Under the skin of polishing - from nano to macro

Lead Research Organisation: University of Huddersfield
Department Name: Sch of Computing and Engineering

Abstract

This proposal brings together experts in complementary areas of physics, chemistry and engineering, to explore new science with potentially high practical impact.

Processing glass and similar materials to precise, polished surfaces is the "hidden gem" behind many products and services we take for granted - both in precise control of the distribution of light (e.g. anti-glare headlamps), or to focus light in imaging. From medical X-ray cameras to satellite optics, precise, smooth surfaces are required, with surface errors but small fractions of a micron (maybe 1/1000 the width of a human hair), with roughness down to a few atoms. Also, highly localised defects can scatter light, reducing contrast, or lead to component failure in high-power laser applications.

Polishing 'rubs' surfaces to remove damage from prior hard-grinding, and then controls surface-contours to meet design requirements. Historically, these steps were performed by highly-skilled craftspeople, who are in ever-shorter supply as they retire. Modern CNC machines now take much of the drudgery out, but even so, multiple polish/measure cycles are needed to reach refined levels of quality. The basic reason is that, after some 400 years of optical manufacture, the underlying 'rubbing' processes are still far from perfectly understood.

A practical setup typically deploys some kind of rotating tool, fed with a liquid slurry containing a fine abrasive powder. The tool moves over a glass surface, often with complex contours. Details of fluid-flow at the microscopic level between tool and glass are complex, and control local interactions of individual abrasive particles with the glass. Then, at the atomic ('nano') scale, chemical-attack, plastic-flow and brittle-fracture perform a complex 'dance', controlling how material is removed.

Prior work at various institutions has tended to focus on fluid flow OR nano-scale removal, representing distinct disciplines. But, modelling fluid-flow alone (computational fluid dynamics) omits chemistry and fracture-mechanics. Conversely, nano-scale molecular dynamics omits important fluid-flow issues. What nobody has done before, as we propose, is to combine these distinct approaches, supported by real-time process-monitoring data, and high-performance computing. Then CFD can provide molecular dynamics with predicted particle-trajectories, and particles in CFD can be treated as chemically-reactive rather than inert. The models can then by brought together in a unified large-scale and predictive macro model of removal-processes. Often, scientific breakthroughs arise at the INTERFACES between disciplines - precisely where this proposal focusses.

This model will be further developed through polishing trials of complete surfaces, drawing on real-time process-data to predict removal, and post-process measurement of what material has been removed where, plus any defects. This promises to reveal how a surface progresses in real-time, when it is smothered with slurry and invisible to direct inspection. Processes can then be tuned 'on the fly' to keep removal on-target, and improve accuracy of the result. Our aim is then to reduce the number of process cycles required, and give insight into why defects arise and how to control them.

In implementing the above, the mathematical and computer models developed at nano, micro and macro scales will describe fundamental aspects of molecules and fluids. This will be generally applicable, including different materials and abrasives. Another important application arises where the methods could be transformative - processes underlying materials wearing in mechanical systems (bearings, slide-ways, human joint-implants etc). So, what starts out as fundamental research into "intentional wear" in processes such as polishing, promises to have a profoundly significant impact on our understanding and control of "incidental wear" in things that rub - and wear-out - in everyday life!

Publications

10 25 50
 
Description Capital investment in an Instrument to Measure Particle Size Distribution (PSD)
Amount £34,954 (GBP)
Funding ID ST/W005425/1 
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 03/2022 
End 06/2022
 
Description Capital investment in equipment for measuring complex objects
Amount £101,715 (GBP)
Funding ID ST/X004945/1 
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 11/2022 
End 03/2023
 
Description IAC collaboration
Amount € 14,458 (EUR)
Funding ID AAM003825 
Organisation Institute of Astrophysics of the Canary Islands 
Sector Academic/University
Country Spain
Start 08/2022 
End 11/2022
 
Description Under the skin of polishing - from nano to macro
Amount £522,021 (GBP)
Funding ID EP/V029304/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 07/2021 
End 12/2023
 
