Arc Welding Continued

Arc Welding Processes

Lesson ObjectivesWhen you finish this lesson you will understand:• The similarities and difference between the remaining arc welding processes• Advantages and disadvantages of these arc welding processes• Need to select between the processes

Learning Activities1. Look Up Keywords2. View Slides; 3. Read Notes, 4. Listen to lecture5. View High Speed

Videos6. Do demo on web7. Do on-line

workbook

Keywords:Gas Tungsten Arc Welding (GTAW), Straight Polarity(SEN), Reverse Polarity (REP), Plasma Arc Welding (PAW), Keyhole, Electrogas (EGW), Electroslag Welding (ESW), Stud Welding,

Gas Tungsten Arc Welding (GTAW or TIG)

Effects of Polarity

Gas Tungsten Arc Welding

Advantages• Superior quality welds, generally

free from spatter, porosity, or other defects

• Precise control of arc and fusion characteristics

• Weld almost all metals• Used with or without filler wire• Easily automated• Used in all positions• Intricate geometries weldable

Gas Tungsten Arc Welding

Disadvantages• Less economical than

consumable electrode processes for sections thicker than 3/8 inch

• Lowest deposition rate of all arc processes

• Tungsten inclusions• Higher operator skill

Required• Sensitive to drafts

Gas Tungsten Arc Welding

Turn to the person sitting next to you and discuss (1 min.):• In all the previous arc welding processes metal wire or electrodes material melts and droplets of metal deposit on the weldment. Some of that metal as it goes through the arc ionized into metal ions and electrons which conduct the electricity through the arc. In GTAW there are no metal ions (or very few metal ions) in the arc since the tungsten electrode is non-consumable. What carries the current in the GTAW arc?

Linnert, Welding Metallurgy, AWS, 1994

AWS Welding HandbookEd 8 Vol 1 1987

Stinchcomb, Welding Technology Today, Prentice Hall, 1989

Advantages

• Greater Energy Concentration• Improved arc stability over other processes• Higher heat content, Higher travel speeds• Greater penetration capabilities• Finer sections can be welded with low current PAW than GTAW

Disadvantages

• Operator skill required is slightly greater than for GTAW• Equipment more expensive• Orifice replacement necessary

Take a moment this evening to view the High Speed Videos of Arc Welding Processes on the “Video

Page” of the WE300 Website

Turn to the person sitting next to you and discuss (1 min.):• The keyhole mode of welding is used because the weld speed can be very fast where molten metal flows around the hole and collides and solidifies in the rear of the hole. What might happen to the shape of the trailing weld pool if the speed was increased too fast?

AWS Welding HandbookEd 8 Vol 1 1987Flux cored Shielding

AWS Welding HandbookEd 8 Vol 1 1987External Shielding Gas

AWS Welding HandbookEd 8 Vol 1 1987

Advantages

• Used for thick weldments• Produces sound welds• Increased cost effectiveness as thickness increases

Disadvantages

• Once started, the weld must continue• Coarse grained Heat Affected Zone

Turn to the person sitting next to you and discuss (1 min.):• If insufficient cooling water is supplied to the shoes on electroslag welding what is likely to happen:a.) the shoe will warp and liquid steel will flow outb.) the shoe will melt and water will be absorbed by the weld metal later causing delayed or cold cracking.c.) an explosion will occur

Cary, Modern Welding Technology, 1989

Cary, Modern Welding Technology, 1989

Cary, Modern Welding Technology, 1989

Do the “Arc Weld Demonstration” from the Demonstration Web Page on the WE300

Website