3 Fundamentals of press design

402 Sheet metal forming and blanking
on the punch is obtained by measuring the elastic deflection of loaded
components. Load cells or strain gages can be located directly in the
primary force path or indirectly in the secondary force path, for example
in the press frame. The positioning possibilities of individual sensors
for force, acoustic emission and displacement measurement are
indicated in Fig.4.9.8.A defect in the production process is indicated by
a deviation in the force curve, for example a rapid drop in the forming
force during the deep drawing process as soon as a crack appears in the
sheet metal. Furthermore, controlling the blank holder force during
press setting also helps to avoid formation of wrinkles in drawn parts.
A method similar to force measurement is acoustic emission monitoring.
The dynamic processes taking place at the die during a blanking or
forming operation cause high-frequency acoustic emissions, so-called
structure-born noise. Measurements of the acoustic emission are carried
out by measuring the degree of vibration using accelerometer. In case of
troublefree production, always the same vibration curve is produced.
Production of a defective part can be detected by the presence of an
press
frame
connecting rod
slide
cover plate
die
Fig. 4.9.8 Positioning of sensors at the press for process monitoring
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
force
displacement
acoustic emission