The effect of punch contraction, springback and compaction tooling design on the cutting edge of positive WC-Co compacts
Date
2011-11-02
Authors
Ovcina, Denis
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Abstract
In the current work the effects of machine-tool deflections, component unloading, and
component-tool interactions on the dimensions of positive WC-Co compacts were
determined on the basis of various tests performed using different compact geometries,
compaction materials, tool designs and press decompression settings. Specifically the
machine-tool deflection was defined and examined in terms of the punch-ram system
contraction along the vertical axis of the press, component unloading in terms of axial,
radial and volumetric compact springback, and component-tool interaction in terms of
contact between the ejecting compacts and the die-wall. A new tool design was
introduced to study the springback behaviour of compacts and compared against the
conventional tooling design which makes use of a tight-fitting upper punch and die
combination. As a result of the new tool design, positive compacts that were formed had
near perfectly sharp cutting edges. Contraction experiments allowed for the determination
of the contraction profile along several points of the machine-tool system especially
contraction of the upper punch-ram. This quantity was found to be independent of tool
geometry; a significant result which allows for the prediction of contraction behaviour
and therefore increased control over the final pressing position of a variety of other
production punches. Natural springback behaviour of positive compacts was studied on
the basis of the determined contraction measurements and the newly introduced tool
design which allowed for the formation and ejection of compacts free from die-wall
contact and associated frictional influences. Axial and radial springback, as well as their
fractional counterparts, could be expressed in terms of the same functions of the pressing
force, dependant only on the hold-down setting (geometric and material factors being
accounted for and embodied in the pressing force parameter). This new result simplifies
the prediction of linear springback and its effect on the net shape of production items.
Volumetric springback was found to be independent of compact shape which can then be
used to make general predictions regarding the effect of three-dimensional springback on
the total net shape of compacts in production. Both relative and volumetric springback
were also found to be independent of the compaction material and hold-down setting.