Fiber Placement Systems

Fiber placement is basically a hybrid of filament winding and tape laying and is a continuous process for fabricating composite shapes, by laying thermoset or thermoplastic preimpregnated tows (in tow or slit tape form) onto a mandrel or tool having concave or convex surfaces. There is no limit to the fiber angle and tows can be added or removed as and when necessary. 

Rber placement head Tow restart rollers Colllmaled fiber band 

There are basically two types of mold release agents—an external release, applied to the mold and an internal release, incorporated in the resin mix. 

It is most important to choose an effective mold release and obviously, the mold must have originally been correctly designed to achieve an effective release, free from porosity. 

When applicable, a release agent should be fully cured before molding. Recently, there has been a trend to use water based products in a move to go green and change from solvent systems. Mold releases can be divided into the following groups  

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Figure 21.80 Processing head for Viper 3000 7-axis fiber placement system. Source Courtesy Cincinnati Machine.

Raytheon Aircraft have designed the Premier I cabin around a sandwich of inner and outer carbon fiber layers around a layer of honeycomb material. The carbon fiber/epoxy tows were applied by a Cincinnati Machine Viper 7-axis fiber placement system, producing a structure 20% lighter than an A1 one (Figure 23.19). 

Fig. 31. Seven axes of motion on fiber-placement system can steer prepreg tow or slit tape around compound-curvature shapes to make highly contoured parts. Courtesy of Cincinnati Machine.

Fig. 32. CNC Viper fiber-placement system lays individual tows on a mandrel, shown here making a helicopter rotor blade spar at Bell Helicopter Textron (Fort Worth, Tex.). Courtesy of Cincinnati Machine and Bell Helicopter.

Another interesting approach to avoid autoclave curing is electron-beam (EB) or E-beam curing, often combined with automated fiber placement (AFP). EB curing activates the cross-linking process of the resin system by... 

One experiment that is now possible would be to use the emission from a single molecule as a light source of sub-nm dimensions for near-field optical microscopy [97]. Of course, this would involve the technical difficulty of placement of the single emitting molecule at the end of a pulled fiber tip or pipette. In all cases, improvements in SNR would be expected to open up a new level of nanoscopic detail and possibly new applications. Because this field is relatively new, the possibilities are only limited at present by the imagination and the persistence of the experimenter and the continuing scientific interest in the properties of single quantum systems in solids. 

The infusion behavior is identical to standard VARTM processes where the vents are placed at the last location of fill. The membrane layer enables any point of the fabric surface to be connected to the vacuum port thus reducing the need for an optimized placement of the venting system. Nevertheless, the post-infusion behavior can be significantly different compared to standard VARTM processing. No resin bleeding occurs as the vent is placed on the impermeable membrane surface. Hence, the pressure behavior and consequently the overall thickness gradient and fiber volume... 

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