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requires an engineer to consider the manufacturing process of the designed product in the
development phase. A good design of the product is unable to go to the market if its
manufacturing process is impossible or too expensive. Integration of process simulation, rapid
prototyping and manufacturing can reduce the risk associated with moving from CAD to CAM
and further enhance the validity of the product development.
3. Importance of Computer Aided Injection Mould Design
The injection moulding design task can be highly complex. Computer Aided Engineering (CAE)
analysis tools provide enormous advantages of enabling design engineers to consider virtuallyandpart, mould and injection parameters without the real use of any manufacturing and
time. The possibility of trying alternative designs or concepts on the computer screen gives the
engineers the opportunity to eliminate potential problems before beginning the real production.
Moreover, in virtual environment, designers can quickly and easily asses the sensitivity of specific
moulding parameters on the quality and manufacturability of the final product. All theseCAE
tools enable all these analysis to be completed in a meter of days or even hours, rather than weeks
or months needed for the real experimental trial and error cycles. As CAE is used in the early
design of part, mould and moulding parameters, the cost savings are substantial not only because
of best functioning part and time savings but also the shortens the time needed to launch the
product to the market.
The need to meet set tolerances of plastic part ties in to all aspects of the moulding process,
including part size and shape, resin chemical structure, the fillers used, mould cavity layout, gating
mould cooling and the release mechanisms used. Given this complexity, designers often use
computer design tools, such as finite element analysis (FEA) and mould filling analysis (MFA), to
reduce development time and cost. FEA determines strain, stress and deflection in a part by
dividing the structure into small elements where these parameters can be well defined. MFA
evaluates gate position and size to optimize resin flow. It also defines placement of weld lines,
areas of excessive stress, and how wall and rib thickness affect flow. Other finite element design
tools include mould cooling analysis for temperature distribution, and cycle time and shrinkage
analysis for dimensional control and prediction of frozen stress and warpage.
The CAE analysis of compression moulded parts is shown in Figure 1. The analysis cycle starts
with the creation of a CAD model and a finite element mesh of the mould cavity. After the
injection conditions are specified, mould filling, fiber orientation, curing and thermal history,
shrinkage and warpage can be simulated. The material properties calculated by the simulation can
be used to model the structural behaviour of the part. If required, part design, gate location and
processing conditions can be modified in the computer until an acceptable part is obtained. After
the analysis is finished an optimized part can be produced with reduced weldline (known also Machining of the moulds was formerly done manually, with a toolmaker checking each cut. This
process became more automated with the growth and widespread use of computer numerically
controlled or CNC machining centres. Setup time has also been significantly reduced through the
use of special software capable of generating cutter paths directly from a CAD data file. Spindle
speeds as high as 100,000 rpm provide further advances in high speed machining. Cutting
materials have demonstrated phenomenal performance without the use of any cutting/coolant fluid
whatsoever. As a result, the process of machining complex cores and cavities has been