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Plasma table and long plate 400"+

mgselin

Plastic
Joined
Aug 5, 2011
Location
Duluth, MN
We are running an hypertherm 260 with a Messer Titan operating system. My issue is we are cutting extremly long parts, lets say 300"x11", or 400"x20". The parts come out true at the ends and they are straight to within tolerances. The problem is after a couple of feet into the part the width widens about .040" +- .010". I've tried several different options to resolve this; welding the slates on the tabel to the frame then tacking the plate to the slates hoping it would stop any plate movement, not welding the plate down, programming the part to cut in different orders, letting the software program it naturally, tabbing the part, not tabbing the part, using higher amp tips, lower amp tips. I'm posting this thread hoping someone here has ran into this and can give me a little insight on it, or can point me to a resource that can help with this. Any information is appreciated. thanks
 
We have several customers who routinely cut over 600 inch parts, and have modified machines to allow others to cut up to 760". I've seen a lot of weird stuff over the years.

1 case similar to yours was noted that the parts had a wave in them that they just couldn't make go away. I took a close glance at the master rail and could tell it wandered around quite a bit. To check, stick a couple washers on the sides of the rail at each end and pull a thin piece of nichrome wire, or even some 15 pound or so fishing line nice and tight. Eyeball or measure the space with a caliper and make sure the master rail is dead on straight, or any further troubleshooting is pointless.

I noted 3 places where the rail was off well in excess of .080" from straight. It turns out the operators were bumping the 28,000 pound capacity forklift up against the master rail to stop it rather than using the brakes... sigh...

The only other issue might be that you need to cut the part so the last side cut is restrained by the biggest section of remaining plate, not a thin skeleton on the edge, although that's unlikely to be the issue after just a few feet.

If by some chance the plate is walking in the kerf, once you know your kerf width, you can always drop some nails or bolts into the kerf as the part is cut that just fit the kerf. This keeps the plate from moving in the kerf. This trick works really well cutting thicker plate that you need to turn later and really want to avoid a deviation on the start/stop point.

Good Luck!
 
As one edge is heated it expands then contracts bowing the stock, its a basic fact you can not avoid by cutting using any thermal cutting method. The only solution is to run twin torches, cut both sides at once - simultaneously. Like that the both expand and contract equally the part sees no bow so does not get fat - thin like your seeing now. Simply go back and cut each end to shape with one head at the end. Alternatively stop measure the deviation and just change the long straights to compensate for the curvature your seeing. In my experiance it stays a pretty constant amount so long as the cutting power levels - speed - sheet thickness remains unchanged.
 
As one edge is heated it expands then contracts bowing the stock, its a basic fact you can not avoid by cutting using any thermal cutting method. The only solution is to run twin torches, cut both sides at once - simultaneously. Like that the both expand and contract equally the part sees no bow so does not get fat - thin like your seeing now. Simply go back and cut each end to shape with one head at the end. Alternatively stop measure the deviation and just change the long straights to compensate for the curvature your seeing. In my experiance it stays a pretty constant amount so long as the cutting power levels - speed - sheet thickness remains unchanged.

This is what we had suspected and adjusting our program to compinsate is what we are trying to avoid. We also aren't looking at using multiple heads as an option. I understand that laser is is a thermal cutting method but would we have enough reduction in heat build up to consider adding this to our machine? By the way I appreciate the feedback, we had to hit the ground running here.
 
We have several customers who routinely cut over 600 inch parts, and have modified machines to allow others to cut up to 760". I've seen a lot of weird stuff over the years.

1 case similar to yours was noted that the parts had a wave in them that they just couldn't make go away. I took a close glance at the master rail and could tell it wandered around quite a bit. To check, stick a couple washers on the sides of the rail at each end and pull a thin piece of nichrome wire, or even some 15 pound or so fishing line nice and tight. Eyeball or measure the space with a caliper and make sure the master rail is dead on straight, or any further troubleshooting is pointless.

I noted 3 places where the rail was off well in excess of .080" from straight. It turns out the operators were bumping the 28,000 pound capacity forklift up against the master rail to stop it rather than using the brakes... sigh...

