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2. Identify those tasks related to the design of the cooling
system which could be improved by providing additional
information,
3. Analyse production and maintenance procedures to elaborate
an approach for analysis that does not disturb the production,
4. Elaborate a structured data model that combines relevant infor-
mation in context of the produced parts,
5. Develop a measurement approach and related equipment,
6. Carry out energy measurements for a representative sample of
injection moulds,
7. Expert-analysis of measurement data to identify key conse-
quences of design decisions in relation to energy efficiency.
3 ENGINEERING OF INJECTION MOULDS
Analysing the moulding cycle, the following elements are strongly
influenced by the mould design:
a) Residual cooling time
b) Mould movement (open, close)
While the time for mould movement depends a lot upon the injection
moulding machine and its environment such as robot for taking out
parts, minimum residual cooling time is directly linked to the design
of the mould and its cooling system. Taking a close look at the
cooling system can help improving mould performance a lot. Our
studies have shown that residual cooling time is the key factor
driven by mould design towards highly productive and energy
efficient moulds.
As an example, when building a new two-cavity mould for a housing
of a filter, it was possible to reduce cycle time from 58 seconds
down to 34.7 seconds only by improving the cooling system of the
mould. This was achieved by using regular water cooling and
regular drilled holes in the mould steel. Only by means of an
optimized mould design the new mould was able to run
approximately 1.67 times more quickly compared to the old, slow
running mould.
a) b)
Figure 1: Filter housing made of Polypropylene.
a) Isometric view, outer undercuts.
b) Isometric section cut, inner undercut.
Depending upon the number of parts needed, the designer might
consider reducing the number of cavities. This would save
investment for the mould and make it possible to use a smaller
injection moulding machine.
The amount of cavities in a mould is mainly a cost-driven decision
[11], depending upon production volume and mould cost.
Furthermore, the mould complexity and injection moulding machines
available in the production plant have influence upon the reasonable
amount of cavities in a mould. Ideally the total cost of ownership
shall be analysed as described in [14]. For the filter housing case
study mould, the number of cavities was kept to two.
This example shows that good mould performance does not
necessarily mean having to use high-end cooling technology like
mould inserts with conformal cooling lines made by laser, using
special mould materials or special cooling technology such as CO2-
cooling or similar (all these principles are having reasonable
applications, but in many cases it is possible to achieve good
solutions with regular technology).
3.1 Limiting Factors During Tool Design
Especially in automotive industry timing schedules are very narrow
and the budget for mould and mould design is limited. Despite
modern CAD-Systems, mould design is still a bottleneck-activity
when manufacturing a new mould.
For big moulds it is common practice to start mould manufacturing
long before mould design is fully finished. This creates quite a time
pressure for the mould designer, as he has to keep finishing bit by
bit of his design in a way that mould manufacturing can continue
without disruption. Furthermore, this can limit the design alternatives