Fiber reinforced polymersCopyright: KEmikro
Fiber reinforced polymer (FRP) is employed in a growing field of applications, especially for cars and airplanes. The reason for this is that FRP achieve large stability and low weight. However, the fabrication of FRP up to now is comparatively time consuming and, therefore, also expensive.
In the future, a solution of this problem could become the fabrication of FRP by ultrasonic welding . By this process so-called organo sheets are fabricated from carbon fiber reinforced polymers (see the adjacent figure). In a single step, such a composite material is fabricated with a cycle time of a few seconds. For fabrication, not much more is required than an ultrasonic welding machine commercially available for some 10,000 € and as expendable materials the matrix material in form of polymer foil and the fibers.Copyright: KEmikro
For fabrication, the fibers are placed between foils from thermoplastic polymer onto the anvil of an ultrasonic welding machine. In the adjacent figure, there are shown only two foils and one layer of fibers. However, up to 13 fiber layers have already successfully employed in a single fabrication step. The sonotrode of the ultrasonic welding machine presses the stack of foils and fibers onto the anvil and generates ultrasonic vibrations. The vibrations result in friction between fibers and polymer and the heat, generated this way, softens the polymer flowing around and enclosing the fibers. After switching off of the ultrasound, the pressure is retained until the polymer is hardened around the fibers to the desired composite material.
Up to now a filling degree of 39 % and a strength of 500 MPa have been achieved with carbon fibers and a matrix from polyamide 6 (PA6).
In the adjacent video there is show the continuous fabrication of CFRP by ultrasonic welding. It is desirable to develop larger ultrasonic welding machines allowing the quick production of wider samples.
 A . Gomer, W. Zou, N. Grigat, J. Sackmann, W.K. Schomburg, “Fabrication of Fiber Reinforced Plastics by Ultrasonic Welding”, J. Compos. Sci. 2 (2018) 56 - 69, doi: 10.3390/jcs2030056