Composites Manufacturing and Fabricating


Reading Assignment

  • 8.5Composite Materials (review)
  • 14.5 Fabrication of Composite Materials



Introduction to Composites

Composites Manufacturing

Most processes are slow and require considerable amounts of hand labor.

Fabrication of particulate composites

  • Consist of discrete particles dispersed in a ductile, fracture resistant polymer or metal matrix
  • Processed by introducing particles into a liquid melt or slurry
  • Powder metallurgy methods

Fabrication of Laminar Composites

  • Include coatings, protective surfaces, claddings, bimetallics, and laminates
  • Processes are designed to form a high-quality bond between distinct layers
  • If metals are used, composites can be produced by hot or cold roll bonding
    • U.S. coins use this process
  • Explosive bonding bonds layers of metal
    • Pressure wave induces bonding
  • Adhesive bonding
    • Gluing
    • Pressing of unpolymerized resins
  • Sandwich structures
    • Corrugated cardboard
    • Honeycomb structure



Fabrication of Fiber-Reinforced Composites

  • Matrix and fiber reinforcement provide a system that has a combination of properties
  • Fibers can be oriented in a way that optimizes properties
    • The fibers can be continuous or discontinuous
    • Discontinuous fibers can be combined in a matrix to provide a random or preferred orientation
    • Continuous fibers can be aligned in a unidirectional fashion in rods or tapes, woven into fabric layers, wound around a mandrel, or woven into three dimensional shapes

Production of Reinforcing Fibers

  • Many are produce through conventional drawing and extrusion processes
  • Materials that are too brittle, such as Boron, carbon, and silicon carbide, are produces by deformation processes
  • Individual filaments are often bundled
    • Yarn- twisted assemblies of filaments
    • Tows- untwisted assemblies of fibers
    • Rovings- untwisted assemblies of filaments or fibers

Processes Designed to Combine Fibers and a Matrix

  • Casting-type processes
    • Capillary action
    • Vacuum infiltration
    • Pressure casting
    • Centrifugal casting
  • Prepegs- sheets of unidirectional fibers or woven fabric that have been infiltrated with matrix material
  • Mats- sheets of nonwoven randomly oriented fibers in a matrix
    • Mats can be stacked later into a continuous solid matrix
  • Individual filaments can be coated and then assembled
    • Drawing through a molten bath
    • Plasma spraying
    • Vapor deposition
    • Electrodeposition
    • Can be wound around a mandrel with a specified spacing and then used to produce tapes
  • Sheet-molding compounds are composed of chopped fibers and partially cured thermoset resins
  • Bulk-molding compounds are fiber-reinforced, thermoset, molding materials with short fibers distributed randomly

Fabrication of Final Shapes from Fiber-Reinforced Fibers

  • Pultrusion- continuous process that is used to produce long lengths of relatively simple shapes with uniform cross section
    • Fishing poles, golf club shafts, and ski poles


  • Filament Winding
    • Resin coated or resin-impregnated filaments, bundles, or tapes made from fibers of glass, graphite, and boron
      • Produces cylinders, spheres, cones and other containers



Lamination and Lamination-Type Processes

  • Pre-pegs, mats, or tapes are stacked to produce a desired thickness
    • Cured under pressure and heat
  • High strength laminate with a smooth, attractive appearance
  • Laminated materials can be produced as sheets, tubes, or rods


  • Final operation in lamination is curing
    • Typically involves elevated temperatures and/or applied pressure
  • Manufacturing processes that require zero to moderate pressures and low curing temperatures can be used to produce simple curves and contours
    • Boat bodies, automobile panels, aerospace panels, safety helmets, etc.

Lamination Processes

  • Vacuum bag molding process
    • Entire assembly is placed in a nonadhering, flexible bag and the air is evacuated
  • Pressure bag molding
    • A flexible membrane is positioned over the female mold cavity and is pressurized to force the individual plies together
  • Parts may be cured in an autoclave
  • Compression molding
  • Resin-transfer molding
  • Hand lay-up (open mold processing)
    • Successive layers of pliable resin-coated cloth are placed in an open mold and draped over a form
    • Slow and labor intensive process
    • Low tooling costs
    • Large parts can be made as a single unit


  • Additional Processes
    • Spray molding
      • Chopped fibers, fillers, and catalyzed resins are mixed and sprayed onto a mold


  • Sheet stamping
    • Thermoplastic sheets are reinforced with nonwoven fibers and press formed
  • Injection molding
    • Chopped or continuous fibers are placed in a mold and then a resin is injected
  • Braiding, three dimensional knitting, and three-dimensional weaving

Fabrication of Fiber-Reinforced Metal-Matrix Composites

  • Continuous-fiber metal-matrix composites can be produced by filament winding, extrusion and pultrusion
  • Fiber-reinforced sheets can be made by electroplating, plasma spray deposition coating, or vapor deposition of metal onto a fabric or mesh
  • Casting processes
  • Products that use discontinuous fibers can be produced by powder metallurgy or spray-forming
  • Concerns with metal-matrix composites
    • Possibility of reactions between the reinforcements and the matrix during processing at the high melting temperatures
  • Graphite-reinforced aluminum is twice as stiff as steel and 1/3rd to 1/4th the weight
  • Aluminum reinforced with silicon carbide has increased strength as well as hardness, fatigue strength, and elastic modulus
  • Often fail due to flaws in the matrix
  • Fibers or mats may be passed through a slurry mixture that contains the matrix material and then dried, assembled and fired
  • Chemical vapor deposition
  • Chemical vapor infiltration
  • Hot-pressing

Secondary Processing and Finishing of Fiber-Reinforced Composites

  • Most composites can be processed further with conventional equipment
    • Sawed, drilled, routed, tapped, threaded, etc.
  • Composites are not uniform materials, so care should be taken
  • Sharp tools, high speeds, and low feeds are generally required
  • Many of the reinforcing fibers are abrasive and quickly dull the cutting tools

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