What composite manufacturing processes are there?
There are a wide variety of processes and technologies used to manufacture FRP composites. Some minimize cost, optimize speed, or achieve the highest possible performance. They include hand lay-up, chopper gun, sheet molding compound, filament winding, pultrusion, resin transfer molding, resin infusion, resin film infusion, pre-preg, vacuum bagging and autoclaving.

HAND LAY-UP

Hand lay-up is the original method employed in manufacturing FRP composites and involves laying dry fiber reinforcement such as chopped strand mat or woven fabric in a mold and 'wetting' this out with resin. 'Stippling' by making short stabbing motions with a brush, or rolling with a 'nip' roller removes air from the fiber. Hand lay-up is an 'open molding' process whereby volatile chemicals such as the styrene in polyester resin exit the laminate into the air. Typically the resin cures under ambient temperature and atmospheric pressure. Hand lay-up often results in relatively weak, heavy laminates with a low Fibre Volume Fraction.

Hand Lay-up Benefits

  • Low tooling cost
  • Low material cost
  • Medium component cost
  • Low capital equipment cost
  • Suitable for use with core materials
  • Compatible with a wide range of resin & fiber types
  • Fiber orientation can be optimized for good mechanical properties

Hand Lay-up Disadvantages

  • Manual manufacturing process
  • High labor cost, labor intensive process
  • Resin control results in heavy laminates
  • Poor presentation quality on rear surface
  • High skill required for consistent tolerances
  • Low viscosity resin limits mechanical properties
  • High skill required for optimized fiber orientation
  • High skill required for high Fiber Volume Fraction
  • Resin shrinkage with commonly used polyester resin
  • Resin control results in thermal & mechanical limitations
  • Commonly used chopped mat limits mechanical properties
  • Low productivity increased by elevated temperature curing
  • Safety: styrene emissions from polyester resin & open molding

   • Click here to see illustration of hand lay-up process

CHOPPER GUN

Designed to speed manufacturing, chopper guns are used to spray a mixture of chopped fiber mixed with resin into a mold. This results in a laminate with very short fibers that are randomly orientated and a very low Fiber Volume Fraction. Similar to hand lay-up, composites manufactured using chopper guns can provide strength but at the expense of excessive weight and high material quantities.

Chopper Gun Benefits

  • Low tooling cost
  • Low material cost
  • Low component cost
  • Low capital equipment cost
  • Suitable for use with core materials
  • Semi-automated manufacturing process
  • Medium productivity increased by elevated temperature cure

Chopper Gun Disadvantages

  • High labor cost, labor-intensive process
  • Poor presentation quality on rear surface
  • Limited to glass fiber roving reinforcement
  • High skill required for consistent tolerances
  • Very short fibers limit mechanical properties
  • Poor resin control results in heavy laminates
  • Low viscosity resin limits mechanical properties
  • Resin shrinkage issues with commonly used polyesters
  • Poor resin control results in thermal and mechanical limits
  • Safety: styrene emissions from polyester resin & open molding

   • Click here to see illustration of chopper gun process

SHEET MOLDING COMPOUND (SMC)

Sheet Molding Compound is a specific form of FRP that is commonly used in the production of removable 'hardtop' automotive convertible roofs and truck body panels. It is composed of preformed material containing reinforcing fiber, resin, catalyst, fillers, thickeners, mold release agents and other ingredients. Similar to the process used to form steel automotive panels, SMC is stamped between two matched metal molds and heated. Unlike most composites SMC enables a degree of mass production necessary to cost-effectively manufacture high production volumes.

SMC Benefits

  • Low labor skill
  • Low labor cost
  • Low component cost
  • High production volumes
  • Automated manufacturing process
  • Good presentation quality on both surfaces
  • Resin control promotes good Fiber Volume Fraction
  • High viscosity resin optimizes mechanical properties
  • Safety: Low emissions due to closed molding process

SMC Disadvantages

  • High tooling cost
  • Medium material cost
  • High capital equipment cost
  • Not suitable for use with core materials
  • Typically limited to glass fiber reinforcement
  • SMC-R uses short fibers that limit mechanical properties
  • SMC-C uses uni-directional fibers that limit isotropic properties

   • Click here to see illustration of SMC process

FILAMENT WINDING

This production process is used to produce round or oval shaped, hollow-section components such as pipes and tanks. Fiber 'tows' are pulled from creels through a resin bath and wound around a rotating mandrel. Fiber orientation is controlled by the speed the mandrel rotates and the angle of the fiber-feeding mechanism. Resin content is controlled by nip rollers.

