EDM is a precision non-traditional machining technique. It is widely used to manufacture mechanical parts. It has unique advantages over conventional cutting methods for machining certain parts. Under certain special conditions, parts with good surface finish can be obtained by machining parts using EDM. It also meets the requirements of design drawings well and achieves a certain machining accuracy. Therefore, EDM is becoming more and more common in various industries. The next part of this paper will first discuss what EDM surface finish is and the factors that affect it. After that, we will introduce the methods of measuring surface finish. Finally, we will discuss how to improve EDM surface finish and the application areas of EDM machining.
What is EDM surface finish?
EDM surface finish refers to the roughness and smoothness of the surface of a workpiece obtained by the EDM process. We can use surface roughness parameters to measure how good the EDM surface finish is. These parameters include Ra (the average height of the contour) and Rz (the maximum height of the contour).
The Ra value represents the average of the absolute values of the deviation of the surface from the average height, usually in micrometers (μm). Smaller Ra values indicate a smoother surface, while larger Ra values indicate a rougher surface, where a smaller finish is generally desired.
In contrast to Ra, Rz refers to the maximum height of the contour. Over a sample length, Rz is the average of the 5 largest peak heights and the 5 largest valley depths. Although Rz also reflects surface roughness, Ra is relatively more commonly used.
The good or bad surface finish directly affects the use of parts, assembly performance, and appearance quality. In EDM, the surface finish can be controlled and improved to a certain extent by reasonably adjusting the discharge parameters, electrode material, working fluid, and other factors. Many different processing needs can be met if this is done.
Factors affecting the surface finish of EDM
In order to obtain the ideal surface finish, some influencing factors need to be paid special attention to when using EDM technology. The common ones are discharge parameters, electrode material and shape, workpiece material, working fluid and machine accuracy. These factors are critical to the quality of the resulting surface finish. It is possible that a very small improvement can produce unexpected results.
Discharge parameters
Discharge parameters generally refer to three main aspects: discharge current, discharge voltage and pulse frequency.
The magnitude of the discharge current directly affects the EDM surface roughness. This is because higher pulse currents increase the discharge energy, which leads to uneven melting and vaporization of the material due to the release of energy in a short period of time, which in turn leads to a rougher surface. On the contrary, lower discharge currents do not.
The level of discharge voltage affects the size of the discharge gap and the amount of discharge energy. The proper voltage helps to maintain a stable processing condition and obtain a better surface finish.
Pulse frequency determines the number of discharges per unit time. Higher pulse frequency increases the machining speed, but may also lead to an increase in machined surface roughness. Therefore, a higher pulse frequency can be selected when performing rapid removal of excess material. However, in order to ensure a good surface finish during finishing, the frequency should generally not be too high.
Electrode material characteristics and shape
The influence of the electrode material on the surface finish should not be ignored. On the one hand, the characteristics of the electrode material such as thermal conductivity, hardness and abrasion resistance will affect the stability of the machining process and the machining effect, which in turn affects the surface finish. For example, the use of good thermal conductivity of the electrode material can reduce the heat-affected area of the machining process, so as to obtain a smoother machined surface. Copper electrodes, on the other hand, have good electrical conductivity and abrasion resistance, and thus can achieve relatively high surface finish grades.
On the other hand, the shape and size of the electrode material will also affect the EDM surface finish. By designing a reasonable electrode shape can reduce the phenomenon of side corrosion and carbon accumulation during processing, and improve the precision and surface finish of processing.
Workpiece material
The influence of workpiece material on EDM surface finish is most intuitive. For parts with high surface finish requirements, try to choose materials with good electrical conductivity and high thermal conductivity for EDM processing, so that it is easier to control the distribution of heat during discharge processing, which is conducive to obtaining a better surface finish. Usually high hardness materials can withstand high energy discharge, but the finish may be reduced. Therefore, we should choose the suitable material according to the finish and functional requirements of the product so that we can get the lowest production cost.EDM is suitable for a wide range of materials and meets the unique needs of different applications.
Working fluid
Different types of working fluids have different effects on the EDM process and also affect the final surface finish. In general, different working fluids have different cooling, chip removal and de-ionization properties. Working fluids with good cooling and insulating properties can reduce the heat-affected zone and carbon buildup during the machining process, thus improving the surface finish of the machined surfaces. For example, deionized water is often used for high-precision machining, while oil-based working fluids are better in terms of cooling and chip removal properties and are therefore used in some specific machining environments.
In addition, the concentration and temperature of the working fluid can also affect the results of the machined surface. Too high or too low a concentration may result in increased roughness of the machined surface. Appropriate temperature can improve the cooling effect and lubrication performance of the working fluid, which can help to obtain a better machined surface finish.
Machine accuracy
The performance of machine tools such as precision, stability and stiffness also affects the finish of EDM machined surfaces. High-precision machine tools can better control the parameters of the machining process, so as to obtain a more stable and accurate machining results. Therefore, it is crucial to do a good job of maintaining and servicing the machine tool in daily life.
Surface finish standardization and measurement
After the workpiece EDM processing is completed, to judge the quality of the surface of the workpiece, it is necessary to measure the first to obtain the value, and then based on the finish standard to judge the results of the measurement, to determine whether the finish is qualified.
