CNC wire-cut EDM
CNC wire EDM (wire EDM for short) is a specialized machining method that uses a continuously moving thin metal wire (electrode wire) as an electrode to etch away material through pulsed discharge. It is widely used in mold manufacturing to produce complex-shaped parts, such as punches, dies, and special-shaped cutting edges in punch dies, and cores and cavities in plastic molds. Compared to traditional cutting, wire EDM is not limited by material hardness and strength and can process difficult-to-machine materials such as hardened steel and cemented carbide. It offers high precision and excellent surface quality, making it particularly suitable for machining complex two-dimensional contours and fine structures. It is a key technology in mold precision machining.
The basic principle of CNC wire EDM is based on the spark erosion effect. A high-frequency pulse voltage is applied between the wire electrode and the workpiece. When the two are brought within a certain distance (usually 0.01-0.05mm), the medium (usually deionized water or an emulsion) is broken down, generating a spark discharge. The instantaneous temperature reaches over 10,000°C, melting or even vaporizing the metal on the workpiece surface. Simultaneously, the wire electrode continuously moves, carrying away the eroded material and achieving continuous cutting. Wire EDM can be divided into fast wire EDM (electrode wire speed 8-10m/s, reciprocating) and slow wire EDM (electrode wire speed 0.2-0.3m/s, single-use) based on the speed of the electrode wire. The two differ significantly in machining accuracy and surface quality.
Fast-wire WEDM is the most widely used type of wire cutting in my country. It uses molybdenum wire (0.12-0.2mm diameter) as the electrode wire and achieves cutting through a reciprocating motion. With low equipment costs and high processing efficiency (typically 20-80mm²/min), it is suitable for machining low- to medium-precision mold parts. Fast-wire WEDM typically achieves a machining accuracy of ±0.01-±0.02mm, with a surface roughness of Ra1.6-3.2μm. While not as precise as slow-wire WEDM, its lower processing costs have made it a dominant choice among small and medium-sized mold manufacturers. For example, the die of a punch (made of Cr12MoV, quenched to 58HRC) was machined using fast-wire WEDM, achieving a dimensional error of within ±0.015mm for the contoured cutting edge, fully meeting the precision requirements of common stamping parts.
Wire-cut machining uses brass or galvanized wire as the electrode wire (diameter 0.05-0.3mm). The electrode wire moves in one direction and is not reused. Combined with a high-precision servo system and closed-loop control, the machining accuracy can reach ±0.001-±0.005mm, with a surface roughness of Ra0.025-0.8μm. It is suitable for machining high-precision, high-surface-quality mold parts. Wire-cut machining is typically equipped with automatic wire threading and multiple cuts (3-5 times). The initial cut removes most of the excess material, and subsequent cuts refine the accuracy and surface quality, effectively reducing machining distortion and heat-affected zones. For example, the punch of a precision connector mold (SKD11 material, 10mm thickness) was machined using wire-cut machining. After four cuts, the cutting edge dimensional error was ≤±0.002mm, and the surface roughness was Ra0.1μm, meeting the product’s precision fit requirements.
Process parameters for CNC wire EDM (electrical discharge machining) significantly influence machining quality and efficiency. These parameters primarily include pulse width, pulse interval, peak current, wire speed, and feed rate. For roughing, to improve efficiency, larger pulse widths (20-100μs) and peak currents (10-30A) are used, resulting in machining efficiencies exceeding 100mm²/min, but with poor surface roughness. For finishing, smaller pulse widths (2-20μs) and peak currents (1-5A) are used, sacrificing efficiency for high precision and low surface roughness. For example, for machining a 20mm thick Cr12 steel part, the roughing parameters are: pulse width 50μs, peak current 20A, efficiency 80mm²/min; finishing parameters are: pulse width 5μs, peak current 3A, efficiency 5mm²/min, and surface roughness Ra 0.8μm.
CNC wire EDM offers unique advantages in mold manufacturing: First, it can process complex shapes such as irregular holes, narrow slits, and sharp corners (minimum fillet radius 0.02mm), structures difficult to achieve using traditional machining. Second, it offers high machining precision, making it particularly suitable for precision fitting mold components (e.g., gaps between the punch and die ≤ 0.01mm). Third, it eliminates the need to manufacture complex electrodes; the electrode wire trajectory can be controlled through programming, shortening the mold manufacturing cycle. Fourth, it offers high material utilization, effectively utilizing scrap to process small parts. For example, the irregular punch (containing 12 sharp corners and 8 narrow slits) of a mobile phone casing stamping die was formed in a single operation using slow-wire EDM, avoiding the multiple clamping errors associated with traditional milling. This achieved dimensional consistency of ±0.003mm and significantly reduced mold commissioning time.
With technological advancements, CNC wire EDM is moving toward higher precision, greater efficiency, automation, and intelligent processing. Five-axis EDM machines enable taper cutting and three-dimensional surface machining, meeting the processing needs of complex molds. Intelligent systems monitor machining status in real time, automatically adjusting process parameters to reduce wire breakage and errors. Seamless integration with CAD/CAM software enables full automation from design to processing. These technological advances have further expanded the application of wire EDM in mold manufacturing, providing reliable support for the production of high-precision, complex molds.
