Spot Welding Process Explained

The question describes a welding process that uses a high current, passes it through a melted joint, and is done under external pressure. Let's look at the options provided to see which process fits this description.

We need to identify the welding method based on these specific characteristics:

• High current (around $\text{50,000A}$)
• Current passed through the melted joint
• Welding performed under external pressure

Let's consider each option:

• Gas welding: This process uses a flame from burning gases (like oxygen and acetylene) to melt the base metal and filler material. It doesn't involve passing a high electric current through the joint, nor is significant external pressure typically applied during the welding itself (beyond basic handling).
• Forge welding: This is an older method where metals are heated to a plastic state (below melting) and then joined by hammering or pressing them together. It uses heat but not an electric current passed through a melted joint, though pressure is crucial.
• Spot welding: This is a type of resistance welding. In spot welding, the workpieces are held together under pressure by electrodes. A very high electric current is passed through a small area (a "spot") of the workpieces. The resistance to the current flow at the interface between the workpieces generates heat, which quickly melts the metal at that spot. The pressure from the electrodes forges the melted metal together as it cools, forming a weld nugget. This process clearly involves high current, melting at the joint interface, and significant external pressure. The current levels mentioned in the question (e.g., $\text{50,000A}$) are typical for spot welding thick or highly conductive materials.
• Arc welding: This process uses an electric arc between an electrode and the workpiece to melt the base metal and a filler material. While it uses high current, the primary joining action is through the deposition of melted filler material or the fusion of the base metal, not by passing current through an already melted joint specifically under high external pressure as the main joining mechanism. Pressure might be used in some arc welding variations (like submerged arc welding with rollers), but it's not the fundamental forging pressure applied simultaneously with high current flow at a focused spot like in spot welding.

Comparing the characteristics given in the question with the descriptions of the welding processes, spot welding is the only one that fits all three key criteria: high current ($\text{50,000A}$), passing current into the melted joint area (resistance heating melts the spot), and welding under external pressure.

Therefore, the welding process described is spot welding.