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cover and iron cover. Intensive studies on this kind of cooling
channels have not been carried out adequately. In this paper, milled
groove cooling channels method is continued to investigate for
larger plastic part in automotive industry. Further more, the
influence of cooling channels’ configuration to the thermal behavior
of the mold cavity and the way of optimization are addressed in the
upcoming sections.
The conformal cooling channels are different from straight-
drilled conventional cooling channels. In conventional cooling
channels, the free-form surface of mold cavity is surrounded by
straight cooling lines machined by drilling method. It is clear that
the distance from the cooling lines and mold cavity surface varies
and results in uneven cooling effect. On the contrary, in the
conformal cooling channels, the cooling paths match the mold
cavity surface well by keeping a nearly constant distance between
cooling paths and mold cavity surface. It was reported that this kind
of cooling channels gives better even temperature distribution in the
molded part than that of the conventional one. Figure 1 shows an
example of a conformal cooling channel for a supposed free-form
molded part.
Besides SFF method, milling by CNC milling machine is an
alternative method for making the conformal cooling channels,
even though it is not flexible than the SFF method. However, milled
groove cooling channels method can be applied to any material
which is used to make the mold. In addition, it is not necessary to
machine the cooling channel precisely, so the machining time can
be reduced by applying high-speed machining and high material
removal rate technology. Milled groove cooling channels pattern
can be designed freely to avoid interfering with other features in the
mold such as ejector pins or other components.
The milled groove cooling channels are modeled by extruding
the cooling layouts including lines and curves with a thickness d in
XY plane up to the offset surface of the cavity impression. There
are two ways to make U-shape milled groove cooling channels. The
first method is applied when milled groove is deeper than the
permitted length of ball end milling tool. In this case, the big pocket
is machined first then the U-shape pockets are milled with a
constant depth into the offset surface of the mold core and mold
cavity as shown in Fig. 2. An inserted block is also machined and
assembled to the main mold cavity part to make complete U-shape
mill groove cooling channels for a haft mold. Sealing by O-rings is
required to prevent coolant leakage. The second method should be
used when the deepest milled groove is shorter than the length of
the milling tool. In this method, the pocket milling operation is
performed for the cooling channel groove in the cavity part as
shown by a cross-section in Fig. 3. A similar pattern core insert on which their bottom surfaces must be offset from the mold
impression to keep the constant cross-section of cooling paths is
also milled. A complete U-shape cooing is obtained when the mold
cavity part and core inserts part are assembled and fixed by socket
screws. The cross-section of a U-shape cooling channels is depicted
in Fig. 3. In heat transfer analysis and finite element method,
cooling channels are treated as beam elements; hence equivalent
diameter de based on equivalent cross-sectional area is defined as
follows: Milled groove cooling channel burdens the mold manufacturing
cost compared to straight-drilled channels due to extra expenditure
of mold material and milling operation. In plastic injection molding,
trade-offs are sometimes required. It can be seen that the volume of