Complex Shape of Chopped-Fiber Composites

[ceramax]

If a precision forming process can be developed to product composites in complex shapes, are there any engineering needs for such a process? The process would use chopped fibers like carbon, ceramic or polymer in up to 2" long, to form fiber reinforced polymer, metal or ceramic matrix composites.

Thanks very much,

 

[SWComposites]

What you are describing is bascially "bulk molding compound" which has been around for a long time and has been used for lots of parts. Aerospace grade "chopped prepreg" molding compounds are now being marketed by several material vendors and are being used for complex shape parts.

 

[ceramax]

Could you describe to me some details about "bulk molding compound", such as fiber length, and volume content?

Thanx.

 

[SWComposites]

Do a Google search on "bulk molding compound" and you will get links to a bunch of vendors that sell various products. Fiber lengths vary from about 0.25" to 3.0" and fiber volume contents in the range of 40-60%, depending on the material.

 

[ceramax]

Thanks, SWComposites. I did the search. It seems that the "bulk molding compound" means that a mixture of fiberglass and polyester and/or vinyl ester undergoes irreversible crosslinking (thermoset) during the molding process, converting it to an infusible, solid state.

My question is why DOE still is calling for proposals to develop a manufacture process for fiber-reinforced plastics for lightweight auto structural application. Does the BCM has some limitations like curing time, high viscosity for high fiber loading or other issues. Is there another method in developing call as "P3" process?

 

[CompositeGeek]

Ceramax,
There is a process called the P4 process developed by Owens-Corning for manufacturing fiber preforms rapidly and combining it with RTM (resin transfer molding). Check out the National Composite Center in Dayton Ohio for details. They manufacture a variety of products including Sonoma Truck inner bed liners. They claim remarkable fiber volume values for this technique and the ability to orient chop fiber direction similar to woven fabric. I have participated in some testing and the claims are somewhat overstated IMHO, but not completely unfounded.

DOE is looking at these methods to improve speed of production, reduce vehicle weight, waste reductions etc.

Composites and Airplanes - what was I thinking?

There are gremlins in the autoclave!

 

[gwolf]

High strength plastics are remarkably good now, check out "Torlon".