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mmsonline.com April 2017 MMS 75 FEATURE O n-machine probing with a spindle-mounted touch-trigger probe is commonly used on CNC milling machines to speed and simplif y setups. After an automatic probing routine iden- tifies the location of several points on a fixtured part or workholding device to establish the part's exact location on a machine, the machine's CNC can automatically adjust the native work coordi- nate system to match it. This eliminates shimming, part nudging and other time-consuming duties that would otherwise be required to get the part leveled and aligned to perfectly match the machine's coordinate system. The same goes for electrical discharge machin- ing (EDM) equipment, be it for wire, sinker or hole-drilling EDM processes, in that probing cycles automatically establish workpiece and electrode alignment and size to reset the coordinate system and calculate 2D or 3D work offsets. That said, a touch-trigger probe isn't always necessary for EDM equipment. In some cases, the electrode itself can be used as the probe. Brian Pfluger, EDM product line manager for Makino's Die/Mold Technologies division in Auburn Part-Probing Possibilities for EDM Probing options for electrical discharge machining equipment range from simple to sophisticated. Here are options for wire, sinker and hole-drilling EDM. BY D E R E K KO R N Hills, Michigan, notes that while probing on EDM equipment isn't new, there is a trend toward using probing not only to reduce setup times, but also to measure machined features for process con- trol and validation. Here, he breaks down common probing options for the three EDM processes: • Wire EDM. The simplest form of probing on a wire machine is to use the wire energized at a low-voltage setting to electrically touch-off a part. This 2D probing routine can be used to identify the program starting point and determine part feature locations and sizes in some cases. How- ever, probing accuracy using this method isn't high, and probing routines are essentially limited to locating edges, corners and hole centers. (Most machine tool builders of fer canned cycles for these types of probing routines. Mr. Pfluger notes that canned cycles like these on Makino's Hyper I control with tablet-like interface include hyperlinks to supporting video and instructions for these and other cycles.) The wire-probing pick-up cycles utilized by wire EDM require a clean and qualified surface on a workpiece that is free from debris and burrs. In addition, wire quality and wire cleanliness have an impact on probing pick-up accuracy. Poor- quality wire that might have oil or paraffin on its surface will reduce probing precision. Similarly, high-speed coated wire isn't as accurate as tra- ditional plain brass wire for probing, and it is the A-type coated wire that provides the best pick-up As an alternative to using a touch-trigger probe, a dial indicator can be used to perform 3D part level- ing. This method is less accurate than touch-trigger probes and isn't automatic, but it is less costly in that it uses a measurement device that most shops already have.