New Machine Build- Plasma Cutter Feedback

[lclore]

Hello Everyone-

I have been researching plasma cutters for a month and reading threads in this site all nite. I would kindly like to request feedback from the forum readers with experience in automated plasma cutting.

The need to cut both 6061 Aluminum and 316SS tube, with diameter ranging from 1.5" to possibly as high as 3.0". Wall thickness is always 0.065". Simply put, the cuts in the tube will be a recess for inserting a plastic molded part. Therefore, it is desirable to maintain a cut tolerance of +/-0.01" repeatability or better. The thin wall will not allow much of a bevel I would think. I can deal with a bevel so long as it is repeatable. Altering properties of material hardness resulting from the cutting process is not a concern. A dis-coloration around the cut-edge is tolerable so long as it is ~0.035" or less.

I spend most of my time in general purpose motion control for custom automated machines- this is good in that I'm not worried about material presentation to the torch... but this is bad in that I have no idea how to select & buy a plasma cutter. My research leads me to believe that Thermal Dynamics & Hypertherm have very nicely engineered solutions for automated cutting equipment & have systems that can meet the requirements. Both companies have been very professional in my contact with them.

I don't know if I can do it with a standard unit or if High Definition is absolutely required to stay with in the repeatability tolerances.

This is a small company (3 employees- me, myself & I) and I am banking heavily on the success of the product that this cutter will produce- pull this off & I have the better mousetrap over my offshore competition. Stimulus $ went elsewhere... and I am stuck balancing cost against a prudent equipment selection. A High Definition Cutter is not out of the question, but I need to understand why that's a requirement to the need better.

Thanks in advance for your thoughtful responses.

Lee

[jimcolt]

For the thickness of the wall and the diameter of the tubing in your application....you definitely need to use power levels in the range of 20 to 30 amps.....any more and you will likely not be able to accelerate and maintain adequate speed to produce a good quality cut.

The tolerances that you require are as much a function of torch height control and machine motion (in terms of following error and the ability to maintain the cut speed that the plasma arc requires)...as it is a funtion of the plasma. Excellent motion, torch height and a good, low powered plasma may allow for a .010" tolerance...although that is on the tight end for plasma.

I would suggest looking at a good quality low end plasma that has good arc energy density......the Hypertherm Powermax45 uses technology derived from Hypertherm's hih definition line of plasma's.....although it is not considered high definition.

A Powermax45 will cost in the $1600 or so range....and an HPR130 (high definition) plasma from Hypertherm will run in the $32,000 price reange. A big difference in price for a rather limited application......I think the 45 may work due to its low power cutting capability...

Jim Colt Hypertherm

[CNCCajun]

"I would suggest looking at a good quality low end plasma that has good arc energy density......the Hypertherm Powermax45 uses technology derived from Hypertherm's high definition line of plasma's.....although it is not considered high definition."

Thanks for the info on the PowerMax 45 . . .

Jim, when do you suppose Hypertherm will apply this technology to their 1000 & 1250 machine . . . ? or would that hurt their sales on the high definition machines?

Seems like a good time to release a line of machines for the "growing" small CNC industry . . .

Steve

[jimcolt]

Steve,

We introduced the FineCut consumables for the Powermax600, 1000, 1250 and the 1650 over 3 years ago.....that is technology derived from our high definition class plasma systems.

The 45 uses this technology along with a new conical flow torch design that does take this a step further....however it requires some slightly different output characteristics in regards to gas flow, current ramps, and timing to make it work at it best. There are no current plans to introduce the Powermax45 torch technology or design into the previous models at this time......

Hypertherm in the past has offered upgraded torch replacement kits as new technology was available....and I suspect there may upgrade available at some point in the future.

While this FineCut and conical flow technology is a great improvement to air plasma cut quality on thinner materials....it is not even close to competing with our HPR130, 260 and 400 in terms of high definition cut quality, speed and operating costs. The true high definition technology requires very precise gas flow control, current control, a liquid cooled torch, and a special vented nozzle design, as well as the ability to use oxygen as the plasma gas. These systems are high end industrial plasma's that produce high volume cutting with tight tolerances and very low operating costs......however they are usually out of the price range for entry level plasma system users!

