Mold processing EDM
Electrospark machining (EDM) in mold processing utilizes the high temperatures generated by pulsed spark discharges between an electrode and a workpiece to remove material. It is particularly suitable for machining high-hardness, high-toughness mold materials (such as hardened steel and cemented carbide), as well as complex mold cavities and holes. The machining principle is based on the spark erosion effect. When the electrode and workpiece are brought close together in an insulating liquid, a pulsed spark discharge occurs between the electrodes, reaching instantaneous temperatures exceeding 10,000°C. This causes the metal on the workpiece surface to melt or even vaporize, thereby removing material. This machining method is not limited by material hardness and can process complex structures that are difficult to handle using traditional cutting methods, making it a key component in mold manufacturing.
The main equipment for EDM machining includes a pulse power supply, a machine tool body, a working fluid circulation system, and an electrode clamping device. The pulse power supply provides high-frequency pulse current to control the energy and frequency of the spark discharge. The commonly used pulse width is 1-1000μs, and the peak current is 1-500A. The machining accuracy and surface quality can be controlled by adjusting the parameters. The machine tool body consists of a bed, a worktable, a column, etc., to ensure the relative motion accuracy between the electrode and the workpiece. The positioning accuracy can reach ±0.001mm, and the repeatability accuracy is ≤0.0005mm. The working fluid circulation system usually uses kerosene or deionized water as the working fluid, which serves as insulation, cooling, and chip removal. The working fluid is forced to circulate through pump pressure. There are two chip removal methods: flushing oil and pumping oil. For deep cavity machining, flushing oil is required to ensure stable machining.
The choice of electrode material for EDM (Electrode Discharge Machining) depends on the machining requirements. Commonly used materials include copper, graphite, brass, and copper-tungsten alloy. Copper electrodes offer excellent conductivity and plasticity, resulting in high surface quality (Ra ≤ 0.8μm), making them suitable for precision cavity machining. Graphite electrodes are heat-resistant, have low wear, and offer low material cost, making them suitable for large cavities and rough machining. Copper-tungsten alloy electrodes combine the advantages of copper and tungsten, with minimal wear, but at a higher cost, making them suitable for high-precision, long-life mold machining. The manufacturing accuracy of the electrode directly impacts the machining accuracy of the workpiece. Typically, the dimensional accuracy of the electrode must be one to two grades higher than that of the workpiece, with a surface roughness of Ra ≤ 0.4μm. For complex electrode shapes, CNC milling and wire cutting can be used.
EDM process parameters significantly influence the machining results, primarily including pulse width, peak current, pulse interval, and machining polarity. For roughing, to improve efficiency, a larger pulse width (50-1000μs) and peak current (50-500A) are used, resulting in machining efficiencies of 100-500mm³/min, but poor surface roughness (Ra 5-20μm). Semi-finishing uses medium parameters (pulse width 10-50μs, peak current 10-50A), achieving surface roughness Ra 1.6-5μm. Finishing, using a smaller pulse width (1-10μs) and peak current (1-10A), achieves surface roughness Ra 0.1-1.6μm and a machining accuracy of ±0.001-±0.01mm. For example, the rough machining stage of the mold cavity uses a peak current of 200A, a pulse width of 500μs, and an efficiency of 300mm³/min; the fine machining stage uses a peak current of 5A, a pulse width of 5μs, and a surface roughness of Ra0.8μm.
EDM (Electrodischarge Machining) is widely used in mold manufacturing, primarily for cavity machining (such as the dies of plastic molds and die-casting molds), hole machining (such as the die cutting edges of punch dies), complex curved surface machining, and micromachining. For complex cavities in plastic molds (such as mobile phone case molds), multi-axis EDM can achieve curved surfaces, patterns, and other details in a single process, with an accuracy of ±0.005mm. For irregularly shaped cutting edges in punch dies, direct machining using formed electrodes avoids the difficulties of traditional grinding. EDM can also be used for mold repair, such as by locally etching away worn areas on punch cutting edges to restore edge dimensions. With technological advancements, EDM has been integrated with CNC and CAD/CAM technologies, enabling automated programming and processing. This has significantly improved the efficiency and precision of mold machining, providing a reliable foundation for the manufacture of complex molds.
