EDM Tolerances

That’s a trick title. Most of the time design engineers aren’t concerned with the tolerances associated with EDM process directly and I will tell you why.

First some background. EDM, or Electrical Discharge Machining (thanks again Wikipedia), is a material removal process wherein a large amount of electrical energy is delivered to the workpiece, burning material away. Energy is delivered through an electrode, either a block of conductive material (known as sinker, cavity, or volume EDM), or a wire (known as wire EDM). In both types, tools are mounted on machines with CNC controls.

EDM'd Moldbase and Electrode
EDM'd Moldbase (left) and Electrode (right)
Image via Eroda Tools, Ltd.

EDM processes are typically very slow and not suitable for volume production. However, EDM is typically very accurate and very effective on hard materials making it a great process for making plastic, sheetmetal, and other types of tooling. This is why design engineers are not usually concerned with the tolerances introduced by the EDM process; they are usually most interested in the tolerances of the parts coming off the tooling.

In this ongoing discussion of part tolerances (start here) I wanted to bring up EDM before talking about injection molding, metal stamping, metal forming, and other tooling-dependent processes because EDM is where the tooling starts. And you know how I love the fundamentals.

Author: admin