What tolerance is typically achievable with Lasers, Waterjet, & High Def. Plasma?

As the title states: What should /could I reasonably expect when considering what type of process when quoting plate work?
Example: 1/2" thick A36, or 3/4" thick A516Gr70

When I drop off work at certain customers, I get to see other shop's parts in the receiving area.
Other shop's parts will be burned to shape on the OD, while mine are always machined.
The only reason I am forced to machine the outsides, is my plate vendors (5 local suppliers) say they cannot hit the +,- 0.01" tolerance with their lasers, waterjet, or high def plasma.



So, would someone please tell me if I should be looking for new vendors, or is +,- 0.01" not a realistic expectation????

Thanks,

Doug.

doug925 said:

As the title states: What should /could I reasonably expect when considering what type of process when quoting plate work?
Example: 1/2" thick A36, or 3/4" thick A516Gr70

When I drop off work at certain customers, I get to see other shop's parts in the receiving area.
Other shop's parts will be burned to shape on the OD, while mine are always machined.
The only reason I am forced to machine the outsides, is my plate vendors (5 local suppliers) say they cannot hit the +,- 0.01" tolerance with their lasers, waterjet, or high def plasma.



So, would someone please tell me if I should be looking for new vendors, or is +,- 0.01" not a realistic expectation????

Thanks,

Doug.

Click to expand...

.
i know with plasma cutter at the orifice tip where the air comes out wears bigger its accuracy and performance goes down until tip is replaced
.
so accuracy during the day can actually vary

On our Flow waterjet, I think they claimed ±.005" positional accuracy when we bought the machine.

It can hold better than that, depending on the operator, material thickness, if it's a cloudy day or not...

Our lasers can do better, however you still have some taper on the edges, depending on thickness of the plate. On that thickess, I think about 5 or 6 thou taper per side is reasonable. This could be much higher if operator has it running too hot or slow, or conditions set incorrectly.

The waterjet can keep the edges more perpendicular since we have the 5axis one and it compensates, but it's slow as shit compared to a 6kW laser. They have 3axis ones that can compensate too.

±.01" shouldn't be a problem on a laser. You might want to look for another vendor. Is the profile geometry on your plates complicated? Or just rectangular shapes?

edit
Maybe they are lazy and don't bother adjusting kerf settings? On either machine, you can use cutting compensation just like a mill or lathe. Cut one, measure, adjust and you should be pretty damn close. It's not rocket science.

Do you order the material? Or vendor supply? How bad is the scale on the plates? We cut a lot of A588 and A572 and the scale can be very nasty at times. It can make laser cutting a pain unless the plate is relatively clean. Lately the guys have been blasting the bad ones with a pressure washer and it helps some.

I agree, 0.01" is definitely doable on a flow machine. Depends a bit on material and thickness, and a lot on the operator and effort put in.

So the real question is, how much effort is your supplier's operator typically putting into accuracy?


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thesidetalker said:

±.01" shouldn't be a problem on a laser. You might want to look for another vendor. Is the profile geometry on your plates complicated? Or just rectangular shapes?

edit
Maybe they are lazy and don't bother adjusting kerf settings? On either machine, you can use cutting compensation just like a mill or lathe. Cut one, measure, adjust and you should be pretty damn close. It's not rocket science.

Do you order the material? Or vendor supply? How bad is the scale on the plates? We cut a lot of A588 and A572 and the scale can be very nasty at times. It can make laser cutting a pain unless the plate is relatively clean. Lately the guys have been blasting the bad ones with a pressure washer and it helps some.

Click to expand...

1) Mostly, the shapes are rectangles, or squares.
2) I bet it has a lot to do with the accuracy that they feel is doable with (maybe) high turnover employees. Or it could be they just don't want to mess with tighter tolerance stuff.
3) Vendor supplied

Thanks for the info.

I'd always thought a good water jet was a little better, more like .003, although we (a fab shop) rarely order WJ so I have little personal experience. Almost bought a business that had two Flows so thats where I got it from...buddy may have been blowing sunshine. Laser .003, Hi def Plasma (have 2 of them) 1/32. That's the theory anyway.

For fabrication I love laser cut because we can design with tabs - speeds up fitting a lot. Still, not worth owning one (yet), the expensive and expensive to run, so we suffer through with the plasmas

I have found that laser cutting is pretty damn close on thin plate but once you get above 3/8 or so they can be way out. I have the same problem regarding competitors ,I would speak to your customer about it as it could be that they like the look of your parts better so making you a preferred supplier or they might prefer the other guys cheap and cheerful methods.

I had posted before about getting some 1 1/8" thick plate Hi-def
plasma cut, and accidentally leaving the 1" tapped holes on the dxf file.

