OPTIMIZATION OF THE POLISHING PROCEDURE USING A ROBOT ASSISTED

OPTIMIZATION OF THE POLISHING

PROCEDURE USING A ROBOT ASSISTED POLISHING EQUIPMENT

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Marielle Gagnolet •••• 2008 01 25

Handledare: Sabina Rebeggiani Examinator: Bengt-Göran Rosén

Ett examensarbete utfört enligt kraven för Högskolan i Halmstad för en Magisterexamen i Teknisk Produkt- och Produktionsförbättring

GAGNOLET Marielle 4GM

REPORT OF INDUSTRIAL PLACEMENT

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AAKK NNOOWWLL EEDDGGMM EENNTTSS

I would like to thank all the people who helped me during these 5 months, to adapt myself in an other country and also to carry out my project; especially:

� Mr. Bengt-Göran Rosén, Professor and director of the lab, for his warm welcome to Halmstad University, and for sharing his knowledge to help me.

� Ms. Sabina Rebeggiani, PhD student, for her patience, for always being available when I needed, and for helping me in this project.

� Mr. Zahouani, Professor at the ENISE for giving me the opportunity of carrying out my internship in Halmstad University.

� Mrs. Levy, English teacher at the ENISE, for being always available in case of problems.

� Mr. Frédéric Cabanettes, who helped me with all the procedure to come here and for being available along these 5 months.

� Mr. Stefan Rosén and Ms. Karin Westerberg from Toponova AB for their instructions and guidance in performing optimal measurements on the stylus and the interferometer.

� Mr. Kim Lorenzen, Mr. Jens Grønbæk, Mr. Lars Sørensen (from Strecon A/S) and all the employees of Strecon A/S for their welcome to Strecon and their collaboration in this project.

� Mr. Alf Sandberg from Uddeholm Tooling AB, for his trust leaving us leading this project.

� Mr. Zlate Dimkovski, Mrs. Bibbi Johansson, Mrs. Monica Lindström and all the people of the university for their help along this semester.

� All the students I met during my stay in Sweden and who made this experience become unforgettable and humanly enriching for me.



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AABBSSTTRRAACCTT

Today, manual polishing is the most common method to improve the surface finish of mould and dies for e.g. plastic injection moulding, although it is a cumbersome and time-consuming process. Therefore, automated robots are being developed in order to speed up and secure the final result of this important final process.

The purpose of this thesis is to find out some clues about the influence of different parameters for the polishing of a steel grade called Mirrax ESR (Uddeholm Tooling AB) using a Design of Experiment. The report starts with a brief description of mechanical polishing (the techniques and polishing mechanisms) and ends up with the optimization of the polishing procedure with a polishing machine, the Strecon RAP-200 made by Strecon A/S.

Even if all the runs of the Design of Experiment couldn’t be carried out, the surfaces studied revealed some information about the importance of the previous process (turning marks not removed) and about the link between the aspect of the surfaces and the roughness parameters.



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SSUUMM MM AARRYY

AAKK NNOOWWLL EEDDGGMM EENNTTSS ....................................................................................................................................... 1

AABBSSTTRRAACCTT..........................................................................................................................................................................................................................................................................................................................22

SSUUMM MM AARRYY ........................................................................................................................................................... 3

II NNTTRROODDUUCCTTII OONN................................................................................................................................................. 4

PPAARRTT II :: PPRROOJJEECCTT SSCCEENNAARRII OO ........................................................................................................................ 5

1. PRESENTATION OF COMPANIES........................................................................................................................ 5 11..11)) HHAALLMMSSTTAADD UUNNIIVVEERRSSIITTYY ....................................................................................................................... 5 11..22)) UUDDDDEEHHOOLLMM TTOOOOLLIINNGG AABB .................................................................................................................... 5 11..33)) SSTTRREECCOONN AA//SS........................................................................................................................................ 6 2. THE PROJECT................................................................................................................................................... 7 22..11)) TTHHEE PPRROOJJEECCTT EENNVVIIRROONNMMEENNTT ................................................................................................................ 7 22..22)) DDEESSCCRRIIPPTTIIOONN OOFF WWOORRKK ......................................................................................................................... 7

PPAARRTT II II :: LL II TTEERRAATTUURREE SSTTUUDDYY....................................................................................................................... 8

1. A FEW POLISHING METHODS............................................................................................................................ 8 2. MECHANICAL POLISHING ................................................................................................................................ 8 22..11)) PPOOLLIISSHHIINNGG EEQQUUIIPPMMEENNTT ........................................................................................................................ 8 22..22)) PPOOLLIISSHHIINNGG TTEECCHHNNIIQQUUEESS,, ““ RRUULLEESS”” ........................................................................................................ 9 33.. POLISHING MECHANISMS............................................................................................................................... 11 33..11)) HHIISSTTOORRYY ............................................................................................................................................. 11 33..22)) AABBRRAASSIIOONN AANNDD PPOOLLIISSHHIINNGG ................................................................................................................. 11 33..33)) CCHHAARRAACCTTEERRIIZZAATTIIOONN OOFF AA PPOOLLIISSHHEEDD SSUURRFFAACCEE.................................................................................... 14

PPAARRTT II II II :: PPOOLL II SSHHII NNGG SSTTAANNDDAARRDDSS............................................................................................................ 16

1. NECESSITY OF STANDARDS............................................................................................................................ 16 2. MEASUREMENTS........................................................................................................................................... 16 22..11)) MMEEAASSUURREEMMEENNTTSS DDEEVVIICCEESS................................................................................................................... 16 22..22)) MMEEAASSUURREEMMEENNTTSS AANNDD RREESSUULLTTSS.......................................................................................................... 17

PPAARRTT II VV:: DDEESSII GGNN OOFF EEXXPPEERRII MM EENNTTSS ((DDOOEE))............................................................................................ 18

1. PRESTUDY..................................................................................................................................................... 18 11..11)) TTHHEE MMAACCHHIINNEE ..................................................................................................................................... 18 11..22)) TTHHEE PPAARRAAMMEETTEERRSS............................................................................................................................... 19 11..33)) CCHHOOIICCEE OOFF TTHHEE MMAATTRRIIXX ...................................................................................................................... 20 11..44)) AASSSSIIGGNNMMEENNTT OOFF TTHHEE FFAACCTTOORRSS TTOO TTHHEE CCOOLLUUMMNNSS............................................................................... 21 2. EXPERIMENTS AT STRECON........................................................................................................................... 23 22..11)) PPAARRTT 11:: PPRREEPPAARRAATTIIOONN OOFF TTHHEE EEXXPPEERRIIMMEENNTTSS ..................................................................................... 23 22..22)) PPAARRTT 22 :: FFLLOOWW OOFF WWOORRKK .................................................................................................................... 24 3. ANALYSIS OF THE RESULTS........................................................................................................................... 25 4. RESULTS AND DISCUSSION............................................................................................................................ 25

CCOONNCCLL UUSSII OONN OOFF TTHHEE PPRROOJJEECCTT ................................................................................................................ 31

FFUUTTUURREE .............................................................................................................................................................. 31

PPEERRSSOONNAALL CCOONNCCLL UUSSII OONN............................................................................................................................. 32

RREEFFEERREENNCCEESS.................................................................................................................................................... 33

AAPPPPEENNDDII XX........................................................................................................................................................................................................................................................................................................................3355



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II NNTTRROODDUUCCTTII OONN Currently in my 4th year at the ENISE, I made this year my second industrial placement. After a first experience in Andrezieux-Bouthéon (France) in the car industry working in the production, I decided this year to have an experience in a research lab and also to go abroad. It was for me the opportunity to discover a working environment very different from what I already knew, to deal with another language and so improve my English. It was also for me a challenge to go there alone, meet other people from different countries, and of course to discover another country and its culture, both in every day life and at work. Attracted by Scandinavian countries and given the partnership between the ENISE and the Halmstad University in Sweden, I made this internship in its mechanical lab, managed by Professor Bengt-Göran Rosén. This lab deals with a few PhD students, working for different companies like Volvo, Uddeholm Tooling AB… I worked with one of them, Sabina Rebeggiani, on a project about the optimization of a polishing machine.



