EDM Tooling

EDM tooling, electrodes, fixtures, materials, guides and other supplies are used in electrical discharge machining (EDM), a highly-accurate manufacturing process for creating shapes within components and assemblies. EDM connects a metal workpiece to a power supply and uses a shaped tool or electrode to erode material in order to form the desired geometry or pattern. The electrical discharge is of very short duration and high current density. There are two basic types of EDM machines: wire and probe. Wire machines pre-drill a hole in the workpiece and then feed an electrode through the hole. Sinker machines cut workpieces without pre-drilling holes and typically use a machined graphite or copper electrode. To create a potential difference between the part and the electrode, the workpiece is often immersed in a circulating dielectric fluid.

EDM tooling requires materials such as electrodes and wires. Some electrodes are prefabricated with letters, numbers, or symbols. Others are prefabricated for machining internal threads. Tube-shaped electrodes with a single bore or multiple bores are used in drilling and trepanning applications. Ram or sinker electrodes have a three-dimensional configuration that creates an imprint or cavity in a machined workpiece. Electrode holders clamp electrodes in place to ensure a high degree of precision and repeatability. Special guides called ferrules are made of ceramic materials and used to feed through electrodes or wires. Zinc-coated wire provides superior corrosion resistance, spark formation, and flush characteristics. Dielectric fluids conduct sparks at an applied voltage, cool the workpiece and the electrode, and flush away eroded debris. Typically, dielectric fluids include additives such as surface cleaners and corrosion inhibitors.  

Electrodes for EDM tooling are made from a variety of materials. Graphite is the most commonly used material because of its good machinability, wear resistance, and low cost. Carbides are compounds of a metal or metalloid and carbon. Tungsten is a refractory metal with an elevated temperature strength and low conductivity. Tungsten carbide is valued for its wear resistance. Silver tungsten is expensive, but useful in making deep slots under poor flushing conditions. Molybdenum, a refractory metal with good strength and arc erosion resistance, is used to make small-hole EDM electrodes. Both copper and tellurium copper are well-suited for machining applications that require a fine finish. Copper graphite is expensive, but provides better conductivity and flexural strength than pure graphite. Brass does not wear as well as copper or tungsten, but is easier to machine and can be die cast or extruded for specialized applications.

Companies that provide EDM tooling services vary in terms of capabilities. Some suppliers specialize in electrode design and offer services such as material selection and application-specific tool design. Others have full-scale electrode manufacturing facilities or provide repair or replacement services such as brazing and tool installation. Reverse engineering creates new tools by analyzing existing dies, models, molds, tools, or parts. Reconditioning maximizes tooling life through processes such as redressing, regrinding, sharpening, and reconditioning.

EDM tooling services are located across the United States and throughout the world. Certifications and quality requirements include both ISO 9001 and ISO 9002. Some suppliers are certified by original equipment manufacturers (OEMs). Others meet military specifications (MIL-SPEC). QS-9000 is a quality standard for suppliers of DaimlerChrysler Corporation, Ford Motor Company, and General Motors Corporation. QS-9000 is based on the 1994 edition of ISO 9001, but contains additional requirements that are particular to the automotive industry. Specifically, QS-9000 applies to suppliers of production materials, production and service parts, heat treating, painting and plating and other finishing services.

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