The only other issue might be that you need to cut the part so the last side cut is restrained by the biggest section of remaining plate, not a thin skeleton on the edge, although that's unlikely to be the issue after just a few feet.

If by some chance the plate is walking in the kerf, once you know your kerf width, you can always drop some nails or bolts into the kerf as the part is cut that just fit the kerf. This keeps the plate from moving in the kerf. This trick works really well cutting thicker plate that you need to turn later and really want to avoid a deviation on the start/stop point.

Good Luck!

One of the first test we did was check our rails with a monofilament line. The rails were true within a couple thousands. This system was installed only a few months ago and there is no chance of bumping these rails with any lift haha. Rather then nails or bolts our software allows us to leave 1" sections of steel to hold the part to the skeleton, and then cut the steel (tabs) out after the all the parts are cut out. Water cooling is not an option for us seeing we have the "Slagger" clean out system installed below the table. Thanks for the info I appreciate it.
 
Why don't you want to adjust the programmes? Or is it like a zillion slightly different bits?

A Laser may well help, so might running the plasma on a different gas combination. Anything that increases speed and reduces heat input would help. Cost wise a secound plasma head would be a lot cheaper! 2 heads will solve the issue and near double your cutting speeds a lot of the time. Its very very common on gas profilers to run multi heads to gain speed as well as for stripping plates to custom widths. Other options to burn the profiled parts and shear the plates after to cut out- free the parts along the long edges. Can require some real effort in things this size though!
 
Ah, downdraft tables.... I hate them and in our area almost everyone uses water tables. I much prefer the water table, because there are far less issues with thermal stress, still it's hard to believe it's entirely caused by relieving the stresses in the plate, especially if you have tried tabbing the plate, and verified that the rails are straight.

The HPR 260 is a great plasma cutter, and while I'm not a big fan of the Titan, it works well enough. In your testing, did you perhaps try cutting with the height control turned to manual rather than in a voltage tracking mode?

It's entirely possible that your height control does the initial height sensing, sets the torch standoff, then freezes the height at that point for the start of the cut. If it didn't the torch would dive into the plate as it was piercing. Typically the control allows a bit of time for the machine to ramp into the cut before removing the height or corner freeze and allows the torch to begin it's standoff based on the automatic voltage control tracking method of height control. It's possible that as the system transitions from initial height control to voltage tracking that the torch is diving into the plate (or climbing away) creating a fatter or thinner kerf until things get established properly.

You should be able to adjust the delay after intial arc transfer before AHC takes effect, or adjust the gain on the AHC if it's too sensitive.

It's also possible you have a minor restriction to flow in the plasma system that takes a while to even out causing a tracking or height issue. In order to cut dead on, the height must be very stable and accurately controlled with plasma.

And while this may sound stupid, you might want to manually see if you can detect any play in the torch carriage motion. The Titans that use the Wittenstein Alpha series gearboxs are notorious for spinning the little tiny pinion at the bottom of the input shaft allowing odd and random motion. If you take them apart you will see that the input shaft has a nice 5/8" bore to couple to the servo motor. the other end has a tiny pinion pressed and glued in to the end with about a 3/16" shaft. these have a nasty tendancy to spin f the machine ever goes into an estop or collision type quick stop and the drives don't get the chance to ramp down the speed under a normal decel curve. It's quite common on the rail axis, but not so common on the cross axis, which is where your issues would appear to be.
 
This is a fairly common issue on long thermally cut parts.....although I have also run into issues like this with waterjet cutting long thin part...meaning it was internal stresses in the material that caused the cambering issue.

Normally...we have resolved the camber with a water table applications by raising the water level so that it keeps the part cool, minimizing heat related distortion.

Another method you may want to try...and this is commonly used to resolve thermal camber issues with laser cutting (as well as to stop small parts from "tipping up" and causing collisions). Reprogram your part with non continous cuts...leaving some 1/2" long tabs to hold the part firmly in the base metal skeleton. Allow the part to equalize in temperature (the temperature from the cutting process will move into the part, away from the edges) then using another layer in your part program go back and cut the tabs out. This has worked adequately in a few applications.

