Aluminium swarf

[JAParticipant @ja]

[JAParticipant @ja]

I have been turning down a 3” diameter aluminium bar (HE30) to 1.5” over a 2” length. The swarf either comes off as about ¼” coils or a near straight ribbon. The coiled swarf usually breaks up after it has reached 1” in length and is relatively easy to handle. The ribbon swarf is horrible. It goes everywhere, getting caught in anything and everything like the tool post and always eventually wrapping itself round the work. After each pass the carriage and tailstock has to be moved out of the way to remove the stuff from the job. This takes as long as the cutting pass over the 2”. The tool used is a high speed steel home ground knife with a top rake of about 20 degrees.

Can anyone suggest a way of prevent the ribbon type swarf from forming or a way of breaking it up as it forms, please?

JA

[EmgeeParticipant @emgee]

Hi JA

20 degrees sounds a lot to me, you could try about 7 degrees with a chip breaker groove ground in behind the cutting edge.

I normally use insert type tooling unless a special is needed, then like you it's HSS ground to suit the job.

Emgee

[Marcus BowmanParticipant @marcusbowman28936]

Can you fix a piece of steel just behind the cutting edge, to force the ribbon sharply upwards, so that it breaks? That might be a piece of steel taped to the toolpost, or it could be clamped in place along with the tool, by the screws that secure the tool in the tool post. Mind you; I use a polished carbide tip designed specifically for aluminium, and it is just as good at filling the place with long strips of swarf. That tip has a built-in chip breaker, but its tiny. I'm thinking of something much larger.

Marcus

[Neil WyattModerator @neilwyatt]

As Marcus suggests, anything that forces the swarf ribbon to turn through a sharp angle should work.

[Martin ConnellyParticipant @martinconnelly55370]

You could try cutting back in sections then finish off the required profile in one go. For example cut just 1/2" (or other suitable small fraction of an inch) at a time up to 1.9" and down Ø1.6" to keep the swarf ribbons shorter then finally finish off the last 0.1", when the material removal rate will be lower due to the smaller diameter, in single passes.

Martin

[AjohnwParticipant @ajohnw51620]

20 degrees sounds fine to me for aluminium. Do you have back rake as well, maybe around 15 degrees. That will tend to lead the swarf away from the work and in a sensible direction.

The standard fix for this sort of problem is a swarf hook. The nearest thing to a sensible one off the web is this

**LINK**

However I would bend one up out of 3/16 or 1/4 mild steel with a bent handle on one end.

I need a new keyboard – missing letters. You could increase the clearance angle into the cut to circa 20 degrees as well if the machine is struggling to take deep cuts.

John

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Edited By John W1 on 06/12/2015 10:12:00

Edited By John W1 on 06/12/2015 10:16:07

[Anonymous]

I find that the carbide inserts for aluminium break up the swarf if you use them with decent feed rates. I normally run from 4 thou to 16 thou per rev depending upon the nose radius. The bigger the radius the higher the feedrate.

Andrew

[Steve WithnellParticipant @stevewithnell34426]

Posted by Emgee on 05/12/2015 19:05:50:

Hi JA

20 degrees sounds a lot to me, you could try about 7 degrees with a chip breaker groove ground in behind the cutting edge.

I normally use insert type tooling unless a special is needed, then like you it's HSS ground to suit the job.

Emgee

The way I grind the chip breaker groove, is to use one of those thin cutting discs with my Dremel clone and it does work well.

My old mentor always ground his HSS tooling with one eye on how he wanted the swarf to come away from the work. It is a serious consideration – if you start getting long unbroken ribbons of steel swarf coming off at speed, it can be dangerous – ie you don't want it round your neck.

Steve

[Clive FosterParticipant @clivefoster55965]

Thermal effects considerably influence chip coiling and breaking. Obviously if the chip is to roll up the outside of the bend needs to be longer than the inside of the bend. The outside of the bend is the just cut surface and will be hot due to the energy imparted during cutting and will expand. So if it is sufficiently more hot than the inside the chip will naturally tend to curl up. Problem with aluminium is that it conducts heat so well that the chip cools to near enough even temperature before the chip can bend. Feeding harder, as Andrew suggests, puts more heat into the chip which increases the thermal gradient and helps it bend. Mist or air blast cooling on the outside of the work can help too. Flood cooling not so much as it cools the cut area and lubricates the top of the tool so making it easier for the chip to flow over the tool top and round the chip breaker. If the chip has to work harder to flow over the tool it stays hotter due to the extra energy needed. I imagine this sort of effect is why a straight chip will suddenly start to curl when a large built up edge forms on the tool. Cutting and chip flow being less efficient everything stays hotter. Under the right conditions built up edges can get pretty big. I've had them up over 1/8" thick during rough cutting. Finish is awesome but coming back for the next cut with the built up edge still on makes it ploughed field time.

When the chip cools the locked in thermal stresses weaken it so it snaps much easier too. The ductile nature of aluminium doesn't help here.

Chip breaking is pretty complicated as there are several effects involved and its a matter of finding a set-up and style of working that gives a reliable balance which works well over a decent range of situations for your machines, and materials. Good luck. The insert manufacturers have labs full of people working on this and they haven't come up with a simple one size fits all approach. Yet!

Clive

[VicParticipant @vic]

I use a Tangential tool much of the time and I quite often get this problem of "ribbon" swarf. Has anyone tried modifying the standard grind to help alleviate the problem? I have considered trying to design a new tool holder with a separate adjustable chip breaker but I'm not convinced it's worth the effort!

[JonParticipant @jon]

Unfortunately no tool ever made will chip break 6082 I work with it every day for 20 odd years. Other grades chip breakers may work.

