A turbine blade with penny for size comparison.

The applications of EDM small hole drilling might be expected to be very limited in scope. Indeed, it would be difficult to think of a more innocuous phrase than small hole drilling, a phrase befitting a niche technology. But this belies the reality of EDM small hole drilling as a machining method used in many industries, industries that value precision and the characteristic of EDM to drill through very tough materials. Its use in gas turbines is the best illustration of what EDM small hole drilling can do in your industry.

Gas Turbines and Hole Popping

A diagram of a typical jet engine, a common type of gas turbine.

A gas turbine is a highly adaptable type of internal combustion engine that converts the impulse generated by the combustion of compressed air and fuel into useful work. How this work is harnessed determines whether a gas turbine is part of a power generator or a jet engine. A jet engine harnesses the jet of exhaust gases created by combustion for thrust, for example. Common to all gas turbine engines, however, is a turbine located downstream of the combustion chamber, which gives them one of their most important characteristics—they are self-sustaining. The compressor that allows for efficient combustion is powered by the electricity generated by the turbine. But for such a critical role, gas turbines are subjected to an extremely hostile environment of intense heat and centrifugal forces, and it is no surprise that the alleviation of this problem has been a major impetus in gas turbine development.

The primary limiting factor in gas turbine development has been heat, and research looking to alleviate the problem of heat has focused on two areas. One area is material science. Since the problem of heat was recognized, many cutting edge alloys have been developed that can resist both the heat and centrifugal forces found inside a gas turbine. But today, this is not enough. Temperatures in modern gas turbine engines can exceed the melting point of even these advanced alloys. This prompted the second wave of gas turbine development, which focused on cooling methods. One of the most prevalent cooling methods is called film cooling. In film cooling, air is directed through holes drilled on the surface of a turbine blade, creating a film on the surface of the blade that acts as a barrier to super hot exhaust gases. Modern turbine blades combine advanced, adamantine alloys with cooling holes, to which only EDM small hole drilling is suited.

The characteristics that suit EDM small hole drilling to applications such as turbine blade cooling hole drilling are its ability to drill through very hard materials, an absence of machine tool pressure, and pinpoint accuracy. An EDM electrode never makes physical contact with its workpiece, which means that an electrode will work regardless of how hard the workpiece is. This lack of physical contact also eliminates machine tool pressure, which can prevent working on a delicate workpiece like a turbine blade, and create burrs and other deformities. This lack of machine tool pressure also contributes to the great accuracy of EDM small hole drilling. Below are just some of the applications of EDM small hole drilling. This list is not comprehensive, but only suggestive of hole popping’s great versatility.

Fuel Injection

Fuel injection has essentially supplanted carburetion in automotive engines. Due to the superior precision with which fuel can be delivered to a combustion engine, fuel injection engines boast superior fuel economy, less toxic emissions, and require less maintenance than engines using carburetion. A fuel injector uses very small nozzles to atomize gasoline or diesel fuel, ensuring a precise and predictable delivery of fuel. This is why EDM small hole drilling is the favored machining method. A lack of precision in the diameters of nozzle openings could hamper proper functioning of a fuel injector.

The fuel injectors of liquid fuel rockets also use holes drilled with EDM small hole drilling.

A diesel fuel injector.

Spinnerets for Synthetic Fibers

The manufacture of synthetic fibers requires arrays of spinnerets to produce masses of consistent strands. A spinneret is essentially a small hole, and so EDM small hole drilling is often used to create these arrays of spinnerets.

A spinneret for weaving synthetic fibers like rayon.

Biomedical Technology

The association of medicine and biotechnology with great care and precision is so tight that the term surgical is practically synonymous with the precise. The perception does not stray far from the reality, especially in the biomedical field. Engineering must meet the incredibly complex demands of human biology, often in places where a disconnect between anatomy and engineering can lead to serious impairment or even death. This is why EDM small hole drilling is used in biomedical technologies ranging from artificial hearts to dental drills.

An artificial heart.

Injection Molding and Die Casting

Those who are already familiar with EDM know that sinker EDM is often used for creating molds in the related fields of die casting and injection molding—other machining methods cannot work with pre-hardened materials. Hole popping complements sinker EDM in the drilling of runner holes, which direct molten metal or plastic into the cavity of a mold.

A die for injection molding.

Complement to Wire EDM

Small hole drilling is essential in wire EDM applications when a start hole is needed. A start hole is a hole through which wire can be threaded. This allows wire EDM to be used in the interior of a workpiece.

Cutting Tools

Conventional machining uses brute force to cut or drill through a workpiece, and so a drill or saw must be harder than the target material. A drill or saw that needs to cut through a very tough workpiece must be harder still, sometimes so hard that conventional machining techniques can no longer be used to make the tool itself. This is where EDM comes in. EDM small hole drilling can be used to create coolant channels in drills, which is vital when drilling into extremely hard substances.

A drill-bit with coolant holes.

Safety Wire

On a jet airliner, structural integrity is a top priority. In order to ensure great structural integrity, bolts are often fastened together using safety wire, each bolt preventing the loosening of the other. For safety wire to work, holes must be drilled through bolt heads through which safety wire can be threaded. This is an ideal application for small hole EDM.

Two bolts secured to each other using safety wire.

Automotive and Racing

Lifters are a common and critical component in internal combustion engines, as they regulate the opening and closing of valves. Hydraulic lifters use oil pressure to adjust their points of contact with the camshaft as thermal expansion in an engine increases, which reduces engine wear. Oil flows through hydraulic lifters using holes drilled by EDM.

A hydraulic lifter.