EDM machine wire, electrode and machining fluid care

⚙Care and inspection

• Remove brass powder and dirt regularlyWire guide (diamond guide)

  Remove it about every 50 machining hours and soak it in a diluted industrial acid solution or wash it in an ultrasonic cleaner

  Brass chips, brass powder and dirt build up around the diamond part. The clearance between guide and wire greatly affects machining accuracy. Sodick estimates the life of a diamond guide at roughly 4,000 hours in straight cutting (depending on the machining)^[1][2](1 source, for reference)

• Fit a guide of the specified diameter, and fit it verticallyWire guide (diamond guide)

  Use the guide diameter specified by the machine manufacturer. Wash it with a degreasing cleaner or similar and wipe it dry, then fit it with the screws adjusted so that it sits vertical

  The clearance between guide and wire greatly affects machining accuracy^[1](1 source, for reference)

• Index the contact to a new position and clean itPower feed contact (energizer)

  Shift the position where the wire touches, following the machine manufacturer's procedure. Makino machines are built so that the position can be changed quickly without tools

  The power feed contact carries the machining current to the wire, and re-positioning it keeps machining in good condition^[3](1 source, for reference)

• Decide the replacement time by pressureMachining fluid filter

  Replace it when the filter pressure gauge exceeds the specified pressure (Sodick: roughly 0.2 MPa). Many filters for EDM machines have a filtration rating of about 3–5 µm (MANN+HUMMEL's main products)

  The filter separates the sludge produced by machining from the machining fluid. Clogging degrades fluid quality and affects accuracy and surface roughness. Mitsubishi Electric switches the flow through the filter between roughing and finishing to extend filter life (up to 45% lower running cost than its previous model). The new model estimates how clogged the filter is and optimizes pump output^{[1][4][5][6][7]}

• Decide the replacement time by how well the resistivity recoversIon-exchange resin

  Judge the resin's life by the decline of its ion-exchange capacity. Sodick recommends replacing it when resistivity falls below 50,000 Ω in typical metal machining. The resin maker Sunresin says wire EDM water needs a conductivity below 20 µS/cm

  It removes excess ions and keeps the water conductivity constant. The higher the resistivity is held (the lower the conductivity), the faster the resin is used up. Mitsubishi Electric says that lowering conductivity (raising resistivity) extends resin life but worsens surface roughness, and that improved power supply control cut resin running cost by up to 25% (MV series). Wire, filters and resin account for about 80% of running cost^[1][8][6]

• Drain and dispose of the water from a spent resin containerIon-exchange resin

  Turn the container upside down to drain the water. Treat the drained water as industrial wastewater, in the way set by the local authority

  The ion-exchanged water in the container must be handled as wastewater^[1](1 source, for reference)

• Prevent rust on the workpiece and machineMachining fluid (water)

  Do not raise the water conductivity more than necessary. Rust countermeasures include a bipolar power supply circuit, sacrificial electrodes, additives and removal of machining debris. Another method is to pass the water through ion-exchange resin that has anticorrosive ions fixed to it (Iwate University)

  Iron corrodes even in low-conductivity water (about 10 µS/cm). Corrosion progresses through minute current flow between the electrode and the workpiece, and through contact between dissimilar metals^[4][9]

• Choose a wire to suit the machiningWire electrode

  For general metal machining, brass wire (copper and zinc at 65/35 or 60/40). For speed, zinc-coated wire; for fine work under φ0.10 mm, piano-wire-coated wire or tungsten wire

  The wire material and construction change how the discharge occurs. Poor roundness of the wire increases waviness on the machined surface (OKI Electric Cable improved waviness by about 30% with a wire of higher roundness)^[1][10]

• Sort used wire and send it for collectionWire electrode

  Brass wire whose main components are copper and zinc is accepted for collection regardless of manufacturer (Sodick's collection program). Do not mix in special wires such as steel or tungsten

  It cannot be collected unless sorted^[1](1 source, for reference)

• After use, wash and apply rust-preventive oilWorkholding fixtures (pallets, vises)

  After every use, remove the machining sludge with a degreasing cleaner or similar, then apply rust-preventive oil

  Fixtures used underwater lose accuracy from sludge and rust^[1](1 source, for reference)

• Monitor deterioration and loss, and handle top-up and waste oil properlyEDM oil

  Top up what has been lost (some manufacturers sell a top-up oil that allows for the additives left behind when the oil evaporates). Dispose of used oil as industrial waste (waste oil)

