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Core element of the injection moulding process is the injection mould
itself that is operated on the injection moulding machine while
requiring a pump and cooling water as well as additional equipment
for drying granulate and handling / transportation of produced parts.
These appliances consume electrical energy, which is the key energy
source in injection moulding. As presented in [8], shares of energy
consumption for hydraulic injection moulding systems split up as
follows: Mould temperature regulation (36,1%), the machine drive,
screw and control (47,2%), the plasticising unit heating (16,7%).
The machine, as the main consumer of energy seems to be the first
lever towards a more energy efficient production. In fact, a 30% to
60% cut of energy costs can be achieved by investing in new
machinery, changing from old hydraulic to all-electric machines [9].
This measure is regularly taken into account while planning
infrastructure investments. This principle is also applicable for the
other equipment such as dryers, pumps, etc..
Targeting only at the appliances directly consuming electrical energy,
leaves out the injection mould. Our key idea was to analyse the
combination of mould, machine, material and auxiliaries. The
required energy per part is considered as being quite stable when
combining a part specific mould with a specific machine. There are
two categories of sub-processes in the injection moulding processes:
Energy consumption is partially determined by granulate
plasticising, closing and opening the machine. Those
parameters are directly influenced by the shot weight, part
geometry and mould size. These are considered as stable
determinants (focus part – machine – combination).
In contrary, the mould temperature regulation and the
plasticising unit heating are mainly characterised by consuming energy over time. Especially in machine-idle-
situations in the injection moulding process. E.g. residual
cooling time can be considered as machine idle time.
The definition of residual cooling time is: Minimum theoretical
cooling time that is required for solidifying under optimal cooling
conditions, due to material and volume, plus additional cooling time,
due to inefficiencies of the mould’s cooling system minus processes
in the injection moulding cycle overlapping cooling time.
The logical assumption was to aim at a reduction of such inefficien-
cies (i.e. improving the cooling system) for being able to reduce
specifically the energy required for temperature regulation and
plasticising unit heating (focus mould – machine combination).
2.2 Challenge Addressed
The mould’s cooling system is an integral part of the injection mould
and determines its cooling efficiency. Cooling channels are usually
manufactured by drilling. The holes are joined (intersecting holes or
by hoses) or separated by plugs to create a directed flow of cooling
liquid inside the mould. It is not easy to make substantial changes to
the cooling system once it is manufactured. Therefore, the design of
the injection mould is the ideal stage in the life cycle for having an
impact on cooling inefficiencies. As also [10] identifies, it is
extremely challenging to forecast future energy consumption of a
mould precisely at the design stage.
The assessment whether an injection mould’s cooling system is
optimally designed can’t be solely connected to the minimisation of
cooling inefficiencies. To determine the degree of optimality of the
injection mould’s cooling system and its impact on the energy
efficiency in manufacturing, key performance indicators (KPI) are
needed. The most important KPI in injection moulding is and will be