Design Guide - Solvay Plastics

Design Information
In this section, basic design principles and general
recommendations are presented to assist the design
engineer in designing plastic components that meet
the cost/performance requirements of their applications.
Guidelines are given on the effects of stresses caused
by assembly, temperature changes, environmental
factors, and time as it relates to creep.
Of the various materials available to a design engineer,
thermoplastics offer the greatest variety, versatility
and freedom of design. Plastics can be translucent or
opaque, rigid or flexible, hard or soft. Plastic materials
are available that provide a wide range of chemical
resistance, from chemically inert to selective solubility in
certain environments. Broad versatility is also available
for other properties like strength, stiffness and impact
resistance, lubricity and thermal capability. Blends and
alloys are possible that further increase the material
choices for a particular application.
At times, designing with plastics may appear more
complicated than with metals. But the diversity of
products, conversion processes, and secondary
operations (welding, inserts, printing, painting,
metallizing) available with plastics gives the designer
unprecedented freedom as shown in Table 45.
A designer may be tempted to make a plastic part that
merely duplicates the dimensions of a metal part without
taking advantage of the versatility of the plastic material
or the design freedom offered. This approach can lead
to inefficient designs or parts that are difficult to produce,
or whose performance is less than optimal.
The following sections discuss those areas of
mechanical design and stress analysis that relate to
designing with plastics, comparing metal to plastics and
discussing factors that are specific to plastics alone.
Table 45: Design Benefits of Amodel Resin
over Metals
Amodel Resin
Characteristics
Amodel resins are fabricated
by the injection molding
process, which allows
substantial design freedom
Amodel resins
are thermoplastic
Amodel resins resist
chemicals
Benefit in Design
Ribs, bosses, or cored
sections can be readily
incorporated.
Snap fits can be molded in,
simplifying assembly.
Eliminate many secondary
operations such as drilling,
tapping, boring, deburring,
and grinding.
Metal inserts can be easily
used where necessary to
optimize part strength.
Features from several metal
parts of an assembly may be
combined into a single part,
simplifying assembly and
reducing cost.
Parts may be joined with
ultrasonic or vibration
welding rather than fasteners.
Color may be molded-in
rather than added afterward
as paint.
Parts will not rust, and resist
corrosion.
Design Information
Amodel ® PPA Design Guide
63