INCREASING DEEP RIB EROSION PERFORMANCE

TECTIP No. 012


   
SUBJECT:    Improving Erosion Performance       
APPROVAL:    Ken Baeszler
PREPARED BY:    Ken Baeszler
AGIE SYSTEM TYPE:    Die-sink EDM

OBSERVATIONS:   
Sinking thin deep ribs in mold cavities can sometimes be difficult, since flushing deteriorates proportionately with depth in most cases. There are a few “tricks” that can apply to this application.   
       
ACTIONS:

• Using high spark energy combined with low average amperage.  With a good quality graphite, it is possible to use as much as 50 peak amps and at least 75 Ms on time on an electrode as small as 1.0” wide and .050” thick. This type of spark energy is only allowable when using a very high off time and voltage. Typically at least 320 ms off time is used in conjunction with an 85 volt gap. Preferably, a 300 volt open gap should be used, if that option is available on your system.
• Why would we use such strange settings? To take advantage of the large overcuts associated with the high spark energy, but at the same time preventing the electrode from disintegration by using high off time and voltage to reduce our average amperage.
• Opposing Flush - Contrary to all conventional schools of flushing, it is acceptable to use opposing flush in rib cutting operations, providing that the nozzles are located on the thinnest side of the ribs. Very little flush pressure should be used for the first .200” of depth, then the flush should be set to 10-15 PSI depending on the size of the rib. This high flush pressure is necessary to “pump” the debris out of the work zone, and to prevent build up that would normally be associated with opposing flush.

Note: this technique should only be used when the electrode can be adequately undersized, and there is a draft angle of at least ½ degree per side.