Aluminum Structures
Typical Components:
Ribs, Beams, Covers, Skins
Material:
Aluminum 2000 series, Aluminum 7000 series, Aluminum Lithium
Metallurgical Expert Knowledge on Aluminum:
While pure aluminum has low specific gravity, good corrosion resistance, excellent thermal conductivity, and electrical conductivity, it is too weak and ductile to be used on its own. The most commonly used aluminum alloys for airframe construction are the 2000 and 7000 series.
2000 series aluminum alloys
Contains 1,9-6,8% copper content and often contains additions of manganese, magnesium and zinc. They are used for forgings, extrusions and liquified gas storage tanks in civil transport and supersonic aircraft. These alloys have lower crack growth rates and thus have better fatigue performance than the 7000 series alloys. Therefore, these are used on the lower wings and body skin.
Commonly used 2000 series alloys are 2224, 2324, 2524.
These alloys are often cladded with 99,34% pure aluminum for increased corrosion resistance.
7000 series aluminum alloys
The Al-Zn-Mg system offers the greatest potential for precipitation hardening though copper is often added to improve stress corrosion cracking resistance (with the drawback of reducing weldability). Stress corrosion cracking resistance decreases with increasing Zn:Mg ratio.
Aluminum Lithium
Commercial aluminum-lithium alloys are characterized by their low density, high specific modulus, excellent fatigue, and cryogenic toughness properties.
The marriage of Li and Al reduces density by 3% and increases the elastic modulus by about 6%.
In contrast to new materials systems such as fiber-reinforced composites, low density aluminum alloys do not require large capital investments by the producer in new fabricating facilities.
Trends in the industry
"The use of aluminum in aerospace represent more than 50% of all the material consumed and remain relative constant overtime."
The next generation aircrafts are called hybrid-designs when fiber-reinforced materials are associated to new economic aluminum structures.
Challenges
Aluminum part machining requires short takt time. Productivity is being measured as material removed in liters per minute.
Due to the relatively soft material properties, the material is being machined on high horse power machines (75-150kw) with spindle speeds up to 33,000 RPM.
Requirements
- Tool geometry to absorb the available machine power and convert to very high metal removal rate, avoiding build up edge and tool breakage at the same time.
- High quality tool balancing.
- Coolant design optimized for high speed machining.
Tooling Solutions
Hydraulic Chucks