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PPAARRTT II :: PPRROOJJEECCTT SSCCEENNAARRII OO

1. Presentation of companies

11..11)) HHaallmmssttaadd UUnniivveerr ssii ttyy

Halmstad is located on the Western coast of Sweden and counts 86.000 permanent inhabitants. Tourists, businessmen, members of the armed forces and the students ensure the prosperity of the entertainments and the culture throughout the year. The university offers to Halmstad new prospects interesting for the future, where knowledge and competences play an increasingly important part. The university offers at the same time single and famous programs and lectures. Nearly 7000 students study Medical and Social Sciences, Economy, Behavioral Science, Health as well as Engineering. The majority of the programs are directed towards the innovation and the entrepreneurship. Many projects and theses emerge, with terms, from a productive cooperation between the students and the industry.

11..22)) UUddddeehhoollmm TTooooll iinngg AABB ((UUTTAABB)) The first firm of UTAB for steel production was found in 1668 in Stjärnfors in Värmland (Sweden). From small mills and workshop hammers in the late 17th century, UTAB grew into a steel, power and forest products group.

Nowadays, UTAB is the world’s leading supplier of tooling material and related services; it is a multinational company which acts locally in more than 100 countries. UTAB is working for tool manufacturers, tool users and their suppliers about steel in general, that is to say from the production of different kind of steel, to their treatment and their fields of application.

Halmstad



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11..33)) SSttrr eeccoonn AA//SS

Strecon A/S is a Danish company located in Sønderborg (Denmark). It is specialized in development, engineering, manufacture, sale and service of tooling solutions based on the strip-winding technology.

The principle of this technology is to wind a thin strip of high-strength steel (0.1 mm thickness) around a core of hardened tool steel or tungsten carbide while maintaining a controlled winding tension. An optimal stress distribution is obtained by varying the winding tension from strip layer to strip layer, and the state of stress in the wound coil section of the product is equal to a conventional pre-stressing system with "several hundred" stress rings. This strip-winding principle gives the product a loadability that in many cases is 50% higher than conventional compression ring solutions.

If the strip-winding technology is the main product of Strecon, the company also has a strong competence in:

� FEM modeling of precision forging and diamond synthesis tools and processes.

� In-house developed models and material tests to optimize the FEM simulations.

� In-house manufacture of key processes, e.g. strip-winding, turning, grinding, and finishing.

With this project of a polishing machine, Strecon is trying to acquire knowledge in high surface finishing, the polishing of tool steel.

They built a first prototype this year and are working with this in order to build another machine in 2008.



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2. The project

22..11)) TThhee pprr oojj eecctt eennvvii rr oonnmmeenntt

UTAB produces among other things a steel grade called Mirrax ESR (old name “Stavax Supreme”) which is commonly used for plastic mold steel. Mirrax ESR is an Electro Slag Remelted (ESR) material hardened and tempered to a hardness of 50HRC. Given the use of this steel, the polishing operation is essential. Currently, manual polishing is the most common method to improve the surface finish of mould steel, although automated robot processes are being developed to speed up and secure the final result of the polishing process. A most desirable outcome from a polishing process is to achieve a consistent surface finish from tool to tool in order to have a reliable production process.

Moreover, Strecon is building a polishing robot: the Strecon RAP-200 (Robot Assisted Polishing) which is still under development (Figure 1). The purpose of UTAB in this project is to find an automated polishing process for their steel, able to give mirror-like surfaces. With reference to Strecon, this project should increase their knowledge of this process (influence of the different parameters) and allow them to optimize their polishing machine.

22..22)) DDeessccrr iipptt iioonn ooff wwoorr kk

Title of the project: Optimizing the polishing procedure for plastic mould steel by using a robot assisted polishing equipment

The objective of this project is to more closely evaluate a robot assisted polishing equipment by examining the surface quality during various polishing procedures for the plastic mould steel Mirrax ESR. The final objective is to give guidelines on optimum polishing procedures for this steel grade, which is of a very high quality for moulds but difficult to polish.

Different steps should schedule this project:

� Literature study on polishing techniques and polishing mechanisms

� Characterization of polishing standards

� Study of Design of Experiments in order to prepare experiments at Strecon

� Experimental polishing work performed at Strecon A/S in Sønderborg, Denmark

� Surface characterization after various preparation steps via grinding and polishing at Halmstad University

� Analysis of the results of the Design of Experiments with the Software Modde 8 [Umetrics Inc, www.umetrics.com]

Figure 1: Strecon RAP-200 Picture from Strecon



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PPAARRTT II II :: LL II TTEERRAATTUURREE SSTTUUDDYY I started this project by reading many scientific articles, in order to acquire knowledge about the polishing process since it was a process almost unknown for me. First, I studied the different techniques used within industry to then focus more on the mechanical polishing which is directly linked to the project. Finally, I also tried to find information on polishing mechanisms from a metallographic point of view.

1. A few polishing methods There are many different polishing techniques used in the industry, such as:

� Laser polishing [1]

� Chemical mechanical polishing [2], [3]

� Magnetic polishing [4]

� Electropolishing [5], [6]

� Electron Beam Irradiation [7]

� Electrical Discharge machining [8]

� Mechanical polishing...

These techniques are presented in Appendix I, apart from mechanical polishing which is the technique used in this project. Therefore it will be more explained in the next chapter.

2. Mechanical polishing Mechanical polishing is the removal of material to produce a scratch-free, specular surface using fine abrasive particles. [12]

22..11)) PPooll iisshhiinngg eeqquuiippmmeenntt [[1122]] Polishing is typically done using polishing cloths, specially designed lapping plates, or stones. Polishing with a cloth or lapping plate requires the use of free abrasive, and is a very low damage process when performed properly. There are 4 basic types of abrasives:

� SiC: Rough lapping, rarely used for applications that require smooth surface finishes. � Al 2O3: Sharp, angular structure. Used when fine surface finishes are required. � B4C: Harder than the other abrasives (except from diamond); blocky crystal structure.

Excellent removal rates; used for fast removal with moderate surface quality needed. � Diamond: Hardest material, sharp, angular structure. High removal rate and high

surface finishing quality.



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Figure 1: Polishing stones [source: www.joke.de]

Figure 2: Examples of polishing carriers and free abrasive suspensions [source: www.joke.de]

For rough polishing, the abrasives are in the form of stones: abrasives are hold by a soft or hard bond (for example resin bond). These stones (Figure 1) are directly in contact with the surface to polish (with or without lubrication depending on the stone).

For finer polishing, free abrasive suspensions are used with polishing cloths, polishing plates, or other carriers. A soft or hard material is used as a carrier such as cast iron, copper, composites, wood etc. A paste mixed with abrasives is applied on the material and the movement of the carrier implies removal of material (Figure 2).

