Graphel Carbon Products’ Blog Nationwide

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EDM Cavity

As the cut progresses through the work metal a cavity starts to form. The deeper this cavity becomes, the harder it is for fresh dielectric fluid to get into the cavity to remove debris and quench the work piece and electrode. In order to get smooth, even flow of dielectric through the gap, flushing becomes an essential part of the EDM process.

Good flushing allows the work piece particles and eroded electrode particles to be removed from the gap. Flushing also allows fresh dielectric into the gap. Both are necessary to maintain stable cutting and to prevent arcing.

It is the volume of oil moving through the gap that performs particle removal. Turbulence in the tank would indicate not enough volume and too much pressure. The ideal pressure is usually between 3 to 5 psi. Flushing at higher pressure may actually prevent the flow of particles out of the gap and the dielectric renewal in the gap. High pressure also tends to wear the electrode.

The balance of volume and pressure is important. Roughing operations where the gap is large would require high volume and low pressure for good oil flow. Finishing operations where the gap is smaller may necessitate higher pressure to improve the oil flow.

The three basic types of flushing are pressure, suction, and external. The choice of flushing method may be limited by the application. The electrode shape and size may prohibit through the electrode flushing.

Pressure Flushing

This is the most common method of flushing. Pressure flushing forces the dielectric fluid through holes in the electrode into the gap between electrode and workpiece. Fluid and particles flow up the sides of the cavity. Pressure flushing through the electrode helps cool the electrode.

Suction Flushing

This is the opposite of pressure flushing. Fluid and particles are pulled out of the gap through holes in the electrode or workpiece. This method reduces secondary discharge and tapered walls.

Nozzles or tubes may be used to direct streams of fluid into the gap opening. Fluid and particles are pushed out the opposite side. This is the least desirable method of flushing. Poor flushing conditions can trap particles which may cause DC arcing and pitting.

EDM machining is considered by most to be a thermal removal process. The most convincing support for this claim is the removal of material from the electrodes by melting and/or vaporization by a thermal process, along with pressure dynamics established in the spark-gap. The spark gap generates an electrical force on the surface of the electrode that removes material.

Electric discharge machining (EDM), sometimes referred to as spark machining, spark eroding, burning, die sinking or wire erosion is a manufacturing process whereby a desired shape is obtained using electrical discharges (sparks). Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. One of the electrodes is called the tool-electrode, or simply the ‘tool’ or ‘electrode’, while the other is called the workpiece-electrode, or ‘workpiece’.

Electrode gap (spark gap) is the distance between the electrode and the part during the process of EDM. Electro-mechanical or hydraulic systems are used to respond to average gap voltage. To obtain good performance and gap stability a suitable gap should be maintained.

The EDM process is based on the thermoelectric energy. This energy is created between a workpiece and an electrode submerged in a dielectric fluid with the passage of electric current. The workpiece and the electrode are separated by a specific small gap called spark gap. Pulsed arc discharges occur in this gap filled with an insulating medium, preferably a dielectric liquid like hydrocarbon oil or de-ionized (de-mineralized) water. In this process there is no direct contact between the electrode and the workpiece thus eliminating mechanical stresses, chatter and vibration problems during machining.

As an electrode moves toward the workpiece the spark gap is reduced so that the applied voltage is high enough to ionize the dielectric fluid. Short duration discharges are generated in a liquid dielectric gap, which separates electrode and workpiece. The material is removed from tool and workpiece with the erosive effect of the electrical discharges. The dielectric fluid serves the purpose to concentrate the discharge energy into a channel of very small cross sectional areas. It also cools the two electrodes, and flushes away the products of machining from the gap.

Engineering materials having higher thermal conductivity and melting points are used as a tool material for EDM process of machining. Copper, graphite, copper-tungsten, silver-tungsten, copper graphite and brass are used as a tool material (electrode) in EDM. They all have good wear characteristics, better conductivity, and better sparking conditions for machining. Tungsten resists wear better than copper. The factors that affect selection of electrode material include metal removal rate, wear resistance, desired surface finish, cost of electrode material manufacture and material and characteristics of work material to be machined.

Choosing Dielectric Fluid for Sinker EDM Applications
April 2018

Choosing the correct dielectric fluid for your EDM application is not always as straightforward as it might seem. Many criteria need to be taken into account. Some are obvious, such as degree of metal removal and electrode wear, while others are much more subtle.

Dielectric fluid is a material whose main purpose is to prevent or rapidly quench electric discharges. Dielectric liquids are used as electrical insulators in high voltage applications to provide electrical insulation, suppress corona and arcing, and to serve as a coolant.

