7/21/2014 Lesson 2 - Common Electric Arc Welding Processes

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LESSON II

2.3.2.2 Direct current electrode negative (DCEN) is produced w hen the electrode is

connected to the negative terminal of the pow er source. Since the electrons f low from the

electrode to the plate, approximately 70% of the heat of the arc is concentrated at the w ork,

and approximately 30% at the electrode end. This allow s the use of smaller tungsten elec-

trodes that produce a relatively narrow concentrated arc. The w eld shape has deep penetra-

tion and is quite narrow . See Figure 8. Direct current electrode negative is suitable for w eld-

ing most metals. Magnesium and aluminum have a refractory oxide coating on the surface that

must be physically removed immediately prior to w elding if DCSP is to be used.

2.3.2.3 Direct current electrode positive (DCEP) is produced w hen the electrode is

connected to the positive terminal of the w elding pow er source. In this condition, the electrons

flow from the w ork to the electrode tip, concentrating approximately 70% of the heat of the arc

at the electrode and 30% at the w ork. This higher heat at the electrode necessitates using

larger diameter tungsten to prevent it from melting and contaminating the w eld metal. Since

the electrode diameter is larger and the heat is less concentrated at the w ork, the resultant

w eld bead is relatively w ide and shallow . See Figure 8.

2.3.2.4 Aluminum and magnesium are tw o metals that have a heavy oxide coating that acts

as an insulator and must be removed before successful w elding can take place. Welding w ith

electrode positive provides a good oxide cleaning action in the arc. If w e w ere to study the

physics of the w elding arc, w e f ind that the electric current causes the shielding gas atoms to

lose some of their electrons. Since electrons are negatively charged, these gas atoms now

are unbalanced and have an excessive positive charge. As w e learned in Lesson I, unlike

charges attract. These positively charged atoms (or positive ions as they are know n in

FIGURE 8

Electrode Oxide HeatPolarity Penetration Cleaning Concentration

Direct Current

Alternating Current

Medium Penetration

Medium WidthBead

Good

Cleans Oxideon Each Half

Cy cleAlternates BetweenElectrode and Work

Straight PolarityElectrode Negativ e

DeepPenetration

NarrowBead

Direct Current

Rev erse PolarityElectrode Positiv e

Shallow Penetration

Wide BeadMaximum

None AtWork

AtElectrode

GAS IONS

+

_

ELECTRONFLOW

_

_

+

+

EFFECTS OF CURRENT TYPE - GAS TUNGSTEN ARC WELDING

Lesson 1The Basics of Arc

Welding

Current

Chapter Table of

Contents

Lesson 2Common Electric

Arc Welding

Processes

Lesson 3

Covered Electrodes

for WeldingMild Steels

Lesson 4

Covered Electrodes

for Welding Low AlloySteels

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Lesson 5

Welding Filler Metalsfor Stainless Steels

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Lesson 6

Carbon & Low AlloySteel Filler Metals -GMAW,GTAW,SAW

Glossary

Lesson 7

Flux Cored ArcElectrodes CarbonLow Alloy Steels

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Lesson 8Hardsurfacing

Electrodes

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Lesson 9

Estimating &Comparing Weld

Metal Costs

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Lesson 10

Reliability of Welding

Filler Metals