Materials Chapter 5. Plastics Material Selection

Material Selection
Material Selection
• Getting the optimum balance of
performance, quality and cost requires a
careful combination of material and plastics
part design
• Once end use requirements have been
specified, the designer can begin searching
for plastic materials that are suitable for the
Material Selection
• Material selection/screening process is
accomplished by comparing material
properties with a property profile derived
from the end use requirements
• Best to select 3-6 materials during the initial
process based on the property profile and
Material Selection
• Material Selection should be based
primarily on the functional requirements of
the parts
– Those items without which the part will not
• Then go to design considerations
– Those items involving manufacturing factors
without which the part cannot be made
Material Selection
• Functional requirements are physical properties
– The ability to operate over a wide range of temperatures
– Resistance to chemicals and environments
– Any other condition that can be described by testable
• Some functional are more important than others
– These should be given a top priority
Material Selection
• Design considerations are the
Raw material costs
Processing cost
Tooling costs
Familiarity of material
Acceptance of material in the market place
Material Selection
• Final choice of material almost always
involves compromises between functional
requirements and design considerations
Property Profile
Step 1
• Develop property profile
• The polymer required is classified and
ranked according to the following
representative grouping of functional
• The list can be expanded or filtered to fit
particular needs
Step 1
High strength to weight
Ordinary strength to weight
High Temperature resistance
Ductile at low temperatures
Resistant to chemicals
Dielectric constant
Arc resistance
Slow burning
Very low density
Ordinary density
Wear resistance
Friction coefficient
Acceptable for food
Post-consumer recyclable
Weather resistant
Step 2
• It is now possible to refer material property
data sheets and databases to arrive at a short
list of candidates that match with the
property profile developed in Step 1
• If similar application exist, begin with the
current materials
Step 3
• Material properties are used to select likely
candidates with corresponding property value or
ranking listed
• Best to begin with properties that cannot be
enhance by design
Coefficient of thermal expansion
Chemical resistance
Softening temperature
Step 3
• Then go to mechanical properties, which
can generally be enhanced by design
– Wall thickness
– Ribs
– Reinforcements
Step 4
• The next step in the elimination process is to
consider items such as
Creep modulus
Dielectric strength
Mold shrinkage
• The designer may want to consider statistically
designed experiments to narrow the list of
Material Selection Example
• There are a wide range of properties within
polymer families and between families
• The problem here is to select a injection
moldable polymer based on mechanical
properties as a first priority
• The property profile is developed first
Material Selection Example
• Property Profile
Material Selection Example
Material Selection Example
• In the preceding table all the resins checked
yes meet the preliminary specification
• The next step is to consider secondary
matters such as creep, dielectric strength,
shrinkage and cost.
Material Selection Example
Material Selection Example
• From the data in the preceding table, the higher
cost resins can be eliminated first
• The filled resins can be eliminated next because
they are more difficult to process
• This leaves 6/6 nylon and PPO
• The HDTUL of nylon is must lower than PPO
• The shrinkage values for PPO are much less than
• PPO is the best choice
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