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Q's for cutting corrugated

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motoguy
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Location: Central MO, USA

Q's for cutting corrugated

Postby motoguy » Wed Mar 21, 2018 1:21 pm

I have my first customer request for products from corrugated tin. Customer is supplying the material, so I'd like to minimize the "learning curve" as much as possible. Customer is being used loosely, as this is a friend, and I'm likely going to do these for her for free anyway. Still, I'd prefer not to eat up a bunch of her material.

I'm running a Bulltear 6x12 circa 2016, with steppers and CommandCNC, Ohmic, HyT, etc. Here are the things I understand/questions I have for corrugated:

1) Need to have essentially 0 delay between pierce and cut. This means set pierce height .01" above cut height, and set pierce delay to 0.
1a) I have a 50' torch lead, which means I have to rely on the ARKOK signal, or the torch has moved 1/2" or so before it starts cutting. So, I cannot use the "Disable Hold" button.

2) DTHC needs to be set to "fast" (my slow/medium/fast are all default settings).
3) Cut the regular 10" straight line along the "fold", to get voltage settings needed. Make sure the peak of the folds is exactly in line with the X axis, so the torch stays a fixed distance above the metal during the cut.

* 4) DTHC needs to activate instantly. How do I achieve this? Would I do this by setting DTHC min cut distance and DTHC delay time (in tool settings) both to 0?
* 5) Can I use finecuts on this, or am I limited to the regular 45A consumables/process? I'm concerned that the shape of the finecut shield will lead to collisions issues in the "valley" of the material
* 6) Max recommended Z accel settings in the manual is 100ipm. Recommended cut speed for the thin material is 325/350 ipm (something like that). I've read that the Z settings need to be equal (or greater) than the X/Y cut settings. Matt at Bulltear recommended I take the Z up to 100ipm. Does this mean I need to slow the cut speed down to 100ipm as well? I assume if I leave the cut speeds at 325/350, and the Z at 100, the Z will not be able to move fast enough to track the folds of the metal?

Any other useful information/recommendations/suggestions?
Bulltear 6x12 w/ Proton Z axis & watertable
CommandCNC/Linux w/ Ohmic & HyT options
Hypertherm Powermax 85 w/ machine torch
Solidworks, Coreldraw X7, Inkscape, Sheetcam

daddog
Posts: 2
Joined: Fri Apr 30, 2010 8:04 pm

Re: Q's for cutting corrugated

Postby daddog » Thu Mar 22, 2018 4:12 pm

The main thing I do is lay down a sheet of expanded metal to support the corrugated and then lay a 2x4 board across the far end and clamp it down to keep it from moving. I do this because the torch head will contact the corrugated some and try to drag it around. I have also found that the older tin, closer to 20ga, cuts a lot better that new tin (29 ga).

motoguy
Elite Contributing Member
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Posts: 1082
Joined: Tue Aug 25, 2015 12:05 pm
Location: Central MO, USA

Re: Q's for cutting corrugated

Postby motoguy » Mon Mar 26, 2018 6:40 pm

Well, the corrugated is kicking my butt today. I was able to get some stars to cut, eventually. The torch kept crashing the material at the outside "points". I was running my Z at 225ipm, and cutting at 200ipm. The torch was tracking the ribbing quite well, but when it got to that hard direction change (outside point of star), it'd crash every time. I slowed down to 100ipm, played with VAD settings from 90% through 99%, increased the target voltage, etc. In the end, what worked was creating some Sheetcam cut rules that turned off THC .1" before, and turned back on THC .1" after, sharp corners. I was then able to cut the stars pretty reliably.

So, I decided I needed to try something else, with curves instead of straight lines and points. One of the customer's requested pieces was a hen profile, similar to this: Image. No matter what I tried, I could not get this to cut without crashing. All the little curves and details around the legs and such would crash the torch into the material. I created a cut rule that increased the voltage at the corners/curves (instead of disabling THC, as I did for the star above), but that didn't help. The torch climbed high enough that it lost arc and shut off.

