2009 - 2011
PRODUCTIVITY IMPROVEMENT IN GRINDING SAPPHIRE WATCH
GLASSES THROUGH SCIENTIFIC PROCESS ANALYSIS AND
SUBSEQUENT PRODUCTION SYSTEM MODIFICATION OR REDESIGN
Ing. Pierre-Marie POCHON, Prof. Jacques GIOVANOLA
Subject of project
The objectives of this project are to improve productivity and technical performances for the grinding of watch glasses. These
objectives will be achieved by combining a fundamental investigation of the deformation and fracture mechanisms in single crystal
sapphire with a technological investigation of current grinding practices to establish processing maps relating process parameters
and process outcome. The current market position of the company will thus be strengthened and new market segments will open up
in the field of technical sapphire parts.
Fundamental study of Technological study and
Second line of investigation
deformation and fracture of formalization of the
single crystal sapphire manufacturing process
+ Development of improved
To investigate the feasibility of ultrasonically assisted
grinding of sapphire, a facility to perform a basic study
on this process was designed.
• CNC system, 3 Cartesian axes
Establishing the fracture behavior. Machining a specific radius with a
• UAG 20 [kHz]
Brinell indentation, 200 [µm] small grinding wheel.
A statistical experiment planning
approach serves to delineate the process
parameter space that will be
Relating the basic deformation to the
grinding response of sapphire allows us
to establish guidelines for process The workpiece will be excited by a 20 [kHz] sonotrode
optimization. with an amplitude of the harmonic vibrations between 2
and 20 [µm] peak-peak.
The combination of the processing parameters guaranteeing successful
machining in the shortest time and most economic way will serve to
establish the specification list for modification of the system.
Torque on the spindle, machining parameters (feed rate,
depth of cut, …) and surface quality are recorded.
In the last phase of the project we will develop and validate redesigns
of production to reach an acceptable rejection rate of 5%.