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04-28-2010, 09:27 PM #1
plasma cut ss304 slugs or watercut slugs
I have a little problem here
just did a job in ss 304 plasma cut round slugs. it was od 145mm with an id of 90mm and 20mm thick. it needed to be turned to od 133mm id 97mm and 15mm thick.
not the bloody thing just eated inserts on turning the outside diameter that had a huge tit on it from the plasma cutting.
after doing those 25 parts they complain about the price that it was more then double the the steel ones i did some months before and asked what could be done to make it cheaper.
I dont know a thing about watercutting but i assume it doesnt work harden the OD as much as plasma cutting and it would be runder to start with, But would it be much more expensive then plasma cutting?.
the reason why i havent opted for water cutting in the first place because my customer supplier the slugs himself.
04-28-2010, 11:54 PM #2
We had been supplying a set of milled Aluminium parts to a regular customer and he then wanted to change to SS304. Our new price was nearly three times the Aluminium price.
After explaining to the customer the longer machining time and the increased tooling costs he was quite happy with the price.
Actually we went one step further and managed to simplify some of the parts to reduce the overall cost of the set. We had been working with the customer on the original design so we had a good idea of where we could save some costs.
Maybe you need to sit down with your customer and show him your feeds and speeds and the tooling costs so he understands the difference between the two materials.
And yes, water cutting will be more expensive than plasma; I don't know what tolerances you are working to but your customer may be happy with a watercut part with no extra machining.
04-29-2010, 12:13 AM #3
thx for the info allready.
these are repeated jobs so for the first time the price wasnt the big issue but it will be for the other parts in the future.
i still need finish the parts no mather what the ring are welded on a tube and the tube is welded in a flange. after the welding they need to be faced an the hole in the ring will need to be made on tolerance and in line with the flange.
the only thing i can see to make it cheaper is to reduce the slugs diameter so i wont have to take 10mm on dia every time.
04-29-2010, 12:49 AM #4
Apart from reducing the mount of metal to be removed, I suggest you speak to your tip suppliers ''insisting'' on a demonstration, if the tip can't hack it - no money.
04-29-2010, 02:01 AM #5
I know how it is. I have to turn plasma cut 304 and 316 all the time. It is BRUTAL on the carbide. I haven't tried EVERY brand and grade of carbide, but so far Sandvik grade 2025 seems to be the best. I would have to think that waterjet cut blanks would not be as bad. I don't know the up-front cost difference would be.
04-29-2010, 02:55 AM #6
There are a few different choices for plasma cutting stainless steel. If the edges are cut with an air process, they will be oxidized and hardened. If these same parts were cut with H35 (argon/hydrogen) as the plasma gas and nitrogen as the shield gas, then they would be machineable using standard stainless steel machining techniques. All plasmas produce a very high temperature arc, but often the hardening is created by the chemical effects that are exacerbated by the high temperature.
Typically a low cost bidder for plasma cutting will be using a low cost machine with an air plasma....does a nice job on a lot od materials, but edge metalurgy on steel, stainless and aluminum is affected. A shop that has an industrial grade plasma such as a Hypertherm HPR260xd (high definition) can do a much better job, assuming the operator is choosing the correct gases and processes.
An abrasive water jet would do a better job in terms of heat affected zone, edge hardening, however the cutting cost would be considerably (maybe 5x) higher due to low cutting speed and abrasive cost. It is possible, however, that the water jet part may not need secondary machining...so it may be a better choice.
Jim Colt Hypertherm
04-29-2010, 03:37 AM #7
Why cant you make them from BAR STOCK sluged to length plus a 1/8?
1....Face and bore the first side and turn a short OD for 2nd chucking
2....Hold on OD or a finished ID and complete the part...
And if your customer insists on supplying those crappy slugs from plate, it's gona be a time and materials price...
04-29-2010, 03:44 AM #8
Have the plasma cutter set up for more than 360 degrees of cut, and that 'tit' should go away.
Try 370 degrees of rotation, that should do it.
