Subject Area of

Aeronautical-Mechanical Engineering

B.Eng(Hons) Aeronautical & Mechanical Engineering

Final Year Project Report

ELECTROCHEMICAL LABELING OF METAL NON-

PLANAR SURFACES

Name: Rodrigo Folgueira (S10004004)

Supervisor: Ruslan Gareev

Date: May 2011

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Author’s Declaration

Statement 1

This work has not previously been presented in any form to Glyndwr University or at

any other institutional body whether for assessment or for any other purposes. Save for

any acknowledgements, references and/or bibliographies cited in the work, I confirm

that the intellectual content of the work is the result of my own efforts and no other

person.

Statement 2

It is acknowledged that the author of this work shall own the copyright. However, by

submitting this copyright work for assessment, the author grants to the University a

perpetual royalty-free license to do all or any of those things referred to in Section 16(I)

of the Copyright, Designs and Patents Act 1988 (viz: to copy work; to issue copies to

the public; to perform or show or play the work in public, to broadcast the work or to

make an adaptation or the work).

Signed……………………………………………………………………………

Date………………………………………………………………………………

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Acknowledgements

I would like to take this opportunity to thank the Glyndwr University for allowing

me to study here the final year of “Aeronautical and Mechanical Engineering”

and make here my final project.

I also would like to thank to my supervisor Ruslan Gareev who has helped me

along the process of completing the project.

Finally, thank my family the opportunity that they have given me to study abroad

and my friends and colleagues who have helped me (especially Ainara

Aranbarri).

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Abstract

This report describes the process of designing a tool for labeling metals that

have non-planar surfaces.

For labeling the metals the system that is going to be used is the

Electrochemical Discharge Machining (EDM).

The EDM consists in a manufacturing process which gives the desired shape

using electrical discharges (sparks). Material is removed from the workpiece by

a series of rapidly and continuous discharge occurring between two electrodes

(the workpiece and the electrode), separated by a dielectric fluid and connected

to a power source (capacitor).

Is not going to be designed only the tool, it will also be designed a system of

dielectric fluid distribution (distribution channel), a system for cleaning fluid (a

ventilator with a filter), the tool holder and a base for all.

The material selected for the tool is the Graphite since it has optimal

characteristics for use in this kind of electrochemical process.

The dielectric fluid to make the process work consists in kerosene because it

has no rust problems and no dangerous gasses are produced with this fluid.

The tool and other parts of the system are going to be designed using the

“AutoCAD 2007” program as we can see in the figure 1, and will be rendered by

“AutoCAD 2011” as we can see in the figure 2.

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Fig 1. 3D Wireframe view

Fig 2. Realistic view

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Index

B.Eng(Hons) Aeronautical & Mechanical Engineering ....................................................... - 0 -

Final Year Project Report .................................................................................................. - 0 -

Acknowledgements ................................................................................................................... - 2 -

Abstract ..................................................................................................................................... - 3 -

Index .......................................................................................................................................... - 5 -

1 Introduction............................................................................................................................ - 7 -

2 Aims of Project ....................................................................................................................... - 9 -

3 Review of literature .............................................................................................................. - 10 -

3.1 Definition of Electrochemistry1 ..................................................................................... - 10 -

3.2 Electrical Discharge Machining (EDM)2 ......................................................................... - 10 -

3.2.1 Definition ................................................................................................................ - 10 -

3.2.2 History3 ................................................................................................................... - 11 -

3.2.3 Generalities4 ........................................................................................................... - 12 -

3.2.4 The process2 ........................................................................................................... - 14 -

3.2.5 Advantages and Disadvantages of the EDM2 ......................................................... - 17 -

3.3 The electrode ................................................................................................................ - 18 -

3.3.1 Definition of electrode ........................................................................................... - 18 -

3.3.2 Graphite electrode ................................................................................................. - 18 -

3.4 The graphite5 ............................................................................................................. - 19 -

3.4.1 Properties5 .............................................................................................................. - 20 -

3.5 Advantages of the EDM with electrode shape .............................................................. - 21 -

3.6 Disadvantages of the EDM with electrode shape ......................................................... - 21 -

3.6 Metals6 .......................................................................................................................... - 22 -

3.7 Dielectric liquid7 ............................................................................................................ - 23 -

4 Design Process ...................................................................................................................... - 25 -

4.1 Ventilator....................................................................................................................... - 25 -

4.2 Electrode ....................................................................................................................... - 26 -

4.3 Distribution channel ...................................................................................................... - 27 -

4.4 Holder ............................................................................................................................ - 29 -

4.5 Capacitor ....................................................................................................................... - 30 -

4.6 Door ............................................................................................................................... - 30 -

4.7 Part that holds the tool ................................................................................................. - 31 -

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4.8 The whole ...................................................................................................................... - 32 -

5 Results and Discussion ......................................................................................................... - 32 -

5.1 Election of the process .................................................................................................. - 33 -

5.2 Election of the dissolution ............................................................................................. - 34 -

5.3 Construction of a distribution channel ......................................................................... - 35 -

5.4 Election of the material ................................................................................................. - 35 -

5.4.1 Generalities ............................................................................................................ - 35 -

