Reduction of torch amps in corners?

For general topics and questions that do not fit into any of the other categories or forums.
Post Reply
Black Forest
Posts: 133
Joined: Thu Jan 31, 2013 11:40 am

Reduction of torch amps in corners?

Post by Black Forest » Sun May 17, 2015 2:54 am

Do any of the control systems interface with the plasma source to reduce amps when slowing for corners and intricate details? Everything I have read seems focused on having as rigid and fast acceleration as possible in order not to widen the kerf in these areas. So it would seem the logical solution to improve cut quality would be for the system to look ahead and adjust the cutting parameters to suit. Or have I missed something really obvious?

User avatar
acourtjester
Elite Contributing Member
Elite Contributing Member
Posts: 3568
Joined: Sat Jun 02, 2012 6:04 pm
Location: Pensacola, Fla

Re: Reduction of torch amps in corners?

Post by acourtjester » Sun May 17, 2015 7:42 am

I think you want to talk to Tom at CandCNC about his MP3500 DTHC-IV setup
http://www.candcnc.net/index.php/digita ... ht-control
DIY 4X4 Plasma/Router Table
CandCNC DTHC-IV & Feather Touch
Hypertherm PM65 Machine Torch
Drag Knife and Scribe
Miller Mig welder
13" metal lathe
Small Mill
Everlast PM 256 tig

jimcolt
Elite Contributing Member
Elite Contributing Member
Posts: 3006
Joined: Mon Jul 20, 2009 11:18 pm
Location: New Hampshire

Re: Reduction of torch amps in corners?

Post by jimcolt » Sun May 17, 2015 8:47 am

We have been doing this on high end (expensive, over $100k) industrial plasma systems for over 25 years. It does help, however high acceleration is better, and here is why:

The nozzle in a plasma torch is used to constrict (squeeze) the high temperature plasma arc. It actually increases the energy density of the arc to about 15,000 amps per square inch when operated at it (the nozzles) maximum design amperage. Industrial high definition, liquid cooled torches achieve closer to 60,000 amps per square inch energy density (you cannot do this in an air cooled torch).

So....when you reduce the amperage you reduce the energy density of the arc. This creates a "softer" arc that will change the cutting characteristics (angularity, concave/convex cut edge shape, dross formation, etc.) to the point where it often is unacceptable. If you could (at the same time) reduce the amperage and change the nozzle orifice size....then the process would certainly work better!

On some of the high end systems the amperage reduces during cornering and the cut and shield flow gases pressures are changed at the same time.....which helps to maintain the energy density level.

I have no doubt that reducing current in corners and intricate details could be used successfully in an air plasma system, however the specs would likely be different from machine to machine based on acceleration rates, etc. You also would need to either freeze the height control or alter the arc voltage...as changing current would affect the arc voltage/ height relationship.

Jim Colt Hypertherm

Black Forest wrote:Do any of the control systems interface with the plasma source to reduce amps when slowing for corners and intricate details? Everything I have read seems focused on having as rigid and fast acceleration as possible in order not to widen the kerf in these areas. So it would seem the logical solution to improve cut quality would be for the system to look ahead and adjust the cutting parameters to suit. Or have I missed something really obvious?

Black Forest
Posts: 133
Joined: Thu Jan 31, 2013 11:40 am

Re: Reduction of torch amps in corners?

Post by Black Forest » Sun May 17, 2015 10:46 am

In the look ahead the software would have to tell the THC where or if to adjust based on what the cutter is coming up on.

I guess it isn't as simple to implement as a TIG foot pedal !

Would a Hypertherm air plasma have the capability to adjust on the fly fast enough if and I know it is a big if, if the software was there?

tcaudle
Elite Contributing Member
Elite Contributing Member
Posts: 1123
Joined: Tue Feb 28, 2012 6:47 pm

Re: Reduction of torch amps in corners?

Post by tcaudle » Sun May 17, 2015 3:18 pm

Its a combination of the CAM (SheetCAM) using its unique "Cut Rules" that let you set triggers based on the toolpath geometry. There is one called "on Inside Corners" and On Outside Corners" and another "ON All Corners". You can setup things it will do at those trigger points (based on an angle less than #, both going in and coming out . You can adjust the feedrate and run a beginning code and ending code. That is 1/2 of the process. Then you need a control system that will take custom G codes codes and do things like reduce the current then set t back at the end. The Hypertherm 65 - 125 are the only air plasma systems where you can get an OPTION to use RS485 to remotely control the cut current and air pressure. The control system has to be able to talk to the RS485 port on the Hypertherm and make the changes dynamically. A single command to do both (turn off the THC and lower the cut current )helps. Using RS485 the delay time is between 040 and .1 sec to see the reduction/return.cycles.

A somewhat useful method is to slowdown (if your table mechanically cannot make the turn at the higher feedrates) and turn off the THC temporarily so it does not dive. The kerf will be slightly wider but it depends on how much you have to slow down.

All of this is embedded in the G-Code because it defines the toolpath and is generated before the cut ever starts.

Black Forest
Posts: 133
Joined: Thu Jan 31, 2013 11:40 am

Re: Reduction of torch amps in corners?

Post by Black Forest » Mon May 18, 2015 6:19 am

Thank you Jim and Tom.

Post Reply

Return to “CNC Plasma Cutters General Forum”

Easyscriber engrave attachment for Hypertherm torch's