Figure 1 - Grinding through electrolytic in-process dressing (or ‘ELID’ for short) is an efficient technique for processing extremely hard and brittle materials such as ceramics (ZrO2, Si3N4), cermets and hardened steel. This grinding technique allows metal-bound grinding discs to be used, which are after all highly durable and difficult to adjust compared with discs with resins or glass. Moreover, ELID grinding allows a work piece with good geometrical accuracy in combination with a highly smooth surface to be obtained, making a polishing stage redundant.
By means of an electrolytic process - the coolant acts as an electrolyte - the metal grinding wheels are kept constantly sharp during the processing procedure. A passivation layer of oxides forms on the circumference of the grinding wheel, which reduces the retention force of the matrix on the abrasive grains, meaning removing blunt granules from the grinding disc is made easier. This means that new granules are constantly being exposed on the disc surface. The procedure furthermore allows grinding wheels with extremely fine granules to be used (ca. 1 µm), which can result in very low surface roughness (see two examples below).
Figure 2 - The principle of ELID grinding
The figures below show two examples of ELID surface grinding. The WC-Co piece of the left measures 40 bij 50 mm, a surface roughness Sa of 0,007 µm (Sz of 0.063 µm) and a straightness of 1 µm in both width and length. The figure on the left showed a component in ZrO2 of 50 mm long and 20 mm wide with a roughness Sa of 0.006 µm (0.050 µm Sz) and a straightness of 0.6 µm over its length.
Despite ELID grinding being a success primarily in Japan, the technology is not yet commercially available to us, and for the time being can only be found in lab environments (such as the PMA department at KU Leuven).