Overview of Composite Processes 120

This class covers the basic methods for processing composites, as well as some of the materials used for these processes.

  • Difficulty Beginner

  • Format Online

  • Number of Lessons 16

  • Language English


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Course Outline
  • Objectives
  • Processing Composites
  • Bulk Molding Compound
  • BMC Processing, Viscosity, and Storage
  • Sheet Molding Compound
  • Preforms
  • Prepregs
  • Lay-up and Spray-up Molding
  • Vacuum Bag and Autoclave Processing
  • Compression Molding
  • Resin Transfer Molding
  • Injection Molding
  • Reaction Injection Molding
  • Filament Winding
  • Pultrusion
  • Summary
  • Describe the basic process for making composites.
  • Describe bulk molding compound.
  • Describe BMC processing, viscosity, and storage.
  • Describe sheet molding compound.
  • Describe preforms.
  • Describe prepregs.
  • Distinguish between lay-up molding and spray-up molding.
  • Distinguish between vacuum bag processing and autoclave processing.
  • Describe compression molding.
  • Describe resin transfer molding.
  • Describe injection molding.
  • Describe reaction injection molding.
  • Describe filament winding.
  • Describe pultrusion.
Vocabulary Term


A pressure vessel that promotes faster curing through a combination of vacuum and heat.


The foundation of a compression mold that supports all the other machine components.


The part of a vacuum bagging system that absorbs excess resin.


The part of a vacuum bagging system that allows air circulation throughout the assembly.

bulk molding compound

BMC. A molding compound that combines a resin, initiator, filler, and reinforcement into a sticky dough-like material.


Placed into a mold. A charge is a piece of molding compound, and placing the compound in the mold is referred to as charging the mold.

chopped fiber

Discontinuous pieces of fiber that have been cut into lengths of 1-3 in. (2.5 to 7.6 cm).

chopper gun

The part of a spraying device that chops continuous strands of fiber so that they may be sprayed on to a surface.

closed mold

A two-sided mold.


A material made by combining a binding resin with small filaments of solid material. Composites have the strength of metal, the light weight of plastic, and the rigidity of ceramics.

compression assembly

The large, upper section of the compression press that holds the male die half. The compression assembly moves up and down, allowing the male die half to shape the plastic material on the female die half.

compression molding

A molding process during which resin is placed between two dies of a mold and subjected to pressure and heat to create a finished part.

compression press

Compression mold. A type of closed mold in which reinforcement is saturated with resin and treated with pressure and heat to form a part.

continuous fiber

A long fiber that covers the entire dimension of a part without a break or interruption. Continuous fibers are used in mat and cloth reinforcements.


A rack upon which spools of fiber are mounted on a filament winding machine.


The development of primary bonds that form between polymer molecules. Thermosets are heavily cross-linked, while thermoplastics are not cross-linked, or they are cross-linked to a weaker degree.

daylight opening

The farthest space between the base and the compression assembly on a compression press.


The process of removing air, usually through compression, from a composite laminate or prepreg. Debulking increases the density of the composite part.

extruder screw

A long screw that turns inside the barrel of the extruder machine. The extruder screw heats and mixes the resin.


A sheet of material created by weaving fibers together.

feed zone

A section of the injection screw that moves resin into the barrel.


A reinforcing material whose length is greater than its height or width. Fibers are larger than whiskers or particles.


Reinforcement material made from extremely fine strands of glass. Fiberglass is the most commonly used composite reinforcement.

filament winding

A process during which strands of fiber are soaked in resin and wound around a core in the desired pattern.


A solid material, such as talc or limestone, that is ground to a fine powder and added to the resin. The filler thickens the resin and reduces its overall cost.


Chemically inactive or having a limited ability to form chemical reactions.


An ingredient used to facilitate chemical reactions.

injection molding

A molding process during which resin is heated in a barrel and then injected into a mold by a reciprocating screw. The resin then cools in the mold and is ejected as a solid part.

injection screw

A device in the injection molding machine that melts, mixes, and moves the molten resin through the machine. The injection screw is in the barrel.

lay-up molding

A manual molding process during which reinforcement in the form of a fabric or a mat is positioned into the mold and saturated with a resin.

liquid molding

The general term for a variety of composite processing technologies in which resin is injected into a mold containing a dry fiber preform. Also known as resin infusion molding.