Benefits of Filament Winding

  • Low labor skill
  • Low labor cost
  • High production volumes
  • Medium component cost
  • Automated manufacturing process
  • Compatible with a wide range of resin & fiber types
  • Resin control promotes good Fiber Volume Fraction
  • Low viscosity resin limits mechanical properties
  • Controlled fiber orientation optimizes mechanical properties
  • Low material cost using fiber tows rather than woven fabrics

Disadvantages of Filament Winding

  • High tooling cost
  • High capital investment in equipment
  • Not suitable for use with core materials
  • Low viscosity resin limits mechanical properties
  • Poor presentation quality on outer surface of laminate
  • Safety: volatile emissions if molding process is not enclosed

   • Click here to see illustration of filament winding process

PULTRUSION

This process is used to produce solid rod and structural profile shapes including channels, angles, beams and hollow sections. It is similar to the extrusion process used to form aluminum and thermoplastics. Fiber tows are pulled from a creel, through a resin bath into forming guides and through a heated die, which impregnates the fiber, controls resin content and cures the laminate. Pultrusion is an automated process that produces high volumes.

Benefits of Pultrusion

  • Low labor skill
  • Low labor cost
  • Medium tooling cost
  • Medium component cost
  • Automated manufacturing process
  • Good presentation quality on all surfaces
  • Compatible with a wide range of resin & fiber types
  • Resin control promotes good Fiber Volume Fraction
  • Low material costs use fiber tows rather than woven fabric
  • High productivity increased by elevated temperature curing
  • Controlled fiber orientation optimizes mechanical properties

Disadvantages of Pultrusion

  • High capital investment in equipment
  • Not suitable for use with core materials
  • Fiber orientation limited to one direction
  • Low viscosity resin limits mechanical properties
  • Limited to relatively simple cross-sectional profiles
  • Safety: volatile emissions if molding process not enclosed

   • Click here to see illustration of pultrusion process

RESIN TRANSFER MOLDING (RTM)

Matched molds corresponding to the upper and lower surfaces of a component are required for this process. Dry reinforcement fibers are placed in one side of the mold, the mold is closed using the second tool and resin is injected into the mold cavity. Once the reinforcement fiber is 'wet out' the inlets are closed and the laminate cures. Resin injection and curing can be at ambient or elevated temperatures, and dry reinforcement fibers can be 'pre-forms' pre-pressed to fit the mold shape. A variation of RTM is Vacuum Assisted Resin Injection (VARI), which uses vacuum opposite the inlet ports to draw the injected resin through the reinforcement fibers.

Resin Transfer Molding Benefits

  • Low material cost
  • Medium labor cost
  • Medium component cost
  • Medium capital equipment cost
  • Semi-automated manufacturing process
  • Good presentation quality on both surfaces
  • Safety: low emissions due to closed molding
  • Compatible with a wide range of resin & fiber types
  • Resin control promotes good Fiber Volume Fraction
  • Fiber orientation can be optimized for good mechanical properties
  • Pressure consolidation promotes high mechanical properties

Resin Transfer Molding Disadvantages

  • High labor skill
  • Not suitable for use with core materials
  • Low viscosity resin limits mechanical properties
  • Low productivity can be increased by elevated temperature curing
  • High tooling cost due to matched molds that withstand high pressure
  • Poor resin control can lead to voids & expensive scrap components