5.4.2 Costs ....................................................................................................................... - 36 -

5.4.3 Cutting Speed ............................................................................................................. - 36 -

5.4.4 Electrode wear ....................................................................................................... - 37 -

5.5 Construction of the electrode ....................................................................................... - 38 -

5.7 Procedure ...................................................................................................................... - 38 -

5.8 problems ....................................................................................................................... - 41 -

5.8.1 Erosion .................................................................................................................... - 41 -

5.8.2 Wear ....................................................................................................................... - 41 -

5.8.3 Other ...................................................................................................................... - 41 -

6 Conclusions........................................................................................................................... - 42 -

7 References ............................................................................................................................ - 45 -

8 Useful vocabulary8 ................................................................................................................ - 49 -

9 Annexes ................................................................................................................................ - 51 -

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1 Introduction

Companies working in the metal sector are faced with the problem of labeling

the metals when they do not have planar surfaces.

That is why the main idea of this project is constructing of an electrochemical

tool for labeling metal parts with complex surfaces, and calculating regimes of

the labeling.

Another problem that can occur is that there are more than hundred different

kinds of metals and many more alloys. For a metal sector company must be

necessary to label all this metals and alloys. Then, will be easier to recognize

what metal is that is needed.

The method that will be used for making possible that the tool work is the

Electrical Discharge Machining (EDM), with the electrode shape variant. Known

as Ram EDM.

The EDM is a machining method that is based on two phenomena, the

electrochemical dissolution of the material and thermal erosion due to electrical

discharges (sparks) that occur between the electrodes (workpiece and tool).

The electrode selected for this tool is a Graphite electrode because it has got a

high temperature of vaporization and is more resistant than other materials.

With this electrode the problem about the erosion in the electrode is solved, and

when the erosion appears is not a problem to change the tool because it has a

low price compared to other materials such as copper, tungsten, platinum,

molybdenum…whose price is much higher.

The dielectric fluid that is going to be used is Kerosene because it has the best

properties for the EDM proceedings. Kerosene has no rust problems and

compared with deionized water has not produced dangerous gasses.

After designing the tool it will be designed a distribution channel where the

dielectric fluid will circulate, inside these pipes there will be some ventilator with

filter whose work is to clean the fluid for a correct electrical conductivity.

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All these parts of the system will be connected to a holder that supports the

whole.

The electrode is connected to a power source, a capacitor, that will be also

designed, and is activated when is necessary for making the desired label.

All of these parts of the ensemble will be designed by AutoCAD, taking care

about the sizes, the distances and the materials.

In the figure 3 is possible to see a scheme of a EDM basic construction:

Fig 3. Scheme of an EDM process

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2 Aims of Project

The main purpose of this project is to design a tool for labeling metals that have

non-planar or complex surfaces.

The principal idea making this report is to learn about electrochemical process,

about the electrochemistry area in the engineering.

The investigation research has given extensive knowledge on the subject and

the necessity to solve problems help in this learning area.

It has gained extensive knowledge of electrochemical processes, with emphasis

on the EDM. (Materials, processes, lubricants, dielectric fluids ...)

Moreover, it has also developed skills in the design field, having to design

different parts of the system.

And finally, in the mechanical aspect also has to study how to calculate different

measures.

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3 Review of literature

3.1 Definition of Electrochemistry1

Electrochemistry is a branch of chemistry that studies the transformation

between electrical and chemical energy. In other words, the chemical reactions

that that take place at the interface of an electrical conductor, the electrode (that

can be a metal or a semiconductor) and an ionic conductor, the electrolyte.

That is why electrochemistry has been separated into two main sections. The

first is electrolysis, which refers to those chemical reactions that occur due to

the action of an electric current. The second is referred to those chemical

reactions that generate an electrical current.

3.2 Electrical Discharge Machining (EDM)2

3.2.1 Definition

Electric discharge machining (EDM) 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’.

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When the distance between the two electrodes is reduced, the intensity of the

electric field in the volume between the electrodes becomes greater than the

strength of the dielectric (at least in some point(s)), which breaks, allowing

current to flow between the two electrodes. As a result, material is removed

from both the electrodes. Once the current flow stops new liquid dielectric is

usually conveyed into the inter-electrode volume enabling the solid particles to

be carried away and the insulating proprieties of the dielectric to be restored.

Adding new liquid dielectric in the inter-electrode volume is commonly referred

to as flushing. Also, after a current flow, a difference of potential between the

two electrodes is restored to what it was before the breakdown, so that a new

liquid dielectric breakdown can occur.

3.2.2 History3

In 1770, the English physicist Joseph Priestley studied the erosive effect of

electrical shock. The result of the investigation of Priestley, the EDM process

was invented by the Russians Dr. BR Lazarenko and Dr. NI Lzarenko in 1943.

They developed a controlled process for machining metals. For the initial

process used a spark machining process that took place between two electrical

conductors immersed in a dielectric fluid. The effect of shock generator that

uses this equipment, was used for many years.

Further research entered the field of electrochemistry and contributed to many

of the characteristics of the machining method that we know today. In 1952, the

manufacturer Charmilles machine created the first spark machining process.

