Diamond turning of half-meter scale metal mirror with on-machine surface measurement

Project Code: EPSRC_2023_13

Project Introduction

In the late 1668 Sir Isaac Newton built one of the earliest known functional reflecting telescopes out of metal alloy, the diameter of the primary mirror is about 33 mm. The recently launched James Webb Space Telescope (JWST)’s primary mirror consists of 18 hexagonal mirror segments with a diameter of 1.32 meters. The ever-increasing demand on the form accuracy and surface finish of large metal mirrors poses a great challenge on the fabrication process. 

This research project aims to explore and investigate the optimised fabrication process of half-meter scale ultra-precision mirrors with nanometer surface finish and sub-micrometer form accuracy using the diamond turning. The on-machine surface measurement is used to compensate form errors and evaluate surface finish. 

Project Details

Off-axis aspheric mirrors are widely used in optical engineering, such as Augmented Reality (AR), Virtual Reality (VR), laser and space applications. Diamond turning has been an efficient way to fabricate this kind of mirrors. However, with the increasing of mirror sizes, the machined form accuracy becomes more difficult to control. The machine kinematic errors will be amplified when the workpiece diameter increases. The larger surface amplitude will also contribute to motion errors of the feeding axes.  

With the advent of on-machine surface measurement (OMSM), the closed-loop machining of large metal mirror becomes possible. Because the OMSM can keep the datum and avoids the re-alignment error caused by the off-machine metrology process. Optical point-based probe is an ideal choice for OMSM due to its compact size, high measurement frequency and resilience to machine vibration. However, the data processing of OMSM data becomes a challenge due to the scanning path is a non-uniform spiral path rather than the uniform mesh grid. Conventional surface filtration and analysis algorithms can be applied directly. 

The objectives of this project include: 

• Measure machine kinematics errors. 
• Generate machining tool path with compensation of machine kinematics errors. 
• Develop optimized machining strategy for the large mirror. 
• Realize the closed-loop machining of the large mirror with OMSM. 
• Develop surface characterisation algorithms for OMSM data. 

The Ultra-precision Manufacturing Lab at the University of Huddersfield has state-of-the-art facilities to advance this exciting research, such as the world’s most advanced 5-axis ultra-precision diamond turning machine. The research can also enjoy the easy access to various metrology instruments, including surface profilometer, XCT, CMM, SEM, etc. 

Entry Requirements

1. Hold a high-grade qualification, at least the equivalent of a UK First or 2:1 class degree or MSc in engineering or related disciplines 
2. Be proficient in both written and spoken English, and possess excellent presentation and communication skills 
3. Willingness to conduct experiment on CNC, and programming. 

This call is open to UK Applicants only. 

Applicants should be of outstanding quality and exceptionally motivated.

The studentships are funded for 3 years subject to satisfactory annual performance and progression review, and will provide for tuition fees and a tax-free stipend paid monthly.

Please note that there are more projects than funded studentships available and therefore this is a competitive application process which will include an interview. Shortlisted candidates will be contacted for an interview in person or via Teams. After interview the most outstanding applicants will be offered a studentship.

Queries about the application process are welcome and should be directed by email to [Email Address Removed].

Informal enquiries about individual projects should be directed to the lead supervisor listed for each project.

Application details

• Complete the Expression of Interest Form 2023
• Provide copies of transcripts and certificates of all relevant academic and/or any professional qualifications.
• Provide references from two individuals

Completed forms, including all relevant documents should be submitted via-email to [Email Address Removed]

Please note: if you do not attach all the relevant documentation prior to the closing date of 15 June 2023 your application will not be considered.