Title Bespoke six-axis force-measuring fixture 
Description This is a custom-designed unit to measure the absolute forces and torques, from DC to circa 200 Hz frequency range, in CNC polishing and similar processes. It was designed in our laboratory as a collaboration with an academic visitor from the Fine Optical Engineering Research Center, Chengdu. It was then manufactured by that Institute and delivered to us for assessment and calibration. That work is currently in progress, in collaboration with the University of Agder, Norway. They are using a machine learning rather than analytical technique. 
Type Of Material Improvements to research infrastructure 
Year Produced 2022 
Provided To Others? Yes  
Impact It is too early for impact, as the unit is currently in the commissioning phase, and will require calibration before final use. It will provide unique, real-time, process data for basic research in the underlying mechanisms of material removal, and machine learning algorithms to improve process-convergence. 
 
Title Deflectometry for surface-metrology 
Description Construction in our laboratory of a bespoke optical deflectometry test system, for measuring surface forms of regular and complex optical surfaces. Such metrology data essential for closing the process-loop in optical polishing, and relating the onset of surface-artefacts to measurable in-process data acquired. Such diagnostic information is vital to developing an understanding of the chemical/mechanical removal mechanism is at the nano and micro scale. The work includes an infrared equivalent of the above, for measuring rough surfaces (e.g. after grinding and polishing) when they are not capable of forming an optical image. 
Type Of Material Improvements to research infrastructure 
Year Produced 2023 
Provided To Others? Yes  
Impact This has led to a a collaboration with the Institute of Astronomy, Canary Islands (IAC), under which IAC provided the principal hardware free of charge for our group to develop the optical and IR deflectometry tests. At the end of the project, a version of the test will be supplied to IAC, and another retained in our laboratory. IAC has arranged for two of their staff to spend several months in our laboratory from March 2023. Working with our staff, they will use our optical manufacturing machines to produce prototype lenses for a new astronomical spectrograph for a large telescope. These lenses contain surfaces that are "free forms", which are difficult to measure. The defectometry test is the measurement method of choice for this application. 
 
Title High-speed spindle 
Description Our collaborator Zeeko Ltd has provided a high-speed (up to 35,000RPM) grinding spindle, which we have adapted to be carried by one of our industrial robots. 
Type Of Material Improvements to research infrastructure 
Year Produced 2022 
Provided To Others? No  
Impact The high-speed is required for effective use of the compliant Shape Adaptive Grinding tools, which conform to complex surface-contours, and deliver low levels of sub-surface-damage. This gives the optimum input conditions for polishing trials. Current status is that we are optimising the software configuration of the robot to minimise tracking errors as it traverses a complex part. This facility is also required for an STFC project in polishing moulds and dies, and human joint and cranial implants. Cranial samples have just been delivered us. 
 
Title Slurry Management data-logging system 
Description Optical polishing is a process that proceeds blind - there is no way to measure the surface whilst it is being processed, because it is completely obscured by abrasive slurry. In order to understand fundamental processes at work in removing material on a piece of glass undergoing optical polishing, more indirect methods are required; specifically accumulation of real-time process-data. This data comprises forces, torques and, in the context of this record, properties of the abrasive slurry being used. We have therefore taken a commercial recirculating slurry management tank and system, and added real-time sensor technologies and data-lodging hardware/software to record slurry temperature, pH and particle size distribution every few seconds. 
Type Of Material Improvements to research infrastructure 
Year Produced 2023 
Provided To Others? Yes  
Impact This is work in progress, but within the period of the EPSRC project, we are optimistic the real-time data-modelling will provide meaningful results underpinning the CFD and MD modelling by our collaborators on the Huddersfield-campus, and LJMU, respectively. 
 
