Ultrasonic welding uses sound waves and pressure to bond metal foils or sheets at relatively low temperatures. This joining method is often used in the manufacture of lithium ion batteries. Unfortunately, surface contaminants can be inadvertently incorporated into the weld region under this process. These contaminants play a significant role in bond formation, strength, and durability. For example, poor-quality welded bonds have contributed to electrical shorts in lithium ion batteries, leading to expensive and hazardous product failures. Current industrial practices lack the ability to check the quality of an individual weld, especially given the wide variety of materials and size and shape of metal pieces being welded.

Researchers at the Pacific Northwest National Laboratory have developed an approach for monitoring the ultrasonic welding process and characterizing the resultant bonds. Their device measures acoustic signals or vibrations in materials throughout the welding process and analyzes the data in real time to predict or determine the quality of the weld. The results of this nondestructive analysis are expressed as a bond quality index value. The approach can also provide feedback during the welding process so that the welding can be adjusted to prevent defects.

The weld monitoring approach can indicate a true bonding of the metal pieces, a softening or light adhering of one or more of the pieces, or a failed bond. Monitoring and checking quality of every ultrasonic weld can make it easier to reliably weld dissimilar materials, alloys, or composites. Monitoring the process also makes it easier to make complex three-dimensional structures with ultrasonic additive manufacturing. 

APPLICABILITY

PNNL’s ultrasonic weld monitoring approach can be used with a wide variety of metals and their alloys, such as aluminum, copper, gold, iron, magnesium, molybdenum, nickel, platinum, silver, titanium, and tungsten. The approach could be useful for monitoring ultrasonic welds in the electrical, computer, automotive, aerospace, and medical industries. One of the most promising commercial applications may be to monitor the manufacture of lithium ion batteries.