EDM machining is reputable for having numerous benefits, including creating complex shapes, having no burrs, and manufacturing final products that require minimal to no polishing. However, this modern approach to manufacturing has its fair share of disadvantages. These downsides are primarily due to the procedure’s material preference, speed, and costs. The limitations include the following;
- Scarce expertise – EDM machining services aren’t widely available because of the limited number of professionals in the field.
- Slow procedure – EDM machining uses a slow material removal rate to achieve the desired results and accuracy of complex shapes. However, 5 axis milling can significantly reduce production time.
- High power consumption – EDM machining is not power-friendly and often leaves workshops specializing in this manufacturing approach with extremely high electricity bills.
- Cost and time limitations – EDM machining runs on additional costs and time to create electrodes for sinker or ram EDM.
- Formation of overcut – Since the EDM machining procedure aims at perfection, it can produce overcuts sometimes.
- Material limitation – EDM machining can only produce electrically non-conductive materials with particular set-ups of the procedure.
- Fire hazards – Using combustible oil-based dielectrics in EDM machining is a potential fire hazard that needs to be carefully contained to avoid accidents.
- Electrode wear – EDM machining results in excessive tool wear, which makes it challenging to reproduce sharp corners.
Despite the various limitations of this manufacturing procedure, there are several tricks and tips you can use to hack its precision and efficiency.
Process Premise
Low-speed EDM machines have a process parameter library. The process parameters are typically obtained under specific conditions, i.e., temperature 20±3°C, electrode wire, humidity 40-80%, and workpiece material. If the actual working conditions and environment differ from the ones set and the original process parameters are used, processing results can have significant deviations. Therefore, working conditions and the specified conditions on the process parameter library should be as close as possible.
Deviations in processing results might occur if some conditions still need to meet the standards or change during the manufacturing process. Some of the methods to ensure there is efficiency and precision in EDM machining include;
- Flushing specification – try to maintain a maximum of 0.5 bar difference of comparison between the indicated water pressure gauge and theoretical values.
- Use cutting wire that focuses on efficiency for Ra≧0.35µm surface roughness and cutting wire that focuses on the surface for Ra<0.35µm surface roughness.
- Keep a range of a 0.05~0.10mm gap between the nozzle and workpiece. This can be facilitated by a precision machining manufacturer using CNC machines.
- Ensure the water µS<10 during finishing. Please replace the purified water or resin if necessary.
- A brass or galvanized wire with a tensile strength of 900 N/m² is an ideal electrode. Use brass wire for processed surface roughness above 0.35 microns and galvanized wire for roughness below 0.35 microns.
- Ensure that you incorporate HRC55 heat treatment for Cr12 steel as a working material before EDM processing.
The Influence of Temperature on Machining Accuracy
Room temperature changes have a significant influence on machine accuracy. Its impact is reflected in shape, size, and position. The greater the changes in temperature, the larger the workpiece size, and the more evident the temperature influence becomes. For instance, a workpiece of 200mm in length gets a 0.01mm size error when there’s a 5 degrees temperature difference.
The thermal aspects of a CNC machine significantly influence machine accuracy. This accounts for about half of the machining procedure’s accuracy. There’s a significant difference in the accuracy between a machine’s thermal equilibrium state and long-term shutdown state.
The science behind this is that temperatures of each motion axis and the spindle of CNC machines are proportionately maintained at fixed levels after running for some time. With changes in processing times, CNC machines’ thermal accuracy tends to stabilize. This reckons high-precision machines can achieve stable processing accuracy under thermal equilibrium and stable temperature environments.
So, how can you achieve efficiency and precision, considering the temperature significantly influences CNC machining?
A stable environment is ideal for high-quality and high-precision low-speed EDM machining. You should ensure that the working area is free from airflow, and direct sunlight and temperatures should be monitored. For the machine tool to achieve working accuracy, there should be a temperature range of 20±3º.
Factors Affecting Machining Efficiency
Many factors affect the efficiency of EDM machining. However, there are two major cases you should consider checking.
- Limitation of clamping and parts structure. The high-pressure water can’t be effectively flushed because of the limited structure of the parts and the clamping. The support fixture affects some parts and others by the clamping screw position and the pressure plate. Moreover, some are affected by the position of the upper nozzle, where an operator is worried if it won’t fall to its lowest when touched.
You can raise the bottom surface if the cause is the support fixture. Raising the upper nozzle can counter problems with the clamping screw position and pressure plate. In cases of a raised lower surface, use a fixture with a support surface on the identical plane as your working surface or directly clamp the workpiece on the work surface.
- Inefficiency in the wire transport system. Some maintenance routines are performed in a hurry to get back to manufacturing, and the team can sometimes miss out on some key factors. For example, the wire transport system should get equal attention as it can be the root of CNC machining inefficiency.
You should check if the cooling water of the lower conductive block is normal. Furthermore, check if there’s cooling water for the given block since copper powder will be dropped in the cutting procedure – it should be drenched and cleaned. The lower guide wheel rotation on the lower arm should be flexible – check and clean. Check if the take-up wheel is standard and if there is a need to readjust the wire speed and tension.
Conclusion
EDM machining is an efficient approach to achieving perfection for complex designs. Unlike conventional manufacturing processes, EDM prides itself on accuracy and quality delivery in every project. Although characterized as costly and time-consuming, the end products of EDM machining require no polishing.
The manufacturing procedure also has its set of limitations. However, with numerous tips and tricks, you can quickly engage in several operations to improve the efficiency and precision of CNC machines. Proper maintenance and constant monitoring of your machines are crucial to achieving ultimate results.
