The parting of die plates or punches into sections is one of the
most challenging problems in the design of sectional pressworking dies.
Success calls for using all your design experience and ingenuity, but it
helps to keep in mind these commonsense rules, tested and proven over
many years of actual practice:
* Regular shapes. Each component part, section, segment, or insert
should have a basci cross-sectional shape that is square or at least
* Minimal machining. It is best to make the division so that only
one section needs to be machined while the others are straight or need
very little machining, Figure 1.
* Few divisions. Keep divisions to a reasonable minimum. However,
it may be better to make one more division if it makes machining or heat
treating easier, Figure 2.
* Alignment. Try for the best alignment, centering, and matching
of die shapes, Figure 3.
* Divisions at corners. Locate divisions where there are sudden
changes in cutting contour–the shapr corners of die openings, Figure 4.
* Symmetry. Sections should be symmetrical wherever possible. The
center line or axis of symmetry should also be the parting line so that
both halves of the die plate will be exact, mirror images, Figure 5.
With multiple dies and identical openings, simultaneous machining
operations can produce considerable savings, increase uniformity, and
simplify broken-section replacement.
* Simple sections. In dies with irregular cutting contours, to
make each die section as simple as possible to simplify machining and
heat treatment. This simplification can make the die section
cutting-contour lines straighter or arcs with larger radii, Figure 6.
* Die angles. Make breaks so that the included angle of the
cutting edge is never acute. Right angles are okay (certainly popular),
but obtuse angles are optimum, Figure 7. Locating parting lines either
along or at right angles to cutting-contour lines easily avoids acute
* Corner radii. Breaks should never be made through a corner
radius, even for the slightest radii, Figure 8. Separate at a point
outside the arc to eliminate machining two curved corners instead of one
and the difficulty of making them match. If a break or curve cannot be
avoided, make the parting line at a right angle to the tangent line,
* Limit size. With large tools, try to keep single sections no
longer than 10″ to 12″ to avoid heavy distortions in heat
* Machining access. With complicated contours, always take into
account machining difficulties such as cutting-tool accessibility. This
may mean making sections shorter (more breaks).
* Punch holding. Composite punch sections must be held together by
a punch-holder plate, which will be thicker than for solid punches (by
up to 1-1/2″ or 2/3 of punch length). The receiving hole for the
punch assembly must be carefully machined so the sections lock together
safely, tightly, and accurately. This can be a press fit or even a
* Avoid coincidence. When both punch and die plate are sectional,
it is important to keep the joints of the punch sections from coinciding
with the joints in the die plate, Figure 9. an offset of as little as
3/16″ is usually sufficient.