The frame for inexpensive bicycle usually is made from welde

The frame for inexpensive bicycle usually is made from welded low carbon steel (Refer to Figure Q2). This material can be heated to straighten and is easily welded using a wide variety of welding techniques. For lightweight and high performance materials, the assembly process for bicycle frame is not easy. Titanium offers strength of heat treated steel at approximately half of the weight. Magnesium while not as strong as steel or aluminium, is the lightest-weight engineering metal. Would these materials be appropriate for a bicycle frame construction? Justify your answer. If the titanium and magnesium are possible to be used for bicycle frame, what is the suitable fabrication technique to produce the tubing? What is the suitable joining process that is suitable to assemble the tubing made from titanium and magnesium? Justify your answer.

Solution

i. Several properties of a material help decide whether it is appropriate in the construction of a bicycle frame.

Density, Stiffness, Yield Strength, Elongation, Fatigue limit & Endurance limit are the main properties considered.

Titanium has about 56% density of steel which makes it better. Titanium is half as stiff as steel. So they are roughly comparable in terms of the stiffness-to-weight ratio.

Because of the relationship between titanium\'s high strength, low density and moderate modulus, most fabricators choose tube diameters that provide a supple, shock-absorbing ride. To push titanium down into the realm of the super light, the modulus becomes a problem, because then the frame gets too flexible.

Elongation for titanium is 20%-30% while it is 10%-15% for steel, which gives titanium advantage.

The tensile strength of titanium is also excellent. Similarly, fatigue strength of Ti is favourable too.

So, overall,Titanium is an excellent choice for making bicycle frames but the high cost limits it to high-end bikes.

Magnesium being the lightest (64% density of aluminium) , has been used in the past in the form of I-beams instead of tubes. However, it was discontinued due to reliability issues.

ii. Even with advances in materials, manufacturing processes and design, the best frame tubing for the buck is plain-gauge. These are tubes that don\'t rely on butting or oversizing or exotic blends, but are straight and strong and easy to manufacture. As a consequence they are cheaper.

Extrusion is most common fabrication method for tubing.

iii. Tungsten Inert Gas (TIG) aka Gas Tungsten Arc Welding (GTAW) is the most common joining method used for bicycle frames.