Tech Tuesday: Using A Plasma

[mikey_d05]

Welcome to Tech Tuesday. The way this works is simple. I bring up a topic related to off roading in some way, ask questions, get feedback, basically interview you guys. If you have something useful to say, add it, if not, just read.

Plasma Cutters

What is a plasma cutter?
Why should I get it?
What does it do?
How hard is it to use?
What benefits does it provide over a simple oxy-ace torch?
Are there any drawbacks to a plasma cutter?
Do they require any special type of household power?
What are the metal thickness limits?
Do they make portable ones for the trail?

Links

[MrK5]

I know I'd like to have one.

[kitimatdude]

I used to have one.
It was old, ran on 3 phase power, and only worked half the time it seemed.
It would burn up tips fast also. they were like $25 each. It took 4 big guys to load it in a pickup truck.
I hear the new little ones are good tho.

[filo]

From a couple of guys at work who have used them extensively:
The trick to not ruining tips is to keep the tip 1/4-3/8" away from the work.
They do make guards that slip on the nozzle to keep the tip at the correct distance from the work/metal.


Oh, I WANT ONE!!

[VegasBruce]

Directly from Millers website.

Buying A Plasma Cutter
Q: What is Air Plasma?

A: Plasma arc cutting is a process where an open arc, much like in TIG welding, can be constricted by passing through a small nozzle, or orifice, from the electrode to the work-piece. The gas used, typically air, combines with an electrical current to create a high temperature plasma arc. When placed in contact with an electrically conductive material, the arc passes through the metal, melting a thin area. The force of the arc pushes the molten metal through the work-piece and severs the metal.

Q: What types of metal and applications can be used with a Plasma cutter?

A: Plasma will cut any metal that is electrically conductive including steel, aluminum, copper, and stainless steel. Keep in mind that your cut will be de-rated a little with the softer metals like aluminum, copper, and stainless. Rating refers to the thickness a plasma cutter can cut at a rate of 10 Inches Per Minute.

Q: Is there a lot of skill involved with Plasma cutting?

A: No. Depending on what you are cutting and a steady hand there is not a lot of training involved to operate a Plasma cutter. The torch should remain at a 90-degree angle and depending on the machine you can keep a standoff or drag either the tip or the drag shield on the metal.

As far as controls on the machine there are only two, which include the on/off switch and the amperage control. The on/off speaks for itself and the amperage is only going to change when you want to cut thicker material, but most operators will leave the amperage switch on full output for all thickness of metal.

Q: What are the necessary air requirements?

A: Compressed air is the most popular gas used for plasma cutting. You can use an air compressor or a bottle of compressed air. The CFM (Cubic Foot per Minute) is important because that is the amount of air that will be distributed per minute and will keep your Plasma machine running consistently. The PSI (Pounds per Square Inch) is the actual air pressure required to operate the machine. All machines need different PSI and CFM. For instance the Miller Spectrum 375 requires 4.5 CFM at 60 PSI to achieve a 3/8-inch rated cut, while the Spectrum 375 X-TREME requires 5 CFM at 90 PSI.

The other gas used is nitrogen, but the only advantages to using it are when cutting stainless steel. You will get a cleaner cut but the cut thickness will be diminished a little. With some exotic metals a gas mixture may be needed.

You will also want to have dry air when operating a plasma cutter. Miller offers a couple of Dryer/Filters that are designed to keep the air dry and clean. Dry air is important because if there is moisture in the line it will travel with the air and exit the end of the torch. This is not necessarily dangerous but will shorten the life of your consumables because the arc will follow the moisture in all directions and erode the tip prematurely.

Q: How big of a Plasma cutter do I need to buy?

Start by determining the type and thickness of metal you’ll be cutting and the desired cutting speed. Miller uses three standards: rated, quality and sever cuts. A rated cut is the thickness of mild metal that an operator can manually cut at a rate of 10 inches per minute (IPM). A quality cut is rated at a slower speed but on thicker metal. A sever cut is the maximum thickness a plasma cutter can handle. The travel speed is slower and the cut may require clean up.

For instance, at 10 IPM the Spectrum 1251 with an output of 100A @160 VDC is rated for a mild steel thickness of 1-1/4”. By slowing the travel speed, the operator can achieve a quality cut on a thickness of 1-1/2”. At a slower travel speed, the same machine can achieve its maximum cutting thickness of 1-3/4”.

Q: What kind of input power will I need?

A: Miller Spectrum plasma cutters have a wide range of power options.

The Spectrum 125C is available in 115V or 230V options. The Spectrum 375 and Spectrum 375 X-TREME can operate off 115V or 230V. The Spectrum 375 X-TREME can easily switch between the two, since the operator only has to choose the correct Multi-Voltage Plug for the receptacle.

Both 375 models as well as the Spectrum 625 (230V) offer Line Voltage Compensation, (LVC™), which allows the voltage to vary by +- 10 percent without affecting output. This will be an important consideration if you’re work area is subject to dirty power or brownouts.

