Lincoln Electric SVM161-A service manual Figure B.7

B-9 OPERATION B-9

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DC Electrode Positive Polarity. (Direct Current Reverse Polarity) (see Figure B.5)

In this case, there is a continuous flow of electrons from the workpiece to the electrode. The reverse polar- ity is used for welding alloys covered with a layer of refractory oxide.

With this polarity the electrode functions as anode and is subjected to a high degree of heat; the workpiece is bombardment by positive ions sent from the electrode which break the surface oxide.

A.C. (Alternating Current)

(see Figure B.7)

Alternating Current welding is typically used for Tig welding aluminum (and its alloys) or magnesium. The polarity alternates between Electrode Positive and Electrode Negative (EN). During the positive half-wave the oxide is broken. During the negative half-wave, the electrode cools, the workpiece melts and penetration occurs.

In Electrode Positive Polarity, high currents cannot be				FIGURE B.7
	+			+		+
used, since they would cause an excessive wear of the
		-			-		-
electrode.
	30% MAX. PENETRATION		50%			70% MAX. CLEANING

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NOTE: (The Invertec® V205-T AC/DC™ cannot be used for Electrode Positive TIG welding without special adapters.)

FIGURE B.5

	+
	1
–	e-

D.C.-Pulsed TIG

(see Figure B-6)

The use of pulsed direct current allows better control of the weld pool during certain operating conditions.

When compared with traditional TIG welding per- formed at the same average current, pulsed welding results in a smaller heat affected zone which results in fewer deformations and reduced chance of cracking and gas entrapment.

Increasing the frequency constricts the arc, increases stability and improves weld quality.

FIGURE B.6

T
		DC TIG - NOT PULSED
Is
O		t
T		DC - PULSED TIG
Is
m
Ib
O	T	t

Greater % EN = MORE PENETRATION 50% (EN) Lesser % EN = more CLEANING

Changing the wave balance alters the ratio between the cleaning and the penetrating current.

A.C.-Pulsed TIG

When AC welding, a pulsed current can be used, with similar effects to those described in pulsed direct cur- rent welding.

	FIGURE B.8
AC TIG - NOT PULSED		AC - PULSED TIG
I		Ip
		Im
		Ib
O	t	O	t
		T	f = 1 to 10Hz
			T= 1/ f

INVERTEC® V205-T AC/DC™