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assembly) to be manufactured using a particular process or processes. In addition, if a mould is
used to produce an item, there are therefore automatically inherent restrictions to the design
imposed at the very beginning. Taking injection moulding as an example, in order to process a
component successfully, at a minimum, the following design elements need to be taken into
account:
1. .geometry;
. draft angles,
. Nonre-entrants shapes,
. near constant wall thickness,
. complexity,
. split line location, and
. surface finish, 4. cost.
In injection moulding, the manufacture of the mould to produce the injection-moulded
components is usually the longest part of the product development process. When utilising rapid
modelling, the CAD takes the longer time and therefore becomes the bottleneck.
The process design and injection moulding of plastics involves rather complicated and time
consuming activities including part design, mould design, injection moulding machine selection,
production scheduling, tooling and cost estimation. Traditionally all these activities are done by
part designers and mould making personnel in a sequential manner after completing injection
moulded plastic part design. Obviously these sequential stages could lead to long product
development time. However with the implementation of concurrent engineering process in the
all parameters effecting product design, mould design, machine selection, production scheduling,
tooling and processing cost are considered as early as possible in the design of the plastic part.
When used effectively, CAE methods provide enormous cost and time savings for the part design
and manufacturing. These tools allow engineers to virtually test how the part will be processed
and how it performs during its normal operating life. The material supplier, designer, moulder and
manufacturer should apply these tools concurrently early in the design stage of the plastic parts in
order to exploit the cost benefit of CAE. CAE makes it possible to replace traditional, sequential
decision-making procedures with a concurrent design process, in which all parties can interact and
share information, Figure 3. For plastic injection moulding, CAE and related design data provide
an integrated environment that facilitates concurrent engineering for the design and manufacture
of the part and mould, as well as material selection and simulation of optimal process control
parameters.
Qualitative expense comparison associated with the part design changes is shown in Figure 4 ,
showing the fact that when design changes are done at an early stages on the computer screen, the
cost associated with is an order of 10.000 times lower than that if the part is in production. These
modifications in plastic parts could arise frommould modifications, such as gate location, At the early design stage, part designers and moulders have to finalise part design based on their
experiences with similar parts. However as the parts become more complex, it gets rather difficult
to predict processing and part performance without the use of CAE tools. Thus for even relatively
complex parts, the use of CAE tools to prevent the late and expensive design changesand
problems that can arise during and after injection. For the successful implementation of concurrent
engineering, there must be buy-in from everyone involved.
5. Case Study
Figure 5 shows the initial CAD design of plastics part used for the sprinkler irrigation hydrant leg.
One of the essential features of the part is that the part has to remain flat after injection; any