注塑成型塑料部件设计英文文献和翻译(5)
• All extremities should fill at the same pressure.
Designers may also have some specific quality requirements,
such as minimising the maximum shear stress, uniform end-
of-fill temperature, uniform volumetric shrinkage, and uniform
warpage. Some requirements may be imposed on a particular
location or area of the plastic part, such as the shear stress re-
quirement at the vicinity of snap fits and screw holes.
To enable the designers to specify these criteria rather than
hard-wire them in a computer program, we modify the part fea-
ture by replacing the existing constraint attribute with two cri-
teria attributes: a verification criteria attribute and an evaluation
criteria attribute. Each of these attributes contains a list of crite-
ria. The verification criteria refer to those that must be satisfied,
such as the first three criteria listed above; while the evaluation
criteria refer to those that should be minimised, such as the last
three criteria listed above. Case-specific requirements may also
be classified as either verification criteria or evaluation criteria.
Part feature is further extended to include a new attribute for
storing a list of variables from which the verification and evalua-
tion criteria can be constructed. These variables are thus referred
to as criteria construction variables. The following is a list of
some of these variables (the units are put inside the brackets,
where “SD” stands for standard deviation):
• v1 = maximum shear stress (MPa);
• v2 = maximum shear rate (1/s);
• v3 = maximum pressure (MPa);
• v4 = maximum flow front temperature (
◦C);
• v5 = minimum flow front temperature (
◦C);
• v6 = maximum end-of-fill temperature (
◦C);
• v7 = minimum end-of-fill temperature (
◦C);
• v8 = maximum cooling time (s);
• v9 = minimum cooling time (s);
• v10 = actual injection time (s);
• v11 = maximum volumetric shrinkage (%);
• v12 = minimum volumetric shrinkage (%);
• v13 = maximum clamp tonnage (tonnes);
• v14 = uniform end-of-fill temperature (SD);
• v15 = uniform cooling time (SD);
• v16 = uniform volumetric shrinkage (SD);
• v17 = uniform warpage (SD);
• v18 = uniform filling time at extremities (SD);
• v19 = uniform pressure at extremities (SD);
The new attribute stores a list of criteria-construction vari-
ables selected by the designers from these commonly used vari-
ables. Each selected variable may itself be used as an evaluation
criterion, such as “v1 = maximum shear stress” and “v15 = uni-
form end-of-fill temperature;” or it may be used to construct
a criterion with or without other variables; for example, the vari-
able “v1 = maximum shear stress” may be used to construct
a verification criterion:
v1 < 0.25MPa,
which corresponds to an example of the first item of the list of
requirements mentioned in the beginning of this section, where
the maximum recommended shear stress for the material type is
0.25MPa. Another example, corresponding to the fourth item in
the list, is that “cooling time should be uniform and minimised.”
If the designers select the variables “v8 = maximum cooling
time” and “v9 = minimum cooling time,” then an evaluation cri-
terion may be constructed as:
minimising (v8−v9),
which represents the intention of achieving a uniform cooling
time (note that this may be more precisely represented by “v15 =
uniform cooling time”).499
When more than one evaluation criterion is constructed,
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