Problems trying to cut custom part.

[mdwalker]

I had a request to cut some custon screens. Simple design but it has 4923 pierces. Each screen is 6" wide x 54" long & with holes that are .063" dia. Basically a peirce. They are cut from 3/16" hot roll steel. Cutting on Samson 5x10 with Design Edge using Hypertherm Powermax 1000 using 60 amp consumables. Not at the shop right now so I don't remember settings other than I know I was cutting at 60 amps. I have 15 - 20 years experience with Hypertherm plasma cutters, 5+ years with PlasmaCam DHC2, & 1+ month with Samson 5x10 & Design Edge so I am experienced at setting up the cuts. Doesn't mean I am right, just not a newbie, lol. I know there are companies that make this screen but the customer wants me to cut it. I could buy a new Powermax 85 for what they are paying for 4 screens so my job is to find a way to cut them with best quality possible. Now for the problem: Estimated cut time for 1 screen is under 2 hours. Actual time for 1 was 3 days. Started cutting fine and cut first few hundred holes with no problem then started having misfires on torch. The cnc would continue running but the torch would sometimes fire but wouldn't pierce the metal like when you don't have good ground. It would skip sometimes 1 hole & sometimes several then start firing again for a few holes and sometimes it wouldn't fire at all, but the cnc would run just as if torch was cutting. Sometimes the red warning light on front of plasma cutter would come on when torch misfired but not always. Changed out nozzle, electrode, shield, made sure internal torch parts were clean & moving properly. Hole quality is acceptable but having to go back & re-cut the holes it misses is very time consuming. Not sure if the short cycle time on the cutter is causing problems or if maybe something else. Any suggestions? I did check all grounds, both the plasma cutter ground & table to earth ground. Everything is clean and tight. The table is new and the grounds are on a clean part of the table that hasn't even been used. I did try grounding cutter to material just to make sure it was getting good ground through table grates but same problem.

[SCHIDTHEAD]

That sux mdw, I have had that problem with fine consumables only and cant get an answer why it does it. I feel ya on having to trace back up the code and re-cut. I just dont use em anymore till I can find the time experiment and narrow it down some more.

[kbenz]

that's a lot of piercing......... which is what eats up your consumables and is most likely causing the misfires after "several hundred pierces"

[CNCCAJUN]

My 2 cents . . .

I would think some jobs are not worth doing . . .

Better yet, sub it out to a laser table . . . or a water jet cutter . . .

Sounds like a major beating on consumables, not to mention drives . . .

Steve

[jimcolt]

It would be helpful to see the wear on your consumables.....if I could see the front exit orifice of the nozzle as well as the front (hafnium) end of the electrode...I could probably help determine your starting issue.

Misfiring in a Hypertherm torch is caused by:

- worn out consumables
-moisture or oil in air supply
-low line voltage to plasma
-high air pressure setting (should be right at Hypertherm specs when flowing)
-Material blown back between nozzle and shield (piercing too close or without adequate pierce delay)
-Material build up on front of shield
-incorrect (too close) pierce height
-hole programmed with lead out....which forces the arc to "snap off" due to material dropping out. Holes should be programmed so that the end of cut allows current ramp down with metal under torch.

And any combination of the above will exacerbate the misfiring.

Also...if everything above was being done correctly.....using the 60 amp Hypertherm brand shielded consumables....I would expect perhaps 400 to 600 maximum starts before the electrode is worn to the point that it will start misfiring. Personally...I would set everything up correctly and use the 40 amp shielded consumables and expect better hole quality as well as more starts...perhaps 600 to 800 starts with the 40 amp process.

Better yet...upgrade your torch with the newer technology Duramax torch for about 50% more life.....better cut quality as well.

There are industrial plasma systems such as the Hypertherm HPR130xd that will get 3500 to 4500 starts on one set of consumables and will provide even better cut quality....these system cost close to 10x the cost of an air plasma system and use high frequency starting technology....meaning that they would wreak havoc on many of the PC based machine control computers on many entry level cutting machines.

Can you provide more detail regarding what consumables and the condition of them when they start misfiring?

Best regards, Jim Colt Hypertherm

I had a request to cut some custon screens. Simple design but it has 4923 pierces. Each screen is 6" wide x 54" long & with holes that are .063" dia. Basically a peirce. They are cut from 3/16" hot roll steel. Cutting on Samson 5x10 with Design Edge using Hypertherm Powermax 1000 using 60 amp consumables. Not at the shop right now so I don't remember settings other than I know I was cutting at 60 amps. I have 15 - 20 years experience with Hypertherm plasma cutters, 5+ years with PlasmaCam DHC2, & 1+ month with Samson 5x10 & Design Edge so I am experienced at setting up the cuts. Doesn't mean I am right, just not a newbie, lol. I know there are companies that make this screen but the customer wants me to cut it. I could buy a new Powermax 85 for what they are paying for 4 screens so my job is to find a way to cut them with best quality possible. Now for the problem: Estimated cut time for 1 screen is under 2 hours. Actual time for 1 was 3 days. Started cutting fine and cut first few hundred holes with no problem then started having misfires on torch. The cnc would continue running but the torch would sometimes fire but wouldn't pierce the metal like when you don't have good ground. It would skip sometimes 1 hole & sometimes several then start firing again for a few holes and sometimes it wouldn't fire at all, but the cnc would run just as if torch was cutting. Sometimes the red warning light on front of plasma cutter would come on when torch misfired but not always. Changed out nozzle, electrode, shield, made sure internal torch parts were clean & moving properly. Hole quality is acceptable but having to go back & re-cut the holes it misses is very time consuming. Not sure if the short cycle time on the cutter is causing problems or if maybe something else. Any suggestions? I did check all grounds, both the plasma cutter ground & table to earth ground. Everything is clean and tight. The table is new and the grounds are on a clean part of the table that hasn't even been used. I did try grounding cutter to material just to make sure it was getting good ground through table grates but same problem.

[jim_v]

It would be helpful to see the wear on your consumables.....if I could see the front exit orifice of the nozzle as well as the front (hafnium) end of the electrode...I could probably help determine your starting issue.

Misfiring in a Hypertherm torch is caused by:


-hole programmed with lead out....which forces the arc to "snap off" due to material dropping out. Holes should be programmed so that the end of cut allows current ramp down with metal under torch.

And any combination of the above will exacerbate the misfiring.

Jim, just to clarify, all my holes should be programed without a lead out, so the arc just stops on the edge of the circle?

[jimcolt]

That will provide the best electrode life. You will have to experiment a bit with the end of cut delay so the slug drops from the center of hole and that there is minimal divot. On most industrial cnc machines holes are done with an overburn....meaning you continue cutting on the hole radius about .150" past the lead in kerf....and shut the plasma off before the motion stops....which makes for a smoother hole. I have not figured out how to do that with the PlasmaCam software!

Jim

[mdwalker]

That will provide the best electrode life. You will have to experiment a bit with the end of cut delay so the slug drops from the center of hole and that there is minimal divot. On most industrial cnc machines holes are done with an overburn....meaning you continue cutting on the hole radius about .150" past the lead in kerf....and shut the plasma off before the motion stops....which makes for a smoother hole. I have not figured out how to do that with the PlasmaCam software!

Jim

Jim,

On the new DesignEdge software there is a setting called "Overcut to Reduce Undercutting". According to the video guide this setting is to cut past the lead-in unlike the "Time to continue cutting at end of path" setting that just continued firing the torch for a specified time after motion has stopped at the end of a cut. Would that be the same as the overburn setting?

Danny

[jimcolt]

I'll try it out when I get a chance...I'm not sure...


Jim