A. About EDM Scale (Electrical Discharge Machining)
EDM Scale is resistant to the etchants we use to perform the texturing process. If it is present in even small amounts on the surface to be textured, the area affected will either not etch at all or may etch only intermittently. Neither of these conditions will give your mold component an acceptable visual appearance if we attempt to texture over the scale. It is much simpler and drastically more cost effective to bench or polish out the EDM Scale prior to attempting to texture the component. The areas that are the toughest to polish - the radii and tight corners - are the most notorious for finding EDM Scale that has not been eradicated by polishing, however, it is not uncommon to find EDM Scale on other areas of the cavity as well. If EDM Scale is noticed once the tooling is in our facility, it creates a timing and cost issue that holds up the processing of your tooling.
A highly polished finish does not guarantee complete EDM removal. If you have used the EDM process to cut your tooling or areas of your tooling, be sure that your benching source vigorously attacks the EDM Scale first, then begins to apply the finish ( stone or emery ) that is required. Simply going to emery paper only disguises the EDM Scale within the emery finish - it is usually still there. EDM Scale causes needless delays and extra costs since it must be removed in order to properly process the tooling with a texture. This is one of the most common problems we encounter, and our sales engineers are more than ready to show you how to identify the problem in your own shop so as to ensure that your project is not delayed. EDM SPARKS OR "ARC OUTS" EDM cause a different problem from scale. Since they are so hard ¨C often up to 70 Rc, and so deep into the steel surface, they usually cannot be polished out. They will not etch at all and due to their hardness, it is very difficult to repair them after texturing. This condition can often only be resolved by drilling out the spot, then pinning it or welding it and then repairing the texture by hand. This becomes a larger problem if the spark is located in an area of the cavity that is inaccessible, as in a rib or deep pocket, where the condition most often occurs. Try to avoid this condition at all costs as it is very difficult to repair.