A good liquid dielectric should have high dielectric strength, high thermal stability and chemical inertness against the construction materials used, non-flammability and low toxicity, good heat transfer properties, and low cost. Liquid dielectrics are self-healing; when an electric breakdown occurs, the discharge channel does not leave a permanent conductive trace in the fluid.

Sinker EDM machines typically use hydrocarbon oil for their dielectric fluid, into which both the workpiece and spark are immersed. In contrast, wire EDM machines normally use deionized water, into which only the sparking area is immersed. Whether oil-based or water-based, the dielectric fluid used in EDM machines serves three critical functions:

• Controlling the spacing of the sparking gap between the electrode and workpiece
• Cooling the heated material to form the EDM chips
• Removing EDM chips from the sparking area

Although they’re considerably smaller than those produced in milling or turning processes, EDM does produce chips. These tiny, hollow spheroids are composed of material from both the electrode as well as the workpiece. Just like any chip, they need to be removed from the cutting zone, which is accomplished by flowing the dielectric fluid through the sparking gap.

As the dielectric fluid breaks down—whether as the result of age or contamination—the risk of unstable discharge increases. Control electronics can compensate to a certain extent, but the only real solution is to continually pump clean dielectric fluid through the cutting zone to flush it. The more conductive particles in the fluid, the more difficult it is for the machine to maintain stable electrical thresholds inside the sparking gap.

Because the lifespan of dielectric fluid depends on a host of factors, such as its type and the efficiency and quality of your EDM fluid filters, it has no definitive expiry date. As a rule of thumb, however, if you’re using an oil-based fluid and it’s over five years old, it should probably be replaced. You can also perform sight and smell comparisons between used and new fluids, but the best way to determine whether your dielectric fluid needs to be replaced is with a refractometer.

Choosing the right dielectric fluid for your EDM application is not always as straightforward as it might seem. Many criteria need to be taken into account. Some are obvious, such as degree of metal removal and electrode wear, while others are much more subtle.

SINKER EDM BASIC TERMINOLOGY – PART II – FLUSHING
MAR 2018 Blog

It’s been said the 3 most critical things about a good sinker EDM burn condition are flushing, flushing, and flushing. This is still true today but modern machines have built in technologies that assist with flushing even when the operator doesn’t think about flushing. More on these in a bit.

Flushing is a critical part of the EDM process, as it removes contaminated fluid and eroded particles, and replaces them with clean, temperature controlled fluid. This removes contamination from the spark gap that could develop into undesirable conditions like slow, unstable burns, pitting of the work piece, and possibly destructive DC arcing. Flushing also helps cool the work piece by replacing warmed EDM fluid with chilled fluid. Spark temperatures, even though extremely small, can be in the 15,0000 to 22,0000 F range.

There are a few basic types of flushing. The first discussed here will be Injection Flushing, called such because cooled dielectric fluid is injected through the electrode into the spark gap. This is the most efficient type of flushing for many jobs as it basically pressurizes the spark gap around the electrode to keep a continuous flow of fluid going from the bottom of the cavity up the sides, and out the top. This removes eroded particles and keeps the work area cool. Injection flushing is particularly effective for large, deep, and/or complex shaped burns.

Things to be careful of when using injection flushing:

• Over burn at the top of the cavity due to secondary erosion. This is caused by excess conductive debris being washed out of the burn making the sparks longer.
• A post created where the flushing hole is. This can become unstable as it gets taller and moves around under flushing pressure inside the flushing hole. This can cause sporadic short circuit problems with the burn.
• The area around the flushing holes can become distorted and worn unevenly due to the flow and pressure of the flushing.

Another basic flushing style is Suction Flushing. With suction flushing, a vacuum line is attached to the bottom of a cavity or detail being burned, and the fluid and debris flows downward to the suction point. Suction flushing is very effective in burns with materials that develop smaller debris particles, like carbides. Many times suction flushing will be used together with a part holding fixture, and it is not uncommon to see suction and injection flushing used together on some applications.The last basic flushing style covered here will be Lateral Flushing. Also referred to as Cross Flushing or Sweep Flushing, this form of flushing uses external nozzles to cause of flow of dielectric fluid across the part being EDM’d. Lateral flushing is, in general, the least effective form of flushing discussed here. IF the burn is very shallow and not too big of an area, lateral flushing is effective. It is also effective in setting up flow directions with some burns. Flushing nozzles placed in opposite corners of a cavity can cause a swirl effect around the entire electrode. As with injection flushing, a drawback is deformation of the electrode by the flow and impact of the fluid eroding the electrode in some areas.

