EDM Machining: Intro to EDM Process and Materials

CNC Machining, custom metal parts, precise mold

Cutting parts from stock material using EDM (Electrical Discharge Machining), a fast expanding and adaptable production technique.
EDM machining has several advantages, including the ability to work with very hard materials like hardened steel, titanium, and tungsten carbide. It is also suitable for producing intricate shapes, and there is minimal tool wear since the electrode doesn’t physically touch the workpiece. However, it is a slower process compared to traditional machining methods and is typically used for applications where precision and complex shapes are critical. EDM machining is widely used in manufacturing, tool and die making, and the aerospace and medical industries.
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CNC EDM Machining

EDM Machining Process

EDM is an unconventional subtractive machining method, often controlled by CNC technology, used to craft components by removing material from a solid block. Unlike conventional CNC machining that employs sharp cutting tools, EDM machining relies on the controlled flow of electricity and thermal energy, earning it the status of an electro-mechanical process.

The EDM machining process hinges on controlled electric spark erosion, with electric sparks acting as the “cutting tool” to erode or eliminate material from a workpiece, shaping it as required. The sparks are meticulously activated and deactivated to produce a consistent, controlled material removal rate.

A distinguishing feature of EDM machining is its non-contact nature, where it doesn’t exert physical cutting forces on the workpiece. This quality makes it particularly suitable for intricate and delicate structures with complex geometries.

On a microscopic level within EDM machining, the process unfolds as follows:

  • Electric spark erosion takes place amid the anode (a component on the Electrical Discharge Machine), the cathode (comprising the tooling material or part), and a dielectric EDM fluid.
  • The dielectric fluid becomes ionized, with positive ions impacting the cathode’s surface, raising temperatures to thousands of degrees Fahrenheit, vaporizing the metal.
  • Microscopic vaporized metal fragments flow into the dielectric fluid, forming chips that are then flushed away from the machined part’s surface. Occasionally, chips may adhere to the part’s surface, leading to localized rough textures, with different materials displaying varying degrees of chip adhesion.

Part movement in EDM machining is typically controlled through pre-programmed input movements. For conductive materials, the workpiece closes the electrical circuit.

EDM Machining Methods

EDM machining utilizes two primary methods:

Sinker EDM:
This involves a pre-shaped or pre-formed electrode, often CNC machined, possessing the desired cavity’s geometry. The electrode is pressed into the workpiece to create the intended cavity. It’s also known as die-sinking EDM or cavity-type EDM and is well-suited for producing internal gears and similar geometries.

Wire EDM:
In this method, a thin metal wire is used to cut through the material and shape the desired part.

EDM machining can be applied to conductive materials, including metals and graphite (a non-metallic conductive material commonly used for sinker EDM electrodes). However, it’s not suitable for non-conductive materials. Furthermore, EDM machining is generally more expensive than traditional CNC machining, so it’s often reserved for components with thin walls or complex geometries.

Ideal Materials for EDM Machining

EDM A2 Tool Steel/Steel

Steel is a top choice for Electrical Discharge Machining, prized for its exceptional wear resistance and toughness. A2 Tool Steel and other steel grades find common use in crafting fixtures, tools, gauges, and more.

During EDM, steel exhibits four distinct metallurgical layers on the cut cross-section:

  • An unaffected section farthest from the point of impact.
  • A tempered layer next to the unaffected layer, slightly harder but not reaching the hardening temperature.
  • A rehardened layer above the tempered layer, forming martensite, which is hard but brittle.
  • A melted and resolidified layer (the white zone) with rapid resolidification and pillar crystal growth. Carbon content may change due to interactions with the dielectric fluid.

Tips for EDM machining of A2 Tool Steel/Steel:

  • Shorten the spark duration to minimize the thickness of brittle metallurgical layers and attain a fine finish.
  • Maintain proper flushing to prevent chip bridges, which can lead to burns.
  • Increase off time to avoid double sparking ignitions, preventing constant burning arcs.

EDM Aluminum

Aluminum is a widely used metal due to its strength-to-weight ratio, cost-effectiveness, and recyclability.

EDM Aluminum tips:

  • Opt for a higher pulse power supply no-load voltage to reduce debris attachment to the EDM electrode wire.
  • Ensure even fluid flow for the top and bottom portions of the EDM wire.
  • Implement effective filtering in the dielectric fluid to facilitate quick debris removal.
  • If certain metal wires pose difficulties, try using a brass wire instead.

EDM Brass

360 Brass, renowned for its machinability, serves various applications like gears, lock components, and ornamental parts. Brass is a suitable choice for EDM wire and tubing as well as an EDM electrode material.

EDM Copper

Copper alloys, like 101 and 110, are prized for their thermal and electrical conductivity, making them ideal for electrical applications. Copper EDM generates a re-cast layer without the same microscopic issues seen in steel, thanks to its superior heat distribution.

Tips for EDM Copper Alloys:

  • Reduce the EDM spark duration to minimize sublimation.
  • Increase amperage to maintain spark intensity as with less conductive materials.
  • Use negative electrode polarity with high amperage to reduce electrode wear and enhance material removal.
  • Ensure adequate, turbulence-free flushing to maintain effective debris removal.

EDM Titanium

Titanium is a growing favorite, valued for its corrosion resistance, high strength, and light weight. It’s used in aerospace, marine, and sports equipment.

Tips for EDM Titanium Alloys:

  • A slight increase in pulse-on time can reduce tooling wear.
  • Decrease pulse-on current and time to minimize the white layer thickness.

Sungplastic is the top supplier of CNC EDM. Sungplastic also specializes in CNC Machining, Injection Molding, Die Casting, Metal Stamping, Rapid Prototyping, and 3D Printing, as well as custom-designed parts or prototypes for batch manufacturing and high volume production, whether small parts or large parts.

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