Surface finish standard
Surface finish standards are specific criteria and methods used to measure and characterize the roughness of a workpiece. Understanding surface finish standards is important to ensure product quality and functionality. Common standards include ISO 4287, ASME B46.1 and JIS B0601. ISO 4287 is a surface finish standard developed by the International Organization for Standardization (ISO). It defines roughness parameters as well as measurement methods.ASME B46.1 is a surface roughness standard developed by the American Society of Mechanical Engineers (ASME) that covers roughness measurements and evaluations.JIS B0601 is a surface roughness standard developed by the Japanese Industrial Standards (JIS) that defines roughness parameters used in Japanese industry.
Yonglihao Machinery is a supplier that specializes in machining mechanical parts. We have high-precision EDM production equipment. We will pick the right surface finish standard to process the parts according to the customer’s requirements and the drawings.
Measurement Method of Surface Finishes
After using EDM to process parts, we usually measure the surface finish of the parts. There are many ways to measure surface finish, and each method has advantages and scope of application. But there are also disadvantages. You should choose the right common measurement method. Do this based on the actual processing situation.
Stylus method：The stylus method is a measurement method for contact surfaces. Usually, the contour meter (roughness meter) uses a stylus to gently stroke along the surface to be measured, and the vertical displacement of the stylus is converted into an electrical signal by a sensor, which leads to the surface roughness parameter directly. The entire measurement process is highly accurate and suitable for a wide range of surfaces but may cause damage to soft surfaces. Because it is relatively simple and fast, it is also a relatively common measurement method.
Interferometry： The principle of interferometry is to utilize light wave interference to assess surface roughness by observing the shape and distribution of interference fringes. It is a non-contact measurement method. The accuracy is high and the surface is undamaged. However, the range is small and the environmental requirements are strict. So, it is for parts with high requirements for surface finish.
Comparison method： Compared with the first two methods, the comparison method is a relatively simple measurement method. First, choose the roughness standard sample, and then compare it with the EDM processed surface, through the eyes and hands to touch the way to judge the roughness level. For some surface finish requirements that are not particularly accurate parts, we can usually use this method. This method is simple and intuitive, but the requirements for the measuring personnel are higher, and the measurement results will be affected by subjectivity.
Light Source Method： The light source method uses various angles and intensities of light to shine on the object’s surface. It evaluates the finish by looking at the distribution and intensity of the reflected light. This method can show microscopic surface unevenness better. But, it needs the light source and observation conditions to be consistent. However, the operation is relatively complex, and the requirements for inspectors are high.
Methods to improve EDM surface finish
In order to obtain the required surface finish, you can usually optimize the EDM parameters and improve the surface finish by post-processing techniques. Although this does not necessarily guarantee a particularly high level of precision, it does provide some improvement over the previous method.
Optimizing EDM parameters
Select appropriate processing parameters such as current, voltage and pulse frequency, which have a direct impact on the surface quality of EDM processing. Through experimentation and simulation, we can find the best machining parameters. They will give us a higher surface finish.
If in the finishing stage, smaller currents and pulse widths can be used to reduce the surface roughness and improve the finish. But also consider the processing efficiency. It must meet finish requirements while being as fast as possible.
Post-processing technology
To improve the surface finish of EDM, on the one hand, after EDM processing, the surface can be further processed by grinding, polishing and other post-treatment processes to remove surface burrs and bumps and improve the surface finish. On the other hand, the surface can also be specially treated by chemical treatment or electrochemical polishing to obtain higher finish and performance.
Common applications requiring superior surface finish
When using EDM technology, it is possible to process conductive materials that are highly hard and difficult to machine. Since it is non-contact machining, there is also no mechanical stress that can cause deformation of the part. It has a wide range of applications in areas such as aerospace, medical devices and mold making.
Aerospace
In the aerospace field, many parts need to withstand extreme temperatures and pressures, and therefore have very high requirements for surface finish and material properties. edm can meet these requirements and ensure the accuracy and reliability of parts. For example, in the manufacture of aero-engine parts, EDM is used to machine complex shapes and high hardness materials to achieve high precision and high finish surfaces.
Medical field
In the medical field, EDM can accurately machine parts with complex shapes. It also provides excellent surface finish to meet the high standards of implants. For example, artificial joints and precision surgical instruments can be machined using EDM.
Mold Manufacturing
Many parts are manufactured using molds. Therefore molds have certain requirements for the precision and finish of the parts. For example, in precision injection molds for making plastic products, the cavity surface needs a very high degree of finish. This finish ensures the surface quality of the plastic products and aids demolding. In addition, EDM technology can also be used in the processing of stamping molds.
Conclusion
Achieving the best surface finish in EDM is a pursuit of great significance. By optimizing the EDM parameters and post-processing techniques, the surface finish of the parts will be better. It will also be more widely used in more industries with the continuous development of technology. If you still have questions about EDM technology, you can contact us for answers. Also, if you still have EDM projects and needs, please contact us. We will be happy to give you top-notch Wire EDM Machining Services. We look forward to hearing from you!
FAQ
How does EDM achieve a mirror effect?
You can achieve a mirror finish in EDM by:
●optimizing process settings
●choosing high-quality electrodes
●using high-quality working fluids
●using state-of-the-art EDM equipment
●applying proper surface treatments.
What are the common post-treatment techniques for EDM machining?
Common techniques include polishing, grinding, and shot peening. They are all designed to remove recast layers and refine surface texture.
Does the type of dielectric fluid affect the surface finish of EDM?
Yes, the fluid’s quality and management greatly affect debris removal and cooling. This, in turn, affects the surface finish.