Double-checking the quality of your EDM tube electrodes is critical to maintaining high performance in your shop. Below are some key considerations for assessing integrity, consistency and working condition:

• The material composition of the electrode tube
  • This data would normally be provided by the vendor or manufacturer of the drilling tube, but some simple checks should be done when receiving the material in house. Was the correct material (copper, brass, carbide) sent? Is the electrode configuration correct (single hole vs multi-channel, type of multi-channel)?
  • This can be achieved via visual checks or by requesting the supplier to provide written certification of the material composition and material purity. The latter is typically only required in more controlled production environments typically found in the medical and aerospace industries
  • Changes in the material composition of the fast hole tube and drilling electrode or the type of single/multi-channel being used often result in varying cycle times and electrode wear
• Variations in the outside diameter of the electrode tube
  • Proper and consistent electrode OD is critical to ensuring proper finished hole size and to guarantee the proper clearance between electrode and fast hole tube guide (sometimes referred to as die guide)
  • It is important to measure the outside diameter along the full length of the electrode in order to verify size consistency
  • The electrode should also be rotated on a flat surface to check for any out-of-round conditions
  • The recommended way to check is a hand-held micrometer (ideally a unit with a consistent friction thimble)
  • Out-of-size and out-of-round electrodes can result in size differences in the final part. They can also easily jam within the die guide and even cause damage to the guide itself
• Variations in the inside diameter of the tube electrode
  • This is easily one of the more difficult items to inspect but important because of the impact it can have on the cutting process
  • Changes in ID will cause a change in the flushing flow rate (more or less flow restriction)
  • Different IDs also cause different burn rates as the surface area that the electrode has available to discharge from varies. If one electrode has an OD of 1mm and an ID of 0.8mm and another electrode has the same OD but an ID of 0.9mm, then the electrode with the smaller ID has a lot more surface area to discharge from than the electrode with the larger ID. This will cause significant performance differences
  • Both gauge pins and vision system inspections can be used to check the electrode ID. This should also be performed along the full length of the electrode in order to verify consistency
  • These types of variances of a tube’s inside diameter can result in inconsistent cycle times, different wear factors, and also different wear characteristics (tapered/bullet-nosing wear). Large changes in wear factor from electrode to electrode can create issues in production environments or applications that have minimal break-thru distances (often found in aerospace parts)
• Straightness of the electrode tube
  • This check is to verify how concentric and straight a tube electrode is
  • To test for straightness, the electrode can be rolled on a flat surface (desk or surface plates work well). The electrode should not wobble or hop when rolling. No measuring equipment is required – a visual inspection is sufficient
  • Electrodes that are not consistently straight will cause reliability issues with automatic loading, can cause hole size accuracy to vary, and can prematurely clog or wear the electrode guide
• Vendor consistency
  • Key to proper process control is consistency. With EDM Fast Hole tubes/tube electrodes, inside and outside diameters as well as straightness can vary by individual electrode or from batch to batch. It is critical for a shop to monitor how a specific vendor’s delivered materials vary over time, and to understand how these variables impact a specific part application.
  • A good way to check this is to track the vendor’s delivered products over time and establish a quality history of the supplied items. Some suppliers provide certifications and perform their own internal quality check. However, this is not a standard in the industry and the end-user is left with the responsibility of verifying and qualifying the electrodes they are using for their production
  • In order to achieve the most reliable results, end-users should demand material, sizing, and quality consistency from their suppliers
  • It is important to keep in mind that a specific end-user’s needs will dictate the level of consistency required for a specific application