Shielding Gases - A major Shielding Gases - A major consumable in Weldingconsumable in Welding

On an average 2 Tons of gas used per tonne of wire

Extensive research on Shielding gases to improve welding performance quality and economy

CO2 widely used previously, now replaced with

Argon based mixtures With improved Argon availability, rapidly

increasing application in India

Shielding Gas FunctionsShielding Gas Functions Protects the weld from atmospheric

contamination

Stabilises the welding arc

Defines metal transfer mode along with welding parameters

Controls weld geometry

Controls weld composition / properties

Shielding Gases for Arc Welding Shielding Gases for Arc Welding processesprocesses

GAS PHYSICAL PROPERTIES

Ionisation Potential(ev)

Density(kg/cm2)

Argon 15.75 1.784

Helium 24.58 0.178

Hydrogen 13.59 0.083

Nitrogen 14.54 1.161

Oxygen 13.61 1.326

Carbon Di-oxide(Dissociation Potential)

15.89 1.977

Spatter generation from Spatter generation from Argon-COArgon-CO22 mixtures mixtures

00.10.20.30.40.50.60.70.80.9

1

100 0

80 20

60 40

40 60

20 80

0 100

Shielding Gas Composition (%)

Sp

atte

r (g

m/m

in)

Spatter (dip)

Spatter (spray)

CO2

Ar

Fume Formation Rate Fume Formation Rate COCO22 vs. Argon mixture vs. Argon mixture

0

0.1

0.2

0.3

0.4

0.5

120 140 160 180 200 220 240 260 280 300

Current (amps)

Fu

me

fo

rma

tio

n r

ate

(g

m/m

in)

CO2

Argon mix

Effect of CO2 and O2 on welding speedEffect of CO2 and O2 on welding speed( 4mm throat fillet on 6mm plate)( 4mm throat fillet on 6mm plate)

010203040506070

Welding speed

cm/min

Gases for GMAW of Gases for GMAW of Carbon / low alloy steels Carbon / low alloy steels

ARGON

CO2

Excellent arcperformance withleast spatter for

thin sheet

Superiorperformance for

heavy section andpositional welding

Commonlyused

O2

Improvedperformance forgenrtal purpose

welding

Superiorperformance

with flat beads &high speeds for

universalapplications

Shielding gas profiles & Shielding gas profiles & effect on weld lengtheffect on weld length

Ar-CO2-O2 Ar-CO2 CO2

weld length1.2 m weld length

1.15 m weld length1 m

Savings with Argon / COSavings with Argon / CO22 / O / O22 gas mixtures gas mixtures

Process Savings in wire ----------------------

Globular

SPRAY

From reduced spatter 5 % 10 - 15 %

From flatter weld 10 - 20 % 10 - 15 %

Total Savings 15 - 25 % 20 - 30 %

Savings in arcing time -----------------------------------

15 - 25 % 20 - 40 %

Savings in power Equivalent to arcing time

Equivalent to arcing time

Savings in gas volume assuming flow rate same as CO2

Equivalent to arcing time

Equivalent to arcing time

Savings in weldshop productivity ------------------------------------------------

From improved welder productivity From reduced spatter cleaning and weld dressing time

5 - 10 %

upto 50 %

5 - 10 %

upto 75 %

WELDING TRIALS AT HERO HONDA MOTORS LTD

ROBOT : YASNAC ARC MOTOMAN P-17 BODY R/L CD-100 BODY R/LINVERTOR : AUTO 350 TB WELDING WELDINGWIRE : ER 70-S6, 1.00 mm

AR-CO2 ARGO-U AR-CO2 ARGO-U 80:20 80:20

Welding Parameters Amps 100-110 100-110 100-110 110-120 Volts 20 16-18 16-18 18-19 Gas flow (litres/min) 20 15 17 14

Trial Results Wire consumed (mts) 5.21 3.97 4.38 2.94 Gas consumed (litres) 14.6 8.75 10.48 6.06 Time (secs/job) 44 35 37 26

Data computed Reduction in wire 23.8 32.8 consumed % Reduction in gas 40 42 consumed % Increase in welding 20.5 29.7 speed %

Direct Welding Cost ElementsDirect Welding Cost Elements

70%

2%7%21%

LABOUR

WIRE

GAS

POWER34%

8% 12%

46%

UK INDIA

Spatter generatedSpatter generated 1 metre of weld at 260 amps 1 metre of weld at 260 amps

using 1.2mm dia. A18 solid wireusing 1.2mm dia. A18 solid wire

CO2 19.1 grams

Argon/CO2 Mix. 8.6 grams

Argon/CO2/Oxy Mix 5.5 grams

Benefits of using gas mixturesBenefits of using gas mixturesThree component with oxygenThree component with oxygen

Improved arc stability leading to lower spatter loss

Improved weld bead geometry leading to weld metal saving

Faster welding speeds leading to higher productivity and reduced labour costs

Improved weld quality leading to lesser rejects Reduced clean up time Lower distortion

Benefits of using gas mixturesBenefits of using gas mixturesThree component with oxygenThree component with oxygen

Improved aesthetics due to bright bead and neat finish

Higher weld metal strength and toughness Reduced welder fatigue due to ease of

welding

Lower distortion

Lower fume levels than Argon/CO2

MODES OF METAL TRANSFERMODES OF METAL TRANSFER

DIP TRANSFER

Low current - low voltage used to produce short circuiting arc, freq. 200 times / minute.

Used for sheet metal and postional welding

SPRAY TRANSFER

Higher currents and voltage used , droplet size same as or lower than the wire diameter.

Higher deposition rate penetration and fluidity of the molten pool , increases the productivity

MODES OF METAL TRANSFERMODES OF METAL TRANSFER CONTD.CONTD.

GLOBULAR TRANSFER

An intermediate stage between dip and spray transfer . droplet sizes are more than the wire dia . Produces excessive spatter and erratic arc behavior viz. CO2

PULSED TRANSFER

Controlled method of spray transfer. Heat input to the job is controlled by low background current with high pulses using special type of equipment