Having problems cutting thick material

[Danno]

I've had my plasma table running now for about 4 months with zero problems cutting up to 3/16 thk steel.
I recently had to do a job where I had to cut 3/8 mild steel and have run into a bit of a problem.
When piercing the 3/8 plate, the splash of slag that ends up on top of the plate is higher than my cut height, which results in my torch crashing into it.
I'm using a Hypertherm 45 and CandCNC Bladerunner electronics.
My pierce height is .150 and cut height is .060 as stated in the Hypertherm manual. I've tried increasing my cut height to .080, but the problem persists.
I've also increased my delay time before plunge from .9s to 1.2s, but no luck.
I've also decreased my plunge rate to 15 in/min from the recomended 32 in/min.
What else could I try? I've had the torch not crash on a couple of parts, and the resulting part is perfect.
Thanks for any help.
Dan

[Danno]

My THC delay was set for 1 second, and would make the torch go below my cut height right after the plunge. I've increased this to 3 seconds and the result is much better.
I would still like to know how to reduce the initial pierce slag from forming on top of the workpiece.
Dan

[Hworks]

Increase your lead-in length and get passed the slag before coming down to cut height
Andy.

[Danno]

I didn't know I could do that !! At the moment I'm just plunging straight down.
If I use a lead in, will that cause problems at the end of my cut with the slug staying on the part? Just wondering!
Thanks

[Beefy]

Hi Andy,

you caught my attention about the lead in length and getting getting past the slag before coming down to cut height.

My cam is Sheetcam and as far as I know it doesn't have a facility to do that. What software are you using to produce your gcode. Does yours have a special function to do this. Something else just came to mind, the torch would be cutting / travelling at pierce height along the lead in so the THC Delay setting would have to be long enough to allow for this too before the torch dropped down and the cut voltage steadied out at the proper cutting height.

Could be a useful new feature for Sheetcam. I've just been using water based anti-spatter spray to overcome this problem.

When doing small holes for instance, anti-spatter spray is used to improve the hole quality, probably due to not having the slag screwing up the cut in that confined area.

Keith.

[Danno]

I'm also using Sheetcam.

[jimcolt]

Long lead ins, indexing from pierce height to cut height (without colliding with pierce slag....but before the end of the lead in), and anti spatter spray (on top of plate will minimize pierce spatter....and will improve the shape of holes as pierce spatter affects the arc....affecting the roundness of the bottom of holes).

These are all pretty normal ways to improve holes and minimize start stop cut anomalies. Some machines, software, cnc can do most of this automatically.....while others have to have part programs manipulated (Gcode) to make this work best.


Jim Colt Hypertherm

Hi Andy,

you caught my attention about the lead in length and getting getting past the slag before coming down to cut height.

My cam is Sheetcam and as far as I know it doesn't have a facility to do that. What software are you using to produce your gcode. Does yours have a special function to do this. Something else just came to mind, the torch would be cutting / travelling at pierce height along the lead in so the THC Delay setting would have to be long enough to allow for this too before the torch dropped down and the cut voltage steadied out at the proper cutting height.

Could be a useful new feature for Sheetcam. I've just been using water based anti-spatter spray to overcome this problem.

When doing small holes for instance, anti-spatter spray is used to improve the hole quality, probably due to not having the slag screwing up the cut in that confined area.

Keith.

[Hworks]

I am relatively new to this myself, my machine is a Dynatorch and i can configure the THC for different materials and keep a library, but basically up to 1/4" i will pierce at 300% of cut ht but thicker than that i increase the pierce by two parts, initial arc then additional retraction from the plate while its piercing. After piercing, the lead-in begins and torch ramps down to cut ht. Example photos show 3/4" rings i cut yesterday with 65A settings, arc start at .200 retract to .400 and allowing 2 secs for pierce is plenty time as i have a watertable and i can hear the air hit the water before torch begins to move.
I draw most of my shapes and code them using Wecim, i have a library of lead-ins and lead-outs that i have configured and choose from depending on what the material / job is, letters to be cut in 1/4" plate i will use short leads, for oxy cutting, then i have other leads about 1" long. these pics you can see both the leads, inner and outside
I hope this helps,
Andy.

[Danno]

Are you making rings for the London Olympics ?

[Beefy]

Thanks for that info Andy.

I looked at my Sheetcam software to see what the ramp function would do on a lead-in. It appears the ramp simply comes down at 45 degrees from pierce height to cut height, at the plunge feedrate I program. So if say my pierce height was 4mm and my cut height was 2 mm, that's 2 mm difference and the ramp down at 45 degrees would only be 2 mm away from where the pierce started, not enough to avoid a big spludge of pierce slag I suppose.

So in We-cim can you program over what distance the ramp down to cut height would be.

Cheers,

Keith.

[Hworks]

I use Wecim to draw shapes and define leads in and out, straight , curved, whatever angle of approach or exit I need.
Dynatorch settings allow me to configure heights, time, speed on lead-ins and speed and thc freeze on lead outs.

Andy

[Hworks]

Beefy,
what system do you have controlling your torch?

Andy.