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Abstract: Injection molding is one of the most popular manufacturing methods for the cost-effective mass production of the
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plastic parts. Filling analysis of the molten polymer provides useful information to investigate the process conditions to
ensure successful replication. To validate appropriate gate location for a NEEDLE COVER, flow fronts and flow stresses for
four different gating options and three different design options are analyzed and compared to the field results. Based on the
results, the optimum gate location for the minimum flow stresses and uniform fill patterns appears to be at gate 3. Thus it also
provides minimum possibility of part warpage throughout PORT HOUSING and NEEDLE HOUSING. The results of
analysis on the increased wall thickness, lower melt temperature, and longer injection time indicated that higher melt
temperatures were recommended to achieve successful molding. Injecting the polymer at a longer time (1.2 second) leads to
a significant increase in flow stresses throughout the part and the increase of wall thickness achieve successful replication of
the parts.4207
Keywords: Injection molding, Filling analysis, Fill pattern, Flow stress, Gate location
Introduction
Injection molding has been used to realize cost-effective
mass production in the field of manufacturing. It has a wide
variety of applications from housewares to automotive parts.
Short cycle time, good replication accuracy, and high
productivity are typical advantages of injection molding as
one of the most popular manufacturing methods [1-3].
The quality of injection-molded parts primarily depends
on the behavior of molten polymer in the replication process
[4-6]. The behavior can be analyzed by using process
parameters, including flow front, flow stress, injection time,
melt and mold temperature, etc. [2]. Mold design, including
gate location and wall thickness, also directly affects the
flow behavior of the molten polymer. The gate location in
the mold design is one of critical aspects to avoid short shot
and to reduce flow stress in the advance of flow front [7,8].
The various numerical methods have been employed to help
understand the flow behavior for the successful replication
of the parts [11,12]. The careful design of gate location and
process parameters can lead to high quality products.
Cavity filling analyses of the Needle Cover were performed
to determine the appropriate gate location and to suggest any
design improvements if needed. Finite element models for
the numerical analysis were constructed using MOLDFLOW
(Moldflow, Framingham, MA). Depending on the gate
location, the flow fronts and flow stresses were quantified to
avoid the incomplete filling and the hesitation of molten
polymer during molding. The effect of wall thickness, melt
temperature, and injection time were also investigated in
conjunction with the gate location and proper processing
conditions.
Analyses
Injection Molding Conditions
The material used in the analysis was polypropylene. Most
of the analyses were performed at a mold temperature of
30 o
C, and a melt temperature of 240 o
C. One set of analyses
was performed at a melt temperature of 220 o
C to get a better
understanding of the effects of lower melt temperature. The
injection time of 0.6 second to fill the cavity was chosen
primarily to minimize flow stresses in the part.
Figure 1 shows a CAE model for the simulation of cavity
filling with molten polymer. The model consists of a
NEEDLE HOUSING, a COLLAR, and a meshes with triangular elements.
Filling Analysis for the Gate Location
In order to determine the optimum gate location for the
part, four different gating options were studied. The results