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C ompression Molding . Jonathan Chodosh , Sherif Madkour , Jesse McGrath. Compression Molding: What?. Is a processing technique that combines forming the product along with simultaneous curing of the resin. High Pressure Higher Temperature Curing Agent. Development.

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c ompression molding

Compression Molding

Jonathan Chodosh, SherifMadkour,

Jesse McGrath

compression molding what
Compression Molding: What?
  • Is a processing technique that combines forming the product along with simultaneous curing of the resin.
  • High Pressure
  • Higher Temperature
  • Curing Agent
development
Development
  • 1909 whenLeo Hendrik Baekeland
      • phenol-formaldehyde resins
  • Patents on a automatic compression machine date back to 1930
  • Development of C.M was hindered by reaction knowledge.
thermosets
Thermosets
  • Heat compression causes an irreversible chemical charge in the plastic which solidifies the part .
  • The plastic won’t soften, so the mold doesn’t need to be cooled.
  • After short interval, the press is opened and the molded part is removed.
  • Any plastic remaining in the mold is removed by compressed air. The operator breaks the flash.
thermoplastic
Thermoplastic
  • Preheated in a dielectric heater.
  • The mold is cooled to a point where the plastic retains enough integrity to be removed from the mold without partial distortion.
  • The same steps used for thermosets are repeated here as well.
advantages
Advantages
  • Molds are inexpensive
  • Labor costs vary
  • Great for large parts
  • Minimum waste
  • Dimensional accuracy
  • Warping and shrinkage minimized
  • Fast cycle(1-5 minutes)
  • High volume output
  • High quality surfaces
  • Complex parts
disadvantages
Disadvantages
  • No delicate pieces
  • Uneven parting lines
  • High initial investment
  • secondary operations (e.g. trimming)
  • Mold depth is limited
  • Product consistency
considerations
Considerations
  • Mold heating
    • Temperature, heating rate and heating method
  • Compression rate
  • Max compression force
  • Curing time
    • How long until part can be removed from mold.
  • Mold cooling rate
  • Mold cycling rate
equations
Equations

T*= (T-T0)/(T0-Tad) = Reduced Temperature

t*= (xt)/(h’)2 =Reduced Time

y*= y/h = distance form slab centerline

T0=Original Temperature

Tad=Adiabatic Temperature

X=Thermal Diffusivity

h’=Heat Transfer Coefficient between. Mold and polymer

h= half thickness of slab.

range of materials
Thermoset

Thermoplastic

  • Bulk molding compound (BMC)
  • Sheet molding compound (SMC)
    • Unidirectional tapes
    • Woven Fabrics
    • Chopped Strands
    • Randomly oriented fabrics
  • Preforms
  • Pellets
  • Sheets
  • Extruded

Elastomers

  • Extruded
Range of Materials
typical products
Typical Products
  • Automotive parts
    • Hoods, bumpers, fenders, spoilers, etc.
  • Medical equipment
    • Caps and plugs to blood separation machines and ultrasound equipment
  • Aerospace
    • Electrical connectors to guided missiles
slide15

http://www.rdmoulds.com/rdmoulds/ma/24%20front%20bumper%20molds.jpghttp://www.rdmoulds.com/rdmoulds/ma/24%20front%20bumper%20molds.jpg

http://www.tqc.co.uk/images/bumper7.jpg

slide16

http://www.compositesworld.com/uploadedimages/Publications/CW/Articles/Internal/hoodHyundai.jpghttp://www.compositesworld.com/uploadedimages/Publications/CW/Articles/Internal/hoodHyundai.jpg

transfer molding
Transfer Molding
  • Hybrid between Injection and Compression molding
  • Cross linking reaction is started prior to placement in the mold
      • Resin is heated and put under pressure
  • “Slushy mix” is then forced into the Mold.
  • This point on Transfer molding follows the Compression molding process.
benefits constraints of t m
Advantages

Disadvantages

  • Rapid production rates
      • Largest Benefit over C.M.
  • Geometrical Accuracy
  • Intricate Parts Possible
  • Expensive molds
  • Expensive equipment
  • Much material loss
  • Size limitations of products
Benefits/Constraints of T.M.
references
References
  • http://composite.about.com/library/glossary/c/bldef-c1203.htm
  • http://twistertechnology.com/Process%20Capabilities.html
  • http://www.me.gatech.edu/jonathan.colton/me4793/compmold.pdf
  • http://www.daprorubber.com/index.aspx
  • http://www.rdmoulds.com/rdmoulds/ma/24%20front%20bumper%20molds.jpg
  • http://www.tqc.co.uk/images/bumper7.jpg
  • http://www.compositesworld.com/uploadedimages/Publications/CW/Articles/Internal/hoodHyundai.jpg
  • http://www.bsu.edu/web/jebutcher/compressionmolding.htm