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Electrical discharge machines – Technology

Emerging trends in Electrical Discharge Machines

Spark erosion machining is a modern technique with a distinct advantage as a result of the use that is becoming more and more decisive.

SHS continues to be an indispensable technique. Today, EDM has revolutionized the way the majority of high precision molds, dies and complex machined parts are being produced. The most enthusiastic users of EDM solutions to the challenges ahead in metal cutting industry. The capacity of the machine both hardened carbide parts and the highest level of accuracy and superior finish without operator intervention amount that would have been a dream, when erosion of spark came into existence.

These days EDM is not as an obscure term as it was a few years ago, but there are all sorts of vague statements available. For years, researchers have done much Studies on the release process of EDM. Various hypotheses have been made, but still, even now, to understand the differences the discharge process exist.

It is very difficult to describe such a complex process, which most areas are invisible and are accompanied by physical and chemical phenomena such as noise, heat, light, electromagnetic radiation etc. Until now, they are not fully understood or quantified. Various theories, mathematical models, estimation of the state of deficiency has been advanced, but all are approximations, and according to the manufacturer has approached the state more away, is a leader in the field of EDM.

EDM is a process where the cutting of materials and material being cut does not touch, there is always a physical difference between both. Probably this difference, which has created the perception gap in the understanding of the EDM, it is also said that EDMing is an art. Over 20 years, many innovative ideas have made the lot predictable process.

Ater the second world war, the scientist Russian BR & NI Lazarenko Lazarenko EDM process invented and since then there has been ongoing research. In the past 20 years, EDM has become 6-8 times productive.

It is very essential to know the basic input / output of EDM to understand and appreciate innovation in the field of EDM

INPUT

v electrode material

v equipment part work

v Di electric media.

EDM process

v High Temperature

v Electromagnetic forces

OUTPUT

cutting speed v

v accuracy employment

v Finish.

Traditionally, EDM has been classified into two distinct categories because of the different ways in the adoption process execution.

1. EDM EDM EDM sink or SCUBA or RAM

2. EDM

SINK EDM:

We all know that the fact that job ended EDM can be no better that the electrode used. Performance parameters output as surface finish, accuracy and overall productivity depends mainly on the selection electrode material. It is a known fact that 70% of the work and 20-30% is the cost in the manufacture of the electrode. In the past 15 years, He has been the phenomenal development of the quality of material available graphite electrode in particular. Graphite is now imported easily accessible, which is mainly used in countries overseas.

In India, we are witnessing a change of copper as electrode material graphite. To choose the right material, the supplier provides nearly 15 types of graphite materials and feature complete performance

Decide what material to use for example: "copper or graphite" depends mostly effective method of producing the electrode, employment size, finishing requirements, multiple electrode options. In general, if you ask the user to Asia EDM, the choice is copper and graphite if the user is from USA. In summary, graphite is preferred when the size of the electrodes is larger, it is easily and faster machined on a machining center. Good structure and fine grain sintered graphite imported is now available in India. A major problem in machining graphite in the dust. It is a real headache unless the machines are mainly equipped with special vacuum system to handle dust.

Copper is the material most popular in India because it is cheap and can be machined on a single machine as the tower. electrode copper wire EDM manufacturing is the most popular and fastest method so that graphite EDM is very slow and painful, hence mostly avoided.

From the perspective of the EDM process, graphite is thermally very stable and therefore the subject, electrode wear, very low while copper has been relatively wear.

Although the EDM machine should produce a replica of electrode used, the wear electrodes does not allow it to easily occur and affect the precision and finish of job.

Must

1. The use of multiple electrodes, for example roughing and finishing of the electrode.

2. Dressing the electrode during the EDM process using landfill Electric Car dressing.

3. Change of electrode during the EDM process.

4. Using Orbit 2D/3D cycles to compensate for electrode wear.

5. The use of adaptive control the EDM process to monitor precisely to reduce electrode wear. These different characteristics and strategies are used to achieve the precise size and finish the die or mold.

Innovations in CNC technology has also found its place too in EDM, EDM is a very slow process, speed TNC plays no significant role in improving productivity.

There But

1. Improves EDM process production cycle of some canned, in terms of EDM

which is called as ORBIT CYCLE.

1. Uses adaptive control the EDM process by continuously monitoring the difference

condition and modulate EDM pulse.

1. Simplifies the manufacture of the electrode with multiple segments

electrodes and the use of ATC (Automatic tool changer).