Agie in 1969 launched the first numerical control (CNC). Seibu created the first

machine for cutting electrical wire and in 1972 the first system was made in

Japan.

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3.2.3 Generalities5

The electrical discharge machining is a working method that is used mostly with

hard metals. To make this system work, metals should be conductors of

electricity. It does not need a previous heat treatment to harden. It is also

posible to use metal alloys.

Ideally, the EDM could be defined as a series of breakages and restorations

between workpiece and electrode through the dielectric fluid. However, it should

be pointed out that this would only be an idealized model of the process. For the

process to be successful, must take into account many variables, such as the

removal of the debris from the electrode is likely to Be always partial. Therefore,

the electrical properties of both the fluid and the electrodes can be different from

their nominal values and may even vary over time. The distance between

electrdo and part is often taken as the spaces through the beam, but also is a

value variable. The control of this distance should be the focus of study in these

processes. Moreover, not all current flow is the ideal type described at the

beginning, but can be interfered with by the debris. The electrode control

system may not react as fast sufientes to prevent the two electrodes (workpiece

and tool) to get in touch and create a short circuit. Dielectric fluid cleanliness

may not be appropriate, this would result in the fluid continue with debris and

the current flow varies subtracting value to the properties of the electrode and

arcing-rays, with the consequent change in the desired final shape the tool.

For obtaining a specific geometry, the EDM tool is guided to the exact point

desired close to the piece, it is best not to touch the workpiece, but in reality this

can happen due to the implementation of motion control application specific. In

this way a large number of electric discharge (lightning) occurs, each

contributes to the removal of materials from both tool and part, where they form

small craters. The size of the craters is a function of technological parameters

established for the specific job at hand. These craters create the desired shape

on the piece.

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These small discharges would cause the gradual erosion of the electrode. This

erosion of the tool is also known as wear. Strategies are needed to counteract

the harmful effects of using the geometry of the workpiece. One possibility is the

continual replacement of the electrode tool during a machining operation. This

is what happens if a continuous wire electrode is used as a substitute. But this

is an extra cost of the project, which is trying to find solutions such as using a

material more resistant to wear. The tool can also be used so that only a small

part of her participation in the machining process and this part is changed

regularly when worn.

Another strategy is to use a set of electrodes with different sizes and shapes

during the same operation of EDM. This often refers to the strategy of multiple

electrode, and is more common when the negative electrode (tool) is a replica

of the desired shape and progress towards the target along a single direction.

Usually, the electrodes of this type have very complex shapes. This type of tool

may be used only in the case of a production line and is always the same or the

same parts to be produced; otherwise, it would be a huge expense to have to

design all the pieces in final tools.

In any case, the severity of wear is strictly dependent on the technological

parameters used in the operation (eg polarity, maximum intensity, open circuit

voltage). Therefore, the wear is a major problem in the area.

The problem of wear of graphite electrodes is being addressed. In one

approach a digital generator, controllable within milliseconds, the polarity is

reversed electro-erosion takes place. It produces an effect similar to

electroplating which is continually being eroded graphite deposit back into the

electrode. In another method, called "Zero Use" circuit reduces the frequency

with which the discharge starts and stops, is maintained for as long as possible.

With all of this is to demonstrate that graphite is the best option since wear is

less with a consequent increase in the use of the tool. This translates into less

wasted time between tool changes and significant savings in machining tools.

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3.2.4 The process2

Electrical Discharge Machining (EDM) is

the process of machining electrically

conductive materials by using precisely

controlled sparks that occur between an

electrode and a workpiece in the presence

of a dielectric fluid, is possible to see a

simple scheme of the process in the figure

3.1

Fig 3.1 Scheme of the EDM

The EDM process is the generation of an electric arc between a workpiece and

an electrode in dielectric medium particles to start the piece until you get to play

it forms the electrode. Both the piece and electrode must be conductive, so you

can set the electric arc to cause material removal.

EDM is not like other machining operations in that the electrode does not make

physical contact with the piece for material removal. The electrode must always

be spaced away the workpiece by the distance required for sparking, known as

the sparking gap.

Another basic fundamental of the process is that only one spark occurs at any

instant. Sparking occurs in a frequency range from 2.000 to 500.000 sparks per

second.

The spark removes material from the electrode and the workpiece, which

increases the distance between the electrode and the workpiece at that point.

Basic components of EDM

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This causes the next spar occur at the next-closest points between the

electrode and workpiece. (Figure 3.2).

EDM is a thermal process; material is removed by heat. The area heated by

each spark is very small so the dielectric fluid cools the vaporized material and

the electrode and workpiece surfaces.

A dielectric material is required to keep the sparking gap between the electrode

and workpiece, this dielectric material is normally a fluid.

The main characteristic of dielectric fluid is that it is an electrical insulator until

enough electrical voltage is applied to cause it to change into an electrical

conductor.

The time at which the fluid changes into an electrical conductor is known as the

ionization point. When the spar is turned off, the dielectric fluid deionizes and

the fluid returns to begin an electrical insulator.

This change of the dielectric fluid from an insulator to a conductor, and then

back to an insulator, happens for each spark.

