Rapid Prototyping And Toolings

Published Date: 02 Nov 2017

Name of faculty Name of student

VINDHYA INSTITUTE OF TECHNOLOGY & SCIENCE, INDORE

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Jan.-June-2012

Recommendation

We are pleased to recommend that the thesis work of Mr. name of student entitled " title of thesis" to be accepted in partial fulfillment of the degree of Bachelor of Engineering in Electrical & Electronics Engineering.

Prof. A. J. Siddiqui, Prof.Rahul Agrawal

Executive Director Head of Department

EX VITS, Indore VITS, Indore

Supervised by:

Prof.Name of Faculty Prof. R.S Tare

Principal

VINDHYA INSTITUTE OF TECHNOLOGY & SCIENCE, INDORE

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Jan.-June-2012

Certificate

This is to certify that this Thesis entitled "Title of thesis………." submitted by Mr. name of student towards partial fulfillment of the requirement for the award of the degree of Bachelor of Engineering in Electrical & Electronics Engineering is a satisfactory account of his work based on syllabus and is approved for the degree of Bachelor of Engineering in Electrical & Electronics Engineering.

Table of content

ACKNOWLEDGMENT................................................................................................ii

ABSTRACT................................................................................................................. iii

DECLARATION...........................................................................................................v

TABLE OF CONTENTS..............................................................................................vi

LIST OF FIGURES ................................................................................................... viii

LIST OF TABLES..................................................................................................... xiii

PUBLICATIONS.........................................................................................................xv INTRODUCTION ...............................................................................................1

1.1 AIMS AND OBJECTIVES.......................................................................................3

1.2METHODOLOGIES..................................................................................................3 LITERATURE REVIEW AND BACKGROUND .................................................5

2.1 RAPID PROTOTYPING AND TOOLING .....................................................................5

2.2 ELECTROFORMING ................................................................................................7

2.3 SPRAY DEPOSITION................................................................................................9

2.4 EDM...................................................................................................................10

2.5 LITERATURE REVIEW ..........................................................................................12

EXPERIMENTALDESIGN ................................................................................16 EXPERIMENTAL PROCEDURES.......................................................................20

5.0 EXPERIMENTAL RESULTS .............................................................................26

5.1 EXPERIMENT 1 ....................................................................................................26

5.1.1 Solid Electrodes compared to Electroformed Electrodes ...........................27

5.1.2Workpieces machined by different electrodes...........................................31

CONCLUSIONS ..................................................................................................76

List of Figure

Figure 2.1 – Electroforming Process

Figure 2.2 – Spray Metal Deposition Process

Figure 2.3 – Sodick Mold-Maker 3 NF40

LIST OF TABLES

Table 3.1 – Machine Settings or Finishing, Semi-Roughing and Roughing Cuts.......17

Table 3.2 – Actual Settings or Finishing, Semi-Roughing and Roughing Cuts ..........17

Chapter 1

Introduction

INTRODUCTION

To compete in today’s industry environment, companies must keep up with the leading technologies and processes and also push the boundaries and develop new and improved productsand processes. The Manufacturing Industry is an area where time, efficiency and accuracy are the major driving forces behind innovation and research. The most competitive companies are those who continually reduce process times, increase efficiency and improve accuracy. Rapid Prototyping and Tooling is an area that has and is continuing to reduce production time and increase efficiency and accuracy in developing and manufacturing prototypes compared to traditional prototype manufacture.

The main function of Rapid Prototyping (RP) is to give the manufacturing the neededonfidence to go on to tooling and mass manufacture of the product they have designed. Once the product has met the design criteria through RP it is then needed to meet the functional criteria and that is where Rapid Prototyping has developed and evolved into Rapid Tooling. RP is an extremely useful process but it cannot always provide the manufacturer with a functional prototype in the material of choice. Rapid Tooling can provide this solution giving the manufacturer a functional prototype in the material of choice and that allows functional testing to be done on the product. The use of Rapid Tooling means a reduction in the time-to-market for a

Product and also better testing to meet functional criteria. Rapid Tooling is also useful in helping start production and getting the product into the market, while the more expensive and durable traditional tool is being produced for the mass manufacture of the product. Therefore the competition lies in researching possible ways to increase the effectiveness of Rapid Tooling and reducing the time and cost of getting the customers product to market. Electro-Discharge Machining (EDM) is a manufacturing process that has been affected by developments in Rapid Prototyping and Tooling. EDM is commonly used by toolmakers for complex injection moulds, punch dies and cavities made from hardened tool steels. EDM is ideal for materials and complex shapes that traditional machining processes are unable to perform.