22..22)) PPooll iisshhiinngg tteecchhnniiqquueess,, ““ rr uulleess”” Manual mechanical polishing is still the best way to get mirror-like polished surfaces with complicated geometry since the operators can adjust the process according to the surface look. That is why each polisher, thanks to his experience, has his own technique of polishing. Nevertheless, hereunder are given some operative suggestions for correct polishing [source: Lucchini Sidermeccanica & Zanola, www.lucidaturastampi.it] which can sometimes be hardly reproducible with a machine. Of course, the preliminary process before polishing (grinding, turning...) is as important as polishing process itself and in both cases, basic rules are:

� Use cleaned polishing tools: the cleanness at every phase of the polishing processing is of great importance. While passing to a finer-grained abrasive medium, a good cleaning of the treated piece and of the operators hands is necessary, in order to avoid undesired abrasive particles or dust in the following steps.

Joke WS Diamond paste

polishing plate

wood polishing cloth



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� When using a finer grain size, it is better to polish in a shifted direction of 45° in comparison with the previous one, until the surface presents only the defects due to the current polishing direction (see figure 3).

Right at the moment when all the imperfections of the previous processing are gone, it is a good practice to keep on polishing for further 10% of the already spent time before passing to a finer-grained abrasive medium. That is to remove the surface layer warped by the mechanical stress due to previous mechanical preparation steps. Change of polishing direction is important even to prevent the forming of depressions and unevenness.

� Pressure and heat should be kept as low as possible, because it could badly influence

the structure and the hardness of the material. When possible, the use of conspicuous quantity of cooling liquid is suggested.

� When polishing big and flat mould surfaces, avoid the manual use of disk, to reduce

the risk of getting an extended irregularity of shape. Polishing costs and wear and tear on tools can be reduced just following these specific rules:

� Polishing movement should start from corners, edges, i.e. from less reachable areas. � Polishing pressure should be fitted according to the tool hardness and to the grain size

of the paste. � Polishing should be executed in room without draughts and dusts. Hard dust particles

can easily contaminate and spoil an almost finished surface. � Each tool should be used for just one type of paste and be kept in air tight containers. � The paste should be laid on the tool in case of manual polishing, on the piece in case

of machine polishing. � It is necessary to be careful and to possibly protect edges and sharpened corners in

order not to round them. � Hard removing of material needs hard polishing tools and coarse-grained paste.

Problems in mechanical polishing: It is very difficult to know when the polishing operation is finished, in fact, it is important not to polish too much in order to avoid overpolishing (Such problems are discussed in Appendix II).

45º

Figure 3



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33.. Polishing mechanisms

33..11)) HHiissttoorr yy Polishing is an old manufacturing process but the mechanisms behind it have been and are still subjects of enquiry for a considerable period of time.

� According to Hooke, Newton, Herschel (<1900): Polishing is a cutting process. � At the beginning of the 20th century (1921): Beilby proposed the flow hypothesis

which is that asperities might reach melting temperature during contact rubbing; high spots of the surface are molten and flow into the roughness valley. An amorphous smeared layer, the so called “Beilby layer”, would cover the surface.

Beilby also meant that material removal rate correlate with melting point and not with hardness.

� 1971: Samuels declined the flow hypothesis. According to him; polishing is a cutting

process close to abrasion. In fact, experiments were made and material removal could be observed by measuring weight loss during polishing. So, even if there is a melting process during polishing, there is a cutting process or abrasion because of this material removed.

33..22)) AAbbrr aassiioonn aanndd ppooll iisshhiinngg

� Step by step polishing A step by step polishing shows clearly a rapid decrease of the roughness values already in the first seconds of the polishing process. After the elimination of the deepest furrows of the previous grinding process, a significant decrease cannot be observed anymore. Polishing scratches are visible on the figure 1 below, indicating the abrasive nature of the polishing process.

Figure 1: Development of the surface topography by step-by-step polishing [9]



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But also, on figure 2, interrupted scratches can be observed. There are two possible reasons why such a fact occurs:

- The cutting depth provided by the grain can vary while it is pushed against the material.

- The scratches can gradually be covered by a flow of material of the surface top layer.

� Abrasion

If is difficult to know if there is a melting of material during polishing, but it is sure that abrasion occurs. So, based on the assumption that the material removal is predominantly of abrasive nature, the chip formation can be divided into the following three steps:

1. The polishing grain comes in touch with the material surface, which will be elastically deformed. Due to the relative motion of the two friction partners, on the one hand, shear stresses arise on the workpiece surface and on the other, compressive stresses are generated due to pressure applied by the polishing grain over the surface.

2. As soon as the yield strength of the

material is exceeded, the bulk material deforms plastically. This leads also to material accumulations beside the scratching trace.

3. Then, the tensile strength is locally

exceeded and the result is a chip formation.

Figure 2: Detail of interrupted scratches [9]

Graphic representation of the chip formation, where Vc is the cutting speed [9]



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� Grinding

We can try to understand the polishing process thanks to grinding process. We will then try to find the link between grinding and polishing. In a grinding process, we can see that abrasion occurs but not all the time. In fact, there are three modes of interactions between the grit paper and the workpiece:

1. Lapping: The grain rolls between the specimen and the preparation disk which implies the creation of small cavities with strong deformation. (Figure 3)

2. Grinding: The grain is fixed and acts as a machine

tool, i.e. the rake angle is correct for cutting a chip, so it must be positive or 0. (Figure 4)

3. Plowing: If the rake angle is negative, there is no chip formation anymore and only a

groove is made in the specimen surface: material is displaced into a ridge, on each side of the groove. (Figure 4)

� Link between polishing and grinding First, the equipment for polishing is different: instead of grit paper, we can have for example polishing cloths, but we still have a grain in contact with the workpiece and we still produce scratches, and that is why we can link these two processes. The choice of polishing cloth also depends on which step of polishing it is:

0 - +

Positive

angle Negative angle

CUTTING PLOWING

Figure 3: Traces of Lapping [9]

Figure 4: Grinding (cutting process) and plowing [10]

[10]



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For rough polishing (Ra>>1µm); hard cloths are used since it implies a higher load and larger chips, whereas for final polishing (Ra < 1µm), softer and more resilient cloths will make smaller scratches and less deformation on the surface. We can bring out four main differences between polishing and grinding:

- A lower contact pressure is applied during polishing - The use of different type and size of abrasives and their holding methods - Type and diamond mesh size of diamond disc - When free abrasives are used, the grains are not fixed

33..33)) CChhaarr aacctteerr iizzaatt iioonn ooff aa ppooll iisshheedd ssuurr ffaaccee The best way to understand polishing mechanisms is probably to analyze polished surfaces.

Figure 1: Schematic sketch of the dislocation substructures observed beneath a surface

polished on 6µm diamond abrasive [11]

A 3D-sketch representing the microstructure of a polished material is shown on figure 1. Three different structures can be distinguished:

- The sub grain structure: The grains are small and tend to be equiaxed in shape. - Recrystallized grain: Grains are larger than those in the sub grain structure. It is better

to describe this structure as partly recrystallized because sub boundaries and dislocations can be observed in the electron microscope, and that parts of the



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boundaries of recrystallized grains were not often sharp. These grains are mostly identifiable by the presence of annealing twins.

- The slab cell structure: Cells free from dislocations and separated by diffuse

boundaries composed of arrays of dislocations and dislocation tangles. The cells usually have a length of several micrometers and a thickness of approximately 0,1-0,2µm.

