A Few Misconceptions in the EDM Industry
Due to fierce CNC EDM market competition, many manufacturers promote “mirror EDM,” “high efficiency machining,” and “expert systems.” On the surface, EDM performance seems homogenized. However, some users find the machines ineffective or feel misled after purchase.
This happens because the industry measures EDM performance by technical indicators like surface roughness, machining efficiency, electrode loss, and expert system presence. These indicators have limitations. Some manufacturers misuse them to exaggerate capabilities. This paper discusses how these indicators relate to real CNC EDM performance, aiming to guide rational industry needs.
1. Evaluating Surface Machining Performance of CNC EDM Machines
Surface roughness is a key indicator of CNC EDM machining quality. However, judging a machine solely by its best surface roughness value is one-sided. To truly assess performance, we must consider multiple machining scenarios. This article discusses three important aspects: mirror surface finishing, uniform matte surface processing, and high-quality textured surface machining.
Optimal Surface Roughness
Many CNC EDM machines claim a best surface roughness of Ra0.2µm or Ra0.1µm. Surface roughness depends on machine performance, machining area, shape complexity, and workpiece material. Larger areas, complex shapes, or greater depths make fine finishes harder. Mirror steels like S136 and SKD61 enable mirror finishes; other materials, such as SKD11, cannot. The typical “optimal” Ra0.2µm usually involves a small 10mm electrode machining shallow surfaces on mirror steel. Some manufacturers ignore accuracy and efficiency in these tests. In real production, machining areas are often larger and shapes more complex, making mirror finishes difficult. A benchmark test involves machining a 50×50×5mm cavity with coarse and fine electrodes. It requires uniform mirror finish within 0.01mm precision and total machining time under 15 hours. Machines meeting this benchmark can satisfy actual mirror EDM needs.
Mirror and Matte Surface Processing
Mirror finish tests alone do not fully reflect CNC EDM performance. For example, a 20mm square electrode shallow surface test usually achieves Ra<0.2µm with proper parameters. Mirror machining produces stable, uniform discharges and glossy surfaces. However, matte EDM finishing (Ra0.22 or Ra0.4µm) is actually more difficult. Matte EDM uses negative polarity, small current, short pulses, and precise capacitance matching. Unstable machines produce carbon deposits and inconsistent surfaces. Thus, uniform matte surface processing better reveals pulse power supply quality. Many industry users require surfaces between Ra0.8µm and Ra2.5µm. Ordinary CNC EDM machines can meet these needs with subsequent polishing. However, some products need high-quality textured surfaces, like Ra1.6µm (VDI24) grain finishes, requiring uniform microscopic particle morphology. Some machines meet roughness standards but fail microscopic inspections, showing inconsistent discharge pits and defects.
Comprehensive Surface Performance Evaluation
The best surface roughness value alone is insufficient to evaluate CNC EDM machining performance. Instead, a comprehensive evaluation must consider whether the machine can perform practical mirror finishing, uniform matte surface processing, and high-quality textured surface machining. Only by covering these three aspects can the true machining capability of the CNC EDM machine be assessed accurately.
2. Maximum Machining Efficiency
Maximum machining efficiency varies among CNC EDM machines. Some machines label 300mm³/min, others 500mm³/min. Users may think higher numbers mean faster machining. However, maximum efficiency mainly depends on the maximum machining current. Higher current means faster rough machining but rough surface finish. In real production, high current is rarely used. Thus, maximum machining efficiency is a limited reference for real machining speed.
Roughing Efficiency Differences Are Small
Generally, roughing efficiency differences between CNC EDM machines are minor. The main efficiency differences appear during finishing. Finishing involves multi-stage processing and complex factors. These include machining allowances, technology, and processing conditions. Because of this complexity, specific indicators cannot accurately evaluate finishing efficiency.
Evaluating Finishing Efficiency by Application
We use practical application examples to compare finishing efficiency. Under the same conditions and requirements, total processing time is compared. This comparison must avoid manual intervention in process or electrical parameters. Otherwise, human adjustments greatly affect efficiency. For example, a cavity processed with default settings may take 20 hours. Adjusting the program can reduce this to 8 hours. High-end machines have less adjustable space but better adaptability to complex tasks. Thus, overall machining efficiency shows a clear advantage in such machines.
3. Expert System for EDM
The intelligence level of CNC EDM machines has improved significantly. Most manufacturers advertise “expert systems” that auto-generate programs and discharge parameters. Users only input machining area, electrode material, workpiece material, and requirements. This simplifies operation and optimizes machining without experience. However, some companies overly rely on these systems, causing low efficiency and poor results.
Complexity of EDM Processes
EDM processes vary widely. Machining areas range from sharp points to large surfaces. Depths vary from shallow to deep cavities. Shapes differ from simple squares and rounds to complex cavities. Surface requirements span coarse to fine VDI levels. Electrode materials include copper, graphite, and cemented carbide. Workpiece materials range from steel to titanium alloys. Machining goals vary: efficiency, low loss, surface effect, etc. Different conditions require different discharge parameters and optimizations.
Evaluating EDM Expert System Quality
Advanced CNC EDM machines have extensive processing parameter libraries. These develop over long periods and optimize automatically during machining. Such systems meet fully automated operation needs and reduce operator skill demands. In contrast, ordinary CNC EDM machines have limited parameters and only simple tool search interfaces. Operators must manually configure electrical parameters, similar to conventional machines. Therefore, evaluating an expert system requires assessing parameter completeness, production suitability, and adaptability.
4. Conclusion
The above for CNC EDM machine tools for several common indicators, pointed out its one-sidedness. It is recommended that EDM users should choose the appropriate CNC EDM machine tools rationally according to the processing requirements, and not be blinded by some one-sided publicity indicators and application cases.