Dielectric fluid provides important functions in the EDM process:

Controlling the sparking-gap

between the electrode and workpiece.

Cooling the heated material to

form the EDM chip.

Removing EDM chips from the

sparking area.

Fig 3.2 Scheme adding electricity

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EDM requires a very precise flow of electricity in the form of a spark; fire is not

an accurate or acceptable description of the EDM machining process this is that

I need to calculate very accurately, the distance between the piece and the

electrode.

Fig 3.3 Hole after the sparks

When the process is finish, as it is possible to see in the figure 3.3, the

workpiece has finely a hole that is the label in the case of this studio.

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3.2.5 Advantages and Disadvantages of the EDM2

Some of the advantages of EDM include machining of:

* Complex shapes that would otherwise be difficult to produce with

conventional cutting tools

* Extremely hard material to very close tolerances

* Very small work pieces where conventional cutting tools may damage the

part from excess cutting tool pressure.

* There is no direct contact between tool and work piece. Therefore delicate

sections and weak materials can be machined without any distortion.

* A good surface finish can be obtained.

* Very fine holes can be easily drilled.

Some of the disadvantages of EDM include:

* The slow rate of material removal.

* The additional time and cost used for creating electrodes for ram/sinker

EDM.

* Reproducing sharp corners on the workpiece is difficult due to electrode

wear.

* Specific power consumption is very high.

* Power consumption is high.

* "Overcut" is formed.

* Excessive tool wear occurs during machining.

* Electrically non-conductive materials can be machined only with specific

set-up of the process.

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3.3 The electrode4

3.3.1 Definition of electrode

An electrode is an electrical conductor used to make contact with a nonmetallic

part of a circuit. An electrode in an electrochemical cell is known as either an

anode or cathode. The anode is now defined as the electrode at which

electrons leave the cell and oxidation occurs and the cathode electrode in which

electrons enter the cell and reduction occurs. Each electrode may become the

anode or cathode depending on the direction of current through the cell

3.3.2 Graphite electrode

The electrode is made from graphite because it has a high vaporization

temperature and is more resistant to wear. The electrode will have the opposite

to the desired shape, resulting in the work piece.

Also copper is a great material because it has really great conductivity

characteristics, but the problem is that for being a soft metal it is faster wear.

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3.4 The graphite5

Carbon has two allotropes, Diamond and Graphite; the difference being more

interested in this case is that graphite has the property of being electrically

conductive and the diamond not. Graphite is the most stable form of carbon in

normal conditions. Therefore, it is used in thermochemistry as the standard

state for defining the heat of formation of carbon compounds. The graphite can

be considered the highest grade of coal, just above anthracite and also called

meta-anthracite.

Propierties Isostatic Resin Antimony

Density g/cm3 1.85 1.80 2.40 Porosity % 13 0.2 0.5 Elastic module GPa 11 20 25 Compressive Strenght MPa 98 200 220 Flexural Mpa 49 80 90 Maximum temperatura ºC 1500 250 350 Expansion Coefficient 10-6/ºC 5.5 3.8 4.0 Thermal conductivity W/mk 116 10 15

Chart 1. Characteristics of the Graphite

Characteristics of the Graphite:

For work in wet/dry.

Low termal expansión.

Corrosion resistance.

Low coefficient of friction.

Excelent termal shock.

Self-lubricating.

Fig 4. Example of pure Graphite

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Graphite has various other characteristics. Thin flakes are flexible but inelastic,

the mineral can leave black marks on hands and paper, it conducts electricity,

and displays super lubricity. Its best field indicators are softness, luster, density

and streak.

3.4.1 Properties5

Graphite has a layered structure, flat. In each layer, the carbon atoms are

arranged in a hexagonal grid with a separation of 0.142 nm, and the distance

between the planes is 0.335 nm. The two known forms of graphite, alpha

(hexagonal) and beta (rhombohedral) have very similar physical properties

(except that the graphene layers stack slightly differently). Layers contribute to

its lower density.

The acoustic and thermal properties of graphite are highly anisotropic, since

photons propagate very quickly along the tightly-bound planes, but are slower to

travel from one plane to another.

Graphite can conduct electricity due to the vast electron delocalization within

the carbon layers (a phenomenon called aromaticity). These valence electrons

are free to move, so they are able to conduct electricity. However, electricity is

only conducted in the plane of the layers, so that the powdered lead.

Graphite and graphite powder are valued in industrial applications for its self-

lubricating and dry lubricating properties. There is a common belief that

graphite's lubricating properties are solely due to interlaminar flexible joint

between the sheets in the structure. Lubrication is due to the presence of fluids

between the layers, such as air and water, which are absorbed by the

environment. This molecular property is unlike other layered dry lubricants such

as molybdenum disulfide. Recent studies suggest that an effect called

superlubricity also may account for the lubricating properties of graphite. The

use of graphite is limited by its tendency to facilitate pitting corrosion in some

stainless steels, and promote galvanic corrosion between dissimilar metals (due

to its electrical conductivity). It is also corrosive to aluminum in the presence of

moisture.

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3.5 Advantages of the EDM with electrode shape

It is applicable to brittle materials.

It can produce very inclined holes on curved surfaces slide smoothly.

