Machine Tools And Devices For Special Technologies Plasma machining Slovak University of Technology Faculty of Material Science and Technology in Trnava.

Machine Tools And Devices For Special Technologies

Plasma machining

Slovak University of TechnologyFaculty of Material Science and Technology in Trnava

Processing by plasma

Plasma is considering like fourth state of substance,

Plasma is high ionised gas: Free electrons, Positive electrons, Neutral atoms,

Plasma is electric conductive: Partly ionised (10 – 15 000 °C), Completely ionised (around 100 000°C)

Properties of plasma

Electric conductivity,

Final electric charge = 0,

Movement of elements is possible to directed by magnetic field,

Plasma is possible to stop by magnetic „wall“ possible to cover in magnetic container

Becoming of plasma

Nuclear reaction,

Electron beam

Electric charbe.

In technical praxis has meaning only plasma originated by electric charge.

Plasma origin

Voltage between electrodes – ionisation of gas between electrodes – electric charge,

Charge can: Turn off, Glow discharge, Permanent arc discharge

We need permanent arc discharge.

Permanent arc discharge

Arc discharge is needed to stabilise by cooling.

Stabilisation: By shape of jet of plasma burner, By flowing gas, By water,

In intensity cooling is diameter of arc smaller and his temperature is higher.

Temperature of plasma arc

Temperature depend on using plasma gas.

nitride – round 7 000 °C

helium – round 20 000 °C

Sing of plasma for metal processing

cutting, welding, Coating of surface layers, Hard surfacing, Machining.

Cutting by plasma

Cutted metal is melted by high temperature of plasma arc and is blowing out by plasma gas.

Plasma is created: Water, Mixture of gases (most often Ar, H

2),

Mixture water and gas

Plasma cutting – stability of plasma beamStability of plasma beam is

achieved by stabilisation gas.

Depended arc – cut material is anode. It secure asked stability in small flash of gas too.

Plasma cutting – materials

Aluminium – soft cutting of surface, stabilisation by water, thickness of cutting till 100 mm.

Copper – cutting is difficult, with thickness above 25 mm the material is taking up to the bottom part.

Austenitic steels – soft cutting surface, thickness till 100 mm.

Beams of plates – needed is to strong constringe because they are welded.

Deposition of surface layers by plasma

Material is heated fast and partially is melted.

By high speed (above 200 m/sec) is shed to support.

Here is used independence arc.

Deposition of surface layers by plasmaThese coats increased resistance of base material

against:

High temperatures, Oxidation and corrosion in high temperatures too, Thermal fatigue, Mechanical wear by erosion and abrasion.

Deposition of surface layers by plasmaSize of the powder grain is necessary to adapt to

power of burner. Big grains are not melted and small can steamed.

High temperature of plasma aided these chemical reactions:

oxidation – safety by inert gas, reduction – safety by inert gas, Thermal reduction – short staying in burner,

high speed of plasma flow.

Deposition of surface layers by plasma

Sprayed coat is porous. Porous can be till 15%, size of poruses 20 – 200 μm.

Melted elements gain spherical shape.

When they are more melted and when the speed of their impact is higher then the structure of coat is denser.

Deposition of surface layers by plasmaAdhesion is decreased with thickness of coating.

The layers are thick 0,1 till 2 mm.

In thick coatings is several layers – increased inside strain, layers leafing.

Plasma welding

High stabile welding process, Fine forming of weld, mainly weld root, Welding without supporting of weld root till 10 mm

of thickness, It is not become blowing out of welding pool, Jet has very small section, Only 10 – 30% of plasma gas is plasma,

remainder stabilised and positioning arc, Arc is burning by high frequency

Plasma welding

Plasma gas is mixture Ar + H2, Ar + He, or clean Ar.

Safety gas is usually Ar.

Advantages: Simply preparation of connection, Good formation of weld, Possibility of process mechanisation, High productivity.

Plasma welding

Plasma welding is used for: Connecting of plates with small and medium

thicknesses – one layer weld (steel plates to 6 mm, without adjusting of rims),

Welding of chrome-nickel steels, Welding of Ti and his alloys, Welding of copper and her alloys, Welding of aluminium and his alloys, Welding of nickel and his alloys, Micro plasma welding – thin plates and wires

Plasma hard surfacing

Powder additional (hard surfacing) material – is not possible to do the wire of these material.

Temperature of plasma arc till to 30 000K.

Output speed of plasma gas more than 1000 m/sec.

Base material is melted and become metallurgic mixturing with liquid additional material.

Is needed to use preheating of the base material.

Plasma hard surfacing

Plasma hard surfacing – MIG

Additional material is a wire that is one electrode and next is second (W, Cu) cooling electrode.

Arc burning between electrodes melting hard surfacing additional material.

Plasma machining

Machined material is melted and evaporated.

Plasma gas is N2, H

2, Ar, air and their

mixture.

Thermal inluenced area under 1 mm.

Surface quality and accuracy answered like roughing.

It is used for hard machining steels, coppers, aluminium and etc.

Plasma machining

High rate of removing (10 x more than in classical machining of heat-resisting steels).

Here is originated smoke, dust, UV emission – cutting under the water.

Machining by straight plasma beam

Machining by additional plasma beam

Devices for plasma beam processingDevices have next main parts:

Source of electric energy – insuring the electric energy for burning of arc,

High frequency ionisator – burn on the arc, Direct box – directed all process, Plasma burner, Container of plasma gases – get to burner the

plasma gas.

Plasma burner

Plasma burner is cooling by cooling liquid (water), jet must by strip the insulation from other parts.

Function of burner: Input of electricity to electrode, Input of plasma, focusation and safety gas, Shaping and directing of arc, Positioning of electrodes.

Plasma burner

Construction of plasma burners: With gas stabilisation, With jetting of water.

Part where is the plasma originated - plasmatron.

Dividing of plasmatrons: transfer (with transport of arc), notransfer (without transport of arc), combinated

Burner with gas stabilisation

Burner with water jetting

No transfer and transfer plasmatron

Plasma hard surfacing automat

Plasma cutting machine tool

Plasma cutting machine tool

Plasma cutting machine tool