That means rakes, type of tool in fact everything will come off continuous. Manually break it up by stopping feed rate momentarily as in interrupted cuts.

6082 is a bad one for stiction constantly clogging up tools with or without coolant. Put something behind in an attempt to break up the continuous chip will only deflect and or aid clogging. It has a spring like quality in T6 whereas others can be brittle or gummy, then of course theres the free machining gorgeous any tool works.

Heres an old action shot 14 years ago, 5 1/4" dia facing off 1/2" one pass 1000rpm on power cross feed, just keep an eye on whats happening and listen for tonal change. Will have to interrupt the cut to break the chip.

Current lathe has a lot bigger hold so don't need to stop so often and keep emptying.

Two hours in compressed, longest strand around 6ft mostly 2ft.

Wire cutters and pliers come in handy.

Can turn back wards towards tail stock pushing the built up or wrapped around chip off the round being turned, just need to move tool out the way to clear the debris.

[“Bill Hancox”Participant @billhancox]

Jon

Some heavy cutting there. Looks like 2 pints worth of swarf at the going scrap rate.

Cheers

Bill

[JAParticipant @ja]

Many thanks for the replies. Jon, I am impressed. I have been using pliers, a bodging screwdriver and various rakes to remove the stuff. I might make a proper hook.

I finished the roughing out this afternoon and tried various things to prevent the ribbon swarf. Nothing really worked. A knife tool with a very small top rake did not help and was less happy at machining (worse finish) than the tool with a 20 degree top rake. Speed changes, feed rate and whether cutting fluid (Cora B) was used or not had no effect. Light cuts did though. The main thing that stopped ribbon swarf from forming was the work diameter, under an inch there was very little ribbon swarf.

Looking at the chip formation, if the chip coil coming off the tool could make a complete turn without hitting the work it continued as a coil. If it hit a ribbon was formed.

I am going to have rough out another aluminium bar in a few weeks time (unless the cold or medical profession get in the way). Until then I will give it some thought. From what Clive says (I guess that he may have a theoretical knowledge about machining) there must be quite a bit published about swarf formation in addition to just the mechanics of machining. Also I might try to find and use the turning inserts and holder I bought a few years ago at a show and have never used.

JA

[Clive FosterParticipant @clivefoster55965]

Jon

Looks familiar, but not too familiar if you see what I mean. If I were forced into doing much such work I'd be very tempted to investigate whether the swarf could be persuaded to run up a short tube with a suitably constricted end and a closed coupled set of rotating blades to wack it off scissors fashion into short lengths. Say 1/4 or 1/2 inch long. Those unrolled chips come off in a pretty predictable trajectory so it ought to be do-able unless the wack off bit needs more power than can be got from a sensibly compact motor.

JA

Theory of chip breaking is dead simple. Just put enough stress across its thickness that a crack runs right though and breaks the end off. By the very nature of how the chip comes off the workpiece there are always plenty of short cracks in it, some longer than others. So you just have to persuade a reasonable fraction of the long ones to run right through. Sharp bend over a chip breaker, whether ground or add on piece will do it. Coiling up obviously stresses the metal and helps drive a crack as does heating and cooling.

Practice of course is whole 'nuther matter. Especially with ductile and springy materials which tend not to crack easily. The mass production, millions of parts per year, folk generally manage to sort it. Which may involve cheating by using a different alloy but for ordinary folk its somewhere between an art form and "Hey I got lucky this time". Reading around there are plenty of suggestions in the "this worked for me" class but everything I've tried has, objectively, been in the lucky today class when it worked.

That said I have an alloy job round about new year time so if it turns troublesome I might try the tube idea. Even without the wack it off bit it should be possible to stop the swarf wrapping around the cutting area so it can just be grabbed by the handful at the end of every cut. Judging by my luck this year it will just jam up in the tube!

Clive

[Joe PageParticipant @joepage27051]

Clive – you have reminded me of my last place of work. I used to machine rubber's, polyurethanes and pretty much every high-tech plastic there is. We used a vacuum system to suck the swarf into a hoover. When the machines indexed their turrets it dragged the swarf back out of the hoover and generally made a mess. The machine I worked on did up to 700mm and you can imagine the lengths of swarf, especially when your doing upwards of 10mm cuts, 0.3 feed. My machine had a swarf cutter, so pieces were atmost 6" long. It was two blades shaped like an X, so they self sharpened themselves, driven by a motor, worked quite well. I'm sure it could be done with aluminium.

Edited By Joe Page on 06/12/2015 21:20:10

[Gordon WParticipant @gordonw]

I usually feed by hand, the interrupted cut chops the swarf up. Use auto feed for finishing if needs be. JFI I was talking to men last night and not one had ever heard of swarf.

[MuzzerParticipant @muzzer]

The chipbreaker shape seems to be rather critical but there seem to be several out there claiming to work eg Becker:

Lach:

Never tried them obviously but looks almost convincing.

 

Murray

 

Edited By Muzzer on 07/12/2015 17:57:39

[JonParticipant @jon]

Good find Murray top video don't look like 6082 but fairly similar characteristics.
Do have all those tips specific for aluminium apart from the last one used.
Notice the tips starting to build up on cutting edge and will rapidly get worse often with 2 secs warning. Very soon dimensions will change diameter turned will become larger as tip isn't cutting as well, clean off send back down back to normal, not the other way round.
Good tips the WNT though have remarkable results with Arno, Seco, Kennametal, Iscar, Teautec and many other specialist tips for the purpose.

Cnc they use free machining unless specified, almost anything works entirely a different animal and a joy to work with. I don't buy it due to almost double the cost more importantly its not as good as 6082 for its springiness and anodising qualities.

Best format for profiled tools ie ground to a specific shape as mentioned earlier, break the cut up manually like Gordons said.

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