The need
PPUK’s customers require that piston rings be chrome plated to reduce wear in the hostile environment of diesel engines. Chrome plating is done via electrolysis, placing the piston ring in a vat filled with a chrome solution and applying a current. It is a slow process which is hard to control accurately. For PPUK it takes 24 hours and represents a major constraint on productivity, which creates bottlenecks. Furthermore, the chrome plating can sometimes be unevenly distributed, requiring further work to produce the required finish.
PPUK worked with NPL through the Analysis for Innovators (A4I) Programme to better understand and find ways to improve product quality and speed up the process.
The solution
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.
The impact
This allowed PPUK to identify the optimal conditions – such as the best temperature and current density – to grow the plating to the desired thickness and surface finish as quickly as possible, greatly improving its’ productivity.
The changes are expected to halve plating times, reducing electricity costs and speed throughput, thereby clearing a bottleneck in their manufacturing. For their largest customer, PPUK currently only meets 15% of demand, so increasing capacity represents a significant opportunity to grow revenue.
The project not only helped improve this process, but the understanding of DMAIC provided them with a methodology they can apply to other areas. This is immediately useful. One finding of the project was that chrome was deposited unevenly, prompting PPUK to move to a different style of anode in their plating instrument. They can now repeat the experiment with the new anodes to identify the best approach following the change.
This work was done as part of the Analysis for Innovators programme.
