Most mold builders are familiar with the 5S workplace organization method for lean manufacturing, which embraces the concepts of sort, set in order, shine, standardize and sustain. Each aspect focuses on avoiding waste and can easily serve as a basis for continuous improvement within mold shops that use EDM and graphite. The sort, set and standardize principles of 5S can help guide EDM operations toward efficiency, minimizing waste and associated costs. This is critical in most mold shops, as EDM is often the bottleneck to reducing mold delivery times.
This 5S principle involves evaluating necessary items with regard to cost, preventing accumulation of unnecessary items, removing any unnecessary items with proper storage or disposal, and segregating and identifying materials.
It is not unusual for mold shop managers to request that employees increase productivity by better utilizing their current assets. This often creates the need to review internal processing, including how graphite is purchased and processed. Graphite is typically ordered based on specific size requirements of a new mold or in larger blocks that will be cut into pieces for the repair of existing molds. Sorting requires establishing rules for the storage and disposal of blanks, remnants and spent (consumed) electrodes. These rules might include, for example, dating and labeling all new electrodes with a job and electrode number. Sorting also requires establishing a pre-determined value for remnant storage and disposal based on the typical electrode sizes used within an operation. These values may vary greatly depending on the mold types produced.
Pre-determined values allow the operator to immediately decide where unused graphite should be stored. Shelved remnants should be stored by size for future use ,
while pieces not used within 24 months are candidates for disposal. Spent electrodes should also be marked by the EDM operator immediately after use as “store,” “rework” or “discard,” and then placed in the appropriate area. These rules prevent operator indecision and reduce buildup of graphite inventory that may have little or no value.
Some operations still prefer to purchase large blocks of graphite on a competitive, cubic–inch basis, rather than purchase each electrode blank to size. This gives the EDM department the luxury of same-day electrode production. However, there is a severe cost penalty associated with this technique, as there are hidden costs related to graphite material utilization. The cut graphite block illustrated represents what might be typical of any EDM mold department cutting graphite on an as-needed basis. After cutting approximately 180 pieces from the block into sizes necessary to meet daily EDM requirements, almost 25 percent remains as remnant material (visible in blue), which may or may not be usable. Not only is this poor material utilization, but this shop will incur costs associated with sawing labor, equipment maintenance and accumulated remnants.
For new EDM mold requirements, purchasing large blocks of material rather than individually sized blanks seldom makes economic sense. For shops focused on mold repair operations or in emergency situations, purchasing graphite blocks may still be necessary, but this has been largely replaced by the ordering of graphite to size, as needed. In this approach, mold designers identify areas within the mold that will require EDM, create blank sizes and then indicate those specific blank sizes on a purchasing list .