In die and mold production, the EDM cycle can account for 25 to 40% of the toolRoom lead-time [1, 2]. The electrode production represents over 50% of the cost andtime of an EDM operation [2]. The goal is to reduce the time and cost of the EDMcycle and to do this, alternate methods of electrode production is a key area ofresearch.

Since conception EDM electrodes have been manufactured from solid conductivemetals including copper and tungsten, and also from non-metals mainly graphite.Using traditional machining operations in producing complex electrodes from solidcopper or graphite may require the production of several smaller electrodes andjoining them together, or running several machining cycles to get the required cavity shape. Therefore increasing the complexity of the electrode increases the electrodeproduction time and also increases the machining time if several machining cycles are required. Investigation into alternate methods of electrode production is required toreduce cost and time. To gain a good comparison of the various electrode manufacturing methods, the experiments include the use of Electroformed Copper, Copper Spray-deposition and traditional Solid Machined Copper Electrodes tested under several machining conditions.

Electroforming is a process that can be controlled to a high degree and can operate with precision and reliability. Electroforming can be employed to produce electrodes with complex shapes that in the past would require the use of several conventional techniques that might include machining, pressing and welding to manufacture a similar electrode.

The other manufacturing process used in attempts to produce copper electrodes isSpray Deposition or Spray Metal Deposition as it is also named. Spray metaldeposition has been used to produce moulds for many different moulding processes.It is possible for the moulds to be manufactured quickly and inexpensively for thoseprocesses [4-9]. As a different rapid prototyping technology and quick productiontechnology, spray metal tooling is used in a flexible system for producing smallnumbers of parts. Spray metal deposition is normally used to produce moulds but inthis project it is used to spray into a mould to produce the electrode shells.When comparing the different electrode manufacturing methods, the machiningonditions include a roughing setting, semi-roughing setting and a finishing setting.The performance of the EDM process is measured with respect to machining rate orMaterial Removal Rate (MRR), electrode wear (TWR), and surface finish of the workpiece (Ra).

The design of the electrodes evolved from previous research in the design and use of

electroformed electrodes. The tool used by Subramanian was found to produce

excess wear on the protruding surfaces and very little wear on the cavities. Therefore

it was decided to do the tests using separate portions of similar design. The tools

developed include a simple conical shape, a triangular protrusion and a more complex

shape that would be almost impossible to machine a similar cavity. The simple and

complex designs are used to compare the various manufacturing methods

1.1 AIMS AND OBJECTIVES

In the proposed research an attempt will be made to investigate the following:

(a) Testing the viability of electroformed copper electrodes for EDM by

conducting electrode wear studies,

(b) Testing the performance of an electroformed copper electrode in comparison

to a machined copper electrode, based on tool wear and economy of tool

manufacture,

(c) Study the effect of texture of the EDM tool on the work piece material, and

(d) Developing Rapid Tooling for EDM and injection moulding by using Spray

Metal Deposition technique .

1.2 METHODOLOGIES

This project involves the following steps:

• Development of CAD models of Electrodes

• Rapid prototyping and tooling to produce electrode master patterns,

• Electroforming negative tool to produce copper shells for electrodes, and

backfilling to give the shell support,

• Machining of Solid Copper Electrodes for comparison to alternatively

produced electrodes,

• Production of Spray-metal copper shells for electrodes,

• Testing Electrodes comparing Material Removal Rate (MRR), Tool Wear Rate

(TWR) and Surface finish for the different production methods,

• And evaluating results and developing conclusions.

Chapter 2

Literature review

LITERATURE REVIEW AND BACKGROUND

The tremendous advancements in EDM technology have been achieved for more than

50 years through the collective efforts of many dedicated engineers from some of the

world’s leading institutions and research centres. The research fields mainly cover

EDM control systems and EDM technology. EDM control system includes the servo

control unit and the parameters that control the system. EDM technology covers the

machine abilities and electrode research.

