Modeling EDM

For all its novelty, electrical discharge machining is a seemingly simple machining method, where sparking between an electrode and a workpiece causes the slow erosion of the workpiece. However, a closer inspection of the mechanisms through which sparking erodes metal reveals a complex set of physical processes whose relationships are not entirely understood. A single electrical discharge consists of the formation of a plasma channel through the breakdown of a dielectric, melting of workpiece material by the plasma, reformation of the dielectric, and subsequent flushing of molten material by the dielectric.1 When an oil-based dielectric is used, erosion of the workpiece can be accompanied by carbon deposition, which has interesting implications for the microscopic surface structure of both the electrode and the workpiece.1 The complexity of the EDM process means that innovation requires the development of sophisticated models, especially in micro EDM.

The development of efficient micro EDM methods would contribute greatly to the expansion of EDM applications, due to the general trend of smaller and more complex geometries in industry. Yet the widespread adoption of micro EDM has been hampered by both a slow material removal rate and low efficiency.2 Mujumdar et al. describe a model of micro electrical discharge plasma discharge in a deionized water dielectric that takes into account the chemistry of H2O plasma, power balance of electrons and neutrons, and plasma bubble growth.2 This model can be used to predict heat flux,2 bringing researchers a step closer to a thorough understanding of the micro EDM process. As machining grows more sophisticated, so do the models and computational tools used to describe it.

There are many variables that need to be considered in EDM, and some to a greater or lesser degree depending on the goal of machining. The complexity of input parameters and the conflicting nature of material removal rate and surface finish in particular have led Anitha, Das, and Pradhan to find an optimization of machining parameters using neural networks.3 A neural network approximates the structure of a brain, and gives a computer a similar natural learning ability. This combined with the raw computing power of a machine allows for the solving of very complex problems. The application of neural networks by Anitha et al., allowed for an increase in machining efficiency,3 and this approach seems promising for the future of EDM.

1. Ho, K. H., and S. T. Newman. “State of the art electrical discharge machining (EDM).” International Journal of Machine Tools and Manufacture 43, no. 13 (2003): 1287-1300.

2. Mujumdar, Soham S., Davide Curreli, Shiv G. Kapoor, and David Ruzic. “A model of micro electro-discharge machining plasma discharge in deionized water.” Journal of Manufacturing Science and Engineering 136, no. 3 (2014): 031011.

3. Anitha, J., Raja Dasa, and Mohan Kumar Pradhan. “Multi-Objective Optimization of Electrical Discharge Machining Processes Using Artificial Neural Network.” Jordan Journal of Mechanical & Industrial Engineering 10, no. 1 (2016).

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Sias Compact Small Hole Spark Eroder

A Sias spark eroder drill unit.

The last few years have seen the growing prominence of maker culture, due in large part to new and affordable technologies such as microcontrollers and 3D printers, making manufacturing more accessible than ever. These technologies have received a great deal of attention for their contribution to this boom in creativity, while other manufacturing technologies—EDM included—continue to be associated with a top-heavy and aging heavy industry. While this association has a grain of truth to it, EDM has always been heavily used in research and development. But this kind of work was still only done by large companies that could afford to invest in large and expensive EDM machines.

Radnor Technologies aims to change this. A small company founded by Kobus Coetzee, Radnor Technologies produces the Sias table-top EDM drill, combining the capabilities of small hole and die sinker EDM machines in a briefcase sized package. Designed and built by a maker for makers, the Sias EDM machine puts electrical discharge machining within reach of researchers and small-scale machinists. Made with high quality custom-machined components and with a modular design, these machines are built to last. After two years and eight prototypes, Radnor Technologies is on the verge of releasing its first production model.

A Sias spark eroder drilling.

EDM has a history of innovation, opening up machining to novel materials and expanding the possibilities of mechanical engineering. But beyond the achievements of any one company, Radnor Technology’s EDM machine is poised to change the face of the industry, smashing the bottleneck of innovation and giving independent machinists, universities, and laboratories the opportunity to contribute to technological development.