It is possible to work with any conductor materials.

It is a unique manufacturing process to achieve complex configurations

that are impossible otherwise.

The finish in the workpiece is great.

3.6 Disadvantages of the EDM with electrode shape

After the process is often left a layer of molten metal, fragile and extremely hard, to be removed in those parts that require resistance to fatigue.

Graphite is a brittle material, so that manipulation of the electrodes must be very careful.

The electrodes generally require be manufactured, for example, machined on a milling machine to work serving graphite.

The rough surface finish is not perfect.

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3.6 Metals6

This is the periodic table of the elements (chart 2), where it is possible to see

the different kind of metal that are known:

Chart 2. Periodic table of elements

Transition Metals: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Y,Zr, Nb,

Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Pt, Au, Hg, Rf, Pd, Sg, Bh, Hs, Mt, Ds, Rg, Cn. (54 in total).

Alkali metals: Li, Na, K, Rb, Cs, Fr. (6 in total).

Lanthanides: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. (15 in total).

Alkaline Earth Metals: Be, Mg, Ca, Sr, Ba, Ra. (6 in total).

Metalloids: B, Si, Ge, As, Sb, Te, Po. (7 in total).

Actinides: Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Ls. (15 in total).

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Other Metals: Al, Ga, In, Sn, Tl, Pb, Bi. (7 in total).

Unknown OEHM properties: Uut, Uuq, Uup, Uun, Uus, Uuo. (6 in total).

As it is possible to see there are 101 different kind of metals, this number is

going to increase and also there are a lot of alloys that can be used in EDM

process, this is the reason that the tool must make so many different kind of

labels.

3.7 Dielectric liquid7

A liquid dielectric is a dielectric material in liquid state. Its main purpose is to

prevent or rapidly quench electric discharges. Dielectric liquids are used as

electrical insulators in high voltage applications. Its function is to provide

electrical insulation, suppress corona and arcing, and to serve as a coolant.

Chart 3. Common dielectric fluids.

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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.

The deonized water is also used as a dielectric fluid for EDM machines, but is

more common in wire EDM machines.

Water has a few drawbacks. First it causes rust. Second, the electrical

discharge separates the water into pure hydrogen and pure oxygen. A very

explosive pair.

A good compromise then is Kerosene. No rust problem and no dangerous

gasses are produced with Kerosene.

With this characteristics, Kerosene is the best option.

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4 Design Process

4.1 Ventilator

A ventilator is an important part of the ensemble. This is like this because the

fluid must be clean for the correct operation of the process. The function of the

ventilator is to move the fluid inside the distribution channel.

The ventilator has a filter in its backside that cleans the fluid, all the rubbish that

will be stopped in the filter, then, it must be clean regularly for the correct

cleaning of the fluid.

Then, the filtered fluid can be recirculated.

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4.2 Electrode

The electrode is the most important piece of the tool, it must be made of

Graphite because it has got a high temperature of vaporization and is more

resistant than other materials.

With this electrode the problem about the erosion in the electrode is solved.

The design of the electrode is really simple; the only problem is to mix all the

electrodes because 3 of them are necessary to make the final tool.

This is because it is need to label more than hundred kind of metal, but with

three different they can move free on a single axis, it is only necessary to create

a different brand for each metal, adjusting the parameters in a CNC machine

and label it.

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4.3 Distribution channel

The principal reasons of the construction of a distribution channel are because

the dielectric fluid must be filtered, cooled and recirculated.

The distribution channel is a set of welded pipes, fixed and chilled where the

fluid can be recirculated.

At the entry of the channel there are two ventilators with filters, so in the first

step, after the use -after the EDM process- the dielectric fluid is cleaned.

Then, with the help of a pump, the fluid is driven through the set of pipes and In

this way is also cooled this I the reason of the chilled pipes.

At the end of the channel there is another ventilator with another filter, so, in the

last step, the fluid is now clean and cold, is prepare for using it again.

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4.4 Holder

The holder is the place where everything will be joined. Is where the process

occurs.

It must be a tight place, as this will solve the problem of combustion in the case

of the use of kerosene as a dielectric fluid (that is this case).

The sealed box has a tray in the middle, where the piece will be labeled and

care on which the dielectric fluid through a pipe connected in turn to the

distribution channel.

This tray is also connected to a pipe through which the fluid will fall foul and go

to the channel where it is cleaned, cooled and put up again.

In the front, consists of a watertight door through which it is possible to

introduce and bring out the parts once labeled.

The material in this hermetic cabinet will be a heat resistant glass to make it

possible to see from outside the process that is taking place inside.

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4.5 Capacitor

A capacitor is a device that stores an electric charge. EDMs require capacitors

to generate the electric current used for machining. This is an example of a

capacitor with the components that it has:

4.6 Door

This is only a door to cover the hole in the holder which is used to enter the

workpieces for labeling.

This door is hermetic and is made of framing steel.

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4.7 Part that holds the tool

The Graphite tool must be fixed in a piece that will be connected to the

electricity and provides the energy for the tool.

This piece is made of steel and it is need to make three of these, because the

tool has three electrodes.

This piece runs on two rails that offer freedom of movement to make the

changes necessary to obtain the desired piece.

