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