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Sinker EDM: Process, Materials, and Applications

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    Non-traditional machining processes, such as sinker EDM, excel in scenarios demanding extreme precision. Unlike traditional mechanical cutting that can induce stress and alter material properties, these methods utilize other forms of energy, like electricity, for material shaping and removal.

    This article explains one such non-traditional process called die sinking EDM. We will go through the variety of materials it can machine, and its applications across various industry sectors.

    What’s Sinker EDM Machining?

    what is sinker edm machining
    what is sinker edm machining

    Sinker EDM is a type of Electric Discharge Machining (EDM) process for creating extremely precise blind cavities through an electric spark in conductive materials.

    A custom electrode sinks into a dielectric liquid and moves close workpiece but doesn’t make contact with it. As a high voltage is applied, a series of electric sparks between the electrode and workpiece start within that narrow gap. They cause material erosion due to intense localized heat generated by sparks.

    Sinker Electrical Discharge Machining, also known as ram EDM, cavity EDM, volume EDM, or plunge EDM, primarily serves in creating precise plastic injection molds, various dies, and delicate parts. These applications particularly benefit from Sinker EDM due to their inability to withstand the stress from conventional cutting forces. This technology is crucial in manufacturing industries that demand high precision and delicacy.

    How Does a Sinker EDM Machine Work?

    The sinker EDM machine uses the principle of spark erosion to remove metal from a workpiece. These key components facilitate the process:

    ComponentFunction
    Power SupplySupplies high-frequency pulsated current
    ServomechanismActuators that maintain the gap between the electrode and the workpiece.
    Dielectric FluidIt acts as an insulator and creates a path for each discharge.
    Electrode (Tool)It shapes the work surface. Often copper or graphite
    WorkpieceThe material being machined needs to be conductive.
    Dielectric Oil ReservoirHouses the dielectric fluid (hydrocarbon oil, deionized water, or kerosene )
    Pump and Filter System Circulates and cleans the dielectric fluid.
    Chiller System Controls the temperature of the oil to prevent expansion.

    The Process and Its Initial Steps

    The process begins by dipping the workpiece in the dielectric fluid tank, which has a recirculation and filtration system. A servomechanism holds the CNC-shaped, custom tool, which is a positive image of the cavity. It carefully dips the tool in the fluid and consistently maintains a very thin gap between the tool and the workpiece, ensuring precise machining The tool’s motion could be horizontal, vertical, or at any angle, based on the design requirements.

    sink edm process
    Source from: EngineeringClicks

    The electrode and the workpiece are charged oppositely, either positive or negative. The dielectric fluid is an insulator. However, when we supply a high voltage across the dielectric fluid dionizes and creates a path for electric discharge.

    This discharge happens at the point where the electrode and the workpiece are closest. The region of discharge gets extremely hot, reaching over 8000℃. This causes a small portion of the work surface to melt and vaporize. The material is flushed away by the flowing dielectric, creating a cavity in the workpiece that mirrors the shape of the electrode.

    basic diagram of die sinker edm process
    basic diagram of die sinker edm process

    Overcut, Tool Wear, and Material Removal Rate in EDM

    In plunge EDM, you witness an overcut. It is a measure of how much the machined cavity in the workpiece exceeds the size of the electrode. It occurs because the discharge and material erosion process also take place along the sides of the tool. However, it’s very minimal (hundredths of a millimeter) and well-accounted for during the tool design.

    Tool wear is an inherent part of the EDM process. The high temperatures that melt the workpiece also wear the electrode but slightly. This electrode wear is measured as the ratio of work material removed to tool material removed. Graphite is a top choice for sinker EDM electrodes due to its exceptional heat and wear resistance.

    The material removal rate in EDM is controlled by two parameters: discharge current and frequency. Higher discharge current and frequency lead to higher cutting rates. For optimal surface finish, use higher frequency and low discharge current. Mathematically, RMR is a function of current and material’s melting point.  

    RMR(mm³/s)=K×I/Tm

    Where k is the constant of proportionality, with a value of 664 in SI units, I is the supplied current and Tm is the melting point of the workpiece.