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4.8 The whole

This is a scheme of the design, with all of the

parts:

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5 Results and Discussion

5.1 Election of the process

The first problem was to decide what electrochemical machining process would

be more appropriate for the tool whose purpose is to labeling metals.

The first decision was to use the Electrochemical Discharge Machining (EDM)

process but there was a problem with the electrode wear.

There were lots of different types of materials that can be used by its

characteristics, but all of them are not appropriate to use in this system,

because of its high cost. It is a hard cost and effort change the electrode all the

time.

The EDM is the best process for labeling such surfaces therefore it is necessary

to find a solution. This solution is the EDM with electrode shape, this system

uses graphite electrodes, which are more resistant and had a very high thermal

resistance. This makes the graphic perfect for this tool.

Fig 5. Example of simple system circuit

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5.2 Election of the dissolution

Next issue that must be solved is to decide what is the best dissolution, the best

dielectric fluid for this kind of process. The dielectric fluid acts as an insulator

between the workpiece and the electrode. There are many dielectrics which

choose based on the insulation and the electric conductivity of the fluid.

Electrolyte solutions are those in which the solute is dissolved in the solvent

forming ions. It might solve the problem with the following solutions: sodium

chloride (NaCl), potassium chloride (KCl), or sodium sulfate (Na2SO4).

These solutions will be discarded because they do not satisfy the minimum

conductivity and heat stroke.

Another fluid can be the air, but also is not a great insulator, so will not work

according to specifications in EDM.

Next and most popular is the water, concretely the deionized water. But water

has a few drawbacks. First, it causes rust. Second, the electrical discharges

separate the water into pure hydrogen and pure oxygen. A very explosive pair.

A good option then will be the Kerosene, which has no rust problem and do not

produce dangerous gasses.

The only problem with Kerosene is that it is highly flammable. This will be solve

making the process in a sealed chamber, where in case of fire, air is removed

and it will be extinguished.

Crystal Brite was developed to improve the spark erosion process in sinker style

EDM machines. It has allowed users to increase amperage, thus reducing

process times by as much as 30%. Also, it creates a non-conductive channel

allowing the spark to hit its target accurately and at a full charge. It reduces

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carbonization, which reduces gummy residue. But Crystal Brite is a new fluid

used in these systems, so there is no data, no knowledge about it for making a

comparison.

5.3 Construction of a distribution channel

Next point to consider is that the process creates a lot of debris; this is caused

because of the high temperatures during the EDM process. The dielectric

absorbs most of this debris and this makes the process less efficient. This is the

reason for constructing some filters inside the distribution channel.

The function of these filters is to filter and cool constantly the dielectric fluid.

Some ventilators are also useful in this task because they are responsible for

recirculating the dielectric fluid inside the pipes.

5.4 Election of the material

5.4.1 Generalities

The material that is going to be used is the most delicate and has caused more

controversy.

The most common materials that are used for the electrode in the EDM process

are: Copper Tungsten, Graphite, Tellurium Copper, Brass and Copper.

The problem about what material use for the electrode is nothing new, since the

EDM started to be in use this problem has been present.

At first the Copper was the most popular material, it was used nearly 90 percent

of time and Graphite the other 10 percent. But this percentage has changed,

has become the graphite used to be 90 percent of the time.

This has happened because of the advantages of graphite over copper.

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Speaking about the machinability, copper is a soft metal

First, we must talk of machining, which is the most important quality you have to

have a material to be used as an electrode in EDM processes. A material that

can not be machined, can not be used.

Copper is a soft material and has a tendency to wear during the machining

process, which is why it may take about five times more than copper to be

machined. This means that normally require a repair after each use as an

electrode.

In addition, copper not does have the strength to resist tool push, friction or

rough handling heat. This allows you to break to fix the clamping tool.

The graphite on the other hand does not require post-machining process is

mechanized so that two or three times faster than other required materials.

Graphite is easy to machine using standard machining procedures.

5.4.2 Costs

An easy way to choose the material is to focus on the cost of electrode material

alone. However, the cost is a very small percentage of the total cost of the

mold, which may also include the extra time required for machining or polishing,

additional electrodes required by higher attrition rates and more time spent on

the EDM. These factors may affect the final result. Thus, when material costs

are considered part of the total work and not as a separate component, graphite

again has advantages over copper materials.

5.4.3 Cutting Speed

The metal removal rate (MRR), better known as the cutting speed, refers to the

speed at which material is removed from the cavity. Because copper has a

higher range of thermal conductivity, heat from the EDM process will quickly

spread through the electrode. As the temperature of the electrodes increases,

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the electrical resistance also increases, and much of the energy needed to

create the spark EDM is converted into heat within the electrode. On the other

hand, graphite has a lower thermal conductivity than copper, helping to maintain

more or less constant resistance at elevated temperatures. This ensures that

the energy needed to create the spark is actually creating a more efficient

spark. This difference in the thermal conductivity of graphite is a great

advantage over copper, while achieving metal removal rates of approximately

twice the speed.

