How to precisely control the discharge gap between the electrode and the workpiece to ensure machining accuracy during electrical discharging machining of turned parts?
Publish Time: 2025-12-01
In the field of precision manufacturing, traditional cutting processes such as turning, milling, and drilling are often used to produce high-precision metal parts. However, when dealing with complex internal cavities, microstructures, or high-hardness materials, electrical discharging machining becomes an indispensable supplementary method. Especially for brass parts already formed by turning—such as functional parts with precision threads or knurled surfaces—if further operations such as micro-holes, irregular grooves, or deburring are required through electrical discharging machining, how to precisely control the discharge gap between the electrode and the workpiece becomes the core technical challenge determining the final machining accuracy and surface quality.
1. The Nature and Influencing Factors of the Discharge Gap
Electrical discharging machining relies on the instantaneous high temperature generated by pulsed discharge between the tool electrode and the workpiece to erode the material. Its machining profile is not a "direct copy" of the electrode, but rather an "offset profile" determined by the discharge gap. This gap is affected by multiple factors such as voltage, current, pulse width, medium flow state, material conductivity, and thermophysical properties. Brass, as a highly conductive and thermally conductive material, exhibits stable discharge and high etching efficiency. However, its soft nature makes it prone to edge overheating or micro-deformation, especially near machined threads or knurled areas, where even minor gap fluctuations can cause tooth profile distortion or surface roughness deterioration.
2. Dynamic Gap Control Based on Process Parameters
To ensure accuracy, the discharge parameters must be precisely matched. First, using low-energy, short-pulse-width finishing parameters can significantly reduce the discharge channel diameter, controlling the discharge gap within ±0.005mm. Second, optimizing the flushing pressure and flow direction of the working fluid ensures timely removal of etching products, preventing secondary discharge from causing gap expansion or thickening of the surface recast layer. For brass parts, due to their low melting point, the average discharge power must be appropriately reduced to prevent localized overheating that could damage the passivation film or cause micro-area collapse.
3. Electrode Design and Positioning Compensation Strategy
Simultaneously, a precise electrode path is generated using a CAD/CAM system, and the "gap compensation" function is enabled on the CNC EDM machine to automatically adjust the servo feed position. For machining near the knurled area, surface unevenness may cause abrupt changes in the gap. A multi-stage, layered machining strategy can be adopted: first, rough machining to leave allowance, then gradually approaching the target size through multiple finishing passes, with each layer depth controlled within 0.01mm to ensure discharge stability.
4. Integrated Detection and Closed-Loop Feedback Enhance Reliability
Modern precision EDM machines are generally equipped with contact sensing or optical tool setting systems, which can automatically detect the actual position of the workpiece before machining and correct clamping errors. Some high-end equipment also integrates a real-time discharge status monitoring module, which analyzes voltage/current waveforms to determine the gap status and dynamically adjusts the servo feed speed—accelerating the feed when the gap is too large and retracting when it is too small, forming a closed-loop control. This function is particularly important for brass parts that have undergone passivation treatment, as it can avoid initial discharge instability caused by surface film.
In the turning-EDM composite machining process, precise control of the discharge gap is the bridge connecting "macro-forming" and "micro-finishing." By comprehensively considering material properties, surface condition, and structural features, and combining parameter optimization, electrode compensation, and intelligent feedback technologies, discharge gap fluctuations can be effectively minimized. This achieves micron-level electrical discharging machining accuracy without damaging the original precision structure. This not only expands the functional boundaries of traditionally machined parts but also provides a reliable technological path for the manufacturing of high-value-added precision components.