    Benefits and Limitations of Sinker EDM Machining

    Electric Discharge machining is a widely used non-conventional process, especially for high-precision jobs where the delicacy of the workpiece is a concern. Key benefits include

    High Precision

    The first highlight of the process is extreme accuracy and precision. It achieves this precision through controlled spark cutting, with tolerances as low as 0.0001 inches (0.00254 mm).

    Ideal for Complex Blind Cavities

    CNC sinker EDM is ideal for creating blind holes and cavities in irregular shapes. It utilizes custom-designed tools shaped like the cavity, which makes machining complex designs possible that would have been challenging to create with conventional machining. It also allows for hole drilling at acute angles to the surface, where conventional drills would struggle.

    Non-Contact Process with No-Mechanical Force

    Since the electrode never touches the workpieces, no mechanical forces act on the material. This aspect is particularly beneficial for delicate parts that cannot withstand the stress of conventional cutting forces.

    Apart from multiple advantages, the die sinking process does have some limitations:

    High-Operational Cost

    The electric discharge consumes a significant amount of electricity. Additionally, the need to create new custom tools for each unique job adds to the cost. These factors collectively make this process’s operational costs higher than other machining processes.

    Only works on Conductive Materials

    EDM machining is restricted to electrically conductive materials for spark generation. So, non-conductive materials, such as plastics, cannot be machined using this method.

    Materials Ideal for Sinker EDM

    sinker edm electrode
    sinker edm electrode

    In EDM, you select material for two components: electrode and workpiece. The electrode needs to have high strength, temperature, and wear resistance. The common options are:

    Graphite: The most preferred choice for electrodes due to its high strength, temperature, and wear resistance. Offers a cleaning action at low speeds and is cost-effective.

    Brass: An alloy of copper and zinc, used for EDM wire and small tubular electrodes. Easier to machine than copper or tungsten but offers less wear resistance.

    Copper and Copper Alloys: Better wear resistance than brass and highly conductive. More challenging to machine and more expensive than graphite.  Commonly used for machining tungsten carbide or fine finish applications.

    Molybdenum: Has high tensile strength and great conductivity. Ideal for making EDM wire, especially for small slot work and applications requiring small corner radii.

    Tellurium Copper: Suitable for EDM applications needing a fine finish. It has similar machinability to brass and is better than pure copper.

    Workpiece Materials That Can Be Machine with EDM

    For a workpiece, you need a conductive material, one that readily conducts electricity and melts when sparks are generated. You can machine these materials with sinker electric discharge machining:

    Steel Alloys: Hardened steels and other steel types are suitable for die sinking discharge process due to their toughness, strength, durability, and resilience.

    Copper: Highly conductive, copper is an excellent choice for Sinker EDM. However, its quick heating requires the process to be slower and more controlled, particularly when working on components with thin walls.

    Aluminum: Commonly alloyed with other metals to enhance its properties. Its resistance to oxidation and corrosion makes it well-suited for die sinking.

    Titanium: With an exceptional strength-to-weight ratio and corrosion resistance, titanium is often used in medical implants.

    Tungsten Carbide: Known for its high hardness and melting point, tungsten carbide is challenging to machine conventionally. The die sinking is effective for this material, using copper electrodes with negative polarity for low surface roughness. The process, however, is slower due to the metal’s nature.

    Nickel Alloys: Alloys like Inconel, Hastelloy, and Monel, have great heat, corrosion, and oxidation resistance. These properties make them ideal for use in high-temperature applications.

    Applications of Sinker EDM Machining

    The die sinker EDM is primarily best for two use cases: creating complex design cavities and machining delicate parts that cannot withstand mechanical stresses. We see such products in a range of industries:

    IndustryApplications
    AutomotiveRadial and helix gear manufacturing, intricate engine component
    Tool and DieMolds die, and complex tooling components
    AerospaceTurbine components, and airframe structures
    MedicalSurgical tools, implants, and orthopedic devices requiring high-precision
    ElectronicsConnectors, and detailed circuitry elements
    Research & DevelopmentPrototyping complex shapes

    Sinker EDM vs Wire EDM: Comparing Their Differences

    In the sinker electrical discharge machining, an electrode or tool, shaped according to the desired cavity, plunges into the workpiece. That workpiece and tool, both reside in a dielectric tank. When we apply a high voltage across the two materials, the electric spark erodes the materials.

