Functional Surfaces via Electrical Discharge Methods

Lead Research Organisation: University of Nottingham
Department Name: Faculty of Engineering

Abstract

Electrical discharge machining (EDM) is an excellent process of realising complex features in tough materials. EDM makes use of repeated electrical discharges to remove material from a workpiece. Each discharge constitutes a plasma channel which results in removal of a small amount of material from both the EDM machine's electrode ('the tool') and the work piece. Machine parameters and spark conditions are optimised such that under typical conditions more material is removed from the work piece when compared to the tool per discharge. When the plasma arc strikes a localised region is rapidly heated and liberated from the bulk. This 'debris' is then normally evacuated from the spark gap by the so called flushing mechanism. The spark gap is in an incredibly tempestuous place and hence very difficult to understand. However, knowledge of this behaviour is crucial to advancing our understanding of ED techniques for industrial applications.

It has been shown that under the correct physical conditions in the spark gap the debris created by these discharges can be used to apply a coating and build low aspect ratio surface structures. This presents an interesting opportunity to high value manufacturers who are often tasked with machining precision features and then applying precision coatings or, perhaps, repairing worn regions in high value components. However, the physics of this process is not yet fully understood and there remains a requirement to advance this technology significantly from fundamental principles.

This project will explore the technology from a new, multidisciplinary perspective which will incorporate both experimental and modelling activities. The investigators will present a solid understanding of the debris dynamics electrical discharge coating techniques to the community and will use this new knowledge to create complex multi-layer coatings which will have applications in the aerospace, biomedical and tool making industries. Companies operating in these industries thrive on the technological advantage their products possess over competitors. For example all of these products require advanced tribological properties amongst other complex surface characteristics. There is an array of surface modification techniques available to manufactures such as laser cladding, cold/plasma spray, PVD amongst others which have developed rapidly in the last 20 years. However, none of these have been directly integrated into a process which can also remove material. The rapid adoption of all of these coating techniques has been borne out of a solid understanding of the process mechanics, materials science and optimisation for application. In all of the high value applications for these coating techniques surface integrity is critical since failures which occur as a result of corrosion, fatigue or high temperature effects emanate from the surface or near surface. Enhancing surface integrity is the core rationale for surface treatment although coatings are also often applied for aesthetic purposes also.

EDM itself has developed significantly in recent years with modern machine makers claiming to have developed processes capable of the so called 'near zero' recast layer. This is in response to the extensive studies which have been undertaken on the surface damage that results from EDM and is known to induce deleterious tensile stresses. However, no solid solution to this has been developed which means the confidence in EDM surface layers is currently low. However, the application of consolidated coatings may be able to tackle this problem and will be investigated in this project.

The ability to remove material and apply a coating within the same process presents significant advantages. Therefore the use of ED coating methods has great potential to enhance high value manufacturing in terms of enhanced product performance but also through process efficiency savings.

Planned Impact

The impact of this project will be felt in the development of new tools, coatings and coating methodologies for the aerospace, biomedical and tool making industries. Gains made in the technologies which underpin these industries will enhance the competitiveness of companies who adopt these technologies at the earliest stage possible. Since this research has a broad reach the technology also has potential applications in a wider variety of industrial sectors, though specific requirements for surfaces within each sector will differ. Improved methods of surface finishing and functionalisation are sought by a range of industries, which provides a market pull and opportunities for commercialisation.

Industrial developments in this area have a direct societal benefit. Through the development of superior products the finite lifetime of key engineering products can be extended. By augmenting the lifetime of aero-engine components, for example, less planned maintenance is required making the cost of air travel lower. Furthermore, any technique which allows aero-engines to operate at high temperatures enhances efficiency and hence air transport is also greener while being cheaper. It is expected that by 2030 the global fleet of passenger planes will more than double from current figures to 27,800 (Airbus, 2011). Much of this demand will be based in developing nations such as Brazil, Russia, India and China (BRIC). Given the rapid increase in demand for air transport, technologies which enhance the sustainability of this growth will be key.

With respect to bio-implant applications there is also significant opportunity to affect a change. In the UK alone there are approximately 10,000 artificial metal-on-metal surface replacement hip implants in service (Arthritis Research UK, 2013). These are monitored through life and often subject to replacement/revision due to wear. Enhanced coatings techniques have the potential to ameliorate this growing problem which is set to affect more people mean population age and life expectancy increase. Similarly to changes in the aerospace market so too will new opportunities for makers of biotech goods emerge in the BRIC nations.

The tooling industry within the UK is hugely important to the domestic economy. Currently valued at £1.19 Billion (IBISworld industry report, 2013) the industry hosts many SMEs who are significant employers and wealth creators. They will commonly be engaged in supplying tools to larger manufacturing companies. To maintain the competitiveness of the industry improved tooling is continually developed. This generally relates to increasing the time that tools can stay in service or the ability to repair them when they become worn. Both of these activities reduce material consumption and hence the environmental burden of the industry.

