Electrochemical Surface Structuring

Presented bySrinjoy Guha

M. Prod. E. 2nd year

Roll No: 001411702010

Guided byDr. Bijoy Bhattacharyya

Professor, Production Engineering Department

Jadavpur University

05/02/2023Production Engineering Department, Jadavpur University.

Foreward

This is a seminar presentation on “Electrochemical Surface Structuring.” It is a culmination of tasks undertaken by me during the six months’ tenure of 2nd semester of M. Prod. E. course in Jadavpur University. It has been my greatest endeavor to be vivid, lucid and illustrative as much as possible. The document consists of various theoretical explanations along with suitable screenshots to ensure all readers an easy and clear understanding. This has been an honest and sincere attempt from my side to reach a great perfection level within a stipulated and limited time frame. So I ask prior forgiveness from all careful, sensitive and beloved readers for all the unintentional errors those have been committed from my side. However suggestions and criticisms for further improvement of this seminar presentation is highly solicited.

Srinjoy Guha

05/02/2023Production Engineering Department, Jadavpur University.

What is Surface Structuring?

Surface Structuring is the process of manipulating the material surface with the objective of enhancing its tribological properties. This means that with the help of surface structuring the properties of surface can be enhanced. As for example with this we can enhance the lubrication properties of the surface so that application of lubricating fluids get its best functionality.

Along with this we all know that friction is most vital problem on all material surface which makes it life less than actually it should be. This friction can be reduced by proper application of surface structuring process.

That means with proper techniques of surface structuring we can enhance the lubricating properties of the surface, reduce friction, reduce wear. Hence a less wastage of material is noted!

05/02/2023Production Engineering Department, Jadavpur University.

Pros and Cons of Surface Structuring

Pros1. Helps in developing surface properties of material.

2. Frictional wear can be reduced to great extent.

3. Lubricants used get their best functionality.

4. Excellent surface finish of products for precision manufacturing processes.

Cons1. Initial cost of equipment is high.

2. It needs high level of expertise and hence only professional people are authenticated to perform it.

3. If the process isn’t well maintained, negative results may occur i.e. the surface properties can go down further.

05/02/2023Production Engineering Department, Jadavpur University.

Techniques of Surface Structuring

Conventional Techniques

Examples: Grinding, Honing, Lapping

Advantages:

1. Suitable to almost all types of materials

2. Easy equipment setup & low capital cost.

3. Economical process and low skilled labors can perform.

Disadvantages:

1. Low accuracy, noisy operation and poor finishing.

2. Low tool life and higher material wastage.

3. Cant be performed on small dimension components.

Non-Conventional Techniques

Examples: Electric Discharge Machining, Electrochemical Machining

Advantages:

1. Higher accuracy and surface finish and operation with low or no sound.

2. More tool life and lower wastage of material.

3. Fully automated; no chance of human error.

4. Suitable for small dimension components.

Disadvantages:

1. High capital cost.

2. Not suitable for all materials e.g. EDM & ECM requires electrically conductive materials.

3. Complex setup of equipment and experts required to perform.

05/02/2023

An overview of ECM and EMM ECM and EMM are the mostly used process for surface structuring purposes. Electrochemical machining (ECM) is a method of removing metal by an electrochemical process. It is normally used for mass production and is used for working extremely hard materials or materials that are difficult to machine using conventional methods.

When electrochemical machining process (ECM) is applied to micro machining range i.e. 1 micron to 999 micron, for manufacturing of ultra-precision shapes then this is termed as electrochemical micro machining or EMM process.

Rate of dissolution or material removal rate depends upon atomic weight of the material (a), valance (v) of ions produced, machining current (I), and the time (t) for which the current passes. Though the shape of electrodes remain unaltered like ECM. Material removed can be calculated as

MRR= Iaη/Fvρ

Where η= metal dissolution efficiency, ρ= density of material and F= Faraday’s constant= 96500 coulomb.

Applications of ECM and EMM related to surface structuring process:

1. Oxide Film Laser Lithography (OFLL)

2. Micro and Nanometer scaled surface structuring

3. Laser Electrochemical Micro Machining (LECMM)

05/02/2023Production Engineering Department, Jadavpur University.

New Development of EMM for Titanium Surface Structuring

1. Oxide film laser lithography: This process is similar to the ordinary lithography process except the fact that here layer by layer development is made with typical laser spot diameter used for Oxide Film Laser Lithography or OFLL.