The scrap may need to be stabilized, not allowed to fall away.
Plasma will eat anything it its way, you just need to give it the opportunity.
04-29-2010, 04:13 AM #9
Informative thread, Jim - I wasn't aware of this. I don't know about others, but I'd like to see you post a short article on this type of thing (at least in the flame/plasma cutting realm).
04-29-2010, 05:47 AM #10
WATERJET ALL THE WAY! We have done this with 304 and you have no work hardened edges. The other thing about having a work hardened edge is that you want to interpolate it on a CNC mill and never climb cut. 304 gets really nasty when you have a HAZ (heat affected zone). Never plasmacut 304 unless your not going to machine it later or you are going to grind the hard edges.
04-29-2010, 05:56 AM #11
send the 304 to a heat treater and have it annealed after its plasma cut. or like suggested before have the parts waterjet cut.
04-29-2010, 06:28 AM #12
C'mon guys, most of these things are adding more and more costs. Waterjet is sloowwwww = pricey, HT won't fix the oxidation that is likely part of the problem at the surface, and I've machined a bit of it too before, but there's way worse stuff.
The "tit" is something you fix with a belt sander(or angle grinder) in 5 seconds, along with any rolled over slag from the cut. Your first cut on the lathe needs to get below any interruption, preferably with a good negative holder. 10mm thats 2, maybe 3 cuts max DONE within .001.
I must say though, I'm with Gary E on that one, why is it even being made from plate? I've never seen SS plate that was cheaper per pound than round bar, mostly when considering the extra waste... humm. oh and I'd likely trepan the center out vs drilling. Unless I found some hollow bar at a descend(cost effective) price that fits the sizes...
Double the cost of steel for stainless machining is perfectly normal. More time + more tooling = more $, they should know that...
04-29-2010, 09:57 AM #13
As much as it hurts, I gotta go with Gary this time....
I have been dooing a lot of burnouts lately - supplied by customer. I think they are all waterjetted. I can't beleive they are sending out 1200# plates to anneal? Also did a batch of 310SS plates about 4' D and they finished well. I didn't turn those tho. I used a carbide mill. Made 8 plates, ID/OD and the mill is still good! I hafta ass_u_me again that these were walerjetted. I KNOW that a 1045 plate this winter was originally "burnt out" and then they realized their mistake and waterjetted out a new one.
So waterjet must NOT be too expensive as compared to annealing - at least large parts. ???
Also - these have been very nice finish for this type of process IMO. Pretty straight/round. Source is ALRO.
Think Snow Eh!
04-29-2010, 10:10 AM #14
At least here in Finland 140x90 round 304 stainless tubing is available, so it should be there in Belgium too.
I've turned a lot of 304 and 316, lots of hexagonal and round bars. What kind of roughing tool are you using to turn these? Sandvik WNMG 2025 has been the best insert this far i've tried. Should do those parts out of tubing with one insert easily. Remember to use finishing tool like DNMG to finish the rough turned surface, as with stainless the roughing insert will start making a bad surface very soon, but it will still rough those pieces nicely.
What kind of machine and speeds are you using?
I'd start with 80-130m/min cutting speed with 0.25-0.35mm/r feed and 2-4mm depth of cut. Assuming you have WNMG insert with 0.8mm corner radius, and a decent lathe for turning these. If you have a rigid (over 5000kg?) machine, you could try to use inserts with 1.2mm or 1.6mm corner radius.
04-29-2010, 04:30 PM #15
304 is non hardenable, the oxides are the culprit. Go with sand blasting or a run with a flap disc. Sandvick 2025 grade lasts good in stainless. +1 for barstock
04-29-2010, 07:29 PM #16
thx for all the tips all
Just had a meeting last evening about this. waterjet cutting is out of the question. But they are gonna hear for tubing next time but the hard thing is they need only need like 1 meter for each bach and since they dont know how frequently these parts are going to be ,they dont wanna carry the stock of 5 meter extra tube .
if the plasma cut will be cheaper then the tube my adjusted price will be accepted for future runs .
i roughed these with a sandvik cnmg with a radius of 0.8mm grade 2025. 120m/min vc and 0.3mm/rev feed . depth of cut was around 6mm on diameter.
but the toollife was really unstable sometimes i got 5 parts done and the next tip just snapped off after 2 parts. making it sometimes unusable to index the insert so new ones need to be placed. Think i used a full box of inserts to complete the 25 sets .
