EDM comes of age

Headnote

Sales, performance increase

EDM is no longer unconventional or "non-standard" machining. In fact, EDM is now the fourth most popular machining process, selling more than all other processes except milling, turning, and grinding. Sales of EDMs have increased from about 0.5% of the 1960 machine tool market to about 6% of the 1998 market.

EDM's share has increased further in today's soft machine tool market because EDM sales were off less than machine tool sales as a whole. The increasing strength of EDM is based on the rapid improvements in its price/performance ratios, on the new applications made feasible by the improved performance economics, and on shops' increasing awareness of the advantages of EDM.

Sales and performance have increased dramatically for both wire and die sinking EDM, but the two processes have generally been out of phase with each other. Each process has been subject to distinct, significant trends.

Wire EDM

Wire EDM started from scratch in the early 1970s and has made steady progress. The most rapid process improvements occurred during the mid-'80s to the mid-'90s in six key measures of price/performance.

1. Speed The biggest advantage for most applications has been the improvement in nominal (ideal conditions) cutting speed which increased from about 1 sq in per hour in the early '70s to approximately 3 sq in per hour in the mid'70s and then surged about 800% to 28 to 30 sq in per hour in the mid-'90s. The actual average cutting speeds achieved in real applications have always been less than the nominal speeds, but have, also, risen proportionately. The reasons for the speed increases are primarily: higher flushing pressure and faster solid-state generator circuitry that allows optimization of settings. Another reason is the improvement in wire quality and the variety of wire alloys available.

As the speed increased, the number of jobs that could be cut increased proportionately. To take advantage of the speed and to avoid having the faster machines sitting idle at night, EDM manufacturers introduced increasingly effective automatic threading systems, wire breakage prevention strategies, and workpiece loading automation.

2. Workpiece size Initially, wire EDM was almost exclusively used for stamping dies and punches. Early applications had a maximum workpiece height of 2" to 4". As makers...