S.H. Tang et al. / Journal of Materials Processing Technology 171 (2006) 259–267    261

the surface of the product. The product and the runner were
released  in  a  plane  through  the  parting  line  during  mould
opening.
Standard or side gate was designed for this mould. The gate
is located between the runner and the product. The bottom
land of the gate was designed to have 20◦  slanting and has
only 0.5 mm thickness for easy de-gating purpose. The gate
was also designed to have 4 mm width and 0.5 mm thickness
for the entrance of molten plastic.
In the mould design, the parabolic cross section type of
runner was selected as it has the advantage of simpler machin-
ing in one mould half only, which is the core plate in this
case. However, this type of runner has disadvantages such as
 
more heat loss and scrap compared with circular cross section
type. This might cause the molten plastic to solidify faster.
This problem was reduced by designing in such a way that
the runner is short and has larger diameter, which is 6 mm in
diameter.
It is important that the runner designed distributes material
or  molten  plastic  into  cavities  at  the  same  time  under  the
same pressure and with the same temperature. Due to this,
the cavity layout had been designed in symmetrical form.
Another design aspect that is taken into consideration was
air vent design. The mating surface between the core plate
and the cavity plate has very fine finishing in order to prevent
flashing from taking place. However, this can cause air to trap
in the cavity when the mould is closed and cause short shot
or incomplete part. Sufficient air vent was designed to ensure
that air trap can be released to avoid incomplete part from
occurring.
The  cooling  system  was  drilled  along  the  length  of  the
cavities and was located horizontally to the mould to allow
even cooling. These cooling channels were drilled on both
cavity and core plates. The cooling channels provided suffi-
cient cooling of the mould in the case of turbulent flow. Fig. 2
shows cavity layout with air vents and cooling channels on
core plate.
In this mould design, the ejection system only consists of
the  ejector  retainer  plate,  sprue  puller  and  also  the  ejector
 
Fig. 2. Cavity layout with air vents and cooling channels.

plate. The sprue puller located at the center of core plate not
only functions as the puller to hold the product in position
when the mould is opened but it also acts as ejector to push
the product out of the mould during ejection stage. No addi-
tional ejector is used or located at product cavities because
the product produced is very thin, i.e. 1 mm. Additional ejec-
tor in the product cavity area might create hole and damage
to the product during ejection.
Finally, enough tolerance of dimensions is given consid-
eration to compensate for shrinkage of materials.
Fig. 3 shows 3D solid modeling as well as the wireframe
modeling of the mould developed using Unigraphics.

3.  Results and discussion

3.1.  Results of product production and modification

From  the  mould  designed  and  fabricated,  the  warpage
testing specimens produced have some defects during trial
run. The defects are short shot, flashing and warpage. The
short shot is subsequently eliminated by milling of additional
air  vents  at  corners  of  the  cavities  to  allow  air  trapped  to 注塑模具的设计与热分析英文文献和翻译(4):http://www.751com.cn/fanyi/lunwen_513.html