1. Automate manual interruptions such as change of electrodes by using the tool

magazine, and therefore the change of parameters using automatic EDM

selection of predefined codes EDM.

1. Provides a powerful user interface, which allows the user to define only

& Performance, production and automatic selection steps

EDMing EDM and its parameters.

6. Machine Equipped with fuzzy logic based adaptive control

significantly improve the process of EDM, and productivity.

Directly coupled with brushless motors AC are also used by manufacturers to get some faster RAM speeds. This improved performance when machining deep hole EDM, where the rapid retraction of the electrode for a short time is necessary to remove debris EDM in the cavity, therefore, avoid damage to the electrode / cavity due to arcing. Few manufacturers use linear motors to achieve speeds upper RAM.

EDM is a slow process, EDMing greater molds and dies takes time. Otherwise, machines with high speed milling, popularly known as HSM-ups are on the market that can directly machine hardened die plates.

The theory of hard milling is basically the same as conventional milling. hard milling is done on a machine tool specially designed cut is taken to a diet very high (15000-40000). In such cases, the majority of abduction matrix type of material / mold plate is made of high-speed machine and the only complex cavities are machined by EDM process. This scheme not be economic unless dies / molds are large and repetitive nature.

Both processes, EDM and HSM are certain limits and now days, they compliment each other in the Indian job shops and tool rooms.

EDM process has been refined with flexibility repeatability and accuracy that have EDMing high technology specialty in a prominent place that the methods of choice for many types jobs.

EDM wire:

Basic concept of material removal is the same as a sink EDM, but a machine Wire EDM by its design is very different. For example, all the CNC machines are WireEDM where as well-EDM may or may not be a CNC machine.

These machines have been marketed in India in the early 80s. Development in the field of electronics and CNC had a significant impact on wire EDM machines, ie, it has improved performance 6-8 times, compared to the previous version of machines.

Unlike Sink EDM, Wire electrode where EDM is a simple, fixed diameter wire, so that the complexity of the design and manufacture of the electrode will just not.

Effective and high performance machining of hardened parts depends mainly on various factors outside devices the machine itself. It is also important to be assumed that the machine itself. They

1. Wire electrode material.

2. the metal work piece and preparation.

3. dielectric clean water.

4. Clean & controlled environment.

1. Wire electrode material:

Wire EDM has also evolved with the advent of machines to meet the changing demands of machine technology and new applications.

First son was used WEDM by copper wire. Soon brass wire came into existence which is essentially an alloy of copper and zinc. It is an established fact that the higher the percentage of zinc, better cutting speed and break of less wire (We will not go into the theoretical aspects of this.) also improves performance in terms of better surface finish and integrity of the cut pieces in particular carbide and PCD – polycrystalline diamond.

Due to limitations manufacturing processes, wire pure zinc can not be established or made. Existing manufacturing processes to prevent the drawing of reliable and economical wire if zinc content is over 40%. coated wire came into existence with a coating of pure zinc at 100%, but because of the thickness of the coating process limitations can only be a few microns.

In zinc coated wire is consumed quickly due to its vaporization temperature lower., hence its effective use is limited to 80 mm maximum work piece thickness. Diffuse annealed wire with a coating thickness of 30-40 microns and a thermal treatment by a process called annealing broadcasts. It contains 45% zinc provides optimal speed and many manufacturers, including technology Electronica is based on this type of thread.

Researchers are working on technologies to improve the content of zinc. Five years ago, Dr. Dan Tomalin has found a method called "Gamma gradually wire, which allows 65% zinc to maintain the cutting speed increases of 10-50% in many cases.

Now we have options with nearly twenty different types of thread to achieve greater productivity. brass, copper coating, Diffuse brass, steel, brass lined, hard / soft son of molybdenum brass are available to name a few in the world.

As wire diameter is greater than 0.1 to 0.3 mm, current densities are not possible. Thus, the current pulses with a duration very low, down to 1.5 to 2 ms. with high peak currents up to 500A or more are required to be released so uniform. Thanks to innovations in the field of electronics devices fast switching power MOSFET, as allowed to move from short high peak currents. As the number of discharge pulses per unit time, over the removal of material, which is called the rate cut, normally specified that mm2/min.

In the past 20 years, the cutting speed increased by 30 mm2/min. Mm2/min 300., Nearly 10 times.

