• what kind of steel we need to cut
• quality of edge along cut path, distortion, chemical pollution of the edges and geometry of edges.
• cutting line lenght and the complexity degree of shapes of the products
• production approach: manual operator, mechanical or automated process
• maintanace cost: availability and price of service, price of spare parts and it’s durability.

• electric current [A]
• arch currency [V]
• speed of cutting [mpm}
• pressure of gas [MPa] and the flow pressure [lpm]
• construction of an Electrode
• radius of jet nozzle
• position of gas burner relative to cutted sheet of steel

On case of plasma cutting operated by hand the worker decides only about a speed of cutting and the jet distance to the cutted object. Remaining parameters are constant and maintained by driver unit working on preconfigured settings. Electric currency is the key factor which decides about temperature and power of resultant plasma arch. When we inceare electric currency we can achieve faster cutting velocity and we are able to cut thicker steel sheets, but the stability of electrodes lasts shorter. To strong electric currency results in worse quality of cutting and widening of the slit. On the sides can also appear some round edges and warped perpendicularity. If the currency is to weak cutting can fail or give some unnecessary metal sludge in lower parts.
Another parameter which is vital for steel cutting process is a voltage of electric arch and it requires to be provided precisely by computer numerical control (CNC). Because of highly condensed plasma in the arch it voltage have to equal values close to 50 ÷ 200 V. The source of an electric currency needs to give an output about 150 ÷ 400 V on the idle gear. Thanks to high heat energy or plasma arch we can achieve wide range of cutting speeds. The speed of cutting inevitably decides about quality of final workmanship especially in manual operating mode. Obviously, for this kind of relations like speed on the one hand and the quality on the other they correlate in inverse proportionality (but not linear).
To quick movement of cutting header the power of beam is to weak to properly affect cutted area. The space between divided parts decreases till the moment when plasma doesn’t make it’s way through steel sheet and leaving melted steel layer on the bottom which is perplexingly difficult to polish or to get rid off. In consequence when plasma cutting velocity is to low, plasma beam operates to long in one point, burned hole and aperture on both sides of cutted edge becames wider. The edge also diverges from the orthogonal angle of beam, upper side of metal round-offs and the down side sometimes cover with melted steel debris. Plasma jet velocity exhaust from header and it’s temperature comes from combination of following: electric currency, the shape of propelling nozzle, it’s diameter, distance from cutted surface, gas used for creating plasma and the pressure of that gas. The kind of gas has to be matched up with kind of cutted material to get optimal results. Most widely used gases are oxygen, nitrogen, air, argon and combinations of hydrogen with argon or nitrogen. Because of high price of argon, which served for first plasma cutters the technology developers aimed to incorporate different (and cheaper) gasses to make cutting steel by plasma more efficient and affordable.

Todays plasma technologies allow to attain requirements for best quality products and high speed of steel machining. It also saves energy costs. In future we predict that plasma cutting steel technology still will be in good shape in comparison for it’s main competitor like laser steel cutting technology.

• Drilling to 10 cm
• Tapping to 5 cm
• Boring to 20 cm
• Marking
• Plasma Cutting
• Flame Cutting
• Bevel cutting by flame and plasma
• ATC 24 (Automatic Tool Changer) mounted on the carriage
• This machine features a 48 HP / 36kW (1 minute peak) spindle with a CAT 50 taper.

Further informations:
Floor mounted rails for long axis with linear bearing guides and full protection
Personal Computer Controlled with a convenient touch screen
Control Based Dual 32 bit processors, Windows TM
Interface 15″ LCD Glass Faced Touch Screen
Fiber optic link to office network
Extra heavy duty machine design to accommodate machining forces generated by spindle
Four lifter stations in addition to the spindle fitted to the carriage to accommodate up to four independent tools
Machine manufactured from standard components
Dual Rack and pinion drives for long axis to precision hardened and ground helical rack
Precision plasma torches such as the Hypertherm HPR130 and Hypertherm HPR26 or the heavy duty Hypertherm HT4400
Plasma bevel cutting and flame bevel cutting is optional
Other tooling such as gas torches
Marking systems such as ink jet, plasma marking or powder marking
Traverse Speed 20 m/min
Machine accuracy +/- 0.15mm/m
Guiding System Linear bearings on all axes
Drive AC Servo (dual X)
Drive System X & Y Rack and Pinion
Vertical Drives Programmable ball – screw
Maximum tools on main carriage Spindle plus capacity for four lifters
Cutting Widths 2.6 to 6.3m, Other widths also available
Cutting Lengths 6.3 to 50m
Optional Cutting Heads

Oxidization and edge dirtness are not a marketable effect. This quality level depends of type of gas used and kind of steel cutted. For usual stainless steel it is enough to polish 0.5 milimeter deep to remove all the area affected with the heat from the surface. Settling the process of cutting under the water allows to significant oxidization decrease and speeds up the cutting itself. If we compare classic, mechanic way for steel cutting by saw to plasma cutting, we loose less material if we use axe. More, the angle of cutted edge needs to be allowed for further processing to develop a perfect one. If we don’t take it within process of polishing overheated area, we need to add another steep into all production way.

As mentioned before, the plasma cutting process is based on melting down the steel and throwing out it debris with high density electric arch of plasma, which burns between infusibility electrodes and cutted object. Infusible electrode is made of copper with zirconium plate (or hafnium) and needs very intense colling down by air or water. The temperature of plasma stream depends of electric currency, arch narrowness degree and also a kind and ingredients of plasmatic gas.
For steel cutting are used only gas burners with iron arch. The spark on arch is obtained by high voltage electric impulse or by high frequency current. This makes possible to cut every conducting material (cast iron, steel, cuprum, aluminium etc.). Nonmetalic materials can be cutted only with plasma torches based on independent arch.

will be continued…

We can distinct the two groups of plasma when comparing a temperature.

• cold plasma, which is created in plasmatrons – temperature range: 4000 to 30,000 K
• hot plasma, found in the stars and nuclear fusions – above 30,000 K

When the electricity is conducted within the plasma cell, which has very high conductivity property, it has to pass the double layer. This is where almost all voltage potential is dropped. When we look closer to the plasma and electrical currency, we differ a three states:

1. very low electrical currency – no visible effects
2. moderate electrical currency – the visible light appears
3. electrical currency exeeds a given treshold – electric arc forms

The third one is the one we are interested especially when it comes to steel cutting. Steel cutting by plasma precisely. The electric arc allows to cut all electrically conductive materials and it is widely used in the industry in the mid of the previous century. Development of technology and electronics esteblished it in the steel machining world and deployed a strong competitor for the other cutting methods, like laser cutting steel for example. We will continue the topic in the next article.

Plasma cutting machines are dedicated for manual and automated handling. Plasma and air jumble is useful with cutting electrical conducting parts made of steel, alloys, aluminium and it’s alloys, coppers, brasses and even a cast iron. Plasma cutting machines shows it’s versatile also when it comes to different enviromental conditions allowing to cut deep underwater for example. Coeval plasma machines are usually instant ready to use and with special accesories can cut in places with limited access for the other tools.

The main advantages for plasma machines:

• high speed of cutting
• cutting without overheating – quick nailing
• small influence in the area of cutting on the steel
• narrow slit
• allows to cut without overburning thin fabrics.

And here comes some disadventages:

• loud work noise
• strong radiation
• much of exhausts – gases and fumes
• Some structure degeneration in cutting area
• perpendicular keeping is sometimes difficult.

Let’s see and listen some example: