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

Electro erosive machining Material removing by electro erosive machining becoming as a result of electric discharging between electrodes dipping in liquid dielectric. There is used short impulses generated by suitable generator. Marks after electro erosion machining have they crater shape. Size and crater shape depend from quantities of brined energy and discharge duration. Crater shape and them size strongly influence to final surface roughness at machining and dimension accuracy.

Electro erosive machining Electro erosive machining is used at following cases: Complex or irregular workpiece shape, Holes with small diameter, Holes with big big ratio depths to diameter, Numbers small holes, Narrow slots and other. Hardly machined material (high hardness, stronghold and fragility). Working cycle consists of: Discharge, Released energy thermal action, Eroded material removing.

Electro errossion Between electrodes is become the electric discharge, located place is fast heated (melted and particularly evaporated). By metal steams pressure is melted metal springed and become crater. Local temperature on the electrode surface can be higher than °C. Thermal heat till W/m 2. Process is going along bubbles origin in dielectric.

Electro errossion

Electro erosive machining Like this machined surface is resisted against abrasion – microgeometry (craters) is more suitable to origin and defensibility to lubricant film. Roughness of machined surface is in the interval R a 0,2 till R a 6. Dimension accuracy is in the interval 0,02 až 0,002 mm.

Electric discharges we can divide into: Sparkle discharges – are characterized by short impulse period (interval between generator connection and disconnection it = till sec), at high discharging frequency. Non-stationary arched discharges – are characterized by lengthy impulse period (more than 10-4S), at lower discharging frequency. Into discharging canal dominate

Kinds of electro erosive machining Electrospark machining, Electroimpuls machining, Electrocontact machining, Anodomechanic machining, Common attribute are:  Liquid dielectric between electrodes,  Short-time impulse bringing and discharging generation at machining area, surface destroys by excited impulse.

Electrospark machining Workpiece is anode, Tool is cathode, Electrons are not in the contact, Liquid dielectricum helped the ionisation and flowed out eroded metal, Example: Wire cutting, Electrospark deeping,

Electro impuls machining utilize suitable shape and time path arc discharge, Tool is anode (positive pole), Workpiece is cathode (negative pole), Independence impulse generator (frequency, amplitude, times of impulses are not depend on the time of machining and on state of erosive gap) Big removing, worse accuracy and roughness of the surface, Snagging processing,

Electro contact machining Resistive melting of material (contact between electrodes), Low frequency of asymmetric impulses (50 – 500 Hz), Tool is rotated circle electrode, Dimension and shape accuracy is low, Big performance

Anodo mechanic machining Combination of the electro mechanic and electro erosive machining, Material removing is assured by electric discharges and by electrolysis, Tool is steel circle, waist or wire and it is cathode, Workpiece is anode,

Wire cutting Kind os electro spark machining. Tool is thin (0,02 – 0,3 mm) metal wire calibrated in diamantes die plate. Into workpiece is needed to make the hole through that is put into the wire (tool). During cutting the wire is rewinded between two reels to eliminated his vearing. Tool can removed material in every direction. Thick wires are brass, Cu, steel and thin wires (under 0,1mm) Mo, W.

Wire cutting

Speed of the cutting to 300 mm 2 /min, accuracy 0,005 till 0,01 mm, Achieved roughness R a 0,8 till 3,2 Usage:  Complex through holes making e.g. shear tool, template and other.  Exact electro-spark grinding of fine needle by wired electrode (longitudinal precision approximately 30 µM, diameter precision approximately 1 µM)  Exact shaping abrasive disk dressing,  Holes production into very hard conductible material,  Very hard conductible material cutting.

Wire cutting

Čelné otváranie dverý Väčší upínací stôl Lahká výmena filtrov Rýchle napustenie vane

Wire cutting

Wire cutting – component examples

Electro spark deeping as tool is the sharpening electrode, Hollow copies the shape electrode, Removing is depend on frequency and on electricity parameters, By increasing of voltage is the removing increased too or decreased accuracy, Tool is wearing and that is why it made in the sets, Gap between tool and workpiece must to make possible flowing out eroded material,

Electro spark deeping

Electro spark deeping – usage examples

Electro spark deeping – tool electrode Connected to negative pole. Can be produced of several materials:  Aluminium and his alloys – apply to roughing holes machining in steel and in sintered carbide,  Copper and its alloys – exact finishing cuts in steel part, it's good resistant to erosive wear uses carbide machining,  Copper – graphite composition (pressed graphite, lead and copper dust) – used at cast iron machining and creep-resisting alloy machining,  Graphite – uses to steel machining,

Electro erosive machining - dielectric Requests of dielectric and to his function: Flowing out erosion products, Cooling of the electrodes, Assured electric section between electrodes, Fast reconstruction of isolation after discharge (low viscosity, good wettability), To limited corrosion origin, Chemical stability and cheap, High temperature of the ignition.

Electro erosive machining - dielectric Most usage dielectric: petroleum, Transform oil, Silicon oil, Water glass, Kaolin emulsion, Salt solution, Distilled water

Electro erosive machining – flowing of dielectric By flow of working fluid we know:  External washing out – simplest method, inept to deep cavity deepening,  Internal washing out – working liquid is carried by hole in electrode directly to discharging place. Gets worse shape accuracy, suction washing out – achieving high shape accuracy.  Pulsing washing out

Electro erosive machining – flowing of dielectric

Machine tools for electro erosive machining Main parts:  Frame of machine – are whereon located others parts, must keep sufficient rigidity and precision,  Working head with guide on frame,  Worktable for workpiece clamping in container with dielectric fluid,  Dielectric filtration, cooling and distribution system,  Electric pulse generator

Machine tools for electro erosive machining Construction of the machine is portal or rack. Electro erosive deeping machines can be integrated into automatic lines. Speed of material removing is 200 till 700 mm 3 /min. Machines for wire cutting have automatic drilling of holes initial, automatic putting in of the cutting wire as the regulation of that tension. They can cutting material to thickness 300 mm, in speed to 300 mm 2 /min.