Title Data for polishing and associated processes 
Description Data on polishing, grolishing and metrology results for a wide range of removal technologies, and operating parameters, including deployment on CNC polishing machines and robots, and using both free and bound abrasives. 
Type Of Material Database/Collection of data 
Year Produced 2022 
Provided To Others? No  
Impact This data is the bedrock on which we are researching advanced ultra-precision surface techniques, and methods of process automation. It is also being used in processing real components, for example work on the lenses the Institute of Stormy Canary Islands, will start March 2023 
 
Description Mechanical design in support of the project. Development of machine-learning algorithms for process-optimisation. 
Organisation University of Agder
Country Norway 
Sector Academic/University 
PI Contribution Computer aided design of a mechanical kinematic interface between our bespoke force-table and the CNC polishing machine.
Collaborator Contribution Negotiations with Norwegian industry for the manufacture of the interface, leading to its procurement in Norway.
Impact The mechanical interface is being subcontracted for manufacture, funded by the Norwegian University, to be made in Norway and delivered to our laboratory in the UK. The work on machine-learning algorithms is in its early stages of discussion, but is planned to get underway over the next year.
Start Year 2021
 
Description Metrology software development 
Organisation Shanghai Institute of Optics and Fine Mechanics
Country China 
Sector Public 
PI Contribution We have provided data to the collaboration, references to very relevant papers in the literature, and frequent MS-Teams progress meetings.
Collaborator Contribution The partner has written software to process the data from a deflectometry optical test setup, for us to use in our lab in support of the project.
Impact Data analysis software
Start Year 2021
 
Description Molecular dynamics modelling 
Organisation Liverpool John Moores University
Country United Kingdom 
Sector Academic/University 
PI Contribution Our role in the collaboration is to provide real-time process monitoring data, and post process metrology data.
Collaborator Contribution Liverpool John Moores University is providing the molecular dynamics modelling effort in support of the Under The Skin Of Polishing project
Impact The acquisition of the data required for the molecular dynamics modelling has been significantly delayed due to COVID and partial lab closure.
Start Year 2021
 
Description Supercomputer access and technical support 
Organisation Science and Technologies Facilities Council (STFC)
Department Hartree Centre
Country United Kingdom 
Sector Academic/University 
PI Contribution Our role is to provide in-process monitoring data. The acquisition of this data has been delayed due to very limited access to our laboratory due to COVID
Collaborator Contribution Hartree will provide supercomputer resource and technical assistance to the project, but this has not started yet.
Impact This collaboration is at the early stages of development, as the contribution from STFC Hartree requires digital process-data. The acquisition of that data has been delayed due to the very limited access to our laboratory due to COVID.
Start Year 2021
 
Title Software for sensor data-acquisition 
Description Real-time data-acquisition software for bespoke multiple process sensor-system 
Type Of Technology Systems, Materials & Instrumental Engineering 
Year Produced 2022 
Impact Enabling technology essential to underpin data-collection essential for the modelling activities of the partners. 
 
Description Invited keynote presentation 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited keynote presentation to Euspen conference, "Mind the gap! What stands between optical manufacture and its automation?"
Year(s) Of Engagement Activity 2022
 
Description Invited talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact An invited talk tailored for this audience, delivered to the European Optical Society Advanced Manufacturing (EOSAM) conference.

Title, 'A precise (or is it accurate?) introduction to:- Accuracy and Precision'

Established a UK/European consortium to apply for Eureka funding to develop advanced optical manufacturing for fusion-energy
Year(s) Of Engagement Activity 2021
 
Description Invited talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Invited talk to a general audience of students and faculty of the University of Shanghai for Science and Technology. Title, 'A precise (or is it accurate?) introduction to:- Accuracy and Precision'

A research collaboration is at the final stage of negotiation
Year(s) Of Engagement Activity 2021
 
Description Invited talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Invited talk of a general nature presented to the University of Shanghai for Science Technology

Title, 'A career in optics research - a personal perspective'
Year(s) Of Engagement Activity 2021
 
Description Invited talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Undergraduate students
Results and Impact Lecture delivered to the students of the Harbin Institute of Technology

Content was of a general nature, and related to the history, current practice in future of astronomical telescopes.
Year(s) Of Engagement Activity 2022
 
Description Lecture course 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Undergraduate students
Results and Impact Course of eight on-line lectures delivered to students of the Harbin Of Technology

Topic - optical fabrication techniques
Year(s) Of Engagement Activity 2022