3 Fundamentals of press design

Fine blanking
blankingpunch
1
2
innerformejector
5
Fig. 4.7.26 Formation of the lubricant film in the die
Depending on the sheet metal thickness and material strength, the oil
is subjected to different pressure and temperature levels. The oil must be
capable of withstanding these levels of stress to the extent that the lubricant
film remains intact during the blanking process. A low viscosity oil,
for example, is suitable for low material strengths of 400 N/mm 2 up to
a thickness of 3 mm, while for materials with a strength of 600 N/mm 2
the same oil would only be suitable up to a sheet thickness of 1mm. A
high-viscosity oil can be used for a blank thickness of 14 mm and a
strength of 400 N/mm 2 , or for a thickness of 10 mm with a strength of
600 N/mm 2 .
In the past, organic chloride compounds were used as extreme pressure
(EP) additives in fine blanking oils. However, due to the toxicological
effects of the chlorine additives, chlorine-free oils are now increasingly
used. The present developments in this field only permit this
requirement to be fulfilled up to a sheet metal thickness of around
6mm and a strength of around 450 N/mm 2 without detriment to the
service life of dies. Where high temperatures and pressure levels occur,
the use of chlorine-free oils involves a significant compromise in terms
of tool life, although coating the active die elements can help to counteract
this effect.
4.7.4 Fine blanking presses and lines
4
vee-ringplate
lubricant
ejector innerformpunch blankingplate
Requirements
Fine blanking is only possible through the effect of three forces: the
blanking force, the vee-ring force and the counterforce (Fig. 4.7.3).
Accordingly, special triple-action presses are used for fine blanking
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
recesses
lubrication pockets
359