Plastics News Europe - June 2018 - 25

moulds & tooling

traditional toolmaking approaches
require either the manufacture of
complex split tools, or the use of
spark erosion techniques followed by
time-consuming hand polishing.

Rapid production tooling
To make the most efficient use of its
hybrid metal additive manufacturing
technology, OGM's Rapid Production
Toolmaking technique combines the
process with conventional highspeed machining. The basic shape
and simpler features of a core or cavity are machined first from a solid
block of tool steel. This becomes the
base structure onto which the more
complex features are added. If the
overall dimensions of a part have
been defined, but certain features are
still being refined, this approach
means tool making can begin in parallel with the end of the design process, with the complete part definition only required at the final
production stage.
The completed core and cavity
components are then installed in a
standard design of bolster, preassembled and ready for production. To accommodate a wide range of possible
part designs, OGM has built a range
of these standard bolsters suitable for
different sizes of components. The
range can accommodate both simple
two-part core and cavity designs and
more complex components requiring
moveable side cores.
If a customer's part falls outside
the dimensions of its standard modular components, OGM can also manufacture dedicated bolster assemblies. Here again, customers have the
opportunity to save time through
parallelisation: bolsters can be made
once the basic part dimensions are
known, but before detailed design is
complete.

Conformal cooling
The hybrid metal additive manufacturing approach also allows the production of mould features that would
be extremely difficult to manufacture
with any alternative technology. Notably, OGM is using this capability to
produce conformal cooling channels
in moulds with complex geometry.
In conventional mould tools, cooling channels are drilled through the
mould material during tool manufacture. This approach is simple, but it
creates significant limitations in some
part geometries. It can be difficult to
run straight cooling channels close
enough to the mould cavity for efficient heat transfer, for example, especially when parts have elaborated
shapes or lots of complex features.
In many components, cooling
channels have to compete for space
within the tool with other features,

june 2018

Additive product

such as ejector pins or moving inserts.
That's a particular problem in the production of box shapes, such as electronic enclosures. In these designs,
the best position for the ejectors is
usually at the corners, where the
structure is strongest, but those
points are also the hardest to cool.
Even minor shrinkage at the corners
of a box can lead to significant distortion of the adjacent wall.
Sometimes, as in the case of the
slender cores used to create the internal surfaces of thin hollow parts, it is
impossible to provide a straight cooling path through the tool. This requires elaborate workarounds during
tool manufacture. The toolmaker may
drill two parallel channels, connect
them with a cross channel and then
add material to seal its ends. Or they
may insert a baffle into a larger blind
hole to create inlet and outlet pathways for coolant. All these efforts add
cost and complexity to the mould
making process, and some mould
features may be too small to accommodate them altogether.
The solution to difficult part cooling challenges is simple in concept,
but tricky in execution. Changing the
shape of the fluid channels within the
mould from straight lines to curves
allows them to follow the part surface
more closely, wriggle around obsta-

OGM's additive machine

cles like ejector pins, and squeeze
into inaccessible areas. The benefits
of conformal cooling are well known,
but their uptake by industry has been
limited. Using conventional subtractive machining, conformal tools require the construction of moulds using a laminated design. That adds
significant time and cost to the toolmaking process, can result in less durable tools, and does not provide a
solution for all part geometries.
OGM's hybrid approach, by contrast, allows tools incorporating conformal cooling channels to be manufactured automatically in one hit,
with no need for separate finishing
activities. The company has invested
more than a year of intensive R&D effort in the concept, which is called
ConformL. The aim of this work was
the development of cooling channel
designs that make optimal use of the
capabilities offered by the hybrid process. As well as allowing cooling
channels to take any route through
the tool, for example, the new approach also removes the necessity for
those channels to be round. Elliptical,
rectangular and even teardrop designs can maximise heat transfer in
different applications. The hybrid
manufacturing process also allows
better control of fluid flow within the
channels themselves. Special "trip"
features encourage turbulent flow to
increase heat extraction while maintaining a smooth surface finish within
the channel to prevent blockages
caused by mould growth or trapped
debris.
The company is now working on a
range of solutions designed to make it
easier for tool designers and injection
moulders to take advantage of the
new cooling technology. Those offerings will include custom-built inserts
that can be incorporated into conventionally manufactured tools to address
hard-to-cool areas, as well as a range
of standard inserts including ejector
units with built-in cooling channels.

Table of Contents for the Digital Edition of Plastics News Europe - June 2018