2.1 RAPID PROTOTYPING AND TOOLING

Rapid Prototyping (RP) and tooling is a continuation from three-dimensional CAD

modelling. RP uses the CAD data to produce layer information that is fed into RP

machines to produce a three dimensional solid model from a chosen process and

material. Common RP processes include Stereolithography (SL), Selective Laser

Sintering (SLS), Laminated Object Manufacturing (LOM) and Fused Deposition

Modelling (FDM). The majority of RP processes involve the conversion of the CAD

data into cross-sectional information and the model is built layer-by-layer.

In the production of EDM electrodes many RP processes have been previously used.

The most promising process involves the use of stereolithography and producing

models as either positive or negative master patterns. Stereolithography (SL) uses

information from a computer generated three-dimensional model to produce a solid

three-dimensional model from various types of laser-curing polymer resins. The

Stereolithography Apparatus builds the three-dimensional solid model layer by layer.

The computer file is broken down to layers and the SLA reproduces the layer on the

surface of the resin. The part is then lowered by the relative layer thickness, and the

process is repeated until the completed model is produced. The Stereolithography

Apparatus used is developed and marketed by 3D Systems Inc, Valencia, California,

USA. The machines produce models with high detail and accuracy and have the

ability to produce multiple parts simultaneously.

Using the positive master pattern is termed as "Direct Electrode Manufacture" in that

the SL pattern is plated with a conductive material and used as the electrode.

Alternatively, using the SL pattern as a negative and removing the plated shell is

termed as "Indirect Electrode Manufacture".

Research in the area of Direct Electrode Manufacturing process includes work from

Arthur et aland Leu et al. [15]. Results using the direct manufacturing

method have shown advantages in that the electrodes are comparable to traditional

solid electrodes in finishing, semi-roughing and roughing machine settings and

electrode production time is reduced as large quantities of electrodes can be produced

simultaneously. The results also concluded disadvantages including the possibility of

non-uniform distribution of electrodeposited material resulting in unknown plating

thickness, EDM machining time is quite high, the SL master pattern is sacrificial and

the electrodes are prone to premature failure if the plating thickness is less than 180

μm.

Alternatively the area of Indirect Electrode Manufacture has been researched and

developed by Jensen and Hovtun [16], Rennie et al. [17] and Yarlagadda et al. [3, 18,

19]. Advantages for using indirect electrode manufacture include relatively low

manufacturing cost, multiple electrodes can be produced simultaneously, the master

pattern can be reused multiple times and the electrodes can be manufactured to high

accuracy and quality. Jensen and Hovtun were also able to show that the performance

is comparable to solid electrodes.

Jensen and Hovtun [16] found disadvantages that include unacceptably high wear

rate, poor accuracy, long process time and internal details can be problematic. Rennie

et al. [17] provided similar disadvantages in that narrow internal cavities are not

plated to the same thickness as external features and failure still occurs with excess

wear and uneven material distribution. Yarlagadda et al. indicated that different

sections of the tool performed more work than other sections, triangular protrusions

had split and tool failure occurred and course machining can deform the tool.

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2.2 ELECTROFORMING

Electroforming uses electro-deposition of a metallic coating to a mould to produce a

negative copy, which is a hollow shell that is removed from the pattern as the finished

product, or the metallic coating is added to the pattern to produce a platted positive

product on the surface of the pattern. The process is shown in Figure 2.1.

First a mould is produced from the master pattern to be copied. The mould may consist

of a non-metallic substance or sometimes a low-melting-point alloy. A suitable

substance (silicon tooling) used for the production of the mould and plastics, in

particular, have the advantage of producing moulds that have a long service life - i.e.,

can be reused a large number of times. Moulds may comprise one, two or three parts,

depending on the complexity and shape of the model.

For a non-conductive mould the surface of the mould is coated with an electrically

conductive material to allow the electrical circuit to flow. The preferred method is a

fine film of silver sprayed to the surface, other methods include brushed fine graphite

powder or a metallic powder suspended in a thin lacquer.

