Troubleshooting 6061 parting - existing proven program&tooling

[Dylan @ FDF]

I have used PM for a few years searching through and usually finding the right answer for my issue.

Today I have come across an issue I just can't seem to remedy. I have about 20 hours of troubleshooting into it at this point, I will keep it as short and sweet (as possible)

Machine: ST15 and ST20Y(same results either machine)
Coolant: Trim Microsol at about 10%
Tool: Iscar Tang grip/IC20 insert

I will attach some photos, it is a finish I have seen a few people fight against. The typical golf ball/smearing in 6061 and then chatters as you increase SFM.

The important thing to note here - Our ST15 has run about 22000 6061 parts with the above combo, with very little adjustment needed to SFM to keep a satisfactory finish on the parted face for no 2nd OP. This started with a fresh batch of 6061, however I ordered more material from another supplier who uses Canadian mills(we are in Ontario) and I didn't get anywhere, it was the same awful finish using proven program parameters, with no improvement after playing around as I typically would.

Things I have tried:

SFM/Feed in every variable from 200sfm to 1200sfm and .0006ipr to .007ipr - note that it gets much worse with increased feed. Typical parameters run are .0013 to .0018ipr at 350 to 600sfm depending on batch of material and insert sharpness.

New blade(as we just purchased the ST20Y and ordered fresh tooling) to rule out insert seat damage or fractures

Square of holder, checked runout in Y and X for the blade holder on the 20Y, no concerns there.

Part off insert to centerline(.001 or slightly less)

Coolant pressure and % is as usual for the previous 20k parts

Always back parting, leaving anything from .0015" to .025" for finish pass.

Changed chuck pressure between basically anything safe to operate at

Tried G96 and G97 for parting, sometimes I run G96 with a low ipr to finish bushings that leaves a satisfactory finish.

Worth noting that the facing and boring operations have no issues, it is just parting this material off that has been a fight.

Setup the same tooling and material on the new 20Y and used the same program and got identical parting finish, trying to rule out any issues with the ST15 itself. I can also mostly rule out the machine and tool mostly through the fact that we can run 4140 with the same blade and different insert grade and the parts turn out as good as you could want them to. Also ran 303 stainless last week in between troubleshooting and it ran just as it always does.

At this point, I would love for it to be as simple as I got a bad batch of 6061, and when I ordered the stuff from the next supplier it was also garbage. But maybe I am missing something here? I'm just stumped as this tool setup has been very very consistent for a year and a half running lots of nice looking parts.

Order of photos - running at the normal parameters, running higher feed(as feed goes up, finish looks worse, as sfm goes up, chatter intensifies) larger material(1.25" stock, first photos are from 1" stock) using the proven parameters, 4140 running on the same lathe with the same tool/holder and IC908 insert, and final photo is typically the finish we are achieving in 6061.






Any insight is appreciated!

 

[mhajicek]

Did both suppliers get their material from the same source?

 

[Dylan @ FDF]

Did both suppliers get their material from the same source?

Waiting for the cert from the 1st supplier but typically, I believe they stock overseas stuff. We have run lighting rod/imported 6061 through the lathes before and it does need some tweaking but usually I can work through it in a few parts and keep going. This stuff we currently have is a whole new animal.

 

[guythatbrews]

Have you compared hardness?

 

[rklopp]

What's the built-up edge situation? The first two parts look like the chip is dragging on the walls, as if the chip has not bent transversely to make it narrower than the groove. Are the chips breaking, rolling up, or coming out as silly-string? How did they come out in the old days when everything was OK? The third part looks like you've hit a resonant frequency, which you'd expect a speed or feed tweak to fix.

 

[Dylan @ FDF]

Have you compared hardness?

No hardness tester here, closest thing I have is monitoring spindle load during the drilling OP which isn't going to tell me what I need to know hahah.

What's the built-up edge situation? The first two parts look like the chip is dragging on the walls, as if the chip has not bent transversely to make it narrower than the groove. Are the chips breaking, rolling up, or coming out as silly-string? How did they come out in the old days when everything was OK? The third part looks like you've hit a resonant frequency, which you'd expect a speed or feed tweak to fix.

