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Emilian Popa Injection Molding Design Guide Manual 2012

Compression and Transfer Molding

Compression Molding

Compression Molding

- Change is placed in cavity of matched mold in the open position

- Mold is closed by bring the two halves together.

- Pressure is exerted to squeeze the resin so that it fills the mold cavity

- While under pressure the mold is heated which cures the resin

o Thermosets

Compression Molding

- Mold closure types- Flash

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Compression Molding

- Standard thermosets of various types- Molding compounds (mixtures of materials)

o

Thermoset resin (30%)o Reinforcement fibers (10%)

o Fillers (60%0

- Bulk Molding Compound (BMC)- Sheet Molding Compound (SMC)

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Compression Molded Parts

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SMC Equipment

Sheet Molding Compound Compression Molding

- Change is made up from thermoset materials

- Charge is rolled flat

- Multiple layers of SMC can be used in a mold- Longer fibers than BMC

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Compression Molding

- Compression molded parts

o Total force needed per part is determined by:

Projected area of the part (A)

Required cavity pressure for the resin (PA)

Pressure factor that accounts for depth ()

Depth in excess of the minimum amount (de)

Compression Molding

- Compression molding machineso Total force that can be exerted is called:

Press capacity

Machine rating

Machine size

Rated in Newtons or Tons

o Determined by the area of the hydraulic ram and the hydraulic pressure in the line.

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Compression Molding vs Injection Molding

Transfer Molding

- Mixed resin is placed in the transfer chamber- Resin is heated to liquid state

- Plunger presses liquid resin through sprue and runner system to mold cavities.

- Mold is heated- After resin is cured, parts are removed

Transfer Molding

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Product Considerations

- Practically all thermosets can be compression or transfer molded

o Liquids

o Pastes

Liquid resin with filler

o Doughs

Pastes with reinforcement

o Granules

B-staged resin (phenolics)

o Preforms

Granules pressed into a pre-measured shape for easier handling

Cold Forming, Sintering and Ram Extrusion

- Used where heat processing is difficult or impossible

- High pressures- Lower temperatures

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