Which of the following is the slowest method of joint preparation? oxyfuel cutting thermal mechanical plasma arc cutting

The slowest method of joint preparation among the options provided is thermal. Thermal cutting methods, such as oxyfuel cutting, involve the use of a flame to heat the metal to its ignition temperature and then use oxygen to oxidize the metal, resulting in cutting. This process can be slower compared to mechanical methods, which involve physically removing material using tools or machinery, and plasma arc cutting, which uses an electric arc to melt and remove metal.