I created various rules, tried VAD settings, added votage to the target voltage, tried disabling THC at curves and corners, tried increasing voltage at curves and corners, etc. No luck.

In the end, the most reliable way to get the cut was to touch off on a ridge, set Z=0, disable touch offs, disable THC, and disable the ARKOK hold. Basically, I told it where Z=0 was located, it went .06" above that, and just cut at that level. The arc would reach down into the valley, and the torch head would just skim the tops of the ridges. The face side of the cut wasn't as clean as it was using THC, but it's (what I'd call) acceptable for "country" style art work.

I think I'll just cut the rest of her parts using this method, possibly in expanded metal mode, so I don't have to worry about losing the arc. This would let me set the Z a bit higher above the metal as well, so I don't worry about tagging the top of the ridge. I don't know that I'll be able to do anything better using THC. The metal is just so dang thin. I was under the impression it's 20 gauge, but when I measured it, it's .011". That's 31ga material (like home depot sells). Literally as thick as 4 sheets of paper. Even the SLIGHTEST pause blows material away, and causes the torch to crash.

If anyone has suggestions (cutting multiple stacked sheets may be doable, etc), I'm all ears. In the meantime, I'm just planning on cutting her parts from a fixed height tomorrow, and ignoring the THC all together.
Bulltear 6x12 w/ Proton Z axis & watertable
CommandCNC/Linux w/ Ohmic & HyT options
Hypertherm Powermax 85 w/ machine torch
Solidworks, Coreldraw X7, Inkscape, Sheetcam

bigforkg
Posts: 4
Joined: Sat May 05, 2018 3:49 pm

Re: Q's for cutting corrugated

Postby bigforkg » Wed Jun 06, 2018 9:24 am

Did you get it figured out ?

jimcolt
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Location: New Hampshire

Re: Q's for cutting corrugated

Postby jimcolt » Wed Jun 06, 2018 9:47 am

Success with cutting corrugated will vary from machine to machine based on the reaction capability of the THC and the acceleration of the x and y axis. What works with one may not work with another. Here are my suggestions:

- Use the lowest power consumable set for the material cutting, and run the lowest cut speed possible. You should expect dross when you do this, however it is necessary in order to allow the z axis / THC to keep up.

- Run the z axis speed as fast as it will go without oscillation.

- Be sure you have cleaned off a good work clamp connection...this will help the THC work better.

- Do not breath the fumes! (Zinc)

- Don't get upset with the THC supplier....they are designed to handle minor discrepancies in flat plate....not the 3 dimensional contours of corrugated roofing.

Jim Colt

tcaudle
Posts: 1051
Joined: Tue Feb 28, 2012 6:47 pm

Re: Q's for cutting corrugated

Postby tcaudle » Wed Jun 06, 2018 12:36 pm

What type corrugated? Slow down the horz speeds to 180 and lower your Z speed to 200. If the Z is not a low friction ballscrew of there are othe things on the Z it has to lift you hit the torque/RPM stall point of the motor. Its more about Physics. The DTHC iv will respond fase enough but its the limits of the Z and the motor max RPM to get 250 IPM on a Z with 5 TPI leadscrew you have to spin the motor at 1250 RPM That is real close to the unloaded stall point. Any added load will force it to lose steps (equals head crash) I does not sound like your VAD is working. can you see the Blue DTHC enable light going on and off? Believe it of not you may want to lower the acceleration rate on XY so it will lower it's cut speed on sharp turns / CommandCNC tracks for accuracy and uses it's settings to decide if it can make the cut at full speed rather than slowing down. Normally slowing down is an instant head dive (especially at FAST Response)
There is a "dead zone' (Voltage tracking Tolerance setting in the Response curve if you are in Custom leave the Sensitivity and Tracking set to Fast numbers but increase the Tracking Tolerance to 1.5 and see if it helps.

I run corrugated with 45 A consumable and at 180IPM and raise the Preset volts by a small amount to compensate

You have to increase the Touch of negative Limit (in the MANUAL tab to cover the case where itstarts on a peak then touch off in a vally. Make sure you do not have any Soft Limits (min and max travel) on your Z axis settings.


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