Ultrasonic Welding Used For Cadillac ELR’s Battery Packs

How well the batteries of an EV are assembled and built is key to the reliability of any electric vehicle.

With this in mind, General Motors (GM) chose ultrasonic welding, a high-tech manufacturing process used in the aerospace and medical industries, to help ensure high quality for the batteries of the new Cadillac ELR extended-range electric luxury coupe that goes on sale in North America in early 2014.

Ultrasonic welding’s key advantage is exceptional and predictable quality and performance from one battery pack to the next.

GM said that every ELR battery, for example, has close to 200 ultrasonic welds. Each is required to meet stringent quality requirements, enabling Cadillac to offer an eight-year/100,000-mile battery system warranty.

For the company, short cycle times, low capital costs and manufacturing flexibility through the use of automation are other advantages of ultrasonic welding.

“Ultrasonic welding is a far superior joining technology in applications where it can be deployed,” said Jay Baron, president and CEO of the Center for Automotive Research in Ann Arbor, Mich. “Cadillac’s innovative process will produce batteries with superior quality compared with traditional methods – and do it more efficiently. This is one example of technology development that is becoming pervasive in today’s world class vehicles.”

General Motors’ Brownstown Battery Assembly plant near Detroit, uses ultrasonic welding to join metal electrode tabs on the ELR’s advanced 16.5-kilowatt-hour lithium-ion battery system, and does it with a proprietary quality monitoring process. Brownstown uses an automated system to execute millions of these welds each year.

GM said ultrasonic welding uses specialized tools called an anvil and horn to apply rapid mechanical vibrations to the battery’s copper and aluminum electrodes. This creates heat through friction, resulting in a weld that does not require melting-point temperatures or joining material such as adhesives, soldering or fasteners.

An integrated camera vision system is used to shoot a reference image of the weld area prior to the operation to achieve pinpoint accuracy. Quality operators check electrode tabs before and after welding, and the system monitors dozens of signal processing features during each weld.

The battery-specific welding process is a result of collaboration among General Motors’ Manufacturing Systems Research Lab and Advanced Propulsion Center and the Brownstown plant.

GM declared it first applied the process on the Chevrolet Volt – its first extended-range electric vehicle – and further refined it for ELR.

The powertrain is largely based on the Volt's plug-in "extended-range electric" system.

The powertrain is largely based on the Volt’s plug-in “extended-range electric” system.

“This effort is an outstanding example of teamwork between research and manufacturing engineering,” said Catherine Clegg, GM vice president of Global Manufacturing Engineering. “It has helped integrate the use of highly technical, complex technology into a sustainable manufacturing process, which means we can consistently deliver high-quality batteries to our customers for the Cadillac ELR.”

The ELR’s T-shaped battery pack is located along the centerline of the vehicle, between the front and rear wheels for optimal weight distribution. The 5.5-foot-long (1.6 m), 435-pound (198 kilograms) pack supplies energy to an advanced electric drive unit capable of 295 pound-feet of instant torque (400 Nm) to propel the vehicle.

Cadillac said using only the energy stored in the battery, the ELR will deliver a GM-estimated range of about 35 miles (56 km) of pure electric driving, depending on terrain, driving techniques and temperature.

Charging the ELR’s battery can be done with a 120V electrical outlet or a dedicated 240V charging station. The vehicle can be completely recharged in about 4.5 hours using a 240V outlet, depending on the outside temperature.

The Cadillac ELR will be built at GM’s Detroit-Hamtramck Assembly Plant, one of the few high-volume electric vehicle manufacturing facilities based in the U.S.

The ELR battery pack will be built from cell to pack at Brownstown and shipped to Detroit-Hamtramck for assembly into the vehicle.

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