Aerospace’s secret standard


Derek Vanek, technical manager at SIFCO Applied Surface Concepts (ASC) explains why selective plating warrants a wider appreciation in the aerospace market.

When an industry is at its most buoyant, as is the case in the current commercial aerospace market, it creates its own set of challenges. The surge in demand for aircraft orders and maintenance is placing much strain on the manufacturing and associated supply chain. The backlog at Boeing and Airbus illustrates this perfectly. In February 2016, the Airbus backlog was just short of 7,000 while Boeing was nearing 6,000.

Time is money, now more than ever. Aerospace and maintenance and engineering companies need to ensure they are creating efficiencies in all areas. Innovation and collaboration have never been so crucial. It is an exciting time for aerospace manufacturing, yet a time for professionals to become better equipped with knowledge on how they can implement change while maintaining quality standards and industry compliance.

Aerospace is an industry which is highly demanding when it comes to surface finishing performance requirements and it is rightly renowned in its robust standards for the manufacture and repair of high-performance equipment. Components need to be able to withstand friction, extreme temperatures and corrosive environments while continuing to operate at optimum levels. But, the manufacturing processes must also meet ever more stringent health and safety requirements.

 The SIFCO Process includes the application of Cadmium LHE and Zinc-Nickel LHE for corrosion protection
The SIFCO Process includes the application of Cadmium LHE and Zinc-Nickel LHE for corrosion protection

When it comes to plating parts, engineers are faced with a challenge. Cadmium has long been used to provide a sacrificial coating in the aerospace industry. The sacrificial coating corrodes in preference to the substrate, a property which is especially important when the substrate is scratched or damaged. But, government mandates and environmental concerns are driving manufacturers to find alternatives for cadmium. Low hydrogen embrittlement (LHE) cadmium plating remains the choice for aircraft components as the plating provide excellence corrosion protection without degrading the mechanical properties of high strength steels. But due to its toxic nature, there is a tremendous amount of pressure both in Europe and in the US to stop its use. Therefore, identifying a suitable, LHE cadmium replacement is of great interest. SIFCO ASC developed Zinc-Nickel LHE and Tin-Zinc LHE brush plating solutions to meet this challenge. A range of coatings are also available to enhance the other areas of the aircraft, including nickel, nickel-tungsten, cobalt chromium carbide and silver. These coatings improve corrosion protection, wear resistance and electrical conductivity, while enhancing lubricity, performance and in-service life.

A proven process

The aerospace industry was one of the first to widely accept and approve the SIFCO Process - a form of selective plating - to restore worn and corroded metal components. A good example is the Federal Aviation Administration’s Advisory Circular 43.13-1B which contains methods, techniques and practices (including selective plating) acceptable for the inspection and repair of non-pressurised areas of a civil aircraft when there are no manufacturer repair or maintenance instructions. But we believe it is not currently being used to its full potential and there is still much opportunity for companies to make huge time and cost savings – both at MRO and OEM levels.

Although damage from wear, corrosion or mis-machining can be repaired using selective brush plating, the SIFCO Process should not only be considered for repair or salvage. The full range of pure metal and alloy deposits available offer enhanced wear resistance, increased surface hardness, low electrical contact resistance and/or corrosion protection for OEM component applications.

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. Recently, SIFCO ASC was listed as a Boeing Approved Supplier for selective plating services. This was achieved after demonstrating the process controls and manufacturing capability for plating following a comprehensive technical review. It therefore allows SIFCO ASC to provide its cadmium brush plating services to BAC5854 and BAC5849 specifications. SIFCO ASC works closely with customers in the aerospace industry to offer practical, cost-effective options for repairing and enhancing the surfaces of components. A great example is the travel kit we provided for touch-up applications, specifically designed for the aerospace industry and ideal for AOG operations where turnaround time is critical.

SIFCO ASC has designed a robotic system for landing gear repair

Common uses of the SIFCO Process include the application of Cadmium LHE and Zinc-Nickel LHE for corrosion protection on structural components, as well as equipment packages for the application of AeroNikl/Sulfamate Nickel which is used for prebraze applications in engine components. There are a wide variety of nickel and nickel-alloy deposits with characteristics suitable for the range of conditions encountered within the aerospace industry.

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.

There are several steps in which a surface area is prepared to receive an adherent deposit. The appropriate preparatory procedure is determined by both the substrate of the component and the plating solution to be applied.

The thickness of the plating is accurately controlled through use of an ampere-hour meter. Once the required ampere hours are reached, plating is stopped and finished with a final water rinse then dried.

Automating the process

The process can be carried out manually, it can be mechanised, or it can be automated for higher volume applications – something not traditionally associated with selective plating.

For example, one leading aerospace manufacturer tasked SIFCO ASC to design a machine for landing gear repair. The key challenge was localised areas on the bogie beams that were getting damaged while being retracted into the fuselage. As a result, our engineering team worked extensively to design and manufacture a robotic system that would automate the selective plating process and be installed into their production line. This has had a beneficial impact on both cost and production efficiency for the customer, as well as enhancing component supply chain control and traceability.

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. It is specified in the initial engineering design specification as well as being called out for component repair. The various advantages provided by the SIFCO Process, combined with the wide range of engineered deposits, make it an attractive choice for OEM and repair applications. In a sector where time is at a premium, selective plating should always be considered a viable alternative to other methods of metal deposition – especially where already written into a specification.



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