The actual tapping was easy but the material grabbed the tap making extraction difficult. Fortunately I did not break any taps but a tapping guide was an absolute necessity during extraction.

All the turning was done using a couple of HSS left hand knife tools with minimal top rake. The cutting speed was about 110 ft/min and all the cuts were light with slow feeds. The use, or not, of a cutting lubricant made not difference. The main problem was the build up of swarf when machining the inside diameter. The metal came off as a fine nice curly ribbon (just like the text book). The intermittent cut over the bosses did not pose a problem.

I consider the work a success with a good surface finish. The profile of the bosses will be finished by file.

Many thanks for the advice.

JA

Edited By JA on 03/04/2017 19:38:10

> The actual tapping was easy but the material grabbed the tap making extraction difficult.

That's what I have heard, apparently it produces a tenacious curly swarf that loves to jam (and break) tooling.

I haven't got first-hand experience of the stuff.

Neil

I've got a hefty bar of the stuff if you want to play with some.... 'Tis hard work clearing up afterwards though !

I find it "warm" to touch , not like bar of brass or a billet of steel..?? Must be a poor conductor of heat ?

I have a set of taps that are just for Stainless steel and they worked very well and did not grab at all. They must have more back relief than normal taps.

Clive

Thanks for the offer. I don't think I will take it up since I want to finish the model. After that there are other projects waiting.

It is "warm" to touch. Most of my working life was associated with metals that were poor conductors of heat ("warm" to touch). I never had to machine any of them and I would hate to try now. (Mind you we had rings of such a metal about 3 feet in diameter that had 0.125" diameter holes, about 0.200" deep, drilled in it at a pitch of about 0.160". Drills lasted about ten holes and were NOT resharpened).

I agree, it is not easy to clean it up after machining.

JA

I think you would find that "Threadflo" taps would be ideal in this situation, these taps have no flutes, and the thread is formed rather than cut.

Ian S C

An old timer told Me to grind 1/2 of the flute of a tap to ease extraction.Have not tried, just be sure to grind the back half.