METALLURGY PIECE OF WORK

Normally, all manufacturers of machines show the cutting speed and finish on a note of special hardened steel for example Electronica Machine show the cutting speed and surface finish of the steel in HcHc brochure.

Cutting speed and accuracy for various different materials due to the variation in the model of metal behavior during EDMing.

TITANIUM:

This is not very common tools used in the Indian room, but it is an important metal in the aerospace and auto racing in the world. Because of its properties natural, it finds its use in the human body for the replacement of various joints and dental implants.

WEDM clippings about titanium. 90% 100% of the speed tool steel, as the thread used. With water as a dielectric oxidation process, makes blue surface size when cutting titanium.

Special anti generators circuits electrolysis minimize these effects.

COPPER:

The use of copper is very important in many industries, primarily in jewelry, electrical son, coins, of tubes and electrodes for EDM wire cut EDM Pulse so he cuts approx. 80-85% speed tool steel.

ALUMINUM

This metal is commercially available in various alloys. Al has the lowest melting temperature, so it cuts about 250-300% faster than steel. Faster speeds and rougher finish are the results while EDMing aluminum.

CARBIDE

It is extremely hard material, mixed with cobalt as a binder material and then sintered. Cobalt is highly conductive, and provides the strength of carbide. WEDming Then, cobalt background first, letting loose carbide bound. This exposes carbide particles and due to water as a dielectric, electrolysis and oxidation still far Leach carbide exposed. It is a common phenomenon on all machines and WEDM is known that the loss of cobalt, which essentially degrades the life of the tool.

guidelines of the technology are given by the manufacturer to minimize this effect.

CLEAN WATER DIELECTRIC

Water as dielectric plays a vital role in WEDM in achieving optimal performance.

Essential characteristics of the water dielectric following: –

1. It should be "mechanically cleaned" the size of the particles is dissolved must be filtered at the micron. Paper filter cartridge or mineral bed filtration systems are generally available.

2. It should be "thermal own." The water warms due to the EDM process and water pumps, water flows to launch the process of EDM. Water coolers is as an accessory comes standard dielectric to maintain the temperature when cutting metal.

3. It should be "chemically clean. Demineralization of water occurs during cutting and conductivity of water increases. mixed bed resins deionizer are available with automatic conductivity controllers to maintain the conductivity at a recommended level.

CLEAN controlled environment

Environment in which the machine is kept must be maintained at a uniform temperature. Normally, it should be a tool room environment maintained between 20 and 22? C.

The temperature variations during cutting may cause –

– Documents to bend or twist

– Deformation of oil

– Elongation factor due to temperature, this deteriorates the quality of the final piece.

In India, due to end heat of summer, many problems related to part accuracy surfaces.

It is also noted that the cutting speed WEDM drops over 15% for the temperature rise of 10%.

Limits WEDM and their remedies.

Effect Bow & Tap and its remedy.

WEDM machines are designed to generate a cone of qualifications recognized by having an axis parallel to the axis Adjunct Senior XY. But the process itself generates WireEDM some Bow / cone effect which affect the details of employment. Each manufacturer provides some guidelines to overcome these shortcomings by applying cuts base or skim cut or cut after multiple first cut. Accuracy of energy at low skim will depend mainly on three parameters, such as control pulse energy states, without electrode wire vibration travel mechanism and perfect control of water jet.

Many manufacturers increased 5 assists finishing with innovative technology to control their more than three parameters.

Strategy against CORNER:

Thanks to significant mechanical and electromagnetic forces acting on the wire in the spark gap, when cutting the wire, the wire tends to deviate from its planned trajectory, creating damage to the corners sharp corners or very small radius on the job. Each manufacturer provides innovative construction of fuzzy logic control to maintain his corner when cutting wire.

MACHINING submerged:

In these types of machines, son cutting operation is done in a water bath. Under conditions of poor flushing difficult machining such as cutting a cone degree, extrusion, stacking parts, submerged machining is always preferred. Most manufacturers now offer machines submerged.

effect of heat on metal surfaces of the surface integrity:

During the EDM process the surface of the material is affected by many phenomena directly alter the structure of the bedrock. This results in the affected area not to remain part the bedrock.

The defects are mainly due to various processes that are triggered at the beginning of the strike initial EDM spark.

Surface damage

• Due to thermal processes.

• Thanks to a chemical process.

• With electrolysis and corrosion process.

