Titanium tubes and titanium alloy tubes are mainly used in military industry, while PAW method is currently not applied in bicycle manufacturing, followed by noble and complex chemical processes. Pure titanium means nothing because it is too soft. In order for it to have practical value, titanium is extremely difficult to extract because it must be isolated. It is necessary to add another metal as an assistant. Of course, the premise for all of this is to do it based on the inherent properties of titanium itself. So titanium is commonly referred to as an alloy with special properties. From a general perspective, the disadvantage of titanium lies in its high strength, good corrosion resistance compared to mass (high strength, but light weight), low non-magnetic thermal expansion and thermal conductivity, impact toughness (referred to as metal reduction by some domestic car enthusiasts), and high fatigue index. In terms of data science, titanium alloy is called an allotrope metal because it can present different crystal shapes, such as hexagonal or cubic shapes.
The main difficulty is that titanium is very sensitive to the losses caused by friction. For example, at high speeds, if titanium is used in industry, the wear of a pure titanium flywheel on the chain is as severe as the reaction generated during welding. Using such a chemical example to explain would make everyone understand more simply, but not to scare people. Although the hexagonal crystal structure of titanium gives it excellent properties, temperature can alter this structure (this is a chemical change, which does not belong to the same category as the physical changes such as thermal expansion and conduction mentioned earlier). For this reason, titanium is referred to as a saturated crystal structure, as there cannot be any impurities, even a small amount, in titanium alloys. Otherwise, cracks will appear inside the welding line of the titanium pipe. Now that we have a rough understanding of these difficulties, how can we weld titanium alloy pipes.
We cannot approach it with an approximate attitude. When welding, in a high-temperature environment of a titanium alloy frame, all hazardous areas should be isolated with gas to prevent contamination by impurities. This is called bath melting (imagine that when a person takes a hot bath, their whole body is surrounded by hot water, as the name suggests). Therefore, gas is used in a small environment called "supervised gas" welding, There are two ways to invent a welding environment for this gas to be inert. The first method is to use a bell shaped cover, and the other method is to maintain an inert gas at the welding site, requiring a constant source, rich flow rate, and continued stability. The entire environment is enveloped by an airflow. I usually choose argon and helium because they are easy to provide and cheap. In terms of dosage, 75% argon and 25% helium are mixed. For some special situations, such as welding with large local areas, in order to optimize efficiency, an arc is also used to serve as the gas environment.
