Sheet Metal Forming

Fig. 1.15
 
Influence of lubrication on punch wear. Source: Ref 1.9
Fig. 1.16
 
Spring stripper plate. Adapted from Ref 1.3
Fig. 1.17
 
Pilots used to locate the part

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10 / Sheet Metal Forming—Processes and Applications
a proper location before the stripper makes con-
tact. They do not deform the part material. The 
pilots first enter the part, followed by the strip
-
per and finally the punch. The pilot working 
length is longer than the punch length and fully 
extended stripper. Pilot diameters are generally 
0.025 mm (0.001 in.) smaller than the punch 
diameters.
Gibs
Precision in slide gib columns is important 
while using high-quality blanking dies and pro-
ducing parts with high accuracy. The gibs are 
made of steel, and the bushings are made of 
bronze. An eight-track roller gib system, with 
16 roller elements, is generally used. The rollers 
run along hardened gib rails, backlash-free (Ref 
1.1).
Blanking Presses (Ref 1.1) 
Blanking presses are high-speed eccentric or 
link-drive presses. They feature a high degree of 
rigidity as well as small bearing and gib clear-
ances. The slide generally has a maximum 
stroke of 300 to 450 mm (12.0 to 18.0 in.) and 
is mounted using eight guide gibs. Blanking 
presses must be equipped for noise reduction. 
There are a number of factors that influence 
noise, including the impact speed of the punch 
on sheet metal and the slide velocity in the work 
area. A link-drive system generates less noise 
than an eccentric press because of lower impact 
speed. Further noise is generated during mate-
rial breakthrough. Secondary measures such as 
providing closures are applied to reduce the 
noise emission.
High performance, high-speed blanking presses 
run at speeds of 2000 or more strokes per min-
ute (spm), and they are equipped with counter-
balance systems. Forces in the press change very 
rapidly during material breakthrough. These 
forces can cause dynamic displacement in the 
dies, which in turn can affect the service life of 
dies and part quality. Vertical vibrations are 
caused because of play existing in the force 
flow of the press and elastic properties of the 
press. They increase the blanking depth of the 
punch in the die. This results in punch wear. Ec-
centric shafts in roller bearings and hydraulic 
slide adjustment clamps reduce vertical play. A 
control device is often used in high-speed 
presses to detect increase in blanking depth and 
provide automatic correction. The horizontal vi-
brations on the press also exist but are over-
come with the use of accurate slide guidance 
and special configurations on the press body 
and very good tool guidance. Considerable re-
search is being conducted to investigate the dy-
namics of high-speed blanking presses and to 
reduce vibrations due to dynamic forces (Ref 
1.10). High-speed presses are used in applica-
tions where large numbers of high-precision mi-
crosized parts must be stamped. The electronics 
industry has been a major driver for high-speed 
precision requirement in stamping presses. The 
materials to be stamped have become thinner, 
the speed pitches shorter, and the required pre-
cision and repeatability higher. Press capacity 
as low as 200 kN would be sufficient for these 
applications. The stroke length would be ap-
proximately 30 mm (1.0 in.), and a press can 
run at a speed of approximately 2000 spm or 
higher. To prevent deflection of the punches due 
to eccentric loading, the ram guide elements are 
placed in strip level.