[MotoEngineering]

Hi Guys I'm here in Dublin Ireland, looking for some tips on how to cut out a flange without getting so much distortion. I cut out a 9'' OD circle with a 6'' hole with my plasma cutter, out of some 1mm (40thou) mild steel and when I was done it buckled so bad that it was unusable. So I went again with 2mm (80thou) Aluminium plate this time I cut the hole out first then the OD. It still buckled but not quit as bad. I used 18amps and 40psi on the 1mm steel and 28 amps and 40psi on the 2mm Aluminium. It's a hand held Stalwerk 50, a German good quality unit I got nice cuts with little dross. Cutting out flanges is the main thing I do with the plasma cutter so I'm hoping one of you guys can help me out. Thank you in advance.

[Arno]

Heat input into the base material is probably your biggest enemy.

Clamping the material between (alu) heat sink blocks and perhaps bumping up the power on the plasma cutter, using a tip that gives a very narrow cutting arc and moving (much) faster may help to cut down on the heat getting into the material, but in the end for regularly cutting such thin sheet metal I suspect a process like laser or waterjet cutting is likely to have less distortion issues

Or even look at the 'old skool' cold-working techniques for sheet metal like shearing, punching, etc..

Bye, Arno.

[ldbtx]

Arno is definitely right about moving quickly as you cut. If you're currently free-handing a scribed line, which slows you down, you might consider making a guide so you're tracing the ID, allowing you to cut much faster. Or, you might get one of the commercial circle guides. Either way, the faster you can cut, the less distortion you'll have.

Good luck, and have a Guinness for me. They're so much better close to the source.

Larry

[jimcolt]

I assume you may be cutting by hand....so it will be difficult to get a decent cut with no warpage on material that thin unless your plasma cutter manufacturer has nozzles designed for low amperage cutting (20 to 30 amps). Just turning down the amperage with a nozzle designed for 50 amp cutting is a step in the wrong direction as it simply reduces the arc energy density, adds more heat to the material.

On my cnc machine I often cut 1mm plate......at 325 inches per minute (8250 mm per minute) and at 40 amps with a Finecut nozzle. Proper height is critical, speed is critical. I get no warpage at all.

With plasma it is always beneficial to match the consumables and the power level to the thickness your are cutting in order to optimize quality. If I was cutting by hand on 1mm steel, and it was just a straight cut I could guide the torch against a straight edge and move the torch fast....getting excellent quality. For details though....I would probably have the same issues if I cut by hand. Jim Colt Hypertherm

Here is a link to a video showing a simple part cut at 40 amps at 500 inches per minute.https://www.youtube.com/watch?v=3WtlQ34EmII

Hi Guys I'm here in Dublin Ireland, looking for some tips on how to cut out a flange without getting so much distortion. I cut out a 9'' OD circle with a 6'' hole with my plasma cutter, out of some 1mm (40thou) mild steel and when I was done it buckled so bad that it was unusable. So I went again with 2mm (80thou) Aluminium plate this time I cut the hole out first then the OD. It still buckled but not quit as bad. I used 18amps and 40psi on the 1mm steel and 28 amps and 40psi on the 2mm Aluminium. It's a hand held Stalwerk 50, a German good quality unit I got nice cuts with little dross. Cutting out flanges is the main thing I do with the plasma cutter so I'm hoping one of you guys can help me out. Thank you in advance.

[MotoEngineering]

Hi Guys thank you very much for your replies, much appreciated. The Plasma Torch on my Stahlwerk 50 is an AG60 do you know if it is possible to buy different tips to suit thin material for this torch? I didn't know there was different tips for different thickness material. Should I try and change the torch? I was cutting by hand but I had made up a template bar to swing the head in an accurate circle, what height should I be cutting at? what effects does changes in height make? I will in future bolt the plates to an Aluminium heat sink and move as fast as possible and use material as thick as possible. Thank you again for this very valuable info. as I work on my own you guys are my only source of really good info.

[noddybrian]

To the best of my knowledge that Chinese torch has no designated fine cut consumables available but it does come in 3 nozzle diameters maybe try some .9mm designed for 40amp machines may help - the circle cutting trammel sold for that torch has wheels on to maintain the correct height - cheaply sold on Ebay - biggest thing I reckon will help is improvise a turntable & spin the workpiece with the torch stationary - you will have more control of cut speed & keep steadier so can go faster.

[MotoEngineering]

Hi wow a turntable that is a great idea! and 0.9 nozzels are on the way thanks alot that really was a big help, I'm looking forward to my next lot.
cheers Bert

[noddybrian]

Glad to be of some help - I keep meaning to make a freehand cutting turntable for plasma cutting but time / space has kept me from it - I had a similar very heavy one last workshop I had I used for circle cutting with oxy / acet & it helped a lot - if you can't spin the whole sheet your using even though it's more cutting then rough out a square big enough first allow it to cool then cut the circle - once you get a feel for it & just how fast you can maintain the cut you'd be amazed how well it works even with the Chinese plasmas - most people here are judgemental on them - but at hobby level at least they work adequately & are cost effective - let us know how you get on or post pictures if your able to.