Which process generally requires the hottest temperatures?

Welding generally requires the hottest temperatures among the listed processes. This is because welding involves the melting of base metals, which typically necessitates reaching very high heat levels to ensure a strong bond between the materials. The temperatures involved in welding can exceed 3,000 degrees Fahrenheit (about 1,650 degrees Celsius) depending on the specific technique and materials used.

In contrast, soldering generally operates at lower temperatures, as it involves melting a filler metal (the solder) that usually has a melting point below 840 degrees Fahrenheit (about 450 degrees Celsius). Brazing uses higher temperatures than soldering but is still lower than welding, usually in the range of 1,000 to 2,000 degrees Fahrenheit (about 540 to 1,090 degrees Celsius), where the base metals do not melt, but the filler metal does. Fusing also involves joining materials but is typically associated with lower temperature processes compared to welding.

Therefore, welding stands out as the process that demands the highest heat levels to successfully fuse materials together.