In gas–tungsten arc welding (GTAW/TIG) of copper and copper alloys, which current and polarity configuration is generally preferred to achieve adequate penetration and heat concentration considering copper’s very high thermal conductivity?

Introduction / Context:

TIG (GTAW) welding requires selecting a current type and polarity appropriate to the base metal. Copper and its alloys conduct heat rapidly; thus, achieving sufficient penetration and stable arc characteristics demands a polarity that concentrates heat in the workpiece rather than in the tungsten electrode.

Given Data / Assumptions:

• Base metal: copper or copper alloys.
• TIG process with inert shielding gas (typically argon or helium mixes).
• Objective: adequate penetration and reasonable electrode life.

Concept / Approach:

With DCEN (electrode negative), about two-thirds of the arc heat is directed into the workpiece, giving deeper penetration and keeping the tungsten cooler—ideal for high-conductivity metals like copper. DCEP concentrates more heat on the electrode and is mainly used for limited oxide cleaning on materials like aluminum when using GTAW; however, copper does not require the cathodic cleaning action of AC or DCEP as aluminum does. AC is preferred for aluminum/magnesium because of alternating cathodic cleaning and moderated heat distribution, not typically for copper penetration needs.

Step-by-Step Solution:

Verification / Alternative check:

Welding handbooks specify DCEN for copper and most steels; AC is reserved primarily for oxide film disruption on aluminum/magnesium.

Why Other Options Are Wrong:

• AC: mainly for materials needing oxide cleaning; not optimal for copper penetration.
• DCEP: overheats electrode and limits penetration on copper.
• Any one of these / Pulsed EP only: process physics, not preference, dictates DCEN for copper.

Common Pitfalls:

• Assuming AC is universally best in TIG due to aluminum practices.
• Confusing cleaning action requirements with penetration requirements.

Final Answer:

direct current with straight polarity (DCEN: electrode negative)