Rougher than Normal Finish?

Question: My Elox Astra model A25S power supply is giving us a rougher than normal surface finish. We have determined that the ON-Time switches are at fault. We can get what we want by lowering the ON-Time, but something is definitely wrong. How can we debug this?

Answer: There could be a very simple explanation. The Elox model A25S power supply includes an additional multiplier switch in the center of the thumbwheel assembly. The intention of this switch was to allow ON/OFF settings of greater than 999 µs when using metallic electrodes.

In the U.S., many companies use only graphite and it is not uncommon to ignore the multiplier switch. Some EDM operators may not even know what the multiplier switch does.

It is quite possible that the operator inadvertently changed the multiplier to X2. This would cause the ON and OFF time to essentially double. A programmed value of 100 would behave as 200. This would also explain why you are able to compensate by changing the ON/OFF settings.

If the multiplier switch is correctly set at X1, we need to look a little deeper into the cause. The thumbwheel switch connects to the Elox MVB board through a multi-conductor ribbon cable.


Attach the scope probe tip to TP305 and clip the scope ground clip to the “GND” test point on the MVB board. With the scope connected, turn the power on and look at the waveform. There should be a TTL (5V) logic-high. TP305 will show an inverse signal. For example, if the thumbwheel was set to 100-ON and 30-OFF, you would see the 100-ON as logic low and the 35-OFF as logic high.

Try the programmed value that is not behaving correctly. If the ON/OFF time is not correctly found at TP305, then a malfunction of the MVB assembly has been confirmed. The MVB board, thumbwheel switch assembly and ribbon cable should be serviced as a set.

If the scope reveals that the ON/OFF time is being correctly developed, then the problem likely is caused by peak current relays on the output module that are stuck on. Degraded surface finish can be caused by several factors. ON-Time and peak current are the two most prevalent. If a peak current relay is stuck on, it can cause a poor surface finish. Lowering the ON-Time will compensate and improve the finish. It is easy to misdiagnose an ON-Time problem when the fault lies with the peak current.



Elox Astra Resistor Failures?

Question: My Elox Astra power supply is experiencing repeated resistor failures on the output module. We replace the resistors, but they only last a few months. Why is this happening? What can we do?

Answer: There can be many reasons that module resistors fail. The most common is excess heat. The image above shows two Elox resistors. The upper resistor appears as typical in use. The lower resistor shows windings that have become so hot that they have damaged the vitreous enamel coating. The area highlighted in yellow has become so hot that the windings have failed.

The resistors shown have a factory rating of 175-Watts. However, in service, the resistors are actually subjected to slightly more than 750-Watts. This is more than 400% of its rated value. The 175-watt rating is based on convection cooling. With forced-air cooling, the rating is extended. The Astra power supply uses a large blower to draw air in through a filter on top of the power supply and out the rear. That air flow increases the wattage rating of the resistors. Figure 2 shows the blower used in the Astra.

The blower has a rating of 965 CFM in free air. However, as dust and debris becomes trapped in the air filter, the restriction reduces the air flow. At just 0.3 inHg of static pressure, the air flow drops off to 850 CFM. At 0.6 inHg of static pressure, the air flow falls to 710 CFM. As the air flow drops, so does the effective wattage rating of the resistors. The propensity for resistor failure increases proportionally.  

Perhaps the solution for premature resistor failure can be as simple as increasing the frequency of the filter change. However, it is also possible to measure the air flow to determine whether there is a problem with the blower motor itself. Knowing the discharge area on the back of the power supply, we can calculate the speed at which the air should be exhausted from the back. A typical Elox Astra has a discharge port that equates to 10.324” x 10.324” square. With no filter installed, the exhaust air speed is 397 meters/minute, or 14.76 MPH. A simple hand held anemometer can be used to check exhaust speed and determine whether the blower is functioning properly. Below is a spreadsheet to calculate the exhaust speed based on the exit port size and blower CFM in your power supply.

Spreadsheet: Power Supply Exhaust Speed

Another option to minimize resistor failure is to upgrade to a higher capacity resistor. Figure 4 shows a ribwound resistor. The extended ribbing visible in the photo greatly increases surface area. The result is a 171% increase in cooling capability. Or another way to look at it is an ability to survive in a 58% decreased air flow.

