Chapter 18

Processes Used to Form Composite Materials

Objectives

• Open molding process to form composites.• Closed molding process to form composites.• Tailored forming processes for composites.

Open Molding

• In open molding, the reinforcement is saturated with the matrix resin and laid against the form (mold) that creates the outside finished surface of the part.

• Once the resin and fiber are applied, they are rolled out to remove the trapped air and redistribute surplus resin to areas that are not thoroughly saturated.

• After this part of the process is completed, the composite is allowed to cure.

• One of the big drawbacks of open molding is the emission of styrene, which is a component in the resin.

Infusion Molding or Closed System Molding

• Infusion molding reduces styrene emissions by curing the laminate in a closed system.

• It uses atmospheric pressure to squeeze the resin into the reinforcement fibers, similar to the vacuum bagging process.

• The process requires a mold similar to any open molding process and a flexible covering similar to a vacuum bag.

• After curing, the bag is carefully peeled away and cleaned for reuse.• Prepegs: Fiber reinforcements that are pre saturated with resins. Prepegs

enable manufacturers to closely control resin to fiber ratios and atomization of pollutants (styrene) is practically eliminated.

Resin Transfer Molding (RTM) process

• The major difference between open molding and RTM is the use of an inside mold.

• With RTM the inside surface can also be a finished surface.

• Used for pats such as truck hoods.

Pultrusion

• Pultrusion is also referred to as continuous extrusion.

• In the pultrusion process the matrix and reinforcement materials (generally fibers) are pulled through an impregnator or resin bath.

• A die then squeezes these materials together to form them in a composite.

• It then moves through a curing oven.• Uses include side rails for ladders, construction

panels, and roofing panels.

Filament Winding

• In filament winding a spinning mandrel is covered with a resin coated filament to form a tube shaped product.

• Products such as tubes, drive shafts, underground storage tanks are produced by filament winding.

• Mandrels serve as the molds in both wet and dry winding process. Cardboard or wooden tubes are used.

Summary• In open molding, the reinforcement is saturated with the matrix resin and laid

against the form (mold) that creates the outside finished surface of the part. One of the big drawbacks of open molding is the emission of styrene, which is a component in the resin.

• Infusion molding reduces styrene emissions by curing the laminate in a closed system.

• Prepegs: Fiber reinforcements that are presaturated with resins. Prepegs enable manufacturers to closely control resin to fiber ratios and atomization of pollutants (styrene) is practically eliminated.

• With Resin Transfer Molding (RTM) the inside surface can also be a finished surface. Used for pats such as truck hoods.

• Pultrusion is also referred to as continuous extrusion. Uses include side rails for ladders, construction panels, and roofing panels.

• In filament winding a spinning mandrel is covered with a resin coated filament to form a tube shaped product.

Home Work

• 1. What are prepegs and what are their advantages?

• 2. What is the advantage of resin transfer molding (RTM)? Give an application.

• 3. What is pultrusion? What are some uses for pultrusion?