Using direct current and the principle of electrolysis electro-deposition of metallic

coatings are done in an acid or alkaline salt solution containing the metal to be

deposited. The mould becomes the cathode when connected to the negative pole and

the anode or positive pole is usually made from the metal being deposited. The anode

is gradually consumed during the process. Various auxiliary techniques are applied -

such as the use of internal anodes, masking, etc. - to ensure that a uniform and smooth

metallic coating is formed. By the addition of special substances it is possible to

enhance the smoothness, fineness and lustre of the coating. When a coating of the

desired thickness has been attained, the shell is rinsed, removed from the mould and, if

necessary, given a finishing treatment. Next, the shell may be given backing or filling

of low-melting-point alloy, or some other material, to strengthen it. [20]

C:\Users\0000000000000000000\Desktop\151.jpg

Figure 2.1 – Electroforming Process

Electroforming is used for a variety of purposes: e.g., making copies of archaeological

or art objects, printing plates, metal discs in the manufacture of phonograph records,

embossing dies, templates, molds for casting, and many object used in mechanical and

electrical engineering.

2.3 SPRAY DEPOSITION

Spray deposition is a process also known as spray-metal deposition, plasma spray

deposition, plasma spraying and plasma deposition. Research in recent years has

shown advances in the use of spray metal and the resulting properties [4-9].

Spray metal deposition involves spraying atomised molten metal on to a pattern to

produce a copy of the surface required as shown in Figure 2.2. The process produces

a shell on the surface of the pattern that is usually removed and back filled to provide

a low cost alternative to producing a solid metal model. The moulds can be made cost

effectively from wood, metal, plastic, ceramic or even leather. These moulds can

become very inexpensive due to the fact that they can be used more than once.

C:\Users\0000000000000000000\Desktop\images (1).jpg

Figure 2.2 – Spray Metal Deposition Process

The benefits of Spray Metal Tooling are that it cost 75% less and moulds can be made

in 1/5 of the time. There are various applications in which spray metal tooling is

used:

• Prototype Injection Moulds

• Polyurethane Tooling

• Structural Foam

• Thermoform Tooling

• Blow Moulds

• I.S.P. (instant set polymers)

• Spray Metal Tooling can be used to reduce cost of prototype moulds for;

o Evaluating Injection Moulding Compounds

o Make Custom Trade Show Samples

o Test Physical Characteristics of Moulded Products

o Develop Spray Masks From Moulded parts

o Determine if Shrink Fixtures are Necessary

2.4 EDM

The Electro-Discharge Machine, shown in Figure 2.3, used in the project is the Sodick

Mould-Maker 3 NF40 situated at QMI Solutions in Brisbane.

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Figure 2.3 – Sodick Mold-Maker 3 NF40

The EDM system consists of a shaped tool (electrode) and the work piece, connected

to a DC power supply and placed in a dielectric fluid. When the potential difference

between the tool and the work piece is sufficiently high, a transient spark discharges

through the fluid and removes a small amount of metal from the surface of the work

piece.

The amount of metal removal rate, surface finish and tool wear are dependent on the

voltage, current and frequency of sparks. Increase in voltage and current results in an

increase in material removal rate and surface roughness.

Due to the machining process occurring without any machining forces, EDM is the

ideal machining process for very fine detailed machining to be done. EDM allows the

steel to be hardened prior to machining to remove the possibility of distortion after

machining.

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2.5 LITERATURE REVIEW

Research groups have been researching into many areas of Rapid Prototyping and

Tooling. Areas of Rapid Tooling that research has been conducted and is continuing

in include forming tools[21], stereolithography injection mould tools[22, 23], Rototools

for casting[24] and polymer infiltration for rapid tools[25]. These areas in rapid

tooling show that there is still a large scope for potential research to improve

traditional and non-traditional tooling. Harris et al. [22, 23] indicates that production

of low volume of parts can be done in much less time and lower costs using the rapid

tooling technologies. Noguchi and Nakagawa [21] have shown that combining RP

processes (SLA and Sintering) provides a useable method of producing metallic rapid

forming tools. Chan et al. [24] provide a proven case for the introduction of rapid

tooling into a traditionally labour intensive and expensive process.

Areas of Rapid Prototyping have been more extensively investigated and researched.

