Cut problem

[tinman13]

I have been having this issue for a while now and finally have some pictures that show the problem quite clearly. This is 1/2" 304 stainless, cut at 85 amps, 34 ipm. travel speed. As you can see there is a definite tang holding the part to the plate.
I am using Sheet-Cam and Mach 3, with a Powermax 85.
The Hypertherm tec guys recommended a slow down at the last of the cut but I don't have that option....
Does anyone else have this problem and if so what have you found to cure it.
Thanks, Steve

[dnelso]

I have had the same problem when cutting 5/8 steel. I also have sheetcam and mach. I use a large radius arc in and out. That is the best fix i have had so far.
Dave

[jimcolt]

Most plasma cutting software have a function that allows for a delayed off signal for the plasma....this keeps the arc on for a time period at the end of machine motion, which (on stainless especially) allows the bottom of the arc (which lags back at a 15 to 30 degree angle) to "catch up" with the top.

Some of the machines also can look ahead to the end of the cut and do an automatic slowdown.

When cutting materials like stainless or aluminum that do not oxidize easily the plasma arc is cutting with strictly thermal energy (melting). When cutting steel...the 20% oxygen content in air adds an exothermic reaction with the steel, which actually burns a bit ahead of the plasma arc....so less lag in the bottom of the arc.

Jim Colt Hypertherm

[tinman13]

Thanks for the replies, It looks like I will have to live with parts tabbed in as Sheet-cam has no provision to slow the cut speed at the end of the cut.
I have a .5 sec. delay programmed at the end... Makes little difference as the cut jumps over the tab.
I will experiment with stopping the cut a bit short and see how that works out.

Thanks, Steve

[jimcolt]

Use no lead out....then experiment with the delay. If you have a lead out the top of the cut is jumping the kerf from the lead in....which makes it easier for the bottom to skip as well.

Jim

Thanks for the replies, It looks like I will have to live with parts tabbed in as Sheet-cam has no provision to slow the cut speed at the end of the cut.
I have a .5 sec. delay programmed at the end... Makes little difference as the cut jumps over the tab.
I will experiment with stopping the cut a bit short and see how that works out.

Thanks, Steve

[holbieone]

Thanks for the replies, It looks like I will have to live with parts tabbed in as Sheet-cam has no provision to slow the cut speed at the end of the cut.
I have a .5 sec. delay programmed at the end... Makes little difference as the cut jumps over the tab.
I will experiment with stopping the cut a bit short and see how that works out.

Thanks, Steve

You can hand edit your program

An easy way to find the point to where you want to add a slow down would be to , dry run the program to the point where you want the slow down , then use that point for your new end point, the old end point will be next and just add a new feed rate

[holbieone]

Thanks for the replies, It looks like I will have to live with parts tabbed in as Sheet-cam has no provision to slow the cut speed at the end of the cut.
I have a .5 sec. delay programmed at the end... Makes little difference as the cut jumps over the tab.
I will experiment with stopping the cut a bit short and see how that works out.

Thanks, Steve

You can hand edit your program

An easy way to find the point to where you want to add a slow down would be to , dry run the program to the point where you want the slow down , then use that point for your new end point, the old end point will be next and just add a new feed rate

[tinman13]

Today,s update.... These pictures were cut with a .5 pause at end of cut. All else the same as before. I honestly can't see any difference.
I will contact Les from Sheet-cam to see if there is a way program in a slow down at the end of cut, it looks like that is going to be the only option.

Thanks for the suggestions, Steve

[tinman13]

Jim, if I remember correctly don't you use a Torchmate machine? Have you experienced this problem on your machine or does Torchmate have a provision for a slow down function?

I didn't have this problem with the Thermal Dynamics machines and I haven't read about any problems with the older style Hypertherm torches, is this something only with the Duramax torch?

If so what have you found to fix it... or do you just deal with it?

Thanks again for your help, Steve

[jimcolt]

Steve,

I do have a Torchmate machine....but since I have a Powermax45 on it I have never used it for heavier stainless steel cutting. Instead...I use my PlasmaCam machine which has no issues with completely cutting off the stainless at the end of the cut...by using the delay at end of cut function.

I would suggest working with Torchmate to determine the best way to solve the issue through their functions...and I am 100% sure there is an easy method...as the lagging arc when cutting non ferrous metals (stainless and aluminum) occurs with all air plasma cutting systems.

