Plasma cutting

[Paul Allwood]

I've finally had a go at using my new plasma cutter in a real project today - still trying to work out how to use it properly.

It's a Unimig Envy Cut 45 Air. I'm in Australia so it runs off 240 Vac, and it has an on-board compressor. It also has a "smart-cut" feature where I dual up the material and thickness and it sets the current and air pressure.

Below is the third cut I made in 12 mm mild steel plate. The first 2 cuts looked about the same. There's a lot of dross on the bottom of the cut - some stick to the scrap, some stick to the workpiece.



The dross chips away easily.

For the plasma cutters out there, does this look normal or is there something I should do to improve it ?

Here are the settings the machine chose.



It also displays a suggested cutting speed, 400 mm/min in this case. I tried to judge this manually by working out how long it should take to run the whole length of the cut.

 

[North Idaho Wolfman]

Is that an air on board or do you feed it air?
Wet air will do that.
Look like not enough air pressure or flow or maybe too fast of a cut?

 

[hagrid]

More air with a larger ID schnozzle.

 

[Runs With Scissors]

I am far from an “expert”, but I have noticed that "cut speed” tends to be the biggest factor in my cut quality.

Don’t get me wrong, the other factors are important, however; I noticed that if I get a crappy cut, many times I can simply speed-up/slow-down the cut and fix the problem.

To my “un-trained eye” I think you're moving a wee bit slow….

The pressure looks OK to me,….possibly a wee bit low????………. but that is one thing my compressor kinda “struggles with”…as well…..especially with longer cuts….


The “experts advice" is to write down your settings so that you can keep track of them and hence be able to "fine tune” everything……..(But I rarely actually do that ….…I prefer the Ansatz Methodolgy)

 

[Paul Allwood]

Is that an air on board or do you feed it air?
Wet air will do that.
Look like not enough air pressure or flow or maybe too fast of a cut?

Yes, it has an on board compressor.

I'm not sure what it has for air filtering or drying internally, but there is a fitting on the back where I think it draws it's air in. I guess I could fit an external filter/dryer here.

 

[Paul Allwood]

I am far from an “expert”, but I have noticed that "cut speed” tends to be the biggest factor in my cut quality.

Don’t get me wrong, the other factors are important, however; I noticed that if I get a crappy cut, many times I can simply speed-up/slow-down the cut and fix the problem.

To my “un-trained eye” I think you're moving a wee bit slow….

The pressure looks OK to me,….possibly a wee bit low????………. but that is one thing my compressor kinda “struggles with”…as well…..especially with longer cuts….


The “experts advice" is to write down your settings so that you can keep track of them and hence be able to "fine tune” everything……..(But I rarely actually do that ….…I prefer the Ansatz Methodolgy)

Writing the settings on a piece of offcut from the actual cut might work. If it's easy I might even do it.

 

[Paul Allwood]

More air with a larger ID schnozzle.

Thanks. I was using the single nozzle that came with it - I'm not even sure what size it is but will check.

I was also using a standoff bracket that came with it.

Do you think I'm better to use this or a drag tip ? I don't have one yet but might get a supply of whatever consumables I might need.

 

[chim]

Another casual user here. I have a Hypertherm Powermax 30AIR that also has a built-in compressor. It has some sort of dryer built in. Mine is made to use a contact tip. Max steel cutting recommended is 5/8" and the manual lists different cutting speeds and amperage settings for different thicknesses. One way to confirm travel speed is to read the sparks shooting out of the bottom of the cut. You want the sparks to trail the tip slightly. Straight down and you're going too slow. Way behind or shooting upward is too fast. Here are a few things I find useful:

Knock any old weld BB's or junk off that is in the path of the cut.

Use a guide when possible.

Very light tip pressure on the material.

If I can't start at an edge (especially on thicker material) drill a hole and use it as the "edge" to start from to conserve consumables.

Dross is easily removed with a $6 Harbor Freight welder's chipping hammer. It seems to peck off easiest knocking it toward the cut.

 

[McMXi]

or maybe too fast of a cut?

I'm going with this based on the appearance of the cut surface and the amount of molten steel that's not being blown out but rather cooling and solidifying.

That sure is one fancy plasma cutter.

 

[Tarmy]

I have a Miller 625 extreme…my cuts with dried air are vertical clean. I use a setting that is a for a slightly thicker cut than I am doing. my cut lines are straight up and down thru the piece…yours appear to be too short, hence the curve.

The key is DRY AIR and enough of it…keeps that cut clean/uniform and should be no slag/cooling.

 

[John T]

For the plasma cutters out there, does this look normal or is there something I should do to improve it ?

I would disregard the smartset feature and dial it in manually...

For the steel in the picture, I'd go balls to the wall... 45 amps.

for speed... yeah, you might have to move faster.... it's a learning curve.... when you see it blowing clean through ... you will know.

