G. Dewith et N. Sweegers, THE EFFECT OF EROSIONAL WEAR ON STRENGTH AND RESIDUAL-STRESS DURING SHAPING OF CERAMIC MULTILAYER CAPACITORS, Wear, 188(1-2), 1995, pp. 142-149
Shaping of ceramic multilayer capacitors (CMCs) is a prerequisite for
the application of end terminations. This shaping is frequently done b
y erosional wear in a tumbling process. In this study the tumbling tim
e, tumbling speed and loaded volume of the tumbling bottle were varied
to determine the effect on the shape parameters. A power law relation
ship is observed between the roughness, corner radius and weight vs. t
ime while the overall level depends sensitively on tumbling speed and
loaded volume. The tumbling process, however, also affects strength. I
n the first stage of the tumbling process severe damage is introduced
on the surface of the CMC which decreases the strength considerably. C
ompressive residual stress and crack length reduction, both induced du
ring the tumbling operation, are responsible for an important strength
increment in a later stage of the process. The optimum process parame
ters therefore should be chosen considering shape and strength. Small
differences in the loaded volume of the tumbling bottle appear to affe
ct the final strength and shaping considerably. The residual stress in
troduced during the tumbling process was determined by the sin(2) psi
method and indentation techniques. Good agreement between both methods
can be obtained only after taking into account all stress components
in the sin(2) psi, method. After sintering a compressive residual stre
ss of 170 MPa is present in the CMCs. For the tumbled CMCs the amount
of residual stress increases up to about 250 MPa. Experiments with dum
my CMCs, that is identically processed but without metal electrodes, s
how that the residual stress after sintering is an overall stress effe
ct in which the electrodes have an important contribution, The stress
due to tumbling is highly concentrated on the surface, and is not affe
cted by the electrodes.