Jim

[Edwardo]

one thing you also may want to consider when buying a plasma cutter is not only what you need to cut today, but also tommorow or next year! When i was researching as you are now i was really confused on what to buy. I have always had the ( go big or go home ) mentality which has got me in big trouble when i went home. I read in differnt places people saying there plasma cutter or table being too small and wishing they had gone alittle bigger because as time went on they had oppertunities to do other work but were not able to, i have never read anywhere someone wishing they had gone smaller, aside from financing.
I bought a 1250 hypertherm with a 4x8 drop side Dynatorch which i love and till death do we part, but in the last month i have had a few calls for peices bigger than my table is made for???? i know i can idex it, but the point is i thought i had that covered, originally i was going 4x4 plasma scam, hehe sorry Jim, typo....your 1250 though is my 4th child, joined at the hip with my DT. Anyways, the crystal ball is always foggy when making these types of choices because of the future unknown factors.

EDD

[jimcolt]

Yes...the Dynatorch is a good machine.....but I have no trouble at all cutting parts that are up to 12' long on my 4 x 4 PlasmaCam.....indexing the material is a cinch with their software......and I like having the floor space in my small shop for 99.5% of my jobs which are smaller than 4 x 4. The PlasmaCam has great support....there are thousands in the field, and it was less than $10k!

PlasmaCam does make a 5 x 10 machine called the Samson as well....for around $15k.

Glad you are having good luck with your plasma and machine!

Jim

[WSS]

Originally Posted by Edwardo one thing you also may want to consider when buying a plasma cutter is not only what you need to cut today, but also tommorow or next year! When i was researching as you are now i was really confused on what to buy. I have always had the ( go big or go home ) mentality which has got me in big trouble when i went home. I read in differnt places people saying there plasma cutter or table being too small and wishing they had gone alittle bigger because as time went on they had oppertunities to do other work but were not able to, i have never read anywhere someone wishing they had gone smaller, aside from financing. EDD

EDD, I agree with your thoughts on looking to the future. Indexing will work but if you have a 1" or bigger piece then safety becomes an issue and time spent moving it around will eat into cut time. Financially you have to balance size with cost and space. I almost went with a 8' DT gantry but am hoping the 6' will work, the extra K was hard to part with! I have to admit that the stuff Jim is producing off his PlasmaCam table is impressive. Testimony to experience and high quality gear. Both of those will cover the issues of a small table.

My 1650 is due in tomorrow! Funny thing happened today- I ordered a cover for it and 30 electrodes showed up instead. Someone is not happy with the cover they received.

[Edwardo]

WSS, i agree on what you said about balancing cost , size and space... 2 years ago when i was where Iclore is, researching plasma cutter etc, i went to look at a old 8'x16' (essab) or something like that...
The price was right at 10,000 for everything, I beleive it had a hy def plasma with it, down draft system... but it needed 3 phase power, and the size of the table would take up half my shop... i almost bought it thinking i could change this and that to make it work for me, but talking to another member here changed my mind.
Anyways at that period of time i read as much as i could on different equipment, the good and the bad and made my decision from that.
No disrespect Jim, i admire your work.

EDD

[lclore]

Everyone- thanks for the input. I can relate to the "go big or go home" thinking & it usually gets me in trouble when its related to Motorcycles.

Thought I would mention that I contacted Hypertherm & they are sending out some evaluation parts cut with powermax45. no better way to see what I might be getting then to actually see the outcome. Thermal Dynamics will do the same.

From what I can tell, they all interface to the real world the same- give them an enable and on signal, monitor for fault and ready. Pretty easy. Does Air Pressure affect quality? Manuals say a range, but I am guessing best results would be with a regulator on the incoming air line.

Thanks again to all who provided input! This will be fun...

[lclore]

Jim,
I am alittle fuzzy on some things- may just be staring at this stuff too hard... Would you mind to comment on some of these specific questions related to Hypertherm systems?