I could not grind the tit of since it was really big on half of the parts like 20mm high and 15mm width .
04-29-2010, 08:21 PM #17
I do a lot of work with 304 stainless in our lathes and Integrex. I have my own plasma tables and access to dozens of others in the PDX area and when I need to cut slugs from plate that need secondary machining it's ALWAYS cheaper for me to send the plate out and have the slugís water jet cut.
The tit on the plasma cut parts isn't the issue. It's typically caused by the stock walking in the kerf as the part is almost completely cut. If you know the kerf, you can simply throw some nails, or bolts in the kerf as the torch goes around if you're really picky. Done properly there will be almost zero tit.
The true culprit is work hardening. The plasma torch provides concentrated heating, and the mass of the plate cools it quickly enough to work harden the edge. When you go to cut it the work hardened edge will eat inserts. Your only choice is to use a really tough insert and slow down the feeds and speeds to cut through the tough outer layer and clean up the stock. Then you can choose a softer insert suitable for higher speeds and quickly peel off the remainder of the stock. If you are too lazy to swap tools it will take forever to clean up the stock.
When you water jet cut the parts, there is no heat affected zone. The kerf is smaller so you donít have to deal with the tit, and you can cut the stock closer to the net shape.
Water jet cutting isnít cheap, but if you find a vendor with large enough pumps itís not expensive either. My experience has proven that at the end of the job, itís cheaper to water jet cut the parts. Youíll use far less tooling up, and you can use higher feeds and speeds to get the job done in much shorter time. Donít forget how much time you lose swapping inserts.
On the Integrex I love the KM flash toolholders. I can stick In Very hard CNMG inserts to get through the worst of the hard stuff, flick over to a more appropriate grade to fly through most of the rest, and flip to a finishing insert to finish perfectly. All faster than I could index a turret on a CNC chucker.
04-30-2010, 04:35 AM #18
I know that you are not looking for a solution that takes more time but, I used to make a lot of 304 ss flanges out of flat plate. I hand cut them with a plasma cutter and then put them on the milling machine to finish. I used a cobalt roughing endmill and it cut through the plasma cut edge just fine. Of course it is slow to interpolate with a cobalt endmill but it is more flexible than the carbide and seems to cut through the plasma edge with no real problems. I would cut 8-9 plates before changing the tool.
For me it was a case of load the part, program a circle and then a bolt hole circle and let the machine go. I would go off and do something else while I waited for the machine to finish and then load another plate. If I really needed some special lathe work I would do that after roughing the flange on the mill. but usually I just did all the work on the mill.
04-30-2010, 08:13 AM #19
waterjet or plasma blanks
the waterjet parts will be impregnated with the abrasive they used in the waterjet. Plasma parts are hard on the surface. They both will eat tooling.
If you anneal the plasma part it will cut great(heat to red hot and let cool as slow as possible). But the heat will warp part a bit.
04-30-2010, 11:40 AM #20
I've machined a lot of waterjet cut 316SS, usually 3.5" thick" flanges from 10-13" solid bar, cutting the centers out with waterjet. ID was either 6.5 or 8" and I can tell you that at that thickness, the jet is far from straight and smooth, mostly if they try to go just a little fast. Leaves a horrible bumpy finish(you know if you've seen it) and it is very rough on inserts, even worse if they're not cut on center. Sometimes there's not much options but just get it done...
Never really saw any issue of grit impregnated in the metal though, and we had quite a few types cut. (A-286 and waterjet don't like each other, very abrasion resistant). then again maybe a really good microscope could tell what the story is.