Quatro Composites: the Carbon Composite Specialists!
Quatro Composite Process Capabilities: Compression Molding, Bladder Molding, Deflashing, Machining, Painting, and Finishing. From Start to finish, the Process Development used by Quatro Composites to manufacture parts for customers. The Quatro Composites Products Gallery: Parts for the Medical, Audio Electronics, Aerospace, and Automotive Industries. Find a Quatro Composites Sales Representative Here!
View Current Career Opportunities with Quatro Composites Today! Quatro Composites Facilities in Orange City, Iowa and Poway, California. Submit Questions or Inquiries to Quatro Composites Here. Composites 101: A Basic Reference to Carbon Composite Material Properties and Molding Procedures. Quatro Composites' History, Mission and Vision: a Path to Success.
Process Overview: Carbon Composites Molding Essentials
  • Prepreg Molding
    • Bladder Molding
    • Compression Molding
    • Autoclave/ Vacuum Bag
    • Mandrel Wrapping
  • Wet Molding
    • Wet Layup
    • Chopper Gun
    • Filament Winding
    • Pultrusion
    • RTM & VARTM
Composite Molding

There are many ways to build a composite part. The following list describes some of the most common methods.

It should be noted that Quatro has intentionally decided to focus efforts in Bladder Molding and Compression molding. These processes are believed to generally offer the best cost-to-performance results.

1. Prepreg Molding

A. Bladder Molding

Individual sheets of prepreg material are laid -up and placed in a female-style mold along with a balloon-like bladder. The mold is closed and placed in a heated press. Finally, the bladder is pressurized forcing the layers of material against the mold walls. The part is cured and removed from the hot mold.

  • Closed molding process
  • Ideal for complex hollow shapes
  • O.D. is "tooled" surface, I.D. is "as molded"
  • Great cost-to-performance balance
  • Most tennis racquets are bladder molded
  • Average cure cycle range is 15-60 minutes
  • Relatively difficult to locate competent suppliers due to limited process knowledge in industry.

B. Compression Molding

A "preform" or "charge" is placed into mold cavity. The mold is closed and the material is compacted & cured by a heated press.

  • Closed molding process
  • Typical material forms include prepreg unitape & fabric, Sheet Molding Compound SMC, and Bulk Molding Compound BMC
  • The "tooled surface" can be either be one-side or all-sides
  • Excellent detail
  • Tooling is often more expensive
  • Average cure cycle range is 2-20 minutes
  • A relatively common process for SMC and BMC, but more uncommon for Prepreg

C. Autoclave/ Vacuum Bag

Individual sheets of prepreg material are laid-up and placed in an open mold. The material is covered with release film, bleeder/breather material and a vacuum bag. A vacuum is pulled on part and the entire mold is placed into an autoclave (heated pressure vessel). The part is cured with a continuous vacuum to extract entrapped gasses from laminate.

  • Very common Aerospace process
  • Slow cure cycle, usually 60-120 minutes
  • Good process control
  • Yields an excellent laminate
  • Costly process due to slow speed and high labor content
  • Autoclaves are expensive and typically require government approval for safety

D. Mandrel Wrapping

Sheets of prepreg material are wrapped around a steel or aluminum mandrel. The prepreg material is compacted by nylon or polypropylene cello tape. Parts are typically batch cured by hanging in an oven. After cure the cello and mandrel are removed leaving a hollow carbon tube.

  • Common products include golf shafts, arrow shafts, & commercial tubing
  • Part geometry is limited to mandrel extraction (no negative draft possible)
  • A robust and mature process
  • Relatively easy to locate suppliers
2. Wet Molding

A. Wet Layup

Typically, fabric is placed in an open mold and then hand-saturated with a wet resin. The resin normally cures at room temperature, however may be cured at elevated temperatures based on the mold's resistance to heat.

  • Common parts include: skis, canoes, kayaks, and surfboards
  • Low-cost materials
  • Low-cost tooling
  • Considered a "low-tech" process

B. Chopper Gun

Continuous strand fiberglass is pulled into a hand-held chopper devise which also impinges catalyzed resin (normally polyester). The impregnated chopped glass is "split" onto the mold surface. The amount of build-up is completely operator dependent.

  • Used for low-cost & high-volume parts
  • Low strength
  • Tooling is inexpensive
  • Good for large parts with low dimensional tolerance
  • Common parts include: Showers & bathtubs

C. Filament Winding

Typically, fiber bundles are pulled through a wet bath of resin and wound over a rotating steel mandrel. Parts are cured either room temperature or elevated temperatures. Mandrel is extracted, but may stay with part in some cases.

  • Fiber angles are controlled by machine
  • Is usually semi-automated
  • Common parts include pressure vessels, industrial & commercial tubing
  • Uses low-cost materials
  • Limited performance

D. Pultrusion

Fiber bundles and slit fabrics are pulled through a wet bath of resin and formed into the rough part shape. Saturated material is pulled through a heated closed die and cured while continuously moving through die.

  • Common parts include road-side reflector poles & ladder rails.


Fabrics are placed into a mold and wet resin is infused in-process. Resin is typically pressurized and forced into a cavity which is under vacuum in the RTM process. Resin is entirely pulled into cavity under vacuum in the VARTM process.

  • Either one-sided tooling or matched tooling.
  • Good process when dimensional tolerances are important for two surfaces
  • Requires special consideration to assure thorough stauration of reinforcement material. "Race tracking" is a common problem where some areas are left unsaturated. Difficult to detect without expensive equipment.
  • Common parts include boat hulls and aerospace structures.
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