Ask A Scientist
How do motorcycles stay together?
Asked by: Alexandra Naylor
School: Maine-Endwell Middle School
Teacher: Mr. Wagstaff
Hobbies/Interests: Collecting state quarters
Answer from Roy T.R. McGrann
Research area: Engineering design education
Ph.D. School: University of Tulsa
Interests/hobbies: Sustainability engineering, Computer-aided design, history and philosophy, literature, music and cinema
Great question and timely, considering (as I write this) we are celebrating Engineers Week here on campus and mechanical engineering analysis can be used to answer this question. There are many forces acting on a motorcycle. These include the weight of the motorcycle, the weight of the rider, forces due to acceleration and braking (inertial), turning (centrifugal), and shock and vibration forces. There are numerous material joining processes used to construct a motorcycle to withstand these forces. In general, the major types of joining processes are non-permanent (screws, bolts) and permanent (welding, gluing). A motorcycle is a system that consists of several structural sub-systems: including (and simplifying greatly) a frame, engine/drive, and suspensions (including wheels and tires). The frame is the structure to which the other sub-systems are fastened. For example, they might be bolted to the frame. We can say that the frame holds the motorcycle sub-systems together.
There are many types of frame: bent multi-tubular, trellis, cast, and monocoque. A common type is the bent multi-tubular frame. This frame consists of metal tubes forming a “skeleton” for the motorcycle. The metal tubular pieces are held together by the permanent joining process of welding. Welding holds the frame together.
Welding is a process in which the surfaces of metal parts are melted and pressed together so that when they cool they are bonded. Some of the main types of welding processes are: arc, resistance, oxyfuel, and laser beam. Motorcycle frames are often arc welded. In arc welding, an electric arc is the source of heat that melts the metal parts. Filler metal or additional pressure can also be used in arc welding. The principal types of arc welding are shielded metal, SMAW (“stick”); gas metal, GMAW (“MIG”); gas tungsten, GTAW (“TIG”); and plasma arc welding, PAW. During welding, it is very important to keep all impurities away from the hot metal. Oxygen rapidly creates metal oxides (corrosion) at high melting temperatures. An inert gas such as argon is used to shield the weld area from oxygen in the air.