Plastic Injection Molding

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Plastic Injection Molding

• Process and Materials

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Plastic Injection Molding

• Process -
• 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.

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Plastic Injection Molding

• 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.
• Plastic Injection Molding Design Guidelines -
• Use an approximately uniform wall thickness
  throughout your design.

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Plastic Injection Molding

• 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.
• 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.

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Plastic Injection Molding

• Round corners and edges wherever possible.
• For easy release of the part from the mold, add a
  slight taper to the sides (typically 2 deg)

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Plastic Injection Molding

• 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.
• Possible shapes
• A wide variety of simple or complex 2D or 3D
  shapes.

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Plastic Injection Molding

• 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

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Plastic Injection Molding

• Advantages of Plastic Injection Molding -
• Low cost and good repeatability.
• Extremely cost efficient in larger quantities.
• Specifications for Plastic Injection Molding
• 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
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Plastic Injection Molding
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• Thank You