In general, does the heated air of the plasma cutter actually do the cutting work or does electrical current thru the work piece contribute (and at what level)? My reading on this says you have to ground the workpiece- with a rotating tube attached to the end of a servo motor, I don't want any current flowing thru the work piece to ground in whatever random machine frame path it chooses as it will create havoc with the controls and servo feedback (oh yeah, and be a possible safety hazard). Is electrical isolation a requirement to the controls with a separate path to ground? Does it need to be a high integrity (low impedance) path to ground? Is this a safety ground only conducting in the event of a inverter output stage failure?

What safety's are built into the HyperTherm Powermax45 inverter in the event of a failed output stage? I didn't see in the manual any recommended upstream contactors or safety devices. Is the enable input safety rated to some level?

Thanks...
Lee

[Dustin407]

lclore,

I bought a Thermal Dynamics (cutmaster 81...60 amp) unit about three years ago and Im very happy with it. Although it is my first plasma cutter, I dont have aot of personal comparison with others. I was cutting 1/2" steel yesterday with no problem (by hand w/ straight edge). I put a square on it afterwards and almost no bevel at all. Alot of people I see on here all have Hyper units, I still have yet to see one person with a thermal dyn. Im not sure what that means but my unit cuts very well. I see you are going to be cutting alot of alum. I did a huge alum. job last year for epcot out at disney. I was rippin through the alum. w/ no problem and needed very little edge cleanup. Hope my feedback helped.... here is a couple pics for you guys.

[jimcolt]

Lee,

The plasma torch internally raises the temperature of air to its ionization temperature....when a gas reaches ionization...it becomes more electrically conductive. The ionized air is passed through a nozzle orifice, which constricts the flow of air an increases its velocity....then DC current is applied to this ionized stream of air...and the current fllows the path of air to the plate...(connected to the work or ground clamp) completing the circuit. The air is superheated to over 24,000 degrees fahrenheit....which melts pretty much anything in its path.

Air is comprised of approximately 20% oxygen.....and when you are using an air plasma to cut materials that oxidize easily....(steel) an exothermic reaction takes place...adding further cutting power to the process.

So plasma cutting is mostly thermal melting of the plate (when cutting stainless and aluminum) and is a combination of exothermic (like oxy-fuel cutting) and thermal when cutting easily oxidisable materials such as steel.

For your grounding questions:

1. Plasma requires a workpiece ground connection. For rotating workpieces some sort of a brush type connection of adequate design to handle the Amperage level being used (plasma cutters output power range from 12 amps to 1000 amps).....the more sophisticated systems I have seen (such as tube mills that produce irrigation pipes) have used rotational mercury type contacts to maintain a good ground path.
2. On any type of cnc equipment that is used with plasma it is very important to have a good nearby earth ground....each component (plasma, drives, cnc, machine frame, etc.) should be directly connected to this ground source (no daisy chaining of connections) with adequately sized wiring. This protects low voltage signals from being affected by the relatively high plasma voltages. High end industrial plasmas (and some small entry level plasmas) also use a high frequency starting voltage in the 15kV @ 2 megaherts range....this starting voltage is active for a few miliseconds at the beginning of each cut cycle to ionize the plasma gas (air).....CNC equipment nees to be protected through proper grounding and isolation when used with plasmas with high frequency starting.

3. As far as output failure of a Hypertherm plasma...there of course are different types of failures....in theroy there could be a failure that causes the output to be "full on".....this type of failure will quickly be detected by the overcurrent detection in the plasma (any of Hypertherm's systems)...and will cause the unit to shut down. If for some reason this circuitry does not detect and output problem....then there also would be an increase in input current...which will trip the input circuit breaker quite rapidly.

Regardless...plasma is a very safe process. It is virtually impossible with Hypertherm's systems to contact cutting voltage, or open circuit voltage under normal use. I look at some of the import (Chinese mostly) plasma systems and they have exposed torch connections with open circuit voltage of over 300 VDC....very dangerous. I do not understand how these systems pass regulatory tests...

Jim Colt