STEEL + TECHNOLOGY 01/2020 EXTRACT

58 | STEEL PROCESSING
Hot forming of fastener heads and pins
Three-die press accelerates hot heading by
up to 30 per cent
A newly developed upsetting press has been designed with three positions of the die. Hence, it chronologically
separates the “inserting”, “heating”, “heading”, “cooling” and “discharging” operations from each other. This
enables the machine to reduce cycle times by up to 30 per cent.
Up to now, it has been customary to
use dies with two opposing mountings
for hot heading of fasteners
(screws/bolts), ejector pins for mould-making
and perforating pins and needles. A
new pin was inserted in the upper position
while the pin in the lower position was
being headed. The die was then turned
through 180°, the pin cooled down and
was then discharged. Insertion, cooling
and discharge all took place in the same
mounting, with the result that the sum of
these operations determined cycle time.
The consequence: it was necessary to
wait for sufficient cooling, particularly in
the case of thick material, despite the fact
that heating-up and heading had long since
been completed.
To overcome the obstacle and speed up
cycle time, special-machine manufacturer
Krott + Heuter has developed the ZKSTA
series of automatic hot heading machines.
It features a newly developed star die with
three separately cooled mountings
arranged in a star configuration. While a
finished pin is being removed from the first
position and a new one inserted, another
pin is being inductively heated and upset
simultaneously in the second position. The
pin cools in the third position. The star
rotates by 120° to the next position after
each cycle. The process that determines
cycle-time is now heating up, and there is
no longer any need to wait through the
unproductive cooling phase.
Users report that they have been able
to boost the output of their production
lines by up to 30 percent thanks to the separation
of heading, cooling and discharge.
The new machine has now passed its trials
at a renowned manufacturer of punches
and ejector pins.
The technology in detail
The machine described above upsets pins
of diameters between 2 and 8 mm with an
upsetting force of up to 200 kN, although
significantly larger dimensions and upsetting
forces, of up to 1,000 kN, are also possible.
The machine’s high level of precision
also permits the production of fastener
heads with special geometries, such as
types bevelled on one side, for example,
or pins featuring various special head
shapes. The automated machine can also
be used for cold upsetting of softer materials,
such as structural steel, aluminium or
brass.
The pins are automatically inserted,
measured and upset to the precise final
head dimension by means of a servo-controlled
stop plate, with the result that every
individual head is completely filled.
The servo-hydraulically actuated
upsetting cylinder can be operated power-controlled
or deformation-controlled.
Unlike conventional systems, which
require large quantities of hydraulic fluid,
the new system does not include any
external fluid supply. There is no separate
tank for hydraulic fluid, and the machine
therefore has a footprint of only around
1.0 m × 3.0 m.
These heading units have maintenance
intervals of around 20,000 operating
hours. Technically, they are automatic
upsetting machines and are thus not subject
to European mechanical and hydraulic
press legislation.
• Krott + Heuter GmbH, Stolberg,
Germany
The end of the pin is inductively heated and then pressed into
the die by the heading cylinder (left). (Picture: Krott + Heuter)
STEEL + TECHNOLOGY 2 (2020) No. 1