The resistor upgrade is a particularly good idea if the EDM is operated in an area subjected to elevated ambient temperatures. It is also a good idea if there is a need to achieve high levels of repeatability from cut to cut. As a resistor gets hot, its resistance changes. This causes the amperage going into the cut to change slightly. The amperage change affects surface finish and cavity size. The ribwound resistors run cooler, so there is less of a temperature related impact on surface finish and cavity size.


Preventing Elox Astra Electronic Failures

Question: My Elox Astra Power Supply continues to have electronics failures. My maintenance department is blaming conductive dust. We change the air filters regularly, what else can we do?

Answer: The Astra Power Supply requires a high volume of air to cool the components inside. Unfortunately, the air filters on top do not do a very good job of removing dust from the incoming air. In addition, the side doors, control drawer and front panel are not sealed, so dust can enter from multiple places. With the advent of high-speed electrode milling, many EDM departments have environments that are far from conducive to Power Supply longevity.

There are some steps that can be taken to mitigate the problem. One of the most helpful steps is to conformal coat the circuit boards. Chemtronics manufactures an aerosol product called Konform, It is spayed on from an aerosol can like spray paint. It is clear and dries almost transparent. When cured, it provides an electrically insulating barrier that will prevent conductive dust from damaging circuits. It has an added benefit of being very thermally conductive and can actually help eliminate hot spots on the circuit boards. The only down-side to coating the boards is that the coating makes it difficult to troubleshoot the board for service. However, as long as the repair tech knows the coating is there, it can be easily scraped off in the spots where checks need to be made.

Additionally, adding some sealing tape around the door and panel edges can help to prevent unfiltered air from entering through the cracks. A change in air filter to a dust reduction style can also be a help. However this comes with some caveats. The pleated dust reduction filters will reduce the overall airflow. This will require the filters to be changed more often and may lead to high internal temperatures when operating at high-power on hot summer days.

Perhaps the best practice in keeping Power Supplies operational is to do all of the steps above and include an annual deep-cleaning where the units are thoroughly cleaned. This should give you the best chance for long-term operation with minimum down-time.


Beat the Heat

Summer can take a toll on your EDM equipment. Elevated ambient temperatures and brown out power conditions can tax an EDM to the point of failure. Here are a couple of tips to keep your equipment running cool when the temperatures rise.

1. Keep equipment clean.
How many times have you heard that? But it’s true. Dirty filters and dust caked electronics are the number one cause of power supply problems during the summer months. Replace the air filter as needed.

2. Be careful when using an air hose to blow out a power supply.
Use extra care when using an air hose on a dirty power supply. In most cases the dust is full of conductive particles. Blowing the dust could cause the conductive elements to lodge in critical areas that are not part of normal air flow – such as between the pins of sensitive electronic devices. In addition, using too much air pressure could loosen components. Try using a brush with a vacuum to get most of the particles. If you do use and air hose, make sure to turn down the pressure.

3. Be sure that the power supply is set up to match incoming voltage.
It is critical that the power supply transformer be properly configured to match the incoming plant voltage. Even machines that are in service for years are prone to this as it is not uncommon for utility companies to make subtle changes that will affect incoming voltage.

4. Check main blowers.
Your power supply has one or more high-volume blowers used to pull outside air into the power supply and remove heat from inside the cabinet. Over time, these blowers can become caked with dirt and their operation will be degraded. Clean or replace dirty or inefficient blowers.



Elox High Voltage and Capacitance Settings

ELOX EDM High Voltage and Capacitance Settings

Using the right settings on your Elox power supply can make a big difference.

Elox EDM power supplies are designed to operate with a standard output voltage (gap voltage) of 70-80 volts depending on the incoming shop voltage. For most work this open gap voltage works well especially when using a graphite electrode on a common metal work piece like mild steel. If you are working with materials that are difficult to cut such as tungsten carbide, high nickel coatings, low conductive materials like PCD (polycrystalline diamond) and weld slag, you need to take advantage of high voltage and sometimes a combination of high voltage and capacitance. The high voltage setting increases the gap voltage (some Elox power supplies have both hi-pol and elo-pol settings, which are both high voltage settings). This does two things; one is that it increases the physical gap between the electrode and the work piece allowing for better flushing, the other is that it generates a hotter spark allowing the spark to push through low conductivity materials and more effectively melt hard materials with a higher melting point than mild steel.

