Aluminum Finish Issue, Hard Spots?

[LUX93]

I have had some issues in the past with aluminum hard spots that appear when the surface finish is smooth enough. I have seen it in round stock appear as spotting, it almost looks like leopard spots. I think I'm having a similar issue with some bar stock, I'm seeing lines through the material when we flycut the face. The deeper we went the more lines appeared, just closer together. I can hide it using a face mill, but these parts require a very smooth flat surface, and the face mills you can feel an ever so slight hump when you run your finger across. It's barely anything, with an indicator it moves maybe a couple tenths but it's enough to not be acceptable for the application, hence the fly cutting. The stock it 7" wide and 10" long, 6061-T6, from Kaiser who usually produces some of the most consistent aluminum we've had.

 

[Milland]

You may be getting a cutting resonance, not a material defect. Try varying RPM and/or feed to change the frequency, or at worst remove one or two insets from the cutter and see if that makes a difference (again, adjust speed to suit).

You can also look at the fixturing, sometimes adding a vacuum feature to suck the plate down will help a lot.

[Looking at the pics again, that's likely thick enough stock that it's not bouncing into the cutter. Could still be a resonance issue in the rest of the system]

 

[LUX93]

I have ran these quite a few times on the same machine, using the same fixture, same speed. I really don't think it's a vibration issue. These plates are 1-1/2" thick and the fixture plate is too, secured from the bottom with 4 1/2"-13 cap head bolts, so it's a very rigid setup. I'm using a flycutter so it only has two insets, removing one isn't an option. The only vibration would be withing the spindle or flycutter, but I flycut the fixture plates before running these and they came out fine. I'm using PCD inserts too BTW.

 

[Milland]

Sometimes it's worth a call to the material supplier, with the request that they contact the mill. Might want to try that route.

Just for completeness, have you tried touching off the two inserts with a test indicator to see if they're the same level? Or inspect the edges to look for damage?

 

[LUX93]

I have contacted the vendor to figure out what mill they came from because I didn't see the name on the bar. They said it came from Kaiser who's usually a good source, so that got me wondering. The cutter has one insert lower than the other which is typically how we run it, like a rough and finish insert. I did inspect the inserts before we started the job because in the past careless setup guys chipped the diamond inserts so I always look at them before and after the job since they are pricey. Like I mentioned, we flycut both fixture plates before running these plates to make sure everything was perfectly flat, and they cut fine, no issues at all, so if there was a harmonics issue it would also be appearing when doing that, so that's what makes me think there's a material issue. Since there was a material shortage during and after Covid our supplier, Coast Aluminum, was getting material from various mills around the country, and I had several occasions where bar stock had spotting, and they confirmed that is was a manufacturing issue, and it also affects parts that get anodized.

 

[kustomizer]

We have found Kaiser to be consistently hard and easier to machine as the chip control is easier. I get better finishes with Hydro which is consistently softer, makes better finishes but makes stringy chips

 

[LUX93]

Generally most of the stuff we get through Coast comes from Kaiser and it's been consistently good. Since the whole shutdown material was a little scarce so we were receiving from several different manufacturers which is when I started noticing some of the issues. 6061 isn't always great for achieving really fine finishes especially when it's really gummy. I asked my supplier and they did say they make a Kaiser Select which is supposed to be better machining so I'm going to look into that and see what it is. Part of the issue is the better I make the finishes then that becomes the new standard that they expect every time, and they nit pick every little thing on the assembly line, tiny swirl marks from a chip maybe dragging or something, stuff that usually isn't an issue but since they want the parts looking as good as possible. Even the machine marks from where a face mill overlaps is something they don't want, that's why I made this 12" flycutter to make it across in one pass. I tell them that 6061 isn't always going to come out looking as good as a harder better machining material like 2024 or 7075.

 

[CITIZEN F16]

I have contacted the vendor to figure out what mill they came from because I didn't see the name on the bar. They said it came from Kaiser who's usually a good source, so that got me wondering.

If it isn't marked it is likely Chinese 6061 and the vendor lied to you. The only unmarked Kaiser aluminum I have seen is sizes too small to have typical sized markings on. I would find another vendor.

