CAVITIES ERODING LARGER THAN SPECIFIED OVERCUT
TECTIP No. 011


   
SUBJECT:    Overcut Larger Than Specified       
APPROVAL:    Ken Baeszler
PREPARED BY:    Ken Baeszler
SYSTEM TYPE:    Die-Sink EDM Systems


OBSERVATIONS:   
Upon inspection of an eroded cavity, it is found that the cavity is larger than expected.

ACTIONS:   
The three major causes of larger than expected overcuts are as follows:

• Maximum allowable on-time for the electrode area has been superseded.  When the electrode is in “positive polarity”, the electron flow is toward the electrode.  The longer the on-time, the longer the electron flows.  It is possible to have the on-time so high that it starts to “plate” the electrode.  This action creates a larger electrode, which in turn creates a larger cavity.  Measure the electrode to determine if this is the root cause.  If so, reduce on-time until plating action ceases.
• Bad flush conditions are causing debris to “re-erode” on the sidewalls and bottom of cavity. If this is the case, increase debris removal by increasing flush, off time, cycle timer, and/or voltage.
• Thin detail electrodes are vibrating due to over aggressive side flush or settings to aggressive for thin details. If this is the case, switch the side flush to “pulse” flush, The flush should turn on only during the retract cycle of the cycle timer. If the flush variable is eliminated, then reduce the spark energy. It is possible to create electrode “vibration” from too much power.