This issue with cutting stainless exists with all plasma torches....it is not due to the Duramax torch. The Duramax torches do have much faster cut speeds as compared to other torches....so the effect at these higher speeds may be more noticeable....the fix is to slow down at the end of the cut.

Here is why the arc lags on stainless:

Air is 20% oxygen and 80% nitrogen (approximately)....when cutting steel, which is an easily oxidizable metal the oxygen content in air provides an exothermic reaction which combines with the thermal energy of the high temperature plasma jet to cut with an additional boost.....the exothermic reaction actually burns the metal slightly ahead of the plasma jet....effectvely allowing the plasma jet to cut straight down through the kerf. When cutting stainless....which does not easily oxidize, the oxygen content does not provide an exothermic boost to the process. The cut speeds suggested in the operators manual with plasma systems are typically the speeds that produce the least amount of dross...and at that speed there is always a 15 to 30 degree lag in the plasma jet. At the end of the cut....at the optimum cut speed....if the arc is extinguished at the same time as the motion stops, expect an uncut tab at the bottom edge of the cut....which gets worse as the material gets thicker.

To solve this:

- You can cut the whole part slower.....which will straighten the arc, but the side effect will be more bottom dross.

-You can program a slowdown at the end of the cut only to straighten out the arc. Some software can do this as an automatic function....others will need a feedrate change at the end of the cut that is manually entered.

-You can delay the plasma off signal after the motion stops for a time period...this would require more time for thicker material, and will leave a divot at the end of the cut

-You can use a higher powered plasma system. Typically on industrial stainless cutting a plasma of up to 260 Amps is used for stainless above 3/8".


Jim Colt

Jim, if I remember correctly don't you use a Torchmate machine? Have you experienced this problem on your machine or does Torchmate have a provision for a slow down function?

I didn't have this problem with the Thermal Dynamics machines and I haven't read about any problems with the older style Hypertherm torches, is this something only with the Duramax torch?

If so what have you found to fix it... or do you just deal with it?

Thanks again for your help, Steve

[tinman13]

Thanks for the reply Jim,
I am using sheetcam and Mach so Torchmate tech won't be much help. Also this is not limited to stainless as I have the same issue with steel but not as bad.

This brings me to a couple more questions!
Do you use a Powermax 85 on your plasmacam?
Does their software have the option for a slowdown?

The updated pictures were with a .5 sec delay at end of cut, no lead out, I see no change from no delay at end of cut. Plasma off at end has no effect on tab, it jumps over the tab and pauses for the dwell period, then shuts off.

What am I missing?

If I understand your answer correctly my only options are limited; cut slower, or buy a bigger power source!
I can't easily slow down the travel speed at the end of cut. (Les is working on it).


Thanks again for your help,Steve

[jimcolt]

Yes....I use a Powermax85 on my PlasmaCam. I do not have issues with stainless....the parts all drop. I have only cut stainless up to 1/2" on this machine. The software does not have an end of cut slowdown....but does have a timer to keep the plasma on at the end of a cut path....which is what I use to drop cut the stainless. It takes a few tries to get it right....but it works great.

The PlasmaCam does have auto slowdown and height freeze for holes to make round holes with minimal taper and no torch diving.

Sounds to me like the delay at the end of cut is not working...or you simply have not added enough time. The other issue would be if you had a lead out and crossed the kerf...then the problem may be the arc skipped across the lead in kerf.....which no amount of time at the end of cut will fix. The fix for that will be to have no lead out....then work with adding time to kep the arc on at the end of the cut.


Jim Colt

Thanks for the reply Jim,
I am using sheetcam and Mach so Torchmate tech won't be much help. Also this is not limited to stainless as I have the same issue with steel but not as bad.

This brings me to a couple more questions!
Do you use a Powermax 85 on your plasmacam?
Does their software have the option for a slowdown?

The updated pictures were with a .5 sec delay at end of cut, no lead out, I see no change from no delay at end of cut. Plasma off at end has no effect on tab, it jumps over the tab and pauses for the dwell period, then shuts off.

What am I missing?

If I understand your answer correctly my only options are limited; cut slower, or buy a bigger power source!
I can't easily slow down the travel speed at the end of cut. (Les is working on it).


Thanks again for your help,Steve