Spot Coating Ensures Better Connections — and Saves Costs
To produce electric vehicles that are safe, resilient, environmentally friendly and cost-effective, OEMs need to examine every aspect of a vehicle’s electrical infrastructure, starting with the connection between the charging inlet and the battery pack.
Busbars — solid metal conductors — are emerging as the technology of choice for EV charging harnesses and other high-voltage connections within a vehicle. Typically made of copper or lighter-weight aluminum, busbars have important advantages over cables, including the ability to carry more current than the wires or cables they replace. Busbars also take up less space and enable automated assembly: Whereas bending a cable into place is largely a manual task at OEM assembly plants, a robotic arm can install a rigid busbar.
Busbars require a special treatment that applies a protective coating within the connection area to prevent oxidation layers from forming on the copper or aluminum surface. Oxidation increases resistance, which in turn can increase temperatures. If that is allowed to occur, it can reduce a busbar’s performance and limit its lifespan.
Typically, busbars are dipped in a galvanic bath — a process called electroplating — to apply that protective coating. The busbar is submerged in a chemical solution, and an electrical current is applied, depositing a thin layer of coating (tin, nickel or silver) onto the busbar's surface. This process is complicated and costly and poses environmental risk if the chemically treated water is not handled or disposed of properly.
Alternatively, there are “electroless” plating approaches that use a different process but provide the same level of protection.
Engineers in Aptiv’s Intercable Automotive Solutions (IAS) business have developed a spot coating process that can reduce the cost of coating busbars by as much as 80 percent. With the new process, a sprayer applies the protective coating only where it is needed — at the connection points at either end of the busbar.
How it works
The spot coating process starts with a pretreatment process to clean the surface area and remove any existing oxidation. This first process roughs up the busbar’s surface to make it more conducive to absorbing the coating material. The roughness also provides a better electrical contact surface for the busbar.
Next, the coating material — nickel or tin — is fed as a solid wire into an arc spray device, where an electrical arc melts the coating material. Compressed air is used to spray the molten material onto the targeted areas of the busbar, where it forms a protective layer.
Surfaces are coated only where necessary. Targeting those surfaces can save up to 60 percent of busbar treatment costs when copper is the busbar material and up to 80 percent when the busbar is made from aluminum.
While spot coating in general is not a new process in industries such as aerospace, oil and gas, and utilities, the application of spot coating in automotive busbars is an Aptiv innovation.
The benefits are more than financial
The spot coating method delivers a range of benefits beyond cost:
- Environmental impact. The galvanic bath process is complex, requires chemicals and uses water, which must be safely disposed of after the treatment is applied to the busbars. Spot coating does not use chemicals or water. Plus, it is more environmentally friendly because the process occurs within the confines of the spot coating machinery. The only residue that might need to be accounted for is a bit of dust that can be taken care of with an air filtration system.
- Speed. The spot coating process is faster than the galvanic process, which reduces both lead time and process time.
Quality. IAS engineers have conducted validation tests to measure contact resistance and have determined that the spot coating method delivers electrical performance that is equivalent to that of other processes.
Spot coating is just the latest innovation from Aptiv, which has a rich history of providing solutions with a comprehensive perspective. With IAS, Aptiv can integrate its industry-leading high-voltage busbar innovations into EV designs and processes. As the EV market continues to grow, these capabilities will become even more instrumental in helping OEMs differentiate themselves.
