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Development of Sonotrode with Replaceable Knurl Pad for Use in Ultrasonic Welding

October 19, 2020

According to a report recently published by Fortune Business Insights,1 market demand for vehicle electrification was estimated at 8.6 million units in 2018. This market is projected to exhibit a compound annual growth rate of 21.1% in the forecast period, 2019-2026 and reach 40.6 million units by 2026. A big part of this market is the manufacturing of lithium-ion batteries for electric vehicles which requires a significant amount of welding.

Ultrasonic metal welding (UMW) is a primary welding process for the manufacture of lithium-ion batteries. This solid-state technology applies generated ultrasonic vibrations by transducer through sonotrode to the material and causes shearing of asperities of the materials to bond them together.

UMW offers a lot of advantages including reduction of welding time and production cost, as well as a higher quality bond than traditional welding methods. One downside, however, is cost. When knurl pads wear down, a complete replacement of the sonotrode is required. A new sonotrode can cost $2k to $5k depending on the design. Typical heat-treated tool steel sonotrodes (Figure 1a) produce approximately 70,000 welds in UMW of copper before needing to be replaced. A single welding machine in a high-volume lithium battery manufacturing facility may run 10,000 welds per day. Considering that a typical facility has eight or more lines, rough estimates show a $0.5M-$2M annual sonotrode cost per battery manufacturing facility.

Therefore, developing sonotrodes with replaceable knurl pad from wear resistant material (Figure 1b) could be very cost-effective and has the potential to cut tooling costs by 50-75%. A bimetal sonotrode not only could improve the life of sonotrode but would also reduce the fabrication cost because the whole sonotrode does not have to be replaced.

EWI’s capabilities in using FEA for the design and fabrication of ultrasonic tooling for high power ultrasonic systems have enabled it to invest on this concept. Updates on this project will be available later this year.

If you are interested in learning more about EWI’s experience and capabilities in  tool design for ultrasonic application, please contact Amin Moghaddas, Project Engineer, at [email protected].

1. https://www.fortunebusinessinsights.com/industry-reports/electric-vehicle-market-101678