Precision Grinding for Rapid Manufacturing of Large Optics

摘要

Large scale nuclear fusion and astronomy scientific programmes have increased the demandfor large freeform mirrors and lenses. Thousands of one metre class, high qualityaspherical optical components are required within the next five to ten years. Current manufacturingprocess chains production time need to be reduced from hundred hours to tenhours.As part of a new process chain for making large optics, an efficient low damage precisiongrinding process has been proposed. This grinding process aims to shorten thesubsequent manufacturing operations. The BoXR grinding machine, built by CranfieldUniversity, provides a rapid and economic solution for grinding large off-axis asphericaland free-form optical components.This thesis reports the development of a precision grinding process for rapid manufacturingof large optics using this grinding mode. Grinding process targets were; formaccuracy of 1 m over 1 metre, surface roughness 150 nm (Ra) and subsurface damagebelow 5 m. Process time target aims to remove 1 mm thickness of material over a metrein ten hours.Grinding experiments were conducted on a 5 axes Edgetek high speed grinding machineand BoXR grinding machine. The surface characteristics obtained on optical materials(ULE, SiC and Zerodur) are investigated. Grinding machine influence on surfaceroughness, surface profile, subsurface damage, grinding forces and grinding power arediscussed.This precision grinding process was validated on large spherical parts, 400 mm ULE andSiC parts and a 1 m Zerodur hexagonal part. A process time of ten hours was achieved usingmaximum removal rate of 187.5 mm3/s on ULE and Zerodur and 112.5 mm3/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 lowsubsurface damage depth in glass and glass ceramic.