The cut quality on the 7/8" holes was almost good enough to run
a tap thru.

I remember being mentally 'taken down a peg' in my thinking about precision machining
and precision metal working as a process, maybe 15 years ago now.

I was touring a customers plant, and they were showing me several 'new' cnc lathes and machining centers. I was impressed with all the late model low hour 'precision'.
Then the floor manager taking me thru the facility gave me a statement I'll never forget both in impact and scope.

He said, "yea, it all looks shiny and new, but every damn one of these machines have been crashed and messed up within 2 months of being here. Now we have problems with size and quality issues. They definitely are NOT new at this point. They will never be the same".

That blew me away, and made me realize when employees are involved, you can buy the best, most accurate machine tool, and some careless employee can mess it up in short order.
Precision in the hands of careless idiots is short lived.

Your customer may be giving you the best tolerances he can given the state of the equipment on the floor.

1/2" if cut well can certainly be done on a laser with in +-10 thou, for 3/4 yeah maybe just on a good day bump that tolerance up say to 15 thou and i would feel semi confident. Lasers as you get thick in steel though really are a lot more like a gas cutting torch, just with laser preheat as it were, its the oxy jet that really does the work in thicker steels. Now the correct lens - setting and good clean steel its doable, problem is everyone wants faster and cheaper hence cut quality often suffers.

Mcgyver said:

I'd always thought a good water jet was a little better, more like .003, although we (a fab shop) rarely order WJ so I have little personal experience. Almost bought a business that had two Flows so thats where I got it from...buddy may have been blowing sunshine. Laser .003, Hi def Plasma (have 2 of them) 1/32. That's the theory anyway.

For fabrication I love laser cut because we can design with tabs - speeds up fitting a lot. Still, not worth owning one (yet), the expensive and expensive to run, so we suffer through with the plasmas

Click to expand...

I can generally get +\-0.005" by slapping something on the machine and going for it. If the customer indicates tight tolerances I'll make the effort and spend the time to tighten that up.

But then again, if the tolerances are only tight on four holes/two parts and I have the right reamer, a reamer in the drill press is faster.

A lot of what we cut is essentially "art", so most prints/files I see don't even have tolerance called out.


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I reckon my flamecutters are more reliable than laser on stuff more than 10mmm thick ,they cut up to 700mm so the kind of thicknesses I need are spot on ,the worst part is where they blow through on very thick plate ,they should do it well off the job but tend not to then weld the hole up after ,not good when you are going to use it for something important.

For waterjet even between identical machines, the precision and taper varies by the programmed cut quality, and the orifice and mix tube condition. Some folks run cheap orifices that wear quickly, and large diameter mix tubes, where 1/2" steel may be +/- .02". The same machine with a diamond orifice and a good mix tube, at the roughest/fastest cut quality may be +/- .01", and at a good/slow cut quality, +/- .003".

For our Maxiem, with a .03" mix tube, a square in 1/2" steel will typically measure +/- .001" at the top edge of the cut, and vary from +.01" to +.003" per edge at the bottom depending on the programmed cut quality. In 1/2" steel the time cost of the +.003 cut is about double the +.01". This is for small parts - with large parts the precision/repeatability is this good but the absolute positioning accuracy may be +/-.01" or worse. This is an inexpensive 3 axis machine without taper compensation, so taper is reduced by going slow. A 5-axis machine will do the +/-.002" in about the same cut time as ours requires for the +.01", and further may be capable of +/-.001". Doing a high volume of accurate cutting in thick material, 5 axis will save you money. But it's not needed for this accuracy.

What I observe in industry is some waterjet shops esp. doing heavy work have no idea what their equipment is capable of and set a pretty low bar.

sable said:

I have found that laser cutting is pretty damn close on thin plate but once you get above 3/8 or so they can be way out. I have the same problem regarding competitors ,I would speak to your customer about it as it could be that they like the look of your parts better so making you a preferred supplier or they might prefer the other guys cheap and cheerful methods.

Click to expand...

Lasers sidewalls are very dependent on 'depth of focus' a good operator/shop would know that information and be able to pass it on to you. It also is dependent on clearing of the molten material and 'effective focal length' of the lens.

Nice article here.

The importance of focal positions in laser cutting - The Fabricator

Toolbert said:

What I observe in industry is some waterjet shops esp. doing heavy work have no idea what their equipment is capable of and set a pretty low bar.

Click to expand...

+1 to Toolbert's comments, especially the last one. We have an OMAX 2652 and it's we usually assume .001-.002" accuracy on the top side, even for large parts. And lots of operators in our experience have no idea how much better they can do with a bit of care. I've said this here before but it's a fabricator mentality vs a machinist mentality.