Blowouts on bottom of material . .

[CNCCAJUN]

Stopped by a large plasma operation to introduce myself.

While there, the owner quizzed me about a cutting problem he is having.

I told him I was a newbie & told him all about plasmaspider.

He is getting blowout at the bottom of his cuts.

See the (3) holes.

Has anyone seen a blow out at the bottom of a cut like the three (3) holes in this part.

As for the bump in the straight edge, I assume that is a different problem.

He is running a "CUTTING SYSTEMS" table with a HPR Hypertherm.

Thanks,
Steve

Any input would be appreciated.

[trucutcnc]

He's probably using a lead-in with overburn and no lead-out. There is a slight delay between the time motion stops and the torch shuts off. It's just enough to cause what you're seeing. A small lead out about the same as the kerf width gets the cutting jet far enough away from the edge to eliminate the blow out, but not so far that the plasma losing arc. Depending on the controller, a large lead-out on an inside hole can cause a lost arc condition.

[jimcolt]

The Hypertherm HPR systems should be programmmed with an overburn (lead outs are definitely not recommended as they shorten consumable life in any oxygen based plasma), and there should also be an advanced off signal for the plasma. The advanced off (as its name implies) is the cnc shutting the plasma off before the kerf crossing at the end of the cut, the overburn (staying on the hole radius past the lead in kerf by about .150") allows the arc to extinguish while still moving, eliminating the divot at the end of the cut. The Hypertherm HPR systems have a gas and current ramp down that takes as much as 130 milliseconds to completely extinguish the arc, so this technique is standard procedure with these systems. If you can tell me the type of machine and cnc control...I could offer more details on exactly how to set this advanced off signal to work.

Jim Colt Hypertherm

He's probably using a lead-in with overburn and no lead-out. There is a slight delay between the time motion stops and the torch shuts off. It's just enough to cause what you're seeing. A small lead out about the same as the kerf width gets the cutting jet far enough away from the edge to eliminate the blow out, but not so far that the plasma losing arc. Depending on the controller, a large lead-out on an inside hole can cause a lost arc condition.

[trucutcnc]

Depends on the controller. Some have advanced off....some don't. We get the same (long) consumable life on our Ultra-Cut with or without lead-out. Again...not so much of a lead-out that you get a lost arc condition. That WILL shorten consumable life.

[jimcolt]

The Ultra Cut uses a different current and gas ramping technique.....it is patented by Hypertherm and they have to stay outside the boundaries of our ramp current and timing.....so it will act different. Your technique would help with the divot with Hypertherm HPR systems, but would have more of a detrimental effect on electrode life as compared to the overburn method. Also, to use True Hole technology...only the overburn works.

I believe they were talking about a Hypertherm HPR in this thread.

Jim Colt

[Marvinight]

i am having the same problem. im running mach 3 with a hypertherm 65. but it seams like i never had this problem at first.
is there an advanced off in mach3?

[Marvinight]

I get this only on thinner stuff can't find any info on it