DIE-CUTTERS - GENERAL
Die-cutting is a process by which all types of holes,
slots, slits and bends can be made in a fiberboard blank in one operation.
It is usually done by means of various types of metal rule precisely positioned
into a plywood sheet where they are retained by friction. The metal rule
protrudes beyond the surface of the wood and can have a rounded edge for
producing bends, a knife edge for cutting or a serrated edge for perforating
Various thickness and heights of rule may be used according
to the type of board being die-cut, different techniques being used to
obtain a variety of effects. This sheet of plywood and metal rule is called
a cutting-die which is placed in a press, the fiberboard is positioned
on to it and a hardened steel flat sheet is then brought into contact
with the board and pressure applied. The result is a die-cut board which
then requires the surplus material to be stripped from it.
When die-cutting, it is not necessary to have either
bends or cuts at right angles to each other as for other types of conversion
machinery, therefore there can be greater versatility of design incorporating
offset scores and diagonal bends as required, or even right-angled slots.
It is usual to press or die-cut the board from one side
only which does not allow for a normal reverse bend. This difficulty,
can be overcome by inserting two or even three bending rule strips immediately
adjacent to one another centrally over the required position The fiberboard
is then crushed sufficiently to enable it to be folded back reasonably
easily. Alternatively, is possible to use a cutting rule from which sections
have been removed at predetermined distances and depths to give the effect of
alternate cutting and bending. This weakens the board
sufficiently to allow it to fold back without unduly prejudicing the resultant
strength of the pack in the majority of instances.
By putting notches in the cutting rule it in possible
to retain sections. of the blank in position until it is required to dispense
with them, for instance to make a box into a transit/display by the removal
of a section. This can be advantageous to the manufacturer who may wish
to retain a flap in position for further conversion, or to the customer
who may wish to receive a complete set of fittings in one sheet to ensure
that he gets equal quantities of each.
The cutting rules on a cutting-die are surrounded by
sponge rubber strips which help to preserve the cutting edge, but are
used mainly to prevent the die-cut blank from embedding itself on to the
cutting-die after pressing.
Where there is a reasonably large demand for one particular
size and shape of die-cut box another type of machine, which is faster,
can more economically be used. The die-cutting is by a rotary process
where the cutting-die is not a flat sheet of plywood but two half cylinders
of metal to which the rules are welded. Other machines use shaped wooden
bases of plywood with metal rules in a similar fashion. The cylindrical
cutting-dies are clamped to a shaft which rotates over another shaft or
cylinder which acts as the pressure plate and the die-cut blank is then
ejected for automatic stripping on to a vibrating belt. The machine can
be fed blanks but it is better used as an from a hopper unit which holds
the blanks, in-line section of a printer-slotter unit where two color
flexographic printing and die-cutting can be done in one continuous process.
The die-cutting press unit can be followed by a rotary stripper which
has studs welded to half cylinders in a similar manner to the cutting
cutting-die to press out the waste sections from the main blank before
passing on to the vibrating belts.
The method of constructing the cutting-dies is more
costly than for flat bed machines and requires a special machine to compensate
for the difference in diameter between the base of the die and the cutting
edge at the tip of the rule. The cutting face of the rule is the same
as for flatbed work, but the base has to be contoured to take the shape
of the cylinder whatever the angle is to the direction of rotation. It
in advisable to keep a second cylinder on which cutting-dies can be placed
for emergency repair when the main unit is in use.
This is a simple form of rotary die-cutting using one
print cylinder of the printer slotter to hold specially prepared knife
carriers instead of the usual stereo printing rubber. It is only suitable
for a limited amount of die-cutting.
The print cylinder of a printer slotter can be used
to carry a hard rubber bending form for producing reverse bends in the
flaps of cases and trays. It can not truly be classed as die-cutting.
Where there is a demand for small quantities of die-cut
work it is often possible to use a hand-fed platen machine. The cutting-die
is secured to a static back plate and the board to be pressed is, placed
directly onto the pressure plate which is hinged at the bottom (in a similar
manner to an upper and lower jaw). With a good operator it is possible
to unload the pressed sheet and load the new blank in the one machine.
cycle of opening and closing. The size of blank is restricted to one which
can be handled easily for this cycling
In these machines the cutting-die and pressure plate
are parallel to one another at all times, the blank to be die-cut is loaded
into a hopper from which it is fed by kicker bar or auction feed into
a draw roller. A moving belt grips the board and deposits it into a gripper
bar which draws it first into the press unit, then into a stripper unit
before stacking. If the production quantity required is not very large,
or if the internal stripping is negligible,. it may be simpler not to
use the stripping unit as it entails a further machine setting procedure.
Some of the older die-cutting machines, particularly
the larger ones, had automatic die-cutting similar to Auto Platens but
it was necessary to hand feed the blanks straight into the gripper bars.
There were no automatic stripping units.
In the streamlining of production operations in recent
years, the flexibility of the Auto Platens has been increased still further
by the addition of flexographic printing units in line with the die-cutting
and stripping unit s. As with the casemaker gluing machines, only two
machines can be involved between reel store and dispatch.
Speed of throughput can vary from a theoretical 8000
boards per hour on the Rotary die cutters to around 1000 an hour on the
slower machines which are hand fed.
This is a term used for the production of die-cut blanks
when no side trim is necessary. It can be used when the position of scores
or cuts is not critical, to save board or to obtain an economical deckle
With a self-locking base it can be possible to have no trim on the trailing
edge. In exceptional circumstances of bad deckles or economy it may be
possible to have no trim on the leading edge provided that the grippers
can be arranged in positions which will not foul any cutting or bending