2. EMM of multilevel structures: EMM using the photoresist technique is usually applied to single step etching of flat surfaces, using one sided or two sided attack of thin sheet samples. More recently the applications off EMM to the fabrication of two level structures have been initiated.

3. Scale dependent surface structuring: Control of surface topography on the micro and Nano scale is important in many applications (e.g. biomedical) and for that purpose this has been a fast growing technique.

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Scale dependent surface structuring Control of surface topography on the micrometer and the nanometer scale is of

importance in many applications. Electrochemical etching can for example be used for producing polished or grained surfaces of aluminum. The surface topography of biomedical implants plays an important role for cell attachment and differentiation. For example, the surfaces of dental implants made of titanium are subjected to physical and chemical treatments that produce finely textured surfaces in order to reduce the time of recovery for the patients.

Using an ethanol cooled sample holder and an optimized voltage function well defined regular surface structures on 1.5 cm diameter polished disks were made as illustrated by the SEM micrograph.

05/02/2023Production Engineering Department, Jadavpur University.

The sample surface outside the cavities is the original mechanically polished surface,whereas the inside of the cavities has an electro polished surface finish. Varying the cavitysize and distance one, therefore, also varies the ratio between electro polished andmechanically polished surfaces. The effect of these variables on cell response is beingtested at present. Surface topography at the nanometer scale is thought to be atleast as important for cell response as micrometer scale topography. For titanium,chemical etching in hot sulphuric and hydrochloric acid based electrolytes canproduce roughness on a sub micrometer scale. By superposing this type of nano-roughness with electrochemical micro structuring one can produce surfaces with controlled roughness at two different scales. An example of such a surface is given in the below figure.For titanium a similar pore formation mechanism has very recently been reported in presence of fluoride at very long anodisation times. Anodisation in sulphuric or phosphoric acid, leads to the formation of a compact film, which at sufficiently high voltageUndergoes dielectric breakdown leading to formation of a multitude of pores,the size & number of which depends on experimental conditions. The breakdownEvents manifest themselves by marked current fluctuations. As an illustration,the SEM picture of the below figure shows the surface of a porous anodic oxideFilm formed in 1 M H2SO4 by sweeping the voltage up to 125 V.

05/02/2023Production Engineering Department, Jadavpur University.

Interestingly, on mechanically polished samples the pores were quite regularly distributed, almost independent of the grain structure of the underlying substrate. On the other hand, pore formation on flat electro polished surfaces was in general less regular. By porous anodizing of electrochemically structured titanium surfaces containing 30 mm size cavities, scale resolved surface structuring on the micrometer and the nanometer scales could be achieved. An example of such a surface is shown in the below figure.

The ability to fabricate well-defined surface topographies will be useful for reaching a better understanding of the complicated interactions of living cells with implant materials.

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Conclusion In the present paper a brief overview has been given first of the basic principles governing the performance of ECM and further the discussion has been concentrated to EMM. Recent studies on EMM of titanium with and without photoresist discovered, which demonstrate the many possibilities of the process for biomedical and micromechanics applications. In particular, EMM can be used for scale resolved surface structuring on the micrometer and nanometer scales. Using oxide film laser lithography instead of conventional photoresist technique, the usefulness of EMM can be extended to non-planar surfaces and to the machining of multilevel structures for device fabrication. These developments together with a better theoretical understanding of the critical electrochemical parameters are expected to eventually open new fields of application for EMM. Future work should be aimed at finding ways to accelerate the different steps involved in resist-free EMM in order to improve the economic attractiveness of the process. Another possible development could be to use other means of oxide sensitization such as electron or ion beams, which would permit to extend OFLL to machining of nano size features. The techniques described here for titanium can probably be extended to other valve metals such as tantalum or niobium, although the specifics of oxide sensitization may require further study and optimization of the interaction of laser radiation with oxide films.

05/02/2023Production Engineering Department, Jadavpur University.

References

1. “Advancement in Electrochemical Micro Machining” by Dr. B. Bhattacharyya, J. Munda, M. Malapati.

2. “Electrochemical micromachining, polishing and surface structuring of metals: fundamental aspects and new developments” by D. Landolt, F. Chauvy, O. Zinger.

3. “Electrochemical Micro Machining” by Todkar Mahesh.

05/02/2023Production Engineering Department, Jadavpur University.

THANK YOU