RP covers areas like Laminated Object Manufacture (LOM), Stereolithography

(SLA), and Selective Laser Sintering (SLS). These RP processes are often used as the

initial steps to lead in to Rapid Tooling. Mueller and Kochan [26] have researched

and shown that LOM provides a cheap and effective option as the initial steps for

foundry casting patterns. Extensive use of SLA has been used in the initial steps of

prototyping and manufacture in the areas of injection mould tooling [22, 23, 27], sheet

metal drawing [28], precision forming tools [21], and EDM tooling [3, 10, 11, 14, 15,

18, 19, 29, 30].

"EDM has the advantage of allowing tool steel to be treated to full hardness before

machining, avoiding problems of dimensional variability which are characteristic of

post treatment"[14]. EDM (Electric Discharge Machining) or spark erosion is a nontraditional

machining process used on hardened tool steels when complex and detailed

surfaces are required. In die and mould production, the EDM cycle can account for

25 to 40% of the tool room lead-time [1, 2]. The electrode production represents over

50% of the cost and time of an EDM operation [2]. In today’s manufacturing

environment cost reduction is a main goal, and a great emphasis is placed on the

reduction of time to complete tasks.

13

Decreasing time and improving efficiency of processes is the main focus of many

researchers. Advancements in Rapid Prototyping have allowed for great time saving

in current processes. Rapid Prototyping (RP) and associated techniques like Rapid

Tooling have played a major role in research of cost and time reduction. Rapid

Tooling technologies offer an alternative method of production the promises to

drastically reduce the time involved in design and manufacture of tools [1-3, 10-12,

14-19, 21-25, 29-34]. Within RP, Stereolithography is one of the main methods used

in producing tools. RP is now considered to have a vital role in product development,

cost reduction and time saving [31].

The conventional methods of producing electrodes include stamping, coining,

grinding, extrusion/drawing, turning and milling from materials including copper,

brass, steel and graphite. RP Technology can be used directly or indirectly in the

production of EDM electrodes. Main methods of RP electrode manufacture include

sintering [25, 35-37], electroforming [14, 17-20, 27-29, 38-49], and spray metal

deposition [5, 7, 45]. A facility to sinter metal powder wasn’t available for the

research so electroforming and spray metal deposition was used.

The direct method uses a manufactured model as the electrode or a model that has

been coated by deposition or sheet formed. The direct method has been previously

carried out using the following three approaches: Electrically Conductive Plastic

[32](doesn’t have sufficient electrical conductivity at present); Metal Powder

Impregnated SL Resin Substrate [16, 32] (dismissed due to the inability to cure the

composite resin); Application Of Coatings To Substrates (Various routes from SL

model through metallising and coating to EDM electrode have been identified and

show potential to be viable)[10-12, 15].

The indirect method of electrode manufacture involves the manufacture of a negative

mould in which a shell is produced using material deposition or sheet deformation.

The shell is then backed with a suitable resin or low melt alloy [14]. The following

techniques have been used: Coated Electrodes from Negative Pattern (the negative

pattern is used with electroforming, galvanic plating and spray metal. All have shown

promise except spray metal has poor efficiency due to porosity) [1, 14, 16, 32]; Tartan

14

Tooling and Rotational Copper Casting (Has promising results with electrodes in

copper/tungsten claiming better wear rates than graphite) [33]

Experiments using the direct manufacturing [11, 12, 14, 15, 17] and indirect

manufacturing [16] methods have been attempted to differing degrees of detail.

Arthur et al. [11, 12, 14] mainly researches the electroformed electrodes by optimising

the parameters to get the best MRR, TWR and Ra as possible. Rennie et al. [17]

researched into how the wall thickness of the electroformed shell affects the

machining time.

Leu et al. [15] and Jensen et al. [16] have shown comparisons between non-traditional

electroformed electrodes and traditional machined electrodes. Jensen et al. [16] have

shown a general comparison between electroformed electrodes and machined

electrodes but don’t give much detail into performance of the electrodes. Research by

Leu et al. [15] shows a more details comparison of the different electrodes in terms of

MRR, TWR and Ra but their work is on directly manufactured electrodes. There

appears to be insufficient information in the investigation of the efficiency of indirect

manufactured electrodes (using electroforming and spray metal) compared to

traditional solid electrodes through the manipulation of EDM process parameters.

