Walter,
Thanks for inviting me into this thread....there always is a lot of misunderstanding between capabilities, purchase cost and performance between plasma systems and laser systems for cutting sheet and plate.
First....we have to be careful to understand that not all plasma systems are equal. Every day I see people comparing air plasma systems on entry level cnc machines (price range for a 5 x 10 cutting machine that can cut 1/2" steel...under $20,000) to C02 laser systems with 2.5 to 6 kW lasers (price range of $250,000 to $600,000). The only advantage you will see in this type of comparison is that the plasma system is cheaper to purchase.
When comparing plasma to laser, be sure to compare the correct equipment! There are 3 distinct classes of plasma cutters that I classify as 1. Air plasma , 2. Industrial oxygen plasma, 3. High Definition class plasma.
1. Air plasma systems were designed primarily as hand held, portable, low cost plasma cutting systems. Because of their low cost...they have pretty much opened up a lower etchelon market of cnc plasma cutting machines that are well suited for low tolerance cutting applications such as low volume metal fabricating, HVAC ductwork fabricating, metal art fabricating as well as for a variety of maintenance shop uses. The market is relatively large, and many plasma system users have the impression that this is plasma! An air plasma system that can cut 1/2" carbon steel on a 5 x 10 cnc cutting machine with torh height control and CAM software can be had for under $20,000. This system can cut steel parts with tolerances in the plus or minus .030" range, and the cost per foot of cut on 1/2" plate will be in the less than 20 cent range, with cut speeds of about 25 to 30 inches per minute. The air plasma will create a bit of a taper on the cut edge (some systems work better than others) and will have some nitride hardening caused by the nitrogen content in air. Duty cycle ratings of these air plasma systems are generally less than 60% when cutting near max capacity.
2. Industrial Oxygen plasma systems are designed strictly for high duty cycle (100%) mechanized plate cutting on cnc machines. These plasma systems use microprocessor controlled gas and current outputs as well as high tech liquid cooled torch designs that dramatically improve consumable life, as well as increasing cut speed and improving cut quality as compared to air plasma systems. CNC machine builders generally install these plasma systems on cutting machines designed to provide years of trouble free service in high use industrial applications. A typical 5 x 10 machine in this market would be priced in the $60,000 to $85,000 range, and couuld produce cut part accuracies in the plus or minus .020" range. Cut speed on 1/2" steel (130 Amp plasma) would be about 100 inches per minute, and the cost per foot of cut would be in the $.10 range. Cut edge metalurgy is superior to air plasma with a much softer edge (oxygen process) and there will be less chance of edge taper and dross.....secondary operations will be at a minimum. Thes plasma systems are available up to 400 Amps with steel cutting capacity to 2".
3. High definition class plasma. These systems use advance technology in the power supply, gas flow control and the torch to increase the plasma arc energy density to as much as 4 times the energy of an air plasma system. This generates a 60,000 amp per square inch arc energy density, a narrower cut kerf, very square cut edge angularity, minimal edge hardness, and high cutting speeds. The latest technology with these systems (Hypertherm calls it True Hole Technology) eliminates the taper found in plasma cut holes...now you can cut virtually taper free, round holes on gauge to 1" thick steel with plasma....faster than drilling or laser, with ease of use and low cost of plasma. A typical 130 amp high definition class plasma with True Hole technology on a 5 x 10 cnc (precision) machine will sell in the $100,000 to $150,000 price range. This system will cut 1/2" steel at 100 inches per minute with cut part accuracy in the plus or minus .010" range, and with a cost per foot of cut in the $.12 range. High Definition plasma systems are available to 400 Amps for cutting up to 2" thick steel.
That should clarify pricing and operating cost of plasma! Now how does it compare to laser?
Typical rule of thumb: Laser cutting is more productive and more accurate on carbon steel thinner than 3/16", High Definition plasma starts to get more productive above 3/16", and at about 3/8" (with True Hole) becomes very similar to the accuracy of plate lasers. but with higher productivity and lower cost per foot/part.
Other plasma advantages...lower cost, easier maintenance. Easy to use operate, the newest plasma cnc systems require virtually no operator training, with all of the normal operator inputs being set automatically by the CAM software....the operator loads plate on the table, positions the torch, pushes the start button, unloads the cut parts.
If I was looking at cutting a lot of 1/2" carbon steel and needed to choose the best process.....I would first look at my needs in terms of cut part accuracy. Laser will be slightly better at this thickness range...but perhaps plasma is good enough. I would look at Capital equipment cost (plasma will win hands down) and operating cost. Plasma, in this thickness range will produce more parts than laser at slightly looser tolerances, at a dramatically lower cost.
Hopefully this keeps the discussion on this thread going! Couple of pics of typical High Definition class plasma cuts attached. Also wanted to mention one thing....Hypertherm will be demonstrating some new laser technology at the Fabtech show in November, it will be a Fiber Laser.....which is a 1/2" capacity plate laser that can be mounted on a conventional cnc cutting machine...similar to a precision plasma cutting machine. We will demonstrate it side by side with one of our HPRxd (True Hole Enabled) plasma systems for a good comparison!
best regards, Jim Colt Hypertherm