Others can automatically adapt to a wide range of voltages, single or three-phase and compensate for power fluctuations in the supply. The Spectrum 2050, Spectrum 1000 and Spectrum 1251, using Auto-Line™ technology, can accept input voltages ranging 190 through 630 V, single- or three-phase, 50 or 60 Hz. This means you can plug this plasma cutter in anywhere in the world. Even with brownouts or other power fluctuations, as long as the voltage stays anywhere in that range, the cutting quality is unaffected.

These types of units are especially suited for working in the field, using an engine drive’s auxiliary power. In the field, units without this type of technology are prone to erratic cutting arcs, frequent breaker trips and blown circuit boards because they can place a load on the line such that voltage levels drop below the plasma cutter’s operating range.

Q: What about portability?

A: In addition to the ability to work with available power supplies, consider the plasma cutter's weight and size. All of Miller’s plasma cutters weigh less than 100 lbs.(The Spectrum 625, Spectrum 375 and Spectrum 125C all weigh about 60 lbs.) Miller offers the No. 30A Economy Cart for these machines.

For the ultimate in portability, the Spectrum 375 X-TREME weighs only 18 lbs. and comes with its own shoulder strap to allow the operator to easily carry it.

Q: What safety procedures do I need to follow?

A: Proper welding clothing should be worn, as well as a number 5 or 6 shade full-face shield. Good ventilation is a must just as when you are welding. Be aware of potential hazards involved with the process including, high voltages, noise, temperatures, flammable materials, fumes, ultraviolet radiation and molten metal.

[VegasBruce]

More


Plasma Cutting VS Oxyfuel
Q: What advantage does Plasma have over Oxyfuel?

A: Plasma cutting provides numerous advantages over Oxyfuel. It cuts faster; does not require a pre-heat cycle; produces a small and more precise kerf width (the width of the cut); and has a smaller heat-affected zone, which prevents the surrounding area from warping or damaging the paint.

The Plasma process also cuts any type of electrically conductive metal (the Oxyfuel process cannot cut stainless steel or aluminum). Plasma cutting is a cleaner, less expensive and more convenient method of metal cutting because clean, dry air is used for most plasma cutting applications.

Q: What are the basic costs involved in Plasma vs Oxyfuel?

A: To get started in Oxyfuel you will need the complete torch set-up costing around $250. You will need an oxygen and acetylene bottle costing around $250 to own. The tips that have to be replaced over time will go for about $5. As you gas bottles are emptied they can be refilled for about $30 each. After all is said and done you still can only cut steel.

Plasma will require an initial cost $1100 to $2000 depending on what size machine you require. After purchasing the machine your air compressor will provide free air so the only additional cost will be tips and electrodes for about $11 for the pair.

Oxyfuel is going to be less expensive at the start, but as time goes on the purchase of gas, and the limitations will make it more expensive in the long run. Plasma has the initial cost of the machine but after that it is mostly tips and electrodes. So in the long run Plasma is going to be cheaper and more practical for cutting any metal that is electrically conductive.

Q: Is Plasma cutting a good tool for restoring cars?

A: Excellent!! The Miller Spectrum 375 Spectrum 375 X-TREME are both perfect for auto work. Both have a 3/8" rated cut and will sever 1/2". That cut rating will cover anything on a car.

Both models can also plug into 110 or 220V and will give you the same cut off of either input. The difference is portability, which may be a concern if you plan to work in a variety of environments.

Your need for portability may also factor into your decision.

The Spectrum 375 X-TREME is more portable, weighing 18 lbs. compared to the Spectrum 375’s 55 lbs. It is also easier to switch between 110V and 220V with Spectrum 375 X-TREME since it uses Multi-Voltage Plugs (MVP). Simply pick the MVP that matches the power receptacle, plug it into the power cord and the unit is ready to go.

What is real nice about plasma is when you’re doing body-work you do not have to worry about warping or burning the paint. With plasma, the arc is so hot and tight the heat does not have time to spread out and effect the metal. Plasma is much faster and cleaner than anything else you could use (hacksaw, grinding wheel, etc.)

[bggrnchvy]

What is a plasma cutter?

Basically it's a step up box that excited pressurized gas with electricity and uses it to melt metal. The gas is usually just CDA (compressed dry air).

Why should I get it?

Did you miss the part where it runs on gas and CDA? It's only limited in use by its consumables. No more running out of acetelyne late at night on Saturday without access to more until Monday. Oh, and the fact they're fairly compact and aren't explosive.

What does it do?

Melts thin lines in metal.

How hard is it to use?

Anybody can use one, however there is technique so the quality of the cut may be low to an inexperienced user.

What benefits does it provide over a simple oxy-ace torch?

See above.

Are there any drawbacks to a plasma cutter?

You can't use it to pre or post heat metal, aid in bending plate or to do anything but cutting.

Do they require any special type of household power?

The small ones will work on 110v 30a circuits but really 220v is needed for quality heavy gauge cuts.

What are the metal thickness limits?

Totally depends on the size of the unit. 1/8" - several inches. Typical shop or home units top out at 1" sever.

Do they make portable ones for the trail?

Not that I'm aware of. It's more specialized a tool than I think I would need on the trail.