Transcript Plastic Injection Molding

Plastic Injection Molding
Process and Materials
Plastic Injection Molding
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Process :-
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Injection Molding produces plastic parts by forcing molten material into a mold where it cools and
hardens. The molded shape produced is a reverse image of the mold tool. Injection molding is low cost for
simple and complex parts. Tooling adds to the initial cost but is quickly amortized.
Plastic Injection Molding
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With injection molding, granular plastic is fed by gravity from a hopper into a heated barrel.
As the granules are slowly moved forward by a screw-type plunger, the plastic is forced into a heating
chamber, where it is melted.
As the plunger advances, the melted plastic is forced through a nozzle that rests against the mold, allowing
it to enter the mold cavity.
The mold remains cold so the plastic solidifies almost as soon as the mold is filled.
Injection molding is an extremely versatile process for producing a wide range of simple or complex plastic
parts - economically and with a good finish.
Injection molding's efficiency varies by the number of parts you plan to produce.
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Plastic Injection Molding Design Guidelines :-
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Use an approximately uniform wall thickness throughout your design.
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Plastic Injection Molding
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Keep walls thin - typically between 1/32" and 1/10". This allows for proper cooling and reduces cost by
minimizing use of material. Thin walls also reduce problems with material shrinkage. Although some
unevenness will occur due to shrinkage, walls as thick as 1/5" can be used.
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To strengthen parts, instead of using thicker walls, use additional structures such as ribs. When using a rib,
make the rib about half the main wall thickness. Use fillets at the base of ribs.
Plastic Injection Molding
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Round corners and edges wherever possible.
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For easy release of the part from the mold, add a slight taper to the sides (typically ~ 2 deg)
Plastic Injection Molding
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Avoid the above incorrect shapes that are impossible to remove from the mold.
Drawing dimensions should be of the final part - material shrinkage will automatically be considered in the
design of the mold.
Where walls meet at a 90 angle, round inside and outside to at least .05" radius - sharper outside corners
can create molding problems and sharper inside corners will increase tooling cost.
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Possible shapes
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A wide variety of simple or complex 2D or 3D shapes.
Plastic Injection Molding
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Injection molded parts are widely used in:
aerospace, automotive, engineering prototypes, hydraulics and pneumatics, packaging,
architecture, fiber optics, medical and dental, power tools, agriculture, electronics, measuring
instruments, telecommunication, caps, valves, toys, levers, cams, etc.
Example parts
Plastic Injection Molding
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Advantages of Plastic Injection Molding :-
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Low cost and good repeatability.
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Extremely cost efficient in larger quantities.
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Specifications for Plastic Injection Molding
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Material - ABS, acrylic, polycarbonate, high density polyethylene, acetyl,
polyamide, low density polyethylene, polypropylene, filled and blended plastics.
Alternative machines - Mill 3-Axis (for short runs).
Tooling - custom mold for your design.
Reducing costs - minimize size and material volume, avoid sharp corners on all
features - for example a round post is better than a square post.
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Plastic Injection Molding
Material Selection
Plastic Injection Molding
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