More than 45 years ago, a young tool and die maker and plastic injection mold builder named Gordon Shumway saw the EDM process in its infancy and made learning the process his quest. Since then, he’s worked with various major manufacturers as a research and development assistant, instructor and end user of electrical discharge equipment. This firsthand look at the history of the EDM process is part one of a series.
Wire EDM is the most popular non-traditional method of machining conductive material using a wire electrode. It’s perfectly suited for manufacturing complex shapes with great accuracy when other processes are unable to meet accuracy or surface finish requirements.
Today, the wire electrode Is most commonly brass, either coated or uncoated, and most often .010 inch in diameter. (Although wire electrodes are manufactured from many other materials in many other diameters, here we’ll focus on the technology and use of the most common materials and diameters.)
But the history of the brass wire actually dates to the 1970s. At the time, the industry was using solid copper wire with high wear properties. The wire would run from the bottom guide to the upper guide and the scrap (used wire) would be recoiled on the waste spool above the work tank and cutting area.
The first improvement was supplementing the copper wire with brass to enhance its performance. This sparked higher demand and cutting speed wars among manufacturers for this little-known non-traditional machining method.
The next process enhancement came in the form of wire guide and delivery system redesigns to enhance accuracy and speed. Ultrasonic vibrators attached to the guide system created a vibration in the cutting gap that aided in the flushing process, thus improving speed and making it one of the first widely used enhancements.
As cutting speed improved, the need for flushing the gap with dielectric fluid became the next target. The hydraulic action of dielectric fluid was improved by increasing the flow rate and pressure, while larger filtration units and smaller filtration capabilities were developed.
But these process improvements created new issues that have driven industry-wide engineering changes. One of the first major issues was wire lag, or geometrical incorrectness that happens when the mechanical speed of the machine lags the erosion of metal by the wire electrode. This was corrected by increasing tension in the wire transport system by adding tension rollers or mechanical devices to keep the wire taut.
The second noticeable issue was constant workpiece movement from a change in temperature as the wire moved across the working area of the machine. After many machine design changes, these issues were controlled by submerging both the part and the work area, resulting in a constant and controlled thermal process. Because the workpiece was contained entirely in fluid, it also resulted in very forgiving dielectric flushing. This is only the beginning of the EDM process. Over the next several articles, we’ll talk about wire composition and cutting technology optimization, as we strive to understand and improve a non-conventional process that is more conventional than ever.