  Synthetic oils, which resist oxidation, deteriorate and discolor less and last longer, but loss and contamination still progress with use. A case is cited where, after switching from a water-soluble to an oil-based fluid, the viscosity rose, the discharge flow dropped, the fluid level fell and a fire started. When changing oils, recheck the fluid level and circulation^[1][11][12]

• Keep the container tightly closed and store it in a cool, well-ventilated placeEDM oil

  Keep out of direct sunlight and store in a cool, well-ventilated place. Always put the cap back on a container once opened. Keep away from heat, sparks and open flame

  It is a flammable liquid (Class 4 hazardous material under Japan's Fire Service Act). Slight cloudiness or precipitate in cold weather is said not to interfere with use^{[11][13][14][15]}

• Choose an electrode material to suit the machiningTool electrode (copper, graphite, etc.)

  Copper: low resistance and good heat conduction, low wear and suited to mirror finishes, but low rigidity and prone to burrs and warping. Graphite: easy to machine, heat resistant and low wear, so suited to large-area, roughing and high-speed work. Copper tungsten: for machining cemented carbide and fine work. Silver tungsten: good machinability but expensive

  The choice of electrode material changes machining speed, wear and surface roughness greatly. Graphite properties differ by manufacturing method and grain size, and there are many grades^[4][16]

• Measure and manage electrode wearTool electrode (copper, graphite, etc.)

  Look at the electrode wear ratio = electrode wear amount ÷ workpiece removal amount (by weight, etc.). There are 4 kinds of wear: volume, corner, end face and side face, and corner wear decides the shape of the finished form

  Wear directly affects the finished dimensions and shape. When conditions are set up properly with an oil-based fluid, a carbon film forms on the electrode surface and the wear ratio falls to 1% or less (no-wear machining). It does not occur in pure water^[4][16]

• Check the electrode dimensions and damage before mountingTool electrode (copper, graphite, etc.)

  Check that it was made to the undersize allowance that accounts for the spark gap, and that it has no burrs or dents. Mount it securely

  The undersize allowance directly affects the machined dimensions. Poor mounting causes abnormal discharge^[4][12]

• Choose the pipe electrode to suit the hole diameterPipe electrode

  Pipe electrodes for small-hole drilling are about φ0.08–6.0 mm in outside diameter (Sodick). The hole comes out roughly 0.1–0.3 mm larger than the electrode (for example, about φ1.0 mm with a φ0.8 mm electrode). At φ0.1 mm or less the electrode needs strength, so brass is sometimes used

  The hole is widened by the spark gap. With thin electrodes, the material changes machining characteristics (the Iwate Industrial Technology Center checked the difference between copper and brass)^[1][17]

• Keep the electrode tip from jamming in the guideElectrode guide (anti-runout guide)

  Set the motion sequence so the guide is withdrawn together with the electrode, so that the shortened electrode tip is not pulled up into the guide. Start machining with weak electrical conditions and raise the guide after the electrode has advanced a certain amount

  Carbon builds up on the electrode tip and thickens it, and when the shortened tip enters the guide it jams and cannot pass downward^[18](1 source, for reference)

▦Guideline resistivity and conductivity of wire EDM machining fluid (water) (values from published sources)

Resistivity (Ω·cm) and conductivity (S/cm) are reciprocals. Sodick's FAQ writes the unit as "Ω", but here it was converted as resistivity (Ω·cm). Actual set values depend on the machine, machining conditions and material, so follow the machine's instruction manual^{[19][9][1][8]}

÷Converting between resistivity and conductivity, and temperature correction

1. From resistivity ρ (Ω·cm) to conductivity κ (µS/cm): κ = 1,000,000 ÷ ρ
2. From conductivity to resistivity: ρ = 1,000,000 ÷ κ (÷1,000 for kΩ·cm, ÷1,000,000 for MΩ·cm)
3. Water conductivity changes with temperature. To convert to 25 °C: κ25 = κT ÷ (1 + 0.01 × α × (T − 25)). α is the temperature coefficient (%/°C), and is around 2 for most aqueous solutions
4. When comparing, compare values converted to the same reference temperature (normally 25 °C)

Conversion

Conductivity (µS/cm) = 1,000,000 ÷ resistivity (Ω·cm)

Temperature compensation (HORIBA's approximation)

C(T) = C(25) × (1 + 0.01 × α × (T − 25)). α ranges from 0.5 to 2.5, and using 2% covers most aqueous solutions

Worked example: conditions

Water with a resistivity of 50,000 Ω·cm; and water that read a conductivity of 24 µS/cm at 30 °C

