注塑成型塑料部件设计英文文献和翻译(4)

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. 注塑成型塑料部件设计英文文献和翻译(4):http://www.youerw.com/fanyi/lunwen_759.html