5.4.4 Electrode wear

The electrode wear is a concern of all operators for excessive wear EDM

requires the use of more electrodes. The graphite can achieve less than one

percent of wear on the cutting depth, while copper has a tendency to create a

higher percentage of attrition. The melting point of these two materials is directly

related to the wear percentage. Copper has a melting point of about 1000-1100

degrees. As the amperage is higher for high MRR, the copper electrode just can

not stand the heat generated to effectively reduce the workpiece. The graphite,

however, has no melting point, but transforms from solid to gas, while directly

without passing through the liquid physical state. This process is called

sublimation, and usually occurs around 3500 º. Under this resistance at higher

temperatures, graphite can transfer energy from the spark of the workpiece,

which is effective in speed and wear.

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5.5 Construction of the electrode

There are mono hole and multi hole electrodes, this tool consists of three mono

holes.

Despite the importance of the electrode, the construction is really simple. Ths

must me like this because the electrode suffers with each ray, this means that

there is a tear (lower using graphite) and need to be changed from time to time.

5.7 Procedure

Metal is removed from work in the form of crater [fig ] and can be estimated for

single pulse and rate at which it is given.

Fig 6. Scheme of Crater Formation

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Considering the volume of a crater as part of sphere, the crater parameter can

be estimated as measure of energy.

Where:

Wp = Pulse energy (Joule)

Hc = Height of crater (mm)

Dc = Diameter of crater (mm)

K1, K2 = Constants depending on electrode materials and dielectric

n = Constant depending on work tool combination

So the volume of crater Vc from simple geometry:

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So K1, K2 and n values are to be determined from experiments and the material

removal rate can be written in the form

MRR = Vc .f.

Where f = Frequency of operation

n = Efficiency of the material at any setting

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5.8 problems

5.8.1 Erosion

The discharges (sparks) would cause the gradual erosion of the electrode. One

possibility for solve this problem is the continual replacement of the electrode

tool during a machining operation. This is what happens if a continuous wire

electrode is used as a substitute. But this is an extra cost of the project, so one

solution could be to use a material more resistant to wear. The tool can also be

used so that only a small part of her participation in the machining process and

this part is changed regularly when worn.

5.8.2 Wear

The problem of wear of graphite electrodes is being addressed. In one

approach a digital generator, controllable within milliseconds, the polarity is

reversed electro-erosion takes place. It produces an effect similar to

electroplating which is continually being eroded graphite deposit back into the

electrode. In another method, called "Zero Use" circuit reduces the frequency

with which the discharge starts and stops, is maintained for as long as possible.

Graphite is the best option since wear is less with a consequent increase in the

use of the tool. This translates into less wasted time between tool changes and

significant savings in machining tools.

5.8.3 Other

Also is necessary to take care about other parameters used in the operation

like: polarity, maximum intensity, open circuit voltage…

All off them make a big difference in the final result if they are not correct.

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6 Conclusions

At the end of this project, after an extensive research of the subject, it is

possible to say what the best method is, the best material and the best solutions

for designing a tool that can be used for label metals with non-planar surfaces.

The method

The method used is the EDM process that consists in given the desired shape

to the worpiece (the metal in this case) using electrical discharges (sparks).

This sparks remove some material in the workpiece and finally the shape is

obtained.

The electrode

For this method it is necessary a electrode that is going to make the holes

(labels) in the workpiece. For this, the material that has been chosen is

Graphite, because this material has the best characteristics.

Graphite has got a high temperature of vaporization and is more resistant than

other materials. Seen the costs is also better because, it needs less changes of

tools than the others.

The Fluid

There were many options when choosing the dielectric fluid but finally opted for

the kerosene, as the only disadvantage is that is easily combustible, but this

has been solved by a sealed chamber where the process will take place.

The system

There are other essential parts of the whole. It is necessary to clean the fluid

after each use, for this is necessary to construct some filters. The fluid must

also be cooled and for this there have to make a refrigerated distribution

channel. Inside this channel and for moving the liquid, some ventilators and a

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pump are needed. Finally a capacitor is need for provide the energy that is

necessary for the proper functioning of the system

Fig 6. Final, complete design

The designing process

At first is necessary to decide how is going to be the system, when the process

was decided and studied, the first step is to make the holder, the airtight

container where the process take place. Then is necessary to add a door qhere

you can insert and put out the workpiece.

After this the distribution channel must be made, being carefully with the sizes,

then is easy to know the size of the filters/ventilators.

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The last step is to add the tool (the electrode) and fix it to some rails, for which

move freely.

Equations

When a piece must be labeled, first some parameters (heigh of crater, diameter

crater, volume of crater, material removal rate…) must be calculated for the

correct workingof the process.

o Height of crater

o Diameter of crater

o volume of crater

o material removal rate

MRR = Vc .f.

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7 References

Books:

o Electrical Discharge Machining, Elman C. Jameson. (2)

o Electrochemistry, Davies C W.

(1) Definition of electrochemistry:

Chang, Raymond (2007). «Electroquímica». Química (Novena Edición).

McGraw Hill. pp. 1100. ISBN 0-07-298060-5.

García Andrade, David Gabriel. Manual de laboratorio de Fisicoquímica

de los Materiales. Universidad Autónoma Metropolitana.