Damage thermal processes

With the initial strike of the spark on the metal surface, the material is melted and the crater is formed. Molten metal is drawn back into the crater due to spark surface tension.

This material refreezes on the cut surface produce a layer that is very different in properties than the original material. This layer is called "white layer" or layer to redesign.

Immediately below the white layer is a field called "HAZ" heat affected zone.

This layer is formed again tightened due to the temperature exceeded the curing temperature, but not melt the surface. This layer is hard and brittle.

Damage due to chemical effects

EDM surface undergoes a chemical contamination of the electrode and dielectric. From a metallurgical point of view Carbon is the most important pollutant. small amount of carbon has a profound effect on the behavior of the steel. In WEDM machines, the chemistry of ion particles contamination is more or less neutralized by the process of Deion. But in the RAM EDM no such mechanism, therefore, it is always advisable to change periodic dielectric oil.

Damage due to electrolysis effect

WEDM process uses water as a play, a dielectric as the anode and cathode wire as. Operating voltage difference gives rise to a reaction. When water molecules are reduced at the cathode and oxidized at the anode. So more or less say anode part is consumed according to the type of metal used. This deterioration surface causes the work piece.

Consequences

Because of EDM process, different layers as the white layer, a layer of re-hardened hardened layer is formed on the base material.

Today high speed switching, short duration, high-tech pulse peak current allows finer control to minimize these effects, but the thermal nature of the EDM process itself it is impossible to completely eliminate these defects. thickness of the affected area can vary from a few microns, depending Roughing / finishing parameters.

cups skim milk at a lower current can help improve the surface.

Reduced mechanical properties of metal located in the affected layer contributed to the length shortened life.

Effect on surface integrity to effect die / punch made of hard metal surface profile will, therefore, its resistance wear.

New trends in EDM application

EDM in the casting industry

Vertical EDM was a pillar in the mold making operation for decades. In recent years, improved performance WEDM seen its use in industry moldmaking too.

mold making is an age old profession which, in theory, has not changed for centuries.

A portion is reproduced by feeding or forcing a molten material into a pre-printed form or in the cavity. cavity accuracy and better finish mold will result in better replication of part dimensions and the life of the mold. This is especially necessary for the plastic parts that are normally molded as a finished piece.

Fields of application of WEDM In mold:

1. Electrode to:

This is the first use of WEDM in manufacturing molds. Complex copper electrode, multiple electrodes are identical and precise flawless, this wall electrodes that were very difficult and unprofitable consumer time.

2. The basic work of mold:

pocket insert correctly in the plate of the mold base larger and thicker the mold base is the largest economy. Square inserts can be cut easily without corner radius.

3. Mold inserts:

Because cut without cutting and also very fast, without accumulated in details due to stacking.

complicated geometry of the involute gear or spline is virtually impossible to generate on conventional machines toolroom. Wirecut There are no limits on the width of the tooth pressure angle and other characteristics of gear circle. Any cavity involute gear can be cut shrinkage factor at all easy.

4. Extrusion die plate:

Extrusion die plate essentially needs a large project angle that can be cut easily Wirecut.

5. Moulds Gear Watch

gear plastic watch is impossible to do because of the small tooth size. With the use of 50-70 microns wire, cutting this part is very easy.

6. Inserts

connector inserts need several sheets close tolerance, it is quite labor-intensive and very expensive to grind and assemble. All this is avoided using WEDM.

7. Core Ejector Pin hole

Wire EDM can be effectively used to cut all the inserts in the holes of the cavity after hardening. Holes will be right up to the size and have sharp edges to the dead cavity, resulting in no possibility of flushing.

8. Reduce or eliminate polishing

Polishing of molds in India is working hard labor, and can be avoided by EDM wire, which are now able to provide up to 1 μ finish Rmax.

Micro EDM Machining

Micromachining is a basic technology used for the production of miniaturized parts and components.

Until recently, the emphasis was placed on the production of microelectronic components using etching and other techniques for manufacturing picture. Currently, with the enormous resulting need for the development of micro machines, machining technology using machine tools became very popular.

Micromachining is the generic term for very small machines of a millimeter to millimeter in size, as micro-robots, capsules inserted in the body humans for medical treatment, micro-motors, micro-machining using machine tools etc. sensors has the advantage of machining three-dimensional shapes with a ease.