Back to those built in technologies I mentioned earlier. Many modern EDM machines have several technologies that assist with or compensate for poor flushing situations.

• High speed axis drives
Can accelerate/decelerate in multiple-G range
Causes a stirring of fluid and debris in the spark gap
Fresh cool fluid sucked in upon retraction as dirty warmed fluid is forced out

• Rotating C-Axis spindles
Extremely effective in drilling deep holes
Rotation of electrode causes swirling of fluid, keeping debris from gathering in one place

• Highly adaptive advanced control systems
Monitors spark activity in real time
Makes changes to spark parameters to prevent a bad condition in the spark gap

• Programmable flushing systems built into machines

No matter how its achieved, flushing is still a critical part of the EDM process. For more information refer to your machine’s user manual or technical support.

RAM EDM, otherwise known as “Sinker EDM” or “Plunge EDM” has been around for over fifty years. Though widely used, there are some who are unfamiliar with certain EDM terminology.

KEY FACTORS OF SINKER EDM

Since Sinker EDM uses electrical energy to remove material, it stands to reason that the make-up of the material will have a direct impact on the rate of removal. This being the case there are three critical things to keep in mind.

• Since machining with Sinker EDM or Plunge EDM occurs by using electrical energy the electrical conductivity plays a key role in how fast the Spark Gap can ionize allowing a spark to occur.

• Materials that are less electrically conductive will machine slower, such as carbides and PCD.

• Pulse energy (heat) is conducted away from the surface of the part with flushing and temperature controlled dielectric fluid. Some of this heat will dissipate into the work piece. Certain materials, like beryllium copper alloys used in molds, are designed to dissipate heat quickly. This will slow down the metal removal rate of the EDM process.

THE EDM PULSE

When we see a flash of lightning we are witnessing EDM on a grand scale. The lightning bolt is electrical energy flowing between an electrode (cloud) and a (grounded) workpiece in a natural kind of EDM phenomena. This discharge is the same as what occurs in an EDM machine.

• An EDM Pulse is highly controllable and there are parameters to determine the size and intensity of the spark.

• On-Time is the length of time the spark is turned on. This determines the depth the spark can travel into the workpiece. On-Time will have a direct impact on final part size and surface finish.

• Off-Time is the period of time between the end of one spark and the ignition of the next. Off-Time allows for efficient chip removal and cooling in the spark gap.

• The combination of the EDM Pulse On and the Pulse Off is one cycle. It has been said that the EDM process can develop as many as 250,000 cycles per second, but only one spark at a time.

• Amperage is the electrical power of the spark. The higher the amperage, the more aggressive the spark, and the deeper the spark can go into the metal. Like On-Time, Amperage will have a direct impact on final part size and surface finish.

The combination of ON TIME and AMPERAGE are the two parameters that will determine spark length, or overburn. Changing the ON TIME and/or AMPERAGE during a burn will change the size and finish of the final result. All other machine parameters will affect MMR and/or electrode wear, but not spark length. To better understand your machine’s parameters, consult your owner’s manual or machine builder.

In our next post we’ll address flushing.

A key area for improvement in EDM operations is the reduction of consumables. New technologies, machine settings and improved material grade limit ram or sinker EDM electrode wear to 0.1% while maintaining productive machining speeds. For wire EDM, new low-consumption technologies reduce the biggest expense—the wire itself—by as much as 50 percent.

With all EDM machines you experience the benefits of designing and cutting complex shapes and tapered holes with hard metals. You can depend that the machine has the capacity to cut exactly what you want.
Sinker EDM machines use an electrode and workpiece submerged in liquids such as oil or dielectric water. A power supply is connected to the electrode and generates electrical potential between both of the parts, producing a breakdown to form a plasma channel and spark jumps. The sparks initiated by the power supply often times strike one another.

In the sinker EDM process, wear on the electrode starts as soon as the erosion process begins. As metal is burned away on the workpiece, the electrode gradually experiences wear and loses it’s fine details and is dimensionally changed. Minimizing electrode wear is not only critical to reducing costs and lead times, but also improving part accuracy.

From a general sinker EDM perspective, quality graphite electrode materials provide the most productive machining speed. The wear rate of a graphite electrode depends largely on the size of the detail, the electrode reduction amount, and the power settings used. But the grade of the graphite is a contributing factor. Using the correct grade of graphite will limit wear and rate of erosion.

Wire electrical discharge machining uses a single string of thin metal wire to cut thick metals for precise incisions and splits. Similar to Sinker EDM, Wire EDM uses an electrode and spark to cut metal. Using a spark erosion technique, Wire EDM machining submerges the part being cut in deionized water and the wire acts as the electrode, creating a spark that roughs or skims the part into the desired shape without the wire ever coming in contact with the part.

