In the aerospace industry, components are subjected to harsh operating environments. Extremes of temperature, corrosive particulate matter in the air, friction and a variety of operating factors combine to increase the risk of wear and tear, corrosion, and damage.
Component defects and hardware deteriorations can result in shutdowns and unscheduled downtime, affecting the operator’s dispatch reliability and resulting in higher operating/maintenance costs. If not properly maintained, many of these components – or entire pieces of machinery – may need to be scrapped, increasing capital equipment costs and prolonging downtime.
Environmental concerns, costs of raw materials, and stricter government regulations – not to mention cost control and reduced availability of some metals – have resulted in aerospace component manufacturers striving to reduce waste. Worn, corroded, or damaged components from across industry contribute to the 73 million metric tons of ferrous metal, and millions of tons of non-ferrous metals and stainless steel scrapped in the US.
This is where remanufacturing offers a solution. With quality control paramount, it is important to clarify that the remanufacturing industries council describes remanufacturing as a comprehensive, rigorous industrial process, adding that components are returned to like new or in better-than-new condition.
Extending Operational Lifespan
While remanufacturing has a role to play in reducing scrappage and extending the operational lifespan of components, the process itself can be more time-consuming than simply manufacturing a new part. In the aerospace industry, downtime can be costly, making it vital that remanufacturing can be carried out both efficiently and effectively. Here, selective electroplating offers a vital benefit.
Selective plating (also known as brush plating) is a method of repairing and restoring critical dimensions and surface properties of worn components to OEM standards. The process can be used to treat specific areas of a component, with accurate, selective brush plating of materials onto localized surfaces and diameters. As well as typically being faster than alternative surface coating methods, selective plating can be completed on-site, reducing the downtime and cost associated with disassembly, transport, and reassembly.
Given the continuous use and harsh environments experienced when aerospace equipment is in operation, selective plating needs to bond at the atomic level. This is something not provided by traditional surface coating methods, such as thermal spray, which only forms a mechanical bond.
To create this atomic bond, selective plating uses electrochemical principles. An electrolyte solution, containing ions of the deposit material, is introduced between the negatively charged plating surface and the positively charged tool. When the tool – or anode – touches the surface, a circuit is created, with a cover material around the tool providing a reservoir to ensure even distribution. The current within the circuit causes the ions between the interfaces to bond, building up the plating layer and delivering a highly adherent and dense metal deposit.
The range of metals used in selective plating is extensive. The process is suitable for applying any metals that are traditionally applied by tank electroplating, the most common being cadmium, zinc-nickel, nickel, copper, cobalt, nickel-tungsten, cobalt-chromium carbide, silver, gold, and platinum. The SIFCO Process® can be carried out manually, it can be mechanized, or it can be automated for higher volume applications – something not traditionally associated with selective plating.
Benefits of Selective Plating Over Tank Plating
Selective plating is already approved worldwide by most major airlines, landing gear and engine manufacturers, and is specified in overhaul manuals and standard practice manuals. SIFCO ASC works closely with customers in the aerospace industry to offer practical, cost-effective options for repairing and enhancing the surfaces of components.
For example, when looking to remanufacture a turbine interstage case from a PW100 engine, an OEM customer explored tank plating and brazing options, before opting for selective electroplating. With an internal diameter of 5.625", a specified plating thickness of 0.003" using AeroNikl® 250, and limited access to the area that needed plating, precision was key to success.
Tank plating – often used for this type of application – requires extensive masking. As well as being a labor-intensive and time-consuming process that often incurs additional delays shipping the part to outside vendors, tank plating can also require post-plating machining due to edge-build-up. Selective plating allows for more accurate control of deposit thicknesses – a point crucial to meeting the specification – allowing the part to be plated to size with no post-machining. With the process taking place at room temperature, the risk of part distortion is also reduced.
For this particular component, selective plating also offered a far quicker turnaround, with processing times reduced from one-to-two days to approximately just two hours. With the portable nature of brush plating, repairs can be undertaken either in the shop or on the job site – offering process flexibility as well as reducing the impact of external delays and shipping.
Reducing Scrappage and Rework
In the aerospace industry, in particular, the very low design tolerance of manufactured components can result in scrappage due to production defects and strict quality control. Again, selective plating can help overcome this issue, offering a way to swiftly rework parts to ensure that they meet specifications.
When working with an OEM for the aerospace industry, SIFCO ASC was able to specify selective plating to rework a part to avoid the need to strip and replate it. The component in question was an outer ring flange for a turbine jet engine shaft. As part of the original manufacturing process, the part was pre-baked and electroless nickel coated before being post-baked.
After completion, it was discovered that the 0.125" slot was oversized. Rather than stripping and/or replating the part, the customer worked with the SIFCO ASC team to use selective plating so the slot would meet the required specification. After plating with nickel, the part was baked for a minimum of eight hours at 375°F. The masking and plating operations of each part amounted to less than ten minutes, a far faster and more cost-effective process than stripping and replating the part.
Reducing Environmental Impact
As well as extending the service life of assets, saving money and materials versus the cost of replacement, reducing scrappage and improving process efficiency, selective plating also offers substantial environmental benefits.
Using less solution and chemicals, and generating very little waste, as well as reductions in the carbon costs of emissions, transport, and shipping, it’s a more sustainable option. The reduction in fumes and hazardous waste disposal also delivers a safer, healthier working environment.
Maximizing Uptime, Minimizing Costs
Remanufacturing undoubtedly offers a cost-effective and resource-efficient way to extend the service life of machines and equipment. Opting for selective plating offers further benefits, reducing downtime and offering distinct process and environmental efficiencies versus other plating methods.
Selective brush plating has dramatically evolved from its origins of touching up existing plating jobs and is now considered an overarching term describing a highly technical process used for repairing or improving surface properties in an array of circumstances. Its benefits commonly include increased wear resistance, surface hardness and low electrical contact resistance, or corrosion protection, so much so that it is often now specified in the initial engineering design specification as well as being called out for component repair.
This article was written by Tony Arana, Southwest Territory Sales Manager at SIFCO ASC (Independence, OH). For more information, visit here .