The Critical Role of Stainless & Special Steel Bars and Wires in Aerospace Mechanical Systems

Mechanical aerospace components operate in some of the most difficult-to-engineer environments. Most components experience extreme temperature variations, cyclical mechanical loading, extremely high frequency vibrations, large fluctuation in pressure, and corrosive atmospheres. Reliability is the result of all the components that make up an assembly; thus, it is imperative for engineers to be able to choose materials based on their specific needs. Performance of stainless steel and specialty steel bars/wires will impact the fatigue-life, structural stability, precision dimensional accuracy, and the ultimate long term safety of flight-critical assemblies.

Aerospace products need to have a specific mix of mechanical and environmental characteristics in order to be used in an aerospace application:

Each time a flight is made, the structural parts of an aircraft go through many thousands of loading cycles. A single surface defect, or incorrect chemical composition, or non-uniform mechanical property may be enough to cause a crack in a part and result in premature failure. Aerospace standards, therefore, require consistent metallurgy, strict process control, and total traceability of all the material used in a certified aircraft program.

The process of producing rods and wires with aerospace-grade materials involves significant metallurgical controls, an ability to internally produce the material, and inspection systems that are extremely rigid. Each of these processes (melting/refining, drawing, heat treating, and finishing) must be done so as to provide consistent mechanical properties and surface finish.

Manufacturers who supply aerospace programs often have a large variety of stainless steel and specialized grades of alloy available to meet specific performance needs of their customers as related to strength, corrosion resistance, machinability, and fatigue characteristics.

Precision bars for shafts, rods, pins, and linkages, in many cases, are manufactured through machining of high-precision bar stock. Because they are used in a variety of components, including landing gear, flight control, cockpits, etc., they need to provide the following:

The most common Aerospace Grades for this application have been precipitation hardening steel grades and special high-performance stainless steel grades, which will provide the required motion integrity when in service with an applied load. Precision ground bars and shaft-quality bars are commonly specified for such applications due to their dimensional consistency, controlled mechanical properties, and improved machinability. These characteristics contribute to enhanced reliability and efficient component manufacturing.

Fasteners (bolts, nuts, rivets, pins) can be small; however, they play a large part in maintaining the structural integrity of all aircraft. The parts which are used in engine assemblies, fuselage assembly mounts, etc., require:

Wire rod used for cold-heading of aerospace fasteners must exhibit uniform grain structure, clean surfaces, and consistent mechanical properties. Surface defects or inclusions can significantly reduce fatigue life under vibration-intensive conditions. Strict quality control during wire production ensures reliability in highly stressed fastener applications.

In addition to many other assemblies, aircraft also depend on springs, clips, retainers, etc., to provide retaining force or to support a mechanical force in various assemblies. In order to have acceptable performance, these components must exhibit an excellent elastic response and long fatigue life. Commonly specified spring grades such as 302 and 17-7 PH offer excellent elastic response and long fatigue life, enabling service performance across millions of operational cycles.

The hydraulic parts which include valves, connectors, pistons, and fittings that are part of a hydraulic system are subjected to extremely high-pressure, and therefore must have no leaks or corrosion. Due to this property, stainless steels (such as 316L and 321) are commonly used in machining of precision hydraulic parts because they provide both corrosion properties, as well as structural stability at high pressures. As a result, hydraulic components are capable of safe and efficient operation for extended periods of time.

The quality control procedures used by an aerospace manufacturer's suppliers are equally important to the quality of the materials being supplied. Aerospace suppliers use both international quality assurance standards (ISO 9001) and documented traceability procedures to control and track their products through all stages of production.

Aerospace suppliers' quality assurance systems generally consist of a combination of the following:

In order for aerospace parts or systems to be certified to operate safely and reliably, it is mandatory that the suppliers follow these controls so that they can provide repeatable material performance.

High-performance (stainless and special) steel bars and wire for aerospace manufacturing are used to achieve a number of significant improvements that can be measured:

As designers produce lighter, more efficient aeroplanes, precision-engineered bars and wire continue to be the backbone of both structural and mechanical integrity.

Although bars and wires are generally seen as small parts of larger aerospace structures, they are crucial in both actuation systems, structural systems, hydraulic systems and flight-critical mechanism systems. The mechanical properties (strength, ductility), precision dimensions and fatigue resistance of these metal products directly affect the safe operation of an aircraft and its overall service life.

With continued advancements in lightweight, high-strength and more efficient aerospace structures, manufacturers are relying more heavily on material suppliers that have extensive metallurgical knowledge and controlled production processes.

Venus Wires has been providing engineered bar and wire products to demanding markets such as aerospace for over three decades, by offering products that can meet and support the needs of critical applications due to their reliability and quality.

In aerospace, it is often said that performance starts with the material.

Also Read: Essential Quality Standard For Aerospace Product Manufacturers