The price of a wire EDM machine is minimal when compared to the cost of the wire over the life expectancy of the machine. Excessive wire consumption on a wire electrical discharge machine is costly. Technology that allows slower unspooling speeds without compromising results appears to be the answer. Wire is the single highest expense in operating a wire EDM. With even the least expensive EDM wire running $5 to $6 per pound, investing in low-wire consumption EDM machines appears to be the answer.

A key area for improvement in EDM operations is the reduction of consumables. For Sinker EDM users, consider using better grades of quality materials to reduce cost. For Wire EDM users, consider investing in new technology with machine settings that reduce the amount of wire used.

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November 2017 Blog
Karl Schmidt, QMR/SSBB – Quality Manager
Graphel Carbon Products

This past October, a Japanese company named Kobe Steele was found to be falsifying test records and substituting materials for various genuine metallics used in the transportation industry.  Although rare, this can and does happen in the graphite industry.

Graphel Carbon Products has been AS9100 Certified since 1994, and we verify all of our materials and suppliers.  We only sell materials that are genuine and verified, and do not substitute.  As the Quality Manager here at Graphel, I take my position very seriously, and I am very concerned that our customers are purchasing genuine materials, and are not deceived by substitution.

In today’s manufacturing world, materials production and supply have become increasingly complex.  Business moves quickly, information is exchanged almost instantaneously and pressure for immediate performance can be extremely high – even in industries that have long production cycles.  As a result, product shipment and quality assurance can often struggle to keep up.

Let’s start with the definition of substitution:

Product substitution:  Knowing and willful substitution, without the purchaser’s knowledge or consent, of sub-standard, used  or counterfeit or materials those specified in the contract or purchase order.

Although most graphite materials are not used as a robust structural material, they are still a significant part of your customer’s EDM operation.  If your organization does any work in the supply chain of any major aircraft OEMs, whether it’s EDMing of engine hardware, supplying electrodes, or just graphite blocks you will, and do, effect the EDM process.

Consider the following Aircraft OEM specifications:

• • GE spec. P17TF1-S (Electrical Discharge Machining) lists “Electrode Material” as a “Significant Parameter” that “at a minimum, will be controlled within the limits of a control plan” (ref par 3.5 g)

• • Similar requirements are listed for Pratt & Whitney in MES-3251 & 3252

• • AS9100 D states the following in sect 8.4.2 “Type & Extent of Control” of “External Providers”.

Ok, so what does all this mean?  Basically if you buy graphite, you need to require a test report or a certificate of conformance from your provider. You are obligated to validate the accuracy of that report by either an external or internal source within your organization.

Most businesses’ operational profiles involve complicated supply chains that include multiple potential third party suppliers or contractors.  From a business perspective, some feel that there is a transfer of risk when using third party suppliers, but is this really the case?  If a supplier lets you down, where does the buck really stop? How can you ensure that you are working with the right suppliers, and what level of oversight and accountability do you need to ensure quality.  Unfortunately, most of the answers to these questions are unknown, and the operational realities can be obscured.

So, where am I going with this? If you are getting an unbelievably low cost electrode or graphite material, there is probably a reason.

• • Is your electrode or graphite provider AS9100 certified?
• • Can they provide actual or typical material certifications when requested?

• • Are they providing your organization with certificates of conformance?

Graphel Carbon Products is AS 9100 Certified, and has been since the introduction of the standard. Additionally, we are also NADCAP Certified.  We will and do provide certificates of conformance and actual and typical material certificates.

We stand by our products and assure that you are getting the material you have requested.  Graphel Carbon Products makes sure you are getting what you paid for.

Jeff Immelt, previous CEO of manufacturing giant GE recently stated about Artificial Intelligence, “Companies need to become digital to survive – We must turn information into insights and insights into outcomes.”

That implies we have something to think about:

Manufacturing is changing, which isn’t a bad thing. But technology will become difficult to keep up with if we don’t keep an open mind. Though we embrace new technology in some parts of our shop, one trend in particular should be on our radar:

Artificial Intelligence

It will dramatically change our industry. However, coming to terms with that fact can be intimidating. This is often due to a lack of awareness, or a fundamental misunderstanding of AI.

What is Artificial Intelligence?

Simply put, artificial intelligence is the reasoning and processing capabilities of certain machines. In essence, these machines are built to mimic the cognitive process of humans through the implementation of AI processes. But they’re not here to replace us.

