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    including both positional modification variables and sizing mod-
    ification variables, is introduced into the CAD-CAE features.
    The shape modification variable of the part feature is the overall
    thickness (a sizing modification variable). By changing this mod-
    ification variable, the part shape is modified such that the thick-
    ness of all the component features is changed to the same thick-
    ness. The thickness may be varied until the part shape achieves
    the optimal mouldability and other quality measures. Obviously,
    part feature does not have any positional modification variable.
    Component features have both positional and sizing modi-
    fication variables. Before proceeding further, it is necessary to
    emphasize that most of the component features have a corres-
    ponding profile defined in the underlying CAD system. A profile
    is a number of 2D curves either connected or not connected with
    each other. By extruding or rotating a profile, a 3D CAD feature
    can be created, which is then used to construct more complex
    CAD geometry by means of Boolean operations. Figure 2 shows
    the profile of a wall feature. Examples of some commonly used
    profiles of a hole, boss, and rib feature include a circle, two con-
    centric circles, and a 2D triangle respectively.
    With the help of the feature profile, modification variables
    can easily be defined. For example, the positional modification
    variables of a hole feature can be defined by the coordinates of
    the centre of the circle that is used as the profile to create the
    hole feature. The sizing modification variable is the hole radius.
    Figure 3 illustrates these modification variables.
    Similarly, the wall feature, rib feature, and boss feature also
    have their respective positional and sizing modification vari-
    ables. Table 1 lists the modification variables of all the CAD-
    CAE features.
    It is important to note that by specifying shape modification
    variables, different types of shape modification problems, either
    positional or sizing, or modification to different features, can be
    handled in a unified manner. It is not necessary to develop indi-
    vidual methods for the different problems on different features.
    Hence it benefits both model consistency and software develop-
    ment efforts.
    Fig. 3. Positional and sizing modification variablesAssociated with each modification variable are four parame-
    ters: current value, starting value, ending value, and step value. For
    sizingmodification variables such as thickness, radius, and height,
    these parameters are sufficient in defining how the correspond-
    ing variable should be varied during the part-shape-modification
    process. For the positional modification variables, which are the
    coordinates of the relevant key point on the profile, e.g. the cen-
    tre of a circle, it may be necessary to specify how they are varied.
    For example, the hole position may be varied within a rectangular
    range or a circular range on the surface of the hole profile. This is
    problem specific, hence it is up to the designer to specify.
    3.2 Criteria construction variables and the criteria
    for shape modification
    The designer should also specify the mouldability and other
    quality measuring criteria as constraints or targets of the intended
    shape modification operation. Some of these criteria are [16]:
    • Shear stress should not exceed the maximum recommended
    for the material type.
    • Shear rate should not exceed the maximum recommended for
    the material type.
    • Flow front temperature should not be more than 20 ◦Cbelow
    the melt temperature.
    • Cooling time should be uniform and minimised.
    • All extremities should fill at the same time.
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