Most of the modern bicycle frames are made by welding – from tubes made of 6061 and 7005 aluminum alloys. Along with the well-known advantages, welding of such frames also has disadvantages, such as:
(1) Before welding, it is necessary to form shaped ends on each of the frame elements so that they adhere to each other as closely as possible;
(2) Thin-walled structures welding requires highly skilled workers or robotic equipment designed for large-scale production;
(3) The frame must be heat treated after welding to obtain the required strength properties of the aluminum alloy used.
What are the strongest aluminum alloys?
Compared to 6061 and 7005, there are also stronger aluminum alloys, such as 2024 and 7075, which, for example, are used for the manufacture of aircraft fuselages:
|Mechanical Properties (*) / Alloys||6061T6||7005T6||2024T4||d7075T6|
|Ultimate Tensile Strength, MPa||310||380||480||560|
|Tensile Yield Strength, MPa||270||310||310||480|
|Shear Strength, MPa||210||210||290||330|
|Modulus of Elasticity, GPa||69||70||71||70|
|Fatigue Strength, MPa||96||130||140||160|
|Elongation at Break, %||10||12||16||18|
(*) – according to Material Properties Database on makeitfrom.com
The table shows that 2024 and 7075 alloys are much stronger than 6061 and 7005. However, the bicycle frame manufacturers have chosen the 6061 and 7005 alloys precisely because of their ease of welding. Products made of 2024 and 7075 aluminum alloys bend and weld much worse.
How and from which materials the Avial bike frames are produced?
Avial electric bike frames are produced of a combination of elements made from the already classic 6061 and durable 2024 and 7075 aviation alloys. Since the latter alloys are difficult to weld, we use various Hybrid Adhesive Bonded and Mechanical Joints to connect the frame assemblies.
The patent-pending Avial e-Bikes frames are assembled in the same way as the fuselages of modern aircraft – from sets of elements that are connected using rivets and special glue. This method of frame production offers several advantages over the conventional welded bicycle frame, the main one is the ability to obtain a strong, lightweight, and reliable supporting structure. Elements from 6061 and 7075 aluminum alloys are used for the production of Avial Bikes frames.
Hybrid bonded and riveted joints are becoming more and more popular in different branches of engineering, from the aerospace to the automotive industry. Riveted joints are a technologically simple solution for the manufacture of structures that are susceptible to vibration and shock loads. When used together with rivets, the glue seam assumes a significant part of the stresses arising in the node and, redistributing them, relieves the rivets. The strength of such hybrid joints is 1.5-3 times higher than the strength of glued joints alone. At the same time, hybrid connections are characterized by higher reliability during long-term operation.
Hybrid Pedelec frames are manufactured using this technology. The latest prototype of this mid-drive electric bike covered over 4,500 km in urban and off-road conditions. Detailed examinations at each stage of testing did not reveal any weaknesses in the strength of the assemblies, deformations or damage to the frame structure.
We have developed a patent-pending Avial e-Bike frame concept that has passed CAD simulation. The 15-16kg prototype of this electric bike is currently produced for road testing from 6061 aluminum tubes. A feature of this technology is that the two main frame elements bend so that they simultaneously form both the top tube and the down tube, and also the seat stays and chain stays.
All frame elements are connected using glue and special internal locks made of 7075 aluminum alloy, which redistribute the loads that occur on the nodes. Along with the ease of assembly, it is possible to open the rear beam connection and install a single-speed or 8-speed gear hub with a belt drive, as well as a classic chain in combination with a single-speed system or with the 8-speed transmission. We will use this technology for the production of the City Rear Drive model.
Each of the Avial e-Bikes frame technologies is not only simpler and cheaper but also eliminates welding, which can weaken the frame material from thin-walled tubes or profiles, creating heat-affected zones at the joints of the elements. At the same time, according to the results of the tests carried out on a 120kg rider, the hybrid glue-mechanical connection of the nodes provides a strong and elastic structure that can reduce the influence of uneven road surfaces.
Each 3.2-3.5 kg Avial e-Bikes frame can be equipped with not only a 250-500W rear-wheel drive with an integrated controller but also with a 250-350W mid-drive. The mid-drive model can be equipped with Gearsensor for smooth gear changes, that ensure a comfortable, jerk-free ride in all conditions.
The motor bracket can be formed on the Avial Bikes hardtail frame. It is easy to fit almost any modern mid-drive model from most manufacturers’ catalogs on this bracket. The same fastening principle allows mounting on the frame with the same design the bottom bracket and the pedal assembly instead of the mid-drive so that you can use them jointly with the rear-wheel drive.
Avial e-Bikes are equipped with self-produced lithium-ion batteries with a capacity of 10.5 or 14 Ah. For the manufacture of batteries, modern 18650 cells with 3500mAh capacity of the Samsung or LG companies are used, which guarantees the final product a high capacity with a compact size and low weight.
We are currently testing a prototype battery with a patent-pending case, which has additional passive cooling, which allows for even temperature distribution in the stack of assembled 18650 cells. As a result, the temperature of the cells inside the package is practically the same as the temperature of the cells outside the package, which has a positive effect on the battery lifetime.
The use of modern technologies that were developed in aircraft construction and the automotive industry allows us to organize mass production in Europe and, to offer every riding-lover not only affordable but also a comfortable Avial e-Bike with excellent driving characteristics.
Each of the models, that combines classics, constructive simple design and ease of use, can be used both in the city and on out-of-town trips. We develop and test our bikes ourselves, and together with the potential owner we can customize the configuration for him.