Fun & Games with 304SS

[JimDawson]

Just taking a break waiting for some tooling. Time to rant a bit and tell you how much I hate 304 SS.

I have been having fun making some parts out of 304SS. These start out as 3/4 inch round bar. The machine is my Hardinge CNC lathe.

The last batch of about 200 parts came out pretty good with minimal problems, but this batch has been a PITA. The material is harder this run and has been eating tools and tool holders, including two $150 parting insert holders. The second one lasted about 5 parts.

http://www.iscar.com/eCatalog/Family.aspx?fnum=387&mapp=TG&GFSTYP=M


I have now made major modifications to the tool path cutting strategy and feeds & speeds to solve the parting tool issues. Rather than side loading the parting tool as I had been, taking a light finish cut (which had been working fine), I'm using a ''V'' shaped tool to do all but the deep grooving. A parting tool can be used for finish turning, but not in this stuff.

But now with the ''V'' cutter I'm getting about 3 parts out of each edge of some cheap (about $4 each) carbide inserts, I have some good ones designed for SS ($17 each) on order and they should be here this afternoon sometime. I'm down to 120 FPM when I should be running at about 300 FPM and still eating tools. I can't really complain about the cheap inserts, they are not designed to cut SS, and they got me through enough parts to get by for the moment.

All operations are done in the lathe including the slot and lead in chamfer on the end. This is the way they come out of the lathe, from here they go into vibratory deburr and are done.


Oh, then there was the tool change (attempt) without moving the carriage to a safe position and CRASH, there goes a $125 carbide thread mill. That's what happens when you forget to tell the carriage to move to a safe tool change location, G53 is your friend. I now have a a few new lines of code in my software that will hopefully prevent me from doing something stupid like that again. Sometimes you need to make the software smarter than you are

http://internaltool.com/products/mill/34/thread-mills 1/2 shank, 3/4 inch cutter dia. I use this for cutting a 1''-8 internal thread in 6061, about 2'' deep, in one pass.



OK, end of rant, time to go back to work.

 

[eugene13]

Darn good rant

 

[JimDawson]

An update. Got my new inserts a bit ago, they sent the wrong ones I ordered inserts for SS ''DCMT'' and they sent inserts for aluminum ''DCGT''. And yes, I checked my email and I did order the correct inserts.

And another thing, I was sent a job to run, $1700, I turned it down. It was a small aluminum part, about 8 inches square x 1/4 or so thick. But one problem, there was a callout on one dimension of 0 tolerance over about 6 1/2 inches. How the he!! do you even hold a dimension like that let alone measure it, and at what temperature?

I think I'm done for the day.

 

[mmcmdl]

Dont'cha just hate tool changes in the wrong position ? I used to light up the G & L screen with abort cycles quite often ………………….and this was after my boss would swear it was a proven program .

 

[JimDawson]

Another update. I'm slowly working my way through the 304SS parts, running one part at a time. I normally just load a 48 inch bar and press GO and walk away, but now having to do a 100% inspection to check insert condition. As long as one of the dimensions is maintaining 0.6205 the tool is OK. As soon as the dimension hits 0.6210 I can compensate one time, and get it back to dimension but the next time it hits 0.6210 (about 3 parts) it's time to rotate the insert. I am getting about 15 parts/cutting edge, two edges/insert at $19 each.

I lowered the tool 0.010 and that seemed to help, it might have been a bit high to start with.

Only 27 parts to go! About 2.5 hours. I'll be really glad when I get through this batch of material. This has never been a problem before and I have run 100's of these parts. This batch of material is just harder than anything I have gotten before.

Running at 200 FPM, 0.005/rev feed. This seemed to be the best compromise of tool life and surface finish. Running slower actually decreases tool life due to chiping, and running faster just burns the tool. I think what is really killing the tool is the ~3/4 inch of interrupted cut it has to make, but there is no way around this. You can see in the surface where the tool failed and it is always in the area of the interrupted cut.

 

[Winegrower]

Since this material batch of material behaves differently than other batches, perhaps it’s not what it is supposed to be. If it’s a critical part, this could be a big problem...

Maybe worth checking with supplier and customer?

 

[JimDawson]

Since this material batch of material behaves differently than other batches, perhaps it’s not what it is supposed to be. If it’s a critical part, this could be a big problem...

Maybe worth checking with supplier and customer?

You are correct, we will be having a discussion with the material vendor.

In this case we are the customer, it's for our own in-house product so the material is fine for the application. Unfortunately we can't afford to buy traceable and certified material for this application.