Capacitance differs from the high voltage setting in that it produces a higher gap voltage spike at the inception of on-time only. The high voltage setting creates a constant high voltage throughout the on-time cycle. That initial high voltage spike created by the capacitors helps establish the cut and begin to melt the work material.

These two settings can be used in conjunction with each other for really stubborn jobs. They are also necessary a lot of times when a metal electrode is used like steel. Unlike graphite, metals conduct thermal energy very well which can rob heat from the cut, slowing metal removal rates. The high voltage and capacitance settings generate a hotter spark compensating for this issue. There is a cost though. Using high voltage and capacitance can significantly increase your electrode wear, especially if you are using a material like copper that has a lower melting point. Additionally, you should be careful to keep your on-time relatively short when using capacitance. Because of the time it takes to charge and discharge a capacitor, a long on time like 200ms for example, can create a situation where the capacitor is out of phase with the on-time/off-time cycle. This results in the capacitor discharging during the off-time portion of the cycle. At that point DC arcing occurs and your cut will become very unstable or stop all together.

EDM Zap offers EDM training either onsite or at their facility. Contact EDM Zap for more information.


EDM Oil / Dielectric Fluid Tips

EDM Oil / Dielectric Fluid Tips

Use Appropriate Fluid
Use the appropriate fluid – in sinker EDM machines use dielectric fluid. Sounds simple enough, but many shops use a cheap mineral oil in an effort to save money. Fluids not designed for use in an EDM system may be dangerous to the operator, the workplace, and could damage your EDM equipment. Mineral oil does not have the fluid properties to be effectively used in EDM. The savings of a couple hundred dollars isn’t worth the risk. Remember, use fluid specifically designed for EDM.

For low amp fine finishing work, choose a fluid with a low viscosity. The low viscosity allows the fluid to get into the cut of material and help flush out particles. Generally, because these fluids have a low viscosity they also have lower flash point – not for rough cutting with high amperage. For roughing work, choose a fluid with a high flash point.

If you are like most shops and the machine is used for every application, choose a good overall performer. Dielectric fluids EDM 3001 Lite, Clear-3, EDM 3033 provide good overall performance in most EDM situations from fine finishing to roughing.

Petroleum or Synthetic?
Generally a synthetic fluid is better; longer life, better performance, and excellent operator acceptance. However, synthetic fluids cost more and depending on what applications you are using your EDM for, sometimes it makes sense to choose petroleum over synthetic. BUT, be careful when selecting a synthetic. Some low cost synthetics are not fit to be called synthetics. A low grade “synthetic” or “synthetic blend” is not any better than a good petroleum fluid…and it may be worst!

Keep in mind that highly refined petroleum EDM fluids such as EDM 3033 perform almost as good as many synthetic EDM fluids on the market. However, a petroleum fluid life span is usually less than a synthetic. In addition, semi-synthetic Clear-3 provides some of the benefits of synthetic and is economical for most shops. Generally, if your budget allows choose a quality synthetic fluid such as EDM 3001 Lite. It will last up to 6 times longer than petroleum fluids and will pay for itself in the long run.

A simple way of extending the performance of EDM fluid is to replace filters often and to replace them with quality filters. Some filter sizes are available in “cheap” alternatives from an automotive, truck, or industrial supplier but the quality is low. Remember, your EDM machine is only as strong as its weakest link – using a cheap filter affects the performance and shortens the life of the fluid.

Combining Fluids
When dielectric fluids are combined, a mixture of a wider distillation range is generally the result. Distillation implies that lower boiling components of a mixture are among the earliest to vaporize with heat. The resulting material is often higher in viscosity than the initial mixture. Possible effects of mixing dielectric fluids of different distillation ranges are slower removal rates, rougher surface finish, and higher fluid evaporation rates. Generally mixing fluids is not recommended.

Replacing Fluid
If you are replacing your EDM fluid, there are a few things you can do to maximize the performance of the new fluid. Always try and remove as much as possible of the old oil. Clean out your system including any sludge or waste at the bottom of the work tank, base, and reservoir. Drain hoses and pump housing. Remove old filters and clean out the filter canister and replace with a new filter. If you are using an external filtration system or centralized system, take appropriate actions to clean out any hoses, tanks, and reservoirs it may have. These suggestions are especially important if you are replacing a petroleum fluid with a synthetic fluid. Some minor contamination will not affect performance, but heavy contamination will.

