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Carbon fiber composite materials have taken the engineering world by storm. The combination of great tensile strength and low weight has proven to be of immense usefulness in areas ranging from automotive to aerospace applications. For the manufacture of three-dimensional shapes, techniques such as Automated Fiber Placement use either pure rovings for injection molding or already pre-impregnated towpreg or prepreg materials. Towpreg usually features higher filament numbers and is frequently used in automotive parts, which require particularly great robustness.
The Choice of Materials – Towpreg or pure Rovings?
Depending on the exact manufacturing technique employed, a variety of raw materials may be used:
- Pre-impregnated towpreg or prepreg
- Pure rovings, UD Layer Tapes or pre-confectioned tows for resin injection
- Thermoplastic tapes
Raw carbon or fiberglass rovings or tows consist simply of the respective continuous fibers. Using these materials in the production of three-dimensional parts usually requires the injection of resin – either after the preforming on the mold has been completed or during the actual preforming process. This is because pure non-towpreg filament layers would not be able to be turned into one homogenous composite material during the pressure-heating procedure.
Towpregs have the distinct advantage of already being saturated with epoxy – the “preg” part of the term coming from “impregnated”. This means that the procedure of injecting resin into the finished shape, prior to applying temperature and pressure for curing, is unnecessary. Towpreg composites only need to be heat-treated after they are laid into shape, using the prepreg epoxy to form linked matrices. Usually, this means that the composites are put into specialized ovens directly after the layup and pre-curing procedures have been completed.
Towpreg material is essentially a continuous prepreg composite with a particularly high filament count.
Towpregs typically consist of a combination of carbon, basalt or fiberglass filament and a duroplastic resin as binder material. This means that the epoxy linking matrices, once formed after temperature treatment, cannot be dissolved without destroying the finished product. While thermoplastic epoxy would allow for the finished products to be re-shaped and recycled, the typical industrial areas of towpreg application usually require the finished products to be explicitly immaleable under high temperatures. Automobile parts, for example, need to be pressure and heat resistant, though shock absorber parts may be deliberately fashioned from thermoplastic resins instead.
Using Towpregs with the Compositence System
The patented Compositence fiber placement technique allows for the use of pure rovings as well as prepregs and towpregs. The system places the impregnated fibers automatically according to a predetermined pattern, which can be easily planned with the Compositence software suite. Employing towpregs in this manner has the added benefit of lowered production costs, since towpreg tends to be a more low-cost alternative to prepregs. In combination with the already inherent cost-saving measures of the system, this allows for quick and easy planning as well as production of composite parts while minimizing the cost to a degree not achievable with any other system.
High Production Volumes of complex Shapes
Being pre-impregnated, towpreg allows industrial manufacturers, particularly in the automotive industry, to increase their output by eliminating the resin coating or injecting steps of the production process. In combination with Compositence automated fiber placement machines, the material is thus ideally suited for all applications requiring large volumes of preform output while minimizing the risk of human error.