In recent years there has been an increase in demand is the Micro machining technology from various industries, such

• Aerospace

• Medical Devices

• Automotive

Micro machining techniques to generate the parts, even at less than 100 microns only thicker than a human hair – human hair is 75 microns.

These micro-machining techniques are used to manufacture parts as

• medical components

• Micro modules

• Electronic equipment

• microvalves

• Tools for IC

• Sub – Miniature actuators and motors

Productivity & Automation Issues

Today, stores employment strive for the highest level of manufacturing efficiency and productivity.

Automation can be a solution, but automation is not viable for reasons of automation, there are plenty of downtime, which, if it can reduce the opportunity competitiveness.

Typical EDM Job Shop work primarily in four clear stages.

1. preparation program part and part

2. On the job development / alignment / loading / unloading

3. Job cuts

4. Inspection Job

Although WEDM machine is running, many factors of human intentions come into play such as –

1. Wire thread / spool changes.

2. outage.

3. Replacement consumables.

In all the above aspects of the manufacturing jobs that cutting revenue yields.

Although all other aspects are important to look after the shop, they are wasting time and can be expected to minimize them.

Let's see what the point of view Lean Job Shop ", in which automation may be ways to improve productivity. Lean manufacturing, a commitment shortcut for eliminating waste, simplifying procedures and speeding the production might be one of those concepts.

manufacturer modern machine and accessory manufacturer WEDM have contributed to support the user by providing many features and accessories to reduce minimum human intervention and thus reduce the wastage of time and increasing the time available for cutting. Let us review them.

1. Preparation for employment and programming: It involves planning for cutting strategies such as the hole mode, the margins of employment clamping rough / skim cutting machine manufacturers etc. provide guidance and hands on revenue of technology, which can get executed without intervention saving time.

2. Tools: sufficient time can be saved by using tools available now a days of

• Good quality

• Affordability

Offering:

• Single minute exchange of die (SMED)

• one round of tightening die

• And using the single command align function of the machine.

This dramatically reduces the downtime of the machine.

1. Job cuts: Schedule of cut can be improved by selecting appropriate cutting speed and multi-cut strategies.

Although manufacturers do specify maximum cutting speeds, but speed up the means for creating maximum defects, which deteriorates the precision and finish work. The time wasted thereafter to minimize these defects.User must decide the optimal cutting speed rather than the maximum cutting speed to achieve maximum efficiency overall cut.

2. Inspection Jobs: Modern machines are capable of providing quality products that comply with terms of accuracy and finishing, provided that all factors manager listed in the preceding section are met. inspection time employment can be saved by selecting substantially controls on very few dimensions.

losses due to interventions Hour

1. stringing wire:

The defects, misuse of cutting parameters can lead to thread breakage.

son Manuel thread consumes at least 5 minutes when the operator is in front of the machine. This time can be saved by using automatic threading son installation.

Today, this feature is available on most EDM WIRE.

Auto Wire thread time is normally 45 seconds, which much in terms of saving time.

In case of multiple cavity die, on machines with the AWT thread is automatically cut and then threaded, as in the program, thereby achieving complete unattended operation.

2. Loading coil wire / unloading

Change reel line becomes a break in the case of large jobs, where the cutting time is more than 24 hours. Superior kg. Coils up to 45 pounds are available that will last for several days and will eliminate spool change frequently over time.

Special accessory supplied by the manufacturer may be used to reduce human intervention.

3. Blackout

In Indian conditions there are frequent power outages.

Many shop owners have Generators for emergency power. Yet few have integrated auto changeover facility. manual failover generator consumes more time and depends on the operators' attention. This time varies from 5-15 minutes.

Group generator with automatic change the installation will start in 1 minute.

power of the machine with automatic recovery facility resume cutting less than a minute.

4. The replacement of consumables manufacturer provides information on the life of consumables such as micro current guide-wire resin, filters, etc.

predefined schedule supplies replacement will help save time.

Automation

Now a day, especially in developed countries, the machines are equipped with tool magazine / unloading robotic work load / unloading, etc. to operate the machine unattended.

Enhanced performance in terms of cutting speed with higher precision jobs tolerable and Wire EDM surface is popular not only in the tool room, but also for production applications, which was not profitable, it few years ago.

Ultimately, innovations in EDM are intended to simplify the task of EDMing in an economical way to produce tools for long life of the highly competitive tooling, mold making, aerospace, pharmaceutical and many industries such.

About the Author

CEO Electronica Machine Tools Ltd., Pune, India

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