 

[LUX93]

You may be getting a cutting resonance, not a material defect. Try varying RPM and/or feed to change the frequency, or at worst remove one or two insets from the cutter and see if that makes a difference (again, adjust speed to suit).

You can also look at the fixturing, sometimes adding a vacuum feature to suck the plate down will help a lot.

[Looking at the pics again, that's likely thick enough stock that it's not bouncing into the cutter. Could still be a resonance issue in the rest of the system]

I wanted to post an update an let Milland know he was right, it is a vibration issue. We've ran these parts and others with this same tool and parameters and never had an issue so I initially didn't think it was vibration. But I figured I better at least investigate to know for sure. I found an old reject part from a different batch of material and it was leaving the same type of pattern on it, so I'm trying to sort out where the issue is coming from. I'll post an update after I mess around with it some more.

 

[charlie gary]

Have you checked your drawbar tension?

 

[Milland]

Have you checked your drawbar tension?

Good idea. Or check if a metal chip has snuck its way into the spindle taper or adhered to the toolholder taper.

 

[dandrummerman21]

I don't understand what you mean by "removing an insert isn't an option" ?

How much higher is one insert than the other? And how much stock are you removing with it?

In my experience, flycutting with 1 insert gives a much more predictable finish.


There was one job facing die cast parts, about 6" long and 3" wide, the best result was with a single diamond insert in a 4" facemill. More than one insert, finish went to shit.

 

[LUX93]

Have you checked your drawbar tension?

That's actually something I was wondering about, I don't have a drawbar gauge so I'm looking at getting one. Has anyone used the one from Mari Tool? It looks decent and seems to be the most economically priced from the all of them I have seen. I was going to post a thread looking for service techs in the Arizona area. I don't want to call HAAS out since this machine is out of warranty and most of the techs that come out drag their feet all day and charge travel, hotel etc. I can handle a lot of general machine repairs but I want an experienced tech to give the machines a once over.

 

[LUX93]

I don't understand what you mean by "removing an insert isn't an option" ?

How much higher is one insert than the other? And how much stock are you removing with it?

In my experience, flycutting with 1 insert gives a much more predictable finish.


There was one job facing die cast parts, about 6" long and 3" wide, the best result was with a single diamond insert in a 4" facemill. More than one insert, finish went to shit.

Well at this point I'm willing to give it a try. It just takes forever to face these as it is with the two. I haven't tried this particular flycutter with one insert so I'll give it a whirl in a few days when I have some time on the machine.

 

[LUX93]

If it isn't marked it is likely Chinese 6061 and the vendor lied to you. The only unmarked Kaiser aluminum I have seen is sizes too small to have typical sized markings on. I would find another vendor.

I thought that was weird, I have never seen Kaiser material that wasn't labeled down the whole side of the bar.

 

[LUX93]

Good idea. Or check if a metal chip has snuck its way into the spindle taper or adhered to the toolholder taper.

I did check the spindle taper. That's one of the things I harp on the guys to do every day and while running, keep the taper and tools clean. I'm suspecting the drawbar tension isn't where it should be. I'm going to talk to the boss about buying a drawbar force gauge.

 

[charlie gary]

I did check the spindle taper. That's one of the things I harp on the guys to do every day and while running, keep the taper and tools clean. I'm suspecting the drawbar tension isn't where it should be. I'm going to talk to the boss about buying a drawbar force gauge.

It's not unheard of to think everything's fine before removing the drawbar and discovering half of your spring washers have disintegrated.

 

[gkoenig]

2 PCD inserts, with one lower than the other - but is the lower one a wiper insert? If not, why not?

 

[Milland]

2 PCD inserts, with one lower than the other - but is the lower one a wiper insert? If not, why not?

And it's got to be inboard of the "rougher" insert so that it's not taking the primary bite.

I always worry about the rougher/finisher strategy on the same tool due to force transmission through the system. if there's an "impact wave" set up by the rougher, is it damped sufficiently by the time the finisher (wiper or not) goes into the cut?