An EDM wire electrode ceramic guide.

Ceramic and Silicon Nitride EDM Guide Characteristics

The EDM guide plays what is arguably the most important role in the EDM drilling process—holding an electrode in a fixed position as it penetrates a workpiece. Three characteristics fundamental to a guide’s satisfactory performance in this role are tight tolerances, geometry, and toughness. Tight tolerances in a guide’s dimensions are so important because imperfections in a guide only magnify those of the electrode being guided, and the internal diameter of a guide must exceed the diameter of its corresponding electrode by a precise amount. Too tight of a fit, and insertion will be difficult. Too loose, and imperfections are introduced in the drilled workpiece. We can make guides with clearance to your specification, and make sure that internal diameters of our electrode guides straddle the boundary between too tight and too loose, so that your electrodes never stray from their targets. Yet while precision manufacturing of guides alone can ensure precision drilling of a workpiece perpendicular to an electrode, drilling at odd angles introduces problems. This is when the characteristic of guide geometry is so important. Even a perfect guide does not guarantee accuracy when an electrode extends far from its guide. This can be a necessity when drilling at an oblique angle, unless one uses a guide with a long, tapered tip. Our EDM guides are customizable, with variable geometries suitable for whatever your application may be. Even tailor-made custom guides are not immune to wear, however. Toughness is the last characteristic determining a guide’s performance, and merits a discussion of the principal materials found in guide cores: conventional ceramic and silicon nitride.

Ceramic Versus Silicon Nitride

A heap of powdered silicon nitride.
Silicon Nitride Powder

Ceramic and silicon nitride are similar materials in that they can be used for the same EDM drilling applications. What distinguishes the two materials is toughness, stemming from properties of the materials themselves and the ways in which cores of both materials are constructed. Whereas the properties of conventional ceramic are not notable, silicon nitride is an advanced and relatively new compound, engineered for extreme hardness, high resistance to thermal shock, low thermal expansion, and low electrical conductivity, all properties contributing to its relative toughness. But above all these characteristics, it is the friction between the guiding surface and the electrode that determines the durability of the guiding surface material. Silicon nitride eclipses conventional ceramic in this respect both in its inherently low porosity, and in the way it is constructed. The low porosity of silicon nitride gives it a much smoother surface than conventional ceramic, which reduces friction. Silicon nitride guides are also constructed with a unique triangular guiding surface profile, instead of the circular guiding surface profile found in conventional ceramic guides. This reduces friction by minimizing the points of contact between electrode and guiding surface, and provides recesses where disintegrated material that is not flushed can go, without imparting stress on the guide. All the durability advantages of silicon nitride allow it to last on the order of 5 to 10 times as long as conventional ceramic, greatly increasing working efficiency. Silicon nitride’s superior durability also mostly offsets its relatively high cost, its only real disadvantage. Whether you use silicon nitride or conventional ceramic essentially comes down to your budget.

A diagram of a custom silicon nitride barrel guide.

EDM Guide Adaptors

Sometimes guides with a standard 6mm shank will not fit onto your EDM machine. If this is the case, we offer custom EDM guide adaptors. This will ensure that our guides work with your machine.