Automated Dynamics is currently developing an ultrasonic additive manufacturing (UAM) capability. UAM is a process where layers of tape are bonded together using high frequency vibrations to form a structure. What differentiates Automated Dynamics' process from traditional ultrasonic welding methods is that the welding horn rotates to allow for continuous processing. This UAM process has primarily been used for welding metal foils. The process uses an ultrasonic transducer to vibrate the welding horn as it is placing the tape. The horn also acts as a compaction roller, applying a normal (perpendicular) force to the tape. The surface of the horn is textured, which allows it to grip the surface of the tape and transfer the vibrational energy to the substrate. The material is bonded together in the solid state without requiring molten temperatures at the interface.

Figure 1: Ultrasonic Additive Manufacturing welding system [1]

Automated Dynamics is using this technology to develop a process for ultrasonic consolidation of metal matrix composite (MMC) prepreg tapes. This ultrasonic system has been integrated into a processing head on a research workcell (see Figure #3 below), with the capability of being transferred to a full-scale workcell. Initial trials have shown the feasibility for processing the MMC tape. The MMC used here is aluminum reinforced with ceramic fibers (Al/Al2O3). The ceramic fibers offer great strength and stiffness advantages over unreinforced metals as illustrated in figure #2 below.

Figure 2 - MMC Specific Strength & Stiffness [2]

Figure 3: Ultrasonic processing head installed on a research workcell at Automated Dynamics.

Ultrasonic welding with a stationary horn is widely used for welding plastics. It has also been used for composite structures by tacking the pre-form together, which is subsequently post-processed in an autoclave to consolidate the part. However, much of the work performed by Automated Dynamics on UAM with MMCs is directly applicable to in-situ consolidation with polymer matrix composites (PMC). This in-situ process would not require any post-consolidation steps, offering a significantly simpler manufacturing process.

[1] Graff, K.F., "Ultrasonic Additive Manufacturing," ASM Handbook, Vol.6A, Welding Fundamentals and Processes (2011).
[2] Miracle, Daniel B., Aeronautical Applications of Metal-Matrix Composites, ARL, http://www.ml.afrl.af.mil/mcrg/pubs/man05.pdf