Plasma Cutting 1/4" Aluminum

[yeomansjon]

Quick question (I think). I am looking to cut 1/4" Aluminum (6061-T651). I have a HT Pmax 1000, T60 handle, Plasmacam DHC. The HT manual for my setup shows that I can use a 60a nozzle or a 40a nozzle. Am I better off using the 60a since it appears that 1/4" aluminum is centered in its cut range? I am also thinking the faster cut speed may reduce warping but not sure. Anyone with my setup that has experience cutting 1/4 al would be helpful, thanks!

[Largemouthlou]

I have a 1250 HT and cut with the 40.. Yes you can cut quicker with the 60 but it is also putting off more heat. Jim would probably say use the lowest amp nozzle that will cut the material.. The amount of warp age may depend on the design cut as well..

[yeomansjon]

Ok that makes sense, thank you. Fortunately the design is very simple with some long straight cuts and then long inside radius cuts, about 24" I.D at the tightest inside arc.

[Shane Warnick]

I recently cut some signs out of 3/16" aluminum diamondplate with a Hypertherm Poweremax 1250, I cut it at 40 amps but don't remember the speed. I did cut it with the diamonds up, height control worked fine. It did warp, but laid back down after it cooled off. The outside of the sign was an oval, and I cut it within 1/8" of the sheet edges, the inside didn't raise up, but the outside (the castoff) did something fierce where it was so thin. After it was cooled, I had to get some screwdrivers and pry the outer ring off of the center piece just to get it off the table, it sprang back that far. Anyways, I would say cut with the lowest amperage you can, faster is better but with aluminum, the cut is purely a thermal process. Same with stainless. When you cut mild steel there is some oxidation where the material actually "burns" for lack of a better term as it melts and washes out of the cut. This is one reason why you can cut mild steel of the same thickness faster than aluminum or stainless of the same thickness. With non-mag metals, the cutting is purely thermal, so if you increase your amperage and subsequently your speed, you end up with more dross, which is way harder to remove, the kerf is markedly wider (as in almost 1.5x 40a vs 60a) and you get more warping and also, due to the nature of aluminum, the corners that are normally nice and crisp tend to get rounded as it will puddle and melt out especially if there is not a lot of space between two cuts. This was my experience anyways. I have found, though, that as a rule I can usually cut 10% faster than the cut charts in the manuals on non mag metals, and 20-25% faster on mild steel. I can also usually reduce pierce times by 40%, sometimes as much as 60% on the thicker stuff. So instead of a pierce time of 1 second I can get away with 0.4 seconds. Again, this is my experience, I have super clean super dry air (the ONLY advantage I have found to being in the desert thus far) and your experience may vary. If you would like the exact settings I used let me know I will look in my little book and get them for you. Stay safe
Shane

[yeomansjon]

Thank you, I appreciate the feedback. I ended up playing with it last night. I started with the 40a consumables and set my starting configuration to match the settings in the HT manual for 1/4" aluminum. I'm battling height consistency issues so it took a while to get my cut height set but once I did I got a very nice clean cut on my 4th practice line inside a drop out piece. I ended up at a 45 ipm with almost no dross on the bottom and a very thin kerf. The material seemed fairly cool to the tough so I figured I would be ok since I was cutting very little detail in a 4' x 4' piece.

However, because my design is one long cut, the material did move something fierce and thus left me with a lop sided design that I need to figure out how to clean up. The outer metal moved and then sucked back in as it cooled, but by then the damage was done and I had cut along a piece that had moved.

For anyone like me searching '1/4" Aluminum' with a Pmax 1000, my recommendation is to use 40a consumables, cut/pierce height from the book, and 45 ipm feed rate AND some method to keep the aluminum cool or consistent heat. I see other posts about pouring cold water on the material during the cut, others with a water bath below, etc, whatever works for you.

Maybe Jim or others will chime in but I figured I share my experience.

Below is a picture of the design, the hole in the center is the center circle for a 2-part design. I cut it off center to maximize the amount of area on what would be the left over scrap piece.

[hooked]

if you Tab ur parts in a couple of places it will stay more consistant and move together! and then cut ur tabs later with a jig saw! Hooked

[vmax549]

We do a LOT of 1/8 - 1/4" alum for gates and metal arts. YES it creeps all over the place due to expansion. The trick is to LEARN when it IS going to happen and plan for it by cutting detail cuts as far from each other as possible AND learn to do sectional cuts in long runs to allow time for the metal to cool and shrink back to size.

