Sinker EDM vs Wire EDM: Key Differences and Applications

Sinker EDM vs Wire EDM machining is a very debated topic among manufacturers. These two distinct yet related non-conventional machining processes each offer unique advantages and cater to different applications.  

This article delves into the core differences between Sinker and Wire EDM, providing a clear understanding of their respective use cases and applications, essential for manufacturers navigating the complex landscape of machining technologies.

What is EDM (Electrical Discharge Machining)?

Electric Discharge Machining (EDM) is a very precise machining process that employs an electric discharge for material removal. Unlike other CNC machining processes, it’s a non-contact process as the tool doesn’t come in contact with the workpiece – no mechanical forces act on it.

In this process, the material and electrode are dipped in a dielectric medium, and high voltage is applied across the two electrodes. A series of sparks between the electrode and material create immense localized which melts and removes the materials. The removed material is evacuated by the flow of dielectric fluid.

The process only works on conductive metals. Additionally, since the sparks can penetrate tough materials, it is best for metals like titanium, tungsten, and hardened steel.

Sinker EDM: Intricate and Flexibility

Sinker EDM, also known by the names,  ram EDM, or volume EDM is a type of electrical discharge machining process where a customized tool ‘sinks’ in a tank containing a workpiece. The close interaction between the two generates sparks, which melt and remove the material, forming a cavity.

Here, the tool, shaped like a cavity’s positive image, acts as one electrode while the workpiece is another. When high voltage is applied across the two electrodes, sparks generate localized heat (up to 12000°C), which melts and erodes the metal. This residue flows out through the circulating dielectric medium, which is usually hydrocarbon oil.

The key highlight of ram EDM is the custom tool which is CNC machined based on the cavity shape you want to make. For instance, if you need a hexagonal cavity, you will have to make a 3D hexagonal prism. The tool also needs to be a conductive metal. Graphite is a common choice as a sinker electrode.

Advantages

• Excels in creating complex shapes and blind cavities that are difficult to create with other methods.
• Reduced risk of tool/workpiece distortion as there is no physical contact.
• Effective for machining hard materials like hardened steel and exotic alloys.
• Highly precise process, with tolerance as low as 0.0001”.
• No mechanical force on workpieces.

Disadvantages

• Slower than wire EDM and conventional machining process.
• Electrodes wear over time.
• Higher setup and operational costs due to power consumption.
• Only suited for electrically conductive metals.

Applications

The sinker electric discharge machining process finds applications in industries where you need to create irregular, complex internal cavities with extreme precision. Here’s a look at those industrial applications:

Wire EDM: Precision and Possibilities

Wire EDM, as the name highlights, uses a very thin wire (typically brass) as a cutting tool. However, the cutting takes place in a similar manner i.e. sparks originate from the wire and cut the materials. Unlike conventional cutting, there’s no physical contact between the wire and the metal workpiece.

The wire EDM process involves suspending a thin metal wire between two EDM guides (made of diamond), positioned above and below the workpiece. These guides move per CNC (Computer Numerical Control) instructions, which allows for precise and accurate movements according to the design.

A key aspect of wire EDM is the continuous movement of the wire from a spool. This movement ensures that the section of the wire involved in sparking is always fresh, as the sparks also erode the wire. The used wire sections are discarded periodically.

Since the wire used is quite thin, the process excels in high-tolerance cutting. You can achieve intricate and fine cuts with it.  

Advantages

• Ideal for fragile materials as there’s no stress on materials.
• The use of thin wire allows for detailed profile cuts difficult to achieve with traditional machining processes.
• Highly effective for cutting hard materials (titanium, super alloys) which may distort mechanical tools.
• Micron-level precision, ideal for intricate designs and tight tolerances (up to 0.00005”).
• Quicker than sinker EDM process.
• Continuous cutting without interruptions.

Disadvantages

• Higher setup cost.
• Only works on conductive metals.
• An oxide layer forms on some materials.

Applications

Wire EDM is beneficial for industries where you require very precise profiles and cuts. Its major applications are:

Differences Between Sinker and Wire EDM Machining

After a quick review of each process, let’s compare the two methods and see how they are different in terms of process, tools, and applications.   

Machining Process

Both sinker and Wire EDM removal material through spark erosion, however with different routes. In sinker EDM, a custom-shaped electrode “sinks” into the material to create a cavity or 3D shape. It is similar to stamping or molding, where the electrode’s shape determines the final form. In this case, the tool usually moves in one direction to create a cavity.