Also most definitely use an external air filter. something like the Motorguard M60

I like a desiccant filter also .....


My Hypertherm is 45 amps and I run it topped out for almost everything....
Unless I'm cutting very thin material with the fine cutting consumables.

also don't forget eye protection.... I use the grinding mode on my auto helmet 4-5 shade...

good luck.

 

[Sidekick]

With my Hypertherm 45 quality goes down as cut speed is increased past the voltage setting requirements. A 1/2 inch material cut by hand is tough to get perfect and takes quite a bit of air. My CNC monitors cut voltage and the cut is very square but dross can vary. Looks like they show an external regulator and air connection for your machine that may be required once you hit a certain thickness. Send that picture to the company and see what they recommend. Could be something off with a new machine or easy adjustment that built in software requires.

 

[Paul Allwood]

Another casual user here. I have a Hypertherm Powermax 30AIR that also has a built-in compressor. It has some sort of dryer built in. Mine is made to use a contact tip. Max steel cutting recommended is 5/8" and the manual lists different cutting speeds and amperage settings for different thicknesses. One way to confirm travel speed is to read the sparks shooting out of the bottom of the cut. You want the sparks to trail the tip slightly. Straight down and you're going too slow. Way behind or shooting upward is too fast. Here are a few things I find useful:

Knock any old weld BB's or junk off that is in the path of the cut.

Use a guide when possible.

Very light tip pressure on the material.

If I can't start at an edge (especially on thicker material) drill a hole and use it as the "edge" to start from to conserve consumables.

Dross is easily removed with a $6 Harbor Freight welder's chipping hammer. It seems to peck off easiest knocking it toward the cut.

Thanks Chim. I'll get some bigger orifice tips and some contact tips to try as well.

 

[Paul Allwood]

I'm going with this based on the appearance of the cut surface and the amount of molten steel that's not being blown out but rather cooling and solidifying.

That sure is one fancy plasma cutter.

Thanks. It may be a fancy plasma cutter, unfortunately it's not a fancy plasma cutter operator.

 

[Paul Allwood]

With my Hypertherm 45 quality goes down as cut speed is increased past the voltage setting requirements. A 1/2 inch material cut by hand is tough to get perfect and takes quite a bit of air. My CNC monitors cut voltage and the cut is very square but dross can vary. Looks like they show an external regulator and air connection for your machine that may be required once you hit a certain thickness. Send that picture to the company and see what they recommend. Could be something off with a new machine or easy adjustment that built in software requires.

Thanks. I found the section of the manual that describes connection of an external air compressor, but it doesn't explain when or why this is needed given that the unit has an on-board compressor. I've contacted Unimig to clarify.

 

[Paul Allwood]

I have a Miller 625 extreme…my cuts with dried air are vertical clean. I use a setting that is a for a slightly thicker cut than I am doing. my cut lines are straight up and down thru the piece…yours appear to be too short, hence the curve.

The key is DRY AIR and enough of it…keeps that cut clean/uniform and should be no slag/cooling.

Thanks. It was a cool, damp day here when I did this so the humidity would have been high. Looking like I might need to add some sort of air dryer at the air inlet.

 

[North Idaho Wolfman]

Yes you need a desiccant dryer for the air.

 

[jaxs]

As with all things, variables and combination of variables can make diagnosis difficult. Whether fuel or plasma ,oxygen does majority of work by vaporizing/consuming/destroying metal. Excess dross coupled with appearance metal was gnawed rather than nipped is indication of "hanging out" in one place too long. The instant metal burns up/consumed, any farther heat in the area half melts and half consumes metal from each side of kerf, increasing width of kerf. Half melted,half consumed metal cools into dross.

In the real world, as someone already said, your cut is actually something to be proud of.

 

[Paul Allwood]

As with all things, variables and combination of variables can make diagnosis difficult. Whether fuel or plasma ,oxygen does majority of work by vaporizing/consuming/destroying metal. Excess dross coupled with appearance metal was gnawed rather than nipped is indication of "hanging out" in one place too long. The instant metal burns up/consumed, any farther heat in the area half melts and half consumes metal from each side of kerf, increasing width of kerf. Half melted,half consumed metal cools into dross.

In the real world, as someone already said, your cut is actually something to be proud of.

Thanks for the info and explanation it's appreciated.

I was sort of happy with it - I started with one piece and ended up with two. I did take that as a win, but keen to improve it.

 

[Sidekick]

Thanks. It was a cool, damp day here when I did this so the humidity would have been high. Looking like I might need to add some sort of air dryer at the air inlet.

I think any type of dryer will interfere with airflow when added to the input side of a compressor. Probably gonna need an additional dry air feed. On a unit like that I wonder if providing a remote air feed will up the plasma output power because a built in compressor must draw quite a bit of current.