Page 268 - Fiber Fracture

FRACTURE OF SUPERFINE METALLIC WIRES 25 1

-60 ~ 140

Fig. IO. Distributions of the hydrostatic pressure during wiredrawing with no inclusion (a) and with different
ratios of inclusion diameter to wire diameter (b,c).

Increase in the Drawing Stress Due to Inclusions

When the drawing stress during wiredrawing is high, wire breakage occurs easily.
Fig. 11 shows drawing stress as an inclusion passes through the die, as determined using
FEA. The drawing conditions were identical to those stated above, and the inclusion
sizes were assumed to be DilD, = 0.0,0.4,0.6 and 0.8. When Di/D, = 0.8, the drawing
stress was approximately 2.3 times that in the wire without an inclusion (Di/D, = 0.0).
In addition, in wires which contain inclusions with Di/D, = 0.4 or 0.6, the drawing
stress becomes approximately 1.2 times and 1.6 times larger, respectively, than that in a
wire without inclusions. In the drawing of fine wires in particular, the magnitude of this
drawing stress greatly affects the occurrence of wire breakage; accordingly, measures to
prevent inclusions are required. For example, the use of high-quality elementary wires,
operating and processing in a clean room and the use of tools and lubricants which do
not generate metal powder should be considered.