Worked example: result

50,000 Ω·cm = 20 µS/cm. Converting 24 µS/cm at 30 °C to 25 °C with α = 2 gives 24 ÷ 1.10 ≈ 21.8 µS/cm (about 46,000 Ω·cm as resistivity) (calculated estimate)

HORIBA says a different temperature compensation (pure water compensation) applies near the pure water range. The 2% approximation is a guideline; check the instruction manual to see which compensation the machine's resistivity meter uses^[20][1][9]

▦Typical properties of EDM oils (from manufacturers' product data)

Values are typical properties, not guaranteed values. Flash points vary with the test method (PM = Pensky-Martens closed cup, COC = Cleveland open cup), so do not simply compare values from different methods. Class 3 petroleum has a flash point of 70 °C or more and under 200 °C; Class 4 petroleum, 200 °C or more and under 250 °C (Fire Service Act, Appended Table 1, notes). The Daphne Cut HL-25 data sheet gives no class, and its flash point of 87 °C falls within the Class 3 range^{[11][21][13][22][23][15][24][25][14][26]}

÷EDM oil quantity and the designated quantity under the Fire Service Act (calculating the multiple)

1. The quantity of hazardous material handled by an EDM machine is judged by the capacity of the machining fluid tank (before operation, all of the machining fluid is in the tank)
2. Check the oil's class in the product data: for Class 4, Class 3 petroleum (water-insoluble) the designated quantity is 2,000 L; for Class 4 petroleum, 6,000 L
3. Multiple of designated quantity = quantity ÷ designated quantity. When hazardous materials with different names or designated quantities are handled in the same place, add up the multiples for each
4. If the multiple is 1 or more, it can be handled only in a facility licensed under the Fire Service Act (such as a general handling facility). From 1/5 (0.2) up to under 1, it counts as a small quantity of hazardous material and falls under the municipal ordinance's standards and notification. Even below 0.2, the ordinance's standards for EDM machines themselves (safety devices, automatic fire extinguishing system, etc.) still apply

Multiple

Multiple of designated quantity = Σ (quantity of each hazardous material ÷ its designated quantity)

Class 3 petroleum (water-insoluble)

Designated quantity 2,000 L (1/5 is 400 L)

Class 4 petroleum

Designated quantity 6,000 L (1/5 is 1,200 L)

Worked example: conditions

Class 3 petroleum EDM oil used in one die-sinking EDM machine with a 600 L tank. There is also 200 L of spare oil (same class) in the same place

Worked example: result

(600 + 200) ÷ 2,000 = 0.4. Being 0.2 or more and under 1, it counts as a small quantity of hazardous material, and the ordinance's standards and notification are required (calculated estimate)

ENEOS's product data says for Class 3 petroleum that "up to 2,000 L can be stored following the standards of the municipal ordinance (no regulation up to 400 L)". The Hazardous Materials Safety Techniques Association's standard also covers EDM machines that use less than 400 L. Make the final decision by checking with the local fire department^{[27][26][11][28][29][12]}

▦Quantity of extinguishing agent required for an EDM machine's automatic fire extinguishing system (per 1 m² of maximum protected area)

The Hazardous Materials Safety Techniques Association's "Standard for fire prevention of EDM machines" (the same table appears in the Sapporo City Fire Department's explanation). Mechanical foam (aqueous film-forming) was added in the 2016 review after fire tests^[29][12]

÷Calculating the maximum protected area and agent quantity of an automatic fire extinguishing system

1. Measure the 2 sides of the (rectangular) machining tank: a (long side) and b (short side)
2. If a ÷ b is 2 or less, the maximum protected area S = a × b
3. If a ÷ b exceeds 2, use a rectangle whose short side is a ÷ 2: S = a × (a ÷ 2)
4. Required agent quantity = S × the quantity in the table (for each type of agent)

Maximum protected area

S = a × b (a/b ≤ 2), S = a × a/2 (a/b > 2)

Agent quantity

Required quantity = S × quantity per unit area (e.g. aqueous film-forming foam 5.0 L/m², Type 3 powder 4.0 kg/m²)

Worked example: conditions

Machining tank inside dimensions 1.0 m × 0.6 m, aqueous film-forming foam system

Worked example: result

1.0 ÷ 0.6 ≈ 1.7 (2 or less), so S = 0.6 m² and the required quantity = 0.6 × 5.0 = 3.0 L or more (calculated estimate)

The maximum protected area means the exposed surface area of the machining fluid in the tank. The system carries markings such as the type and quantity of agent, maximum protected area, discharge time, and the type and operating temperature of the detector. Check with the system manufacturer or machine manufacturer that it has the capacity the markings state^[29][12]