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1. Introduction Injection molding is the most popular method for producing plastic products because of its high productivity and the manufacturability for making various complex shapes. The
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injection molding process includes six stages: mold closing, mold filling, packing, cooling, mold opening, and part ejection. Among these stages, cooling stage is the most important phase because it significantly affects the productivity and the quality of molded part.10802
Normally, 70%~80% of the molding cycle is taken up by cooling
stage. An appropriate cooling channels design can considerably
reduce the cooling time and increase the productivity of the
injection molding process. On the other hand, an efficient cooling
system which achieves a uniform temperature distribution can
minimize the undesired defects that influence the quality of molded
part such as hot spots, sink marks, differential shrinkage, thermal
residual stress, and warpage.
1,2
Traditionally, mold cooling design is still mainly based on
practical knowledge and designers’ experience. This method is
simple and may be efficient in practice; however, this approach
becomes less feasible when the molded part becomes more complex
and a high cooling efficiency is required. In addition, conventional
straight cooling channels are machined by hole-drilling as close to
the cavity’s surfaces of the mold as possible. The free-form surfaces
of the cavity surrounded by straight cooling lines and the molded
part will be cool unevenly because of the variation of the distances
between the cavity’s wall and cooling lines. This not only results in
potential defects of molded part but also increases the cooling time.
Alternative cooling device such as baffles, bubblers and thermal
pins that are used to cool areas being far from main cooling
channels can improve the cooling quality. However, this method is
not always effective due to the high pressure drop in cooling
channels system, especially for medium-sized and large-sized parts
with free-form surfaces.
The importance of cooling process in injection molding has
drawn a great attention of plastic engineers and researchers. Some
researches have focused on analysis of the cooling system and on
how to optimize the cooling channels layout in terms of cooling
channel size and location by the mathematical calculation and
analytical method.
3-5
These practical approaches were reported to
be more convenient and faster than finite difference and finite
element method. They demand less effort of plastic designers than those of numerical and simulation software. However, these
methods can be applied to simple molded parts. Other approaches
used 2-D boundary element method and sensitive analysis in
conjunction with the gradient optimization algorithm or hybrid
optimizer to optimize cooling channels system.
6,7
More recently,
applying 3-D CAE and 3-D FEM computer-aided simulation have
been widely used to investigate the thermal behavior of the cooling
system and the configuration of conformal cooling channels.
8,9
These researches’ results showed that the conformal cooling
channels give a shorter cooling time and better temperature
distribution than those of conventional cooling channels. Park and
Pham10
introduced an optimization strategy and investigated some
types of conformal cooling layout for an automotive part by
applying analytic formulas. Subsequently, they used CAE flow
simulation for verifying the optimization results and showing the
cooling effect of conformal cooling channels.
To obtain a uniform cooling, the cooling channels should
conform to the surface of the mold cavity. This type of cooling