FOr Highly detailed parts I use a 40a fine cut nozzle cutting at 30 -40 amps at 20-35 IPM. Very fine detail cuts, sharp and crisp. BUT do to expansion it can be tricky to get it all apart after the cutting. Trick is to let it COOL on the table first THEN most of the time things will fall out.

Yes this takes time and CAM work BUT the option is to have a very warped and crooked part .

OR just build a GOOD water table(;-)

(;-) TP

[Shane Warnick]

I have a downdraft table and the air moves pretty good, but I do get some issues with expansion at times. I will pause the machine sometimes when there is a lot of cutting in order to let it cool between cuts, I also have another fan that I will put blowing directly down onto the piece to help cool it faster. I have also poured ice water onto the sheet from a cup but that gets pretty messy, it works but again it is messy.
Shane

[Largemouthlou]

I keep a industrial size spray can with a wand on it next to the table, that way If I'm doing detailed cutting and know it will get hot I follow the torch with a fine mist of water.. it helps a lot and don't make that much of a mess.. I also use it to spray water down in my grounding rod.

Terry,, I use the fine cut for .125 but never tried it on the .25, is the .25 what you slow the fine cut ipm down for or do you do it on .125 as well?

[yeomansjon]

Thanks again everyone, had better success last night. I had to cut some slivers to even out some of my circles and arcs and cutting it in sections definitely helped. For next time, I will use the cool water spray bottle idea.

[jimcolt]

If I have lengthy cuts on rather thin sections I always leave some tabs so that the heat does not cause cambering (side movement). Then program cuts (no need to use a jig saw) to cut the tabs off after all major cutting is done. On high end plasma machines this can be automated in the CAM (nesting ) software. No need for water if you do it this way.

Jim Colt

[muzza]

Another thing you can do is to do some relief cuts to remove excess material away from where your cuts will be leaving a smaller margin of about 8 to 10 mm (5/16" to 3/8") around the cut piece, even with relief cuts to segment it if necessary. That way when you do the final cut the the piece that moves will be the thinner scrap piece and the cut piece will stay put.
Murray

[davidhillman]

I hope no one minds if I dredge up this slightly old thread, but it pertains directly to what I wanted to ask about, and was already helpful for me to read.

I made a couple 1/4" aluminum wing supports for a friend's racecar last night on my Plasmacam DHC2. I didn't have a lot of the problems mentioned above ( one small piece moved a lot, and was ruined, which I didn't understand until reading this thread -- thanks! ), but I did get a ton of dross on the bottom. The top side of the cuts are just fine, but the bottom is going to require some significant cleanup. I cut them wide open at 40a with my Cutmaster 51 using brand new 40a parts ( SL60 hand ). I tried speeds from 30 to 50 ipm on test pieces with no real difference between them. At 50, the top side started to degrade. I cut the wing supports at 40 ipm and .03". I have plenty of air from a 60 gallon 155psi Industrial Air compressor, which was not working hard to keep up.

My manual says, under trouble-shooting;

3. Excessive Dross Formation
a. Cutting speed too slow
b. Torch standoff too high from workpiece
c. Worn torch parts
d. Improper cutting current
e. Non - Genuine Thermal Dynamics parts used
f. Incorrect gas pressure

I don't think any of those were the problem. I'm wondering what else I can try to eliminate all this dross. From the sounds of this thread, it is possible to cut 1/4" aluminum at 40a without a ton of dross... but I'm somewhat at a loss as to what else to change. Everything else worked fine, there's just 1/8" of melted slag hanging off the bottom of these parts all the way around. I don't have dross issues cutting thinner aluminum, nor steels.

Any advice or suggestions would be appreciated. Luckily, I don't have to do the grinding on these parts, but this car will probably be crashed again, so I will someday need to make more of these

--
David Hillman

[tnbndr]

If I have lengthy cuts on rather thin sections I always leave some tabs so that the heat does not cause cambering (side movement). Then program cuts (no need to use a jig saw) to cut the tabs off after all major cutting is done

I would like more information on how you do this! Do you build your tabs in CAD and then do cuts over them on a different layer that gets cut last? Just thinking out loud.