On the first parting pass(leaving about .060" on diamater for finish turn, played around a bit with this as well) it looked like it wanted a bit more feed, then it tightened up into a nice coil. Finish pass I found is happiest taking only about .0015" on the z to center so chip isn't really fully forming, but it looks very similar to the "good ol days"

Third part was the best I could get using G97, I switched to G96 and used a very low rpm, I think around 600 with a low feedrate to get a "decent" finish but it increased the cycle time by almost double doing that. Anything else would have vibration as shown, and only got more aggressive and louder as you tried to feed through, or lower sfm. It's very weird, and frustrating.

 

[guythatbrews]

You can get a down and dirty hardness comparison with a weight and a 1/4 steel ball. Position the steel ball on a faced surface with clay or grease. Drop the weight onto the ball from a known height for each sample. Compare dimple size. If it's much off you can tell.

 

[Dylan @ FDF]

You can get a down and dirty hardness comparison with a weight and a 1/4 steel ball. Position the steel ball on a faced surface with clay or grease. Drop the weight onto the ball from a known height for each sample. Compare dimple size. If it's much off you can tell.

I like that. Thank you for the suggestion! I'll see if I can doing a little experiment tomorrow.

 

[mattthemuppet]

same batch of inserts as before or new batch? Bit of a long shot, but you never know

 

[david n]

What mill? I have had issues with SCM material lately. I won't even let in the shop. Just had 5K of 6061 dropped off today and it I told the supplier no SCM. Kaiser has been iffy too, but not as bad as SCM. Hydro has been runnin the best as as of late................but it can all change in a heart beat. No one ever seems to be consistent 100% of the time..................

 

[Dylan @ FDF]

same batch of inserts as before or new batch? Bit of a long shot, but you never know

I had the same thought, I do have some good used spares, popped them in and it didn't do much unfortunately!

 

[Dylan @ FDF]

What mill? I have had issues with SCM material lately. I won't even let in the shop. Just had 5K of 6061 dropped off today and it I told the supplier no SCM. Kaiser has been iffy too, but not as bad as SCM. Hydro has been runnin the best as as of late................but it can all change in a heart beat. No one ever seems to be consistent 100% of the time..................

First batching waiting to see the mill, second batch is Extrudex. From what I've been reading, it seems like the consistency for a lot of 6061 bar is really going down the drain.

 

[Ox]

A) Doo you have any old bar ends from days gone by?
Even tho you may not have enough material to make a part, I bet you could chuck it up and run the cut-off routine.

B) Have you tried NOT running a second pass on the cut-off?


-------------------------

Think Snow Eh!
Ox

 

[mmurray70]

First batching waiting to see the mill, second batch is Extrudex. From what I've been reading, it seems like the consistency for a lot of 6061 bar is really going down the drain.

How do you find stuff from extrudex? I had batch of stuff from them while ago that was way undersize. Was disappointed when I found out the shitty material came from here in Canada.

Never going to get a perfect finish on aluminum when parting, and if you do some how, it will probably be inconsistent. Is coolant nozzle in exact same place? I made some of those plates for my haas turret with the 2 nozzles. Parting aluminum went much better with one nozzle aimed into the cut, and a second nozzle aimed at middle of blade. Coolant stream hits the blade and then deflects into the groove. https://3d-brandtooling.com/shop/haas-bot-st-sl-20-30-35-coolant-block/

 

[Ox]

First batching waiting to see the mill, second batch is Extrudex. From what I've been reading, it seems like the consistency for a lot of 6061 bar is really going down the drain.

Is this just commodity round bar?

We get special shape bars from the Extrudex on our side of the lake. But one thing that will play a part - is that from my experience, their bars are consistently on the low end of hardness. If they were any lower they wouldn't make "T6" requirements. However, that has only shown up to be a problem for us on deep hole drilling/finish. Well, and it shows up on an external burr as well I guess.

I have already sent some bars out to be heat treated 3 yrs ago) but that was a whole new set of issues, and we were able to make doo by changing out our coolant. (refreshing) Otherwise - just a few points higher and they would run fine.


