Turning aluminium with carbide inserts

Hi

I am having a bit of trouble turning 6063 ally. Ibought a nice new DCMT 07 insert and holder, which cuts amazingly well on mild steel

However with the aluminium it whines, it gets very hot (turns the shop into a bit of a steam bath when using oil ) and the chips birds nest badly.

I have seen specialist inserts for alu with much sharper raised edges and chip breakers and a different coating (silver colour vs the 'brass' tone of mine, titanium compound?). Is it worth getting one of these or is there some art to making a regular carbide insert get along with aluminium?

Part was 50mm diameter, started with 350rpm and increased to ~750 rpm. Tried 0.4 - 0.8mm depth of cut and experimented with tool angles. It seemed a little hit or miss, sometimes the chips broke nicely. It always whined and ran hot though, kind of a constant high pitch like tinnitus as opposed to the obvious rubbing sound I've heard in the past.

Or should I try HSS?

Edited By Ross Lloyd 1 on 17/01/2019 10:07:16

Aluminium and its alloys like sharp, really sharp. Trouble is really sharp tips are weaker than slightly blunt ones so are easily damaged by intermittent cuts on tougher materials like steel. Also don't like tensile forces as encountered when you run the tip a bit past centre during facing off. The thin piece making the actual cutting edge has very little bonding area to hold it on.

Tips for tougher materials like steel are made less sharp. Partly to make them stronger but also to give a less efficient cutting action which puts heat into the material and chip making shearing at the cut line go easier at book, production machine, speeds. Hot chips are of little worry in a modern enclosed CNC machine but much greater rates of metal removal per spindle horsepower / kilowatt of electricity make Chief Accountants very happy.

Putting heat into the aluminium chip as it shears makes the model engineer very unhappy 'cos the cut edge of the chip is near molten as it comes off the metal and tries to weld itself to the tip. If you try you can get some truly impressive built up edges. Best one I had was over 1/8 deep. Cut fine during the pass but coming back for the next one was a spectacular failure. Naturally that was the finish cut so scrapped part. Which was about where I went back to HSS.

If you go HSS polish the top of the tool to promote easy chip flow. Have your side cutters handy to sort out the birds nest of continuous swarf that you will almost certainly get. Chip breaking in alloy at our speeds and cuts is hard to do.

Clive.

Quick answer Ross, yes the polished silver inserts work very nicely on Aluminium alloys.

Another quick answer, use uncoated tips.

Hi Clive, many thanks for such a detailed answer. I have definitely seen the built up edge you mention, its glint caught my eye as I brushed off some chips! Yes the heat is a pain, especially when a long snake of hot swarf decides it wants to meet your hand.

I will try sharpening up one of my HSS toolbits and see if I get on better with that, otherwise I will try out some of those fancy alu inserts. Thanks again!

DCGT is the way to go with a bit of Paraffin or WD40

You may well still get a birds nest but should cut sweetly, a high feed will be needed to get chips too.

Thanks Vic! Do you have a preferred supplier? I am using the DCMT 07 diamond insert at the moment (not sure if it comes in different sizes depending on toolholder?)

Thanks Dave, do you mean uncoated carbide? Thanks!

Ross

The polished silver coloured ones are uncoated.

Ian S C

Hi Jason!

Thats interesting to hear, I have heard the WD40 recommendation before, sounds like its time to nip down B&Q.

I need to learn these insert acronyms too, is DCGT just the specialised alu tip discussed above?

Thank you

Yes. Something like a DCGT 070204 which has a 0.4mm radius tip is a good all rounder being a bit more durable than a 0.2 radius and does not leave a large fillet in internal corners like a 0.8 radius does.

If you are going to use WD40 then the 5lts can and pump bottle is a lot cheaper than aerosol but 5lts of paraffin and a small brush is far cheaper still or put some in an old household cleaning spray bottle.

Edited By JasonB on 17/01/2019 11:08:03

Ross

I meant uncoated inserts, but this is probably clear now from subsequent posts from others

Use the link to see details of inserts for your 07 tooling, I use the 02 insert (0.20mm nose rad) as most of my work requires minimum rad on diam changes, as Jason says the 04 or o8 do provide a stronger tip.

**LINK**

Emgee

The special polished inserts (CCGT) work very well on aluminium alloys; there should be no problem getting finishes on the order of 1µm Ra. I've never had a problem with built-up edges using the inserts, but birdsnesting is an issue.

A while back there was a thread that suggested that increasing the feedrate did not lead to chip breaking. I did some trials and even at 10 thou per rev the swarf did not break. I don't know what the answer is; higher spindle speeds may be, or even higher feed rates?

Andrew

Yes Ross, I use these ones in the 11mm size from JB.

**LINK**

Ross,

You mentioned HSS. It is a viable option. You can get more favorable rake angles with HSS than you can with carbide. The tool needs to be honed to a very sharp edge and the top surface polished. The tangential tool holders work quite well in aluminum. You can change the grind angle to get additional side and back rake.

If you are turning aluminum that is high in silicon tool life can be a problem with HSS.

I do use carbide inserts on aluminum. The advice given by others regarding polished inserts is good. A lot of machinists like WD40 when machining aluminum. I don't like the smell so I use soluble oil coolant in a squirt bottle.

**LINK**

+1 on all your points John, I feel the increasing use of tips in the home workshop may be driven by people not wanting to develop the skills to make a decent HSS tool bit. Hand grinding HSS will require some investment in sharpening equipment and maybe the poor performance of many off the shelf budget grinders pushes people to use ready made tipped tools. I suppose that cost wise you can buy lots of tips for the cost of sorting out a decent grinding setup but once you are setup you can have sharp tools forever and also you can make any specials that you will almost certainly need one day. I view tipped tools as a useful extra to have around but I think I have broken more tips than I have worn out, they are rather fragile and maybe I am a bit careless.

Mike

Recently had to reduce the diameter and bore a piece of 4" round, 6000 series alloy block. Ripped through it with a CCGT insert. Used WD40 as others suggest.

I did have to pull the birds-nests off, but enjoyed high removal rates, and an impressive machine finish.

Cheers, Colin