lapsible core unit for the 3608 internal undercut. The product shown in figure 1 is used
as an example to illustrate the trade-offs involved in the interactive design process, as
well as systematic procedures for UPVC pipe fitting injection mould design.
2. Design of injection mould for an 87.58 8 8 8 8 elbow
An injection mould is an assembly of parts that provides an impression within
which plastic material is injected and cooled. The impression is formed by the
cavity and the core. The cavity is the female portion of the mould and is used to gen-
erate the external form of the moulded part; the core is the male portion of the mould
and is used to form the internal shape of the moulded part. Besides shaping the part, an
injection mould needs to fulfil a number of tasks such as distribution of melt, cooling
of molten material, ejection of the moulded part, transmitting motion, guiding and
aligning the mould halves (Ye et al. 2000). The specification of the UPVC pipe
fitting elbow is given as ‘DIN 1953 Ø50 mm  87.58’, where DIN 1953 is a
German standard for UPVC rubber joint fittings.
2.1. Selection of parting line
A parting line is a mark on the moulded part, where the two mould halves meet.
The parting surface can be flat or non-flat depending on the shape of the part. The
flat parting surface or plain flash line is the best parting line as it is the simplest to man-
ufacture and maintain. The other parting surfaces, such as a stepped parting surface,
profiled parting surface, angled parting surface and complex edge forms, are also
available. They are used for parts with complex geometry.
The 87.58 elbow is cylindrical and highly curved in shape. Hence the parting line
should be the symmetrical line between the two halves of the component for easy ejec-
tion. Due to the presence of the groove undercut, another parting line should be added
to allow the ejection of the part during demoulding. These parting lines are shown in
figure 2. 2.2. Design of cavity
Cavity design involves the layout of cavities, the type of runners, cooling system
layout, as well as guiding units. These inpidual tasks directly affect the quality and
dimensions of the moulded part.
2.2.1. Layout of cavities. For most injection moulding machines, the barrel is posi-
tioned in the central axis of the stationary platen. This determines the position of
the sprue, which is a part of the plastic part that leads the molten plastic to the
mould. The cavities should be arranged relative to the centre sprue so that: (1) all
cavities can be filled at the same time with melt of the same temperature; (2) the
flow length is short to keep scrap to a minimum; (3) the distance from one cavity to
another is sufficiently large to provide space for cooling lines and ejector pins, and
leaves an adequate cross-section to withstand forces from injection pressure; and
(4) the sum of all reactive forces is in the centre of gravity of the platen.
As shown in figure 1(b), side A of the part should make use of a sliding side core to
produce the undercut. For easy incorporation of the side core mechanism, a two-cavity
layout is determined as shown in figure 3. With such a layout, the pressure forces will
be balanced with respect to the sprue location. In addition, cavities will be filled at the
same time since they are placed at an equal distance from the starting injection pos-
ition. The distance between two cavities will provide the space for cooling lines
and ejector pins.
2.2.2 Design of runner system. Figure 3 also shows the runner system designed for
the 87.58 elbow. The gate is chosen at the location that is of equal distance from both
ends of the elbow. In this way, the cavity will be filled up more uniformly during the 硬质聚氯乙烯管接头模具设计英文文献和中文翻译(2):http://www.751com.cn/fanyi/lunwen_18127.html