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Fig. 3. 3D solid modeling and wireframe modeling of the mould.
262 S.H. Tang et al. / Journal of Materials Processing Technology 171 (2006) 259–267
Fig. 4. Extra air vents to avoid short shot.
escape. Meanwhile, flashing was reduced by reducing the
packing pressure of the machine. Warpage can be controlled
by controlling various parameters such as the injection time,
injection temperature and melting temperature.
After these modifications, the mould produced high qual-
ity warpage testing specimen with low cost and required
little finishing by de-gating. Fig. 4 shows modifications of
the mould, which is machining of extra air vents that can
eliminate short shot.
3.2. Detail analysis of mould and product
After the mould and products were developed, the analysis
of mould and the product was carried out. In the plastic injec-
tion moulding process, molten ABS at 210 ◦C is injected into
the mould through the sprue bushing on the cavity plate and
directed into the product cavity. After cooling takes place,
the product is formed. One cycle of the product takes about
35 s including 20 s of cooling time.
The material used for producing warpage testing speci-
men was ABS and the injection temperature, time and pres-
sure were 210 ◦C, 3 s and 60 MPa respectively. The material
selected for the mould was AISI 1050 carbon steel.
Properties of these materials were important in determin-
ing temperature distribution in the mould carried out using
finite element analysis. Table 2 shows the properties for ABS
and AISI 1050 carbon steel.
The critical part of analysis for mould is on the cavity and
core plate because these are the place where the product is
formed. Therefore, thermal analysis to study the temperature
Fig. 5. Model for thermal analysis.
distribution and temperature at through different times are
performed using commercial finite element analysis software
called LUSAS Analyst, Version 13.5. A two-dimensional
(2D) thermal analysis is carried out for to study the effect
of thermal residual stress on the mould at different regions.
Due to symmetry, the thermal analysis was performed by
modeling only the top half of the vertical cross section or
side view of both the cavity and core plate that were clamped
together during injection. Fig. 5 shows the model of thermal
analysis analyzed with irregular meshing.
Modeling for the model also involves assigning properties
and process or cycle time to the model. This allowed the finite
element solver to analyze the mould modeled and plot time
response graphs to show temperature variation over a certain
duration and at different regions.
For the product analysis, a two dimensional tensile stress
analysis was carried using LUSAS Analyst, Version 13.5.
Basically the product was loaded in tension on one end while
the other end is clamped. Load increments were applied until
the model reaches plasticity. Fig. 6 shows loaded model of
the analysis.
3.3. Result and discussion for mould and product
analysis
For mould analysis, the thermal distribution at different
time intervals was observed. Fig. 7 shows the 2D analysis