Recently the UK Knowledge Transfer Network (KTN) established the Surface Engineering and Advanced Coatings Special Interest Group (SEAC SIG). Demonstrating that this technology area is critical to the core manufacturing base within the UK with key players such as Rolls-Royce, Curtiss Wright and Bodycote all boasting a significant presence in the UK. European Union estimates suggest that the UK employs 143,500 in forging, metal coating and general mechanical engineering (NACE Rev 1.1, 2002). Therefore the value of technologies associated with surface improvement to the UK is significant.

A multidisciplinary approach has been taken to address the challenges associated with this project. In doing so, contributions to the knowledge base associated with EDM, manufacturing process modelling and more generically manufacturing technology will made. The competencies which will make this project a success will allow knowledge contributions to be made to these fields and advance the understanding the scientific and industrial communities currently hold.

Publications

10 25 50
publication icon
Algodi S (2018) Modelling of single spark interactions during electrical discharge coating in Journal of Materials Processing Technology

publication icon
Murray J (2016) Physical and electrical characteristics of EDM debris in Journal of Materials Processing Technology

publication icon
Murray J (2017) Formation mechanism of electrical discharge TiC-Fe composite coatings in Journal of Materials Processing Technology

publication icon
Algodi S (2015) Characterisation of TiC layers deposited using an electrical discharge coating process in Journal of Physics: Conference Series

publication icon
Murray J (2018) Defect-free TiC/Si multi-layer electrical discharge coatings in Materials & Design

publication icon
Al-Hamdani K (2020) Controlling ceramic-reinforcement distribution in laser cladding of MMCs in Surface and Coatings Technology

 
Description [2015] As a collaborative team we have developed new coating families for ED Coating (WC and zirconia based). This has been accompanied by fundamental insight of the process through modelling. A test bed has also be developed at Edinburgh to underpin more applied areas at Nottingham. Due to initial hardware issues progress was slow in the project's early stages but these issues have now been overcome.

[2016] Our work has been closely aligned to the process of ED coating which makes use of our Mitsubishi apparatus provided as part of this project. The team has published one paper in the last year and has 4 fourth coming publications. These center on the full characterization of these coatings developing the utility of the tool in question. The project is progressing well and meeting deadlines, however, an extension has been requested from EPSRC which allow the final elements of the impact plan to be executed.

[2018] We have now develped an entirely new coating methos which will lead to a patent with the industrial sponsor.

[2020] This is now the subject of ongoing directly funded work with Mitsubishi electric
Exploitation Route [2015] Plans are now in place to submit a joint publication (Jan 15th). The investigators (including CI J Sun) have identified opportunities for future collaboration including a need to follow on within this research theme beyond project end.

[2016] The above mentioned was accepted for publication (10.1016/j.jmatprotec.2015.09.019) and is the prelude to a significant number of forthcoming publications relating to characterising the performance of new coatings produced by the team. Results are to be presented at the ISEM XVIII conference to be held in Tokyo 2016. The project PI has been awarded a special focus talk in relation to ongoing work which is taking place in his lab.
Sectors Aerospace, Defence and Marine,Energy,Environment,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology,Transport

 
Description [2015] This project is supported by Mitsubishi electric. Researchers at Nottingham are sharing output data with collaborators in Japan and working in coordination with co-funded partners at Edinburgh. We recently met as a team to discuss our first publication (CIRP annals) and discuss progress and next steps. New insight to the edm process has been developed alongside the use of new materials for ED coating. [2016] The first of four publications has been accepted for this [2017] Mitsubishi Electric have recently agreed to continue fnding work in this area at Nottingham. This program of work will run until 2021 and will begin with a year1 budget of 105K 2018/19 Nuhaize Ahmed (PhD student) is now seconded to Mitsubishi. In addtion funding has been agreed to take this activity thorugh to 2022. The student returned from Mitsubishi and has continued work in this area at Nottingham.
First Year Of Impact 2019
Sector Aerospace, Defence and Marine,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology
Impact Types Economic

 
Description Mitsubishi direct funding
Amount £165,000 (GBP)
Organisation Mitsubishi Electric 
Sector Private
Country Japan
Start 02/2020 
End 02/2022
 
Description Rolls-royce direct funding
Amount £165,000 (GBP)
Funding ID none 
Organisation Rolls Royce Group Plc 
Sector Private
Country United Kingdom
Start 01/2018 
 
Description New project with Mitsubishi 
Organisation Mitsubishi Electric
Country Japan 
Sector Private 
PI Contribution Mitsubishi electric directly funded research project to understanding coating technologies.
Collaborator Contribution Fundamental research activity.
Impact see publications.Direct industrial reports.
Start Year 2017