Resistance welding has been an established joining technology for more than 40 years and has been used in the battery industry for almost as long. Since then, a steady stream of advances in resistance welding systems has given users significantly improved capabilities to control various aspects of the process.

For example, the introduction of DC inverter power supplies with basic closed-loop electrical modes provides the ability to accommodate changes in the secondary circuit (the electrical loop from cable connection on the negative side of the power supply or transformer, through the weld head and the parts returning to the positive side) to specifically address part resistance.

Also, polarity switching for capacitance discharge supplies to enable balancing of the weld nuggets, and more recently, the addition of displacement and electrode force measurement, provide manufacturers with more tools to ensure weld quality.

Similar to resistance welding, tungsten inert-gas (TIG) welding, also known as gas tungsten arc welding, has been used in manufacturing for many decades and has traditionally been used for the more challenging welding applications for nonferrous materials.

Advances in high-frequency power supplies increased low-current control and arc stability, enabling much finer welding. This process became known as micro-TIG, a generally non-contact process that offers excellent copper joining while offering a fairly relaxed process window with respect to part fit-up and positioning tolerances of the electrode to the parts.

Laser welding is a newer technology, introduced in the manufacturing marketplace in the mid-1980s. As laser technology has matured, and the awareness of its benefits spread, it has become an established process. Today it is simply another tool in the manufacturing engineer’s toolbox to be used and implemented as needed.

The laser provides a high-intensity light source that can be focused down to very small diameters (0.01-inch). The concentration of light energy is sufficient to melt metals rapidly, forming an instantaneous weld nugget. The process is non-contact, has no consumables, offers instantaneous welding once positioned at the weld point location, provides sufficient control over the process to size the weld nugget according to requirements, and provides a number of implementation methods that can be geared toward individual manufacturing requirements. Laser welding makes it possible to join many materials and material combinations, can weld thick parts, and has no limitation on proximity of weld spots.

There are two types of laser that provide solutions for battery applications: pulsed Nd:YAG and fiber. Both of these lasers offer different joining characteristics that can be selected as appropriate.

Laser welding is excellent for seam sealing, resulting in high-speed, high-quality seams in both steel and aluminum. Laser welding offers significant advantages over mechanical clinching and adhesive methods based on joint reliability, joining speed, and ease of manufacturing. As laser welding is an extremely efficient joining process, the heat input into the battery is minimized. Figure 1 shows a few examples of seam welding of aluminum cans, including a weld cross section, and ball and plug sealing application examples.