Recycle Fluids
It is important that you dispose of fluids properly. There are many organizations that will recycle used dielectric fluid.

Avoid Contamination
Care should be taken to prevent water from contaminating the dielectric fluid. Water in dielectric fluid lowers its dielectric strength and in some cases can cause excessive arcing making it necessary to replace the fluid. In addition, if drums are being stored outside place them on their sides to prevent any water from leaking into drum.

Hydraulic fluid should also be prevented from contaminating the dielectric fluid. In addition to possible filter system damage, it could also cause harm to your machine. Dielectric that has significant hydraulic fluid contamination should be replaced immediately.

Health and Safety
If you have been around EDM machines for a while, you know some EDM oil can smell and irritate the skin. Today, quality EDM fluid is available which can minimize odor and the effects on the skin. High quality petroleum products such as EDM 3033 have virtually no odor and usually do not irritate the skin. Synthetics and most semi-synthetics such as EDM 3001 Lite and Clear-3 also have virtually no odor and do not irritate skin. Of course, there are some individuals that are so sensitive to chemicals that they may react to even the purest of fluids. Many individuals skin is not irritated by the dielectric fluid, but by contaminates and particles introduced during the EDM process. Wiping hands with oily rags or towels which may contain small EDM’d particles could cause many very small cuts which can lead to skin irritation.

It is strongly recommended, as with all chemicals, that you limit exposure. Similar to house-hold products, it is suggested that you wear gloves and have adequate ventilation. Do not put hands in the dielectric fluid when it is not necessary. Use of a barrier lotion or gloves will aid in the protection of skin.



Don’t Ignore Your Hydraulics

A lot of EDM productivity is lost due to neglected hydraulic systems. An un-maintained hydraulic system can affect EDM performance. Is your machine experiencing any of the following symptoms?

  • Unstable cut
  • Head speed slower than it used to be
  • Roughing ok but EDM slows down during finishing
  • Difficulty getting a good surface finish
  • Metal removal rate degraded over time

If you are experiencing any of the above issues, your hydraulic system could be compromised. Many jump to changing their servo valves, only to have the problem reappear weeks later. The root cause of the problem is actually in the hydraulic tank itself. Oil breakdown and normal wear and tear of the hydraulic pump creates shellacs and particles that will cause a hydraulic valve to become slow and sticky.

The solution is to drain all of the oil from the hydraulic tank and carefully wipe out the inside of the tank. Change the filter and refill using the proper hydraulic oil. Use a cycling valve / flush kit to clean the system before installing the servo valve. If the system was performing slowly, the servo valve should be sent out for reconditioning.

Hydraulic maintenance should be performed once a year for machines that run 3 shifts and every 3 years for single shift shops.

How can EDM Zap help?
In addition to offering all the parts you need to replace your Elox hydraulic system, they also rent the cycling valve/flush kit used to clean out the hydraulic system.



Thin Flushless Ribs

Thin Flushless Ribs

To make deep pockets and flushless rib cuts possible you need pulsing functionality. However, a pulser alone will not always make those cuts easy but the ability to pulse rapidly is the key to success. When the ram retracts away from the part it creates a vacuum. That vacuum pressure sucks flush down into the cut to wash debris away. Conversely, when the electrode is pushed back into the cut it displaces that flush causing it to exit the cut, carrying away the debris.

The more rapidly the ram can retract and advance, the more effective it is at flushing debris out of the cut and reducing arcing. It would not be uncommon for a hydraulic cylinder on an older EDM machine to achieve speeds of only 10 to 20 inches per minute (typically the larger the weight capacity of the machine the slower they move). In contrast there are modern servo driven actuators that can move at speeds of 300 or more inches per second.

If you do not want to invest in an electric servo motor conversion upgrade there are a few things you can do to help you achieve success. Make sure your EDM oil is as clean as possible at all times, keep your electrode and fixturing weigh as light as possible, adjust the pulser settings to determine the optimum retract speed, duration and distance for the job and you may need to lower your anti-arc sensitivity if your power supply has anti-arc protection circuitry.

For older EDM’s such as the Elox, the EDM Zap Ram Pulser is an electronic timer that improves cutting conditions in the EDM gap.