3 Fundamentals of press design

Deep drawing and stretch drawing
Table 4.2.2: Deep drawing defects
Defect Possible Cause Prevention, remedy
drawing grooves tool wear replace draw punch/female die,
improve lubrication
tear marks on the base drawing ratio � set too high / use a sheet metal with greater
of the drawn part drawing gap too narrow / deep drawing capability or
curvature on draw punch employ multi-stage drawing
or female die too small / process / extend drawing gap /
blank holder force too great / check sheet metal thickness /
drawing speed too great increase die radii / reduce
blank holder force / reduce
forming speed
vertical tear marks insufficient material in the replace the female die
on upper edge defective area / drawing gap
too wide or drawing edge
curvature too great
on rectangular parts, too much material at the corners change the blank shape /
the corners are higher recess material in the affected
than the side walls areas / trim the edge afterwards
vertical creases in the blank holder force too low / increase blank holder force /
upper area of the body drawing gap too great / curvature renew female die
(vessel wall), also in at the female die too great
conjunction with vertical
cracks
crease formation blank holder pressure too low increase blank holder pressure
at the flange
other non-specific incorrect blank shape / correct blank shape / check
defects / faulty or asymmetrical material location / die and stops / use suitable
irregularly formed unsuitable sheet metal / sheet metals and lubricants
drawn parts incorrect lubricant
– lower yield strength R eL [N/mm 2 ] for sheet metals with an accentuated
yield strength or 0.2% elongation limit R p 0,2 [N/mm 2 ] for those without
accentuated yield strength,
– ultimate elongation A [%]: either relative to an initial length in the
tensile test specimen L 0 of 80 mm (A 80) or to L 0 = 5 · d 0 (A 5), with an
initial tensile test specimen diameter of d 0,
– field of application.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
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