The lack of information on indirectly manufactured electrodes provided the need to

research further into the non-traditional methods of manufacturing electrodes. There

was also a lack of research into using complex shaped electrodes manufactured in

methods other than the traditional machining.

The previous work carried out that lead into this proposed project includes work done

by Ang in 1998 [30], Hung in 1999 [29] and Yarlagadda, et al. in 1999 [19]. Ang

applied Rapid Tooling techniques to produce electroformed electrodes that were used

in experiments to replace traditional machining with non-traditional machining EDM.

Experimental results showed the potential of the electroformed electrodes in

comparison to solid copper electrodes, but inadequate flushing lead to the failure of

the electrodes.

15

Hung [29] performed experiments based on the work of Ang [30] and concluded that

the electroformed electrodes performance was based on the shell thickness. A shell

thickness less than 2mm couldn’t withstand long process times of EDM. Yarlagadda

et al. [18, 19] continued research into the electroformed copper electrodes. The focus

was on using stereolithography rapid prototyping to produce the master patterns and

vacuum casting to produce a negative pattern. The negative pattern was used in the

electroforming process to produce the copper shells. The electroformed copper shells

were backed with aluminium epoxy. Their experiments proved the potential for

applications of electroformed electrodes to EDM.

Chapter 3

EXPERIMENTAL DESIGN

EXPERIMENTAL DESIGN

The experiments in this research are based on a similar procedure to Leu et al. - "A

Feasibility Study of EDM Tooling Using Metalized Stereolithography Models".

The procedure allows an indication of the difference in the performance of different

manufacturing methods. Leu et al. provided a comparison between

electroformed copper electrodes and traditional solid electrodes by running

experiments at three different machine settings for a set time of ten minutes. There

were a total of eight experiments per electrode type at each machine setting.

EDM performance is dictated by the machine parameters and the optimisation of

those parameters has been the basis of research by the majority of research groups in

the field of EDM. Many researches have used methods such as neural networks [50-

54] and Taguchi method [55-57] to optimise performance characteristics and machine

parameters.

Due to time and budget restrictions the number of experiments determined the type of

analysis that could be done. The Taguchi method and neural network experiments

require a large number of experiments to prove the methods and the budget didn’t

allow that size research. Leu et al. [15] completed eight experiments per machine

setting for each electrode type and to get results that are comparable, within the

budget, only two experiments for each machine setting and electrode type were

conducted.

A comparison of the three electrodes (solid copper, electroformed copper and spray

metal copper) will be made using the same machining conditions and measuring the

performance attributes. The performance attributes measured include material

removal rate (MRR), tool wear ratio (TWR) and surface roughness (Ra).

The electrodes will be tested under three machining conditions and measured to

compare the performance attributes. The machining conditions include a roughing

cut, semi-roughing cut and a finishing cut. Using the same machine parameters for all

three electrodes will allow a good comparison to be made.

17

Using additional test experiments it was determined that using standard preset

machine settings for the three different cuts would be the best way to get comparable

results from the different electrodes at the three different cut settings. The codes

chosen for the machine settings are - C110 – Finishing,

C140 – Semi-roughing,

C170 – Roughing

The machine settings for cutting steel using copper electrodes range from C100 to

C190 when aiming for minimal wear to the electrodes. C110 setting was chosen for a

finishing cut because C100 was extremely fine and the machining time was too high

for the timeframe of these experiments. C170 setting was used because the C180 and

C190 settings were too aggressive for the electroformed electrodes and the C170 setting allowed the test electroformed electrodes to actually machine the test pieces.The C140 setting was chosen on the fact that it evenly divided the other two settings.The settings for the three different experiments involve the following parameter settings –

Machine

Setting

Discharge

Pulse Duration on

Quiescent

Pulse Duration

OFF

Quiescent

Time

MA

Peak Current

IP

Servo Voltage

SV

Polarity

PL

C110

012

012

01

002.0

03

+

C140

016

016

01

005.0

05

+

C170

019

019

01

010.0

05

+

Table 3.1 – Machine Settings or Finishing, Semi-Roughing and Roughing Cuts

The values given are not actual values. They are machine setting numbers for thescale on the machine. The actual values for the machine settings are as follows

