Project Title:

Generation of Large Optical Surfaces Through CNC Thermally Assisted Ductile Regime

08.20-6881A
900589
Generation of Large Optical Surfaces Through CNC Thermally Assisted Ductile Regime

Abstract:

Grinding
Ductile Chip formation mechanisms, unlike brittle chip formation typically observed
in diamond grinding of ceramics, do not leave behind surface or subsurface microcracks.
Accordingly, machine processes involving polishing can be eliminated from fabrication
if material removal during grinding occurs through ductile chip formation. A ductile
chip formation is essentially an extrusion process where an instability is created
and a chip is formed. However, this method of grinding requires high specific energy
and can cause excessive machine vibrations, thus affecting the accuracy of surface
generation. The innovation in this proposal is to improve ductile grinding of brittle
materials by introducing a predetermined pattern of microcracks within the intended
depth of cut of the workpiece. This may be achieved by introducing a suitably pulsating
thermal field immediately ahead of the grinding zone. The modulii of the ceramic
material in the thermally induced micro-cracked layer will be considerably lower
than that of the virgin material and extruding the micro-cracked layer to produce
a ductile chip will consume significantly less specific energy.j  Such a process
will not require further polishing. Machine vibrations will be substantially reduced
and low specific energy will allow the use of SiC wheels which will make the grinding
process more economical.
This research could lead to an improved fabrication process for the generation of
large optical surfaces. Other commercial applications are foreseen in surface preparation
of ceramic components for elimination of surface flaws for parts that see considerable
stress at their surfaces.
optical, grinding, polishing, ductile flow, glass, ceramic, microcracks