What distinguishes welding from soldering?

Welding is distinguished from soldering primarily by the process used to join materials. In welding, the metals being joined are melted together, creating a strong bond as they solidify upon cooling. This high-temperature fusion process involves raising the base materials to their melting point, allowing them to intermingle and form a solidified joint that typically has greater strength than the individual materials.

In contrast, soldering involves joining materials at lower temperatures using a filler metal that does not melt the base materials. Instead, soldering relies on the filler metal to flow between the surfaces, creating a bond when it cools and solidifies. This fundamental difference in temperature and method of bonding is what sets welding apart from soldering.

The other options contain inaccuracies about the processes involved. For example, soldering does not require very high temperatures, nor is it specific to plastics. Additionally, while some welding processes may use a filler metal, many forms of welding can occur without it; the defining characteristic remains the melting of the base metals for joining.