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S.H. Tang et al. / Journal of Materials Processing Technology 171 (2006) 259–267 265
Fig. 14. Temperature distribution graph for Node 1838.
Fig. 15. Temperature distribution graph for Node 1904.
stage causes the material to cool from above to below the
glass transition temperature. The material experiences differ-
ential shrinkage that causes thermal stress that might result
in warpage.
From the temperature after the cooling stage as shown in
Figs. 9–17, it is clear that the area (node) located near the
cooling channel experienced more cooling effect due to fur-
Fig. 16. Temperature distribution graph for Node 1853.
Fig. 17. Temperature distribution graph for Node 1866.
ther decreasing in temperature and the region away from the
cooling channel experienced less cooling effect. More cool-
ing effect with quite fast cooling rate means more shrinkage
is occurring at the region. However, the farthest region, Node
284 experience more cooling although far away from cooling
channel due to heat loss to environment.
As a result, the cooling channel located at the center of the
product cavity caused the temperature difference around the
middle of the part higher than other locations. Compressive
stress was developed at the middle area of the part due to
more shrinkage and caused warpage due to uneven shrinkage
that happened. However, the temperature differences after
cooling for different nodes are small and the warpage effect
is not very significant. It is important for a designer to design a
mould that has less thermal residual stress effect with efficient
cooling system.
For the product analysis, from the steps being carried out to
analyze the plastic injection product, the stress distribution
on product at different load factor is observed in the two
dimensional analysis. Figs. 18–21 show the contour plots of
equivalent stress at different load increments.
A critical point, Node 127, where the product experiences
maximum tensile stress was selected for analysis. The stress
versus strain curve and the load case versus stress curves at
this point were plotted in Figs. 22 and 23.
From the load case versus stress curves at this point plotted
in Fig. 23, it is clear that the product experiencing increased
in tensile load until it reached the load factor of 23, which
is 1150 N. This means that the product can withstand tensile
load until 1150 N. Load higher than this value causes failure
to the product. Based on Fig. 23, the failure is likely to occur at
the region near to the fixed end of the product with maximum
stress of 3.27 × 107 Pa.
The product stress analysis reveals very limited informa-
tion since the product produced was for warpage testing
purposes and had no relation with tensile loading analy-
sis. In future, however, it is suggested that the product ser-
vice condition should be determined so that further analysis
may be carried out for other behaviors under various other
loading.
266 S.H. Tang et al. / Journal of Materials Processing Technology 171 (2006) 259–267
Fig. 18. Equivalent stress plot at load increment 1.
Fig. 19. Equivalent stress plot at load increment 14.
Fig. 20. Equivalent stress plot at load increment 16.
S.H. Tang et al. / Journal of Materials Processing Technology 171 (2006) 259–267 267
Fig. 21. Equivalent stress plot at load increment 23.