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17-7 This isn't 17-4

Bobw

Diamond
Joined
Feb 8, 2005
Location
Hatch, NM Chile capital of the WORLD
So we get this giant job and part of it is 36 pieces, 15" long, 3-5/16 wide, 5/8 thick, out of 17-4. Stock is supposed to be 17-4 5/8 thick, 4.5 wide supplied by the customer. It came in waterjet to 4.6 wide out of 3/4 plate, no biggie, a few extra minute. But its 17-7.

Figure no biggie on the 17-7 vs 17-4. Boy was I wrong.

They said they couldn't find 17-4 in that thickness so they got 17-7.

I start running it like its a condition A 17-4, with the proper inserts. Wet, 225 sfm. Nope, 200 sfm, nope, 150 sfm nope, 110 sfm, nope, maybe 5 minutes of life. WTF, I can get an hour plus on 13-8 with 130sfm with these inserts.

So, OK, the PH grades usually machine better heat treated, this is going to an H1050. We can do that in 4 batches and certify it. The customer doesn't like that and will only pay for 2 batches. We dig a bit further and realize that this 17-7 is in a condition A and is only a "semi" PH. It needs to be cold worked to a condition C to be able to be hardened like a ph grade or needs some extra heat treating to be able to be heat treated like a ph grade.

In this case it needs 1450 at 90 minutes and then within an hour brought to 60 +10 for 30 minutes, or brought to 1750 and then to -100. Then it can be normal PH grade heat treated.

I'm glad they didn't like our HT price because I think they are going to eat it on this one.

So, when I get this crap back at an H1050, at about 36C, is she going to behave. Right now she's at a ConditionA, she's at about 5c(85B)[sticky gummy garbage].

Googling I've found a machinability rating of 75% of 12??. I've also been told that 17-4 and 13-8 are the same, thats like saying that A286 and aluminum are the same and titanium and nylon are the same.

Anybody have any experience with this crap? This was quoted as 17-4, I'm willing to give up a little, but not much.
 
Boy, I sure hope it was your customer that made that quick decision to "just send 17-7 because 17-4 could not be found". I would also have to mention something about the extra time and tooling costs to remove the extra material.

I too only have experience with 17-4 and it cuts pretty damn nice if you go in with Ti type principles. It usually mows really nice and is predictable. I am not familiar with 17-7 but they certainly are different or there would not be a 17-7. Obviously is not a structural application.
 
Short of the .75-1.5% Aluminium in it. Stuff pretty much seems like a 304 but with 2% less in chromium and Nickel. Weird, but I guess that bit of Al in it might be enough to screw it up and make it all gummy.

What does the insert failure look like? is it pushing a big burr ahead of the cutting edge and chipping it? whats your chip load?

Sometimes with the tough stuff HSS is what saves the day :(
 
SND, this is weird stuff, I don't think its meant for machining, it seems that it is meant for forming. From what I could find, its a "semi" PH grade. To get to a condition 'A', it takes a funky heat treat. From the top of my head, 2250 for 4 hours, air cool, 1900 for 8 hours, air cool, 1650 for 16 hours, air cool, 1450 for 24 hours air cool. This leaves it at a 5c(85B). Now to get it to behave as a typical PH (heat treat wise), you have to either cold work it with a 40-50% reduction which changes the grain structure from austentetic to martensetic(sp?). OR a mid range heat treat(heat and then cool within and hour to either 60+ 10 or -100), then it can be standard PH grade heat treated.

The inserts.... 45 degree lead 3" 5 flute facemill. The "grey" ones, grade???? Exkenna/Curtis sent them to me and they were fantastic in 13-8 and A286(as good as ANYTHING can be in A286), they also did a damn good job in 321.

Tried from 225 sfm down to 110 sfm. .060 depth of cut, from .010 to .014 per flute of feed. The inserts are just blown out, I'm 99% sure its not a thermal crack, most likely material buildup which then rips the insert apart.

Kind of a moot point now, it went back today, they are sending it out for HT. I'm hoping it behaves when it comes back at an H1050. I've never met a PH grade that wasn't happier when it was heat treated.

I'm not even sure if this part calls out 17-4 or 17-7. This whole project is a giant mess. A286, 302, 303, 304, 321, 13-8, 17-4, 17-7?, 4130, 4140, 4340, 2024, 6061, 7075, delrin, nylon, aluminum bronze, and "commercial quality low carbon steel".

