Sinker EDM: precision machining with electrode discharge

When to choose sinker EDM over another process

Sinker EDM becomes relevant when the part geometry includes sharp corners, deep flat bottoms, fine cavities or undercuts that milling cannot reproduce without compromise. It also stands out for very hard or heat-treated materials, tungsten carbides, hardened tool steels, superalloys, that mechanical cutting would wear tools down too quickly. The process induces no cutting force, which limits deformation on thin walls or fragile inserts. However, it remains slower than conventional milling and is mainly justified for complex geometries or difficult materials, rather than simple shapes that can be produced more quickly by chip removal.

The criteria that truly distinguish two shops

A shop's real capability is reflected in several technical parameters: the number of machine axes (3-axis or with orbiting), the clearance available under the machining head, the type of power generator that determines surface finish quality, and the control of electrode wear compensated by calculation. Typical tolerances range between 0.01 and 0.03 mm on form dimensions, with surface finishes reaching below Ra 0.4 µm on finishing passes. The choice of electrode material, copper, graphite or specific alloys, influences erosion speed and tool life. A serious shop also has appropriate dimensional inspection equipment, profile projector, coordinate measuring machine, and knows how to manage in-house electrode manufacturing by machining or molded graphite depending on the batch sizes targeted.

What to prepare to get an accurate quote

To obtain a reliable quote, you should provide a dimensioned drawing with the actual functional tolerances required, the material and its condition (raw, treated, hardened) as well as the target hardness after machining. Specify the quantity of parts, as it determines the electrode manufacturing strategy, single-piece or batch production. Indicate the expected surface finishes on each zone, any heat or surface treatments planned after EDM, and the desired lead time. Providing a 3D model facilitates the feasibility study and the calculation of the number of electrodes needed to achieve the geometry and internal angles.