Composite Engineering - Manufacturing Processes

Intro to Terms and Definitions for Manufacturing Fiber Composites

Aug 24, 2009

A composite engineer defines the requirements for various fiber composite manufacturing processes. This intro is focused on basic processes for graphite fiber composites.

Composite engineering requires terminology for manufacturing processes that is unfamiliar to personnel in areas outside of composites manufacturing. Thermoset resins and graphite fibers will be the focus for the introduction to the terms and definitions for fiber composite manufacturing processes.

A cure cycle is typically in reference to a time and temperature requirement for a thermoset resin or plastic. Although both the time and temperature requirement (thermo) will vary for different resins, the result will be a chemically "cross-linked" or hardened (set) resin which is strengthened by a fiber.

Filament Winding and Fiber Placement

Filament winding is an automated process of winding fiber around a mandrel by rotating the mandrel or holding the mandrel stationary and moving a winding head around it. Filament winding can be done with prepreg fiber or for wet winding, dry fiber can be drawn through a resin bath immediately prior to applying the fiber to the mandrel.

Fiber placement is similar to filament winding. One of the major distinguishing factors is the fiber is placed directly on the mandrel with the placement shoe during fiber placement, while the winding head will be some distance away from the mandrel during filament winding.

Some types of Molding with Fibers and Resins

Pultrusion is a process used to create a part with a constant cross section. Fiber is run through a resin bath and then pulled through a die where it is subsequently cured. A typical die may be up to 30 inches in length. The part may cure as it progresses through the die, and may require further curing after exiting the die.

An open mold is a mold which does not have a cover or lid. Typically a prepreg fiber will be layered up by hand and then cured at ambient temperature or in an oven at an elevated temperature. If compression is needed, the mold may be put into an autoclave or vacuum bagged.

An autoclave is a pressure vessel that is used to apply pressure and heat to a part in a mold, during the curing portion of the process. Where pressure is required, a vacuum bag may be placed over an open mold and placed in an autoclave. If the extreme pressure of an autoclave is not required, a vacuum is applied to the sealed vacuum bag to reduce the air pressure around the fiber and resin in the mold. The result is the outside air applies pressure to the bag, and subsequently to the curing part.

Spray-up molding utilizes an open mold. Typically both chopped fiber and two parts of a resin are deposited or sprayed on the open mold at the same time. Depending on the resin, the molded part is then cured at ambient temperature or placed in an oven for a cure at an elevated temperature.

A closed mold is typically a two part mold. Think of a clam shell with the interior defining the form and dimensions of the cured part. A closed mold is used in compression molding, resin transfer molding and other molding processes.

During compression molding a press is utilized to apply pressure to a closed mold.Two halves of a mold are placed in a press, open. Typically a prepreg fiber would be placed in the bottom mold cavity. The press is then heated and pressure applied to the closed mold to acheive the time, temperature and pressure requirements for the molded part.

Resin transfer molding, or RTM, utilizes a closed mold. Typically dry fiber is placed into the mold and the mold is closed and sealed with the exception of the ports. On occasion some prepreg material may be utilized as long as the resins are compatible. Resin is forced into the closed mold until the fiber is completely saturated and the mold is void of air. The part is then cured. VARTM is vacuum assisted resin transfer molding. It is the same process described for RTM, with a vacuum applied to assist moving the resin through the stacked fibers and throughout the mold.

Manufacturing Processes for Fiber Composites

The processes identified are intended to provide general definition to very basic manufacturing operations. There are many more similar processes and variations for manufacturing fiber composite products. The graphite golf shaft manufacturing process may be of interest. There is also a similar overview for graphite fiber composite materials terminology which is focused entirely on fiber.

The copyright of the article Composite Engineering - Manufacturing Processes in Manufacture Engineering is owned by Jake Crum. Permission to republish Composite Engineering - Manufacturing Processes in print or online must be granted by the author in writing.