In fact, artificial intelligence is rooted in the idea of creating machines that are as efficient as possible for organizations like us. It’s created as a means to assist us in learning and problem solving, while in turn learning and solving problems. It grows just as we do. And at its best, artificial intelligence allows us and our businesses to achieve our full potential.

Just take a look at what some businesses have already done.

Decrease unscheduled downtime

Unscheduled downtime is a term used to describe a time period in which a company is not producing. This is different than routine maintenance because there isn’t any planning involved. Most disruptions are very costly, and affect delivery schedules. P&G, however, may not have to put too much concern into it anymore.

P&G has decreased their unscheduled manufacturing downtime for personal care products (diapers, toilet paper, etc.) by 20 percent through the implementation of software primarily rooted in artificial intelligence and intrinsically driven to facilitate efficiency. The programs enhance analytics, as well as the ability to optimally connect all phases of the business units.

Analyze industrial variables

A global leader in many facets of manufacturing, Siemens actively searches for ways to maintain their standing in the industry. In fact, for the past 30 years, the company has been researching ways to do it. And the answer they’ve found? Conveniently, artificial intelligence.

Specifically, Mind Sphere, their custom AI system. It has the ability to not only analyze industrial facilities, but also to be applied widespread throughout the majority of Siemens’ departments.

According to their website, and in the context of Siemens’ energy research, Mind Sphere also “significantly reduces the emission of toxic nitrogen oxides without affecting the performance of the turbine or shortening its service life.”

Advances technological knowledge

At Hitachi, the manufacturers’ primary objective is to instill knowledge. So much so, that their use of artificial intelligence involves the notion of instilling knowledge in more than just their people. Specifically, this is seen in their understanding and application of deep learning. And their robots.
Deep learning is the implementation of neural networks to both simple and complex machines. As Hitachi grows in their understanding of it, their goal of allowing machines to do the same does too. Just take a look at their Swing Robot.

Designed with working neural networks, it first analyzed an immense amount of data. From there, it took about 5 minutes, without human intelligence, to figure out how to swing effectively. It sounds like its right out of a movie, but it’s true. AI is beginning to teach itself, which will be beneficial to us all.

Quality is the backbone of your business – without it, you wouldn’t have the reputation in the industry as a quality manufacturer. So, once you have your quality standards set, it’s time to expect the same from your suppliers.

While quality standards will vary, the importance of quality, especially in manufacturing, is a universal requirement. Customers need to be able to trust your brand. To gain that trust, the first thing you need from your suppliers are quality products.

Here are some tips on how to get the quality that you and your customer are depending on.

1. Decide on your own quality standards first.

First and foremost, establish exactly the quality you’re looking for. Have a list of materials and standards that you’re willing to compromise on, and those that you’re not. Is price more important to you, or super-high quality? Establishing all your expectations first will give you a good base to start researching. Also, it will help you eliminate, right away, suppliers that simply can’t meet your standards for any number of reasons.

Also, think about your production needs. Do you require a dedicated production facility for more control? Or, are you willing to go with a shared supplier for a more cost-effective approach? Which is the most efficient for your business model? These are all questions to answer before you think about quality assurance from a supplier.

2. Spend time researching.

Be ready to put time into researching the quality and standards of a variety of suppliers before making a decision. You can visit websites, look at company profiles, ask for references, to see what other customers the supplier is fulfilling.

3. Make sure you “fit” together.

Once you’ve narrowed your suppliers, think about the nature of your organization, business model, and supply chain. Are they prepared for large orders, or quick delivery? Can they supply materials that are only needed occasionally?

Another aspect of fit to consider is location. Would you consider an international supplier for a lesser cost? If so, that’s a consideration, but you may lose some accessibility. If you choose a local supplier, you usually have more control over the quality – but you may have to pay a higher price.

4. Compliance is a must.

After you‘ve narrowed the field further, see what established quality and safety standards the supplier or manufacturer already has in place. This will be a good indication of what they value and how much they value quality standards. Having a base set of standards eliminates a lot of quality control issues from the beginning.

5. Ask for samples.

Ask for samples of the material and test it in your production facility. Have the supplier provide a sample according to your specifications: this includes cuts, finishes, etc. Or consider asking a manufacturer you’re considering to provide a sample of a similarly manufactured article with required tolerances, legs and or angles.

Get the quality that you require.

Finally, it’s about working with the supplier to get what you require from the beginning. You are looking to build long term relationships. When the standards are set, it’s just a matter of choosing the right supplier and holding everyone, including your organization to those standards. Quality can be a time consuming activity, but it is a worthy investment to get the quality worthy of your brand!