   • Click here to see illustration of resin transfer molding process

VACUUM BAGGING

This process can be applied to a number of manufacturing techniques and optimizes mechanical properties by consolidating the laminate stack to achieve a high Fiber Volume Fraction. Curing laminates under pressure dramatically improves mechanical properties, which is why very high performance composites always use this process, whether by vacuum bag, pressure molding or autoclave. When used with hand lay-up, after plies of reinforcing fiber have been 'wet out' with resin, the laminate stack is enclosed by a plastic (or elastomeric) bag and a vacuum source is applied to remove air from between the bag and the laminate. To facilitate this, breather fabrics help evacuate the air and bleeder fabrics absorb excess resin. Peel ply is sometimes used on the rear of the laminate to create a texture that facilitates bonding of subsequent laminate layers. Vacuum Bagging can also be used with resin infusion processes, resin films and pre-pregs and very cost effectively applies one atmosphere of pressure (approximately 14.7 psi) across the entire rear surface of the laminate. The process can be used with ambient and elevated temperature curing and helps minimize volatile emissions that are a characteristic of open molding techniques.

Vacuum Bagging Benefits

  • Medium tooling cost
  • Medium material costs
  • Medium capital equipment cost
  • Suitable for use with core materials
  • Semi-automated manufacturing process
  • Good presentation quality on rear of laminate
    Resin control promotes good Fiber Volume Fraction
  • Safety: Closed molding reduces volatile emissions
  • Low productivity increased by elevated temperature curing
  • Compatible for use with a wide range of resin & fiber types
  • Fiber orientation can be optimized for good mechanical properties
  • Commonly used with high viscosity resin pre-pregs that promote high mechanical properties

Vacuum Bagging Disadvantages

  • High labor skill
  • High labor cost
  • High component cost when used with epoxy & aramid or carbon fiber

   • Click here to see illustration of vacuum bagging process

OVEN CURING

As all FRP composites benefit from resins that are cured at high temperatures, many production processes can incorporate elevated temperature curing. Oven curing is the most common, and this controlled environment enables programmable processing schedules based on ramped temperature increase, dwell and cool down times. Elevated temperature curing can also be achieved via other techniques including heated molds and heating blankets.

Oven Curing Benefits

  • Low labor cost
  • Low labor skills
  • Low material cost
  • Medium component cost
  • Medium capital equipment cost
  • Automated manufacturing process
  • Medium productivity due to faster cure times
  • Compatible with a wide range of resin & fiber types
  • Suitable for use with temperature tolerant core materials
  • Maximizes thermal & mechanical properties of the resin matrix
  • Safety: enclosure helps restrict transmission of volatile emissions

Oven Curing Disadvantages

  • Not suitable for all production processes

   • Click here to see illustration of oven curing process

RESIN INFUSION

Very similar to RTM, resin infusion includes patented proprietary processes such as SCRIMP, RIFT, VARTM, etc. Dry reinforcing fabrics are added to an open mold and the stack is vacuum bagged. Resin is drawn through the reinforcing fibers by a vacuum source opposite the resin inlet, A non-structural fabric promotes resin distribution and 'wets out' the reinforcing fibers from above.

Resin Infusion Benefits

  • Medium material cost
  • Medium component cost
  • Semi-automated process
  • Medium capital equipment cost
  • Good presentation quality on rear of laminate
  • Safety: Closed molding reduces volatile emissions
  • Compatible with a wide range of resin & fiber types
  • Suitable for use with core materials except honeycomb
  • Vacuum consolidation promotes high mechanical properties
  • Fiber orientation can be optimized  for good mechanical properties
  • Medium tooling cost, however aramid or carbon fiber are often used

Resin Infusion Disadvantages

  • High labor skill
  • High labor cost
  • Low viscosity resin limits mechanical properties
  • Low productivity can be increased by elevated temperature curing
  • Poor resin control can lead to voids and expensive scrap components

   • Click here to see illustration of resin infusion process

PRE-PREG REINFORCEMENT

Pre-pregs are reinforcing fibers or fabrics that have been pre-impregnated with pre-catalyzed resin by a manufacturer. They represent the 'state-of-the-art' in composite materials and are the material of choice in high performance applications from Formula 1 racing cars to advanced military aircraft. Pre-pregs commonly use high performance resins such as epoxy and due to the manufacturing process these are high viscosity, which maximizes the mechanical properties of the resin matrix and the final laminate. The pre-catalyzed resins vary depending on the intended use. For example, tooling Pre-pregs can be Room Temperature Curing (RTC) whereas those intended to produce components require elevated temperature curing, usually between 80 and 180 degrees Celsius. Maximizing the very high performance they provide, most Pre-pregs are also processed under pressure, either via vacuum bagging or autoclave. Because Pre-pregs have a limited shelf life at ambient temperatures all require transport and storage at below-zero temperatures to slow down the catalyzing process.