----------------------

Think Snow Eh!
Ox

 

[Ryan at Sparrow]

I have 2 holders for that same iscar insert. I usually leave .015 on the face for a trigon insert to come by and clean up for the finish.

This holder I don't like because it isn't as rigid and will wobble if its stuck out too much causing a terrible finish: https://www.iscar.com/products.aspx/countryid/1/productid/11887

This one is better if you can afford the clearance and theres much less waviness on parting off since its more rigid : https://www.iscar.com/products.aspx/countryid/1/productid/12399

Haven't had one issue with that second tool at all.

 

[Mtndew]

Is the insert bright polished and razor sharp? If not I would definitely get one that is made specifically for aluminum.

 

[lumley32]

i used to have this sort of problem, used to blame the material, had a rep pop in and in passing mentioned it would be worth trying their new through blade coolant parting tool. it sounded like marketing wank, but he offered me the blade, box of inserts, and tool for nothing as a trial.

Long story short, after trying them for a week I ordered them for all our lathes. just checked one machine and the insert has 6936 parts on it, all through 2" 6082T6. we even stopped finish machining one part, it's not perfect but the customer is happy enough with it on that part.

 

[Digital Factory]

What's the diameter of the bar?

The larger the diameter, the more likely it is to have heat treating "defects".

I use defects in quotes because like all processes in manufacturing, there's a tolerance range. It's possible that all of your material in the past was somehow at the upper end of the T651 spec, and now all your material is at the lower end. Chemical composition could play a factor too, but the trickiest part of producing aluminum is the heat treating due to the very short quench delay, so that's the most likely culprit.

Also when I need a material sanity check, I'll order a 1 foot bar off McMaster-Carr. Due to the nature of their business, they're more likely to have older stock in inventory.

 

[Dylan @ FDF]

Thanks for all of the replies guys. I spent some time troubleshooting, was able to focus on some steel and get a mental break for a bit lol. I also had my Iscar rep send over a few tools and inserts to try out to remedy the issue.

A lot of good info in this thread and I have to agree, ultimately I am limited to blade stick out vs coolant delivery. A through coolant blade choked up as short as possible would give me the results I'm really chasing after and I'm going to budget that in for these machines asap.

I ended up being able to choke up the blade, and move the tool holder itself out of the turret for more clearance from the bolt-on coolant block that is used on the ST-15. For the ST-20, some new coolant lines that I can place directly over the cut path will help for the time being.

Iscar rep brought a few groove/part tools and an integral shank holder for the parting blade we already have. The more rigid tools definitely make an immediate difference, I was able to get a parting finish I was happy with on the bushings that I needed to run, although it was at a slower speed than I'd like, cycle time is sacrificed for finish on those parts for now.

I'll attach some photos of the bushing finish as well as the acceptable(high rpm and feed) finish for the spacers that the ST-15 is usually spitting out. I was also very very impressed with the versatility of the Iscar grip groove/turn tool, I make the hex adjuster nuts in one OP on the ST-20 and back groove the diameter under the flange, I was surprised to see how much DOC a grooving tool can take in 4140, and it actually preferred the large DOC for a nice finish. Always learning something new in this trade, which is why I enjoy it so much.

These spacers(made from 1" 6061) are what I'm getting now as a parting finish.






This is the bushing from 1.5" 6061 that I was more worried about the finish with. I found I could get about 75 parts before the dimpling really started to come back in, however I just throw those inserts back in the parting blade when I'm running our rod end spacers and they work totally fine. Parameters for this were 450RPM and .0012IPR with no constant surface speed being used, I found the surface was more consistent without.



Finally, these are some 4140AN parts that the Iscar grip tool was used for. Did a fantastic job at grooving, turning and parting off. I can actually order an aluminum specific insert for this tool and use it for parting as it will work for 90% of the parts we currently do. It's pretty cool being able to do this in one OP now, we previously ran them on the ST-15 for the round profile and then had some soft jaws to finish off the hex and chamfer in the mill.




Hopefully some more people can use this stuff as a reference while learning like I am. Thank you guys for the help and suggestions!