Company News

In the manufacturing of precision molds, electrical discharge machining (EDM) is the core process for creating complex cavities, deep narrow grooves, and micro features. However, EDM processing has always faced a classic problem: the contradiction between efficiency and quality. During rough machining, efficiency is pursued, resulting in rough surfaces on the molds; during fine machining, quality is prioritized, but this leads to a significant increase in processing time. How to find the optimal balance point between the two is a key point that the EDM process needs to overcome.

I. Understanding of Core Parameters

The essence of electrical discharge machining is to use the high temperature generated by pulsed discharge to melt and vaporize the metal material. Several core parameters determine the processing effect.

The discharge current determines the energy of a single discharge. The higher the current, the faster the material is removed, but the surface becomes rougher. The pulse duration is the duration of each discharge, the longer the duration, the more molten material is produced, but it may cause deeper surface damage. The pulse interval is the pause between two discharges, an adequate interval allows the machining debris to be washed away and maintains stable discharge. 

II. Three-stage processing strategy 

We divide EDM processing into three stages, each with different goals and corresponding parameter settings should also be different.

The goal of the rough machining stage is to quickly remove most of the material, with efficiency being the top priority. At this time, a larger discharge current should be adopted, usually between 10 and 20 amperes, and the pulse time should be set longer, approximately 200 to 500 microseconds. After the rough machining is completed, the surface roughness can be acceptable at around Ra6.0 micrometers, and the details will be handled in the subsequent stages.

The task of the semi-finish machining stage is to remove the remaining material left from the rough machining and lay a foundation for the finish machining. The discharge current is reduced to 3 to 8 amperes, and the pulse time is adjusted to 50 to 150 microseconds, seeking a balance between semi-finish machining and quality. The target surface roughness is below Ra2.0 micrometers, and at this time, there should be no obvious discharge pits or carbon deposits on the surface.

The goal of the finish machining stage is to achieve the required precision and surface quality as per the drawings, with quality being the top priority. The discharge current is reduced to 0.5 to 2 amperes, and the pulse time is shortened to 5 to 30 microseconds. Through precise control, the surface roughness can reach below Ra0.4 micrometers, and for high-demand molds, it can even achieve a mirror-like surface effect of Ra0.1 micrometers.

III. Key Technical Points

The lifting strategy for the tool needs to be adjusted flexibly according to the processing stage. During rough machining, the discharge energy is high and a large amount of machining debris is produced, so a more frequent and higher lifting of the tool is required to ensure chip removal. During fine machining, the discharge energy is low, and the lifting frequency can be appropriately reduced to minimize unnecessary time loss. When machining deep holes or deep grooves, the lifting frequency needs to be increased at any stage.

Work fluid management is also crucial. The dielectric strength of the work fluid needs to be maintained stably. The filtration system should promptly remove the metal debris generated during processing. It is recommended to use high-precision filter elements. Fluctuations in the work fluid temperature will affect the machining accuracy and should be controlled within a reasonable range. Aging work fluid can cause unstable processing and requires regular replacement. 

Electrode wear is an inherent characteristic of the EDM process. Most modern equipment offers an automatic wear compensation function, which automatically calculates the compensation amount based on the material combination and processing parameters. For critical dimensions, it is recommended to conduct detection and verification after the first piece is processed, and then fine-tune the compensation value according to the actual measurement results. Special attention should also be paid to the consistency of electrode wear in each cavity of the multi-cavity mold. 

IV. Examples of Efficiency Optimization 

Take a set of automotive precision molds as an example. The cavity depth is 45 millimeters, and the material is SKD11 quenched steel with a hardness of HRC 58. Before optimization, the total processing time was approximately 32 hours.

We took several optimization measures: In the rough machining stage, the current was increased from 12 amperes to 16 amperes, and the pulse time was adjusted from 300 microseconds to 350 microseconds; the lifting frequency of the tool was increased, from once every five discharges to once every three; a two-level fine machining parameter was introduced to replace the original one-level fine machining; new working fluid was replaced and the filtration system was optimized.

After optimization, the total processing time was shortened to 22 hours, reducing by approximately 31%. The surface roughness improved from Ra 0.25 micrometers to Ra 0.18 micrometers, and the electrode consumption did not increase significantly.

V. Optimizing the Inspection Process

When conducting parameter optimization, it is recommended to proceed in the following order: Confirm the material combination and ensure that the parameter range matches; Set reasonable rough processing parameters, prioritizing efficiency; Verify the lifting tool strategy; Increase the lifting frequency when there are frequent short circuits; Set multi-level finishing processing parameters, gradually reducing the current; Check the processing fluid status to ensure normal filtration and working fluid performance; Conduct first-piece inspection and fine-tune the compensation values to form a closed-loop verification. 

VI. Conclusion

The efficiency and quality of electrical discharge machining seem to be contradictory, but through systematic parameter strategies and meticulous on-site management, it is entirely possible to achieve a balance between the two. The key lies in setting clear goals based on the processing stage, selecting the appropriate parameter combinations; precisely controlling details such as tool lift, coolant, and electrode compensation during the execution process; and finally, verifying and optimizing the results through first-piece inspection and closed-loop feedback.

At Haina Mould, we consider EDM parameter optimization as a continuous improvement effort. The processing data of each set of moulds is recorded and analyzed to form an internal process knowledge base, ensuring that technical experience can be consolidated and reused. If you have any technical questions related to EDM processing, please feel free to contact us at any time for discussion and exploration.