There is even 321 parts that get WELDED to the "commercial quality low carbon steel". Why the hell would you spec 321 (high temp and corrosion resistance) if you are going to weld it to a piece of crap steel?

McDonnell Douglas if anybody is interested.

Pain in the ass, but its been good money.
 
I have worked with a tiny tiny bit of 17-7 condition c, but it was 0.017 inches thick and making "piston rings" about 3/4 round. It is wicked stuff. I have a partial coil left used for shimstock and such. Its not your average material, and I don't envy trying to mill it.
 
Bob, check this out

Thanx, I saw that one quickly earlier, one of the better snippets I came across, I actually read it this time. Good thing I didn't machine it, from a condition A to a TH1050 it grows .004 per inch per inch, which would have been really not good on a 15 inch long part with a pretty tight bolt pattern on it.

Willie, I wish this sucker was only .017 thick and 3/4 roun'd. It better behave when it comes back, if not, it will be put to the side and "requoted".

Milling 13-8 today, its almost pleasant compared to that crap. Actually 17-7 has now replaced 13-8 on my 3 most hated materials list. A286 and 321 are the other 2.
 
I've machined it in (I think) RH950 condition. It was Rc 46-48, so whatever condition that is. It didn't seem a whole lot different than 17-4 to me. The customer later switched to 17-4 and tool life was slightly better. We were using Ingersoll tooling along with a key cutter from Harvey. Great surface finish and tool life on everything. On the insert mill, I was running 225 SFM. Tool life was good so I asked the Ingersoll guy how fast I could run it and he said maybe 200 SFM max. LOL. I was using high pressure coolant though, so maybe that helped. I ended up kicking it up to 250 SFM and was getting over 1,000 pcs per index.

I think it's the condition A that's giving you grief.

The other thing I found is that this stuff doesn't like to be rubbed. IIRC, I was feeding around 0.005" IPT. Feeding slow = burrs, lousy finish and worse tool life.
 
Rates 17-4 and 17-7 as 0.28 and 0.20 ratings. I'd have to suspect that that 0.08 involves a lot of heartache.

I'm going with Swisspro on this one, I don't think the .08 was the problem, I think it was the condition, "A" for "All gummy".

Thank god somebody had some good milling experience with this stuff. It shouldn't be problem when it comes back, now I don't have to berate the customer, though I'm still a bit sore wasting a pile of inserts and half a day screwing around with it.

Thanx.
 
There is even 321 parts that get WELDED to the "commercial quality low carbon steel". Why the hell would you spec 321 (high temp and corrosion resistance) if you are going to weld it to a piece of crap steel?

QUOTE]


I dunno the parts your making, but at my work they do (machine only the client welds them) pipe spools. They are inconel pipe, and mild steel flanges. At first it seemed stupid, but the only thing that handles the fluid is the inconel, and buying inconel flanges in the DN300 or DN400 size is very expensive.
 
If you have time, let us know how it turns out.

Jeff

I will, they should be back soon, if I haven't hung the customer up by his toenails and subjected to him to 24 hours of 10 week old hyper puppy licking (its the worst torture I can think of that could possibly let me walk away with only probation).

NUMBER 2, I can understand your situation, makes good sense. This application is a 321 toe hook(its actually a clevis), welded to 'barely' steel on a fricken trailer.
 
I will, they should be back soon, if I haven't hung the customer up by his toenails and subjected to him to 24 hours of 10 week old hyper puppy licking (its the worst torture I can think of that could possibly let me walk away with only probation).
.


I always enjoy your sense of humor!

Jeff
 
Update: Job done. Job sucked.

the 17-7 came back in the 43-45C range. No biggie, it machined much better than the A condition.

I just ran it like I'd run 13-8, which worked great within about .150 of a surface. The inside was still nasty gummy and soft. I'm guessing they butchered the cooling cycle.

The stock was .750 thick, faced down to .625. My finish endmills for the profile were beautiful on the bottom and beautiful at the top of the cut, but that middle section just tore 'em up.

Just ran them as fast as we could and got them out the door. Still made money, just not great money. I really thought it was going to be a gravy job, and it would have been out of 17-4.
 
Update: Job done. Job sucked.

the 17-7 came back in the 43-45C range. No biggie, it machined much better than the A condition.

Just ran them as fast as we could and got them out the door. Still made money,.


That's good to know.

Jeff
 








 
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