Of course the type of structure varies with the type of finishing process and sometimes from place to place across a particular polished surface. As it is shown in figure 2, the structure of the outermost layers changes with increasing fineness of polish, the number of sub grains and recrystallized grains decrease, and the structure consisted almost entirely of slab-sharp cells.

Figure 2: Summary of the structures observed in surfaces of Copper abraded and polished by

various means [11]

According to Samuels, these sub grains bring into disrepute the hypothesis of a Beilby layer since the grains are too large to be a part of a melting layer.



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PPAARRTT II II II :: PPOOLL II SSHHII NNGG SSTTAANNDDAARRDDSS

1. Necessity of standards After a first meeting in Denmark at the end of September, it was decided to measure some polishing standards from two different companies: Zanola and Bales (Figure 1). These standards are a way to show the polishing skills of a company and not only with roughness values but also showing the aspect of the surfaces.

Thanks to these standards we could understand what level of polishing we should try to reach with this new machine.

2. Measurements To characterize these standards, I first had to measure them, in order to compare them to the coming machine polished surfaces. First, the instruments available to measure surface roughness are discussed and then the one I used; secondly, the results of these measurements.

22..11)) MM eeaassuurr eemmeennttss ddeevviicceess Halmstad University uses the equipment of a company located near the university, Toponova AB. Among other things, they have a mechanical stylus and an interferometer. These two devices allow to measure roughness by different ways (optical and contact). The university has a SEM (Scanning Electron Microscope) which allows taking pictures of a sample but does not give numerical information about the roughness.

� Stylus : (Figure 2) It can perform 2D (and 3D measurements by putting profiles together). It consists of a small tip moving across the surface. The vertical translation of the stylus, while it is going over the surface, is converted into a signal. This signal is then exported into a processor to be converted into a number and a visual profile.

Figure 1: Standards from Bales on the left and Zanola on the right



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� Interferometer : (Figure 3) It can perform 3D measurements. It is an optical method using the interference of light: this instrument is measuring the wavelength of light and distances. Two beams are reflected in different ways on two surfaces not parallel to each other. Some beams cancel and others augment each other giving rise to a pattern of alternate dark and light fringes. Their spacing and shape depend on reflector and on the regularity of the surface.

� Comparison : Unlike the stylus, the interferometer is a non-contact technology which means that we cannot damage the surface. Moreover, a lot of noise is disturbing the results when polished surfaces are measured with the stylus (the resolution is too low). That is the reason why I used the interferometer to measure my surfaces.

22..22)) MM eeaassuurr eemmeennttss aanndd RReessuull ttss I measured the three best surfaces of Zanola and Bales (20 measurements of each surface). The results were analyzed with the software MountainsMap [MountainsMap premium 4.1, www.digitalsurf.fr]. Appendix III shows the results of the Zanola samples (a robust Gaussian filter of 250µm was used) for three different steps of polishing: SZ13, SZ15 and the best polished surface SZ17 (SZ17 is machine polished). The Bales sample cannot be used since the results showed surfaces which don’t seem to be mechanically polished. In fact it looks like a melt surface for two of the three different steps of polishing (Figure 5), so we cannot compare these samples to polished surfaces:

Figure 3:Interferometer Figure 2: Diagram of a stylus

SPI A1 3µm SPI A1 6µm SPI A1 15µm

Figure 5: Problems with Bales standards



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PPAARRTT II VV:: DDEESSII GGNN OOFF EEXXPPEERRII MM EENNTTSS ((DDooEE))

1. Prestudy Design of Experiment (DoE) is a structured, organized method that can be used to determine the relationship between the different factors (Xs) affecting a process and the output of that process (Y) [Source: www.camo.com]. In this DoE, the response will be the roughness of the surface (Ra value or other surface parameters). There are different steps to perform a DoE :

� Brainstorming to decide the parameters and their level � Choice of an appropriate matrix, assign factors and interactions to columns � Running experiments � Analysing results � Running confirmation experiments

11..11)) TThhee mmaacchhiinnee When we had the meeting at Strecon at the end of September, Kim Lorenzen and Jens Grønbæk presented their equipment (Figure 1) to us and the results of their first trials with the machine, with different stones, different time of polishing, etc. This polishing machine allows working with flat cylindrical workpieces.

Rotation of the disk

Figure 1 : The polishing machine at Strecon

Vibration direction

Moving direction of the stone on the surface

Bar

Stone/ Carrier

Robot



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11..22)) TThhee ppaarr aammeetteerr ss Then the parameters which influence the polishing process were listed (see the table below):

Process variable Machine Holder Tooling Material Other Initial roughness x Force x Vibration pulstime x Vibration length x Stiffness of ‘bar’ x-dir x Stiffness of ‘bar’ z-dir x Rotation speed x Feed x number of operations Lubrication x Grinding stone (grit size, density, binding (hardness), grit material)

x

Diamond brittle, monocrystalline, grain size

x

Carrier material (wood, felt etc)

x

Material residual stresses, hardness, direction/position, bar dimension

x Mirrax ESR

There are many parameters and of course it is not possible to keep all of these to make a great DoE. That is why we had to make some choices; which parameters we considered as the most important. After some discussions and thanks to some articles about polishing machines [13], [14], [15], we agreed that we should have at the most 5 parameters for this DoE; if we took more, we risked to have wrong or incomplete results (especially concerning interactions between different parameters). Furthermore, some parameters are fixed or difficult to change; for example the material is Mirrax ESR and it is quiet difficult to change the bar. So finally, after studying, comparing and thinking about these parameters, it transpired that some parameters had to appear in the DoE: the force, the grain size, the carrier, the rotation speed, the number of polishing operations and the vibration pulse time of the bar. Moreover, concerning the initial roughness, we are not sure that a smoother surface would give better results with a given experiment than a rougher one, so it is important to check it.



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Finally we had 7 parameters instead of 5; but, the rotation speed and the number of polishing operations both represent the contact time between a point on the disk and the polishing tool so we chose one of them. Then, diamond grain size and carrier are usually linked, we decided to set of « couples » of a grain size and a carrier (soft, hard...) The final parameters were :

� Initial roughness � Force � Vibration pulse time � Diamond grain size and carrier � Number of operations OR Rotation speed

11..33)) CChhooiiccee ooff tthhee mmaattrr iixx The experiments deal with 5 parameters, and we don’t know if each parameter has a linear evolution with the response, which is the roughness of the surface (in a first time Ra). It means that for each variable, there will be not 2 different values (a high and a low value) but three because of this possible non linearity. This is a very important step in the choice of the matrix: only a 3-level matrix is possible. Moreover, it would be a waste of time and money to achieve a full design of experiments with so many parameters: 5 3-level parameters mean 3^5=243 trials so a fractional factorial design is compulsory for example Taguchi designs could be suitable [16]. Taguchi Designs are often used for DoE in the industry; it is the results of many years of study, and all the software of DoE Analysis deal with this kind of matrix. That is why I chose to use it. A tool useful for the choice of the right Taguchi matrix is the degree of freedom: This number depends on the parameters, their level and on the interactions studied. The interactions studied were between:

� Force/ Diamond grain size & carrier � Initial roughness/ Diamond grain size & carrier � Rotation speed/ Diamond grain size & carrier

Calculation of degree of freedom, n: For each 3- level parameters: n=2 For each interaction: n=4

↪↪↪↪n total = 5x2 + 4x3 = 22 In the Taguchi designs, different orthogonal arrays are proposed, depending on the number of parameters, the level of parameters (ex: L9= four 3-level parameters and 9 trials; L27= thirteen 3-level parameters and 27 trials). To choose a Lk Orthogonal Array, it is compulsory to respect the following rule:

degree of freedom (n) < k



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1

2 3,4

5 6,7

9,10 8

11 12,13

Dots: parameters Lines: interactions Numbers: Nb of column

Figure 2 : Linear graph of L27 Orthogonal Array

This condition implies the L27 Orthogonal Array (Figure 1) is compulsory.

