Copper bus bars play an important role in conducting electricity through distribution networks within the power generation industry. These components need to be manufactured to an exacting standard that permits carrying very high currents across mating bus connections with minimal contact resistance. To decrease electrical contact resistance, bus connections are electroplated with a suitable material, such as silver or tin, before they are installed in the system.
Selective plating, also known as brush plating, is already a widely-used method of surface enhancement. The process involves applying electroplated deposits on to localised areas of components with high quality electrolyte solutions and precision anodes, which minimises waste and environmental impact. However, selective plating can be labour-intensive process, with skilled individuals remaining close to the work area to handle chemicals and tooling throughout the process.
A typical bus bar has four distinct faces that require silver plating. This has been done manually, one face at a time, requiring an operator to move a hand-held plating tool (anode) back and forth across the surface until the desired silver thickness was achieved. Thickness was often inconsistent because operational tolerances require the operator to err on the high side. Average process time is 21 minutes to complete a bus bar.
Automation minimises the need for operator intervention, the process becomes safer and the results are more consistent. Through mechanisation of the process, the operator’s direct contact with tooling and chemicals is significantly reduced. A computer program – programmed by the operator – controls the volts, amps, polarity and ampere-hours required for the specific application, including pre-treatment and plating steps.
One company which has greatly benefited from automating its selective plating process is Powell Electrical Systems Inc. The Delta/Unibus Division has significantly reduced the process time taken to selectively plate each side of its copper bus bars by 90%, saving approximately $100,000 (£73,000) in labour costs, according to SIFCO Applied Surface Concepts, which provides electroplating systems for OEM and repair applications.
To overcome the challenge of relatively long processing times and plating thickness issues, a semi-automated dual-plating workstation was designed and built by SIFCO ASC. The first of its kind for this type of application, it allows Powell to selectively silver-plate both sides of the copper bus bars simultaneously and achieve the desired plating thickness uniformly, consistently and efficiently.
The workstation consists of a traversing arm mounted to a stainless steel work table. It moves the bus bars back and forth automatically, allowing the aqueous silver chemical solution pumped over the assembly to deposit on the copper bars. The run-off collects and is recirculated by an intricate system using a power pack, pumps, valves, anodes and solutions work together, prepping, changing, catching, plating and then circulating the plating solution.
Parts are prepped manually and placed into the table manually.
Since the first installation, the efficiency gains and savings achieved have prompted Powell to purchase a second machine.
Commenting on the project, Jessica Heuel, quality assurance engineer at Powell, says: “Being able to significantly reduce the plating operation time has helped remove electroplating as a potential bottleneck in our process, which allows the workers to assemble the bus duct much faster.”