In technology, the phrase "creep" refers to a slow deformation process that is triggered when a material is put under pressure or load. When a metal "creeps", for example, molecules gradually move about in the material and the crystalline structures change permanently. The slow process of deformation can also result in significant damage.
Saving weight, fuel and CO2
In the case of creep age formation, however, these structural changes are intentionally induced. The method was only recently developed specifically for the aerospace industry and is about to be used in general industrial applications as well. It is suitable for materials including the metallic compound consisting of aluminum, magnesium and scandium – known as AA5024.
This alloy is roughly as strong as conventional aluminum materials but around five percent lighter. While this weight saving may appear small, it results in much lower fuel costs and fewer carbon emissions in the aviation industry. To be shaped, AA5024 requires vacuum. The sheet is placed onto the mold and secured around its edges to make it air-tight. While it is heated from the outside using heating mats, the space between the mold and workpiece is evacuated with a vacuum pump.
A matter of familiarization
As atmospheric pressure acts on the sheet, the metal "creeps" into the mold over a certain period of time and "familiarizes itself" with the new contours. The method is suited to many aluminum alloys and presents new opportunities for shaping materials, particularly in the production of curved structures for the aerospace industry. Not only is it more cost-effective than other methods, it also leaves behind less tension in the material than pressing and rolling. Creep age forming machines are much smaller than the "stretching racks" often used in aircraft production. Furthermore, the process requires less energy, produces less waste and delivers more precise results. Even molded parts that have already been welded can be reformed using this approach, without the welded seams being adversely affected. Busch offers highly efficient vacuum pumps to provide the vacuum needed for creep age forming.
Aluminum is the most common metal found in the Earth's crust. It can be combined with almost all metallic – as well as many non-metallic – elements to create an alloy. Many aluminum alloys have a similar strength to steel, but at just one third of its density and with a correspondingly lower weight. The fact that aluminum is both light and strong, as well as being easily available, makes it the ideal material for aircraft production.
What is more, various alloys can be produced using aluminum for a wide variety of tasks. Depending on what is added, the properties can change considerably. Magnesium, for example, makes the light metal more corrosion-resistant and increases its strength. Titanium combined with boron makes the material's granular structure finer. Scandium, a light metal classed as a rare-earth element, helps aluminum to achieve a higher elastic limit. As such, this alloy offers more resistance to tensile strain. The ideal alloy can therefore be selected to suit the differing requirements for various aircraft components.