Parameter Nb runs 1 2 3 4 5 6 7 8 9 10 11 12 13

1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 2 2 2 2 2 2 2 2 2 3 1 1 1 1 3 3 3 3 3 3 3 3 3 4 1 2 2 2 1 1 1 2 2 2 3 3 3 5 1 2 2 2 2 2 2 3 3 3 1 1 1 6 1 2 2 2 3 3 3 1 1 1 2 2 2 7 1 3 3 3 1 1 1 3 3 3 2 2 2 8 1 3 3 3 2 2 2 1 1 1 3 3 3 9 1 3 3 3 3 3 3 2 2 2 1 1 1

10 2 1 2 3 1 2 3 1 2 3 1 2 3 11 2 1 2 3 2 3 1 2 3 1 2 3 1 12 2 1 2 3 3 1 2 3 1 2 3 1 2 13 2 2 3 1 1 2 3 2 3 1 3 1 2 14 2 2 3 1 2 3 1 3 1 2 1 2 3 15 2 2 3 1 3 1 2 1 2 3 2 3 1 16 2 3 1 2 1 2 3 3 1 2 2 3 1 17 2 3 1 2 2 3 1 1 2 3 3 1 2 18 2 3 1 2 3 1 2 2 3 1 1 2 3 19 3 1 3 2 1 3 2 1 3 2 1 3 2 20 3 1 3 2 2 1 3 2 1 3 2 1 3 21 3 1 3 2 3 2 1 3 2 1 3 2 1 22 3 2 1 3 1 3 2 2 1 3 3 2 1 23 3 2 1 3 2 1 3 3 2 1 1 3 2 24 3 2 1 3 3 2 1 1 3 2 2 1 3 25 3 3 2 1 1 3 2 3 2 1 2 1 3 26 3 3 2 1 2 1 3 1 3 2 3 2 1 27 3 3 2 1 3 2 1 2 1 3 1 3 2

11..44)) AAssssiiggnnmmeenntt ooff tthhee ffaaccttoorr ss ttoo tthhee ccoolluummnnss In our DoE, we need five columns on the thirteen available. Nevertheless we must not assign a factor to a column by random, there are some rules. In fact some columns of the matrix can be a parameter but can also allow the study of an interaction so when possible, it is important not to assign a factor to a column of an important interaction. The linear graph of the matrix (Figure 2) gives a way to fill it:

Figure 1 : Taguchi Design ; L27 Orthgonal Array



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Finally, Figure 3 shows the matrix which will be used for the experiments: Parameter

Nb runs 1 D

2 B

3 DxB

5 E

6 DxE

8 A

9 DxA

11 C

1 1 1 1 1 1 1 1 1 2 1 1 1 2 2 2 2 2 3 1 1 1 3 3 3 3 3 4 1 2 2 1 1 2 2 3 5 1 2 2 2 2 3 3 1 6 1 2 2 3 3 1 1 2 7 1 3 3 1 1 3 3 2 8 1 3 3 2 2 1 1 3 9 1 3 3 3 3 2 2 1

10 2 1 2 1 2 1 2 1 11 2 1 2 2 3 2 3 2 12 2 1 2 3 1 3 1 3 13 2 2 3 1 2 2 3 3 14 2 2 3 2 3 3 1 1 15 2 2 3 3 1 1 2 2 16 2 3 1 1 2 3 1 2 17 2 3 1 2 3 1 2 3 18 2 3 1 3 1 2 3 1 19 3 1 3 1 3 1 3 1 20 3 1 3 2 1 2 1 2 21 3 1 3 3 2 3 2 3 22 3 2 1 1 3 2 1 3 23 3 2 1 2 1 3 2 1 24 3 2 1 3 2 1 3 2 25 3 3 2 1 3 3 2 2 26 3 3 2 2 1 1 3 3 27 3 3 2 3 2 2 1 1

A Force B Initial roughness C Vibration pulse time D Diamond size & carrier E Nb of operations/ Rotation speed

Figure 3 : Matrix of the DoE



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2. Experiments at Strecon I was at Strecon from the 4th to the 6th of December in order to carry out the Design of Experiment. For this purpose, the work there had to be divided in two distinct parts:

� The preparation of the DoE, that means to decide of a first step of polishing in order to get 3 different initial roughnesses for the DoE.

� The performing of the DoE.

22..11)) PPaarr tt 11:: PPrr eeppaarr aatt iioonn ooff tthhee eexxppeerr iimmeennttss We started with making trials to determine a first step of polishing. This step is compulsory to get three different roughnesses with some turned and ground disks (9 runs with turned disks with Ra1, 9 ground disks with Ra2 and 9 ground disks with Ra3; figure 1); we measured them, made some trials with two different diamond stones, different number of operations…

Figure 1 : Turned disk (Ra 1) It was also a good introduction before the DoE, to observe how they were working with this machine and how they were measuring the surfaces. At the end of the first day, the first step of polishing was decided (the stone used, figure 2, the number of operations and all the other parameters)

Figure 2: JOKE MF 600 (stone used)



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22..22)) PPaarr tt 22 :: FFllooww ooff wwoorr kk The second phase was the Design of Experiments. We hadn’t time to prepare all the disks; nevertheless, we decided to perform the Design of Experiments with the turned disks. The 3 levels for each parameter were decided: VALUE: 1 2 3 A Force (kg) 2 5 10

B Initial roughness (Ra; µm) 0.1 0.24 0.3

C Vibration (pulse/min) 0 1000 2000

D Diamond size & carrier (Figure 3) 15µm & hard wood 15µm & soft wood 9µm & soft wood

E Rotation Speed (Rpm) 180 400 700

Figure 3: Diamond paste 15µm (left) and soft carrier (right)

All the disks dealt with 6 bands (three on each side), and were marked in order not to be mixed up with what we did on every band. While I was there, we had time to make the 9 runs on the turned disks. Appendix IV shows the matrix of the DoE with all the values of the parameters. Figure 4 and 5 are pictures taken during the DoE on the turned disk: on figure 4 diamond paste is applied on the disk and on figure 5, polishing is performed.

Figure 4: Application of the diamond paste Figure 5: Design of Experiment run 5

carrier



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3. Analysis of the results After the experiments at Strecon, I could start measuring the first 9 areas polished. I measured it with the interferometer with 15 measurements at magnification 10x and could then analyse it with help of MountainsMap. I didn’t use any filter for my surfaces because after comparing the results with and without filters, the difference was not significant so I decided to use a form removal process with polynomial of order 2. For each surface I made a sheet showing the surface and the roughness values, like the one shown on figure 1 in order to make the analysis to be easier (all the results are presented in Appendix V)

Figure 1: Extract of the results obtained with MountainsMap

4. Results and discussion The results were not those expected at the beginning of this project because of technical problems: at the moment I was writing this report, we had some bad news from Strecon. They broke their measurement device so they couldn’t finish preparing the other disks and so, we couldn’t run the rest of the tests before the end of my project. Now, we just have four parameters because the nine polished surfaces done had the same initial roughness. So the problem is that we have 9 points of 27 (See figure 1). With the points we have, it seems that only the influence of the diamond size and carrier could be studied in more detail, since the remaining parameter (force, vibration pulse time and rotation speed) have fixed values in relation to each other.



