Modern aircraft are making use of very high-tech materials, including carbon fiber and advanced composites, for many elements of airframes. But not all elements can be replaced with non-metallic materials. When it has to be metal, aluminum is most often the metal of choice.
Why? Because, all other things being equal, an aluminum part will be about one-third the weight of the same part in steel, copper or brass. And, weight matters in any type of air- or space craft.
As a point of reference, the 747 is about 80% aluminum, the 777 about 70%, and the 787 is 50% aluminum. Although advanced materials are displacing a fair amount of metal, aluminum is still the predominant alloy in use. Titanium is only about 63% heavier, but it is much more expensive and more difficult to fabricate.
Aluminum is readily fabricated by many conventional methods. including casting, extruding, forging, machining, punching, stamping, and so forth. It is less compatible with non-conventional processes, such as plasma, laser and wire EDM due to its comparatively low melting point (1220 deg F). It also has very high reflectance (92% of visible light and up to 98% of infrared) which poses issues for many lasers.
Photochemical machining (or etching) is a non-conventional process that completely avoids the problems of heat and reflectance. The etching process runs at about 135 deg F and has no optical properties. This isn't to say that etching aluminum is not without challenges. It oxidizes readily and is exothermic. At 536 deg F, it will oxidize in water, producing hydrogen, aluminum hydroxide and (a lot of) heat.
Controlling the aluminum etching process started with a metallurgist's deep understanding of the properties and behavior of the alloy. This led to the development of specialized etching solutions and process controls that keep the reaction in check and produce precision components that are smut-free and have smooth, consistent sidewalls.
Photo etching is suitable for aluminum up to .080" thick. With the growing deployment of In-Flight WiFi, the need for lightweight, high-bandwidth antenna systems is increasing rapidly. Chemical etching has long been a go-to solution for designers of terrestrial systems, using mostly copper and brass components. Antenna designs rendered in aluminum are just as readily produced.
Aluminum's thermal conductivity is important in managing heat dissipation in avionics bays. Photo etching can produce partial etch surface features (at no additional time or cost) that can increase the effective surface area of a low profile heatsink by 25% or more.
Etched metal parts in a variety of alloys are found in many different subsystems of aircraft: fuel control systems, hydraulic systems, de-icing boots on prop planes, Faraday grids in aircraft windows, and many more.
Designers of aerospace components should consider chemical etching as a key fabrication method, particularly for parts with unusual geometries. The costs of the etching process are driven by the "real estate;" the length, width and thickness of the part, not by the complexity. Even for screens or grids, the number of holes has no bearing on the cost of the parts, the cycle time or the costs of the tooling (which is typically less than $300 and available in a day.)
The etching process can produce metal parts as small as .020" diameter and up to 24" x 60".
The Comprehensive Guide to Photochemical Machining brings together the information about
- Design rules
- Comparisons to other processes
- Specs and tolerances
The Guide is free and you can get it here: