TABLE OF CONTENTS In the late 1970s, Hercules Aerospace Co. (now Alliant Techsystems) developed the fiber placement process. Shown conceptually in Fig. 7.23, it is a hybrid between filament winding and tape laying. A fiber placement, or tow placement, machine allows individual tows of prepreg to be placed by the head. The tension on the individual tows normally ranges from 0 up to about 2 lb. Therefore, true 0 (longitudinal) plies pose no problems. In addition, a typical fiber placement machine (Fig. 7.24) contains either 12, 24, or 32 individual tows that may be individually cut and then added back in during the placement process. Since the tow width normally ranges from 0.125 to 0.182 in., bands as wide as 1.50 5.824 in. can be applied depending on whether a 12 or 32 tow head is used. The adjustable tension employed during this process also allows the machine to lay tows into concave contours, limited only by the diameter of the roller mechanism. This allows complicated ply shapes, similar to those that can be obtained by hand lay-up. In addition, the head (Fig. 7.25) contains a compliant compaction roller that applies pressure in the range of 10 400 lb during the process, effectively debulking the laminate during lay-up. Advanced fiber placement heads also contain heating and cooling capability. Cooling is used to decrease the towpreg tack during cutting, clamping, and restarting processes, while heating can be used to increase the tack and compaction during lay-down. For the current generation of fiber placement...
