Compression molding

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Compression molding

  1. 1. Compression Molding Neslihan Yağmur 11/12/2012 1
  2. 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. 2
  3. 3. Process Description 3
  4. 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. 4
  5. 5. Process Description 5
  6. 6. Stages in Compression molding cycle 6
  7. 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. 7
  8. 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. 8
  9. 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 9
  10. 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. 10
  11. 11. Materials used in this process • Thermosetting polymers • Fiber reinforced composite • Thermoplastic: -Ultra High Molecular Weight Polyethylene (UHMWPE) - Long Fiber reinforced Thermoplastics 11
  12. 12. Material properties affected by the process Density Strength Anisotropic property (fiber orientation) 12
  13. 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 13
  14. 14. Disadvantages • Curing time large • Uneven parting lines present • Scrap cannot be reprocessed • High initial capital investment 14
  15. 15. Applications & products • Dinnerware • Buttons • Knobs • Appliance Housings 15
  16. 16. Applications & products • Radio Cases • Automotive • ash trays & electrical parts 16
  17. 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 17
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