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Based on the dimensions provided by standard mould set,
thewidth and the height of the core plate are 200 and 250mm,
respectively.These dimensions enabled design of two cavities
on core plate to be placed horizontally as there is enough
space while the cavity plate is left empty and it is only fixed
with sprue bushing for the purpose of feedingmolten plastics.
Therefore, it is only one standard parting line was designed atthe surface of the product. The product and the runner were
released in a plane through the parting line during mould
opening.
Standard or side gatewas designed for thismould.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 0.5mm thickness for easy de-gating purpose. The gate
was also designed to have 4mm width and 0.5mm thickness
for the entrance of molten plastic.
In the mould design, the parabolic cross section type of
runnerwas selected as it has the advantage of simplermachin-
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 comparedwith 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 6mm in
diameter.
It is important that the runner designed distributesmaterial
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 fromtaking 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 themould 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 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. 1mm. 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 bymilling of additional
air vents at corners of the cavities to allow air trapped to 摘要这篇文章主要介绍一种注射模具的生产翘曲测试样品的设计，并对其进行热分析，用于了解热残余应力对塑料模具成型效果的影响。提出了一些设计塑料注射模具时的技术、理论、方法以及其它一些考虑因素。模具的设计可以使用商业计算机辅助设计软件Unigrafics，版本13.0来进行。由于样本的不均匀冷却而引起热残余应力改变的分析模拟已经在逐步开发中，并且可以使用一个叫做LUSAS Analyst, 版本13.5的商业有限元分析软件来解决。这个软件提供了温度分布的等高线图来了解塑料模具的温度分布情况，并通过温度的变化来绘制时间响应曲线，用于表现出塑料注射模制模周期内的温度变动情况。结果表明，相对与其它区域来说，收缩比较容易产生于冷却通道旁边的区域。这种在模具不同区域不均匀冷却就导致了翘曲。