Check out Radnor Technology’s website to learn more about the Sias EDM machine, or visit their Indiegogo page. Radnor Technology needs capital to get this machine into production, and all contributions help turn their vision into reality.

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Holepop Going to SoCal Aerospace Expo 2017

SoCal Aerospace Expo Logo

2016 was an exciting year for Holepop, giving us our first experience at an exposition. Participating in SpaceTech Expo 2016 taught us a great deal about the way expositions work, and exposed us to many valuable customers and collaborators. Our experience also emboldened us to participate in expositions in the future, and we are excited to announce our participation in the upcoming SoCal Aerospace Expo. We relish the opportunity to connect with aerospace companies, companies who value quality and dependability above all else.

Holepop has always focused on the aerospace industry for a couple of reasons. The first reason for our focus is personal interest. Holepop owes its existence in large part to the undeniable cool-factor of the aerospace industry, which motivated Holepop’s founder Chadd Miller in his early efforts to establish the company. All of us at Holepop share this enthusiasm for aerospace, acutely aware of the ways the industry has transformed the technological landscape, and excited for transformations to come. The second reason for our focus is our recognition of how inadequately aerospace has been served by EDM suppliers in the past. Holepop has always operated with this in mind, and our unique, customer-based approach to business is ideally suited to customers heavily invested in research and development who require suppliers to be nimble. Customized solutions are our specialty, and parts with unusual or altogether unique specifications are tackled with aplomb. We work closely with our customers to make sure they receive the parts they need, engineering completely new parts if necessary. Our quality assurance process ensures customer satisfaction.

Though the opportunity to connect with the most prominent and technologically prolific companies in the aerospace and defense industries could be seen as daunting, we are confident in our preparation, experience, and capabilities. SpaceTech 2016 gave us valuable experience in the staging of an exposition booth, and we know that we have a compelling message for aerospace companies. For aerospace companies pushing the boundaries, Holepop EDM Supplies & Electrodes offers solutions that enable rather than constrain creative engineering.

Make sure to visit us from March 8th to 10th at the Los Angeles Convention Center. The SoCal Aerospace Expo seeks to encourage cohesion among aerospace companies and their suppliers, to make Southern California more competitive in the global marketplace. Prominent aerospace companies such as Lockheed Martin and Northrop Grumman will be in attendance, along with other opportunities to network during special matchmaking events. We hope to see you at the expo.

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Breaking Down Dielectric Breakdown

An electrical discharge between two conductors.

Liquid dielectric used in electrical discharge machining serves a few purposes: to flush eroded material away from the workpiece, to cool the electrode and workpiece, and to minimize spark gap size. The mechanisms by which liquid dielectric flushes and cools are fairly obvious. How the spark gap is minimized by the dielectric is a bit more complex and requires an understanding of the physics of electricity and magnetism.

Let’s start with the basic mechanism of EDM: the spark. A spark is created when the attractive force between separated charges grows strong enough to create a conductive channel in an otherwise insulating material. The spark generated when you touch a doorknob after shuffling around on a carpet is a channel of plasma; normally insulating gas particles are separated from their valence electrons (ionization), which momentarily turns that channel of air into a conductor, by which the separated charges evenly redistribute themselves, attaining electrostatic equilibrium.

A certain force between separated charges must be achieved in order to create such a conductive channel, and the agent through which these forces are exerted is called the electric field. When a spark is generated between two objects, charge separation is lost, and the electric field disappears. So the process that allows for the creation of a spark can be described as breakdown of the electric field, and the voltage required to achieve this breakdown is called the breakdown voltage.