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So we don’t have a standard Design of Experiments which means that the data cannot be studied with commonly used software. Instead, we tried to use Simca and Excel to get some information. Unfortunately we didn’t get evidences, even about the influence of the diamond grain size and carrier, but we can still say that the Ra value cannot really describe a level of polishing. Checking the surface aspect gave more information; in fact it is easy to distinguish different kind of surfaces. For example, some of them are scratched in many directions as shown in figure 2 (especially the three surfaces with a rotation speed of 180 Rpm, a force of 5 kg and 2000 vibrations per minute). Whereas the others reveal distinct grooves as we can see in figure 3.

180 400 700 Rotation speed (Rpm)

Force (kg)

10

5

2

Vibration pulse time (Vib/min)

0

1000

2000

Figure 1:Representation of the parameters studied in the Design of experiments performed

15µm & hard wood 15µm & soft wood 9µm & soft wood

Figure 2: Trial 13 (180 Rpm, 5 kg, 2000 vib/min, 1 5µm & soft wood)

Figure 3: Trial 5 (400 Rpm, 10 kg, 0 vib/min, 15 µm & hard wood)



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Figure 4: Disk 4 after DoE

From the previous pictures we could think that the surfaces like figure 2 are the best. When compared to the visual aspect, this was not the case; the shiniest one (Area 2 on figure 4) was actually a surface like the one shown in figure 3.

Figure 3 reveals a problem; are the marks on the surface from the turning process? The initial surface (after the first step of polishing) doesn’t show clearly these turning marks (figure 5) but when we compare the profiles from trial 5 and 13 with the profile from the turned surface (before the first step of polishing), it seems that it is in fact turning marks.

µ m

-2.5

-2

-1.5

-1

-0.5

0

0 .5

1

0 50 100 1 50 200 2 50 300 350 40 0 450 50 0 550 6 00 650 70 0 µm

Len gth = 7 17 µm Pt = 1 .14 µ m Sca le = 3 .5 µm

Trial 13 (180 Rpm, 5kg, 2000vib/min, 15µm&soft wood), disc 4 area 1 µm

-2.5

-2

-1 .5

-1

-0 .5

0

0.5

1

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 µm

Length = 706 µm P t = 1 .3 µm Sca le = 3 .5 µm

µm

-2.5

-2

-1.5

-1

-0.5

0

0 .5

1

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 µm

Length = 715 µm Pt = 1 .46 µm Scale = 3.5 µm

Trial 5 (400 Rpm, 10kg, 0 vib/min, 15µm&hard wood), like disc 4 area 2

Initial surface µm

-1 .5

-1

-0 .5

0

0 .5

1

1 .5

2

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 µm

Length = 848 µm P t = 3.1 µm Scale = 3 .5 µm

Turned surface

Figure 5: Comparison between the surfaces, turning marks

100 µm

100 µm

100 µm

100 µm

Area 1

Area 2

Area 3



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Depending on the surfaces, the turning marks are more or less detectable, and the distance between the valleys confirms the hypothesis that the marks from the turning process were not removed. Probably, the first grinding step was not long enough.

Moreover, the graphs on Excel or Simca couldn’t show evidences; but we could still find some parameters like the mean density of furrows which gave some results:

The two shiniest surfaces are those with the lowest mean density of furrows (green squares in figure 6) and also the lowest number of islands (see results in Appendix V).

500

550

600

650

700

750

800

850

900

0 2 4 6 8 10 12

Mea

n D

ensi

ty o

f F

urr

ow

s [c

m/c

m2]

D4A6 D4A5 D4A4D4A3 D4A2 D4A1

D3A6 D3A5 D3A4TURN (1 surface) Initial (1 surface)

Figure 6 : The mean density of furrows of the different areas

In fact, if we make a classification of the surfaces depending on their gloss (visual comparison of the surfaces), we can see more clearly the link between these parameters (see figure 7):



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Figure 7: Comparison between Number of Islands and Mean Density of Furrows with visual classification of the Gloss

On this graphs we can see the link between the gloss of the surface and the number of islands, where the classification are very close. It is less clear with the mean density of furrows but still we can see that three “groups” of surfaces are always present. These groups can also be seen on a plot representing the ratio Svk/Sk as we can see in figure 8:

D4A5

D3A5

D4A1

D3A6

D3A4

D4A2

D4A3

D4A6

D4A4

720

740

760

780

800

820

840

0,5 1,5

gloss

D3A5

D4A1

D3A6

D4A6

D4A4

D3A4

D4A2

D4A3

D4A5

0

1

2

3

4

5

6

7

8

9

10

0,5 1,5

number of islands

D4A5

D3A5

D4A1

D3A6

D3A4

D4A2

D4A3

D4A6D4A4

200

300

400

500

600

700

800

900

1000

0,5 1,5

D4A3D4A5 D3A6

D4A1

D4A2

D4A6D3A5

D3A4

D4A4

0

0,2

0,4

0,6

0,8

1

1,2

0 1 2 3 4 5 6 7 8 9 10

Svk

/Skl

Figure 8: Ratio Svk/Sk

Gloss Number of Islands Mean Density of Furrows



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Figure 10 shows an Excel analysis of these data, which confirms with numerical values these correlations between the discussed parameters and the gloss of the surface.

Mean density of furrows NoI Svk Spk Sk Svk/Sk Spk/Sk Spk/Svk

Mean density of furrows 1

Number of islands 0,64062 1

Mean volume of islands -0,81550 -0,775

Mean height of islands 0,55847 0,723

Mean surface of islands -0,71044 -0,931

Mean height / surface ratio 0,55191 0,9426

Svk -0,09277 0,2419 1 Spk 0,04367 0,6467 0,292 1

Sk 0,01810 0,6738 0,468 0,895 1 Svk/Sk 0,11534 -0,587 -0,245 -0,902 -0,95 1 Spk/Sk 0,17900 -0,116 -0,478 0,02 -0,42 0,3204 1

Spk/Svk 0,05339 0,5651 -0,034 0,944 0,777 -0,863 0,1737 1 Smmr 0,12398 0,4118 0,824 0,394 0,352 -0,147 0,0079 0,11244

Vvv (10 80 2) -0,01376 0,4694 0,923 0,554 0,749 -0,559 -0,549 0,26655 Sr2 0,14259 0,7168 0,221 0,965 0,935 -0,936 -0,112 0,9268 Std -0,26444 0,3841 0,246 0,793 0,663 -0,76 0,0559 0,75102

Isotropy 0,31193 0,2006 0,422 -0,014 -0,18 0,3382 0,416 -0,177 Diamond stone &

carrier -0,30520 -0,292 0,456 0,263 0,134 -0,073 0,1453 0,14562 speed -0,21392 0,1194 -0,477 0,442 0,341 -0,544 0,0695 0,62079

pressure -0,52813 -0,529 0,467 -0,329 -0,07 0,1566 -0,545 -0,4732 pulse 0,74723 0,3561 -0,047 -0,111 -0,32 0,4209 0,5543 -0,1235 Gloss 0,68367 0,9185 0,275 0,601 0,696 -0,587 -0,241 0,52376

Figure 10: Extract of the correlation table of the data

Finally, concerning the experimental part of the DoE, we can say that a high rotation speed has a bad influence because of the use of free abrasives. In fact, we noticed during the experiments that the diamond paste is thrown away while the disk is rotating (centrifugal force), for 700Rpm but even for 400Rpm.