Pre-Preg Benefits

  • Suitable for use with core materials
  • Safety: High viscosity resin reduces volatile emissions
  • Resin control promotes optimum Fiber Volume Fraction
  • High viscosity resin maximizes mechanical properties
  • Good presentation quality on rear as consolidated under pressure
  • Fiber orientation can be optimized for good mechnical properties
  • Safety: Used with closed molding that reduces volatile emissions
  • Semi-automated production process uses pressure consolidation & heat
  • Universally feature high performance resin, fiber type & reinforcement fabrics

Pre-Preg Disadvantages

  • High labor cost
  • High labor skills
  • High material cost
  • High capital equipment cost
  • High tooling cost as aramid or carbon fiber are frequently used
  • Low productivity can be increased with elevated temperature curing
  • High component cost due to expensive materials and processing equipment

   • Click here to see illustration of pre-preg process

RESIN FILM INFUSION

This process is similar to Resin Transfer and Resin Infusion Molding. Layers of dry reinforcement fiber are laid up in a mold, together with a layer of pre-catalyzed semi-solid resin film. The stack is vacuum bagged and heated in an oven or autoclave so the resin melts, is drawn into the fiber under vacuum, wets it out, and cures.

Resin Film Infusion Benefits

  • Medium component cost
  • Semi-automated process
  • Suitable for use with core materials
  • High viscosity resin maximizes mechanical properties
  • Resin control promotes excellent Fiber Volume Fraction
  • Good presentation quality on rear as consolidated under pressure
  • Fiber orientation can be optimized for good mechanical properties
  • Safety: Low viscosity resin systems reduce volatile emissions
  • Safety: Usually used with closed molding that reduces volatile emissions

Resin Film Infusion Disadvantages

  • High labor skill
  • High labor cost
  • High material cost
  • High capital equipment cost
  • Generally available only with epoxy resin
  • Low productivity increased by elevated temperature curing
  • High tooling cost as aramid and carbon fiber are frequently used

   • Click here to see illustration of resin film infusion process

AUTOCLAVE PROCESSING

Manufacturing very high performance FRP composites relies on the use of an autoclave, a sophisticated pressure vessel that can apply very high pressure and heat to resin and reinforcement fibers. Whereas vacuum bagging very cost-effectively applies one atmosphere of pressure (approximately 14.7 psi) to a laminate stack, autoclaves can apply up to several hundred psi. The very high pressures consolidate the laminate stack, and when used with sophisticated aramid or carbon fiber pre-preg, laminates of very high strength and very low weight result. The extremely high cost of autoclaves restricts their use to producing components for the most demanding applications such as advanced military aircraft and Formula 1 racing cars.

Autoclave Benefits

  • Automated manufacturing process
  • Compatible with a wide range of resin & fiber types
  • High viscosity resins maximize mechanical properties
  • Resin control promotes excellent Fiber Volume Fraction
  • Fiber orientation can be optimized for good mechanical properties
  • Suitable for use with special cores that can withstand high pressures

Autoclave Disadvantages

  • High labor skill
  • High labor cost
  • Very high capital investment cost
  • Safety: Closed molding reduces volatile emissions
  • Very high component cost due to high capital investment
  • Low productivity increased by elevated temperature curing
  • Safety: Low viscosity resin systems reduce volatile emissions
  • High tooling cost as molds must be pressure and heat resistant
  • Good presentation quality on rear as consolidated under pressure
  • High material cost due to use with aramid, carbon & more exotic fibers

....Read More

   • Click here to see illustration of autoclave process

 

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