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experience differential shrinkage causing thermal stresses.
Significant thermal stress can causewarpage problem. There-
fore, it is important to simulate the thermal residual stress field
of the injection-molded part during the cooling stage [8].By
understanding the characteristics of thermal stress distribu-
tion, deformation caused by the thermal residual stress can
be predicted.
In this paper the design of a plastic injection mould for
producingwarpage testing specimen and for performing ther-
mal analysis for the mould to access on the effect of thermal
residual stress in the mould is presented.
2. Methodology
2.1. Design of warpage testing specimen
This section illustrates the design of the warpage testing
specimen to be used in plastic injection mould. It is clear
that warpage is the main problem that exists in product with
thin shell feature. Therefore, the main purpose of the prod-
uct development is to design a plastic part for determining
the effective factors in the warpage problem of an injection-
moulded part with a thin shell.
The warpage testing specimen is developed from thin
shell plastics. The overall dimensions of the specimen were
120mmin length, 50mminwidth and 1mmin thickness.The
material used for producing the warpage testing specimen
was acrylonitrile butadiene stylene (ABS) and the injection
temperature, time and pressure were 210 ◦C, 3 s and 60MPa,
respectively. Fig. 1 shows the warpage testing specimen pro-
duced.
2.2. Design of plastic injection mould for warpage
testing specimen
This section describes the design aspects and other consid-
erations involved in designing the mould to produce warpage
testing specimen. The material used for producing the plasticinjectionmould for warpage testing specimen was AISI 1050
carbon steel.
Four design concepts had been considered in designing of
the mould including:
i. Three-plate mould (Concept 1) having two parting line
with single cavity. Not applicable due to high cost.
ii. Two-platemould (Concept 2) having one parting linewith
single cavity without gating system. Not applicable due
to low production quantity per injection.
iii. Two-plate mould (Concept 3) having one parting line
with double cavities with gating and ejection system. Not
applicable as ejector pins might damage the product as
the product is too thin.
iv. Two-platemould (Concept 4) having one parting linewith
double cavitieswith gating system, only used sprue puller
act as ejector to avoid product damage during ejection.
In designing of the mould for the warpage testing spec-
imen, the fourth design concept had been applied. Various
design considerations had been applied in the design.
Firstly, themouldwas designed based on the platen dimen-
sion of the plastic injection machine used (BOY 22D). There
is a limitation of the machine, which is the maximum area of
machine platen is given by the distance between two tie bars.
The distance between tie bars of the machine is 254mm.
Therefore, the maximum width of the mould plate should
not exceed this distance. Furthermore, 4mm space had been
reserved between the two tie bars and the mould for mould
setting-up and handling purposes. This gives the final max-
imum width of the mould as 250mm. The standard mould
base with 250mm×250mmis employed. Themould base is
fitted to themachine usingMatex clamp at the upper right and
lower left corner of the mould base or mould platen. Dimen-
sions of other related mould plates are shown in Table 1.
The mould had been designed with clamping pressure
having clamping force higher than the internal cavity force
(reaction force) to avoid flashing from happening.