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CCOONNCCLL UUSSII OONN OOFF TTHHEE PPRROOJJEECCTT According to the previous results, and at this stage of the analysis, we can say that:

� It is not possible to describe a polished surface only with a Ra value. � We need to perform all the experiments to make a DoE Analysis and to evaluate the

influence of each parameter. � The turning marks reveal that the first step of polishing is not good enough: We

thought we had removed the turning marks when measuring the initial surface with a stylus but the results showed us the contrary.

� A high rotation speed is a problem because of the moving of the diamond paste. � The shiniest surfaces were those with the turning marks which mean that on these

surfaces, we probably removed more material since we reached the marks from the turning process.

� The surface qualities we got during the tests with the machine seem, at the moment, to be very far from the surface qualities of the polishing standards.

FFUUTTUURREE My project couldn’t be finished on time so we can discuss how it should be organized in a future work on this project and what to focus on:

� As it was said in the conclusion, the most important thing is to achieve a complete Design of Experiment to finally have all the results.

� About the results we got, we couldn’t really see the turning marks on the initial

surfaces before the DoE, even if they were measured. Nevertheless it is important to know when one step of polishing is over, i.e. when the marks from the previous process are removed.

� This project highlighted a point which could be a problem for the machine: the

repeatability. In fact, after measuring the surfaces after the first polishing step, we could see significant differences between the Ra-values of some disks, so it must be interesting to know if it is a problem of the machine or of the accuracy of the measurement devices or both.



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PPEERRSSOONNAALL CCOONNCCLL UUSSII OONN During these five months of work in Halmstad, I learned a lot on multi-aspect: the work, the language, the Swedish culture and the culture of many European countries.

� First, I could improve considerably my knowledge in a subject I didn’t know very well; the study of surfaces, how to measure a surface, I discovered other measurement devices, how to treat the measurements. In this purpose, I had the opportunity to use softwares like MountainsMap to analyse the measurements and also MATLAB, and Simca for treatment of data. Then, my subject was about polishing of steel. The literature study allowed me to prepare and to know the subject before starting working on this project and to acquire knowledge about what kind of polishing processes exist and more exactly what mechanical polishing is, since I didn’t really know in details what this technique was. I also read a lot about the Design of Experiments, which is very useful in the industry and so I could learn how to carry out this kind of experiments and how important it is to prepare carefully the DoE, to be there for the experiments… Moreover, I could see that working for companies which are not located at the same place is really difficult, since it means to communicate by e-mails or by phone and it makes the project go slowly. I also discovered the work in a research lab which is very different from the work in a company, and it is for me the best way to know where I want to be in my future job. I liked working in the research lab since you are not really in a company but you still have a contact with industrial world.

� For this first placement abroad, I had to work always in English, so it was a great experience since it is a constant work to listen and understand people and also to share my ideas in another language even if sometimes it can be difficult. And everyday I was speaking English: at work, in the street, and at home since I was the only French living with 13 other people from Netherlands, Germany, Poland, Austria, Lithuania, Thailand.

� Finally, this stay abroad was a fantastic human experience: I met people from many different countries, co-workers and students. The student house where I lived allowed me to meet a lot of people and to share our culture every day. We discovered the Swedish culture together and also Scandinavian countries doing trips in the cities around, in Sweden, Norway, and Denmark. I think this experience made me be more open minded on the world and people who don’t have the same way of life and to see that there are a lot of differences even between European countries, thing that I wasn’t really aware of before. To conclude, it was a special experience, unforgettable, and very enriching on many points.



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RREEFFEERREENNCCEESS

� Different techniques of polishing: [1] Laser polishing of parts built up by selective laser sintering (2007) International journal of machine tools & Manufacturer 47 A. Lamikiz, J.A. Sanchéz, L.N. López de Lacalle, J.L. Arana [2] Mechanics, Mechanism, and modeling of the chemical mechanical process Jiun-Yu Lai (Massachussets institute of technology) [3] Material removal mechanism in Lapping and Polishing C.J Evans, E. Paul, D,Dornfekd, D.A. Lucca, G. Byrne, M.tricard, F.Klocke, O.Dambon, and B.A. Mullany [4] Magnetic polishing of three dimensional die and mold surfaces (2007) International Journal of Advanced Manufacturing technology Jeong-du Kim & Ill-hwan Noh [5] Basic studies for the electro polishing facility at Desy CARE Conf 05-029-SRF N. Steinhau-Kühl; R. Bandelmann, K. Escherich, D. Keese, M. Leenen, L. Lilje, A. Matheisen, H. Morales, P. Schmüser, E. Schulz, M. Seidel, J. Tiessen [6] VESTA Sterile Technology GEA process equipment division, Tuchenhagen [7] A new polishing method of metal mold with large-area electron beam irradiation (2007) Journal of Materials processing technology Y. Unoa, A. Okadaa, K. Uemurab, P. Raharjo , S. Sano , Z. Yuc, S. Mishima [8] A study on the mirror surface machining by using a micro-energy EDM and the electrophoretic deposition polishing (2007) International Journal of Advanced Manufacturing technology Biing Hwa Yan, Kun Ling Wu, Fuang Yuan Huang, Chun Chieh Hsu

� Polished surfaces: [9] Influence of the polishing process on the near-surface zone of hardened and unhardened steel (2005) Sciencedirect, volume 258 issues 11-12 F. Klocke, O. Dambon, G.G. Capudi Filho [10] The True Microstructure of Materials Materialographic Preparation from Sorby to the Present Kay Geels, Struers A/S, Copenhagen, Denmark [11] The Nature of Mechanically Polished Surfaces of Copper (1998) Elsevier science Inc. Materials characterization D. M. Turley and L. E. Samuels [12] Lapping and Polishing Basics Applications laboratory report 54, South Bay Technology



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� Automated polishing [13] Automated polishing of Die steel surfaces (2002) International Journal of Advanced Manufacturing technology vol 19, no. 4 J.P. Huissoon, F.Ismail, A.Jafari [14] Short papers: development of an automatic mold polishing system (2005) IEEE Transactions on automation science & engineering Vol 2 Ming J.Tsai, Jou-Lung Chang, and Jian-Feng Haung [15] Intelligently automated polishing for high quality surface formation of sculptured die (2002) Journal of Materials processing technology J.H. Ahn, M.C.Lee, H.D.Jeong, S.D.Kim, K.K.Cho

� Design of experiments: [16] Taguchi Techniques for quality Engineering_ Loss function, Orthogonal Experiments, Parameter and Tolerance Design Phillip J.Ross, McGraw-Hill Book Company; 279 pages



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AAPPPPEENNDDII XX

APPENDIX I: A few polishing methods.............................................................................. 36 APPENDIX II: Problems in mechanical polishing............................................................. 39 APPENDIX III Results of standards measurements (Zanola)...........................................40 APPENDIX IV: Matrix of the DoE.......................................................................................41 APPENDIX V: Results of the nine trials of the DoE...........................................................42



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APPENDIX I: A few polishing methods

1. Laser polishing [1] Laser polishing is usually employed for simple geometries. Nevertheless, complex geometry can also be polished, but with a five-axis machine and a correction of the focal position instantaneously. Laser polishing is based on the melting of a microscopic layer and a fast re-solidifying of the melted material. The main parameters which influence the final result are: the laser beam feed rate, laser power and the laser beam diameter → There is also Laser surface texturing which is one of the most recent processes using laser technology. It is a metal additive process. With this process, surfaces tend to have a bad quality.