If you have any concern that this may be a motion issue....rig up a spring loaded pen, tape some paper down to a piece of uncut material an let the machine do a trace of the part...then measure the trace.

Glad you like that HPR260!

Best regards, Jim Colt Hypertherm [email protected]



We are running an hypertherm 260 with a Messer Titan operating system. My issue is we are cutting extremly long parts, lets say 300"x11", or 400"x20". The parts come out true at the ends and they are straight to within tolerances. The problem is after a couple of feet into the part the width widens about .040" +- .010". I've tried several different options to resolve this; welding the slates on the tabel to the frame then tacking the plate to the slates hoping it would stop any plate movement, not welding the plate down, programming the part to cut in different orders, letting the software program it naturally, tabbing the part, not tabbing the part, using higher amp tips, lower amp tips. I'm posting this thread hoping someone here has ran into this and can give me a little insight on it, or can point me to a resource that can help with this. Any information is appreciated. thanks
 
We are currently tabbing our long parts to the skeleton. Internal stress is I'm sure a factor to our problem. After checking the rails we performed a pen test on a 300" rectangle and found from what we could see a .004-.010" variance. There could have been an endless amount of excuses for this small shift. I'm glad to hear all of the ideas though and I hope they keep coming. Thanks



This is a fairly common issue on long thermally cut parts.....although I have also run into issues like this with waterjet cutting long thin part...meaning it was internal stresses in the material that caused the cambering issue.

Normally...we have resolved the camber with a water table applications by raising the water level so that it keeps the part cool, minimizing heat related distortion.

Another method you may want to try...and this is commonly used to resolve thermal camber issues with laser cutting (as well as to stop small parts from "tipping up" and causing collisions). Reprogram your part with non continous cuts...leaving some 1/2" long tabs to hold the part firmly in the base metal skeleton. Allow the part to equalize in temperature (the temperature from the cutting process will move into the part, away from the edges) then using another layer in your part program go back and cut the tabs out. This has worked adequately in a few applications.

If you have any concern that this may be a motion issue....rig up a spring loaded pen, tape some paper down to a piece of uncut material an let the machine do a trace of the part...then measure the trace.

Glad you like that HPR260!

Best regards, Jim Colt Hypertherm [email protected]
 
Alright I am hearing a lot of the same facts about thermal expansion. I do understand this concept and it makes sense. I have one kinda crazy idea and just want to throw it out there. Most of our plate is around 11-14" wide, we have an oxy/fuel head on the machine that is about 12 1/2" away from the plasma headwe. I'm not suggesting cutting with both at the same time, that would be impossible. What I am considering is having the flame on and only an inch or so above the plate preheating the otherside? Comments?? Dont laugh
 
Alright I am hearing a lot of the same facts about thermal expansion. I do understand this concept and it makes sense. I have one kinda crazy idea and just want to throw it out there. Most of our plate is around 11-14" wide, we have an oxy/fuel head on the machine that is about 12 1/2" away from the plasma headwe. I'm not suggesting cutting with both at the same time, that would be impossible. What I am considering is having the flame on and only an inch or so above the plate preheating the otherside? Comments?? Dont laugh

Crazy idea ? yes.

Repeatable for different cut shapes ? no.

As Stuart and Jim have said, you have 2 kinds of problems here. You adding the
torch does nothing but throw in a 3rd problem.

1. The locked in stress's from the rolling process, program lock tabs to keep the
plate from moving, until the very end.

2. The thermal process of cutting, use a water table, and run the water
over top of the plate (submerged plate)
 
I had to throw it out there. Water is not an option for us unfortunately. I think our best and only option to keeping these plates within a .025" tolerance is to adjust our program to compinsate for the thermal expansion.


Crazy idea ? yes.

Repeatable for different cut shapes ? no.

As Stuart and Jim have said, you have 2 kinds of problems here. You adding the
torch does nothing but throw in a 3rd problem.

1. The locked in stress's from the rolling process, program lock tabs to keep the
plate from moving, until the very end.

2. The thermal process of cutting, use a water table, and run the water
over top of the plate (submerged plate)
 








 
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