One common challenge in electroplating is coating thickness variation, especially when plating loose parts like screw machined or stamped components. For mission- and safety-critical industries, aerospace, defense, medical and automotive, there is practically no room for error. Repeatable process ranges are the only way to meet process capability index (Cpk) requirements for Production Part Approval Process (PPAP).
What’s So Bad About Thickness Variation?
Unwelcome plating thickness variation may result in several undesired outcomes. Of primary concern is that unevenly plated parts may not perform as needed. This could lead to much bigger problems such as malfunctions or system failure depending on how and where the part is used. Also, depending on the nature of the defect, the parts may be prone to shorter lifespans due to wear and other surface issues, such as corrosion.
Further, when precious metals such as gold or platinum are being used, overuse of the material leads to waste and increased cost. With precious metal prices at record levels, these expenses can add up quickly and substantially. Electrical conductivity could be affected as well, leading to electrical issues or failure of the device the parts are used in. As you can see, there are plenty of reasons why plating thickness variation should be avoided.
What Causes Plating Thickness Variation?
The geometry of the part being electroplated plays a significant role in thickness variation. Parts with long, thin shapes, blind holes, or deep inner diameters can create challenges in achieving uniform coating thickness. This is especially true if the point of thickness measurement is at the end of the part or on the inner diameter. In these cases, choosing the correct point of measurement (POM) is critical. Electrical current naturally travels to the extreme area of the part being plated so the end of the part or the outside of the part will attract more of the metal being plated than the rest of the part.
How Can These Issues Be Avoided?
One way to reduce the impact of the electrical current accumulating at the ends or outside of the part is to have good part-to-part movement around the cathodes in the plating unit. This requires choosing the correct size plating unit with the proper rotating speed. If a PPAP is required, it is essential to plate the run with the same lot size and equipment that will be used for production runs since the results can be vastly different.
Ensuring good part-to-part movement during the plating process is essential to achieve uniform coating thickness. Proper agitation techniques and the use of specialized equipment can help maintain consistent movement and prevent parts from clumping together. Vibratory plating, for example, offers benefits over traditional barrel plating by providing more controlled movement and better access to all surfaces of the parts for uniform coating. Traditional barrel plating is good for parts that tumble easily but long thin parts may require vibratory plating which can supply a better distribution. Parts with a thickness requirement on the ID may need a process that gives good movement but also promotes good solution exchange.
Incorporating ultrasonic technology in the plating process can improve solution exchange and distribution, leading to more consistent coating thickness. Ultrasonic waves help agitate the plating solution, promoting good plating coverage on the inner diameters of the parts.
The Technic Spouted Bed Electrode Unit is a specialized piece of equipment that can help overcome thickness variation challenges in electroplating. This innovative technology employs a high velocity solution jet to move parts, which helps provide efficient solution exchange and uniform current distribution. This process results in consistent coating thickness on screw machine parts, and other loose piece runs.
In conclusion, electroplating thickness variation can be attributed to factors such as part-to-part movement and part geometry. There are many reasons to be certain that variation is minimized. By implementing solutions such as ensuring good part movement, choosing the right equipment, using ultrasonics, and utilizing advanced technologies like the Technic Spouted Bed Electrode Unit, manufacturers can achieve more uniform and reliable coating thickness in their electroplating processes.
When choosing your plating partner for mission critical components, make sure they have the proper equipment, processes and QA systems in place to minimize thickness variation. Doing so will help ensure that you receive consistent and reliable components that are well within spec, saving you headaches and added expense down the road.
