All About Sinker EDM Machining: Definition and Applications

Sinker EDM is a subtractive manufacturing technology used to produce parts with extreme precision through spark erosion. Spark erosion refers to the process in which a tool, called an electrode, creates cavities in metal workpieces. Sinker EDM gets its name from the fact that the electrode sinks into the raw material. However, it is also possible to have machines that work horizontally or at any other angle. The electrode is slowly moved toward the workpiece until it almost makes contact. A high-voltage spark then occurs between the electrode and workpiece, which melts away the workpiece material closest to the electrode. It is specifically suited to machining blind cavities in conductive metals. The spark erosion process is sometimes referred to as “burning.” For more information, see our guide on the Types of Machining Processes.

Figure 1 below shows a typical sinker EDM machine:

A sinker EDM machine uses spark erosion to remove metal. This means that the machine uses an electrode, either copper or graphite, to create the contours of the part by burning away material from a workpiece submerged in dielectric fluid. The dielectric fluid behaves as an insulator until a sufficiently high voltage is reached. If there was no insulator, a short circuit would be created between the electrode and the part. The dielectric oil also works as a coolant to remove heat from the part to prevent excessive thermal expansion. The oil also cycles through a filter to remove metal particles as well as through a chiller to keep the oil below its flash point.

The electrode and raw material are alternatively either positive or negatively charged. Whenever the electrode gets close to the part, an electric spark jumps between the two. This spark generates a localized temperature that can reach as high as 8,000 °C to 12,000 °C. The extreme temperature vaporizes the metal in a localized area. As the electrode moves down into the part, it erodes the metal in the shape of the electrode. 

The sinker EDM process can be performed on any conductive material; the hardness of the material makes no difference.

The first documented analysis of the effect of spark erosion was made in 1770 by Joseph Priestley, an English physicist. A team of Soviet scientists named Dr. B. R. and Dr. N. I. Lazarenko took this research further in 1943 and invented the electrical discharge machining process. The first practical EDM machine was designed in 1952 by a company called Charmilles to remove broken taps.

Sinker Electrical Discharge Machining is known by many names such as plunge, ram, volume, or cavity EDM.  

Sinker EDM is primarily used to create blind holes or cavities in a part. These cavities often have complex shapes that are impossible to manufacture using conventional machining techniques like CNC milling. The hardness of the material does not affect the ability of the electrode to remove material whatsoever. This means that sinker EDM can be used to create cavities in hardened steels for injection mold making.

Sinker EDM is a very accurate machining process with tolerances that can be as low as +/- 0.004 mm provided optimal machining parameters are maintained. This high level of accuracy is due to the fact that the electrode is guided by a CNC (computer numerical control) machine that controls its movements with great precision. In addition, the electrode wears very evenly, which results in consistent dimensional accuracy. Some sinker EDM machines can even polish a part with a final surface roughness of 0.18 microns.

Who Manufactures Sinker EDM Machines?

There are many manufacturers of sinker EDM machines. Some of the most popular brands include: ONA, OFEK, Makino, Sodick, Mitsubishi Electric, and GF. Most of these manufacturers also produce wire EDM machines. 

What Are the Advantages of Sinker EDM?

Some of the key advantages of sinker EDM are listed below:

1. Accurate: Sinker EDM can produce features with extreme accuracy as long as the electrode is machined accurately. The sinker EDM process does not expose the tool to loads that can flex and distort it, as is the case with CNC machining; as such, features can be more precisely controlled.
2. Blind Cavities: Sinker EDM can produce features with blind holes with irregular shapes like hexagonal holes, for example. Doing irregular shapes with a CNC machine would require very specialized tooling. In some cases, it is impossible to produce equivalent features using standard CNC machining.
3. Simple Tooling: Unlike other machining processes, sinker EDM does not require a tool that is harder and tougher than the material being machined. As long as the metal is conductive it can be machined with sinker EDM. Tooling can be manufactured in-house out of copper or graphite using normal CNC machines.

What Are the Disadvantages of Sinker EDM?

Sinker EDM has many advantages, however, some downsides must be considered before making use of this technology. These disadvantages are listed below:

1. Slow: The sinker EDM process removes very little material when compared to other machining technologies like CNC milling. This increased time means that the individual part cost is higher than if able to use other machining technologies. The increased time can be mitigated by pre-machining the part to get close to the final, desired dimensions.
2. High Operating Costs: The high energy process of spark erosion used in Sinker EDM machines means that they use excessive amounts of electricity. Normal CNC machines consume considerably less energy.
3. Limited to Conductive Material: Sinker EDM machines are limited to conductive materials and therefore cannot machine plastics or composites. 

What Are the Best Sinker EDM Machines?

When deciding on which machine is best suited to a specific application, it is always ideal to first understand the requirements. For example, it may not be necessary to get an automatic tool changer if production volumes are low. Listed below are some of the best sinker EDM machines:

1. GF Form P350: The P350 has excellent tool life management which ensures that electrodes last longer, thereby increasing the cost-effectiveness of using the machine. This machine can also produce highly polished finishes with a surface roughness of 0.12 microns without the need for secondary polishing off of the machine. 
2. Makino EDAF3: The EDAF has a smaller form factor on account of the dielectric tank being situated underneath the machine. It also comes with an automatic tool changer. A drop tank makes loading and unloading the machine simple. 
3. Mitsubishi SV12P: This sinker EDM machine is billed as a high-precision machine with advanced, AI-optimized features that can reduce machining time by up to 30 %.

Is Stainless Steel Suitable for Sinker EDM?

Yes, stainless steel is conductive and can therefore be machined using sinker EDM.

What is the Difference Between Sinker EDM and Wire EDM?

A sinker EDM machine plunges an electrode toward the workpiece material to create blind holes and complex cavities. A wire EDM machine, on the other hand, uses a thin wire to cut a 2-dimensional profile out of very thick material.

Is Sinker EDM Available at Xometry?

Yes, sinker EDM is available at Xometry. Contact us today to learn more about our EDM machining services.

This article presented sinker EDM machining, explained what it is, and discussed how this process is used in manufacturing. To learn more about sinker EDM machining, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities, including CNC machining and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

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