With the simplification of the workpiece and EDM electrode as spheres or points of charge, the voltage between electrodes can be seen as the product of the distance between electrode and workpiece and the electric field strength. Since the strength of the electric field exhibits an inverse square relationship with distance, the product of the electric field with the distance between electrode and workpiece results in an inverse relationship between voltage and distance. The farther away the electrode is from the workpiece, the lower the voltage. Because of the relationship between the electric field strength and voltage, a very strong electric field can achieve breakdown voltages at relatively long distances from the workpiece. In EDM, this means a large spark gap, and a large spark gap introduces randomness and inaccuracy in drilling.

To reduce the spark gap, the electric field can be weakened, and without lowering the voltage, this can only be achieved with the use of dielectrics. By placing a dielectric in between two conductors, the electric field between those conductors is indeed weakened. But dielectrics are insulators with no net charge, and neither of these properties influence electric field strength. Reconciling these properties with the undeniable effects of dielectrics requires a discussion of polarization.

Another situation in which the influence of electric forces on neutral conductors is observed is when a balloon is rubbed against hair, and then stuck onto a neutral insulator, such as a wall. The molecules in wooden paneling exhibit an uneven charge distribution, and an excess negative charge on a balloon creates an electric field that spins the positive ends of these molecules towards the balloon. Since the electric force is inversely proportional to the square of the distance, even the very small distance separating the positive ends of the molecules in the wood from the negative ends creates a slight net positive electric field, the induced electric field. The negative electric field from the balloon interacting with this positive field results in an attractive force.

A dielectric placed between two conductors is similarly polarized. As seen in the balloon example, this induced electric field points in a direction opposite that of the field that induced it (negative balloon inducing a positive wall). These opposing electric fields create a net electric field weaker than the original field, thereby allowing for a very small spark gap.

Without dielectrics, spark gaps would be so large that EDM would not be viable as a machining method. Their ability to dampen electric fields, flush material, and cool the workpiece and electrode make dielectric fluids an essential part of any EDM operation, and while often overlooked, they should be appreciated for their unique properties.

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Superalloys and EDM

Gas turbine engine interior showing all of the compressor blades.

One characteristic that separates electrical discharge machining from more conventional machining methods is its ability to drill through materials that are very resilient with great efficiency. Though many of these materials are elements such as tantalum and niobium, most are elemental mixtures called superalloys. These superalloys generally share a face-centered cubic crystal structure, a structure that imparts great strength through its many chemical bonds. The following materials are used by many of our customers in a wide variety of applications.

  • Hastelloy – Used in the pressure vessels of nuclear and chemical reactors, hastelloy is a nickel-based alloy that resists corrosion.
  • Invar – A material originally developed by Swiss physicist Charles Èdouard Guillaume, invar is a nickel and iron composite with an anomalously low coefficient of thermal expansion. Because of its dimensional stability, it is commonly found in precision instruments.
  • Kovar – Kovar is an alloy designed to match the coefficient of thermal expansion of glass. This allows it to be used as a seal with glass, lending it to use in glass instruments containing a vacuum, such as light bulbs and vacuum tubes.
  • Niobium – The characteristics of niobium lend it to use in many different alloys, with varying applications. It can be added to steels to improve its general strength, used in superalloys to increase hardness, and in superconducting magnets.
  • Tantalum – An element with extremely similar characteristics to niobium, tantalum’s applications overlap quite a bit with those of niobium. Like niobium, it is used in corrosion-resistant materials, while its high melting point lend it to use in vacuum furnaces.
  • Stellite – A corrosion-resistant and very hard material, stellite is used for machine parts and tooling. They are also used for valve components in internal combustion engines.

The same properties that make superalloys so valuable in extreme engineering projects make them very difficult to work with, and many of these materials would in fact be useless if not for machining methods like electrical discharge machining. Electrical discharge machining operates on principles that sidestep the physical properties of superalloys that make them so robust, and does not drill by physical contact. In facilitating the manipulation of superalloys, EDM gives engineers the freedom to use whatever material suits the application, even materials that resist conventional machining.