    In contrast, Wire EDM uses a thin wire as an electrode that continuously moves from a spool through the workpiece, also submerged in dielectric fluid. This wire cuts through the material in the same manner as in die sinking. The difference is the tool (electrode) and cutting capabilities. Wire EDM is for precise cuts while Sinker EDM is for complex blind cavities.

     Sinker EDMWire EDM
    ElectrodeCustom-Shape ElectrodeThin Copper/Brass Wire
    MovementPrimarily in one axisIn two dimensions
    DielectricHydrocarbon oilDeionized water
    ApplicationsBlind cavitiesSharp and precise cuts

    Guidance for Newcomers: Choosing a Sinker EDM Machine

    For those looking to buy a die sinking machine, do consider these factors before making a purchase:

    Scale of Production

    Sinker EDM machines are often used for specific, custom dies and molds. If your business primarily requires unique, one-off productions, outsourcing may be a more cost-effective solution.  However, if your operation involves batch production, and high-volume manufacturing, or you plan to offer EDM services commercially, you can invest in a plunge EDM machine.

    Material Type

    Remember that the sinker EDM process is exclusively working with conductive metals. Suitable materials include steel alloys, copper, tungsten carbide, titanium, nickel alloys, and aluminum. For plastic or other non-conducting materials, this process won’t work.

    Complexity of Parts

    If your products require high-precision, complex geometries, or intricate detailing, Sinker EDM provides the capability to meet these demanding specifications with accuracy and efficiency. However, don’t opt for this method, if a simple CNC machining method could do that job as well.

    Recommendations of Sinker Machines 

    When buying, make sure you’re buying from reputable manufacturers with great customer support. Here are three recommended brands:

    Mitsubishi: It’s a very well-known and reliable name in the electric machining industry. Mitsubishi Sinker EDM machines are automated with AI technology, adaptive, and fully enclosed for added safety. They have five product series in die sinking: SV-P series, SG-Series, EA-S Series, EA-V series, and EA Series.

    GF Machining Solutions: GF Machining Solutions (formerly, Agie Charmilles) is popular for its high-performance machines. They offer four model series in the die sinking category: X series for extreme precision requirements, P series for enhanced productivity, S series for micro-profiles, and Economical E series.

    Makino: Makino’s Sinker EDM machines are known for their innovative technologies that deliver high accuracy and surface quality. Like GF machining, there’s a wide range of sinker EDM machines, from small-sized (EDAC-Series) to large-scale (EDNC-Series).

    Alternatives to Owning a Sinker EDM Machine: Opting for EDM Services

    You can opt for external EDM Services instead of investing in a high-cost machine, especially for specific or one-off projects. It eliminates the need for in-house expertise in EDM technology, as you gain access to skilled professionals. Cost reduction is another advantage. Moreover, you get the flexibility to handle various projects without the commitment and maintenance associated with owning a machine.

    RapidDirect is the one-stop solution for your multiple manufacturing needs. We provide state-of-the-art Wire EDM services, customized for industries that demand the finest cuts. We cater to all types of businesses – whether you’re in the prototyping phase, need a small test batch, or need a high volume of production.   

    Upload your project, and get an instant quote and free DFM analysis from our experienced engineering support team.

    Conclusion

    Sinker EDM is a complex process involving controlled spark generation to machine materials, irrespective of their hardness. Its strength is extreme precision, and material removal without stressing the material. This makes the process ideal for making custom tools, dies, and molds.

     If you’re searching for EDM machining services, either for rapid prototyping, batch production, or low-volume manufacturing. Contact Rapid Direct Today, and get a quick response from field experts!

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