Electrical discharge machining is a process used to shape a workpiece through thermal energy.
It is a non-traditional machining method that plays a pivotal role in various sectors such as aerospace, automotive, and manufacturing. A&M provides a wide range of EDM services such as Spark Erosion,EDM Drilling, and Wire EDM.
EDM Surface Finishing Key Points
EDM is often considered for surface finishing as it works well for several reasons such as:
- Enhanced cutting efficiency and precision.
- Ideal for achieving small radius cuts.
- Non-contact machining process, reducing the risk of material deformation.
- Compatible with a wide range of conductive metals.
- Suitable for cutting delicate and complex geometries.
- Versatile, from prototyping to high-volume production.
Factors Influencing Surface Finish
Picking the right surface finish of the cavity presents an opportunity to reduce manufacturing costs and delivery time while still delivering a high-quality mould.
Here are a number of factors you should consider before selecting an EDM surface finish:
Material of Workpiece
Different materials react differently to the EDM process. Harder materials like carbide and titanium can produce different surface finishes compared to softer materials like aluminium.
Electrode Material
The choice of electrode material (usually graphite or copper) affects the surface finish. Copper tends to produce smoother surfaces than graphite.
Discharge Energy
Higher discharge energy levels result in rougher surfaces, while lower energy levels produce finer finishes.
Pulse Duration and Frequency
Shorter pulse durations and higher frequencies generally yield better surface finishes by minimising the amount of material removed per discharge.
Flushing Conditions
Proper flushing of the dielectric fluid helps in removing debris efficiently, thereby improving the surface finish.
Polarity
The polarity of the electrode can influence the finish. In some cases, reversing the polarity can produce a smoother surface.
What is the Effect of EDM on Surface Integrity?
Surface integrity is the condition of a surface after a workpiece has been modified during the manufacturing process. Conventional material removal processes like CNC can often leave machining marks or damage on the workpiece which requires manufacturers to use post-machining finishes.
EDM is a much more efficient and high-quality process for manufacturers as no additional treatment is needed. The integrity of the surface finish during the EDM process is determined by the formation of thermally altered layers and the transference of controlled electrical discharges between an electrode and the workpiece.
Although EDM has zero-directionality as well as the ability to make smooth surfaces in most manufacturing processes, there are factors to consider which may hinder the surface integrity of a workpiece. For example, if you require a quick EDM process, you can expect a blasted-like texture to be left behind as well as microcracks which can hinder the functionality of the workpiece.
More Surface Integrity Considerations
Recast Layer
A thin layer of material that has melted and resolidified on the surface. This layer can affect surface properties and may need to be removed in some applications.
Microcracks and Residual Stresses
The EDM process can introduce microcracks and residual stresses which may affect the part's mechanical properties.
Heat-Affected Zone (HAZ)
The area affected by the heat generated during EDM. Minimising the HAZ is important for maintaining the integrity of the material.
How to Achieve a High-Quality EDM Finish
Parameter Optimisation
To attain a high-quality EDM finish, it is essential to fine-tune your parameter optimisation such as using a high-frequency EDM programme with low amperage and brief pulse on-times. The frequent sparks gradually remove small amounts of material from the workpiece, helping to shape it into the required mould. The duration of the pulse on-time refers to the interval between the spark, electrode, and workpiece when the dielectric voltage reaches ionisation levels.
Surface Polishing
Post-EDM polishing can be employed to achieve the desired surface finish.
Fine Material Structure
Another key factor in producing a high-quality EDM surface finish is the corresponding relationship between the pore size and the material particle size. Both of these elements play a vital role in the material’s ability to produce a fine finish.
If the structure of the electrode material cannot produce the specified surface finish, the EDM machine will keep running without ever achieving the desired surface finish.
Overall, a finer material structure results in a smoother surface finish that requires less polishing
Use Advanced Techniques
Additionally, you can use advanced techniques like powder mixed EDM (adding conductive powder to the dielectric fluid) can enhance the surface finish.
Consider Your Applications
Depending on your workpiece, each application may require specific adjustments to ensure that the final surface meets the functional and aesthetic requirements.
Different Types of Surface Finish
Rough Finish:
Obtained with high energy, large pulse durations, and lower frequency. Used in applications where the surface finish is not critical.
Semi-Finish:
Achieved by using medium energy and pulse durations. This is a compromise between material removal rate and surface quality.
Fine Finish:
Obtained with low energy, short pulse durations, and high frequency. Used in applications requiring high precision and excellent surface quality.
Applications Requiring Specific Surface Finishes
Requires fine surface finishes to ensure the longevity and performance of the tools.
Medical Devices:
Often demand very smooth surface finishes to meet stringent hygiene and performance standards.
Require specific surface finishes to ensure aerodynamic performance and reduce fatigue failures.
Aerospace Components:
EDM Surface Finishing Frequently Asked Questions
What materials can you cut on EDM?
Any conductive material such as steel, titanium, aluminium, brass, alloys and superalloys can be cut using the EDM method.
What is ‘Surface Roughness’ in EDM?
Which parameters control the EDM process?
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Need more information?
To see how A&M could support your next complex manufacturing project – simply call us, or use the form below.
To see how A&M could support your next complex manufacturing project – simply call us, or use the form below.