The core around which resin-impregnated fibers are wound to create a part. Mandrels are used in filament winding.


A pipe or channel used to move fluids or gases.


A sheet of material covered with fiber reinforcements. Reinforcements can be discontinuous (chopped) or continuous.


The material that binds together the reinforcing fibers of a composite. The matrix is usually a viscous material that hardens to give shape to the composite part and to protect the fibers from damage.

metering zone

A section of the injection screw in which resin is pumped to the mold area to be formed.

molding compound

A type of ready-made composite in which the matrix and reinforcement have already been combined. Molding compound is available in bulk form and sheet form.


An inert gas used in autoclaves to prevent oxidation during the curing cycle.

open mold

A single-sided mold.


A material's chemical reaction with oxygen. Oxidation causes rust and tarnish to form on metal surfaces.


An aligning device on a filament winding machine. The payoff guides fibers as they are pulled onto the mandrel.


A pump that pushes resin through a cylinder into the mold.


A type of plastic that is often chemically complex. Polyurethane is used for padding and insulation in furniture, clothing, and packaging, and in the manufacture of resins for adhesives, elastomers, and fillers.


A tough but flexible fiberglass structure that is roughly the same shape as the final product. Resin must be poured over the preform in order to create a composite.


A ready-to-mold sheet of fiber reinforcement that has been preimpregnated with resin.

pressurized injection

A process during which resin is added to a closed mold via a pump plunger.


A molding process in which heated resin cures as it is pulled through a die. Pultrusion is a variation of the extrusion process, during which resin is pushed through a die.

reaction injection molding

RIM. A type of injection molding in which the matrix and reinforcement are mixed together and injected into the mold at the same time.


The part of the composite that provides strength, stiffness, and the ability to carry a load. In manufacturing, fibers are the most commonly used reinforcement.


A substance made from either synthetic or natural polymers and used for composite matrices. In essence, a resin is a polymer that has not been processed into its final form.

resin infusion molding

The general term for a variety of composite processing technologies in which resin is injected into a mold containing a dry fiber preform. Also known as liquid molding.

resin transfer molding

RTM. A type of liquid molding in which resin held in a separate transfer chamber is added to the mold through pressurized injection. RTM is the most commonly used liquid molding process.


The part of a vacuum bagging system that adheres to the vacuum bag and creates an airtight assembly.

Seemans composite resin infusion molding process

SCRIMP. A patented process during which a series of manifolds distributes resin quickly and evenly over a preform with vacuum assistance. SCRIMP is used for extremely large parts.

sheet molding compound

SMC. A rolled-up sheet in which the ingredients are not mixed together all at once. Instead, a pre-mixed, pre-initiated paste of resin and filler is applied to a moving sheet of film onto which strands of fiberglass are applied.


A cylindrical device used for storing, winding, and unwinding fiber.

spray-up molding

A manual molding process during which an operator uses a spray machine to simultaneously apply resin and chopped fiberglass strands to an open mold.

structural reaction injection molding

SRIM. A type of injection molding in which thermoset resin is injected into a preform and subjected to pressure and heat until it cures.


A polymer in which the molecules are not cross-linked, or they are cross-linked to a weaker degree. A thermoplastic polymer can be reshaped or reformed by reheating the polymer.


A polymer that cannot be remelted or reformed once it has cured, due to a molecular process called cross-linking that occurs during curing.

transition zone

The section of the injection screw around which resin is melted.

vacuum bag

The part of a vacuum bagging system that forms an airtight seal over the entire assembly.

vacuum bagging

A type of compression molding in which a bag is placed over the mold and the vacuum compresses the bag and squeezes out any air or excess resin.

vacuum-assisted injection

A process during which resin is added to a closed mold and a vacuum is activated to aid in resin distribution.


A measure of a fluid's thickness, stickiness, or resistance to flow. When molding parts from composites, the resin must have the proper viscosity.