Aluminium

The requirements placed on a high-quality aluminium bicycle frame are many and varied. The Al frame should be as light as possible while offering maximum rigidity, display a distinctive optical design and unique character of the tubes, possess certain damping properties and above all have a long service life.

ROTWILD aluminium frames made of Al 6066 T6

In our ROTWILD aluminium frames we use exclusively high-grade aluminium 6066 T6 alloy as the base material. This enables us to build very light, extremely durable aluminium bicycle frames. Al 6066 T6 contains a greater number of alloy constituents, namely silicon, copper, magnesium and chromium, which ostensibly results in a somewhat higher weight (density) compared with the standard Al 6061 T6 alloy. However, Al 6066 T6 offers significantly better properties in terms of the dynamic fatigue strength of the frame.  

If we consider the ratio of density to fatigue strength, the benefits of Al 6066 T6 become very apparent. The material yield strength, which is important for welded constructions, rises and therefore increases resistance to shock fractures. This is a particularly great advantage in full-suspension bikes where travel exceeds 140 mm because the stresses acting here have risen considerably in recent years due to improved spring/shock absorber systems and tyres as well as the higher speeds associated with these developments.

Hydroforming as a production process

Tubes for modern, high-quality aluminium bicycle frames are produced in a process known as hydroforming. It allows the tubes to be shaped individually and produced with a high level of process reliability.

In the actual hydroforming process, the preformed tube section is first placed into a die. This die comprises a lower and upper die, and represents the final contour of the component. The form is closed and the tube ends are sealed by hollow axial punches. The tube section is pressurized at up to 4,000 bar by filling it with a water/oil emulsion through the hollow punches. The high internal pressure is responsible for forming the tube section. The tube is pressed against the die and assumes the contour of the outer die in the process. Additional strain hardening of the material also takes place during the forming operation. In the final step the finished component is removed from the die.

The production technology of hydroforming enables complex tube geometries to be made from aluminium. This allows us to adapt the cross-sections, tube shapes and wall thickness optimally to the load conditions in the frame. The tube geometry and design can also be adjusted to other requirements such as position of water bottles, bearings, etc.

Forging

The advantage of forging is that the fine structure of the metal can be selectively altered. Controlled cooling enables additional material properties to be given to the component. As a result of the process, forged parts exhibit a higher strength than comparable parts milled by CNC and therefore offer a higher safety factor.

Aluminium blanks are used as semi-finished products for the forging process. Their alloy constituents must be identical to those of the tubes for the subsequent welding process. The blanks are generally produced using a casting process. This results either in profile rods or a separately preformed blank, which is already adapted to the final shape of the finished forged part. During forging the workpiece is formed into its desired final shape by hammering and compression.

Read more about aluminium alloys in our knowledge database

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