Machine

Setting

Discharge

Pulse Duration on

Quiescent

Pulse Duration

OFF

Quiescent

Time

MA

Peak Current

IP

Servo Voltage

SV

Polarity

PL

C110

80 micro sec

20 mic sec

X2

002.0

03

+

C140

180 mic sec

20 mic sec

X2

005.0

05

+

C170

350 mic sec

019 mic sec

X2

010.0

05

+

Table 3.2 – Actual Settings or Finishing, Semi-Roughing and Roughing Cuts

Chapter 4

EXPERIMENTAL PROCEDURE

EXPERIMENTAL PROCEDURE

The experimental results compare the performance of the different electrode

manufacturing methods at the three different machine settings. The aim is to compare

the electrode performance at different workloads on the electrode from roughing cuts,

semi-roughing and finishing cuts. The three settings cut at different speeds so the

depth of cut for the finishing cut was reduced. This was to prevent the machining time

from climbing too high.

The selection of electrode shapes (Figure 4.1) was to help compare different areas of

tool manufacture and performance. Tool shapes were developed from previous

research carried out by Subramanian [3], who showed that trying to test the different

geometries in one tool was not as helpful so the shapes were developed separately.

The three shapes developed highlighted the tools machining performance and the

ability to cope with a broad range of tool features and shapes. The new tool shapes

include smooth curved surfaces, sharp corners, low draft angles and complex deep

holes and this differs from previous work carried out by Leu et al. [15] because their

research was done using very simple shaped machining into a flat work piece. The

complex shapes were also used to get an indication of the limitations of the

Electroforming and Spray Metal processes to produce the various shapes and then

their suitability to be used in the EDM process.

The electrodes were all set up in the same conditions and the similar shapes made the

same cuts at the same settings. The depth of cut is measured from the top surface of

the work piece and the experiments begin with the depth of the hole in the near net

casting. The first four experiments are 1mm cut added to the previous measurement

and the final two experiments are 0.5mm extra.

Chapter 5

Result

EXPERIMENTAL RESULTS

A total of six experiments were carried out. Due to manufacturing costs two sets of

three solid copper electrodes, six sets of three electroformed electrodes and two sets

of three spray metal electrodes were produced. As explained later in this chapter the

spray metal electrodes didn’t work as expected. Due to the porosity and uneven

thickness in the spray metal electrode shells the backing material penetrated and made

the electrodes unusable. Therefore the performance of the spray metal electrodes

failed before making it to the EDM stage.

5.1 EXPERIMENT 1

A roughing cut was used in the first set of experiments with the machine set on a

standard machine setting of C170. This produced high MRR and Ra with low

machining time and TWR.

The machine and actual settings were as follows:

Nominal Actual

Machine Setting: C170 C170

Discharge Pulse Duration (ON): 019 350μsec

Quiescent Pulse Duration (OFF): 019 30μsec

Quiescent Time (MA): 01 X2

Peak Current (IP): 010.0 10A

Servo Voltage (SV): 05 60V

Polarity (PL): + +

The following is the depth of cut for the first set of experiments:

Cone Electrode – 28mm

Triangle Electrode – 26mm

Base Electrode – 19mm

5.1.1 Solid Electrodes compared to Electroformed Electrodes

The performance of the electrodes can be compared in several ways. Tool wear shows

the durability of the electrode itself. Results of experiment 1 show that the tool wear

is greater in the electroformed electrodes. The following have been given the same measurement scales to give a true indication of thecomparison in wear. Figure 5.1 shows that solid electrode has very little wear andany wear that has occurred is less than 0.05mm. The electroformed electrode hasn’tperformed as well as the solid electrode and this is emphasised by the

wear being greater than 1mm on the sharp corners and over 0.1mm around the edges.are shown as an example of the difference in wear and in theOne of the problems encountered when using the electroformed electrodes was theability to damage the electrode when beginning the experiment. The expanded view in fig 5.2

C:\Users\0000000000000000000\Desktop\1RQS5UX01weldingelectrodes.jpg

Fig 5.1 A perfect welding electrode

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Fig 5.2 solid electrode making

shows the damage that can happen. The damage was caused by a lack of

conduction through the electrode holder and the electrode. During the setup the

electrode came in contact with the work piece and did not produce a circuit to registerin the z axis.Thegreen line gives an estimate on the shape of the original electrode.

