Manufacturing Process
Compression molding
Extrusion
   
Compression/extrusion

In compression moulding, two matched (usually steel) mould halves are mounted in a (normally hydraulic) press with movement limited to the axis normal to the plane of the mould.  This process tends to be associated with a variety of materials, including (but not a limited list):

  • prepreg continuous fibres in epoxy resin
  • prepreg short fibres in polyester resin (sheet moulding compound - SMC)
  • dough moulding compound (SMC)
  • bulk moulding compound (BMC)
  • prepreg short fibre in a thermoplastic matrix (glass mat thermoplastics - GMT)
The moulds may be heated or the composite may be preheated and formed in relatively cool moulds.  A limitation on the process is the uniaxial force applied - as a consequence while horizontal surfaces are subject to compression loads as the component surfaces change to vertical there is little or no component of the force acting to consolidate the material in that plane.  Further near vertical surfaces may be subjected to wrinkling during mould closure.  These issues may be resolved by the use of rubber-block moulding or hydroforming (pressurised liquid contained in a flexible membrane) wholly or partially substituting the male mould half.

 
Fundamentals of Composites Manufacturing: Materials, Methods, and Applications
 
     
 
Extrusion

A thermoplastic process whereby pellets, granules, or powder are melted and forced through a die under pressure to form a given, continuous shape. Typical shapes extruded are flat films and sheets, filaments and fibers, strands for pelletizing, and webs for coating and laminating. Also used for forming composite preformed materials from mixtures of a matrix powder and short fibers suitable for MMCs. Widely used for continuous production of film, sheet, tube, and other profiles; also used in conjunction with blow molding. Thermoplastic or thermoset molding compound is fed from a hopper to a screw and barrel where it is heated to plasticity then forwarded, usually via a rotating screw, through a nozzle possessing the desired cross section. Production lines require input and takeoff equipment that can be complex.

Low tool cost, numerous complex profile shapes possible, very rapid production rates, can apply coatings or jacketing to core materials (such as wire).

Familiar products manufactured by extrusion include: pipes, ingot, guttering, window sills and insulation on wires.


Recommended Books
 
December 1998
describes all aspects of Resin Transfer Moulding (RTM) for aerospace st
Liquid Moulding Technologies: Resin Transfer Moulding, Structural Reaction Injection Moulding, and Related Processing Techniques
   


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