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Plastics
Design Resources
Injection
Molding Manufacturing and Services
Plastics Engineering Services | Plastic Molding Design Services
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Designing With Plastic Design
Considerations
If the product
consists of more than one component, determine if the components can be combined into
a single molded part, eliminating extra materials, molds, molding operations,
and assembly procedures? Can integrating them into the molded part eliminate
hardware or other components? Caution should be exercised in that some cases,
trying to design multiple features into a single component can result in a
complex part that results in the tooling to be more expensive or the part too
difficult or unreliable to mold. This is especially true when the mold must open
in many directions to eject the molded part.
Selecting
Material
There are a wide
variety of injection moldable thermoplastic materials. Often, material the used
is selected based on experience one that the molder or material supplier
recommends. Unfortunately, proper material selection can be a complex process.
The plastic designer should consider the following criteria.
Operating
Temperature Requirements
Determine the
normal and extreme operating temperature requirements of the component, which
you are designing. The plastic, which, you select, should have the capability to
withstand the normal, as well as extreme, operating temperature required of the
product. Be sure to check shipping temperatures, sources of internal heat, and
any assembly or finishing operations that may expose the component to extreme
temperatures. Mechanical and electrical properties usually depend on
temperature.
Stress Levels
Consider the
operating load and stress levels that, the component will be subject to. The
operating stress is a significant consideration in many applications. Elevated
stresses on a component tend to decrease the components resistance to the
operating conditions. Stresses incurred during snap fits, molding operations,
forming or assembly
Operating
Environment
Every substance,
solid, liquid, or gas that can come in contact with the plastic part over its
expected life span should be considered for chemical compatibility. If the
compatibility information is not obvious from the product literature, the
designer should consult the material supplier and/or request or conduct specific
testing if necessary. Some plastics are highly susceptible to erosion, or
similar damage when exposed to particular substances.
Assembly
Check to ensure
that the proposed material lends itself to the expected assembly operations. For
example, certain classes of materials are difficult to solvent bond, while
others may not work well with ultrasonic methods or thermal processes
Finish
Determine whether
plastic resin can be easily molded into the proposed product with the desired
final appearance. If not, can the part be easily and economically finished?
Cost
To determine the
economics of using a particular resin, consider the cost per pound in the
applicable color and purchase volume. In addition, look at the specific gravity
and typical molding cycle times of the particular resin grade, since these
affect the final molded part cost. The cost per unit volume of a particular
plastic resin (or any material) is as follows:
Cost/in.3 =0.0361 x
Specific Gravity x Resin Cost/Pound
The material cost
of a part is obtained by multiplying the cost/cubic inch by the part volume.
Finally, a very rough part cost estimate is obtained by doubling the material
cost of the part.
Availability
Check to see that
the chosen resin will be readily available in sufficient quantities when needed
for production.
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