NPL set out to better understand the plating process and how it could be improved upon to make the process more efficient, whilst also improving how evenly the plating is applied. It worked closely with PPUK to design and conduct experiments to pin down the optimal approach.
The first step was to statistically analyse PPUK’s existing measurement systems for chrome plating thickness, to assess the variability in the measurements.
This led to the introduction of more rigorous measurement systems, based on a statistically proven Standard Operating Procedure and understood capability of equipment.
NPL then designed experiments, carried out by PPUK, to understand how different variables affect the plating process and identify the optimal combinations. This process was run according to the Define, Measure, Analyse, Improve and Control (DMAIC) framework.
This started by defining a set of variables which could affect the speed and quality of the deposition process, including density of the electrolyte, temperature and position of the object in the tank. By varying each of these in a methodical way and measuring the changes to the plating thickness across the piston ring’s surface over time, PPUK were able to establish cause and effect between the variables and the outcomes.
The measurements were analysed by NPL using Minitab analysis software, allowing them to identify whether each change directly impacted the plating process, whether that change was linear, and whether changing combinations of variables differed from changing them individually.