2. Chemical Mechanical Polishing [2],[3]

Chemical Mechanical Polishing, or CMP, is an old wet slurry technology. During the CMP process, a wafer surface is polished for planarization using a slurry and a polishing pad. The abrasive particles in the slurry grind against the sample surface, loosening material. The chemicals in the slurry then etch and dissolve the material. This process is very common in the semi conductor industry, for the polishing of small components like integrated circuits.

3. Magnetic polishing [4] During magnetic polishing, the polishing pressure in the tool-workpiece interface is produced by the permanent magnet included inside the polishing tool. Two stages are necessary to get a good quality: - A first-stage polishing of initial rough surfaces which uses the abrasive wheel for material removal function. - A second-stage polishing, i.e., fine polishing, after the first rough polishing, which uses the magnetic brush for material removal function instead of abrasive wheel.

Picture: www.agc.co.jp



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4. Electropolishing [5],[6]

In basic terms, the object to be electropolished is immersed in an electrolyte (typically phosphoric and sulphuric acid) and subjected to a direct electrical current. The object is maintained anodic, with the cathodic connection being made to a nearby metal conductor. In electropolishing, the metal is removed ion by ion from the surface of the metal object being polished.

During electropolishing, the polarized surface film is subjected to the combined effects of gassing (oxygen), which occurs with electrochemical metal removal, saturation of the surface with dissolved metal and the agitation and temperature of the electrolyte. Electropolishing selectively removes microscopic high points or "peaks" faster than the rate of attack on the corresponding micro-depressions or "valleys."

5. Electron beam irradiation [7]

Electron beam irradiation is a technology using the phenomenon of explosive electron emission. At first, a magnetic field is generated by the solenoid coil mounted on the outer side of the chamber. At the moment when the magnetic field takes a maximum intensity, pulse voltage is loaded to a ring shape anode. In the chamber, the electrons start to move towards the anode. Simultaneously, the electrons move spirally because of the applied Lorentz forces. Next, argon atoms are ionized by the repetitious collision with electrons, which generates plasma near the anode. When the plasma intensity takes a maximum, pulse voltage is applied to the cathode. The electrons are accelerated by high electric field due to electric double layer formed near the cathode, and the explosive electron emission occurs. Then, EB with high energy density is irradiated to the workpiece surface. This process is a fast method, and also allows having a better corrosion resistance after irradiation.

Picture: www.delstar.com



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6. Electrical discharge machining [8]

Electrical discharge machining (EDM) is a thermal process that involves melting and vaporisation of the workpiece electrode. It is widely used in the aerospace, mould making and die casting industries for manufacturing plastic moulds, forging dies and die casting dies made from hardened tool steels. The EDM process uses electrical discharges to remove material from the workpiece. Each spark produces a temperature of between 10,000-20,000°C. Consequently, the workpiece is subjected to a heat affected zone (HAZ), the top layer, which consists of recast material. The thickness, composition and condition of this layer depend on the discharge energy and the set-up of the workpiece, tool electrode and dielectric fluid.



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APPENDIX II: Problems in mechanical polishing (Lucchini Sidermeccanica & Zanola) Major problems during the polishing may be found when an excessive polishing, called “Overpolishing” is carried out. Actually it may happen that the longer a surface is polished, the worst its conditions become. The “Overpolishing” is linked to two distinct phenomena that are called “orange peel” and “pitting”.

Figure 1: Roughness trend in comparison with polishing duration time

1) Orange peel This phenomenon results from the overcoming of the yield point in micro areas of an inhomogeneous surface. Depressions develop on the piece surface at level of softer micro-areas; this is commonly called “Orange peel”. The causes of this phenomenon can be:

- Excessive pressure performed during the polishing processing. - Irregular areas of residual austenite more sensitive to

permanent deformations than other tempered structure. - Chemical-structural inhomogeneity of the initial material -

2) Pitting The very small cavities that can be observed in a flat surface during the polishing phase commonly derive from inclusions that are removed from the surface during the polishing process. Generally the removed particles are sulphides or oxides, which, not only differ in hardness and stiffness from the metallic matrix surrounding them, but also are characterized by a middle/low adhesion to the metallic material. The main factors responsible of the forming of pitting are:

- polishing duration and pressure - steel pureness (especially for what concerns hard non metallic

inclusions) - the type of used polishing tool - the abrasive medium

The differences in hardness between matrix and non metallic inclusions are the main cause of pitting. During the polishing process, the matrix will be more rapidly removed than the hard non metallic particles (Figure 3). Gradually the polishing hits the hard particles until these ones come off the material which causes cavities.

OVERPOLISH

OVERPOLISHING

Figure 3: Inclusions’ behaviour during

polishing

Figure 2: Surface with Orange peel aspect



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APPENDIX III: Results of standards measurements (Zanola)

SZ13 polishing 3µm

SZ17 polishing 0,25µm

SZ15 polishing 1µm



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APPENDIX IV: Matrix of the DoE

1 2 3 5 6 8 9 11

Nb trials Disc band

D_Diamond paste

B_initial Ra DxB E_Rpm DxE

A_ force DxA

C_vibration pulse

1 5 4 15 hard 1 1 180 1 2 1 0 2 5 5 15 hard 1 1 400 2 5 2 1000 3 5 6 15 hard 1 1 700 3 10 3 2000 4 3 4 15 hard 2 2 180 1 5 2 2000 5 3 5 15 hard 2 2 400 2 10 3 0 6 3 6 15 hard 2 2 700 3 2 1 1000 7 7 4 15 hard 3 3 180 1 10 3 1000 8 7 5 15 hard 3 3 400 2 2 1 2000 9 7 6 15 hard 3 3 700 3 5 2 0 10 6 1 15 soft 1 2 180 2 2 2 0 11 6 2 15 soft 1 2 400 3 5 3 1000 12 6 3 15 soft 1 2 700 1 10 1 2000 13 4 1 15 soft 2 3 180 2 5 3 2000 14 4 2 15 soft 2 3 400 3 10 1 0 15 4 3 15 soft 2 3 700 1 2 2 1000 16 8 4 15 soft 3 1 180 2 10 1 1000 17 8 5 15 soft 3 1 400 3 2 2 2000 18 8 6 15 soft 3 1 700 1 5 3 0 19 6 4 9 soft 1 3 180 3 2 3 0 20 6 5 9 soft 1 3 400 1 5 1 1000 21 6 6 9 soft 1 3 700 2 10 2 2000 22 4 4 9 soft 2 1 180 3 5 1 2000 23 4 5 9 soft 2 1 400 1 10 2 0 24 4 6 9 soft 2 1 700 2 2 3 1000 25 8 4 9 soft 3 2 180 3 10 2 1000 26 8 5 9 soft 3 2 400 1 2 3 2000 27 8 6 9 soft 3 2 700 2 5 1 0

initial roughness: 1--> ground disks with 2 polishing steps 2--> turned disks 3--> ground disks with 1 polishing step

9 trials performed



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APPENDIX V: Results of the nine experiments



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OPTIMIZATION OF THE POLISHING PROCEDURE USING A ROBOT ASSISTED