Aluminum Aircraft Parts: Extrusion Vs Roll FormingMatt Kerster
Aluminum is a ubiquitous material in aircraft and the various shapes and configurations of aluminum aircraft parts almost always derive from two basic forming processes: extruding or roll forming.
While the reality is that most personnel handling and installing, replacing or repairing aircraft parts and components really don’t care how the part was produced. In fact, they may not even know the difference. So, a good question to ask is whether one method is better than the other?
Metal Forming 101
We don’t want to insult anyone’s knowledge, so indulge us a bit while we review some things you may already know, and that is the basics of roll forming and extrusion.
According to information at the Virginia Polytechnic Institute and State University website,
“In general, “rolling” is a process that uses a pair of rolls to form materials. There are two rolling techniques, hot-rolling and cold roll-forming based on the temperature of the metal being used. If the temperature is above the crystallization temperature of metal, the process is called hot-rolling; otherwise it is called cold-rolling.
In hot-rolling, hot-molten steel is passed several times through pairs of rolls to achieve the desired profile. Most structural steel components such as I-Shape, L-Shape, etc. are hot-rolled. Cold-rolling can increase the material strength and improve the surface finish. Cold roll-forming uses thin sheets of steel to form into various shape sections such as floor and roof panels or C or Z shapes.”
The same webpage goes on to explain that “extruding” is a process for producing metal components by pushing or drawing the material through a die, or mold, to create the desired cross-section. With extrusion processes, components with complex cross-section can be produced. Much like roll forming, there are two methods of extrusion: hot-extrusion and cold-extrusion.
Metal extrusion is a production process that has been employed for a long time. An entry in Wikipedia describes the beginnings of metal extrusion.
” In 1797, Joseph Bramah patented the first extrusion process for making pipe out of soft metals. It involved preheating the metal and then forcing it through a die via a hand-driven plunger. In 1820 Thomas Burr implemented that process for lead pipe, with a hydraulic press (also invented by Joseph Bramah). At that time the process was called “squirting”. In 1894, Alexander Dick expanded the extrusion process to copper and brass alloys.”
Manufacturers have used this popular process as a common method for creating a variety of metal parts and other products. Because of the relatively low tooling costs and its ability of forming lightweight parts, aluminum extrusion is a trusted method for many manufacturers.
Roll Form Aluminum
Roll forming involves the continuous bending of a long strip of sheet metal, often aluminum, into a desired cross-section. The strip passes through sets of rolls mounted on consecutive stands, each set performing only an incremental part of the bend, until the desired cross-section, or profile, is produced.
There are pros and cons to both methods that depend largely on need, time and budget. Engineers and manufacturers all have opinions on the strengths and weaknesses of both methods. But the bottom line for most end-users is whether the part is easily acquired easily made available.
Choosing Between Roll Form and Extrusions
Roll forming is considered a more “material-efficient” and, therefore, leaner process for component parts and many assemblies. The roll form tooling is more cost-effective high volumes such as thousands of feet or parts. In addition, roll forming is a faster process producing a greater amount of feet per hour.
On the other hand, extruding aluminum allows the ability to add slots and openings in a part during the initial manufacturing process, whereas with roll formed parts, this is performed in secondary post-processes. Another advantage for extruded aluminum is that the dies are less expensive to manufacture. These dies are a single piece of metal and fabrication is simplified. Roll forming involves an intricate die, and several passes of the material, to form the desired shape. The rolls and dies used in roll forming are more expensive than those used with extruded aluminum.
Extruded aluminum parts generally have more material, which can be an advantage when considering the comparative strength versus a roll formed aluminum part.
The biggest design difference between extrusion and roll forming comes down to secondary, value-add operations. Before any secondary operations can be added to an extruded part, it must go through a secondary aging process in an oven. Meaning, extruding cannot produce a part or product with multiple bends and secondary operations in a continuous progression.
Roll forming is a good choice for producing parts with complex designs such as multiple bends and requiring secondary operations, such as hole punches, notches or slots.
Both extrusion and roll forming can be used to produce long parts like seat rails efficiently. But the length of an extruded part or product is limited by the amount of material in the work piece as well as the profile. In contrast, the only length limitation of roll forming is the length of the coil being fed into the line, which in turn produces less scrap than sheet metal.
A blog article at Sky Scape Architectural Canopies points out that,
“Most industry experts agree that there are clear advantages to extruded aluminum. For one thing, the dies used in the extruded aluminum process involve a single piece of metal that is simple to fabricate and thus less costly than a roll formed die. The extruded aluminum process also allows the flexibility of adding slots and other openings during production; in roll forming, an additional post-process is required — which adds to the production time and cost.
But the main advantage with extruded aluminum is that the finished product has greater strength and durability than a roll formed product, because it uses more material in the fabrication process.”
Regardless of whether you need 100 feet of an aluminum extrusion product, or just a few feet of stainless-steel tubing, AAA Air Support promises to always ship out your part orders quickly and efficiently. Our goal always is to provide your company with the means to complete that project or get that airplane back in the air in AOG situations.