Compression molding is a process that molds material into a confined shape by applying pressure and usually heat. The process involves placing a charge in a mold cavity, closing the mold, applying pressure to squeeze the material and fill the cavity, and heating under pressure to cure the material. There are two main stages - plastication where the material is compressed and heated, and flow once the yield stress is exceeded allowing the mold to fill. Parameters like material quantity, pressure, temperature and cure time must be controlled. Common applications include dinnerware, buttons, and automotive parts.

1. Compression Molding
Neslihan Yağmur
11/12/2012
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2. Compression Molding
Process
The process of molding a material in
a confined shape by applying
pressure and usually heat.
Compression molding process is followed
by two step first one preheating and
pressurizing.
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3. Process Description
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4. Process Description
Charge 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.
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5. Process Description
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6. Stages in Compression molding
cycle
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7. Stages in Compression molding
cycle
The various stages of the
compression molding cycle time can
be represented as a function of the
force required to close the old at a
constant rate.
In the “plastication” stage the force
increases rapidly as the polymer
feed is compressed and heated.
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8. Stages in Compression molding
cycle
The second stage flow commences,
once the yield stress of the
elastomer is exceeded.
tc is the point at which the mold
fills and compression of the melt
occurs.
Mold filling the majority of chemical
reaction should take place after tc.
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9. Parameters
1.The quantity of molding material
2.Pressure of the molding process
Range of pressure 2000-3000 psi(13.8-20.7 MPa)
3.Mold temperature
Temperature range 300ºF to 375ºF (149⁰C- 191⁰C)
4.Cure time variables.
The period required to harden thermosetting material to partial and
complete polymerization is called cure time
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10. Types of compression molding
• Sheet molding compound(SMC)
Sheet molding process involves placing a
reinforcement, such as a glass mat, between
sandwiching layers of a thermoplastic and
heating the materials to produce a single sheet
of material.
• Bulk molding compound(BMC)
Bulk molding compounds by producing a billet
of molten material that is placed into a
compression molding press which molds the
molten material into a part.
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11. Materials used in this process
• Thermosetting polymers
• Fiber reinforced composite
• Thermoplastic:
-Ultra High Molecular Weight Polyethylene
(UHMWPE)
- Long Fiber reinforced Thermoplastics
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12. Material properties affected by the
process
Density
Strength
Anisotropic property (fiber orientation)
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13. Advantages
Low cost
Uniform density
Uniform shrinkage due to uniform flow
Improved impact strength
Dimensional accuracy
Internal stress and warping are minimized
Short cycle time
High volume production
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14. Disadvantages
• Curing time large
• Uneven parting lines present
• Scrap cannot be reprocessed
• High initial capital investment
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15. Applications & products
• Dinnerware
• Buttons
• Knobs
• Appliance Housings
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16. Applications & products
• Radio Cases
• Automotive
• ash trays & electrical parts
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17. References
Polymer Processing Fundamentals, A.
Tim, Carl Hanser Verlag, Munich, 1998
Effect of Molding Parameter on
Compression Molded Sheet Molding
Compounds Part, Jin-Ho Jeong, Journal
of Materials Processing , 1997
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