Chapter 6

Conclusion

CONCLUSIONS

Manufacture of three different shapes of electrodes in three different manufacturing

methods was achieved. The solid copper and electroformed copper electrodes were

manufactured successfully to the experimental stage however the spray metal

electrodes were unusable.

The experiments with the solid electrodes and electroformed electrodes were

conducted with success at three different machines setting and comparisons were able

to be made. The solid electrodes consistently performed better than the electroformed

electrodes at all machine settings as shown in the summary graphs of the performances

in Machining Time, MRR and TWR.

The major problems encountered with the electroformed electrodes included:

• problems with setup and conductivity,

• shell thickness is hard to control and cavities are difficult to build evenly,

• the electroformed shells are easily damaged,

• the backing material doesn’t have the same conductivity as the copper,

• the copper shells are prone to warping under thermal stress,

• Delamination is possible,

Although the solid electrode has outperformed the electroformed electrodes in the

Majority of the experiments, the solid electrodes are much more expensive to produce.

The standard workshop is more likely to have a machining centre to machine solid

electrodes as opposed to an electroplating system to produce electroformed electrodes.

So the convenience of the solid electrodes will often out way the use of electroformed

electrodes.

The cost of electrodes becomes a major factor as soon as the electrode manufacturing

process becomes more comparable. Even though the solid electrodes out performed

the electroformed and spray metal electrodes, the cost of manufacture plays a vital role

in the tooling process. This research has shown that the cost of solid electrodes is

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$810 each which is six times that of electroformed and spray metal electrodes at $130

each.

Solid electrodes take approximately six hours to produce where as a single

electroformed electrode will take up to 50 hours to produce. The cost of production is

sometimes not the critical factor when rapid tooling is required. For low numbers of

electrodes it is probably more economical in terms of time to use traditional

machining. However when a large number of electrodes are required, electroforming

will take a similar amount of time to produce one electrode as it will take to produce

an infinite number of electrodes and therefore becoming faster as long as more than 10

electrodes are required..

The research has given similar results to research done by Leu et al. [15], Jensen et al.

[16] and Arthur et al. [14] in that the traditionally produced electrodes performed in a

similar manner to the non-traditional (electroformed) electrodes. If the electroformed

electrodes could be produced with a much more even shell thickness it might reduce

the erratic performance of the electroformed electrodes. Although the electroformed

electrodes performed on average comparable to the solid electrodes there seemed to be

a greater difference between the best and worst performances of the electrodes at each

machine setting.

It is recommended that more refinements need to be done on the electroforming

process to get a greater understanding of the performance characteristics of the

electrodes. Also a greater number of experiments need to be conducted to prove the

repeatability of the electroformed electrodes. Leu et al. [15] conducted eight

experiments at each machining level and others like Arthur et al. [14] conducted over

72 experiments in Fractional Factorial Experiments and Taguchi methods to optimise

the parameters for MRR and the same amount of experiments would be needed to

optimise TWR and Ra. Optimising the machine parameters using Fractional Factorial

Experiments and Taguchi methods is a way that research could promote the use of

electroformed electrodes.

The electroforming process could be a viable option for the EDM process if the

electrodes could be produced more robust and consistent shell thickness.

with the shell thickness produced warping and delamination on some of the larger flat

surfaces. With greater control over the wall thickness and greater heat conductivity of

the backing material would give better performance of the electroformed electrodes.

With more investigation into spray metal applications and capabilities it would prove

to be a promising method of electrode manufacture. This project was unable to apply

the time and resources needed to research spray metal to the degree that would be

needed to get the process to a usable standard.

Other areas in EDM that could benefit from more research include:

• Flushing systems for deep cavities,

• Conductive backing materials for the electrode shells,

• Setup and tooling for the electrode attachment to the EDM tool

post to increase the conductivity,

• And investigation into the thermal stresses occurring in the

electroformed electrode shells and backing material