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Our Space Tech Banner

Top of the Space Tech banner for Holepop EDM Supplies & Electrodes

The fast-approaching Space Tech Expo has kept us preoccupied for the past couple of months in feverish preparations, and has given us opportunities to think about how we want to present ourselves, as an EDM hole popper supplier. Not content to settle for a 3’ by 6’ pop-up display, we opted for a custom-printed 9.5’ by 7.5’ backdrop. The design of the banner presented some unexpected challenges. It took us weeks to make sure the material was fire retardant alone. The design of the banner itself went through multiple iterations before we were completely satisfied. The end result properly conveys our belief that we only improve by being challenged, and that space exploration has presented some of the greatest challenges in human history, propelling human development to an unprecedented extent. See for yourself.

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Our Relationship with Research

Headline for space tech newsletter article about Holepop and Case Western Reserve University.

Working with companies in the aerospace and defense industries puts us in close proximity to cutting edge technologies on a daily basis. It’s only natural that industries of all kinds are incubators of new technologies—what sells is often unprecedented, more efficient and simply better than what has come before, while the capital of big businesses allows for large research and development budgets. But sometimes it takes inquiry unfettered by the incentives of free-market capitalism to make really interesting discoveries, those inspired by a naive sense of wonder and raw curiosity. It is often this sense of wonder that propels us along the road to careers in the aerospace and defense industries in the first place, and we certainly haven’t lost sight of this at Holepop. This is why we value our relationships with those in academia. The profit margins may not be as high, but our contributions to academic research are a genuine source of pride for us.

We recently partnered with Dr. Jeffrey Pigott at Case Western Reserve University in his studies of seismic anisotropy. Check out our press release about Jeff and his research about the Earth’s core here. Collaborating with colleagues Dr. James Van Orman and Professor Henry Scott at Indiana University South Bend, Dr. Pigott has used our electrodes to cut zinc slugs. Using these slugs, Dr. Pigott can simulate the pressures and temperatures found in the Earth’s core, furthering our understanding of Earth and materials science. Scientific research often takes us in unexpected directions, and it’s not enough to say that the efforts of academics is not valuable to society because of the absence of financial returns. The benefits of scientific discovery to society sometimes cannot be directly measured, but are almost never completely intangible. It is in keeping with this philosophy that we have relationships with researchers like Jeff, and we hope to help many like him and those at Case Western Reserve University in times to come.

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Holepop at Space Tech Expo

Space Tech Expo logo.

As a business grows, there come certain points where a significant change has to be made, whether it be a shift in the culture or the addition of new staff or even whole departments. These changes are often natural consequences of growth and are often themselves catalysts for many future changes. It is with this in mind that we announce our future exhibition at the Space Tech Expo in Pasadena from May 24th to 26th. Attendees of many trade shows, we will finally be on the other side of the table, speaking to anyone interested in our electrodes and other EDM products.

Exhibiting at the Space Tech Expo is an exciting and potentially fruitful opportunity for us, but it brings many challenges. Should we prove able to convey a comprehensive and technical knowledge of electrodes, consolidate and unify the aesthetics of our brand, and avoid all of the potential logistical pitfalls of a major trade show, we are sure to benefit greatly from the exposure. Additionally there is the less tangible and possibly more valuable benefit of maturation. To come out of this experience unscathed will mean the emergence of a new and improved Holepop. We feel up to the challenge, and are ready for the changes to come.

If you are interested in visiting us, we will be at booth 9114. We’ll be showing off some genuine jet turbine blades, with cooling holes drilled with EDM. We’d love to discuss our manifold services, and we hope to see you there!

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Why We Love The Martian

Mark Watney surveys the desolate landscape of Mars in the movie, The Martian.

