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system is called conformal cooling channels. The application of this
new kind of cooling channels is based on the development of solid
free-form fabrication (SFF) technology. Some of works studied the
advantages of the conformal cooling system and how to optimize
the conformal cooling channels in injection molding tools.
11,12
The
results were reported that conformal cooling channels offer better
temperature uniformity within the mold cavity and better molded
part’s quality compared to straight cooling channels. SFF or rapid
prototyping technology brings the opportunities to fabricate very
complex conformal cooling channels inside the mold core and mold
cavity,
13
but this technique is still expensive, especially for large-
sized mold. On the other hand, the kinds of metal powders used in
rapid prototyping techniques, for example 3D printing, selective
laser sintering, electron beam melting, and laser engineered net
shaping, are limited. It means that the choice of mold material with
appropriate thermal and mechanical properties for making
conformal cooling channels by SFF is narrower than that of
conventional mold. These issues hinder the popular use of rapid
prototyping technique for making large injection mold.
Although a great of attention has been paid to improve the
performance of the cooling system, most of the published works are
only feasible for simple plastic parts. One of the evidence is that all
the examples used in various case studies are very simple.
8
Some of
works
3,6,7,12,14
relied on 1-D or 2-D heat transfer analysis meanwhile
the geometry of plastic parts are usually complex, and they need a
3-D analysis. Moreover, sensitive analysis, finite element or
boundary element coding for optimization of some specific cases
are still academic and lack of generalization, so they are
inconvenient to apply in reality. On the contrary, some of works
8,9,15
applied 3-D CAE tools to solve the cooling problem for some more
complex parts. Yet, the method of reducing the cooling time and
optimizing the configuration of conformal cooling channels of these
studies were not adequate.
This paper is intended as a contribution to solve this on-going
problem by introducing U-shape milled groove conformal cooling
channels fabricated by CNC milling machine instead of rapid prototyping method. This approach is suitable for medium-sized
and large-sized molded part with free-form surface. The relation
between the configuration of cooling channels and cycle averaged
thermal behavior of the mold cavity are investigated thoroughly.
The size, location, and layout of cooling channels for a quite
complex molded part are optimized by the combination of an
applicable analytical model based on the equivalent model,
computer-aided 3-D heat transfer analysis, and effective
optimization strategy. This approach would therefore offer a more
feasible and practical way to design an optimal conformal cooling
channel and to meet the requirement of reducing the cooling time
and increasing molded part quality with less effort of plastic
designers.
2. U-shape milled groove conformal cooling channels
Milled groove cooling channels in spiral form has been used for
flat parts with round and circular shape in order to obtain better
temperature control. This kind of cooling channels is more
expensive to make comparing to straight-drilled one, but produces
high-quality and distortion-free parts such as precision gears and
compact discs.
16
Sun8
proposed a modified milled groove method
applied to medium free-form parts with two case studies of mouse