Naveira, Alicia Alba (2008). «Corrosión». Química Inórganica para

estudiantes de ingeniería química (Tercera Edición edición). Editorial

Ceit. pp. 278. ISBN 978-987-1063-10-9.

(2) Electrical discharge machining:

http://www.directindustry.es/prod/sgl-group/grafito-para-electrodo-de-

maquinas-de-electroerosion-edm-39873-392886.html

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http://lacomunidad.elpais.com/cnc37/2009/4/13/los-trabajos-nuestra-

empresa-badalona-barcelona

(3) History:

http://www.atlantaedm.com/articles/a8-history-of-edm.php

(4) Electrode:

Faraday, Michael (1834). "On Electrical Decomposition"Philosophical

Transactions of the Royal Society. Archived from the original on 2010-

01-17.

http://www.webcitation.org/5mq8a85S3.

(5) Graphite/propierties/generalites:

http://www.carbosystem.com/materiales_grafito.html

C.Michael Hogan, Marc Papineau et al. (December 18, 1989) Phase I

Environmental Site Assessment, Asbury Graphite Mill, 2426-2500

Kirkham Street, Oakland, California, Earth Metrics report 10292.001.

(Report).

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Klein, Cornelis and Cornelius S. Hurlbut, Jr. (1985). Manual of

Mineralogy: after Dana (20th ed.).

Taylor, Harold A. (2000). Graphite. Financial Times Executive

Commodity Reports. London: Mining Journal Books ltd..

Taylor, Harold A. (2005). Graphite. Industrial Minerals and Rocks (7th

ed.). Littleton, CO: AIME-Society of Mining Engineers.

(6) Metals:

Atkins, P. W. (1995). The Periodic Kingdom. HarperCollins Publishers,

Inc..

Ball, Philip (2002). The Ingredients: A Guided Tour of the Elements.

Oxford University Press.

Brown, Theodore L.; LeMay, H. Eugene; Bursten, Bruce E. (2005).

Chemistry: The Central Science (10th ed.). Prentice Hall.

Pullman, Bernard (1998). The Atom in the History of Human Thought.

Translated by Axel Reisinger. Oxford University Press.

(7) Dielectric liquid:

http://books.google.com/books?id=FGowlP_lKK8C&pg=PA85&dq=dielec

tric+liquids&lr=&num=50&as_brr=3&cd=6#v=onepage&q=dielectric%20li

quids&f=false

(8) Useful vocabulary:

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http://www.salonhogar.net/quimica/nomenclatura_quimica/electroquimica

.htm

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8 Useful vocabulary8

Capacitor: a device that stores an electric charge. EDMs require capacitors to

generate the electric current used for machining.

Cathode: In EDM, a term to denote the workpiece, or the negative terminal of a

battery.

Computer Numerical Control (CNC): the use of computers, programs, and

precise motors to automatically control tool movement and carry out sequences

of machining operations.

Deionized water: water that does not contain any dissolved solids. Deionized

water is used as a dielectric fluid for wire EDM machines.

Dielectric fluid: In EDM, a liquid medium that fills the gap between the

electrode and workpiece and acts as an insulator until a specific gap and

voltage are achieved. Used to remove chips and cool the electrode/wire and

workpiece. It It then ionizes and becomes an electrical conductor, allowing a

current (spark) to flow through it to the workpiece. It also serves to cool the work

and to flush away the particles generated by the spark.

Discharge: The EDM spark.

Electrical Discharge Machining (EDM): a widely used nontraditional

machining process that removes metal through the repeated sparking of an

electrical current. During machining, the workpiece and an electrode are

immersed in a dielectric fluid.

Electrically conductive: able to effectively convey an electric current with low

resistance.

Electrode: a device used to convey an electric current, which can either leave

or enter the electrode. EDM machines generate an electric spark between an

electrode and the workpiece.

Gap (Spark Gap): The distance between the electrode and workpiece when the

spark occurs.

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Gap contamination: the presence of unwanted particles between the electrode

and workpiece that can disrupt the machining process and damage the part or

tool components.

Graphite: a black, soft form of carbon that conducts electricity and is easily

machined. Graphite is the most common EDM electrode material due to its

excellent wear resistance during machining.

Hardness: the ability of a material to resist penetration and scratching.

Insulator: A substance which blocks the flow of electric current.

Melting point: the temperature necessary to change a solid to a liquid.

Nontraditional machining: the use of a variety of chemical, thermal, and

electrical processes to machine metal workpieces. EDM is a nontraditional

machining process.

Off time: the period during an EDM cycle when no spark exists between the

electrode and workpiece. Metal is cooled and flushed away during the off time.

On time: the period during an EDM cycle when an electrical spark exists

between the electrode and workpiece. Metal is melted and vaporized during the

on time.

Overcut: the difference between the size of the electrode and the size of the

cavity created during machining.

Spark gap: the smallest space that exists between the electrode and workpiece

where the spark occurs.

Vaporize: to transform a material into a gas through the application of heat.

Wear resistance: the ability of a material to resist the gradual wearing away

caused by abrasion and friction.

Worktable: the machine component that supports the workpiece and any

workholding devices during machining.

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9 Annexes