In contrast, wire EDM uses a continuously moving wire that acts like a saw, cutting through the material along a predetermined two-dimensional path. This process is more similar to contour cutting, where a wire follows a programmed path to shape the material. However, there’s no physical contact in both cases.

Geometry and Design Capabilities

Both methods use different tools and consequently produce different geometries. Sinker EDM, with its tool dipping into the material, excels in creating complex 3D geometries, blind cavities, and intricate molds. The shape of electrodes limits the design.

On the other hand, wire EDM creates detailed 2D profiles and intricate patterns. It can cut very fine details and best suits high-tolerance parts.  

Tooling Requirements

In wire EDM, the primary tool is a thin wire, usually made of brass or any coated metal, which is uniform in length and cross-section. This wire serves as a cutting tool and is fed continuously during the machining process.

In contrast, sinker electric discharge machining requires a custom-shaped electrode, often made of graphite or copper. It’s custom CNC made for each project. The electrode’s shape directly corresponds to the positive shape of the desired cavity in the workpiece.

The dielectric fluid also differs. In sinker machining, the tank has hydrocarbon or kerosene oil as a dielectric medium. Whereas, in wire EDM, deionized water is a common choice.

Surface Finish

The surface finish achieved by wire EDM is generally finer and smoother due to the uniformity and thinness of the wire used in cutting. Initially, the surface is rough, but wire EDM is performed in a series of steps to achieve that fine finish.

Whereas, Sinker EDM may produce a slightly rougher surface finish. This is because the discharge occurs along the various edges of the shaped cutting tool, which may not be as uniform as in wire EDM.  

Material Thickness

Since the tool has to penetrate inside the material in the die sinker EDM, the process is ideal for making blind cavities in thicker materials. Whereas, wire cutting is best suited for cutting thin metal sheets. It may cut up to several inches but the process becomes slower as we raise the thickness.  

Precision

Both wire and sinker EDM are capable of achieving high precision, typically around 0.0001 inches. However, wire EDM can often exceed this level of precision; some high-end machines can achieve tolerances of 0.0005 inches.

Applications

Both processes fall under the umbrella of EDM, but they cater to distinct application domains due to their unique operational characteristics.

Wire EDM is best for scenarios demanding high precision and intricate detailing, particularly high-tolerance parts of an airplane, microchips, intricate medical devices, and precise custom tooling.  Conversely, die-sinking  EDM is ideal for applications requiring substantial 3D geometries, such as mold and die-making, particularly in the automotive and manufacturing sectors.

Finding Common Ground: Sinker and Wire EDM Together

Besides multiple differences, we do see some similarities between sinker and wire EDM:

• Basic Principle: Both operate on a similar working principle, spark erosion.
• Mechanical Stress: Neither the sinker nor the wire is in contact with the workpiece so no stress on it.
• Dielectric: Both operations require a dielectric medium to work.
• Machining Hard Materials: Both work only on conductive metals and hard materials that are difficult to machine with conventional tools.
• Customization and Flexibility: Sinker EDM helps in creating customized cavities while wire EDM helps in customized profiles.

Making the Right Choice: Your EDM Guide

When opting for a machining method, evaluate the scale of production, materials, design and precision requirements, and budget. Make sure the machining process you’re choosing is also designed for those needs.

For instance, if you want to make precise aircraft parts, and sensors or cut intricate profiles, wire-cutting EDM is the best choice. Whereas, if you need to create injection molds, custom dies or complex cavities, die sinker EDM is the ideal choice.

In need of such specialized services? At RapidDirect, we provide highly customized wire EDM solutions. Whether you are in the initial stages of prototyping, require a small batch for testing, or need large-scale production, we have the expertise and technology to deliver exceptional results.

At RapidDirect, we understand the importance of precision and efficiency. Upload your project details to receive an instant quote and benefit from a complimentary DFM (Design for Manufacturing) analysis by our experienced engineering support team.

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Conclusion

In the sinker EDM vs Wire EDM machining battle, there’s no one winner both cater to different needs and each has its strengths. Sinker EDM is best for the creation of complex-shaped geometries, particularly blind cavities. Whereas, wire EDM shines due to its precision – ideal for intricate profile cutting.