dc.description.abstract |
Large scale nuclear fusion and astronomy scientific programmes have increased the demand
for large freeform mirrors and lenses. Thousands of one metre class, high quality
aspherical optical components are required within the next five to ten years. Current manufacturing
process chains production time need to be reduced from hundred hours to ten
hours.
As part of a new process chain for making large optics, an efficient low damage precision
grinding process has been proposed. This grinding process aims to shorten the
subsequent manufacturing operations. The BoX
R
grinding machine, built by Cranfield
University, provides a rapid and economic solution for grinding large off-axis aspherical
and free-form optical components.
This thesis reports the development of a precision grinding process for rapid manufacturing
of large optics using this grinding mode. Grinding process targets were; form
accuracy of 1 m over 1 metre, surface roughness 150 nm (Ra) and subsurface damage
below 5 m. Process time target aims to remove 1 mm thickness of material over a metre
in ten hours.
Grinding experiments were conducted on a 5 axes Edgetek high speed grinding machine
and BoX
R
grinding machine. The surface characteristics obtained on optical materials
(ULE, SiC and Zerodur) are investigated. Grinding machine influence on surface
roughness, surface profile, subsurface damage, grinding forces and grinding power are
discussed.
This precision grinding process was validated on large spherical parts, 400 mm ULE and
SiC parts and a 1 m Zerodur hexagonal part. A process time of ten hours was achieved using
maximum removal rate of 187.5 mm
3
/s on ULE and Zerodur and 112.5 mm
3
/s on SiC.
The subsurface damage distribution is shown to be "process" related and "machine dynamics"
related. The research proves that a stiffer grinding machine, BoX, induces low
subsurface damage depth in glass and glass ceramic. |
en_UK |