On July 20, 1969, more than 600 million people watched as mankind landed a human on an extraterrestrial body for the first time in history. This moment galvanized an entire generation to study science, mathematics, and physics. It was a moment of unalloyed optimism in human progress and—more importantly—the vehicle of human progress, science. After Apollo 11 humans walked on the lunar surface five more times, already making space travel seem routine, and marking the beginning of a slow loss of interest in space travel. The awe that accompanied the first lunar landing slowly evaporated as developments in the aerospace industry over the next decades made space travel easier and easier, while our goals for space exploration became less and less ambitious. The moon landings gave way to the space shuttle, a vehicle whose relatively mundane missions were never publicized or followed in the way that The Apollo Program’s were. Then of course the Challenger and Columbia accidents made people question whether the scientific discoveries made possible by space shuttle missions were worth the inherent dangers. People became disillusioned with NASA. Out of this disillusionment has grown a perception that NASA takes public funds away from more pragmatic programs. It is popular to point out how many of the homeless could be fed for the cost of a single rocket launch, for instance. And among those that have stayed loyal to space exploration, a sense of frustration has grown around the ever waning budget of NASA. But with The Martian, it seems like those days of disillusionment are coming to an end.

The Martian, taken by itself, is a very solid science fiction movie. It has a scrupulous approach to science that makes it one of the most believable science fiction movies I have ever seen—which is important, since it does not take place too much further in the future. It has an interesting cast of characters, none of whom seem superfluous. It has good performances from all actors and actresses involved. And it has a compelling story. But I think the film goes beyond these basic qualities. Watching this film left me with a feeling of complete contentment. It made me excited about the possibilities of a life devoted to the scientific. The Martian is all about what humans pushed to their limits can do with science. It depicts Mark Watney, a stranded astronaut using his wits and the technology around him to survive on a barren planet millions of miles away from Earth. It shows the collaboration of the people at JPL and NASA, as they figure out how to get Watney back home safe. It goes beyond showing the scientific achievements of one nation, encompassing humanity in its depiction of a China ready and willing to cooperate with the U.S. when NASA’s initial efforts fail. And it shows the impact of a single epiphany of genius, when Rich Purnell’s idea of gravity assistance allows for the ultimate rescue of Mark Watney.

It merits asking, when a mission to Mars may still be decades away, what role The Martian has to play in the alleviation of current disillusionment with the space program and space travel in general. This film marks a turning point—inasmuch as it reflects and influences the zeitgeist—where people are more idealistic and hopeful about space travel. It is films like these that can lead to a fundamental change in public opinion. A public that is excited about space exploration can lead to the political will that might send people to Mars. That is not to say that space exploration is still languishing. Private sector companies like SpaceX and Virgin Galactic are picking up the slack of the public sector. Recently SpaceX landed the first stage of its Falcon 9 rocket, a revolutionary development in rocketry that could make launching payloads much cheaper than ever before. To me and to everyone else at Holepop, The Martian represents a renewed sense of hope in the progression of the human race.

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Precautionary Tips for Handling EDM Machines

A German caution sign.

Harnessing powerful forces to do precision work can get messy when those forces are not harnessed properly. In a machining environment, it is of the utmost importance that you are not lulled into complacency. What follows is a discussion of the dangers associated with electrical discharge machining and what you can do to avoid them.

Electric Shock

You may not be surprised to learn that electrical discharge machining presents a hazard of electrical shock. As an EDM operator, there are certain things you can do to minimize this risk.

  • Never touch the electrode while the machine is in operation.
  • Make sure that your work area is grounded.
  • Make sure that the area around the machine is dry.
  • Do not wear conductive clothing or accessories such as jewelry.


  • Wear appropriate eyewear, and never look directly at the spark.
  • Wear closed toe, non-slip shoes with rubber soles. Shoes should be comfortable as well, since you may be standing for extended periods of time.

General Safety Tips

  • Keep your machine well-maintained. Your machine should clean and lubricated. When it needs maintenance, make sure the work is done by a well-qualified professional.
  • Know your machine. One of the best ways to prevent accidents is to not do anything whose consequences you are not well aware of. Learning the idiosyncracies of your machine will minimize the unexpected.
  • Keep the area around your machine free of flammable materials.
  • Stay alert and give your undivided attention to machining. Intoxication on the job should be avoided.
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