Dispensing in Electrical Vehicle (EV) Battery Assembly
Electrification is an emerging trend that the automotive industry has been grappling with in recent years. We’ve seen major investment from both traditional auto makers and new players in the development and manufacture of electrical vehicles (EV). There are many types of EVs, such as Battery EV (BEV), Plug-in Hybrid EV (PHEV), and Hybrid EV (HEV). But regardless, one of the key elements of any EV is the battery.
Today, most EV batteries have three major levels of assembly: cell, module, and pack (see Fig. 1). The battery cell is the most fundamental unit of each battery. It contains one anode and one cathode pair to provide a specific voltage of electricity through a chemical reaction and to restore chemical energy through the recharge process. The battery module consists of tens to hundreds of individual cells, which are typically connected in parallel, to better accommodate the variation of internal resistance and capacity between cells and to better manage the heat generated by the charge and discharge process of each cell. The battery pack is composed of a few to over ten modules typically connected in series, which are fully enclosed in a metal casing. Due to the large power capacity required, the battery pack can be as big as the vehicle chassis. Because of that, it is very common to see EV designs with the battery pack at the very bottom of the vehicle.
Even though we still see different OEMs with different processes, all OEMs are facing similar challenges in their battery manufacturing. A few examples of these challenges are heat management, weight management, and seal.
Heat is a natural by-product of the battery’s chemical reaction process, and it needs to be carefully managed to avoid fire hazard and extend the battery lifespan. For this reason, a lot of thermal paste (sometimes called heat gel) and gap filler are commonly used in the battery module assembly process to fill every tiny bit of space between the battery cells, and to squeeze out any air which helps quickly dissipate the heat. More thermal paste results in better heat management.
The second challenge is weight management. With a large chassis-sized battery, the heavier it is the more overall weight of the EV and the more power required to move the vehicle. This results in reduced range for equal battery power density. So it is highly desirable to have the proper volume of thermal paste at the precise location on and in between the battery components. However, given the numerous types of process variation manufacturers face (part-to-part variation, dispense material property variation, dispense barrel changes, robot programming, etc.), consistently dispensing the right volume at right location has turned out to be a challenging engineering problem.
The design and manufacture of a battery pack also must endure a rugged work environment. One of the key requirements is water and air seal performance of the pack metal casing assembly. This large seal makes sure no water or fumes can leak through, which is imperative to the performance, functionality, and safety of the battery. For this purpose, a Form In Place Gasket (FIPG) is increasingly chosen as the preferred sealing solution over the traditional pre-formed rubber gasket. This makes sense, because FIPGs are automatically dispensed to save cycle time, and they usually have higher overall performance than traditional gaskets. Plus, due to the excessive size of the sealing perimeter, a traditional rubber gasket would be difficult to design, manufacture and install. In battery pack assembly, the FIPG is typically dispensed on a small flange of the metal casing around the bolt holes before it gets finally bolted down. The challenge is to ensure there is no gap in the bead path, which would compromise sealing performance, while avoiding dispensing too much material which could lead to squeeze-out and blocked bolt holes, which are a significant and often costly manufacturing challenge. It is also seen that some OEMs are even using high-profile inverted V-shaped urethane beads as the sealant to better accommodate the variation of the metal casings. This results in a bigger challenge for dispensing process control.
Coherix Predator3D provides a unique solution to dispensing inspection and process control ensuring the proper volume is applied at the desired location of the part without penalty to production cycle time. Some of the Predator3D’s process control capabilities, like AutoRepair™ and Z-Tracking™ , have broadened many of our customer’s understanding of dispensing process controls and raised the performance of their dispensing to much higher levels.