Determination of Thermal Contact Conductance of Metal Tabs for Battery Ultrasonic Welding Process

With the development of hybrid and electrical vehicles in recent decades, battery pack manufacturing has placed an urgent demand on the proper design of battery assembly and battery joining process such as ultrasonic welding. Knowledge of material thermal properties, especially the thermal contact conductance between metal tabs, is a prerequisite for developing computational model of ultrasonic welding. The existing experimental methods for measuring thermal contact conductance largely rely on the steady-state temperature condition established by two pieces of bulk materials in contact. Those conventional methods can be difficult to be used for the measurement of thin gage materials and coatings. We present a new experimental system specifically designed for thin materials, which is based on transient temperature evolution induced by a pulsed heating. Specimens are uniformly loaded between an optical window and an infrared (IR)-transparent window under desired contact pressure. An intense pulse of flash light is irradiated on one side of the specimens through the optical window and the temporal profile of the temperature on the other side is recorded by an IR camera. A simple and effective data reduction scheme is developed taking advantage of a readily available finite element heat transfer model. Figure 1 plots the measured gap conductance between different materials as a function of contact pressure. The measurement results obtained with the new approach are consistent with those available from open literature. The new approach developed herein is applied to study the effects of surface condition and bulk property variations on the thermal contact conductance of materials commonly used in battery tab joining.

Fig.1 Pressure-dependent thermal contact conductance at various material contact interfaces